History of Medical Imaging Author(S): William G

History of Medical Imaging Author(s): William G. Bradley Source: Proceedings of the American Philosophical Society, Vol. 152, No. 3 (Sep., 2008), pp. 349-361 Published by: American Philosophical Society Stable URL: http://www.jstor.org/stable/40541591 . Accessed: 02/01/2015 11:00

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This content downloaded from 141.213.236.110 on Fri, 2 Jan 2015 11:00:38 AM All use subject to JSTOR Terms and Conditions Historyof Medical Imaging1 WILLIAM G. BRADLEY Professorand Chairman,Department of Radiology Universityof California,San Diego

IMAGING beganin November1895 withWil- helmConrad Roentgen's discovery of the X-ray.Working withan earlycathode ray tube called a Crooke'stube, he noticedthat the invisible rays were able to penetratesome solids (like humanflesh) better than others (like bone or metal).He confinedhimself to hisbasement laboratory in Würzburg, Germany, for six weekswhile Frau Roentgenbrought him meals.During that time he discovered mostof what the world would know about X-rays for the next twenty years.For his efforts he was awardedthe first Nobel Prizein 1901. X-rayis thebasis for what we radiologistscall "planefilms" or sim- ply"X-rays" used commonlyfor evaluating the chest and bone frac- tures.The originalX-ray films had to go througha wetdeveloper pro- cessin a darkroom. If the study was crucial,the radiologist would read itwhile it was stilldripping wet. The term"wet reading" is stillused for an emergencyradiology report even though many X-rays today are ac- quireddigitally without any film at all. As theX-ray beam became more powerful, patient motion could be visualizedand "fluoroscopy"became possible. In the 1920s,radiolo- gistsbegan giving patients radio-opaque barium as a swallowor an en- ema and takingfilms as thebarium traversed the gastrointestinal tract. That is how cancersof theesophagus, stomach, and bowelas well as ulcers,diverticulitis, and appendicitiswere initially diagnosed by radiologists.Fluoroscopy is stillin commonuse today,but it has advanced considerably.In theearly days the images were so dimthat radiologists had to wearred goggles all dayto minimizethe time needed to accom- modateto thedim light when they went back into the fluoroscopy suite. Today,with modern image intensifies, that is no longernecessary. In addition,many of the diseasesinitially diagnosed by fluoroscopyare nowdiagnosed by computed tomography (CT: see below).

1Read 26 April2007.

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X-rayis also thebasis of mammography,which is a dedicatedsys- temthat takes high-resolution images of the breasts, looking for breast cancer.Over the years,the X-raydose of the mammogramshas decreased,making the examination safer. In addition,the film of theold dayshas beenreplaced with digital plates of charge-coupleddetectors thatfeed the images directly to high-resolutionworkstations (so-called "fullfield digital mammography"). X-raytomography was introducedin the 1940s,allowing "tomo- grams"or slicesto be obtainedthrough tissues without the over- or under-lyingtissue's being seen. This was achievedby rotating the X-ray tubeso thatonly the desired slice of tissuestayed in focusduring tube rotation.Tomography per se is no longerperformed, having been replacedwith CAT (computerizedaxial tomography) scanning or CT (see below). Both CT and MRI are tomographictechniques that display theanatomy in slicesrather than through and throughprojections (like an X-ray). X-rayis also thebasis of "angiography,"or theimaging of blood vessels.In theearly days a radiodensecontrast agent like iodine was in- jecteddirectly into the artery of interest.When imaging the brain for a suspectedstroke, brain tumor, or vascularmalformation, this usually requireda directcarotid puncture with a needlesomewhat larger than a soda straw.In thelate 1950s,the Seldinger technique, in whichthe arterialpuncture takes place in thefemoral artery in thegroin, was im- portedfrom the Karolinska Institute in Stockholm.A flexibleguide wire is insertedthrough the puncture needle and a plasticcatheter is passed overthe guide wire and runthrough the blood vesselsto theorgan of interest.Iodinated contrast can thenbe injectedto makea diagnosis,e.g., vascularnarrowing of the carotid artery (which could lead to a stroke) or narrowingof thecoronary arteries (which could lead to a heartattack).Today, interventional radiologists and cardiologistsroutinely ex- pand narrowedvessels with a balloon ("balloon angioplasty"),often followedby a coilof wire (called a "stent")to keepthe vessel open after theprocedure. In the1950s nuclear medicine entered our armamentarium ofdiag- nosticimaging tests. In thesetests, the source of theX-rays is not an X-raytube but ratherradioactive compounds, which typically emit gammarays as theydecay. They are combinedwith other compounds thatare takenup as partof thedisease process to studya particular problem.For example,Technicium 99m can be combinedwith méthy- lène diphosphonate,which is takenup by bone beinginvaded by a tumor.So, forexample, cancer of the breastor lung,which tends to spread("metastasize") to thebones, can be easilydetected by sucha nuclearbone scan.

