Microbubble enhanced ultrasound with low mechanical index promotes therapeutic angiogenesis in hind limb ischemia mouse model

Background: Microbubble enhanced ultrasound (MEUS) can augment tissue perfusion by angiogenesis yet the best treatment ultrasound power in the initial ischemia period is uncertain.

Purpose: Considering the mechanical index (MI) is the most commonly used parameter for regulating diagnostic ultrasound power, here, we explored the effects of MEUS mediated by different MI on perfusion and sought to characterize the angiogenesis in the early stage of ischemia.

Methods: Experiments were conducted on hind limb ischemia mouse model (HLI) and MEUS was administrated in the first week every other day following induction of HLI for four times. MEUS was conducted with a modified diagnostic ultrasound in combination with a lipid microbubble at 3 MHz and 21 cycles employing MI 0.3 (0.8 MPa), 0.7 (1.32 MPa) and 1.3 (2.78 MPa), respectively. Semi-quantitative visual score and blood perfusion quantitation by contrast-enhanced ultrasound were performed before each treatment. Hematoxylin-eosin staining and immunohistochemistry with CD31 were performed after four times treatment.

Results: The results showed HLI mice in MI 0.3 mediated MEUS group longitudinally exhibited more blood perfusion in calf muscle and less visible necrosis compared to other experimental groups in the early stage. Additionally, diffused inflammatory cells with greater number of vessels in calf muscle were observed in MI 0.3 group.

Conclusions: Low MI mediated MEUS had significantly greater effects on augmenting muscle blood perfusion and reducing necrosis in the initial period after HLI surgery. These effects are most likely mediated by angiogenesis stimulated by low MI mediated MEUS.