Optical clearing agents improve photoacoustic imaging in the optical diffusive regime.

Acoustic resolution photoacoustic microscopy (AR-PAM) takes advantage of weak acoustic scattering to image fine structures, such as the subcutaneous microvasculature, providing a spatial resolution on the order of tens of micrometers. However, the amplitude of AR-PAM deteriorates sharply with depth, as a result of light scattering and acoustic attenuation caused by structures such as the skin. Optical clearing techniques can enhance optical transmittance by decreasing the scattering of light through tissues. However, it is unknown whether optical clearing agents (OCAs) can be used to improve AR-PAM. We applied different types of OCAs to rat dorsal skin in an ex vivo study to determine the effects of OCAs on photoacoustic detection. We identified three OCAs that improved the photoacoustic amplitude for further in vivo testing. With the use of an appropriate penetration enhancer, PEG-400 significantly improved the photoacoustic amplitude for detection of deep-sealed blood vessels, while glycerol alone improved the image quality of shallow vessels. In contrast, DMSO application resulted in decreased photoacoustic amplitude in the in vivo trials.