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The mostexciting test in nuclearmedicine today is positronemis- siontomography or "PET" scanning.Instead of emittinggamma rays, theseisotopes emit positrons when they decay. Positrons are positively chargedelectrons. Following emission, a positroncombines with a local electronand annihilates,emitting two 511 kevphotons in oppositedi- rections.By noting the arrival time of the two photons at thedetectors aroundthe patient("coincidence detection"), the sourceof emission can be localizedin space. MostPET is basedon a positron-emittingisotope of fluorine (F-18) thatis incorporatedinto a glucoseanalog called fluorodeoxyglucose (FDG). Sinceglucose uptake is increasedin mostcancers, FDG PET has becomea mainstreamtechnique to diagnoseboth the primary cancer and cancerthat has metastasizedto otherparts of thebody. More re- centlyPET has beencombined with CT as "PET-CT."This combines themetabolic (albeit low resolution)information of PET withthe high spatialresolution of CT, facilitating localization of the cancer for biopsy, radiationtherapy, or surgery. Ultrasoundwas firstused clinically in the1970s. Unlike X-ray and nuclearmedicine, ultrasound uses no ionizingradiation - just sound waves.As the soundwaves pass throughthe tissueand are reflected back,tomographic images can be createdand tissuescan be character- ized.For example, a massfound on a mammogramcan be furtherchar- acterizedas solid(possibly cancer) or cystic(most likely benign). Ultra- soundis also usefulfor the noninvasive imaging of theabdomen and pelvis,including imaging the fetus during pregnancy. Early clinical ultra- soundunits were bulky machines with articulated arms that produced low resolutionimages. Today ultrasound can be performedby a portable unitno largerthan a laptopcomputer. Computersreally entered the world of medicalimaging in the early1970s withthe advent of computedtomography (CT scanning) and thenmagnetic resonance imaging (MRI). CT was a majoradvance thatfirst allowed multiple tomographic images (slices) of thebrain to be acquired.Prior to theadvent of CT in 1973,we had onlyplane films of the head (whichbasically just show the bones) or angiography (whichonly suggests masses when the vessels of the brain are displaced fromtheir normal position). Basically there was no wayto directlyim- age thebrain. In CT an X-raytube rotates around the patient and vari- ous detectorspick up theX-rays that are not absorbed, reflected, or re- fractedas theypass throughthe body. Early CT unitsproduced crude imageson a 64x64 matrix.Early computers took all nightto process theseimages. Today's multidetector row CTs acquiremultiple submilli- meterspatial resolution slices with processing speeds measured in milli- secondsrather than hours. Iodinated contrast agents are usedwith CT

This content downloaded from 141.213.236.110 on Fri, 2 Jan 2015 11:00:38 AM All use subject to JSTOR Terms and Conditions 352 WILLIAM G. BRADLEY since theyblock X-raysbased on theirdensity compared with that of normaltissue.

