Correspondence Continuing Education for Nuclear Pharmacists

THE UNIVERSITY OF NEW MEXICO COLLEGE OF PHARMACY ALBUQUERQUE, NEW MEXICO

The University of New Mexico

Correspondence Continuing Education Courses for Nuclear Pharmacists and Nuclear Medicine Professionals

VOLUME 111, NUMBER 3

● Radiopharmaceuticals for the Scintigraphic Assessment of Hepatobiliary Function

by:

Anne-Line Anderson, M.S,

Co-sponsored by: mpi pharmacy services inc an ~mersham company ● The University of New Mexico College of Pharmacy is approved by the American Council on Pharrnaceulical Education as a provider of continuing pharmaceutical education. Program No. 180-039-93-006. 2.5 Contact Hours or .25 CEU’S M UI Editor

Director of Ptimcy Continuing Education

William B. Hladik III, M.S., R. Ph. College of Pharmacy University of New Mexico

Production Spectiist

Sharon I. Ramirez, Staff Assistant College of Pharmacy University of New Mexico

While the advice and information in this publication are believed to bc true and accurate at press time, neither the author(s) nor the editor nor the publisher can accept any legal responsibility for tiny errors or omissions that may bc made. The publisher makes no warranty, express or implid, with respect to the mtiterial contained herein.

Copyright 1994 University of New Mexico Phamcy Continuing Education Albuquerque, New Mexico RADIOPHARMA CEUTICALS FOR THE SCINTIGR.APHIC ASSESSMENT OF HEPATOBILL4RY FUNCTION

STATEMENT OF OBJECTIVES

The goal of this correspondence lesson is to increase the reader’s knowledge and understanding of current hepatobiliary radiopharmaceuticals. To that end, this course discusses hepatobiliary anatomy and finction, hepatocyte uptake, metabolism, and excretion of endogenous and exogenous compounds, and the pathway of bile excretion. In addition, gallstone formation, composition, and treatment is reviewed. The course presents information related to the development of current hepatobiliary radiopharmaceuticals, optimal characteristics of such agents, and the in vivo and in vitro properties of agents available for routine use in the U.S. This is followed by a discussion of the clinical use of hepatobiliary radiopharmaceuticals, including augmented cholescintigraphy, and a review of quantitative methods for the assessment of hepatocyte function.

Upon successful completion of this mate~l, the retier shouti be able to:

1. Describe hepatobiliary anatomy and function. 2. Explain the major functions of the hepatocyte. 3. Describe the biliary uptake and excretion pathways for bile acids and organic anions. 4. List three major components of bile. 5. Explain the origin, conjugation, enterohepatic circulation and function of bile acids. ● 6. Describe the origin and excretion pathway of bilirubin and how it affects hepatocyte excretion of other organic anions. 7. Discuss the factors that affect gallbladder filling and emptying. 8. Explain the current understanding of the underlying causes for gallstone formation. 9. Explain methods used in the treatment of gallstone disease. 10. List the required chemical and pharmacologic characteristics of an ideal hepatobiliary radiopharmaceutical. 11. Discuss the development of current hepatobiliary radiopharmaceuticals. 12. Explain the role that analysis of structure-activity relationships has played in the development of improved cholescintigraphic agents. 13. List hepatobiliary radiopharmaceuticals currently available for routine use in the U.S. 14. Describe the preparation and radiochemical quality control of Tc-99m iminodiacetic acid (IDA) analogs. 15. Compare the in vivo characteristics in humans of routinely used Tc-99m IDA radiopharmaceuticals. 16. List the four organs that receive the highest absorbed radiation doses from Tc-99m iminodiacetic acid (IDA) radiopharmaceuticals. 17. Understand how drug therapy can interfere with the movement of cholescintigraphic agents through the hepatobiliary system. 18. List the principal applications for cholescintigraphy. 19, Describe how hepatobiliary imaging studies are performed. 20. Explain the three types of pharmacologic interventions used in augmented cholescintigraphy. 21. Discuss the various causes of cholecystitis. 22. Explain the two most common causes of neonatal jaundice and the role of cholescintigraphy in the ● differential diagnosis. 23. Discuss the current status of methods for quantitation of hepatocellular function. 24. Describe the hepatocyte uptake and handling of Tc-99m galactosyl-neogly coalbumin.

1 COURSE OUTLINE Ix. HEPATOBILIARY IMAGING

I. INTRODUCTION A. Imaging Methods and Analysis 1. Patient Preparation II. HEPATOBILIARY ANATOMY AND 2. Imaging Technique and ● FUNCTION Analysis

111. HEPATOBILIARY PHYSIOLOGY B. Augmented Cholescintigraphy 1. Cholecystokinetic Agents A. Bile Acids 2. Morphine B. Lipids 3. Phenobarbital c. Organic Anions D. Organic Cations c. Cholecystitis E. Pathway of Bile Excretion D. Sphincter of Oddi Dysfunction F. Gallstones E. Biliary Obstruction F. Bile ~kage and Reflux IV. CHAR4CTERlSTICS OF O~IMAL G. Nanatal Jaundice ~PATOBILIARY RADIOPHAR- MACEUTICALS X. QUANTITATION OF HEPATIC FUNCTION

v. DEVELOPMENT OF CURRENT A. Measurement of Hepatic Extraction ~PATOBILIARY RADIOPHAR- Fraction (HEF) Using Tc-99m IDA MACEUTICALS Analogs B. Quantitation of Hepatic Binding A. Historical Perspective Protein Rweptors B. Technetium-99m Pyridoxylidene Amino Acid Complexes c. Technetium-99m Acetanilido- iminodtacetates D. Relationship BetweerIBiodistribution RADIOPHARMACEUTICALS and Chemical Structure FOR THE SCJNTIGRAPHIC ASSESSMENT OF VI. COMMERCIALLY AVAILABLE HEPATOBILIARY FUNCTION HEPATOBILIARY RADIOPHARMACEUTICALS By:

A. Agents Available in the U. S. Anne-Line Anderson, M.S. B. Radiochemical Quality Control Clinical Professor of Radiological Sciences Methods Department of Radiological Sciences c. In Vitro Stability ‘Division of Nucledr Medicine D. Pharmacoklnetics in Humans University of California, Irvine, Medical Center Orange, California VII. RADIATION DOSIMETRY

VIII. PRECAUTIONS INTRODUCTION A. Drug Interference 1. Narcotic Analgesics He~atohiliary radiopharmaceuti cals are an 2. Nicotinic Acid . important adjunct in the differential diagnosis of acute 3. Total Parenteral Nutrition Due to the excellent (TPN) Therapy and chronic abdominal pain. 4. Miscellaneous Drugs physical and biological properties of current Tc-99m labeled radiopharmaceuticals, cholescintigraph y is B. Adverse Reactions considered to be both a noninvasive and very sensitive c. Use During Pregnancy and in Nursing test for evaluation of the functional Sbdtusof the cystic Mothers duct and the gallbladder. Hepatobiliary imaging can also be helpful in the differentiation between surgical

2 and medical jaundice, and it is an excellent method for blood by the hepatocytes, including bile acids and visualizing the pathway of bile following surgery or bilirubin. The alternate pathway of excretion is trauma. The greatwt impact has been on the secretion back into plasma and subsequent clearance diagnostic evaluation of suspected acute. cholecystitis by the kidneys. The biliary excretory system begins ● (l). More than 90% of cases of acute cholecystitis with the bile canalicular network, which drains into a result from cystic duct obstruction by gallstones, series of progressively larger ducts that eventually which cause stasis in the gallbladder followed by combine to form the common hepatic duct. This is chemically-induced inflammation and mucosal injury joined by the cystic duct from the gallbladder to form (2). Biliary tract disease caused by gallstones the common bile duct, which empties into the (cholelithiasis) is a major mdical and surgical duodenum through the sphincter of Oddi. Just prior problem in many parts of the world. It is estimated to entering the duodenum, the common biIe duct is that 20 million individuals in the United States have usually joined by the pancreatic duct. During fasting, gallstones. Although gallstones do not cause bile is diverted into the gallbladder where it is symptoms in the majority of individuals, gallstone- concentrated and stored. In response to a meal, the related disease afflicts up to two million Americans sphincter of Oddi relaxes, the gallbladder contracts, annual]y, leading to direct health care costs exceeding and concentrated bile empties into the duodenum. $2 billion per year. Cholelithimis is the most common single indication for abdominal surgery in the HEPATOBILIARY PHYSIOLOGY United States, with around 500,000 cholecystectomies performed annually (2). The epidemiology, symptoms, The first step in hepatobiliary excretion is up~dke diagnostic workup, and available treatment for across the hepatocyte membrane. Receptor binding cholecystitis and some other abnormalities of the sites on the sinusoidal plasma membrane of hepatohiliary system will he reviewed in the following hepatocytes are responsible for selective uptake of a sections. variety of endogenous and exogenous compounds. Specific carrier-mediated active transport systems HEPATOBILIARY ANATOMY AND FUNCTION appear to exist for various classes of compounds such as organic anions, bile acids, organic cations, and ● The 1iver is tie largest organ in the body, weighing neutral organic compounds (3,5), Distinct transpofi 1200-1600 g in normal adults. The hepatic mechanisms exist for inorganic ions as well; the parenchyma contains a complex network of blood transport of these ions in and out of hepatocytes is vessels and excretory ducts. The liver has dual blood regulated by various “pumps” that maintain conditions supply with about 80% coming from the G.I. tract via required for optimal cellular function (2). Research the portal vein, and the rest being supplied by the within the last 10-15 years has providd a great deal hepatic artery (2,3). The blood is mixed in a vast of new knowledge regarding the mechanism by which network of hepatic sinusoids lined by endothelial and hepatocytes handle electrolytes and other solutes (5), Kupffer cells. These cells are part of the However, only a few of the carrier-mediated transport reticuloendothel ial system and remove foreign systems of the liver have been systematically studied particles from blood by phagocytosis. Pores or (3). The liver is important for the elimination of fenestrae between the endothelial cells allow plasma to weakly polar and non-polar compounds that are poorly flow into the space of Disse, where it comes in excreted via the kidneys because of protein binding contact with the hepatic parench ymal cells. The and tubular reabsorption. The chemical properties parenchymal cells (hepatocytes) account for 60% of that determine if a compound is primarily excreted via liver cells and 80% of organ volume. The the hepatobiliary pathway are discussed in the next hepatocytes are polygonal cells, 30 pm in diameter, section. When protein-ligand complexes enter the and are organized in pIates to form a continuous three- proximity of hepatocyte carriers with high ligand dimensional lattice. A network of exchange vessels affinity, the ligand is removed from the protein and nourishes each parenchymal cell on several sides. The taken up by the hepatocyte. A primary function of the hepatocyte is charged with the ~dskof detoxi~ing and hepatocfie is to convert nonpolar drugs and toxins excreting harmful compounds and of regulating into more water-soluble compounds that can be plasma levels of beneficial nutrients (3,4). The effective y excreted. However, compounds that are various transport pathways for hepatocyte uptake and relatively polar and are ionized at physiologic pH may ● excretion are discussed in the next section. The be excreted unchanged into the biliary tract (3,5). hepatocyte also performs the important function of bile The hepatobiliary system produces approximately formation. “Biliaryexcretion is an essential pathway 600 ml of bile daily. Bile acids, water and for the elimination of many substanc~s removal from electrolytes constitute the major components of bile.

3 Compared to other bodily swretiom, bile is relatively demonstrated to bind bile acids (5,6). The secretion rich in lipids, principally cholesterol and the of conjugated primary bile acids into the canalicular phospholipid lecithin. Bile also contains a variety of lumen haa been shown to take place via a carrier- other lipophilic substances, including vitamins and mediated transport mechanism distinct from that of steroids. Bilirubin, which giva bile its yellow color, other organic anions (2,3). Different primary bilo normally reprwenta IWS than 1% of total biliary acids compete for biliary secretion, but sulfated bile solids. Physiologic control of bile secretion is complex acids appear to use the general organic anion transport and incompletely understood. Hepatic bile flow is mechanism for canalicular secretion (5,6). Evidence closely related w the size of the bile acid pool, indicates that canalicular membrane transport is the determined by the rate at which bile acids are rate-limiting step in overall hepatocyte bile acid processed through the liver. Changes in the rate of trmsport (5), and that the excretion step is easily bile acid delivery to the liver correspond to the impaired by liver disease (3). feeding cycle. This is usually referred to as the bile acid dependent portion of canalicular bile formation. Lipids Other, bile-acid independent, factors are also believed Secretion of the two major lipids in bile, lecithin to take part in the regulation of canalicular bile and cholesterol, is coupled with the secretion of bile secretion, but these factors and their significance are salts. In humans, the liver is normally the most active not well understood (2,3 ,5,6). site of cholesterol synthesis. Elimination of cholesterol from the body takes place by the B~le Acids catabolism of cholesterol to form bile salts, and also Bile acids (also referred to as bile salts) are the by direct secretion into bile. Bile salts, along with end-products of cholesterol degradation and the major lecithin, solubilize cholesterol in bile in the form of organic constituents of human bile. Thti primary bile mixed micelles and mixed lipid vesicles. The exact acids, cholic acid and chenodeoxycholic acid are mechanism for transport of lipids through the synthesized in the liver. They are virtually completely hepatocyte is not well understood (3,5). conjugated, usually with glycine or taurin, before being excretd into bile. Bile acids are natural ionic Organic Ardons detergents and play an important role in the Although organic anions make up a minor absorption, transport and secretion of lipids, such as component of bile, biliary clearance is an important fat-soluble vitamins and cholesterol (2,5). Bile acids route of excretion for this group of compounds. are effective y (95%) absorbed from the intestinal tract Bilirubin, the principal end-product of heme and returned to the liver in portal blood, bound to degradation, belongs to this class of compounds. It is albumin. The removal of bile acids from sinusoidal often used as a model compound for the transport of blood is very efficient, allowing bile acids to circulate other organic anions such as certain dyes, drugs, and through the liver and intestines eight to 10 times per hormones (5). Examples of compounds that share the day (2,5). This enterohepatic circulation effectively organic anion pathway for hepatobiliary excretion with preserves the bile acid pool. bilirubin include the dyes sodium sulfobromophthalein The mechanisms responsible for hepatocyte uptake (BSP) and indocyanine green (ICG), the radiographic and secretion of bile acids are not completely contrast agent iopanoic acid, and several understood, but are clearly different from the cholescintigraphic radiopharmaceuticals such as the mechanisms responsible for handling other organic iminodiacetic acid (IDA) derivatives (7). The anions such as bi~irubin. Different bile acids are not transhepatic transport of these organic anions is rapid handled identically, and it is generally accepted that and may occur by several cellular pathways (3,5). each bile acid undergoes its own enterohepatic Some compounds are metabolized in the liver prior to circulation (6). Certain bile acids, for example biliary secretion, wherein others are excreted taurocholate, enter the hepatocytes via a sodium- unchanged. The normal liver has a very large dependent, carrier-mediated active transport capacity for excretion of organic anions and can mechanism (3). More hydrophilic bile acids process up to ten times the normal daily production of presumably enter hepatocytes by non-ionic diffusion bilirubin (2). (2,5). Following hepatocyte uptake, bile acids are As much as 80% of bilirubin is derived from transported across the cell toward the canalicular pole. hemoglobin following its release due to the destruction There is evidence that cytosolic binding proteins and of senescent red blood cells in the reticuloendothelial various hepatocyte organelles play a role in the system, primarily in the spleen (3,7). Bilirubin is intracellular storage and transport of bile acids. poorly water-soluble and is a neurotoxic substance if Glutathione S-transferases (ligandin) have been allowed to accumulate in the body (2). Unconjugated

