In vivo optical imaging modalities are mostly limited to cell cultures, superficial tissues, and intravital imaging since they lack either resolution or penetration depth.1 In contrast, optoacoustic (OA) imaging—combining features of optical and ultrasound imaging—has been used to visualize hemoglobin in depths of approximately 3 cm in patients with Crohn’s disease.2,3 Realizing an even higher resolution, raster-scanning OA mesoscopy (RSOM) provides intrinsic optical tissue contrast down to 10-20 μm resolution at still high penetration depths of several millimeters.