Fig. 2

Bolus tracking technique for identification of contrast arrival. Patient with descending aortic dissection with suboptimal increase in contrast opacification within the region of interest (ROI) and failure to trigger the scan (a). The initial CTA ROI was placed in the false lumen (b). The contrast opacification of the false lumen does not reach the threshold required to trigger the scan as seen on on bolus tracker HU-time graph. Repeat injection with placement of ROI in true lumen resulted in adequate evaluation of dissection