Photoacoustic microscopy with subwavelength resolution and enhanced spatial isotropy by using an aspheric acoustic mirror group

Photoacoustic microscopy (PAM) is an emerging biomedical imaging modality, combining good acoustic resolution in deep tissue and rich functional biomedical information. Spatial resolution and spatial isotropy are two of the most important indexes of a PAM. In this study, we propose a PAM scheme based on an aspheric acoustic mirror group to achieve the subwavelength resolution and enhance the spatial isotropy. The mirror group consists of an ellipsoid acoustic mirror and a parabolic acoustic mirror. The ellipsoid acoustic mirror expands the cone angle of signal collection, and the parabolic acoustic mirror reduces the cone angle of the PA beam. Their combination equivalently expands the numerical aperture of acoustic detection. Phantom experiments demonstrate that the proposed scheme can achieve the subwavelength resolution. Simultaneously, its spatial isotropy is improved from 48.2% to 96.7%. An in vivo mouse brain imaging experiment examines the biomedical practicability of the method. This method may be found wide potential applications in biomedicine.