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Observer accuracy in the identification of low-contrast objects in computed tomography (CT) was studied. Thresholds were established for detection of lesions of various sizes and attenuation differences in CT images produced at different radiation doses. Noise reduction was important in identifying certain types of lesions. Detection was not accurate when the standard deviation of the mean of an organ exceeded the difference in the means of the lesion and the surround region.

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The diagnosis of infected synthetic grafts is difficult using traditional radiographic techniques. In four cases, computed tomography demonstrated small pockets of gas in the clot around the grafts, a distinctive finding for an infected prosthesis. Further experience is required to determine whether this will prove to be a reliable diagnostic sign. The gas collections in infected grafts differ from normal gas in their multiplicity and occurrence more than 10 days after surgery.

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Computed tomography (CT) was used to study 79 patients with suspected gallbladder disease. First and second generation scanners were used to determine the efficacy of CT in detecting cholecystitis or cholelithiasis. Manifestations of gallbladder disease such as hydrops, opaque and nonopaque gallstones, chronic cholecystitis with thickened inflammatory walls, and secondary liver abscesses can be easily detected. It is a useful technique for individuals in whom the gallbladder has failed to opacity on oral cholecystography. The scanning method is described, and estimates of reliability are given including its accuracy, limitations, and place in the management of gallbladder disease, especially cholelithiasis. When conventional radiographic examinations or ultrasound fail to give definitive diagnostic information, CT can be a useful alternative with an overall diagnostic accuracy greater than 80%.

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The authors are preparing a series of communications on CT-guided biopsy procedures to be published in future issues of this journal. The present article, which previously appeared in the Cleveland Clinic Quarterly, is intended to serve as an introduction to the concept of CT-guided biopsies. Because the principles of the biopsy procedure remain the same, we do not believe that a "rewrite" of the previously published article would be required. We hope that by presenting this article and subsequent articles concerning the use of CT-guided biopsies, the reader will acquire an appreciation of the proper role of this exciting new technique in comparison to the available imaging modalities. We believe that as individuals become more experienced with the imaging capabilities of these CT devices, they will want to develop the technique of obtaining biopsy confirmation of the imaging diagnosis.

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In a group of 188 patients, 192 computed tomographic (CT) scans of the pancreas were done, and the diagnostic accuracy of CT determined relative to other modalities. CT was the most effective method of detecting neoplastic and inflammatory diseases. The full extent of the disease process, including involvement of the retroperitoneum and metastasis to the liver, was visualized with one examination. Calcification and cystic collections associated with pancreatitis were also clearly seen.

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Forty-four patients with confirmed biliary diseases were studied to determine the value of computed tomography (CT) in the diagnosis of biliary pathology. The results indicate that CT is useful and highly accurate in differentiating between obstructive (surgical) and nonobstructive (medical) disease entities. Of the cases with proved obstruction, 88% were correctly identified. All of the nonobstructive cases had positive CT correlation. In addition, the underlying cause of the occlusion was determined in the majority of cases.

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Computed tomography (CT) is effective in detecting intraabdominal abscesses. Loculations of fluid and extraluminal gas are clearly localized in relation to other organs. Of 22 abscess in this series, CT successfully detected 20; comparative information with gallium, techneticum, and ultrasound scans is presented. In addition to localizing these collections, CT can be used to guide needle aspiration and drainage procedures. Three sizes of needles were used to aspirate specimens and/or provide drainage. This was accomplished successfully in 12 of 14 CT-guided procedures.

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PIP: With the advent of whole body computed tomography (CT), an early diagnosis of hepatic tumors may be posible and laparotomy for diagnosis unnecessary. The CT scanner used was the whole body Delta unit. Patients were examined after an iv dose of 100 cc of Renograffin 60. Solid and cystic components of lesions can thus be determined. Case reports are given of 2 patients. The 1st patient had been taking Ovulen-21 for 21 months. Her liver scan revealed a large filling defect in the right lobe of the liver. Abdominal angiography showed an avasuclar mass displacing the right kidney. A CT scan depicted a large mass replacing the right lobe of the liver. The density of the mass indicated a fluid-filled cyst. At laparotomy a cyst involving the entire right lobe of the liver was found. Several nodules were present in the cyst wall. The diagnosis was cyst-adenoma of the liver. The other patient had taken Ovulen-21 for 7 years. An enlarged liver and symptoms of cholecystitis were present. The CT scan revealed a bolbous mass in the right lobe of the liver. The tumor was of the same density as the liver. At laparotomy a large hepatic adenoma was found. A 2nd mass was present in the left lobe. The tumors were not resected; cholecystectomy was done. Because of bleeding, a hepatic artery was ligated. Postoperatively, a repeat CT scan showed a large area of decreased density. At reoperation a large hematoma with necrosis of the hepatic adenoma was found and drained. The CT is an accurate method of performing percutaneous biopsies and aspiration procedures. An exact position of the needle tip can be obtained. CT-guided biopsies have also been done on masses in other areas.^ieng

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This work examines the scope and accuracy of CT in the detection of tumors, abscesses, cysts, and parenchymal disorders of the liver. While CT remains an emerging modality, it is shown to be equal to nuclear medicine in detecting mass lesions. It has also been possible to distinguish obstructive from nonobstructive jaundice. Presently, CT is not well suited to the study of cirrhosis. Technological advances in CT design and contrast agents offer promise of significantly improved resolution.

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