Assessing hyperthermia‐induced vasodilation in human skin in vivo using optoacoustic mesoscopy

Abstract

The aim of this study was to explore the unique imaging abilities of optoacoustic mesoscopy to visualize skin structures and microvasculature with the view of establishing a robust approach for monitoring heat-induced hyperemia in human skin in vivo. Using raster-scan optoacoustic mesoscopy (RSOM), we investigated whether optoacoustic (photoacoustic) mesoscopy can identify changes in skin response to local heating at microvasculature resolution in a cross-sectional fashion through skin in the human forearm. We visualized the heat-induced hyperemia for the first time with single-vessel resolution throughout the whole skin depth. We quantified changes in total blood volume in the skin and their correlation with local heating. In response to local heating, total blood volume increased 1.83-and 1.76-fold, respectively, in the volar and dorsal aspects of forearm skin. We demonstrate RSOM imaging of the dilation of individual vessels in the skin microvasculature, consistent with hyperemic response to heating at the skin surface. Our results demonstrate great potential of RSOM for elucidating the morphology, functional state and reactivity of dermal microvasculature, with implications for diagnostics and disease monitoring. Image: Cross-sectional view of skin microvasculature dilated in response to hyperthermia. K E Y W O R D Shyperemia, induced hyperthermia, optoacoustic techniques, skin, vasodilation

Non‐invasive imaging in dermatology and the unique potential of raster‐scan optoacoustic mesoscopy

“…Uniquely among dermatological imaging techniques, RSOM can, therefore, comprehensively monitor reactivity of the dermal microvasculature to local heating at single‐vessel resolution (Fig. g) . The structure and function of cutaneous vasculature may reveal information about systemic disorders such as cardiovascular diseases and diabetes mellitus, so RSOM may eventually improve the risk assessment in these widespread medical conditions.…”

“…1g). 63 The structure and function of cutaneous vasculature may reveal information about systemic disorders such as cardiovascular diseases and diabetes mellitus, 64 so RSOM may eventually improve the risk assessment in these widespread medical conditions. RSOM's ability to image epidermis morphology and vasculature down to capillary level has already been shown to deliver valuable information, which we highlight below in the context of several dermatological diseases.…”

“…Scale bar, 500 lm. Panels a-d modified from Aguirre et al (2017) 33 ; panel e, modified from https://omlc.org/spectra/hemoglobin/; panel f, modified from Schwarz et al (2016) 61 ; and panel g, modified from Berezhnoi et al (2018) 63.…”

Fully automated identification of skin morphology in raster‐scan optoacoustic mesoscopy using artificial intelligence

“…For best performance, RSOM should be performed using ultra‐wideband (UWB) detection, spanning a range of 200 MHz . UWB‐RSOM can generate high‐resolution images of neovascularization in a growing tumor, visualize neovascularization in neoplastic gastrointestinal tissues, and observe clinically relevant features of the skin microvascular structures . For this imaging technique to be clinically relevant, it is necessary to accurately define the regions and subregions of tissue in the field of view .…”

“…8 UWB-RSOM can generate high-resolution images of neovascularization in a growing tumor, 9 visualize neovascularization in neoplastic gastrointestinal tissues, 10 and observe clinically relevant features of the skin microvascular structures. 11,12 For this imaging technique to be clinically relevant, it is necessary to accurately define the regions and subregions of tissue in the field of view. 10,13 For example, skin images should be annotated to indicate the boundaries of epidermis, dermis, and, within the dermis, the areas that have a dense microvascular structure (herein referred to as the vascular plexus), since identifying particular features in each of these subregions may facilitate disease diagnosis and assessment of its severity.…”