Computed body tomography

0016~6085/78/0074-0002$02.00/0 GASTROENTEROLOGY 74~287-293, 1978 Copyright0 1978by the AmericanGastroenterological Association

Vol. 74, No. 2, Part 1 Printed in U.S.A.

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COMPUTEDBODYTOMOGRAPHY JACK WITTENBERG, Departments of Radiology, Massachusetts

M.D.,

AND JOSEPH T. FERRUCCI,

Massachusetts

JR.,

M.D.

General Hospital and Harvard Medical School, Boston,

The detectors measure the X-ray attenuation caused by the various anatomical structures in the path of the beam. A series of measurements, taken at 180 different angles or more, result and provide the basis for quantitatively characterizing small points, called pixels, within the scanned area. The superior capacity of the computer tomography systems in tissue characterization resides in the greater ability of these detectors, compared to conventional X-ray films, for recording small differences in tissue density. The computer, having received an electrical signal from the detectors, calculates the X-ray attenuation value in each pixel and within minutes or less an image is produced. The numerical information is available in a display matrix composed of pixels whose dimensions average 1.0 by 1.0 mm2 in the “X-Y” dimension and 1.3 cm in the “Z” or axial dimension. In the clinical setting, these numerical values are cumbersome and are most commonly converted into an anatomical image by assigning variable shades of gray, black, or white to each number or groups of numbers. 7 Numerical values of any anatomical area, however, can be obtained on the television Technical Background monitor by simple manipulation of the accompanying The most commonly used systems consist of an X-ray dials. The range of numerical values (EM1 units) astube and photomultiplier detectors mounted opposite signed to tissues is -500 for air to +500 for compact each other on a frame which rotates around the patient. bone. Water is arbitrarily assigned a value of 0; fat This frame is contained within a gantry fashioned in measures approximately -40.7 Most normal solid abthe shape of a doughnut into which a supine patient is dominal organs and accompanying blood vessels range placed. The X-ray source projects a fan-shaped beam in attenuation values between +lO and +40. Crosswhose “Z” dimension encompasses a variable axial sectional images of the body are displayed as if the thickness of the body. The actual scanning procedure viewer is observing the image while standing at the consists of a repetitive sequence of bilateral traverses patient’s feet. As in conventional radiology, the paof the X-ray tube in synchrony with the detectors while tient’s left side is on the viewer’s right. the entire frame rotates about the patient. In the first Examination Technique generation of machines, the scanning time had durations of 2% to 5 min.3, 4 However, in the newer CBT As with all properly performed radiological proceunits, information is gathered in a short duration (20 dures, the CBT examination must be carefully designed set) during which the patient suspends respiration.5a6 to answer specific clinical questions. It should be underThe absence of respiratory motion is a critical factor stood that CBT is not ‘?a whole body examination” but because any movement of abdominal organs resulting in fact is a regional study which must be precisely from a diaphragmatic excursion causes degradation of focused on a specific organ or area of interest so that maximum information is gained with minimal X-ray the final reconstructed image. exposure. A fundamental requisite for successful imaging is the availability of a cooperative patient who can Received August 1, 1977. Accepted September 12, 1977. Address requests for reprints to: Jack Wittenberg, M.D., Depart- suspend respiration and remain motionless during the ment of Radiology, Massachusetts General Hospital, Boston, Mas- scanning sequence. Localization of the area to be scanned can be accomsachusetts 02114. Computed tomography is a remarkable new technique which mathematically integrates X-ray information transmitted through the body into excellent anatomical images in a cross-sectional dimension. Conceptually, it can be thought of as a sensitive, radiographic “film”, which more completely represents the spectrum of physical densities previously lumped into four general radiographic categories-air, fat, soft tissues, and bone. Originally designed for cranial application by Godfrey Hounsfield,’ a &year experience with this noninvasive technique has resulted in major alterations in the radiographic approach to neurological disorders.2 More recently, technological advances have provided the capacity to utilize this technique in the remainder of the body. Initial results indicate that computed body tomography (CBT) will also be an effective tool for imaging many abdominal diseases, particularly those in the solid organs. While CBT is presently still in its infancy, a review of the principles, methodology, and early clinical application of this promising new technique seem warranted.