Magnetic Resonance Imaging

MRI also evolved duringthe 1970s, initiallyon resistivemagnets with weak magneticfields, producing images with low spatial resolution. Even then,however, it was obvious that the softtissue discrimination of MRI was superiorto thatof CT, allowingearlier diagnoses. MR also had the advantagethat it did not requireionizing radiation like X-ray- based CT. Over the 1980s and 1990s, superconductingmagnets became common,initially at 1.5 Tesla and now at 3 Tesla. (Tesla is a measure of magneticfield strength. The earth'smagnetic field, for example, is .00005 Tesla. Thus a 1.5 T magnethas a fieldstrength 30,000 times strongerthan that of the earth.) Most clinicalMRI today uses the hydrogennucleus because it is so abundantin waterand becauseits nucleus has a propertyknown as spin. Hydrogennuclei (singleprotons) resonateat frequenciesin the radio- frequencyrange. The exact resonancefrequency depends on the local value of the magneticfield. When a protonresonates, it emitsa radio- frequencysignal that can be detectedby a radio antenna(usually in the formof an RF coil around the body part beingimaged). An MRI scannerconsists of a large (usually solenoidal, supercon- ducting)magnet with a 100-centimeterroom-temperature bore and a very uniformmagnetic field (like 1 part per million [ppm] variation over a 30 cm volume). When imagingis performed,resistive electro- magnetsjust insidethis bore are temporarilyactivated, generating magnetic field gradientsalong the x, y, or z axes in the magnet.These weaker gradientfields add or subtractfrom the main magneticfield, creatinga linear variationin net magneticfield along the threeaxes. Justinside the gradientcoils are radiofrequency(RF) transmitand re- ceive coils. When exposed to radiowaves at a particularfrequency, only those protons at the rightvalue of the magneticfield resonate. Since the strengthof thegradient fields and the frequenciesbeing transmitted are known,the location of the hydrogennuclei can be determined.For example,if one gradientcoil along, say,the x axis is activated,there is a linear variationin magneticfield, and thereforeresonance frequency, along the x axis. In practicethe body is exposed to an RF pulse con- tainingmultiple frequencies. By separatingthe complex radio signals comingfrom the body into differentfrequencies (using a Fouriertrans- form),each hydrogennucleus's position along a particulargradient axis can be inferred.The greaterthe numberof protonsat a point,the

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Figure 1. Seventy-four-year-oldman who arrivedat the hospitalseven hours followinga stroke(not in timefor tPA). A. T2WI on admissionis normal.B. Diffu- sion image on admissionshows restrictedmotion of water in the hyperintense basal ganglia- whichis the core of the stroke.C. Perfusionimage (mean transit timemap) showsthe largerarea at riskfor extension of the strokeif thereis no treatment.The differencebetween B and C is calledthe "ischemie penumbra" and is the brainat riskfor the extensionof the stroke.D. T2WI twelveweeks later shows thatthe initialperfusion (MTT) map accuratelypredicted the size of the resultinginfarcì (stroke). greaterthe amplitude of thesignal at a particularfrequency. By know- ingposition and amplitude,one can producean MR image(fig. 1). ConventionalMR imagingassumes that all protonsresonate at ex- actlythe same frequency at a givenfield strength. In actuality,protons in differentchemical environments may resonate at slightlydifferent frequencieseven if the field strength is thesame. (This is thebasis for nuclearmagnetic resonance or "NMR" in chemistry.)By makingthe magneticfield 10 timesmore uniform, e.g., 0.1 ppm,over a smallre- gionof thebrain and by suppressingwater, different chemical species withslightly different resonance frequencies (or "chemicalshifts") can be detected.This is knownas "MR Speçtroscopy"(MRS). It givesus the abilityto performchemical analysis of thebrain noninvasively (fig. 2). Forexample, with MRS we can detectN-acetyl aspartate (NAA), which is a markerof normalneurons. When normal brain is replacedby tu- moror infection,the NAA in thatpart of thebrain is decreased.NAA is also decreasedin dementia.We can also detectcholine, which arises frommembrane turnover. It is elevatedin tumorsbut not in abscesses. Thus two processesthat might appear similar on conventionalMRI,

