783 0361-803X/93/1604-0783 © American Roentgen Ray Society Detection of Focal Hepatic Lesions with Spiral CT: Comparison of 4- and 8-mm Interscan Spacing Bruce A. Urban1 Elliot K. Fishman Janet E. Kuhlman Akira Kawashima Joseph G. Hennessey Stanley S. Siegelman Received September 2, 1992; accepted after re- vision November 6, 1992. 1All authors: Department of Radiology and Ra- diological Science, The Johns Hopkins Hospital, 600 N. Wolfe St., Baltimore, MD 21205. Address correspondence to E. K. Fishman. OBJECTIVE. The objective of this study was to determine if spiral CT with 4-mm interscan spacing results in increased confidence in or rate of detection of focal hepatic lesions when compared with spiral CT with 8-mm interscan spacing. MATERIALS AND METHODS. Spiral CT scans of the liver of 42 consecutive patients with suspected hepatic disease were independently reviewed by three senior radiologists in two sets: one set was reconstructed with 8-mm interscan spacing and one set was reconstructed with 4-mm interscan spacing. The slice thickness was 8 mm for both data sets. The number and sizes of focal hepatic lesions were docu- mented. RESULTS. Thirty-three of the 42 patients had least one focal lesion. The lesion size varied from 2 mm to 21 cm. When 8-mm interscan spacing was used, 297 lesions were detected (21 2 were considered definite). When 4-mm interscan spacing was used, 31 8 lesions were detected (258 were considered definite). Therefore, 7% more lesions were detected with 4-mm interscan spacing than with 8-mm interscan spac- ing (p = .05), and 22% more were diagnosed definitively (p < .01). If lesions larger than 4 cm are excluded, 10% more lesions were detected with 4-mm interscan spacing, and 33% more were diagnosed definitively. Of the lesions detected exclusively with 4- mm interscan spacing, 69% were less than 1 .0 cm in diameter. CONCLUSION. Spiral CT with smaller interscan spacing (4 instead of 8 mm) results in increased confidence in and rate of detection of focal liver lesions. The additional benefit is most significant with smaller lesions. AJR 1993;160:783-785 The recent introduction of spiral volumetric CT has provided a new rapid-scan technique for evaluation of focal pathologic changes in the chest and abdomen. Several groups [1-8] have already described the potential benefits in the detection of disease involving the head and neck, lung, liver, biliary tree, kidney, and pan- creas. These advantages result from scanning during a single breath-hold, which results in contiguous scan volumes independent of the patient’s breathing and motion and superior enhancement with bolus administration of contrast material [9]. The acquisition and reconstruction parameters of the spinal data set are arbitrarily selected by the radiologist. These include table incrementation speed, slice thick- ness, and intenscan spacing during reconstruction. With smaller intenscan spacing, more images through a volume of interest can be provided without an additional dose of radiation to the patient. The purpose of this study was to determine if the increased number of images obtained with smaller intenscan spacing results in increased detection on greater confidence in the detection of focal liver lesions. Materials and Methods The study group consisted of 42 consecutive patients referred for evaluation of suspected primary or metastatic hepatic tumor. The group included 16 men 31-77 years old (mean, 66 years) and 26 women 25-75 years old (mean, 57 years). Patients with diffuse disease and/ Downloaded from www.ajronline.org by 52.73.204.196 on 05/17/22 from IP address 52.73.204.196. Copyright ARRS. For personal use only; all rights reserved