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plished by reference to external landmarks such as the xiphoid process or the iliac crest. Before obtaining the first section, a dilute solution of oral, water-soluble, iodinated contrast material is usually administered to find certain intestinal landmarks such as the duodenum and, as well, to avoid mistaking any fluid-filled loops of bowel for abdominal masses. Barium is not used because its limited water solubility creates a nonhomogeneous mixture which more easily causes artifacts. Immediate review of the first image documents the actual level of the first section and allows determination of the levels for subsequent scanning (fig. IA). Whereas the thickness (Z axis) of the section is operator-controlled, the majority of examinations are intended to provide a 1.3-cm section width which offers a reasonable compromise between patient X-ray exposure, duration of examination, and quality of information gained. The number of additional sections obtained depends on the size of the organ or anatomical area under investigation. For example, on the average, a normal pancreatic gland will be entirely imaged by 3 to 4 additional

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contiguous sections (fig. 1, 23 to E). Motion such as intestinal peristalsis, occurring during the interval of actual scanning, seriously degrades the final image so that a peristalsis-inhibiting agent is routinely used during the scanning procedure. After completion of the scan sequence, the data are processed, reviewed, and additional sections obtained if necessary. The computer processing time may require up to 4 min per section and often accounts for the major amount of patient examination time which, on average, is approximately 1 hr. Intravenous iodinated contrast material (IICM), usually in doses used for standard intravenous urography, may be administered before or during additional scans for further clarification of a pathological process. However, unlike computerized cranial tomography, contrast enhancement has proved to be of only modest additional value in CBT. The absorbed radiation dose resulting from a CBT examination is dependent on the radiographic physical factors, duration of each scan, number of sections obtained, and distance between sections. On the average, the integrated body doses are less than 5 rads from either the slow8 and fast9 scan devices and can be considered within the range of dose received from a barium enema (M. M. Ter-Pogossian, personal communication). Gonadal dose varies according to the area of the torso scanned. Minimal doses are delivered to the gonads when scanning the upper abdomen, but doses are considerably increased during pelvic scanning, particularly in the female. Application of CBT

FIG. 1. Normal abdominal anatomy. A, initial section displays the body and tail of pancreas (small white arrows) situated anterior to the left kidney (large white arrow) and posterior to the fund of the stomach (black arrow), whose density has been enhanced by the ingestion of iodinated contrast material. B, this section represents the contiguous 1.3-cm section scanned just superior to A. The body and tail of the pancreas are again appreciated. The tail of the pancreas extends laterally to the spleen (large black arrow). The right crus of the diaphragm (small black arrow) lies posterior to the inferior vena cava and blends medially with the aorta. C, D, and E are contiguous 1.3-cm sections taken inferior to A, demonstrating the head and uncinate process of the pancreas. The latter is identitied in E by its position posterior and to the right of the superior mesenteric vein (black arrow) and artery (large white arrow).

Major refinements were required to adapt the technology used in computerized cranial tomography for body scanning and the first results have been available only since 1974.1°The bulk of present information has been accumulated on prototype scanning units.“, 5,ti Early experience was gained with body units whose duration of scanning of 2% or 4% min dictated tolerance of artifacts resulting from respiratory motion. In spite of this initial limitation, useful diagnostic information was clearly available and sufficiently encouraging to warrant development of units capable of faster scanning. At present, production of prototype models of 11 different manufacturers are being used in clinical facilities.” The most recent extensive clinical experience has been gained with second-generation machines capable of scanning within an 18 to 20-set breathl3 Prototype units capable of scanholding period. 5,6*12* ning during intervals of 6 set or less are currently being clinically evaluated and may provide greater precision in the near future.14 The ensuing review will analyze the experience gained with the first two generations of scanning devices. The illustrations in this review were obtained on a prototype EM1 CT 5000 general diagnostic scanning unit (EM1 Medical Inc., Northbrook, 111.)capable of completing a single scan within 20 sec. Pancreas. The entire pancreas is usually only detected on multiple contiguous sections because of its oblique orientation in the abdomen. Contours of the