This content downloaded from 141.213.236.110 on Fri, 2 Jan 2015 11:00:38 AM All use subject to JSTOR Terms and Conditions 354 WILLIAM G. BRADLEY e.g.,tumor and abscess,can be differentiatedon the basis of the choline levelby usingMRS. In fact,the more malignant the brain tumor, the higherthe choline and thelower the NAA levels. Byvarying the timing of theRF pulses,different types of MR con- trastcan be produced.These can be based on fundamentalNMR pa- rameterslike the Tl and T2 relaxationtimes, or theycan be basedon motionof water or blood (justto namea few).For example, on an image thatis sensitiveto T2 differences(a "T2-weighted image"), we can distinguishdifferent forms of hemoglobinand tellwhen bleeding oc- curred.Oxyhemoglobin (the circulating form of blood),for example, has a longerT2 thandeoxyhemoglobin, which is foundin hematomas in thebrain after twenty-four hours. The shortT2 ofdeoxyhemoglobin makesit darkon a T2-weightedimage and allows us to distinguish ischemiestrokes (which might respond to clot-bustingdrugs like tPA [tissueplasminogen activase]) from hemorrhagic strokes (which are a contraindicationto tPA). Whena task(like finger tapping) is performed,the part of the brain thatcontrols the fingers paradoxically gets more blood thanit needs, leadingto lessoxygen extraction. Since oxygenated blood has a longer T2 thandeoxygenated blood, subtraction of images with finger tapping vs. thoseperformed at restshows the part of thebrain involved in the task.This permitsus to performa techniquecalled "functional MRI" (fMRI),which allows us to see theparts of thebrain involved in any task.This richness of contrast mechanisms is theprimary advantage of MRI overCT. FunctionalMRI is complementaryto anotherimaging technique called "magnetoencephalography"or "MEG." MEG is similarto the morefamiliar EEG (electroencephalograpy)although it is betterthan EEG forlocalizing signals coming out of thebrain. The electricalsig- nalsof EEG are distortedby the scalp and otherconducting tissues be- tweenthe brain and theelectrodes on theskin. The electricalcurrents pickedup by EEG also produceweak magneticfields picked up by MEG- but withoutthe distortioncaused by the scalp. Because the magneticfields coming out of thebrain are manyorders of magnitude less thanthe earth's magnetic field, MEG needsto be performedin a specialmagnetically shielded room. MEG can be usedto localizeseizure activityfor possible surgery. Like fMRI,it can be used to show brain activationwith a certaintask. While fMRI is based on blood flow,its temporalresolution is on theorder of seconds. MEG, on theother hand, has temporalresolution on theorder of milliseconds. The magneticsig- nals detectedby MEG are usuallydisplayed on a three-dimensional MRI thathas beenblown up likea balloon(see avi #1in thelink in the SuggestedReadings below).

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The sensitivityof MRI to motionallows us to imagemicroscopic watermotion ("diffusion imaging") and macroscopicblood flow ("MR angiography").In diffusionimaging, strong gradient pulses cause wa- terdiffusing randomly in theextracellular space of the brain to getout of phaseand to lose signal.In acutestroke, water in theextracellular spaceof the brain moves into the cells as cytotoxicedema where its mo- tionis limited.Since the water no longerdiffuses normally in thisarea ofstroke, it no longergets out of phase and showsup on a diffusionim- age as an area of brightness(fig. 1). Byperforming a related technique knownas "diffusiontensor imaging," both the magnitude and thedi- rectionof diffusioncan be shown.Major whitematter tracts (axons) in thebrain can be demonstrated,since water tends to diffuseparallel (ratherthan perpendicular) to axons. Diffusiontensor imaging (DTI) can be usedto showthe white matter connections between the parts of thebrain that light up on fMRIduring a task.DTI (fig.3) can also show whetherwhite matter tracts are intactnext to a braintumor, or have alreadybeen invaded. This allows the neurosurgeonto avoid cutting intactwhite matter tracts during surgery (fig. 3). Likethe use ofiodinated contrast agents in CT,MR also has an in- travenouscontrast agent based on paramagneticgadolinium (Gd). Brain tumorsthat turn bright, i.e., "enhance,"using iodine on CT also en- hanceusing gadolinium on MRI. Gadolinium(Gd) can also be usedto perform"perfusion" imaging of the brain, which provides a measureof cerebralblood flow,mean transit time, and cerebralblood volume.By comparingthe diffusion and perfusionscans in strokepatients, thera- peuticdecisions (like giving the thrombolytic agent tPA) can be made (fig.1). The relative cerebral blood volume (rCBV) is decreasedin strokes, but is increasedin braintumors. The rCBV representsthe capillary density,which is increasedby new blood vessel formation ("angiogenesis") in braintumors. Thus the area ofthe tumor with the highest rCBV reflectsthe most malignant part of thetumor and becomesthe target forthe neurosurgeon's biopsy (fig. 4). MR angiographycan be performedwith or withoutGd. We typi- callyperform it withoutGd in thebrain and withGd whenevaluating thecarotid arteries or otherarteries throughout the body (fig. 5). In the settingof stroke,for example, we maybe able to see a narrowedca- rotidartery, which can be treatedeither by surgery or byan angioplasty and stent.A majordifference between contrast-enhanced MR angiog- raphyand thecatheter angiography described above is thatthe former involvesa low-riskvenous injection, while the latter involves a more invasivearterial injection. Both catheter angiography and contrast- enhancedMR angiographycan showthe flow of blood overtime (see avi #2in thelink below).

