RSom

Raster-scan optoacoustic mesoscopy (RSOM) is a high-resolution imaging modality in optoacoustics. It combines pulsed laser illumination with ultrasound detection to map tissue absorption at the mesoscopic scale. In RSOM, short laser pulses illuminate a region of tissue; absorber molecules such as haemoglobin convert absorbed light into rapid thermoelastic expansion that emits ultrasonic waves. A sensitive ultrasound detector, scanned over a grid in a raster pattern, records these waves and, through image reconstruction, yields three-dimensional maps of optical absorption. By using multiple wavelengths, RSOM can provide functional contrast related to blood content and oxygenation.

RSOM excels at noninvasive visualization of the skin’s microvasculature, including capillaries and small vessels within the epidermis and dermis. It offers label-free imaging because it relies on endogenous chromophores and does not require contrast agents. The technology provides high spatial resolution at the mesoscopic scale and has a relatively large field of view for its depth range, typically reaching a few millimeters. Applications span dermatology research, vascular biology, and monitoring angiogenesis or responses to therapy. Limitations include sensitivity to motion, longer acquisition times than conventional ultrasonography, and depth limits set by optical scattering. RSOM is mainly a research tool today, with ongoing work aimed at speeding up imaging and supporting clinical translation.