Effect of region-of-interest placement in bolus tracking cerebral computed tomography angiography

Premature or delayed triggering of semiautomatic contrast tracking during intracranial computed tomographic angiography can occur due to artifact from dense contrast in the superior vena cava or brachiocephalic veins near the anterior aortic arch. We determine if placement of bolus tracking region-of-interest in the posterior thoracic aorta can prevent suboptimal intracranial arterial opacification. Intracranial computed tomography angiographies from 80 patients performed on the same scanner were retrospectively evaluated. Thirty-seven consecutive patients with bolus tracking region-of-interest (ROI) placed in the anterior thoracic aorta (group A) and 43 consecutive patients with ROI placed in the posterior thoracic arch (group B) were identified. Two neuroradiologists scored the quality of intracranial computed tomography angiography on a four-point scale. Quantitative measurement of intracranial arterial opacification was also performed. The proportions of patients with poorest quality score as well as the proportions of the patients with the worst degree of intracranial arterial opacification (< 10th percentile) were compared between groups A and B using two-sample proportion test. Qualitative evaluation of the intracranial computed tomography angiography showed 4 (11 %) patients in group A with poor quality (score of 1), while all patients in group B scored 2 or higher (p = 0.028). Seven (19 %) patients in group A had the lowest quantitative score (mean arterial opacification < 10th percentile) while 1 (2.5 %) patient in group B had the lowest score (p = 0.018). Bolus tracking in the posterior thoracic aorta reduces the chance of suboptimal intracranial computed tomography angiography.