Visualization of skin morphology and microcirculation with high frequency ultrasound and dual-wavelength photoacoustic microscope

Skin aging is characterized by color and wrinkle caused by degeneration of collagen and elastin in the dermis. Recently, the volume, diameter and branching of the micro vessels in the skin are proved to affect these biomechanical changes. Thus, high resolution imaging for both micro structure and micro vessels of the skin is desired. In the present study, dual-wavelength photoacoustic microscope (PAM) combined with high frequency ultrasound (HFUS) is developed to visualize both the morphology and microcirculation of the skin. Two Nd:YAG laser light sources with the wavelength of 532/556 nm, pulse width of 1.2/3.6 ns, pulse energy of 16 μJ/pulse and repetition rate of 1 kHz were equipped in the HFUS-PAM system. The optical fiber for laser delivery was inserted through the center hole of the concave ultrasound transducer with the central frequency of 75 MHz. Both HFUS and PA signals were acquired at the sampling rate of 500 MHz and the resolution of 12 bits. The transducer was scanned by voice coil actuators to obtain 3D dataset of HFUS and PA signals. Oxygen saturation of the micro circulation was calculated by the PA signals alternately obtained at 532 nm and 556 nm. 3D image of the layered structure and the micro vessels representing oxygen saturation in the 6 mm x 6 mm x 3 mm volume of the skin was successfully obtained with the system. HFUS-PAM will provide important information of skin morphology and microcirculation for assessment of skin aging.