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body and tail are clearly displayed because of the inherent differential contrast material provided by the surrounding retroperitoneal adipose tissue. The superior mesenteric artery, similarly identified because of the fat surrounding it in the root of the mesentery, serves as a constant landmark for locating the body of the pancreas which lies just anterior to it (fig. 2A). The oral, water-soluble, iodinated contrast material identifies the second and third portions of the duodenum and provides a useful landmark for localization of the pancreatic head and uncinate process. The intrapancreatic portion of a normal caliber common bile duct is occasionally identified; the normal-sized pancreatic duct cannot be detected. However, both may be identified when dilated such as in the presence of an obstructing lesion of the ampulla of Vater.” Experience with adenocarcinoma of the pancreas has thus far demonstrated that its detection depends on recognition of an alteration in size and/or contour of the gland”, 6,l5 (fig. 2B). Lesions which have not reached the periphery and distorted its contour remain undetected. Carcinomas of the body and tail are usually quite readily detected because most have achieved considerable size by the time diagnostic studies are undertaken. On the other hand, detection of tumors of the head of the pancreas has been less successful because their strategic relationship with the common bile duct prompts earlier diagnostic maneuvers. Native attenuation coefficient values have not proved to be sufficiently accurate for distinguishing between normal and malignant tissue,“, I4 nor has IICM provided an aid in this differentiation.5 Local extension of pancreatic tumors to critical adjacent organs (aorta, inferior vena cava) is readily displayed and provides sound evidence of unresectability (fig. 2B). Liver metastases and dilated intrahepatic bile ducts are secondary signs sought in all

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cases of suspected pancreatic neoplasm. Although large series have not, as yet, been accumulated, Stanley et al., using a fast scan device, have reported the correct diagnosis in 16 of 18 patients with pancreatic adenocarcinoma.5 Haaga et al., using a slower scanner, detected pancreatic malignancy in 13 of 17 patients ultimately proved to have carcinoma; they found CBT in this group of patients to have an accuracy approximately equal to that of angiography. l5 Detection of inflammatory disease of the pancreas depends on the extent to which it is accompanied by alteration in size, shape, or tissue composition. Although machine precision is not yet adequate to detect the edema associated with acute pancreatitis, small calcific deposits, undetected on plain abdominal radiographs, are readily demonstrable. The diminished attenuation coefficients of uncomplicated pseudocysts and abscesses allow their accurate detection and localization. However, the differentiation between pancreatitis and neoplastic disease or the detection of their coexistence is, as yet, impossible based on morphology or tissue density characteristics;‘5 diagnosis of such patients still requires endoscopic retrograde cannulation and clinical correlation. Liver. In transaxial section, the normal liver presents with a highly variable contour whose homogeneous density may be altered by the presence of fat’* and/or occasionally vascular structures’6 (fig. 3A). The anterior portion of the liver is divided by a fissure which contains fat surrounding the falciform ligament and ligamenturn teres.12 Posteriorly and medially a second fissure is invariably identified because of the presence of fat which surrounds the gastrohepatic ligament and the ligamenturn venosum. However, the boundary between the right and left lobes, based on surgical vascular anatomy, is not defined by these fissures but rather by

FIG. 2. Pancreas: normal versus cancer. A, the majority of the volume of a normal pancreatic gland is shown in this single section because of its horizontal orientation. Its smooth contours are readily visible because of surrounding lower density fat. Surrounding structures include stomach (horizontal large arrow), duodenum (vertical large arrow), inferior vena cava (vertical small arrow), superior mesenteric artery (small horizontal arrow) emerging from the aorta, and the left kidney (double arrows). B, this adenocarcinoma of the pancreas is recognized by its enlarged, lobulated appearance (small white arrows). The tumor has infiltrated the fat plane posteriorly so that its density blends with that of the aorta (black arrow). The medial aspect of an enlarged spleen is also evident (horizontal white arrow).

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FIG. 3. Liver: normal and abnormal. A, this section of a normal

a line drawn from the gallbladder fossa anteriorly to the fossa for the inferior vena cave posteriorly.12 The amount and distribution of parenchymal fat is quite variable; typically the largest amount exists in the hilum and may be associated with columnar-shaped, fatty accumulations which radiate toward the periphery of the liver. Intrahepatic portal and hepatic veins are not usually evident but may be identified, particularly in the anemic patient, as columnar-shaped, branching, low density structures. Intrahepatic fat deposits or venous channels may be confused with dilated bile ducts; in the case of vascular structures, opacifkation with IICM will allow positive identification.‘” Despite

