Ultrasound imaging with bolus delivered contrast agent for the detection of angiogenesis and blood flow irregularities

Highly increased blood flow and vascularity after angiogenic gene therapy have raised concerns of shunting and hemangioma-like blood pool formation that might decrease effective perfusion and ruin the beneficial effects of the therapy. Contrast enhanced ultrasound is a promising noninvasive tool for studying skeletal muscle perfusion. The objectives of the present study were to test bolus and infusion administrations of ultrasound microbubble contrast media in imaging vascular growth in skeletal muscle and assess the functionality of vessels grown with angiogenic gene therapy. Contrast enhanced ultrasound was used to study changes in skeletal muscle perfusion in normal and gene-transduced rabbit hindlimbs 6 days after gene transfer. Adenoviral gene transfer of VEGF (10 e9–10 e11 viral particles) or β-galactosidase control gene (10 e11 viral particles) was done under anesthesia and induced up to 16-fold increases in relative tissue perfusion. Contrast intensity versus time curves were plotted and analyzed for contrast kinetics. Bolus administration of the contrast media was highly feasible in analyzing skeletal muscle blood flow and its kinetics. Maximal signal intensity of the bolus signal reflected relative changes in both blood flow and volume equally to the infusion method. Flow irregularities were detected after angiogenic gene therapy. In conclusion, bolus delivery of ultrasound contrast agent is highly feasible for the relative analysis of both quantity and quality of blood flow after angiogenic gene therapy. The kinetics of blood flow can and should be studied more extensively in both preclinical and clinical trials of angiogenic gene therapy since there is increasing evidence of flow irregularities in angiogenic vessels.