4 (indirect) bilirubin passes into plasma where it binds Organic Cations noncovalently to albumin, Because of the large Dmpite the fact that most dregs are positively binding capacity of albumin, large amounti of charged at physiologic ph, relatively little is known unbound, unconjugated bilirubinrarely occur clinically about the hepatic hmdling of organic cations. What ● except in the nwnate, in whom the capacity and is known is the rwult of work with model compounds affinity of albumin to bind bilirubin are less than in such as procainamide ethobromide and adults (7). From the spleen, bilirubin is transported to chlorpromazine. The overall process appears to be the liver sinusoids via portal venous blood. After similar to organic anion handling in many respects. dissociation from albumin, bilirubin is taken up by the For example, competition between different cations hepatocytes. Special domains of the sinusoidal has been demonstrated. Organic anions do not hepatocyte membrane have high affinity for organic compete for the uptake and secretion of cations, and anions such as bilirubin. Good evidence exists that biliary excretion of cations is not altered by bile acid hepatocyte uptake of bilirubin and related compounds infusion (5). No successful cholescintigraphic involves a carrier-mediated, saturable process. radiopharmaceutical belongs to the organic cation Compounds in this class exhibit mutually competitive class. inhibition of uptake, but there is no competition between these anions and bile acids. Several transport Pathway of Bile Excretion proteins in the sinusoidal membrane appear to mdiate Hepatic bile, which is normally produced at the the uptake process (3,5,7). IrI the hepatocyte, rate of about 600 ml per day, may enter the bilirubin is conjugated to form water-soluble duodenum directly, or it may flow into the gallbladder derivatives suitable for excretion in bile. The process where it is concentrated and stored (2,3,5). of conjugation and transport across the hepatocyte to Gallbladder filling and emptying is affected by a the canalicular membrane involves a complex number of factors, including the rate of hepatic bile interaction with multiple intracellular hepatocyte secretion, sphincter of Oddi contraction, cystic duct components. The hepatocyte has a mechanism for pressure, serum levels of the hormone cholecystokinin temporary storage of bilirubin; this may be (which stimulates gallbladder contraction), and predominantly associatd with the cytosolic protein possibly by cholinergic mechanisms. The gallbladder ● ligandin (2,3,7). Ligandin may also act aa a carrier can store only 30-50 ml of bile, but due to its protein to facilitate diffusion of bilirubin to the remarkable ability to concentrate bile by absorption of endoplasmic reticulum where esterification takes place fluid through the gallbladder mucosa, it can (2,3). More than 85% of bilirubin is normally accommodate the total volume of hepatic bile (2). In conjugated with glucuronic acid; the majority is in the addition, it has been demonstrated that periods of form of diconjugates (2,3,7). Although it is not gallbladder filling are punctuated by brief periods of possible to sample bile at the point of canalicular partial emptying of concentrate bile, and that much excretion, evidence indicates that the transport of of the bile secreted at night may bypass the conjugated bilirubin and related organic anions across gallbladder altogether (5), During gallbladder storage the canalicular membrane involves a saturable, carrier- hepatic bile is concentrated by removal of an isotonic mediated process. Different organic anions compete solution containing primarily Na’, HCO~– and Cl ‘. for excretion, but organic cation and unsulfated bile The resulting bile has a very high concentration of acid transport is not affected. More than one carrier bile salts and Na’ m well as K+ and Ca2’ (5). system may be involved in the secretion step, which appears to he the rate-limiting step of overall Gallstones transhepatic bilirubin transport (2,3,5). From the bile The formation of gallstones represents a Fdilure to canaliculus, biliruhin conjugates pass with the bile into maintain certain biliary solutes, principally cholesterol the small intestine. Very 1ittle reabsorption takes and calcium salts, in a solubilized srdte (5). place; normally more than 90% of bilirubin is ex- Gallstones have traditionally been divided into two cretd in feces either unchanged or as intestinal major types: cholesterol stones and pigment stones metabolic products (7). Elevatiom in serum direct (2). In the United Srdtes, more than 75% of stonw (conjugated) bilirubin above the normal range of ().3- are considered to be chol~terol stones. Th~e stonw 1.0 mg/dl may be of prehepatic (e.g., hdemolysis), are formed in the gallbladder and contain more than hepatic (hepatitis, cirrhosis), or cholestatic (obstruction 50% cholesterol by weight. Since cholesterol is not ● of bile flow) origin (8). Because conjugated bilirubin radiopaque, most of these stones are not visible on is water-soluble, urinary excretion is observed in plain abdominal radiographs (2). Their formation is patitinta with direct hyperbilirubinemia (2). clearly related to supersaturation of bile with cholesterol, but this ~one does not explain the

5 pathogenwis, since supersaturation is common in side eff~ts than CDCA, and combined therapy using normal fasting subjects without stone formation (2,8). both drugs is more effective than either drug done. It is not well understood how other promoting factors The optimal oral dose is 10 to 15 mg/kg/day (2,6,8). are involved but this is an active area of research. Not all patients with gallstone disease are suitable Pigment stones can be subdivided into black and candidatw for this type of therapy, however. The ● brown stones. Both typw contain sufficient amounts drugs are not effective for highly calcified stones, and of calcium salta to be radiopaque. Brown pigment work best for buoyant stones lms than 15 mm in stones are seen mainly in the Orient and are almost diameter (6). Presence of a functioning gallbladder is always associated with biliary bacterial infection. The dso required. Complete treatment rndy take as much primary calcium salt in brown stones is bilirubinate. as two years, and the drugs are relatively expensive. Brown stonw contain more cholwterol than black Even with a carefully selected patient population, the stones, and are usually formed in the bile ducts rather success rate for complete gallstone dissolution is on]y than in the gallbladder. Black pigment stonw are 40-60% (8), and recurrence rates of up to 50 % in five composed of a mixture of calcium salts including ye~s have been reported (6). The true success rate of bilirubinate, carbonate and phosphate salts, and are stone dissolution is actually unknown, since current usually formed in the gallbladder. Black stones have diagnostic methods have limited resolution. Tiny been linked with chronic hemolytic disorders and residual stones may be missed, and when bile reverts cirrhosis (2,6). to its supersaturated state afier the drug is Although this classification of gallstones may be discontinued these residual stones may start growing. useful for the purpose of selecting an appropriate Extracorporeal shock wave lithotripsy (ESWL) is course of therapy, in reality gallstones have been another non-surgical method for removal of gallstones found to cover the full spectrum from “pure” (2,8). By sending focused shock waves from outside cholesterol stones to stones of variable calcium and the body, stones can be reduced to 2-3 mm particles bile pigment content, leading to the classification of that can easily pass into the intestinal tract. The many stones as “mixed.” Even so-called “pure” technique works best in patienw with single small cholesterol stones contain calcium salts in the center, stones, and can be combined with dissolution therapy. and current rwearch suggesw that the precipitation of Because these non-surgical treatments of cholesterol calcium in the biliary tree is a critical event in the cholelithiasis have no lasting effect on the underlying initial nucleation of both cholesterol and pigment cause of gallstone formation, and does not prevent stones (5,6). recurrence, the overall therapeutic results have so far Over the years, numerous epidemiological studies been disappointing. have been undertaken to try to uncover the causes for gallstone formation. This, in turn, would presumably CHARACTERIS~CS OF O~IMAL HEPATO- lead to ways of preventing the formation of gallstones. BILIARY RADIOPHARMACE~CALS Diet, sex, obesity, and hormonal status are some of the factors that have been implicated (6). Much work Hepatobiliary radiopharmaceuticals are usd to remains to be done to understand the factors that obtain scintigraphic images and functional data that either promote or prevent cholelithiasis. A better can be used to evaluate hepatocyte function, the undersbdnding of the pathogenwis of gallstone patency of intrahepatic ducts, the functional sratus of formation is expected to lead to better methods to treat the cystic duct and the gallbladder, and also the patienfi with gallstone diseme, At the present time patency of downstream portions of the biliary tract cholecystectomy is the only therapy proven to cure (10). The optimal or ideal radiopharmaceutical for cholesterol gallstone disease (2,9). This type of evaluating the functional status of an excretory surgery has recent]y become less traumatic due to pathway such as the hepatobiliary system would be an refinement in technique. Laparoscopic agent that passes through rapidly in bolus form. The cholecystectomy is now widely used in many parts of agent should not be partially cleared by other the world and has been found to reduce both pathways or localized in arem outside the pathway of postoperative pain ad the recovery period, as well ks interest. In other words, the extraction efficiency cost (2). should be 100%, and excretion steps such as Pharmacologic dissolution of cholwterol gallston~ membrane transport and metabolism should be rapid. using orally administered bile acids has been There should be no reabsorption of the original extensively investigated. Two compounds have been compound or of any radiolabeled metabolizes. In o found to be effective in clinical studiw: addition, the radiopharmaceutical must be labeled with chenodwxycholic acid (CDCA) and ursodaxycholic a radionuclide with suitable half-life and radiation I acid (UDCA). UDCA has been reported to have less emissions. The labeling must be stable, and the 6 1 combination of half-life and clearance rate should be and convenient availability, Tc-99m is widely such that the radiation doso to the patient is not too regarded as the radionuclide of choice for diagnostic high at dose levels required to obtain satisfactory imaging (15). Technetium-99m is the decay product images. If quantitation of function is- desired, the of Mo-99 (tl,q = 2.75 days), and can be obtained as clearance rate should only be affected by the an isotonic, sterile and pyrogen-free solution of functional status of the excretion pathway, and not by sodium pertechnetate from commercially available concentration changes of other substances that are Mo-99/Tc-99m generator systems. The physical half- handled by the same pathway. life of Tc-99m is 6.02 hours; this is generally well- Hepatobiliary imaging goes back to the -suitedto hepatobiliary excretion kinetics. It decays to introduction of I-131 rose bengal by Taplin and Tc-99 by isomeric transition, emitting abundant (89%) coworkers in 1955 (11). As will be explained further 140 keV photons and minimal amounts of non- in the next section, I-131 Rose Bengal is not an ideal penetrating radiations. Labeling of suitable radiopharmaceutical for hepatobiliary imaging. It was compounds with Tc-99m using well-established replaced in the 1970s by Tc-99m-labeled compounds methods results in radiopharmaceuticals of high purity with more optimal characteristics. Investigations have and stability. The photons from Tc-99m are optimal continued to the present time with the aim of for detection by standard nuclear medicine imaging developing even better agents to study specific aspects equipment and r~sults in a low patient radiation dose of hepatocyte function. per usable photon. A number of chemical properties have been found to be of impowance for a substance to be excreted DEVELOPMENT OF CURRENT HEPATOBIL- efticicntly by the hepatobiliary pathway. Although IARY RADIOPHARMACEUTICALS interrelated, these properties can be conveniently divided into three groups: molecular weight, polarity, Historical Perspective and rnolecular structure. Compounds with molecular Despite its many shortcomings, 1-131 rose bengal weight below 300 are preferentially eliminated in the (11) was the principal radiopharmaceutical for studies urine, whereas bile is the dominant pathway above of hepatobiliary finction for many years. Rose bengal 500 Da (12). Animal studies have shown a marked is a halogenated fluorescein dye, principally species difference in the extent of biliary versus tetrachlorotetraiodo-fluorescein. It can be effective y urinary excretion for organic anions in the 300 to 500 radioiodinated by exchange labeling methods to yield Da range (13), It has long been recognized that lipid a preparation of high specific activity. Iodine-131 is volubility of a molecule is an important determinant of a beta emitter with a relatively long physical half-life its biliary excretion (12). Lipophilic groups bind (8 days). Its photon emission of 364 keV is not strongly to albumin, which prevents filtration by the optimal for standard imaging equipment, and the kidneys and increases ligand volubility in circulation. administered dose was limited to about 300 pCi (111 Although molecules preferentially eliminated in bile MEtq), resulting in poor quality images. Due to the have an overall hydrophobic structure, the presence of relatively slow transit of 1-131 rose bengal through the one or more polar groups (e.g., ionizable groups) is liver, it becomes difficult to visualize the gallbladder an essential requirement for quantitative biliary against the high background activity in the liver. excretion to occur (3). That is why highly lipid- Rose bengal is cleared through the same hepatocyte soluble molecules must be conjugated prior to excretion pathway as bilirubin, but does not compete excretion into bile canaliculi. In a review article, well for excretion at elevated bilirubin levels, adding Firnau (14) compared the molecular structure of a another complication to its clinical usefulness. The number of compounds proposed as hepatobil iary physical disadvantages of 1-131 could be overcome by radiopharmaceuticals. He concluded that for extensive replacing it with I-123, a cyclotron product with a biliary excretion to occur, a molecule may need to principal gamma emission of 159 keV. Iodine-123, exhibit a certain balance between the polar and however, has a physical half-life of only 13 hours. nonpolar aspects of its structure. Another feature of Although 1-123 rose bengal was successfully these compounds was that they all contained at ledst developed (16), its high cost and problematic supply two cyclic structures arranged in two different planes. logistics resulted in very limited clinical use. Although it is not fully understood how changes in Because of the excellent physical characteristics of molecular structure influences biliary excretion, it has Tc-99m, a large number of Tc-99m complexes have been shown that introduction of certain groups afiects been investigated as potential hepatobiliary biliary excretion rate without significantly altering radiopharmaceuticals. The first agent to show lipid volubility or molecular weight (3, 12). promise, Tc-99m-D-penicillamine was introduced in Due to its optimal radiation properties, low cost, 1972 (17). A discussion of all the agents that were

