The next step is a single center, prospective clinical trial intended to test the hypothesis that a formula derived from PCA using specific subject parameters can be used to determine the individual contrast material dose and provide a more consistent level of vascular and parenchymal enhancement during MDCT scanning of the abdomen and pelvis.

500 subjects referred for a "CT of the abdomen and pelvis with contrast material" will be recruited to participate in this trial. Subjects in the first group of 200 will be randomized to either a fixed dose of contrast material (100 subjects) or a customized dose of contrast material based on the experimental algorithm (100 subjects). The second group of 300 subjects will receive a customized dose of contrast material based on the experimental algorithm. All of the subjects will be studied on a single CT scanner located in the Duke Cancer Center. After obtaining informed consent, the subjects will first undergo measurement of their height and weight on a dedicated pair of scales located in close proximity to the scanner.

The subjects will then be placed on the CT scan table in the supine position followed by the acquisition of scout digital radiographs in both the AP and ML projections. These digital scout radiographs are acquired routinely and used by the technologist to plan the scan. From these scout radiographs, single CT slices in the axial plane (n=2) will subsequently be obtained, one through the level of the L4 pedicle and the other through the supra-acetabular pelvis using a field-of-view that includes all of the subject. These slices are not part of the routine protocol but will be acquired using low radiation dose parameters. From these measurements (height, weight and specific body dimensions), a customized dose of contrast material will be specified according to the derived formula. Since the dose will be different in every subject, the rate will need to be adjusted as well. This will be accomplished by adjusting the rate so that the injection duration is the same in every subject. For example, if the specified contrast material dose is 100 mL and the injection duration is 25 seconds, the injection rate will be 4 mL/sec. If the specified contrast material dose is 125 mL and the injection duration is also 25 seconds, the injection rate will be increased to 5 mL/sec. Note that 100 subjects will receive a fixed dose and rate (150 mL of iopamidol with a concentration of 300 mg of iodine/mL at an injection rate of 3 mL/sec for a total dose of 45 grams of iodine) and 400 subjects will be administered a customized dose and rate (X mL of iopamidol with a concentration of 300 mg of iodine/mL at an injection rate of X mL/sec for a total dose of X grams of iodine) and. Also note that for the customized dose group, the maximum and minimum doses of contrast material will be 200 (75 gm iodine) and 75 (22.5 gm iodine) mL, respectively and the maximum and minimum injection rates will be 6 and 2 mL/sec, respectively. Because the injection rate in the customized group is variable, the nurse or technologist establishing intravenous access may choose to use a larger or small caliber angiocatheter than in the fixed group in order to accommodate a higher or lower injection rate, respectively. The caliber of the angiocatheter as well as the venous access site will be recorded along with the dose and rate of contrast material. The rate of administration of contrast material is controlled by a mechanical power injector furnished by Nemoto Kyorindo Co, Ltd. free of charge for use in this study.