Objective: To explore the scan protocol of second generation dual source computed tomography (CT) for CT pulmonary angiogram (CTPA) in patients with suspected pulmonary embolism and determine the proper volume of contrast medium.
Methods: A total of 120 patients undergoing CTPA were recruited. All examinations were performed on a second generation dual source CT. The scan delay was determined with the test bolus technique. Four contrast volume protocols were designed, namely groups A, B, C and D respectively (n = 30 each). For CTPA scan of groups A, B, C and D, 35, 40, 45 and 50 ml contrast medium were injected at an injection rate of 4 ml/s, followed by a saline chaser of 55, 50, 45 and 40 ml respectively. Attenuation profiles of different vascular segments (subclavian vein, vena cava, left atrium, pulmonary trunk, S1 artery, S10 artery) were measured to evaluate the timing techniques. The image quality and artifact of iodine map were analyzed by two radiologists for comparisons.
Results: The percentage of pulmonary arteries exceeding optimal attenuation (> 200 HU) showed that groups of B, C and D were higher than group A (93% - 100% vs 80% - 90%). The image quality of group A was lower than the others (P < 0.05) while the other groups showed no significant difference. The artifacts of iodine map of group A were much fewer than the others (P < 0.05) and group D was much more than the other groups (P < 0.05). Groups B and C had a score of 4.13 and 3.67 respectively without significant difference (P = 0.091).
Conclusion: With the aids of test bolus technique and proper injection protocol (40 ml contrast medium followed by 50 ml saline), the high quality image and low volume of iodine can be realized with second generation dual source CT for CTPA.