Study of Two-stage Injection of Contrast Agent in Combination with Bolus Tracking Technique in Computed Tomography Pulmonary Angiography

Objective: To investigate the utility of a two-stage injection of contrast agent combined with a bolus tracking technique in computed tomography (CT) pulmonary angiography. Methods: We recruited 30 patients undergoing CT pulmonary angiography due to suspected pulmonary embolism at Beijing Tongren Hospital affiliated to Capital Medical University from February to April 2022 as the experimental group, using a two-stage injection of contrast agent combined with bolus tracking technique. The region of interest (ROI) was placed in the pulmonary trunk with a threshold of 100HU. Contrast agent and normal saline injection sequence: (1) contrast agent 10 mL; (2) normal saline 30 mL; (3) contrast agent 20 mL; (4) normal saline 30 mL; the injection rate for all was 5 mL/s. The CT value of the pulmonary trunk was tracked, and scanning was delayed for 10 s after reaching the set threshold. Using the test bolus technique, we recruited 30 patients from January to December 2021 as the control group. First, 10 mL of contrast plus 30 mL of normal saline was injected to measure the peak time of the main pulmonary artery. Then, 20 mL of contrast plus 30 mL of normal saline was injected, and the peak time +1 s was used as the delay time for the scan. CT values were measured for the pulmonary artery, pulmonary vein, subclavian vein, and ascending aorta in both groups. Both groups scored the quality of the pulmonary artery images and the sclerotic artifacts of the superior vena cava. We compared the CT values of the vessels in the two groups using independent sample t-tests. We compared the pulmonary artery image quality scores and the sclerotic artifact scores of the superior vena cava using a non-parametric Mann–Whitney U-test. Results: CT values of the left pulmonary artery, right upper lobe artery, right middle lobe artery, right lower lobe artery, left upper lobe artery, and ascending aorta of the experimental group were higher than those of the control group, and the difference was statistically significant. There was no significant difference in the main pulmonary artery, right pulmonary artery, left inferior pulmonary artery, right upper pulmonary vein, right lower pulmonary vein, left upper pulmonary vein, left lower pulmonary vein, subclavian vein, right arteriovenous difference, and left arteriovenous difference between both groups. Also, there was no significant difference in pulmonary artery image quality scores between both groups, likewise in the sclerosis artifact score of superior vena cava sclerosis. Conclusions: The two-stage contrast agent injection with the bolus tracking technique for CT pulmonary angiography provides stable image quality with a simple and easy procedure. The transition delay time suits most CT devices and deserves a clinical generalization.