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 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. American Philosophical Society is collaborating with JSTOR to digitize, preserve and extend access to Proceedings of the American Philosophical Society. http://www.jstor.org 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 radi- ologists.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. PROCEEDINGS OF THE AMERICAN PHILOSOPHICAL SOCIETY VOL. 152, NO. 3, SEPTEMBER 2008 [349] 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 350 WILLIAM G. BRADLEY 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 de- creased,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 re- placedwith 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 heartat- tack).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. 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 HISTORY OF MEDICAL IMAGING 351 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