Key frames in the B-scan images of artery 1. (a) Four regions of interest in the arterial wall are shown as colored boxes in the B-scan image. The graph of longitudinal strain vs. applied stress for these regions of interest shows a uniform inflection point at the nth frame. The inflection point, or nth frame, was different for each specimen. The initial (b), nth (a), and final (c) frames in the B-scan video confirm changes in vessel circumference during the angioplasty procedure.