7 subsequently proposed is beyond the scope of this Several clinical studies subsequently established the continuing education lwson. Several well-referenced advantage of Tc-PG over 1-131 rose bengal for review articles have been published (10, 18). The two hepatobiliary imaging (25,26). In normals, the groups of cholescintigraphic agents that have common bile duct, gallbladder, and duodenum was undergone extensive clinical investigations are seen 15-30 minutes post-injection, and renal retention discussed below. did not interfere with scan interpretation. However, urinary excretion increased in jaundiced patienti, and Technetium-99m Pyridoxylidene Hlno Acid the biliary tract was not well-visualized with serum Complexm bilirubin levels above 4 mg/dl. The presence of Starting with Tc-99m Pyridoxylidene glutamate activity in the gastrointestinal tract on late (18-24 (Tc-PG) (19), a large number of similar complexes hours) imagw still allowed differentiation between were investigated as hepatobiliary imaging agents. The partial and complete obstruction. condensation of pyridoxal and an amino acid such as Effofi to reduce the amount of urinary excretion glutamate results in formation of a complex known as initially centered on replacing glutamate with other a Schiffs base ligand (Figure 1), which is stabilked amino acids (22,23 ,27), but this did not produce by binding to metallic cations (20,21). In the original significant improvements. Some of the problems preparation, Tc-99m pertechnetate ww added to an associated with the variable mixtures of complexes in equimolar mixture of pyridoxal and glutamate of ph 8- the autoclave products were solved by Kato and 9 and autoclave for 30 minutes at 12@C. In this H-e (28). They developed a new labeling method method technetium is probably reduced by the using stannous ion as the reducing agent in an alkaline aldehyde group on pyridoxal to a lower oxidation state mdium with wcorbic acid as a stabiltier. Two- that can readily form coordination complexes with component kits using several different amino acids Schiffs base ligands. This method resulted in a were prepard; in the final labeling step Tc-99m preparation containing multiple Tc-99m complexes as pertechnetate was incubated with aliquots of the two shown by electrophoresis and HPLC (19,22,23). kit components for one hour at room temperature. However, Tc-PG showed significant promise as a Biliary excretion of this new series of compounds was cholescintigraphic radiopharmaceutical in several found to correlate well with lipophilicity as determined animal species (19,22,23 ,24). Blood clearance was by thin-layer and paper chromatography. Further rapid, and the biliary tract and gallbladder could be improvements were realized when kits containing N- clearly visualized as early as 10-15 minutes after pyridoxylamino acids were introduced (29). This injection. There was no evidence of reabsorption or significantly increased the stability of the Iigmds, and hepatocyte metabolism (23), and acute and chronic (Sn)-N-pyridoxalaminate kits were prepared that could toxicity studies in animals showed a wide margin of be efficiently labeled with Tc-99m in a brief boiling safety for diagnostic purposes (19). The major step. Of the amino acid complexes tested, Tc-99m disadvantage of Tc-PG was the high degree of urinary (Sn)-N-pyridoxyl-5-methyltryptophan was the most excretion, which was reported to be in the range of 20 promising. In rats, over 90% of the activity passed to 50% of injected dose, depending on animal species. through the liver in the first 30 minutes after injection, This may be partly due to a low degree of protein and only 2% was excreted in urine. Continuous binding, which was estimated to be only 20% infusion of sulfobromophthalein (BSP), designed to immediate y following injection in rabbits (23). simulate elevated bilirubin levels, had minimal effect on the rate of biliary clearance as well as the extent of urinary excretion. No hepatobiliary radiopharma- HOOC–CH~CH~fH-COONa ceutical based on pyridoxal and amino acids has been commercially available in the United States, but this N group of agents has been used extensively in Asia and HC4 the Far East.

Technetium-99m Acetanilideiminodiacetatm H0CH2 / OH The development of Tc-99m-N-(2,6- dimethylphenylcarbamoylmethyl) iminodiacetic acid I ~cdimethyl-IDA) was first reported by Loberg and \ CH3 coworkers in 1976 (30). The ligand was synthesized N in a two-step procedure Starting with 2,6- a dimethylailine and chloroacetic acid. The rmulting Figure1. Structure of Pyridoxylideneglutawte. intermediate was then reacted with iminodiacetic acid

3 I to form the dimethyl-IDA complex Figure 2). The organic anion pathway. This suggested that in the iminodiacetic group has excellent chelating properties jaundiced patient, bilirubin maybe able to prevent Tc- and forms a complex with stannous-reduced Tc-99m dimethyl-IDA and related radiopharmaceuticals from at room temperature. Analysis by paper and gel being eticiently excreted by the hepatobiliary system. ● chromatography showed insignificant amounts of Tc- Initial human studies with Tcdimethyl-IDA (37) in 99m in the form of pertechnetate or colloids. Initial normal subjects and non-jaundiced patients showed animal distribution studies in mice showed that Tc- rapid concentration of tracer by the liver, with 14% of dimethyl IDA was cleared rapidly from the blood by the injected dose excretd in urine by 90 minutes. the 1iver, with more than 80% of the injected dose in Activity was present in the biliary tract afier 10 to 20 bile after 50 minutes. Urinary excretion in dogs was minutes. In jaundiced patients as much as 53% of the 17% at 5 hours afier injection (30). This agent injected dose was in the urine at 18-24 hours. Blood clear]y showed great promise, and extensive clearance was delayed and the biliary system was not investigations of Tc-dimethyl-IDA and similar IDA visualized in patients with severe jaundice. However, complexes as potential cholescintigraphic intestinal activity, indicating biliary tract patency, was radiopharmaceuticals followed. Studies of the observed on late images in patients with incomplete chemical structure (31) indicated that the molar ratio common duct obstruction. Safety studies in the same of dimethyl-IDA to technetium is 2:1, suggesting a bis group of patients did not detect any alterations in structural complex. Tin ions are not part of the final various hematological and biochemical tests after complex. Technetium is present in the + 3 oxidation administration of Tc-dimethyl-IDA. Following the state, giving the complex an overall charge of -1, initial successful clinical use of Tc-dimethyl-IDA, Mass spectroscopy studies (32) have subsequently many researchers attempted to prepare an even better confirmed a his-structural anionic ligand complex of radiopharmaceutical by manipulating various parts of Tc +3, presumably octahedral in structure. A mass the basic IDA molecule. The goal was to produce an value of 685 was observed. agent with increased hepatobiliary specificity, decreased renal excretion, and improved competition for excretion in the presence of elevated serum bilirubin levels. Over the next few years some 60 different Tc-99m labeled IDA analogs were tested in animals (27,34,35,39,40,41). Most of the new analogs had d m different Chemiudl substitutions only on the aromatic ‘3 ‘2 ring of the basic IDA structure, and in general it was observed that hepatobiliary specificity improvd with Figure 2. Structure of acetanilidoiminodticetic acid. increased Iipophilicity. Changes introduced in the side chain were less successful, sometimes resulting in Animal distribution and imaging studies using Tc- unstable complexes or increased urinary excretion dimethyl IDA in a variety of animal species confirmd (39,42). The in vivo kinetics of only the more that this complex is primarily excreted in bile, with extensively investigated analogs will be reviewed here. only moderate amounts of urinary excretion When the methyl groups on the phenyl ring were (27,33,34,35). Tc-dimethyl IDA is not extensively replaced by ethyl, increased hepatobiliary specificity protein bound (36) or metabolically altered in vivo and decreased urinary excretion was observed in a (30,31). Safety studies in mice (37) indicated that the baboon model (27). However, these two amdogs LDWfor dimethyl-IDA exceded the proposed human (dimethyl and diethyl) performed essentially identical dose by a factor of 1,000 on a per-weight basis. To in normal humans (43). Increasing the substituent determine the mechanism of hepatobiliary clearance of group in the ortho positions further, as in di-isopropyl Tc-dimethyl-IDA, Harvey and coworkers (38) IDA, did not reduce renal excretion significantly, but performed competitive clearance studies in dogs with the hepatic excretion rate increased (33,43). Urinary BSP, an anion, and oxyphenonium, a cation. The excretion of less than 2 % of the dose 30 minutw after administration of saturating levels of BSP resulted in injection was observed in animals with p-butyl-IDA u decrease in the one-hour cumulative biliary excretion (35) and 2,4,6-trimethyl-3-brumo-IDA (TMB-lDA) from 55 to 1.5% of the injectd Tc-dimethyl-IDA. (41). The p-butyl analog cleared very slowly through The one-hour urinary excretion increased from 13% the liver, a characteristic thought to make it to 44% as a result of BSP infusion. No effect was particularly well-suited for use in jaundiced patients observed with oxyphenonium, demonstrating tiat Tc- (33). The low degree of urinary clearance of TMB- dimethyl-IDA is clearti through hepatocytes via the IDA was later contirrnd in normal humans; this was

9 combined with increasd hepatocyte extraction for rtilng substituent group contributions to efficiency compared @ the di-isopropyl-IDA analog biological behavior without specifying any (43,44). During thae investigations, several physiochemical propertia. One of the limitations of important observations were made, leading to an this method is that activity predictions cannot be made improved understanding of how chemical structure for a compound containing a substituent which was ● affects hepatobiliary vs. renal excretion of Tc-99m- not included m an observation in the original analysis. IDA analogs. It is, however, a useful twhnique in casw where additivity is a reasonable assumption and where only Relationship Betw&n Biodlstribution and Chemical a limited number of substituents are involved (45). It Structure should be pointed out that prdiction of the most The development of new and improv~ dwirable compound is not the primary goal of QSAR radiopharmaceuticals has generally followed pathways analysis. Rather, it should be considered as a tool to similar to those used for other groups of drugs. The rationalize and shorten the path from a lead structure process must begin with the identification of a to an analog with the dmired biological activity. compound with inter~ting biological activity (45). A Structure-activity analysis has been applied in the hypothesis must be arrived at regarding which development of radiopharmaceuticals ordy recently chemical features are relatd to bioactivity. New (15). One of the first examples of the use of SAR in compounds must be synthwized and tested in an radiopharmaceutical development was for the Tc-99m appropriate biological assay to evaluate the hypothesis. labeled cholescintigraphic agents. Since radiophmma- Based on this analysis, several modifications to the ceuticals generally have no pharmacologic action, and original hypothesis may have to be developed and we are primarily interested in in vivo distribution, the tested. This process is intended to disclose how terminology “structure-distribution relationship” changes in the molecular structure affect biological (SDR) is frequently used instead of SAR. activity, i.e., a structure-activity relationship (sAR) iS In 1977, Burns and coworkers (49) reported on the identified. preparation and twting of five different Tc-IDA A number of methods for quantitative SAR analogs. Biodistribution studies in mice revealed a (QSAR) analysis using computers have been developd linear relationship between biliary excretion and the during the last 30 years. QSAR methods utilize natural log of the molecular weight divided by the ● mathematical models which describe the structural charge. A few years later Nurm, et al. (41) reported dependence on biological activities either by on correlations between physiochemical parameters, physiochemical parameters (Hansch analysis), by structural effects, and in-vivo characteristics of a total indicator variables encoding different structural of 33 Tc-IDA derivatives with different combinations features (Free-Wilson analysis), or by three- of substituent groups on the phenyl ring, Lipophilicity dimensional molecular property profiles of the was measured using a reverse-phme HPLC system, compounds (comparative molecular field analysis, and compared to tharetical u values from published COMFA) (46). Hansch (47) examined QSAR between reference tablw. A linear relationship was apparent biological activity and the underlying chemical when the compounds were divided into groups based properties such as atomic chargw, oil-water partition on the location of the substituents. The extent of coefficients, and molecular volumes. The most protein binding was determined in vitro using a HSA- frequently used approach involves the determination of aff’’nity column. Hepatic and renal excretion at 30 the change (T) in the Iipophilicity of a parent minutes were determind in rats, and imaging studies compound caused by the introduction of a substituent in rabbits were used to measure intrahepatic kinetics. group. The value of r is defined as the difference in This body of data was correlatd to gain a better the log of the partition coefficient (log P) between understanding of the relative importance of the size, octanol and water of the parent compound and that of type, and location of substituent groups. No attempt the substituted analog. A basic assumption of this was made to do a QSAR analysis. Increased method is that the effect of an analog of the parent lipophilicity generally resulted in increased hepatic compound equals the effect of the parent compound specificity and reduced renal excretion. Increased plus the effect of one or more substituent groups, in protein binding of the para substituted analogs other words, pdditivity is assumed. At least in the correlated with increasing theoretical Iipophilicity. simplest model it is also assumed that activity of a This was not observed for substituents in the ortho substituent group is independent of other substituents. positions; no correlation was observ~ with either ● The Free-Wilson analysis (48), sometimes referral to protein binding or thmretical lipophilicity. When a as the de novo approach, was one of the earliest single lipophilic group was pr~ent in para position, QSAR methods. It represents a statistical approach hepatocyte transit time increased significant y, whereds diortho substitution resulted in decreased hepatocyte animal studies, good agreement was seen between transit time. Initial studies led the investigators to test predicted and experimental values. additional compounds based on what they had learned. When a group of IDA analogs with various COMMERCIALLY AVAILABLE -ATO- arrangements of methyl and bromo substituents was BILIARY RADIOPHARMACEUTICALS tested, TMB-IDA was found to have the best overall in vivo characteristics in rats and rabbits. Agents Available in the U.S. The structure-activity relationship for Tc-PG At the present time, three radiopharmaceutical kits analogs has also been investigated (50) using deriv- for the preparation of Tc-99m cholescintigraphic atives of Tc-99m(Sn) pyridox ylidenephenyl alanine. agents are available in the United States. They are all Fluoro-, chloro-, and six different alkyl substituents derivatives of Tc-IDA, and are available as lyophilized were introduced in various positions on the phenyl mixtures of the IDA analog and stannous ions sealed group of the phenylalanine moiety. The lipophilicity under nitrogen to prevent oxidation. The Tc-99m of the analogs was determined by measuring the complex is formal by simply adding Tc-99m octanol/buffer partition coefficient. In vivo pertechnetate solution followed by a brief incubation distribution studies in rats showed that increasd period at room temperature. During their lipophilicity correlated well with a decrease in renal development, these IDA analogs have been referral to excretion. Generally, many of the observed effects of in the literature by a variety of names and acronyms. substituent groups on the phenyl ring corresponded to The generic names of commercially available IDA what had been observed with the Tc-99m IDA derivatives are as follows: analogs. Preliminary SDR work with a different group of potential hepatobiliary radiopharmaceuticals dimethyl-IDA: Iidofenin relatd to indocyanine green has also been reported diisopropyl-IDA: disofenin (51). Indotricarbocyanine, a symmetrical compound trimethyl-bromo-IDA: mebrofenin with two phenyl rings, was synthesized and monoiodinated with I-131. Dihalogenated compounds These are the names adopted by the United States were also prepared by introducing F, Cl, Br or I on Adopted Names (USAN) Council. In addition, the the second phenyl ring. The in vivo characteristics various kit manufacturers have given their product a were studied in several animal models. All the trade name flable 1). The formulation, as given in analogs had rapid blood clwdranceand hepatic uptake, current package inserts (53,54,55), of commercial kits and minimal urinary clearance. Liver clearance rate for the preparation of these Tc-99m labeled IDA was significantly affected by the second halogen analogs are given in Table 1. group, and a correlation was observed between liver

