Computed extended depth of field optical-resolution photoacoustic microscope

TL;DR

This paper presents a wavelet transform-based computed method to extend the depth of field in optical-resolution photoacoustic microscopy, enabling clearer imaging of biological tissues across a larger depth range.

Contribution

The novel wavelet transform image fusion approach significantly doubles the depth of field in photoacoustic microscopy without losing lateral resolution.

Findings

Depth of field extended by two times in simulations

In vivo mouse brain vasculature imaging demonstrated feasibility

No sacrifice in lateral resolution achieved

Abstract

Photoacoustic microscopy with large depth of focus is significant to the biomedical research. The conventional optical-resolution photoacoustic microscope (OR-PAM) suffers from limited depth of field (DoF) since the employed focused Gaussian beam only has a narrow depth range in focus, little details in depth direction can be revealed. Here, we developed a computed extended depth of field method for photoacoustic microscope by using wavelet transform image fusion rules. Wavelet transform is performed on the max amplitude projection (MAP) images acquired at different axial positions by OR-PAM to separate the low and high frequencies, respectively. The fused low frequency coefficients is taking the average of the low-frequency coefficients of the low-frequency part of the images. And maximum selection rule is used in high frequency coefficients. Wavelet coefficient of the MAP images are compared and select the maximum value coefficient is taken as fused high-frequency coefficients. And finally the wavelet inverse transform is performed to achieve large DoF. Simulation was performed to demonstrate that this method can extend the depth of field of PAM two times without the sacrifice of lateral resolution. And the in vivo imaging of the mouse cerebral vasculature with intact skull further demonstrates the feasibility of our method.