Visualization of vasculature using a hand-held photoacoustic probe: phantom and in vivo validation. 
Assessment of microvasculature and tissue perfusion can provide diagnostic information on local or systemic diseases.  Photoacoustic (PA) imaging has strong clinical potential because of its sensitivity to hemoglobin.  We used a hand-held PA probe with integrated diode lasers and examined its feasibility and validity in the detection of increasing blood volume and (sub) dermal vascularization.  Blood volume detection was tested in custom-made perfusion phantoms.  Results showed that an increase of blood volume in a physiological range of 1.3% to 5.4% could be detected.  The results were validated with power Doppler sonography.  Using a motorized scanning setup, areas of the skin were imaged at relatively short scanning times ( < 10 ??  s / cm 2 ) with PA.  Three-dimensional visualization of these structures was achieved by combining the consecutively acquired cross-sectional images.  Images revealed the epidermis and submillimeter vasculature up to depth of 5 mm.  The geometries of imaged vasculature were validated with segmentation of the vasculature in high-frequency ultrasound imaging.  This study proves the feasibility of PA imaging in its current implementation for the detection of perfusion-related parameters in skin and subdermal tissue and underlines its potential as a diagnostic tool in vascular or dermal pathologies.