clearance rate and the polarity of the halogen Table 1 Formulation of mmmerdally available Te9m h?palnbiliary radlOph*~,reutical, substituent. Trade Name Manufatlurcr K!t r“ntenls ‘“- Preparation and Storasc The QSAR method of Free and Wilson (48) has (Qneric Name) . . . . . ?whn~an HIDA Merck rto$$t I,dofenin 10 mg Add 2.10 ml .rc.Wm t;rlwhnetale. been used to investigate the effect of various alkyl (Lidofcnin) Canada for SnCl, * ?H,O up to lINJ mm (3 7 CBq) Mallinchdt, 1.. O.*11lng It,ctd>atlonlime 15minut<%. substituents on the phenyl ring of Tc-99m IDA HC1, “r N,(IH !. ad)ust Use wilh,n 6 hours, pt[103.q-i 1. Store at 2-W

complexes (52). Seven analogs, including 1Ivpatc>lil,, hPon t I>hanna Uwfrtlln Zfl !mg Add 4-5 ml Tc-Wm FrlLYIII!*laIe, (~wlenin) snc~ . 211,0 12-lM mC, (444-7700 MBq) unsubstituted Tc-99m IDA, were initially usd. The u24 U6 !,1s Incubation ttt>le 5 minute I lCL andlur NaOH 10 Use with,n b hours. analogs wero substituted in either the para or both aqwt pll to 4-5 store at 15.WC.

ortho positions. The following in vivo parameters Ch”l,tec ~“ibb Dlagno$!im M.hr”(en,n 45 mg Add 1.5 ml 1 c.WIn pcrt?chnelate, (Mebrof,nin) snF, .211,0 UP 10 1~ mci (37~ MBq). were determined in rabbits: activity in urine at 30 0%tolu3n2g, Incubat,<,n l,mC, 15 nllllu(m. Use with,. 18 hours minutes, time to reach maximum liver uptake, and Sbre at 15K. Methylptrabcnup105 2 mg liver clearance half-time. The response measures usd n“pylparabn up to 058 tllg HCI“rNaU11 to ad)wt [,[1 in this QSAR model were the log of the to giveap!1of42.57 in the t=onstitutti pr~uct experimen~dlly measured values. A computer model allowed calculation of the contribution to biological activity for each of the substituent groups @ara or di- ortho), as well as the activity of the unsubstituted Tc- Radiochemical Quality Control Methods IDA. It then combined this data to give predicted The most common radiochemical impurities in numbers for a total of 16 related Tc-IDA analogs Tc-99m radiopharmaceuticals prepared with (including those tested). An additional analog was stannous ion rductant are Tc-99m pertechnetate subsequently tested and added to the data set. Within (TcO,”-) and rduced, hydrolyzed Tc-99m (R-Tc) the range of experimen~dl errors associated with species. A number of rapid thin-layer

11 chromatographic methods have been dmcribed for the taken up by the hepatocytw, with relatively little renal separation of Tc-99m complexes from these two excretion in normals (Table 2). Of the three agents, impurities (56). In order to separate the Tc-99m IDA Tc-99m mebrofenin reachw maximum liver uptake complex (Tc-IDA) from TcOq–and R-Tc, two instant sooner than the others, and also has the fastest liver thin-layer chromatographic (ITLC) systems must be transit time as expressed by hepatic excretion half-time ● used. Silicic acid (SA) ITLC strips in 20% methanol (time from maximum liver uptake to 50% of can be used to separate TcOQ–~ = 1.0) from the maximum), All the agen~ reach maximum liver other components (R~= O) (57). The amount of R-Tc uptake within 10-15 minutw after injection, and can be determined using silica gel (SG) ITLC strips activity in the common bile duct is usually seen within and either water or acetonitrile:water (3: I) ~ the 10 minutes. The gallbladder is usually visualized solvent (41,57). In these systems both TcOd-and Tc- within 30 minutes, and intestinal activity is apparent IDA move with the solvent front, and only R-Tc by 60 minutw in 80% of patients (43). remains at the origin. More time-consuming, but reliable, gel chromatographic and paper Table z fi-ecukfntim of hepat~lllary raflophmmtlck h nm,ls (w) . . . ..— electrophoretic methods can also be used (42,57). Agent % bin Bld % h m Urine 1lepatic E.xcreli(m at w mum M W“, 24 Hr t ,,1 Min.) Several repoti have been published regarding the .,.,. -..,.- presence of an intermediate reaction product during T..% Iido[eni. 3,0*05 7.6.t.1,0 15.5? 2.7 42*5 the formation of Tc-99m IDA complexes (41,58). T* dti(e.i. 2,0t06 6.1 t 1,0 II,]*1 5 19+3 T- mebrolenir, 08.+ 0,1 06A0.I 1,5?03 17+1 This can be observed during HPLC analysis, but ——”. separation is insufficient using ITLC methods. This does not appear to be a problem as long as suff~cient In patients with increased serum bilirubin levels, incubation time is allowed following Tc-99m blood clearance and hepatic transit of Tc-99m IDA pertechnetate addition. analogs is usually delayed, and a larger proportion of the dose is excreted in urine. However, extensive In Vitro Stibility clinical use has shown that both Tc-99m mebrofenin Majewski, et al. (59) studied the in vitro stability and Tc-99m disofenin can be used successfully in of several Tc-99m IDA analogs. The amounts of Tc- jaundiced patients (10,43,44,62@), wherein lidofenin 99m in the form of TcO,’ and R-Tc were determined is more severely affected and should not be used. The by ITLC methods (57) up to 24 hours following effect of BSP and bilirubin on the hepatocyte uptake ● preparation. All Tc-99m Iidofenin preparations of Tc-99m mebrofenin was studied in vitro using contained <4% TcOd”-and < 1% R-Tc up to 8 hours isolated rat hepatocytes (41). Uptake decreased after preparation. The corresponding numbers for Tc- somewhat with increasing concentrations of both BSP 99m disofenin were < 2% and < 1%. There was no and bilirubin, but the decrease was only about 25% at significant change in percent R-Tc for either agent up a bilirubin level of 20 mg/dl. Similarly, bilirubinemia to 24 hours. Some increase was observed for TcOd-, induced by bilirubin infusion in rabbits with normal but it did not significantly exceed 10% in any liver finction did not significantly alter pharmacokine- preparation. Technetium-99m mebrofenin was not tics of four different Tc-IDA analogs (35). It has been included in this analysis. It should be noted that Tc- suggested by POWSCU(60) ti~t it is not high serum 99m rnebrofenin can be used up to 18 hours after bilirubin levels per se, but rather altered hepatocellular preparation, whereas the other producm should not be function due to liver cell damage, that limits the biliary used past six hours (Table 1). The difference is due excretion of Tc-IDA amlogs. This view is supported to the presence of bacteriostatic additives in the by Sarkar (61), who reported normal hepatic uptake mebrofenin kit, but it also indicates that the and excretion of Tc-lDA in a p~tient with a plasma manufacturer has been able to show that the agent bilirubin level of 36 mg/dl. This patient suffered from retains high radiochemical purity. a hereditary biliary conjugation disorder, but did not have parenchymal hepatic disease. Pharmacokinetics in Humans The in vivo behavior of current hepatobiliary RADIATION DOSIMETRY imaging agents in humms generally reflects what was observed in animal studiw, although some species The recommend injected dose for hepatobiliary differences have been observed. The scintigraphic scintigraphy in non-jaundiced patients is 5 mCi (185 delineation of hepatobiliary anatomy is primarily MBq) or less; in jaundiced patients a higher dose, up ● determined by the degree of hepatic uptake as well as to 10 mCi (370 MBq) can be used. The estimated the rate of elimination from the liver into bile. All absorbd radiation doses according to the current agents are rapidly cleared from the blood and manufacturer’s package insert (53,54,55) are given in

12 I I Table 3 for normal and jaundiced individuals. The cholescintigraphic radiopharmaceuticals (71), This MIRD scheme for dose calculations using publishd appears to be a dosedependent toxic effect, and liver “S” valuw for an average 70 kg man was used for finction returns to normal after nicotinic acid intake these calculations. Different assumptions may result is stopped or reducd. ● in different dose &stimates, and large individual Total Paretieml Nuttion (TP~ ~empy. differences in weight, organ size, and clearance Absent or delayd visualization of the gallbladder has kinetics may result in actual doses that deviate by been reported in patients who are receiving TPN more than an order of magnitude from published therapy (72). This may result in false-positive images estimates. The effect of a fatty med given at the end in patients without grdlbladder disease. During TPN of hepatobiliary scintigraph y on the absorbed radiation therapy, the gallbladder is relatively inactive, which is dose has been reported by Wu and coworkers (65). thought to result in bile stasis and the formation of A scheme for estimating absorbed radiation dose to highly viscous gallbladder bile that impties the flow newborns from Tc-99m diethyl-IDA has also been of additional bile into the gallbladder. reportd (66). Mkcellaneous Dregs. The effect on gallbladder contractility of a number of drugs including atropine,

T.IIIIc 3. Fslit>>alti abrkd radiation doies [r”., 113mCi (370 MHq) calcium channel blockers, and progesterone has b~n reviewed by Kloiber, et al (73). This is of particular concern in gallbladder ejection fraction studies, a topic that will be discussed later. 1.!”?, 029 1291 045 (4 5) Ow (?8) o 6? (h?) 047(471 OM1 (H])

Cq,llt,lJddcr I ,33 (13.3) OT9 (79) 1.2 (120) 140 (14 o) 137 (1?.7) 125 [12 5) wall Adverse Ractinns small 2.08 (21J8) 018 (1 8) 22 (22(1) 163 (163) 2,W (299) I ho (160) lnt-tine Exceedingly few incidents of adverse reactions

UPPI Large 3 m l?7.~) n 22 (2.21 38 (38 O) 3.25 (32.5) 474 (47 4) 2,48 (24,8) attributed to current hepatobiliary radiopharma- I“i*line ceuticals have been reportd. Single cases of chills Lower Ldrge 1.58 (15.8) 024 (24) 2.8 (28 0) 2 M (225) 3M (364) 197 (1Y 7) IT,t<%d”v and nausea have been observed following injection of Udney 020 [2.0) 026 (2 (,) n 22 (2.2) 019 (19) Tc-99m lidofenin (54). A few cases of itching at the Urln.ry 0 % (S.6) 3.05 (30 5) 092 (9.21 003 (88) 0.29 (29) 242 (24.2) Bladder Wall injection site and development of hypersensitivity ● Ovariw 039 (3 q) 021 (2,1) 082 (n 2) 075 (751 101 (101) O,u (64) reactions such as skin eruptions have also been Tstm 0.06 (0.6) 0.13 (13) 0.06 (0.6) 0.06 (O6) 003 (0.5) 011 (1 1) reportd (53,55). Red Mamw o Za (2.8) 0.15 (! 5) 034 (34) 0.25 (25) Use During Pregnancy and in Nursing Mothers According to the manufacturers, it is not known if PRECAUTIONS hepatobiliary radiopharmaceuticals could cause fetal harm (53,54,55). These radiopharmaceuticals should Drug Interference not be given to pregnant or possibly pregnant women A variety of drugs have been reported to interfere urdess a nuclear medicine study is clearly needed. with the movement of radiopharmaceuticals through Package insefi also state that it is not known if these the hepatobiliary system (67,68). hepatobiliary agents are excreted in human milk. Narcotic Atigesics. Morphine in particular and However, Tc-99m pertechnetate, which may be opiates in general cause impaired emptying of bile into present in small amounts, is known to be excreted in the small intestine because they induce spasm in the brewt milk during lactation and the manufacturers sphincter of Oddi (69). Cholescintigraphy in the therefore recommend that formula feedings should presence of narcotic analgesics will show prolonged temporarily be substituted for breast feeding. Actual visualization of the gallbladder and the common bile measurements of Tc-99m disofenin excretion have duct and no movement of activity into the bowel. recently been performed in a group of six lactating This could result in the erronmus diagnosis of biliary women (74). Up to at least 24 hours following Tc- duct obstruction. This is significant, since narcotic 99m disofenin administration, less than 0.3% of the analgesics are often the treatment of choice for injected dose ‘was found in breast milk, and the patients presenting with severe abdominal pain. authors conclude that interruption of breast feeding is Ideally, hepatobiliary imaging should not be not essential. If intermption is preferred, and it is undertaken until the effect of the drug dissipates, possible to plan in advance, patients should be ● which may require 6-12 hours (70). encouraged to express and save extra milk prior to Nicotinic Acti. Large doses of nicotinic acid have administration of radiotracer; this can then be used been known to cause significant hepatic dysfunction, during the interruption period. resulting in poor hepatocyte uptake of

