Deep Non-Contact Photoacoustic Initial Pressure Imaging

A novel method of imaging photoacoustic initial pressures is reported using an all-optical non-contact system. Visible pulsed excitation wavelengths are used to produce large initial-pressure-induced refractive index modulations in absorbing targets. These localized pressure rises create sharp variation in scattering which are detected with a deep-penetrating interrogation beam. In comparison with contact-based optical resolution photoacoustic microscopy systems, the proposed system offers two major advantages. First, in spite of the fact that the system is non-contact and it does not require any ultrasound coupling medium, it offers in vivo signal to noise ratios exceeding previously reported optical resolution-photoacoustic microscopy. Second, by taking advantage of a focused deep-penetrating short-wave infrared interrogation beam and without requiring coherent detection, it provides optical resolution images to depths of 2.5mm in tissue-mimicking scattering media. In this work, in vivo imaging of microvascular networks, imaging of single red-blood cells, oxygen saturation mapping, and deep-vascular imaging applications are demonstrated.