This content downloaded from 141.213.236.110 on Fri, 2 Jan 2015 11:00:38 AM All use subject to JSTOR Terms and Conditions Figure 2 (above). Forty-five-year-old manwith left temporal lobe seizures. A. Fluidattenuated inversion recovery (FLAIR) MR imageshows tumor in lefttemporal lobe. B. MRS shows elevatedcholine and decreasedNAA. C. Cholinemap guidesneurosurgeon to highestgrade portion of tumorfor biopsy(red area). Figure 3 (left). Fifty-three-year-old manwith left temporal lobe tumor. Diffusiontensor imaging (DTI) shows thatthe white matter deep to the tumoris displaced,not invaded.

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MR is usefulfor the evalu- ation of the heart.With modern systems,the beatingheart can be visualizedwith multiple slicesin variousplanes of an- gulation(see avi #3in thelink below). This is importantbe- cause myocardialwall motion maybe locallyabnormal during andfollowing a heart attack, de- pendingon whichcoronary ar- teryhas become blocked. Twenty minutesfollowing injection of gadolinium,it accumulatesin infarctedmyocardium, showing theexact extent of damagefol- lowinga heartattack (fig. 6). CT can also show a beatingheart in threedimensions (see avi #4 inlink below). Coronary CT angiography(fig. 7) can shownar- rowingof the arteries supplying Figure 5. Seventy-three-year-oldman the which be treated with righthemispheric stroke. Contrast- heart, may enhancedMR shows narrow- and angiogram by coronaryangioplasty ing ("stenosis")of proximalright internal stent(performed by cardiology) carotidartery (arrow). or by coronaryartery bypass graft(CABG; performed by a cardiothoracicsurgeon). MR can be usedto diagnoseand to stageprostate and breastcancer.The primaryuse forMRI in theevaluation of prostate carcinoma is to stagethe disease, i.e., to determinewhether it is extendingbeyond theprostatic capsule (indicating nonsurgical treatment) or is withinthe capsule(in which case surgicaltreatment is possible) (fig. 8). The evalu- ationof breastcancer has beensignificantly improved at 3 Tesla com- paredwith 1.5 T, sincehigher resolution is now possible,showing the spiculatedborders typical of cancer (fig. 9). MR can also be usedto monitorcertain treatments in realtime. MR is now goinginto operating rooms, allowing neurosurgeons to be sure thatall thebrain tumor that can be safelyremoved has beenremoved. (In 80 percentof cases in which neurosurgeons think they have removed

Figure 4 (facingpage, bottom). Fifty-six-year-oldman with left posterior frontal lobe tumor.A. FLAIR imageshows tumor.B. MRS shows elevatedcholine and decreasedNAA consistentwith tumor. C. Relativecerebral blood volume(rCBV) map showsincreased capillary density due to angiogenesis(red area).

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all of a tumor,more can be foundby intraoperativeMRI.) As a resultof its sensitivityto temperaturechange, MR can be usedto monitorthermal abla- tion techniqueslike focused ultrasound.Take the treatmentof uterine fibroidsas an example.Until ten years ago, theonly treatment was a hyster- ectomy.Ten yearsago, uterineartery embolizationbecame possible,sub- jectingthe patient to a groinpuncture insteadof a lowerabdominal incision. Figure 6. Forty-nine-year-oldNow, using MR-guided focused ultra- man withacute myocardialinfarc- sound,certain fibroids can be ablated tion (a.k.a. heartattack). "Delayed withoutever theskin. It can MR ac- breaking hyperenhancement" image also be usedin the brain for neu- quiredtwenty minutes after injec- tumor, tion of Gd shows hyperintensityrogenic pain, and possibly acute stroke. (arrow) in inferiorwall, corre- spondingto siteof infarction. Computed Tomography

Withmodern multidetector CT scanners,CT angiography(CTA) can also be performedfollowing a venousinjection. An excitingapplication of CTA is in thesetting of acutechest pain. In thepast, cardiologists would have to takethe patient to thecardiac catheterization laboratory,perform an arterial(usually femoral) puncture, and threada cath- eterinto the coronary arteries, which supply the heart. Today, coronary

Figure 7. Fifty-two-year-oldwoman with acute heart attack. A. Coronarycath- eterization(arterial injection) shows a narrowingof the midportionof the left anteriordescending (LAD) coronaryartery. B. CoronaryCT angiogramsuperim- posed on CT of heartshows the same thing(but followingan intravenousinjec- tion). C. CoronaryCTA removedfrom the rest of theheart shows narrowed LAD followingvenous injection.

