TECHNOLOGIC ADVANCES IN UROLOGY IMPLICATIONS FOR THE TWENTY-FIRST CENTURY zyxwvu 0094-0143/98 $8.00 + z .OO THREE-DIMENSIONAL COMPUTED TOMOGRAPHY FOR PLANNING UROLOGIC SURGERY Geoffrey S. Young, MD, Stuart G. Silverman, MD, Joachim Kettenbach, MD, Nobuhiko Hata, MD, Polina Golland, MD, PhD, Ferenc zyx A. Jolesz, MD, Kevin R. Loughlin, MD, and Ron Kikinis, MD The development and marketing of new volumetric computed tomography (CT) scan- ners in 1990 made it possible to perform three-dimensional (3-D) imaging of the abdo- men without respiratory artifacts and with clarity similar to that achieved in the muscu- loskeletal and central nervous systems by conventional scanners.6 Before 1990, all CT scanners had x-ray tubes that were connected to the machine’s gantry by electrical cables. This limited the excursion of the tube in any one direction because continuous rotation would wind the cables into a knot. Thus, conventional CT scanning is performed by executing a series of individual CT scan slices during which patients are instructed to hold their breath. Between scans the table is moved forward a certain distance and the process is repeated. If the breath holds are not identical, the imaged organ or region contains gaps or The authors wish to acknowledge the following grants NIH PO1 CA 67165-01A1 (RK, FAJ), PO1 AG04953-14 (RK), NSF BES-9631710 (RK), DARPA F41624-96-2-0001 (RK, FAJ) and Austrian Science Fund, Project Jo 1315- MED OK), Japan Society for Promotion of Science, Tokyo, Japan (NH). skip areas. This limitation is termed “respira- tory misregistration.” The technical advan- tage that made volumetric CT possible was the development of a continuously rotating x-ray tube with slip rings. Slip rings are a pair of matched rings on the tube and gantry that can rotate past one another without limit. This allows for continuous rotation of the tube and the ability to perform a continuous x-ray exposure as the patient is moved for- ward through the CT gantry. The resulting exposure forms a path that looks like a spiral or helix; hence, today volumetric CT scanning often is referred to as “spiral” or ”helical” CT. Spiral CT acquires data in a region of interest using a single continuous x-ray exposure that is fast enough to be executed during a single breath hold, as the patient moves through the gantry, so that respiratory misregistration is eliminated. An entire body region is imaged and a continuous volume of CT data ob- tained. The resulting volumetric CT data set can be used to create axial images at a desired slice thickness and at a desired increment. Standard axial images from spiral CT of the urinary tract have been shown to be helpful From the Departments of Radiology zyxwvutsr (GSY, SGS, JK, NH, FAJ, RK) and Surgery (KRL),Brigham and Women’s Hospital, Harvard Medical School, Boston; and the Artificial Intelligence Laboratory, Massachusetts Institute of Technology (PG), Cambridge, Massachusetts UROLOGIC CLINICS OF NORTH AMERICA VOLUME 25 - NUMBER 1 FEBRUARY 1998 103