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the low density characteristics of bile, normal-sized intrahepatic ducts are too small to be distinguished within the liver. Dialted intrahepatic ducts are detected because of their size and their content of bile which measures, on the average, 8.3 in contradistinction to liver parenchyma which has an average attenuation coefficient of 24.‘” Malignant neoplasms, either primary or metastatic, are most frequently recognized as areas of diminished 17 A single report of a metastatic lesion from the colon with increased attenuation coefficients has been cited and is attributed to extravasation of blood within the lesion.12 Metastatic nodules, when large, are usually rounded, sharply defined lesions (fig. 3B). When smaller (1 to 2 cm) their margins become less distinct, and these are detected with less precision. After the administration of IICM, most metastatic deposits show less increase in density than does normal liver, and this provides a means of improving their definition.‘2, I7 Some metastatic lesions, invariably those with increased vascularity, become isodense with surrounding normal parenchyma after enhancement with intravenous contrast material. I2This phenomenon not only obscures definition of these focal areas of diminished density but also raises the question of whether some or all of these areas of diminished density originally observed on the unenhanced scan represented vascular structures. Cysts are less dense than surrounding normal parenchyma and frequently even less dense than malignant processes. Liver abscesses may be confused with malignant tumors because of their similar densities; either process, when air-containing, is readily identified (fig. 3C). The detection of any of the foregoing space-occupying lesions obviously is dependent on their size, density relative to the normal surrounding parenchyma, patient cooperation, and machine precision. Levitt has reported an 87% accuracy rate for the detection of space-occupying lesions using a 20-set scanner.‘* Cysts and tumors 1 cm or less in diameter have been detected using a fast scanning unit.“. I2Utilizing a 2%min scan device, Alfidi demonstrated that CBT had approximately the same accuracy as radionuclide examination for detecting mass lesions in the liver. Ii Using the same type unit, Grossman reported a comparative study of noninvasive imaging techniques and found that gray scale ultrasonography was slightly more accurate in detecting space-occupying lesions.‘” Similar comparative investigations have not as yet been reported from institutions employing faster scanners. Preliminary experience with the faster scanners indicates that radionuclide and CBT scanning will often be used in complementary roles but that CBT offers the advantage of more specific information about: (1) composition of the mass lesion, (2) normal anatomical variants, and (3) organs and tissues surrounding the liver. CBT appears to be less accurate than radionuclide scanning in the diagnosis of diffuse diseases of the liver such as cirrhosis or hepatitis.” Although excess concentrations of iron”’ and fatz’ (fig. 30) in the liver have been appreciated, the sensitivity for such detection has not as yet been assessed. density_",

liver demonstrates fat in the anterior fissure (horizontal black arrou)) surrounding the ligamenturn teres. The celiac axis (white arrow) is dividing into the splenic and hepatic arteries. The latter is shown coursing to the right into the posterior fissure (uertical black arrow). B, sharply circumscribed, rounded, lower density areas in the liver represent metastases from an adenocarcinoma of the colon. C, a biloculated absress with air-fluid levels is located in the posterolateral aspect of the right lobe of the liver (uertical arrow). Streak artifacts degrade the true density of the left lobe of the liver and are caused by motion of the opacified stomach occurring during the time of scanning. D, diffuse fatty infiltration of the liver is appreciated by the over-all decrease in density of the liver which is normally the same density or slightly higher than that of the spleen ! black arrow). The inferior vena cava (horizontal arrow) and intrahepatic venous channels (vertical arrow) are appreciated because of their higher density relative to the predominately fat containing liver. E, dilated right and left hepatic ducts are evident (black arrows) in this patient with obstructive jaundice caused by adenocarcinoma of the pancreas.

