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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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1223 patients underwent aspiration biopsy with a diagnostic yield of 86.4%; 24.2% of the patients had a small pneumothorax, but only 4.4% required treatment; one patient developed a moderate hemothorax. The method, problems, and complications including morbidity and mortality are discussed. The relative success of aspiration biopsy with different lesions of the lung and mediastinum is identified.

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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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Since the original description of desquamative interstitial pneumonitis in 1967, several investigators have questioned the specificity of the disease. The concept of desquamative interstitial pneumonitis and usual fibrosing interstitial pneumonitis as two manifestations of a nonspecific disease spectrum has been proposed. Twenty-six patients with desquamative interstitial pneumonitis were evaluated with respect to clinicopathologic correlates. Biopsies were reviewed without knowledge of the patients' clinical course. The absolute histopathologic criteria for the diagnosis were (1) intra-alveolar accumulations of free alveolar cells with PAS-positive diastaseresistant cytoplasmic granules; (2) mononuclear cell interstitial inflammation; and (3) absence of necrosis, hyaline membranes, intra-alveolar fibrosis, asbestos bodies, and birefringent crystalline dust material. Transmission electron microscopic studies revealed the dominant alveolar lining cell to be the granular pneumocyte, with a prominent population of free alveolar macrophages. Patients were segregated into group 1 (cellular phase) and 2 (cicatrized phase). Although favorable short-term responses to corticosteroid therapy were observed in both groups, long-term responses were variable. Apparent complete remissions were noted in both groups.

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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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Computer tomography (CT) permits recognition of normal and pathologic structures and renders percutaneous biopsy easy, giving a high degree of diagnostic accuracy with few complications. It is an ideal technique for the biopsy of foci which cannot be reached otherwise.

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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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The usefulness and accuracy of CT scanning in the determination of bone mineral content is studied. The radius in 31 patients of both sexes and varying ages was examined using both the Norland-Cameron bone mineral analyzer and the CT scanner. There was reasonably good correlation (r=.72). Ten cadaver bones were then examined with CT scanning and were sent to the laboratory for calcium determination. These results indicate excellent correlation (r=.97). It is concluded that CT scanning represents the only practical and accurate in vivo method of bone mineral content determination.

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