13 HEPATOBILIARY IMAGING regions of interwt over 1iver parenchyma, common bile duct, or gallbladder. Functional parameters such Biliary disease is highly prevalent in our society, as hepatic extraction fraction or gallbladder ejection and is seen in a variety of settings ranging from fraction can then be evaluated (70). Additional biliary colic in otherwise healthy young women to imagw in the lateral or oblique projections may help ● life-threatening biliary sepsis in elderly patients with define the anatomic location of “collections of radio- severe intercurrent disease. The initial assessment of activity. For example, a lateral view may help distin- patients with symptoms suggwtive of biliary disease guish activity in the gallbladder (anterior) from renal must include a full clinical examination and history. excretion @osterior). Delayed images are obtained if In patients with gallstones, the symptoms may be all the desired information is not obtained during the sufflciently typical to diagnose gallbladder disease first hour. The normal appearance rate of cholescint- from historic information only. Other patients may igraphic tracers in the various parts of the hepato- present with vague and ill-defined symptoms that biliary system has already been discussed. In the could be caused by a variety of pathological conditions evaluation of hepatobiliary images, the physician con- (5,9). Various laboratory tests and imaging modalities siders the various functional steps leading from radio- other than cholescintigraphy add valuable diagnostic tracer delivery to the liver to the appearance of activity information to the workup of these patients, but will in the gut as well as hepatobiliary morphology (75). not be reviewed here. Hepatobiliary imaging is an important diagnostic modality in the differential Augmented Chol@cintigraphy diagnosis of many hepatobiliary abnormalities, which Cholecystokinetic Agetis. In humans, gallbladder will be discussed in the following sections. emptying in response to a fatty meal is primarily due to the release of endogenous cholecystokinin (CCK). Imaging Methods and Analysis This hormone, as well as its synthetic C-terminal Patient Preparation. Patients are fasted for at least octapeptide analog, sincalide, have been used as two hours before the study, preferably overnight, but adjuncts in the evaluation of hepatobiliary disease. not for longer than 24 hours (1,2,70,75). In the Their effects include gallbladder contraction, presence of food in the upper ga.strointestinal tract the relaxation of the sphincter of Oddi, and increased bile gallbladder may be contracting, which interferes with secretion (73,76). A fatty meal or a standardized inflow of radioactive bile and may lead to a false- preparation such as Nw-Cholex, a 50% emulsion of positive study. Prolonged fasting should be avoided corn oil in water, will have the same effect. Xynos, as it may also cause non-visualization of a normal et al (77) reported on the reproducibility of gallbladder. Narcotics or sedatives that act on the gallbladder emptying studies with Tc-99m diethyl-IDA sphincter of Oddi should be stopped six to 12 hours following ingestion of 250 ml milk. Thirty before the examination (70). individuals were studied twice, two to five weeks Imuging Technique and Adysis. The usual dose apart. The milk was given 30 minutes after the range for Tc-99m cholescintigraphic agents is 3-10 radioactive tracer dose. Good reproducibility was mCi (100-370 MBq) for adult patients. In children observed for both gallbladder ejection fraction and for the dose is adjusted according to age and weight. the lag time between milk ingestion and start of Cholescintigraphy is best performd with a large field- emptying. However, use of CCK or sincalide does of-view scintillation camera equipped with a low- provide control of both dose and infusion rate, which energy, high-resolution collimator. The patient is may make it easier to compare studies from different placed under the camera in the supine position such institutions. Sincalide for intravenous administration that the liver, gallbladder, and duodenum is within the is available in 5 pg vials from Squibb Diagnostics field of view. Sequential images are obtained using a under the trade name Kinevac. Reported side effects 20% energy window centered at 140 keV. Imaging include nausea, abdominal pain, and the urge to protocols vary between institutions and depend on defecate. Transient dizziness and flushing have also what information is to be obtained. Typically, serial been reported. The ordy contraindication to its use is anterior images are obtained at five- to 15-minute sensitivity to sincalide. The usual intravenous dose of intervals up to 60 minutes after injection. The first sincalide is 0.02 pg/kg to be infused at a uniform rate image is acquired for 750,000 to one million counts over a three- to five-minute period (70,76,78,79). and subsequent images are acquired for the same time The dose must not be injected as a bolus, and some as the first image (1,70,75). Simultaneous y, a reports advocate a slower infusion rate of up to 15 dynamic study can be obtained at a rate of one frame minutes (73,75) in order to reduce the incidence of per minute and stored in a computer. Time-activity abdominal pain. curves may be generated from this data by placing Gallbladder emptying can be utilized in two

14 different ways in cholwcintigraphy: (a) to empty the radiotracer is visualizd in the common bile duct and gallbladder prior to radiopharmaceutical injection in small bowel, but not in the gallbladder. There must order to optimize subsequent filling, and (b) to study be sufficient activity left in the hepatobiliary trw to the contractile function of the gallbladder. The first permit gallbladder visualization. Imaging is continual ● approach may be useful in patients who have been for another 30 minutes; persistent non-visualization is fasting for a prolonged (> 24 hours) period of time, considered to indicate acute cholecystitis (76,82). or who are on total parenteral nutrition (70,76). As The usual dose is 0.04 mg/kg (up to 4 mg) of previously mentioned, the prwence of very viscous morphine sulfate diluted to 10 ml with saline for gallbladder bile in these patients rndy prevent injection. Administration is by slow I.V, push over radiotracer flow through the cystic duct. Sincalide two to three minutes (76), The increasd intraductal should be given 30 minutes prior to radiotracer prasure causal by morphine can result in symptoms injection (76). It has been suggwted that rather than ranging from epigastric distress to typical biliary routinely pretreating this group of patients, it is better colic. In Choy’s initial study (81) about 40% of to use this technique only when the gallbladder is not patien~ reportd transient cramps. If very severe pain visualized within one to two hours of tracer injection should occur, the effect of morphine can be reversed (80). At this point, sincalide can be injectd, followed with naloxene. Morphine may produce a wide by a second radiotracer dose 30 minutes later. spectrum of unwanted effects such as respiratory IrIgallbladder ejection fraction studies, sincalide is deprwsion, nausea, and vomiting. Administration of not infused until after the gallbladder is visualized. A a single dose as in these augmentation studies appears dynamic study of gallbladder emptying is obtained and to be well tolerated, however (81). There are few used to determine the ejection fraction. Assuming contraindications to the use of morphine. Allergic complete mixing of radiotracer with gallbladder reactions may occur, and it may not be advisable to contents, the percent decrease in activity corrwponds use this approach in patien~ with a history of to the volume being evacuated (73). Although there morphine addiction. False-positive studies can occur is no universal agreement regarding what a normal secondary to many causes, the most common being ejection fraction should be, most investigators feel that chronic cholecystitis (76,82,83). False-negative an ejection fraction below 35-40% is clearly abnormal studies are less common. Studies comparing delayed ,( 75,78,79). It should, however, be noted that ejection irndging to morphine augmentation have shown that fraction can vary significantly depending on both dose the false-positive rate can be decreased using and duration of sincalide infusion (64). Various morphine (84,85), medications may either inhibit or stimulate gallbladder PhenobarbU. Phenobarbital has been used in the emptying, and should be discontinued prior to an pediatric population in conjunction with ejection fraction study, Care is also required in cholwcintigraphy to improve the accuracy of patients with systemic diseases that may have an effect differentiating neonatal hepatitis from biliary atrwia on gallbladder contraction (73). The inability of the (76,86). The general stimulating effect of gallbladder to contract and eject bile normally is a phenobarbital on the liver is well known. helpful piece of information in the evaluation of Phenobarbital incrwdses bilirubin conjugation and patients with suspectd chronic acalculous biliary excretion, enhances bile flow, and increas= the disease, which will be discussed later. hepatic uptake of other organic anions such m the Morphine. Cholescintigraphy is considered common hepatobiliary imaging agents (76,86). diagnostic for acute cholecystitis if the gallbladder is Increased uptake and visualization of the liver leads to not visualized within four hours of a more reliable determination of the underlying radiopharmaceutical injection. Markedly delayed etiology of neonatal jaundice (to be discussed later). In visualization may be observed in patients with chronic phenobarbital-augmented cholescintigraphy, thepatient cholecystitis, bile stasis secondary to prolonged is premeditated orally with 5 mg/kg per day of fasting, and alcoholic liver disedse (81). Morphine phenobarbital for three to sevm consecutive days. augmented cholescintigraphy can be utilized to speed The radiotracer, usually around 1 mCi (37 MBq) Tc- up the differentiation of patients with complete cystic 99m disofenin, is then injected (76,86), Serial images duct obstruction from those who for other reasons are obtained and computer-generated time-activity have impaired flow of tracer into the gallbladder (82). curves can also be generated. Lateral images can help Morphine acts by constricting the sphincter of Oddi, to separate activity in the bowel from renal excretion. ● resulting in a prompt elevation of biliary tract pressure Delayed images are obtained up to 24 hours afier that may cause radionuclide to flow into the injection if the bowel is not seen on earlier imagw. gallbladder (76,8 1). The usual protocol is to If any radiotracer passes into the bowel, the diagnosis administer morphine if, after 40 to 60 minutes the of biliary atresia is excluded. Phenobarbiti is

15 available in a variety of dosage forms, including diagnosd with acute acalculous cholecystitis (5,9). liquids. The safety of phenobarbital therapy in Cholescintigraphy is a non-inv~sive and highly children and neonates has been established (86). sensitive diagnostic test for evaluation of cystic duct Allergic reactions such as swelling have been observed obstruction. Failure to visualize the gallbladder within in individuals who are hypersensitive to barbiturates. 4 hours of radiotracer injection has been 98 % accurate ● in the diagnosis of acute cholecystitis (63). Calculous Cholecystitis and acalculous acute cholecystitis present with Cholecystitis, or inflammation of the gallbladder, identical imaging patterns, As discussed earlier, a may be acute or chronic in its presentation. In acute number of conditions are associated with delayd as cholecystitis the cystic duct is completely obstructed, well as non-visualization of the gallbladder in the which incites an inflammatory response in the absence of complete cystic duct obstruction. The use gallbladder. The acute attack is most often an of sincalide or morphine augmentation as well as exacerbation of underl ying chronic cholecystitis, and delayd imaging up to 24 hours results in increased although it may be convenient to view the two as sensitivity in thwe patients. Depending on the patient separate entities, cholecystitis frequently represents a population and the imaging protocol, the diagnosis of continuum of dise~e (1,8). Acute cholecystitis is acute cholecystitis by Tc-99m IDA scintigraphy has an nearly always associated with gallstone disease. In overall sensitivity of 92-100% and specificity of 95- acute acalculous cholecystitis the cystic duct 100% (63,64,70,76,81). obstruction is caused by edema from the inflamed Chronic cholecystitis is the most common biliary gallbladder. The factors that induce gallbladder disorder but also the most di~cult to evaluate (2,8), inflammation are not well understood, but a number It is most frequently associated with gallstone disease of factors have been implicated, such as lithogenic (8,87) and patients may have experienced episodes of bile, trappd bile acids, regurgitated pancreatic juice, biliary colic. Most patients have functional cystic prostaglandins, and others (8,9). ducts, and although many patients may have delayed Cholecystitis is one of the most common abdominal gallbladder visualization, cholescintigrams are emergencies and must be distinguish from other generally normal. Since biliary calculi can be abdominal conditions with similar symptoms. Prompt detected using ultrasound, the usefulness of diagnosis and treatment is of the essence, particularly cholescintigraphy in this group of patients is limited in patients who are both very ill and elderly. Patients (1,87). A subset of patients with chronic cholecystitis ● may present with a wide variety of complaints and will not have calculi. These patients present with physical findings. Symptoms vary from vague, recurrent right upper quadrant pain, but blood poorly-defined abdominal discomfort to short spasms chemistries, oral cholecystograms, and ultrasound of biliary colic or severe right upper quadrant pain studies are normal (8, 87). Three major categories of that may last for several days (9). The rapid and abdominal disease can produce typical “biliary” pain intense pain of biliary colic is typically caused by a in the absence of gallstones: (a) chronic acalculous stone passing through the cystic duct, but if the stone cholecystitis or gallbladder dyskinesia, (b) cystic duct becomes lodged in the cystic duct the pain will syndrome or sphincter of Oddi dysfunction, and (c) continue until the stone passes through (2,9). Acute irritable bowel syndrome. If the symptoms are due to calculous cholecystitis is self-limiting in 85% of impaired gallbladder evacuation (as in cystic duct patients, but recurrence may eventually follow unless syndrome) and/or impaired gallbladder contraction (as the gallbladder is removed (8). If a stone remains in chronic acalculous cholecystitis and gallbladder Iodgti in the cystic duct the patient will develop dysfunction), the patient could benefit from serious complications such as complete necrosis of the cholecystectomy. A number of recent studies gallbladder wall and perforation (5,8,9). As (73,76,79) support the use of gallbladder emptying previously discussed, cholecystectomy remains the studies using sincalide to predict which patients will only definitive cure for gallstone disease, and may become symptom-free following gallbladder removal. take place as soon as the diagnosis has been established, or after several weeks, when the patient Sphincter of Oddi Dysfunction is stabilized and the inflammatory process has resolved Sphincter of Oddi dysfunction is characterized by (2,8,9). The epidemiology of acalculous cholecystitis a physiologic obstruction to bile drainage from the differs from cholecystitis associated with stones (2). common bile duct into the bowel. It is seen in Acute acalculous cholecystitis has been linked to patients with recurrent pain afier cholecystectomy ● previous surgery, mwsive trauma, extensive burns, (70,75). Sincalide augmented cholescintigraphy has cardiovascular disorders, and malignancy (5,8). been proposed as a method to detect sphincter of Oddi Removal of the gallbladder is warranted in patients dysfunction. The disorder can be identified if there is