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Initial results also indicate that CBT will provide a useful tool for distinguishing between obstructive and nonobstructive jaundice. Dilated bile ducts appear as columnar, branching, low density structures centrally (fig. 3E), but more peripherally may be observed as rounded, sharply circumscribed areas when they ramify at right angles to the X-ray beam.s~‘2~‘6In the latter circumstance, differentiation between metastatic lesions or their coexistence may be difficult. Havrella et al. have demonstrated an 88% accuracy for diagnosing obstructive jaundice and a 77% accuracy for determining its etiology.21 Levitt et al. utilized a faster, 20-set scanning device to investigate 91 jaundiced patients. lRThey were able to distinguish correctly between obstructive and nonobstructive jaundice in 90% of this group, and in 80% the site or cause of obstruction was correctly identified. Although clearly superior to radionuclide scanning in the jaundiced patient, it is presently uncertain whether CBT is more accurate than ultrasonography in detecting the presence of dilated ducts or the etiology of obstruction. The added advantage of CBT compared to radionuclide scanning is its capacity to provide etiological information in the obstructed patient, as shown by Stephens et al., who correctly diagnosed the site of the obstructing lesion in 9 of 15jaundiced patients.12 The gallbladder can be detected as a discrete structure because of the low density of bile. Attenuation coefficient of bile has been noted to vary widely; this has been attributed, in the normal patient, to varying stages of bile concentration.’ Whereas ultimately machine precision may be improved sufficiently to provide exacting information on bile composition, per se, at the present time CBT has little specific application to the diagnosis of gallbladder disease. The versatility and specificity of ultrasound for detecting gallstones clearly indicate it will likely remain the optimal, noninvasive imaging technique for investigating gallbladder disease. SpEeen. The average attenuation coefficient of the spleen is slightly less than that of liver, most likely because of the effect of the greater relative volume of blood. The fatty tissue surrounding the spleen permits the precise identification of its borders; therefore, volume determinations are easily accomplished. Although both tumors and infarcts within the spleen have been detected,g precision for such detection is, as yet, unknown. Schaner et al. have demonstrated lymphomatous involvement in 1 patient, but in 7 others with lymphoma, only nonspecific splenomegaly was detected.22It is anticipated that CBT will be useful in the detection of splenic cysts and in the investigation of patients with suspected ruptured spleens. Gastrointestinal tract. Initial results strongly suggest that CBT will have very limited application to the detection of abnormalities within the lumen and walls of the alimentary tract .6 However, CBT will be very useful for definition of the extramural extent of a lesion or nature of a pathological process contiguous to the gastrointestinal tract. Exact localization of the intraperitoneal extension of an abdominal neoplasm should

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provide greater precision for the delivery of radiation therapy. 23 Intraabdominal abscesses. Haaga et al. reported the successful detection of 20 of 22 abdominal abscesses and their accurate localization in relation to surrounding organs.24All intraperitoneal abscesses were successfully detected; these included those present in intrahepatic, perihepatic, subdiaphragmatic, and pelvic locations. The abscesses themselves were recognized as extraluminal collections of fluid and/or gas. Density readings were sufficiently different from those of neoplasm to allow their differentiation. However, the density characteristics were not sufficiently different from transudates, cysts, or subacute hematomas to be distinguished. Other imaging techniques were used in 15 of the patients in this series, and 10 of the abscesses were detected. Guided needle aspiration biopsy. Estimation of depth on the cross-sectional images provides an ideal guide for performance of percutaneous, guided aspiration of abdominal masses. The capacity to obtain contiguous, narrow “slices” with a cross-sectional dimension permits accurate three-dimensional localization of a detected pathological process as well as documentation of the exact position of the tip of the biopsy needle (figs. 4 and 5). Initial clinical experience with flexible, fine caliber needles indicates that a variety of abdominal masses can be aspirated without accompanying serious complication.25 This technique is being widely adopted as a means for obtaining either cytological or bacteriological information, thereby avoiding the morbidity and mortality accompanying diagnostic laparotomy. Haaga and Alfidi achieved positive cytological information in 12 of 14 patients with neoplasms using a CBT-guided technique. 26Two patients with suspected pancreatic carcinoma and 2 of 3 patients with suspected liver metastases were successfully biopsied. Haaga et al. have also adapted this technique to aspirate the contents of suspected abscesses discussed in the previous section.24In addition to providing specific etiological information, the technique was extended in a limited number of patients to provide partial or definitive drainage of the abscesses. Simple aspiration required approximately 30 min, and no complications were reported. Peritoneal cauity. Ascitic fluid has a variable density reading perhaps related to its protein content; however, because its density is invariably greater than that of fat and less than that of abdominal organs, it is readily identified, l3 The detection of the presence of bloody peritoneal fluid has not as yet been reported although it is theoretically possible if the hematocrit reading is sufficiently elevated. Metastases to visceral and parietal peritoneum are recognized because of the higher density characteristics and identification of parietal peritoneum metastases as small as 1 cm has been reported.” Radiotherapy planning. The advantage of CBT for this application lies not only in precise localization of a tumor but, as well, in similar precision for defining adjacent normal structures and body contours. This

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FIG. 4. Percutaneous thin needle aspiration biopsy of the pancreas. A, a 23-gauge needle (large white horizontal arrow) has been inserted through the anterior abdominal wall (white vertical arrow), but on this section has not reached the mass in the body of the pancreas. Landmarks include low density pockets of gas in the transverse colon anteriorly, the opacified duodenum (black arrow), and the aorta posteriorly with a partially calcified wall (horizontal small white arrow). B, the next contiguous section inferior to A demonstrates the tip of the needle to have traversed small intestine and entered the pancreatic mass. Cytological examination of the specimen revealed adenocarcinoma and the patient suffered no clinically apparent complications from the procedure.

