Recording skin oxygenation by dual-wavelength ultra-wideband optoacoustic mesoscopy.

Microvascular oxygenation is a key physiological marker implicated in many health conditions, ranging from cardiovascular disease and diabetes to cancer, systemic inflammation, or sepsis, where microvascular-level dysfunction often precedes overt pathology. Ultra-wideband raster-scan optoacoustic mesoscopy (RSOM) offers unprecedented non-invasive visualization of tissue microvasculature, achieving three-dimensional (3D) resolution in the 10-30 micrometer range (axial, lateral). Nevertheless, the lack of availability of suitable multi-wavelength illumination sources has generally limited RSOM to single-wavelength studies of microvasculature morphology. Herein, we present a dual-wavelength ultra-wideband RSOM (DW RSOM) system for dynamic mapping of cutaneous microvascular oxygenation by integrating two diode-pumped solid-state lasers at 515 nm and 532 nm. The system was evaluated on healthy volunteers during post-occlusive reactive hyperemia (PORH) tests on the forearm and proximal nailfold (DRKS00037749 registered on 26th August 2025 on the German Clinical Trials Register). The system recorded 3D oxygenation changes, including ischemic decline, hyperemic overshoot, and recovery, consistent with invasive blood gas analyzer (BGA) measurements. Extracted parameters, such as oxygenation gradients and recovery times, correlated with expected vascular reactivity metrics. These findings validate DW RSOM as a portable prototype for the in vivo assessment of microvascular oxygenation in humans at a single microvessel level. By providing quantitative, layer-resolved imaging of skin microcirculation, DW RSOM offers a promising platform for extending single-wavelength RSOM to studying microvascular dysfunction and supports future clinical translation of optoacoustic technologies toward bedside vascular diagnostics.