16

.— a delay in biliary-to-bowel transit of radiotracer and a duct atresia is defined as the lack of lumen in part or fidilure of the sphincter of Oddi to relax following all of the extrahepatic biliary tract, causing complete sincalide administration (76,83). A scoring system obstruction to bile flow. It is considered to be the that combines visual and quantitative criteria haa rwult of a progrmsive, d~tructive inflammatory ● shown improved sensitivity and specificity for the process of unknown etiology that eventually destroys diagnosis of sphincter of Oddi dysfunction (88). the whole bile duct system and results in death from cirrhotic liver disease. Biliary atresia can be treatd Biliary Obstruction successfully by surgery only if performed at a very In the presence of good hepatocyte function, acute early age (5,86,87). Nwnatal hepatitis is a clinical total bile duct obstruction by gallstones can be readil y syndrome that is not associated with a specific viral identified using cholescintigraph y. Hepatic uptake of infection in the majority of cases. There are many tracer will be prompt, with no evidence of hiliary causw for prolonged conjugated hyperbilirubinemia in excretion by four hours. In the later stages of total nmnat~, including me~~bolic disorders, infectious obstruction, hepatic uptake will decrease and diseases, and intoxicants (78,87). In many cases differentiation of obstruction from hepatocellular cholestasis attributable to these causes is mdically disease becomes progressively more difficult. In treatable and reversible (5). The clinical, biochemical partial bile duct obstruction, the biliary tree is and histologic features of these two disorders are often visualized to the level of obstruction, filling defec~ or similar, making the differential diagnosis extremely narrowing may he observed, and some radiotracer will difficult. be seen downstream from the area of obstruction In biliary atresia, the radiotracer does not enter the (70,75). Patients with partial common bile duct bowel. In the absence of significant cirrhosis, obstruction also show reduction in the sincalide hepatocyte function is preserved, and there is rapid induced gallbladder ejection fraction and ejection rate blood clearance and hepatic uptake, resulting in early (43). definition of liver boundaries, which persists throughout the study (76,86). Patients with nwnatal Bilti bkage and Reflux hepatitis in the presence of a patent extrahepatic Hepatobiliary scintigraph y has proven to be a very biliary tree may present with a more variable imaging sensitive method of disclosing and monitoring intra- pattern (86). Depending on the severity of cholestasis and extrahepatic bile leaks. These are seen most and hepatocellular disease, initial liver uptake may be common]y following biliary tract surgery, but can also normal or markedly decredsed. The gallbladder is not be a result of abdominal trauma or inflammatory always visualized. Hepatic clearance is delayd, erosion of the gallbladder wall (75,87,89), The resulting in delayed visualkation of bowel activity. location of bile accumulation depends on the site of However, detection of even the slightwt amount of injury, and images in several different projections will radioactivity in the bowel in these patients identifies be helpful in distin~ishing free bile from normal biliary patency and argues against surgical intervention areds of radiotracer localization. Delayed images (75). If hepatic uptake is extremely poor due to very should also be obtained. Cholescintigraphy is also an high serum bilirubin levels, it may not be possible to excellent technique for demonstrating patency and identifi bowel activity on images. The liver uptake function of biliary-enteric anastomoses (75,89). The pattern still makes it feasible to make a differential non-invasive detection and quantitation of diagnosis. If hepatocyte function is severely enterogastric bile reflux can only be performed using compromise, the activity initially seen in the liver is cholescintigraphy (83). The technique is of value for primarily due to blood pool activity, and it can be the confirmation and follow-up of bile reflux after observed that it will decreme over time at the same surgical interventions. rate as cardiac activity, a pattern not seen in biliary atresia (86). As previously mentioned, pretreatment Neonattil Jaundice with phenobarbital significantly improves the accuracy In the pediatric population, cholescintigraphy is a of cholescintigraphy in differentiating extrahepatic valuable noninvasive technique for the evaluation of biliary atresia from nwnatal hepatitis, at least when prolongti jaundice. Jaundice in the nwnate can have the agent Tc-99m paraisopropyl-IDA was used (86). numerous causes, but conjugated hyperbilirubinemia In a seriu of 27 patien~ with nwnatal jaundice that that persists beyond the first month of life is usually did not receive phenobarbiti pretreatment, Gerhold due to either neonatal hepatitis or biliary atresia (5). and his msociatw (90) reportd that the most useful It is important to identify the cause as early as diagnostic criterion for biliary atresia was absence of possible, because the treatment and prognosis of these intestinal radioactivity up to 24 hours after radiotracer two conditions are quite different. Extrahepatic bile injection. All nine patients who demonstrated

17 intestinal activity did so by three hours, These be measured directly. However, because of the liver’s patients were studied with either Tc-99m disofenin or dual blood supply and the complication of Tc-99m diethyl-IDA. The sensitivity and specificity simultaneous hepatocellular uptake and excretion, this for biliary atresia in their study were 97% and 82%, is not possible using Tc-99m IDA analogs. Juni and respectively. coworkers have calculated HEF by an indirect method ● using deconvolution analysis (9 1,92,93). QUANTITATION OF HEPATIC FUNCTION Deconvolution analysis is a computer-assisted mathematical technique which can correct an organ’s In the early stagw of liver disease, serial time-activity curve for the dynamical y changing quantitative assessment of liver function would be pattern of blood activity (obtained from the heart’s helpful in monitoring therapy and in determining time-activity curve) being presentd to that organ (92). prognosis. However, current noninvasive methods are Care must be taken so that no biliary, renal, or major neither simple nor reliable (8,9 1). Due to the vascular activity or scatter is included in the region(s) multitude of metabolic tasks performed by the liver, of interest used to generate the hepatic time-activity none of the liver function parameters that can be curve (93). In a group of 53 patients with acute easily measured will reflect overall hepatic capacity. jaundice, Juni et al. (91) found that this measure of Another major use of such a method would be to help HEF was most specific during the first few days after differentiate between biliary obstruction and onset of j aundice, with fairly good separation between hepatocellular disease in the jaundiced patient. Up to patients with normal livers (80-100%) or acute biliary very recently, techniques using radiopharmaceuti cals obstruction (65- 100%) versus those with acute have met with limited success. The ideal hepatocellular dysfunction (14-77 %). Another study radiopharmaceutical for quantitation of hepatocyte (93) showed markedly decredsed HEF in patients with function should be highly specific for liver uptake, alcoholic cirrhosis compared to patients with diseases and should remain in the hepatocyte long enough to confined primarily to the biliary tract. It appears that allow sufficient data acquisition. The in-vivo HEF is an improved quantitative measure of hepatic distribution should be solely a function of function compared to other parameters assessd using hepatocellular function, and should not be affected by hepatobiliary radiopharmaceuticals. The deconvolu- factors such as elevated bilirubin levels (38). tion analysis is rapid and entirely automatd and can ● Attempts at quantitation of liver filnction have been be performed using standard commercial nuclear made using Tc-99m sulfur colloid, however, colloids mdicine computers (91). Its clinical utility will be are taken up by reticuloendothelial cells and are not tested further as more institutions add this analysis to specific for the liver. Liver uptake often correlates their hepatobiliary imaging procedures. poorly with hepatocellular function (5). Hepatobiliary radiopharmaceuticals have been studied extensive y, Quantitation of Hepatic Binding Protein Rweptors going back to 1-131 rose bengal. More recently, the In addition to the transport pathways for hepatocyte Tc-99m IDA analogs have been used. Quantitative uptake discussed earlier, the liver also has the ability measurement of liver uptake of Tc-99m IDA analogs to selectively extract macromolecular ligands from is complicated in the jaundiced patient by delayd blood by receptor-mediated endocytosis (2,5). Of the blood clearance and simultaneous renal excretion. receptors on the hepatocyte surface, the Recirculation of tracer and active hepatocyte uptake is asialoglycoprotein receptor is the best characterized. prolonged, and this is further complicated by excretion This receptor is found only on mammalian hepato- into bile of tracer that was taken up by the liver early cytes, and is often referred to as hepatic binding on, Multicompartmental analysis of blood pool and protein (HBP) receptor (94). The hepatic hepatic uptake using pharmacokinetic models of asialoglycoprotein receptor promotes the clearance of varying complexity have been attempted, but results serum glycoproteins that have exposed galactosyl have been discouraging (91). residues made terminal by removal of sialic acid. After binding at the hepatocyte membrane, the ligand- Measurement of Heptitic Extraction Fraction (HEF) receptor complex is internalized and transported to Using Tc-99m IDA Analogs hepatic lysosomes where the complex dissociates and Estimation of the fraction of radiotracer that can be the ligand is catabolized. The receptors recycle back removed by the liver during a single pass, or to the hepatocyte membrane where the entire process extraction fraction, has been proposed as a quantitative is repedted. It has been postulated, but not proven, measure of liver function (91,92). If the tracer could that the HBP receptor participates in the regulation of be presented as a bolus directly into the blood supply turnover of serum glycoproteins. Alterations in of the liver, hepatic extraction fraction (HEF) could asialoglycoprotein receptor binding has been demonstrated in specific physiologic and pathological physiologic rwponse (15). The parameters that states (5). Since the HBP receptor is highly specific govern the rate of a receptor-binding process are the for ligands containing exposed galactose rwidues, this receptor and Iigand concentrations, and the forward type of ligand has been investigated as a potential and reverse binding constats (102). Since the radiopharmaceutical for quantitation of hepatocyte binding of Tc-NGA is highly irreversible (96), the function. There is currently a great deal of interest in reverse binding constant can be ignored (102). A receptor-specific radiopharmaceuticals (15). The mathematical model has been developed that permits potential exists for the utilization of mathematical estimation of kinetic parameters that represent receptor models to obtain in vivo measurements of receptor concentration and forward binding rate from imaging number and affinity from imaging observations using studies using 4+ mCi (148-222 MB@ Tc-99m NGA. receptor-specific radiopharmaceuticals. It is antici- The kinetic model requires liver and heart time- pated that such data may provide a quantitative index activity data for the first 30 minutes after injection for patient diagnosis and management (15,95). plus activity determination in a blood sample taken at Technetium-99m galactosyl-nwglycoalbumin (Tc- three minutes (98, 102). The kinetic model has been NGA) is a synthetic ligand that exhibits high validated by independent in vitro assay of tissue specificity for HBP receptor binding (95,96,97,98). obtaind by liver biopsy (95), Multiple clinical The NGA ligand is prepard by covalently attaching studies using Tc-NGA and Tc-GSA have been the galactosyl unit to human serum albumin (99). The reported from investigators in the United States, number of galactose units per albumin molecule can Europe, and Japan. A recent review article (98) be controlled, and since it is known that the ability of providw an overview of the various liver disorders glycoproteins to bind to the HBP receptor increases that have been studied, which include chronic liver dramatically as more galactose units are added (5), disease, primary and secondary liver carcinoma, liver this gives control of both affinity and binding rate. transplantation, and acute viral hepatitis. This NGA has commonly been radiolabeled with Tc-99m technique for fictional hepatic imaging shows using an electrolytic method (99) for the reduction of promise as a sensitive measure of functioning pertechnetate. In Japan, Tc-99m-DTPA-galactosyl hepatocyte mass, of particular interest when human serum albumin (Tc-GSA) is available as a hepatectomy for hepatocellul~ carcinoma or liver stannous ion containing kit (100). Both methods transplantation is contemplated. Serial studies may result in stable preparations of high radiochemical help document changes in hepatocyte function in purity. Animal studies have confirmd that Tc-NGA patients being trwdted for active viral hepatitis. This is highly specific for liver with a rapid uptake phase technique, while still undergoing validation, holds and a low rate of metabolism and liver exit (97,99). significant potential for obtaining information that is Both renal and gastrointestinal excretion does occur, not readily available using other imaging techniques or but the excretion rate is too low to affect liver tirne- conventio-nal liver function tests. activity curves during the first 30 minutes after injection. Since Tc-NGA is not taken up by the CONCLUSIONS general anion extraction mechanism, it is not affected by high serum bilirubin levels. Its rate of hepatocyte Currently available Tc-99m labeled hepatobiliarv accumulation is dependent on the amount of Iigand radiopharmaceuticals have been developed based o; injected and is proportioned to the number of what is known about the liver’s organic anion galactose units on the albumin (97). This clearance pathway. This group of radiophar- radiopharmaceutical can be designed to have moderate maceuticals serves as an example of the utilization of receptor affinity so that the rate at which it binds is structure-activity relationship analysis during the not governed solely by blood flow, but depends on the development phase. Technetium-99m IDA analogs in concentrations of both ligand and receptor (e.g., a use today satisfy most of the criteria for an ideal second order process) (97). Since Tc-NGA has been radiopharmaceutical to study the hepatobiliary shown to have relatively low toxicity (99), it can be excretion pathway. Although the clearance of these used in a dose large enough to produce a second order agents by the liver is reduced in the presence of high response. Changes in liver and blood time-activity serum bilirubin levels, clinically useful imagw can be curves obtained with Tc-NGA in pigs were observd obtained in most situations. Chol~cintigraphy with when either hepatic blood flow, Iigand-receptor Tc-99m IDA analogs is a noninvasive, highly sensitive affinity, or molar dose of ligand were altered (101). test for the evaluation of the functional status of Tc-NGA appears to exhibit the unique properties of hepatic and cystic and the gallbladder. It is also usd receptor-specific ligands: high ligand affinity, to localize bile leaks and alterations in the bile specificityy, saturability, and distribution in relation to pathway rwulting from surgery or trauma, and to

19 differentiate between surgical and medical jaundice in Clinical Perspectives. Vol I. Boca Raton: CRC the nmnate. Improved diagnostic information maybe Press, 1986:89-116. obtained by utilizing drug-augmented cholescintigraphic methods. Technetium-99m IDA 11. Taplin GV, Meredith OM, Kade H. The analogs do not possess ideal characteristics for radioactive (I-1 31 tagged) rose bengal uptake- ● excretion test for liver fimction using external quantitative assessment of liver function. However, gamma-ray scintillation counting twhniques. J hepatic extraction fraction estimates may be ob~~ined Lub Clin Med 1955; 45:665-678. using a computer-assistd technique that allows continuous correction for blood pool activity, 12. smith RL. me ficreto~ Function of Bile. Receptor-specific agenw, Tc-99m labeled NGA and hndon: Chapman& Hall, 1973. GSA, are currently being evaluated for quantitation of fictional hepatocyte mass. These agents are not 13. Hirom PC, Millburn P, Smith RL, Williams RT. affected by elevated serum bilirubin levels, and are Species variations in the threshold rnolectiar- highly specific for the asialogylcoprotein receptor weight factor for the biliary excretion of organic which is found ordy on mammalian hepatocytes. anions. Biochem J 1972;129: 1071-1077.

