Modified back-projection method in acoustic resolution-based photoacoustic endoscopy for improved lateral resolution.

Abstract

Acoustic resolution photoacoustic endoscopy (ARPAE) is an emerging tool for gastrointestinal tract and esophagus imaging. However, high resolution over large depth of field in ARPAE is still a challenge to be addressed due to the usage of fixed-focus transducers. To solve this problem, a modified back-projection reconstruction algorithm is proposed in this work, which was demonstrated in two dimensions (2D). By employing data from multiple transducer positions and at the meantime considering the geometry of the transducer detection surface, this method offers a significantly improved lateral resolution throughout the imaging depth. The proposed method was evaluated with extensive numerical simulations and phantom experiments. Numerical simulations showed that the depth of focus (DOF) is greatly improved with our proposed method. Results also indicated that the improvement of the lateral resolution is more notable when the transducer has larger numerical aperture (NA) and higher central frequency, and the transducer focus is placed further from the rotation center. Experimental data further indicate there is a 30% to 40% improvement in the lateral resolution of targets in the out-of-focus region with our proposed new method. This work can readily be employed in most current ARPAE systems to improve the obtained image quality, and may promote the advancement of ARPAE toward clinical applications.