In vivo switchable optical- and acoustic-resolution photoacoustic microscopy

Photoacoustic microscopy (PAM) provides high resolution and large penetration depth by utilizing the high optical sensitivity and low scattering of ultrasound. Hybrid PAM systems can be classified into two categories: optical resolution photoacoustic microscopy (OR-PAM) and acoustic-resolution photoacoustic microscopy (AR-PAM). OR PAM provides a very high lateral resolution with a strong optical focus, but the penetration depth is limited to one optical transport mean free path. AR-PAM provides a relatively greater penetration depth using diffused light in biological tissues. The resolution of AR-PAM is determined by its ultrasonic parameters. In this study, we performed an in vivo testing of a switchable OR-/AR-PAM system. In this system, two modes can be switched by changing its collimator lens and optical fiber. The lateral resolution of OR-PAM was measured using a resolution test target, and the full width at half maximum (FWHM) of the edge spread function was 2.5 lam. To calculate the lateral resolution of AR PAM, a 6-lam-diameter carbon fiber was used, and the FWHM of the line spread function was 80.2 lam. We successfully demonstrated the multiscale imaging capability of the switchable OR-/AR-PAM system by visualizing microvascular networks in mouse ears, brain, legs, skin, and eyes.