Effect of patient weight and scanning duration on contrast enhancement during pulmonary multidetector CT angiography

Purpose: To retrospectively evaluate the amount of contrast medium required with 16- and 64-section computed tomography (CT) for a given patient weight to achieve desirable contrast enhancement during pulmonary CT angiography. Materials and Methods: Institutional review board approval was obtained, and informed consent was not required for this HIPAA-compliant study. Eighty-five patients (35 men, 50 women; range, 22 - 87 years) who had undergone 16- section (n = 48) or 64-section (n = 37) CT for the detection of pulmonary embolism were retrospectively evaluated. Contrast medium containing 350 mg of iodine per milliliter was injected at a rate of 4 mL/sec. The injected volume corresponded to the injection rate multiplied by the sum of the scanning delay plus the scanning duration, up to 125 mL. The scanning delay was determined with bolus tracking. Contrast enhancement was measured in the main pulmonary artery and the aorta. For each patient, the injected contrast medium volume per body weight index was calculated. Linear regression analysis was performed, and the Wilcoxon signed rank test was used to assess differences between 16- and 64-section CT. Results: A range of patient weights (45.3-153.0 kg) and contrast medium volumes (76 - 125 mL) were noted. The regression formula indicated that 1.2 mL per kilogram body weight of contrast medium was required to achieve 250 HU. The median scanning duration was shorter for 64-section CT than for 16- section CT (5.7 seconds vs 9.5 seconds, P < .001).Consequently, 64-section CT required 17.6% less contrast medium than did 16- section CT (85.4 mL vs 103.6 mL, P < .001). Median contrast enhancement in the pulmonary artery was 8.9% lower with 64-section CT than with 16- section CT (257.7 HU vs 282.9 HU, P = .11). Conclusion: To achieve consistent contrast enhancement during pulmonary CT angiography, the amount of contrast medium can be adjusted to the patient's body weight.