Purpose: To compare the causes of indeterminate CT pulmonary angiograms using standard mode and high-pitch mode, and determine at what level of the pulmonary arterial tree studies were non-diagnostic.
Methods: IRB approval was obtained. A retrospective review of patients at our institution who underwent a CT pulmonary angiogram, between November 1, 2015 and February 10, 2016 was performed. CT pulmonary angiograms using both high-pitch mode and standard mode were evaluated with positive and indeterminate rates calculated. Causes of indeterminate studies and the level of the pulmonary arterial tree at which the study became non-diagnostic were determined by a board certified radiologist by looking at the images of each indeterminate study. The indeterminate rates were compared between high-pitch and standard modes using a generalized estimating equation.
Results: Five hundred fifty-nine CT pulmonary angiograms using high-pitch mode were evaluated, while 661 standard mode scans were evaluated. 69/559 (12.3%) scans with high-pitch mode were positive and 84/661 (12.7%) scans with standard mode were positive (not statistically significant, p > 0.05). There was a higher rate of indeterminate scans with standard mode compared to the high-pitch mode (80 [12.1%] standard vs. 25 [4.5%] high-pitch, p value < 0.0001). Findings were indeterminate at the lobar level in 4 (16%), at the segmental level in 11 (44%), and at the subsegmental level in 10 (40%) using high-pitch mode. The most common causes of an indeterminate scan using high-pitch mode were motion in 11 (44%), transient interruption of contrast in 6 (24%), and contrast timing in 5 (20%). Findings were indeterminate at the main pulmonary artery level in 1 (1.3%), at the lobar level in 13 (16.3%), at the segmental level in 28 (35.0%), and at the subsegmental level in 38 (47.5%) using the standard mode. The most common causes of an indeterminate scan using the standard mode were motion in 53 (66.3%), transient interruption of contrast in 19 (23.8%), and contrast timing in 15 (18.8%).
Conclusions: High-pitch mode results in statistically significant fewer indeterminate studies compared with standard mode. Furthermore, there were statistically significant fewer indeterminate studies due to motion artifact with high-pitch mode compared with standard mode.
Keywords: CT pulmonary angiography; Indeterminate; Motion artifact; Pulmonary embolism; Transient interruption of contrast.