ACKNOWLEDGEMENT 14. Firnau G. Why do Tc-99m chelates work for cholescintigraphy? Eur J Nucl Md 1976; 1:137- 139. me author would like to thank Betty Trent Jor her skillfil assistance in the preparation of thti wnuscript. 15. Eckelman WC. The development of single-photon emitting receptor-binding radiotracers. In: Nunu References AD, editor. Radiophamaceuticals: Chemistiy and Pharmacology. New York: MarMl Dekker, Inc., 1. Freitas JE. Cholescintigraphy in acute and chronic 1992:167-219. chol=ystitis. Semin Nucl Med 1982; 12:18-26. 16. Serafti AN, Smoak WM, Hupf HB, Beaver JE, 2. Gholson CF, Bacon BR. Essentiak of Clinical Holder J, GilSon AJ. Iodine-123 rose bengal: an Hematology. St, buis: Mosby-Year Book, 1993. improved hepatobiliary imaging agent. J NUC1 Med 1975; 16:629-632. ● 3. Tavoloni N, Berk, PD, editors. Hepatic Trampon and Bile Secretion. New York: Raven Press, 1993. 17. Tubis M, Krishnatnurthy GT, Endow JS, BIahd WH. ~c-penicillamine, a new cholescinti- 4, LeBouton AV, editor. Molecular and Cell Biology graphic agent. J Nucl Med 1972; 13:652-654. of the Liver, Boca Raton: CRC Press, 1993. 18. Chervu LR, Nunn AD, Loberg MD. Radiophar- 5. Zakim D, Boyer TD, ditors. Hepaiology. A maceuticals for hepatobiliary imaging. Semin Nucl Textbook of Liver Diseme. 2nd 4. Philadelphia: Med 1982; 12:5-17. Saunders, 1990. 19. Baker RJ, Bellen JC, Ronai PM. Technetium- 6. Barbara L, Dowling RH, Hofmann AF, Roda E. 99m-pyridoxylideneglutamate: a new hepatobiliary Recent Advances in Bile Acid Research. New radiopharrnaceutical. I. Experimental aspects. J York: Raven Press, 1985. Nucl Med 1975; 16:720-727.

7. Stein JH, editor-in-chief. Internal Medicine. St. 20. Eichhorn GL, Dawes JW. Ihe metal complexes Louis: Mosby, 1994. of vitamin BAand Schiffs base derivatives. J Am Chem Soc 1954; 76:5663-5667. 8. Sherlock S, Dooley J. Disewes of the Liver and Biliary System. 9th ed. Oxford: BlackWell Sci. 21. Davis L, Roddy F, Metz,ler DE. Metal chelatw of Publications, 1993. imina derived from pyridoxal and amino acids. J Am Chem Soc 1961; 83: 127-134. 9. Greenfield LJ, Mulholland MW, Oldham KT, Belenoch GB. Surge~: Scientl~c Principles and 22. Chiotellis E, Subramartian G, McAfee JG. Prac~ice. Philadelphia: J.B. Lippincott Co., 1993. Preparation of Tc-99m labeled pyridoxal-amino acid complexes and their evaluation. Znt J NUC1 ● 10. Fritzberg AR. Advances in the development of Med Biol 1977 ;4:29-41. hepatobiliary radiopharmaceuticals. In: Fritzberg AR, editor. Radiophamaceuticals: Progress and

20 23. Jansholt A-L, Krohn KA, S~ RC, Matolo 34. va Wyk AJ, Fourie PJ, van Zyl WH, titter MG, M. NM, DeNardo GL. Catabolism and protein mnaar PC. Synthesis of five new wc-HIDA binding of Tc-99m pyridoxylideneglutamate. J isomers and comparison with yc-HIDA. Eur J ● NUCl Med 1978; 19:1036-1044. Nucl Med1979;4:445-448. 24. Kubota H, Eckelman WC, Poulose KP, Reba RC. 35. Jansholt A-L, Vera DR, Krohn KA, S~ RC. Technetium-99m-pyridoxylidene-glutarnate, a new In vivo kinetics of hepatobiliary agents in agent for gallbladder imaging: comparison with jaundiced animals. h: Radiophannaceuticak IL 1311-rose bengal. J Nucl Med 1976; 17:36-39. Proc. Second Internat. Symposium on Radiopharmaceuticals. New York: Sot. Nucl. 25. Ronai PM, Baker RJ, Bellen JC, Collins PJ, Med. 1979, 555-564. Anderson PJ, Lander H. Technetium-99 m- pyricloxylideneglutamate: a new hepatohiliary 36. Nicholson RW, Herman KJ, Shields RA, Tests radiophamceutical. II. Clinical aspects. J Nucl HJ. The plasma protein binding of HIDA. Eur J Med 1975; 16:728-737. Nucl Med 1980; 5:311-312.

26. Stadalnik RC, Matolo NM, Jansholt A-L, Krohn 37. Ryan J, Cooper M, bberg M, Harvey E, KA, DeNardo CL, Wolfman EF. Technetium- Sikorski S. T&hnetium-99m-labeld N-(2,6- 99m pyridoxylideneglutamate (P. G.) dimethylphenylcarbamoylmethyl) iminodiacetic cholescintigraphy. Radiology 1976; 121:657-661. acid (Tc-99m HID A): a new radiopharmaceutical for hepatobiliary imaging studies. J NUCl Med 27. Wistow BW, Subrarnanian G, Van H&rtum RL, 1977; 18:997-1004. Henderson RW, Gagne GM, Hall RC, McAf~ JG. h evaluation of We-labeled hepatobiliary 38. Harvey E, Loberg M, Ryan J, Sikorski S, Faith agents. J Nucl Med 1977; 8:455-461. W, Cooper M. Hepatic clearance mmhanism of Tc-99m-HIDA and its effect on quantitation of 28. Kato M, Hazue M. Tc-99m (Sri) hepatobiliary function: concise communication. J pyridoxyliden-minates: preparation and biologic Nucl Med 1979; 20:310-313. evaluation. J Nucl Med 1978; 19:397-406. 39. Chiotellis E, Varvarigou A. ~c-labeled N- 0 29. Kato-Azuma M. Tc-99m (Sn)-N-pyridoxyl- substituted carbamoyl iminodiacetates: relationship arninates: a new series of hepatobiliary imaging betw=n structure and biodistribution. Int J Nucl agents. J Nucl Med 1982; 23:517-524. Med Biol 1980;7: 1-7.

30. Loberg MD, Cooper M, Harvey E, Callery P, 40. Chiotellis E, Varvarigou A, Koutoulidis C. Faith W. Development of new radiophar- Comparative in vivo kinetics of some new ‘Tc- maceuticals based on N-substitution of labeled acetanilido irninodiacetates. Eur J Nucl irninodiacetic acid. J Nucl Med 1976; 17:633-638. Med 1981; 6:241-244.

31. Loberg MD, Fields AT. Chemical structure of 41. Nunn AD, Loberg MD, Conley RA. A structure- teclmetium-99m-labeled N-(2,6 -dimethylphenyl- distribution-relationship approach leading to the carbamoylmethyl)- iminodiacetic acid (Tc-HIDA). development of Tc-99m mebrofenin: m improved IntJ Appl Radiut Lvotopes 1978; 29: 167-173. chol=intigraphic agent. J NUC1 Med 1983; 24:423-430. 32. Costello CE, Brodack JW, Jones AG, Davison A, Johnson DL, Kasina S, tit al. The investigation of 42. Fields AT, Porter DW, Callery PS, Harvey EB, radiopharmaceutical components by fast atom bberg MD. Synthesis and radiolabeling of bombardment mass spwtrometry: the identification twhnetium radiopharmaceuticals based on N- of Tc-HIDA and the epimers of Tc-C02-DADS. substituted iminodiacetic acid: effect of J Nucl h4ed 1983;24:353-355. radiolabeling conditions on radiochemicalpurity. J Label Compd Radiopham 1978; 15:387-399. 33. Wistow BW, Subramanian G, Gagne GM, Henderson RW, McAf& JG, Hall RC, et al. 43. Krishnamurthy S, Krishnamurthy GT. Experimenhl and clinical trials of new ‘Tc- Technetium-99m-iminodiacetic acid organic Iabeld hepatobiliary agents, Radiology 1978; anions: review of biokinetics and clinical ● 128:793-794. application in hematology. Hematology 1989;9: 139. 153.

21 44. Klingensmith WC, Fritzberg AR, Spitmr VM, York The Society of Nuclear Medicine, Inc., Kuni CC, WilliamsonMR, Gerhold JP. Work in 1984. progrws: clinical evaluation of Tc-99m- trimethylbromo-IDAmd Tc-99m-diisopropyl-IDA 57. Zimmer AM, Majewski W, Spies SM. Rapid for hepatobiliary imaging. Radiology miniaturiti chrowtography for Tc-99m IDA ● 1983; 146:181-184. agents: comparison with gel chromatography. Eur J Nuci Med 1982; 7:88-91. 45. Maliski EG, BradshawJ. QSAR and the role of computers in drug design. In: Ganellin CR, 58. Fritzberg AR, bwis D, HPLC analysis of Robetis SM, editors. Medicinal Chemistry, 2nd Tc-99m iminodiacetate hepatobiliary agents and a 4. San Diego: AcademicPress, 1993. question of multiple peaks: concise communication. J Nucl Med 1980;21: 1180-1184. 46. Kubinyi H. QSAR:Hansch Analysis and Related Approaches. New York: VCH, 1993. 59. Majewski W, Zimmer AM, Spies SM, Hingeveld J. RadioChemical evaluation of commercial 47. Hansch C. A quantitative approach to biochemical iminodiacetatehepatobiliaryradiopharroamuticals. structure-activity relationships. Acc Chem Res J Nucl Med Tech 1981;9: 185-187. 1969; 2:232-239. 60. Popescu HI. Hepatic clearance mwhanism of Tc- 48. Frw SM, Wilson JW. A mathematical 99m-N- (acetanilido)-iminodiaceticacid derivatives contribution to structure-activity studies. J Med [letter]. J Nucl Med 1980;21:1 110-1111. Chem 1964; 7:395-399. 61. Sarkar SD. Hepatic clearance of technetium-99m- 49. Burns HD, Marzilli L, Sowa D, Baum D, WaWer iminodiacetic acid derivatives in hyperbili- HN Jr. Relationship betw=n molecular structure rubinemic states [editorial]. J Nucl Med and biliary excretion of tihnetium-99m HIDA and 1992; 33:1551-1552. HIDA analogs [abstract]. J Nucl Med 1977; 18:624. 62. Hernandez M, Rosenthal L. A cross-over study comparing the kinetics of Tc-99m-labeled 50. Kato-AzumaM. Lipopbilic derivativesof *Tc- diisopropyl and p-butyl IDA analogs in patients. (Sn)pyridoxylidenephenylalanine: a structure Clin Nucl Med 1980;5: 159-165. ● distribution relationship (SDR) study of’ technetium-99mcomplexes.Int J Appl Radiat Isot 63. Weissman HS, Sugarrnan LA, Fr&man LM. The 1982; 33:937-944. clinical role of tihnetium-99m iminodiacetic acid cholescintigraphy. In: Fr&man LM, Weissman 51. Reiffers S, bbrwht RM, Wolf AP, Chistman HS, editors. Nuclear Medicine Annual 1981. DR, Ansari AN, Atkins HL. Cyclotron isotopes New York: Raven Press, 1981, 35-80. and radiopharrnaceuticals XXXIII. Synthesis and structure effwk of selective biliary secretion of 64, Krisnamurthy GT, Turner FE. Pharmacokinetics halogenati indotricarbocyanines. Int J Appl Rad and clinical application of technetium-99m-labeled ]SO~ 1983; 34:1383-1393. hepatobiliary agents. Semin Nucl Med 1990; 20: 130-149. 52. lansholt A-L, Scheibe PO, Vera DR, Krohn KA, Stadalnik RC. Correlation analysis of substituent 65. Wu RK, Siegel JA, Rattner Z, Malmud LS. Tc- effects on the pharmacokinetics of hepatobiliary 99m HIDA dosimetry in patients with vdrious agents, J Label Compd Radiopharm 198 1; 18:198- hepatic disorders. J Nucl Med 1984;25:905-912. 200. 66. Hahn K, Lingenfelder B, Wolf R, Eissner D. 53. DuPont Pharma. Hepatolite package insert. Radiation absorbed dose to newborns after Billerica, MA, 1991. application of Wc-diethyl IDA. In: Raynaud C. editor. Nuclear Medicine and Biology. Vol IV. 54. Mallinckrodt, ~C. TechneScan HIDA package Paris. Pergamon Press 1982:2955-2957. insert. St. Louis, MO, 1989. 67. Hladik WB IIf, Ponto JA, Lentle BC, Laven DL. 55. Squibb Diagnostics. Choletw package insert. Iatrogenic alterations in the biodistribution of Princeton, N. J., 1990. radiotracers as a result of drug therapy: reported ● instances. In: Hladik WM W, Saba GB, Study KT, 56. Robbins PJ. Chromatography of Technetium-99m editors. Essentik of Nuchar Medicine Science. Radiophamaceuticals -A Prac~ical Guide. New Baltimore: WiUiams and Wilkins, 1987; 189-219.

