A novel ultrasound method for evaluation of collateral development in limb ischemia

Although clinical studies are underway to evaluate the effectiveness of angiogenesis, there are no validated, non-invasive methods to assess peripheral collateral development. This study was performed to validate a novel ultrasound-based method of assessing collateral formation in a pig model of hindlimb ischemia. Ultrasonography of predefined ultrasound planes was performed on 12 pigs immediately after ligation of the right common femoral artery, and 7, 14, 28 and 42 days thereafter. A custom software program was used to evaluate both color Doppler (CD) and power Doppler (PD) images to generate flow indices. Collateral development was observed with ultrasound as early as 7 days post-arteriectomy and increased dramatically by 28 days. Areas of persistent ischemia resulting from inadequate collateral formation were easily quantified in all images. Collaterals detected on ultrasound were confirmed by angiography and histology, and tissue perfusion by a fluorescent microsphere method. As demonstrated with color and power Doppler measurements, collateral formation is initiated early after ischemic injury in this large juvenile animal model of angiogenesis. This non-invasive method is useful to quantify blood flow, visualize angiogenesis and determine areas of persistent lower limb ischemia, and may have an important role in evaluating new approaches to modulate angiogenesis.