USE OF CONTRAST MATERIAL FOR SPIRAL CT OF THE ABDOMEN - COMPARISON OFHEPATIC ENHANCEMENT AND VASCULAR ATTENUATION FOR 3 DIFFERENT CONTRAST-MEDIA AT 2 DIFFERENT DELAY TIMES

OBJECTIVE. The purpose of this study was to determine the relative eff ects of delay time, contrast agent concentration, and contrast agent v olume on hepatic enhancement and on aortic and portal vein attenuation for contrast-enhanced spiral CT of the abdomen. The effect of delay t ime was evaluated by comparing two different delay times for each of t hree IV contrast media. Three different media were tested to identify whether the effects were different with different iodine concentration s and doses or with different volumes of contrast medium. SUBJECTS AND METHODS. A total of 169 patients who underwent contrast-enhanced CT o f the abdomen with spiral CT imaging were evaluated for enhancement of the liver parenchyma and for postenhancement attenuation of the aorta and portal vein. Total iodine doses of 30 g as 100 ml of iohexol 300 or 125 ml of ioversol 240 and of 40 g as 125 ml of ioversol 320 were e valuated at delay times of 45 and 60 sec and with a low-flow monophasi c injection at a rate of 2 ml/sec. RESULTS. For each contrast medium t ested, a 60-sec delay provided greater hepatic enhancement than did a 45-sec delay (43 vs 32 H for iohexol 300, 37 vs 28 H for ioversol 240, and 50 vs 39 H for ioversol 320; all comparisons, p less than or equa l to .0001). The aortic attenuation achieved in the abdomen after cont rast medium administration was significantly greater with a 45-sec del ay than with a 80-sec delay for iohexol 300 (p = .0290) but not for th e other contrast media. The portal vein attenuation achieved after con trast medium administration was significantly greater with a 60-sec de lay than with a 45-sec delay for all three contrast media (p = .0051). CONCLUSION. When IV contrast material was injected with a low-flow-ra te monophasic bolus, a delay time of 60 sec, longer than that typicall y used for dynamic incremental scanning, provided greater hepatic enha ncement in spiral CT. This result was significant for the three contra st media tested. Aortic attenuation was significantly greater at short er delay times when a smaller volume of contrast material was injected . Portal vein attenuation was greater at longer delay times, suggestin g that the optimal delay time may be longer than 60 sec. Further work to determine the optimal scanning window for hepatic enhancement in sp iral CT by use of time-density curves is indicated.