22 68. Hesslewood S, hung E. Drug interactionswith 81. Choy D, Shi EC, McLeanRG, Hoschl R, Murray radiophamceuticals. Eur J Nucl Med IPC, Ham JM. Cholescintigraphy in acute 1994;21:348-356. cholecystitis: w of intravenous morphine. Radiology 1984; 151:203-207. ●69. Joehl RJ, Koch KL, Nahrwold DL. Opiod drugs cause bile duct obstruction during hepatobiliary 82. Fink-BennettD, BalonHR. The role of morphine- scans. Am J Surg1984;147: 134-138. augmented cholescintigraphy in the detection of acute cholwystitis. Clin Nucl Med 1993; 18:891- 70. Kim EE, Moon T-Y, Delpas-d ES, Podoloff 897. DA, Haynie TP. Nuclar hepatobiliary imaging. Rd Clin North Am 1993; 31:923-933. 83. Drane WE. Nucl~r medicine techniquw for the liver and biliary syskm. Update for the 1990s. 71. Richards AG, Brighouse R. Nicotinic acid - a Radiol C/in NAer 1991; 29: 1129-1150. cause of failed HIDA scanning. J Nucl Med 1981; 22:746-747. 84. Kim CK, Tse KKM, Juweid M, Moz.ley PD, Woda A, Alavi A. Cholescintigraphy in the 72. Shuman WP, Gibbs P, Rudd TG, Mack LA. diagnosis of acute cholwystitis: morphine PIPIDA scintigraphy for cholecystitis: false augmentation is superior to delayed imaging. J positives in alcoholism and total parenteral Nucl Med 1993; 34: 1866-1870. nutrition. AJR 1982;138:1-5. 85. Flancbaum L, Wilson GA, Choban PS. The 73. Kloiber R, Molnar CP, Shaffer EA. Chronic significance of a positive test of morphine biliary-typepain in the absence of gallstones: the cholescintigraphy in hospitalized patien~~. Surg value of cholecystokinin cholescintigraphy.AJR Gynecol Obstet 1993; 177:227-230. 1992; 159:509-513. 86. Majd M, Reba RC, Altman RP. Effect of 74. Rubow S, Klopper J, Wasserman H, Baard B, van phenobarbital on -c-IDA scintigraphy in the Niekirk M. The excretion of radiopharmaceuticals evaluation of nmnatal jaundice. Semin Nucl Med in human breast milk: additional data and 1981 ;11:194-204. dosimetry. Eur J Nucl Med1994;21: 144-153. 87. Grainger RG, Allison DJ, editors. Diagnostic 75. GottschalkA, Hoffer PB, PotchenEJ. Diagnostic Radiology. 2nd ed. Edinburgh: Churchill Nuclear Medicine, Vol. 2. Baltimore: Williams Livingstone, 1992. and Wilkins, 1988. 88. Sostre S, Kalloo AN, Spiegler EJ, Camargo EE, 76. Fink-BennettD. Augmentedcholescintigraphy:its Wagner HN Jr. A noninvasive test of sphincter of role in det=ting acuteand chronicdisordersof the Oddi dysfunction in postcholecystitomy patienh: hepatobiliarytree. Semin Nucl A4ed 1991 ;21: 128- the scintigraphic score. J Nucl Med 139. 1992; 33:1216-1222.

77. Xynos E, Pwhlivanides G, Znras OJ, Chrysos E, 89. Weissman HS, Gliedman ML, Wik PJ, Sugarman Tzovaras G, Fountos A, et al. Reproducibility of LA, Badia J, Guglielmo K, et al. Evaluation of gallbladder emptying scintigraphic studies. J Nucl the postoperative patient with -c-IDA chole- Med 1994; 35:835-839. scintigraphy. Semin Nucl Med 1982; 12:27-52.

78. Fink-Bennett D, DeRidder P, Kolo~si W, Gordon 90. Gerhold JP, Klingensmith WC, Kuni CC, Lilly R, Rapp J. Cholecystokinin cholescintigraphic JR, Silverman A, Fritzberg AR, et al. Diagnosis findings in the cystic duct syndrome. J Nucl Med of bilia~ atresia with radionuclide imaging. 1985;26:1 123-1128. Radiology 1983; 146:499-504.

79. Reed DN Jr, Fernandez M, Hicks RD. Kinevac- 91. Juni JE, Reichle R. Measurement of assisted cholescintigraphy as m accurate predictor hepatocellular function with d=onvolution of chronic acalculous gallbladder disease and the analysis: application in the differential diagnosis of likelihood of symptom relief with cholwystectomy. acute jaundice. Radiology 1990; 177:171-175. Amer Surg 1993; 59:273-277. ● 92. Juni JE, Thrall JH, Froelich JW, Wiggins RC, 80. Freeman LM, Sugarman LA, Weissman HS. Role Campbell DA, Tusca M. The appndd curve of cholmystokinetic agents in WC-IDA chole- technique for deconvolution analysis - method and scintigraphy. Semin Nucl Med 1981; 11:186-193. validation. Eur J Nucl Med 1988; 14:403-407.

23 93. Brown PH, Juni JE, Lieberman DA, QUESTIONS Krishnamurthy GT. Hepatocyte versus biliary disease: a distinction by deconvolution aalysis of twhnetium-99m IDA time-activity curv~. J Nucl 1. A main function of the hepatocyte is: Med 1988; 29:623-630. o A. removal of foreign particles from 94. Stockert RJ, Morell AG. Hepatic binding protein: circulation the galactose-specific r-ptor of mammalim B. breakdown of senescent blood cells hepatocytes. Hematology 1983 ;3:750-757. c. detoxification of harmful compounds D. complexation to make polar compounds 95. Kudo M, Vera DR, Trudwu WL, Stadalnik RC. less water-soluble Validation of in vivo receptor measurements via in vitro radioassay: technetium-99m-galactosyl- 2. The main function of the gallbladder is: nmgl ycoalbumin as prototype model. J Nucl Med 1991 ;32:1177-1182. A. degradation of cholesterol B. storage and concentration of bile 96. Vera DR, Krohn KA, Stadalnik RC, Scheibe PO. c. absorption of unconjugated bile acids Tc-99m galactosyl-nmglycoalbumin: in vitro D. m~lation of canalicularbile swretion characterization of receptor-mdiated binding. J Nucl Med 1984; 25:779-787. 3. The overall excretionrate of organic anions into bile dependsprimarily on: 97. Vera DR, Krohn KA, Stadalnik RC, Scheibe PO. Tc-99m- galactosyl-nmglycoalburnin: in vivo A. the carrier-mdiatti canalicular characterimtion of r~eptor-mediated binding to transport process hepatocyks. Radiology 1984; 151:191-196. B. the number of availablehepatocyte storage sites 98, $tadalnik RC, Kudo M, EckelmanWC, Vera DR. c. the rate of bile formation and excretion In vivo functionalimaging using receptor-binding D. the number of available receptor sites on radiophamaceuticals. Technetium 99m-galactosyl- the sinusoidal membrane neoglycoalbumin as a model. Invest Radiol 1993; 28:64-70. 4. There is no competition for biliary excretion @ between Tc-99m disofenin and 99. Vera DR, Stadalnik RC, Krohn KA. T=hnetium- 99m galactosyl-nmglycoalbumin: preparation and A. bilirubin preclinical studies. J Nucl Med 1985; 26: 1157- B. chlorpromazine 1167. c. indocyanine g=n D. sulfobromophthalein 100. Torizuka K, Ha-Kawa SK, Ikekubo K, Suoa Y, Tanaka Y, Hino M, et al. Phase I clinical study 5. Compounds that are primarily excretd in urine on WC-GSA, a new agent for functional imaging rather than in bile are characterized by being of the liver. Jpn J Nucl Med 1991; 28: 1321-1331. A. of molecular weight above 600 101. Vera DR, Woodle ES, Stadalnik RC. Kinetic B. highly protein bound sensitivity of a receptor-binding radiopharma- c. labeled with radioiodine ceutical: technetium-99m galactosyl-neoglyco- D. strongly polar albumin, J iVucl Med 1989; 30: 1519-1530. 6. Which of the following statements pertainkg to 102. Vera DR, Stadalnik RC, Trudeau WL, Scheibe hepatic bile is &e? Po, Krohn KA. Measurement of rweptor concentration and forward-binding rate constant via A. secreted at an average rate of 25 ml per radiopharmacokineticmodeling of technetium-99 m- hour galactosyl-nmgl ycoalbumin. J Nucl Med B. bilirubin usually represents 10% of total 1991; 32:1169-1176. bile solids c. cholesterol is a major lipid component D. flow is related to the bile acid pool ●

24 7. Which of the following statements pertaining to 13. The best therapy to prevent recurrence of bile acids is @e? gallstones is:

A. primary bile acids are synthesiti in A. laparoscopic cholecyst=tomy o reticuloendothel ial cells B. dissolution therapy with B. circulating bile acids are less than 5 % chenodwxycholic acid protein bound c. shock-wavelithotripsy c. less than 10% of conjugated bile acids D. gallbladderejectiontreatment are reabsorbed in the gastrointestinal tract 14. The major disadvantageof Tc-99m D. bile acids are conjugati with glycin and pyridoxylideneglutamateprepared by the taulin autoclavemethod was:

8. The most importantcharacteristicof bilirubin is A. gastrointestinalabsorptionof that it: radiochernicalimpurities B. very slow blood cl~rance A. promotes G.I. tract absorptionof lipids c. high degree of urinary excretion B. is a degradationproduct of heme D. in vitro instability c. kwps lipids in bile in solution D. promotes bile formation and flow 15. Which of the following statements best describes structure-activity relationship (SAR) analysis? 9. The organic anion pathway for hepatocyte excretion is not followd by: A. SAR analysis is a method to reduce the number of related analogs that must be A. asialoglycoprotein synthesized and testd B. indocyanine gr=n B. SAR analysis makes it possibl~ to c. rose bengal identify new chemical compounds with D. iopanoicacid desird biological activity c. All SAR methods rquire both 10. Acute cholecystitis is a result of cystic duct physiochemical md biological 9 obstruction by gallstones in: measurements D. Lipophiiicity measurements usd in SAR A. more than 90% of cases analysis are usually perfomed in an B. less thm 50% of cases acetronitrile: water system c. most patientswith supersaturatedbile D. patients trtited long-term with opioid 16. In the preparation of Tc-99m dimethyl-IDA, pain killers A. the final complex is a Tc-Sn-bis- 1.1. The presence of calculi in the gallbladder cause complex with dimethyl-IDA symptoms in: B. the oxidation state of technetium is +4 c. the overall charge of the complex is -1 A. patients with short cystic ducts D. the molecular weight of the complex is B. more than SO% of individuals less than 600 c. patients with bilirubin levels above 3 mgldl 17. For the preparation of Tc-99m IDA D. a rninorit y of individuals radiopharmaceuticals,

12. Gallstones classified as cholesterol stontis: A. kits are availabIe that utili= either stannous ion or electrolysis for reduction A. are common in patients with biliary tract of pertechnetate infection B. the shelf-life following addition of Tc- B. contains calcium in the center 99m pertechnetate is 18 hours c. are poorly suited for dissolution therapy c. the agent is ready to use as soon as all with bile salts solids are completely dissolved D. are not usually visualized using D. the usual amount of Tc-99m to add is ultrasound imaging 100 mCi or less

25 18. Clinical studiw with commercial Tc-99m IDA 22. Nonvisualization of a normal gallbladder with radiopharrnaceuticals available in the U.S. have cholescintigraphy is ~t a result ofi shown that A. pain management using morphine A. increased serum bilirubin levels result in B. fasting in excess of 24 hours ● incrti renal excretion for all agents c, fatty meal taken one hour prior to the B. there is no significant change in blood study clearance rak with increasd bilirubin D. total parenteral nutrition therapy levels c. of the firm agents, Tc-99m disofenin 23. Which of the following statements related to has the fastest liver transit kinetics bilia~ tract dim is we? D. in normals, the gallbladder cm usually not be visuali~ until 45-60 minutes A. Cholescintigraphy is a highly sensitive after injection test for evaluation of cystic duct obstruction 19. Which of the following statements related to B. Prolonged cystic duct obstruction leads drug effats on hepatobiliary kinetics is me? to biliary duct inflammation and necrosis A. Nicotinic acid in large doses prolongs c. Cholecystectomy is never indicati in gallbladder contraction patients with non-calculous gallbladder B. Phenobarbital is used to spd up liver disease trmsit of hepatobiliary agents in patients D. Non-visualization of the gallbladder is with poor liver function not highly spwific for acute chnlecystitis c. After administration of morphine, emptying of bile into the gastrointestinal 24. In n~natal jaundice, tract is delayed D. Morphine administration reduces the A. the gallbladder is usually visurdi~ by pressure within the gallbladder four hours on cholescintigraphy B. a dose of phenobarbital should be given 20. In augmented hepatobiliary imaging studies with 30-60 minutes prior to cholescintigraphy cholecystokinetic agents, c. evidence of Tc-99m disofenin in the o bowel at four hours excludes biliary A. a normal gallbladder should eject at atresia least 75% of its content following an D. cauti by hepatitis, the underlying iv. dose of 0.02 mg/kg of sincalide disease process is usually a vims B. viscous bile can be ejected from the infection gallbladder prior to scintigraphy to facilitate gallbladder filling with 25. Which of the following statements related to radiotracer hepatic extraction fraction (HEF) studies is ~e? c. gallbladder emptying initiated by a fatty meal is not a reproducible technique A. Deconvolution analysis is used to D. a gallbladder ejation fraction study is correct liver uptake for blood performed by injwtion of radiotracer background activity 15-30 minutes following sincalide B. The blood time-activity curve is infusion obtained from a region of interest over the hepatic artery 21. Which of the following statements pertaining to c. HEF provides a quantihtive measure of gallbladder filling and emptying is we? hepatic binding prohin receptor affinity D. Corr~tion for kidney activity is done by A. Partial gallbladder emptying takes place obtaining images in the lateral pro] mtion periodically during the tilling phase B. Delayd gallbladder filling may be associated with alcohol ic liver disease c. Gallbladder emptying cannot be induced by a fatty mal unless the gallbladder contains at least 50 ml of bile D. The cystic duct syndrome is associated with impaired gallbladder emptying

26