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Figure 8. Prostatecarcinoma in forty-nine-year-oldman. MRI performedusing an endorectalcoil (shortarrow) shows low intensityon a T2-weightedimage corresponding to thecancer (long arrow). Since it is confinedby the prostatic capsule, it is amenableto surgicalremoval.

CTA (fig.7) allowsus to screenchest pain patients so thatonly the ones witha coronaryocclusion go to thecath lab forangioplasty and stent. The patientsthat have chest pain foranother reason, e.g., pulmonary embolismor aorticdissection, are treateddifferently. If none of these threecauses of chest pain is found,the patient can safelygo homewith- outhaving an invasive,expensive procedure. MultidetectorCT is frequentlythe firsttest ordered in the emer- gencyroom. A CT scan coveringthe entire body can be performedin twentyseconds. The samedata setcan be viewedwith bone windows

Figure 9. Improveddiagnosis of breastcancer at 3 Tesla vs. 1.5 T. A. Typical 256X256 matrixat 1.5T appearssmoothly marginated like benign fibroadenoma. B. Magnifiedimage. C. Subtractedimage, i.e., unenhancedsubtracted from enhancedimage. D. A 512X400 matrixover same fieldof view providesmuch greaterspatial resolution at 3T, showingspeculation typical of cancerinstead of benigndisease. E. Magnified.F. Subtracted.

This content downloaded from 141.213.236.110 on Fri, 2 Jan 2015 11:00:38 AM All use subject to JSTOR Terms and Conditions 360 WILLIAM G. BRADLEY forfractures and softtissue windows for lacerations of the liveror spleen(see avi #5in thelink below). MultidetectorCT can also be used forevaluation of patientswith an acutestroke. CT is excellentfor detecting hemorrhage in thebrain, whichis a contraindicationfor tPA (currently,the only treatment for acutestroke). In addition,CT can producean isotropiedata setwith 0.6 mmspatial resolution. Following administration of iodinatedcon- trast,the same data setcan be usedfor perfusion imaging and CT angi- ographyto showwhere the embolus has lodgedin theintracranial vas- culature.With this information, the neurointerventionalistcan go in and literallygrab the clot, limiting the damage from the stroke. MultidetectorCT can also detectaneurysms in thebrain (see avi #6 in linkbelow) and elsewherein thebody. Since these weakenings of the arterialwall can lead to ruptureand death,it is importantto makethe diagnosisnoninvasively so the neurointerventionalistcan administer coilsinto the aneurysm, causing it to clotoff and notrupture. Similarly CT can be usedto demonstratetumors and to showthe relationship to adjacentbones and blood vesselsto helpthe surgeon in thepreopera- tiveplanning (see avi #7in thelink below).

Conclusion

In conclusion,medical imaging has comea longway in the 110 years sinceRoentgen first discovered the X-ray. The exploratorysurgery of just 10 or 20 yearsago has been replacedwith noninvasive CT and MRI anatomicimaging. It is nowpossible to getinformation at the cel- lularlevel with MR diffusionand perfusionimaging to assistin the managementof strokeand braintumors. We can evenget information at themolecular level now, with PET and MRS. And thisis just the beginning.In thefuture, new contrastagents targeting,for example, angiogenesis will be usedto determinewhether a particularchemotherapeutic drug is workingwithin hours, rather thanwaiting weeks to see whetherthe tumor is shrinkingor growing on MRI or CT. Suchmolecular imaging agents may be visualizedusing different"reporters," e.g., Tc 99m fortraditional nuclear medicine, a positronemitter for PET, or gadoliniumfor MRI. In thefuture we will be able to detectcancer that has notyet produced anatomic change, on thebasis of alterationsin metabolicfluxes at thecellular level. Using hyperpolarizedC-13 MRI, we willbe able to detectdifferences in gly- colysis(pyruvate to lactate)and citricacid formation- which differs in prostatecarcinoma and in normalprostate tissue. Through these ad- vancesin medicalimaging, disease will be detectedless invasively and earlier,allowing for treatment before the disease has progressedto the pointof being incurable.

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