Super-resolution ultrasound imaging of the microvasculature in skeletal muscle: A new tool in diabetes research

Attenuation in the skeletal muscle microvascular response to insulin plays a critical role in type 2 diabetes and obesity-induced insulin resistance. The goal of the project detailed in this paper was to evaluate the use of super-resolution ultrasound (SR-US) imaging for performing a quantitative analysis of insulin-mediated microvascular changes in skeletal muscle. An Acuson Sequoia 512 ultrasound (US) scanner equipped with a 15L8-S linear array transducer was used in a nonlinear imaging mode. C57BL/6J male mice fed standard chow and studied at age 13-16 wk comprised the lean group (N = 5), and 24-31 wk-old mice who received a high-fat diet provided the obese group (N = 5). After administration of a microbubble (MB) contrast agent, the proximal hindlimb adductor muscle of each animal was imaged (dynamic contrast-enhanced US, DCE-US) for 10 min at baseline and again at 1 h and towards the end of a 2 h hyperinsulinemic-euglycemic clamp. The SR-US image processing technique was developed using custom Matlab software. After collecting a stack of DCE-US images and applying a singular value decomposition (SVD)-based spatiotemporal filter, individual MBs were localized and subsequently a SR-US image was generated by mapping the cumulative MB localizations. The insulin-induced skeletal muscle microvascular recruitment resulting from the clamp procedure was evaluated for the lean and obese animals. Lean animals exhibited a considerably greater increase in microvascular recruitment in skeletal muscle during the hyperinsulinemic-euglycemic clamp procedure compared to the obese animals. These results clearly indicate insulin-induced microvascular recruitment in normal skeletal muscle and an impaired microvascular response to insulin in older obese animals.