FIG. 5. Percutaneous thin needle aspiration biopsy of periportal mass. A, a transhepatic cholangiogram obtained in a 56-year-old man 1 year after the performance of a choledochojejunostomy for an obstructing pancreatic mass. The bile duct is slightly dilated and there is extravasation of contrast material into a loculated area at its distal’ end (white arrows). B, a 23-gauge needle has been inserted percutaneously into the mass located in the portal area of the liver (smaZ2arrow). Culture of the aspirated material revealed Escherichia coli and subsequently a small abscess was drained at surgery. A small amount of loculated ascites is present anterior to the right lobe of the liver (large arrows).

technique can also be used to monitor the effectiveness of a given amount of radiation by assessing the tumor volume change at one or more intervals during and after the course of treatment. Munzenrider et al. have reported, in a retrospective study, the advantages offered to the radiotherapist by the availability of CBT,27 and more recently Go&in et al. have shown prospectively that management of the 18 of 20 patients undergoing radiotherapy was significantly influenced by information provided by this device (M. Goitein, J. Wittenberg, and J. T. Ferruci, Jr., personal communication) .

Summary and Comments It is clear from the clinical experience to date that the morphological representation of the abdominal solid organs provided by CBT is superior to all other imaging techniques. This information is gained in a noninvasive manner and is accompanied by only a modest dose of radiation. The latter two features offer strong advantages over invasive techniques, such as angiography, if the pathological accuracy is even similar, as indicated, for example, by the preliminary work of Haaga et al. in diagnosing pancreatic malignancy.15 However, these

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two qualities are not advantages when CBT is compared to more frequently used radiographic tests such as radionuclide examinations and ultrasonography. Each of these are noninvasive techniques and have negligible or no known radiation dose hazards. Additionally, ultrasound examinations provide not only a similar crosssection dimension but also an assessment in the longitudinal plane. Thus a battery of noninvasive radiographic examinations are now available which, by early indications, will each be superior in certain abdominal diseases or in patients with certain body habitus, but in others may still play complementary roles. Insufhcient data are yet available to define the appropriate sequence of tests in any given diagnostic problem. It must be kept in mind that each of these instruments, but particularly CBT, represents a large financial investment for both the provider and the consumer. Because the cost of CBT devices range between $500 and $700,000, injudicious use of such technology obviously represents an enormous waste. Problems in assessing the appropriate utilization of diagnostic techniques are compounded by the rapid pace with which each of these devices has undergone technological maturation, dictating obsolescence of previously accumulated clinical data. Although continued technological evolution is inevitable, major advances beyond the, as yet, untried newest generation of instruments is unlikely in the near future. A critical comparative study of these techniques is therefore in order so that unproductive diagnostic testing can be avoided. The investigations must include a randomized application of these three noninvasive tests, alone and in combination, to the spectrum of commonly encountered abdominal problems. Similarly, a study comparing CBT to standard invasive techniques such as angiography, percutaneous transhepatic cholangiography, and endoscopic cannulation must also be initiated. The stimulus for such investigations must initiate with radiologists who will necessarily require the cooperation of both gastroenterologists and their patients. Although the radiologist must make an independent assessment of the information available from any given imaging examination, the clinical impact of any such information can only be evaluated by the patient’s physician. Thus investigations designed to determine the true efficacy of any diagnostic test will have their greatest credibility when accompanied by an evaluation of their impact on diagnostic and therapeutic decision making (J. Wittenberg, J. T. Ferrucci, Jr., H. Feinberg, et al., personal communication). It is only when information of such quality is available that intelligent decisions of whether to image or not, and in what sequence to image in any clinical problem, will be made. REFERENCES 1. Hounsfield GN: Computerized transverse axial scanning (tomography): part I. Description of system. Br J Radio1 46:10161022, 1973 2. Baker HL: Computed tomography and neuroradiology: a fortunate primary union. Am J Roentgen01 Radium Ther Nucl Med 127:101-110, 1976 3. Alfida R, Haaga J, Meaney TF, et al: Computed tomography of

