Three-Dimensional Spiral CT Angiography of the Abdomen Charles P. Semba, Geoffrey D. Rubin, and Michael D. Dake Spiral CT angiography is a technical innovation in vascular imaging that can produce spectacular three-dimensional reconstructions of the abdominal vessels and organs using modified CT scanning techniques. Rapid volume data acquisition allows contrast material to be imaged in the arterial or venous phase. CT reconstruction in cross-sections avoids superimposition of overlying structures, The combination of these features allows spiral CT angiography to produce extraordinary images of the abdominal vasculature and organs. This review outlines fundamental techniques in spiral CT angiography and summarizes our initial clinical experience at Stanford University Medical Center, Copyright 91994by W.B. Saunders Company T HE KEY FEATURE of spiral scanning that allows for angiographic reconstruc- tions is rapid acquisition of imaging data. Spiral CT slip-ring technology provides continuous 360~ rotation of the x-ray gantry for up to 40 seconds. 1Because the table continuously moves the patient through the gantry during scanning, the imaging data is collected along a continuous spiral path instead of by conventional stationary transaxial slices. The simultaneous table move- ment and continuous gantry rotation (gantry rotation period is 1 second) without an inter- scan delay allow data to be collected very rapidly. When using intravenously administered iodinated contrast, images of the abdomen can be obtained when the contrast is captured entirely during the arterial or venous phase of circulation. A typical high-resolution (< 3-ram collimation) spiral examination of the abdomi- nal aorta can be performed in 30 seconds covering 9 to 18 cm of volume during each 30-second scan. A conventional CT scan may take several minutes to cover the same volume and therefore cannot precisely image during the arterial contrast phase. Spiral CT imaging exclu- sively in the arterial or venous phase of contrast injection thus provides the cornerstone of three- dimensional (3D) angiographic reconstructions. METHODS 3D spiral CT angiography is being investi- gated actively at Stanford University Medical Center using both Siemens Somatom Plus-S (Siemens Medical Instrumentation, Iselin, N J) and General Electric HiSpeed Advantage (Gen- eral Electric Medical Systems, Milwaukee, WI) scanners. Since December 1991, more than 75 patients with a wide variety of vascular prob- lems have been evaluated using spiral CT angi- ography and compared with conventional inva- sive angiography.2, 3 For imaging the abdominal aorta and splanch- nic circulation, a routine scout projection is performed and 5 to 10 conventional transaxial images are obtained in the area of interest using a slice thickness of 10 mm. Based on these initial views, a 9- to 24-cm cylindrical scan volume is selected with the key region of inter- est placed in the center of the scan volume. An 18- or 20-gauge intravenous 3-cm-long angiography catheter is then introduced into the antecubital vein. A test injection is per- formed to properly time the injection bolus to the region of interest. Fourteen scans are per- formed sequentially at 2-second intervals at the most cephalad region to be examined without table movement. Twenty mL of nonionic con- trast (Isovue 300; Squibb, New Brunswick, N J) is injected using an automated power injector (Medrad, Pittsburgh, PA) at 4 to 5 mL per second using an 8-second scan delay. The pa- tient is hyperventilated and instructed to breath hold for the entire dynamic 14-image sequence for a total scan time of 28 seconds. Image analysis is then performed to determine the time in which maximum contrast density is reached at the most cephalad portion of the scan volume. For example, if the maximum density within the top portion of the aorta is reached within 18 seconds, the scanning delay is programmed for approximately 16 seconds. Typi- cal scanning delay for the abdominal aorta is 14 to 25 seconds. 4 From the Departments of Cardiovascular/Interventional Radiology and Thoracic Radiology, Stanford UniversityMedi- cal Center, Stanford, CA. Address reprint requests" to Charles P. Semba, MD, Depart- ment of Cardiovascular/Interventional Radiology, Stanford Universi O,Medical Center, Stanford, CA 94305. Copyright 9 1994by W.B. Saunders Company 0887-2171/94/1502-000655. 00/0 Seminarsin Ultrasound, CT, andMRI, Vo115, No 2 (April), 1994: pp 133-138 133