Solid Hydrogel Couplants for Skin Superficial Blood Flow Imaging With Super-Resolution Ultrasound

The unavoidable pressure at the ultrasound transducer-skin interface leads to a decrease in the accuracy of superficial blood flow visualization. To achieve high-resolution skin superficial blood flow ultrasound imaging, this study introduces a novel solid hydrogel coupling medium designed to overcome issues of inaccurate blood flow caused by probe pressure and near-field acoustic interference.

A solid hydrogel coupling pad, SA-PAM (sodium alginate and acrylamide), was fabricated and its mechanical characterization was performed using tensile testing. The superficial blood flow ultrasound imaging was tested under varying pressure conditions using ultrasound localization microscopy (ULM) combined with long-lasting microbubble contrast agents on rat dorsal skin.

The hydrogel coupling medium demonstrated superior acoustic coupling performance, reducing near-field interference and improving imaging quality. Compared with conventional liquid coupling agents, the SA-PAM hydrogel significantly enhanced the visualization of microvascular structures in both the dermis and subcutaneous layers, even under applied pressure. Three-dimensional super-resolution ultrasound imaging revealed detailed microvascular flow, with improved continuity and higher vessel density at deeper skin layers.

The SA-PAM hydrogel coupling pad offers a novel solution for ultrasound imaging of superficial skin blood flow, providing high-resolution vascular imaging of the skin and reduced image distortion caused by probe pressure. This strategy has promising potential for early detection of diabetes-related microvascular lesions and for the precise monitoring of inflammatory skin diseases, thereby it would support clinical treatment planning and therapeutic evaluation.