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the thorax and abdomen: a preliminary report. Radiology 117:257-264,1975 4. Schellinger D, DiChiro G, Axelbaum SP, et al: Early clinical experience with the ACTA scanner. Radiology 114:257-261, 1975 5. Stanley RJ, Sage1 SS, Levitt RG: Computed tomography of the body: early trends in application and accuracy of method. Am J Roentgen01 Radium Ther Nucl Med 12753-67, 1976 6. Sheedy PF II, Stephens DH, Hattery RR, et al: Computed tomography of the body: initial clinical trial with the EM1 prototype. Am J Roentgen01 Radium Ther Nucl Med 127:23-51, 1976 7. New PFJ, Scott WR: Computed Tomography of the Brain and Orbit (EM1 Scanning). Baltimore, Williams & Wilkins Co, 1975, p 10-22 8. Ledley RS, DiChiro G, Lussenhop AJ, et al: Computerized transaxial tomography of the human body. Science 186:207-212, 1974 9. Sage1 S, Stanley RJ, Evens RG: Early clinical experience with motionless whole body computed tomography. Radiology 119321-330, 1976 10. Wittenberg J: CT: The prospects of computed body tomography. Applied Radio1 5:99-116, 1976 11. Freedman GS: CT in CT or CATS in CONN or computerized axial tomography in Connecticut. Connecticut Medicine 40:763769, 1976 12. Stephens DH, Sheedy PF II, Hattery RR: Computed tomography of the liver. Am J Roentgen01 128579590, 1977 13. Kreel L: Computerized tomography using the EM1 general purpose scanner. Brit J Radio1 50:2-14, 1977 14. Hare11GS, Marshall WH Jr, Breeman RS, et al: Early experience with the varian six second body scanner in the diagnosis of hepatobiliary tract disease. Radiology 123:355-360, 1977 15. Haaga JR, AlBdi RJ, Zelch MG: Computed tomography of the pancreas. Radiology 120:589-595, 1976 16. Kressel HY, Korobkin M, Goldberg HI: The portal venous tree simulating dilated biliary ducts on computed tomography of the liver. J Comput Assist Tomog 1:169-175, 1977 17. Alfidi RJ, Haaga JR, Havrilla TR, et al: Computed tomography of the liver. Am J Roentgen01 Radium Ther Nucl Med 127:6974, 1976 18. Levitt RG, Sage1 SS, Stanley RJ: Accuracy of computed temography of the liver and biliary tract. Radiology 124123-128, 1977 19. Grossman ZD, Wistow BW, Bryan PJ, et al: Radionuclide imaging, computed tomography, and gray-scale ultrasonography of the liver: a comparative study. J Nucl Med 18:327-332, 1977 20. Mills SR, Doppman JL, Nienhuis AW: Computed tomography in the diagnosis of disorders of excessive iron storage of the liver. J Comput Assist Tomog l:lOl-104, 1977 21. Havrilla TR, Haaga JR, Altidi RJ, et al: Computed tomography and obstructive biliary disease. Am J Roentgen01 Radium Ther Nucl Med. 128:765-768,1977 22. Schaner EG, Head GL, Doppman JL, et al: Computed tomography in the diagnosis, staging and management of abdominal lymphoma. J Comput Assist Tomog 1:176-180, 1977 23. Chernak ES, Rodriquez-Antunez A, Jelden G: The use of computed tomography for radiation therapy treatment planning. Radiology 117:613-614, 1975 24. Haaga JR, Alfidi RJ, Havrilla TR, et al: CT detection and aspiration of abdominal abscesses. Am J Roentgen01 Radium Ther Nucl Med 128465-474, 1977 25. Goldstein HM, Zornoza J, Wallace S, et al: Percutaneous fine needle aspiration biopsy of pancreatic and other abdominal masses. Radiology 123:319-322, 1977 26. Haaga JR, Altidi RJ: Precise biopsy localization by computed tomography. Radiology 118603-607, 1976 27. Munzenrider JE, Pilepich M, Rene-Ferrer0 JB, et al: Use of body scanner in radiotherapy planning. Cancer (in press)