Approximate back‐projection method for improving lateral resolution in circular‐scanning‐based photoacoustic tomography

Abstract

Purpose In circular‐scanning‐based photoacoustic tomography (PAT), the effect of finite transducer aperture has not been effectively resolved. The goal of this paper is to propose a practical reconstruction method that accounts for the finite transducer aperture to improve the lateral resolution. Methods We for the first time propose to calculate the spatial‐temporal response (STR) of the employed finite‐sized transducer in a forward model, and then compensate the time delay and the directional sensitivity of the transducer in the framework of the back‐projection method. Both simulation and phantom experiments were carried out to evaluate the lateral resolution improvement with the proposed method. The performance of this new method for imaging complicated targets was also assessed by calculating the mean image gradient. Results Simulation results showed that with this new method the lateral resolution for off‐center targets can be as good as that for the center targets. Phantom experimental results showed that this new method can improve the lateral resolution more than two times for a point target about 5 mm far from the rotation center. Phantom experimental results also showed that many blurred fine structures of a piece of leaf veins at the off‐center regions were well restored with the new method, and the mean image gradient improved about 1.3 times. Conclusion The proposed new method can effectively account for the effect of finite transducer aperture for circular‐scanning‐based PAT in homogenous acoustic media. This new method also features its robustness and computational efficiency, so that it is a worthy replacement to the conventional back‐projection algorithm in circular‐scanning‐based PAT. This new method can be of great importance to the design of circular‐scanning or spherical‐scanning‐based PAT systems.

Photoacoustic/Ultrasound Endoscopic Imaging Reconstruction Algorithm Based on the Approximate Gaussian Acoustic Field

“…The dynamic focus of acoustically focused photoacoustic/ultrasound endoscopic imaging is significantly related to image quality. Since high-frequency ultrasonic transducers are generally used in acoustically focused photoacoustic/ultrasonic imaging, the resolution of the out-of-focus region will be poor [ 35 ]. In this paper, we propose the Gaussian-beam-based back-projection algorithm as a way to achieve fast acoustically focused photoacoustic/ultrasound endoscopic imaging reconstruction.…”

Multi-angle data acquisition to compensate transducer finite size in photoacoustic tomography

“…For the reconstruction category, three methods were selected: Wang, et al. [26] which compensated the time-delay and directivity pattern, Kalva and Pramanik [23] which proposed the modified delay-and-sum (MDAS) algorithm and Chowdhury, et al. [32] which combined a MB method with TIR.…”

“…Wang, et al. [26] proposed an approximate back-projection method by compensating the time-delay and directivity pattern of the finite-size transducer in a circular geometry. As the ROI enlarges (to a radius of 5–6 cm), this method becomes very time/cost consuming (5 min was taken for processing a ROI with a radius of 15 mm) due to a considerable growth in the size of the system matrix.…”

Simulation Study of Acoustic-Resolution-Based Photoacoustic Microscopy for Imaging Complex Blood Vessel Networks

“…It is noted that the summation in SAFT is performed within the NA of the transducer. To enable the summing out of the NA for code implementation simplicity, many other algorithms have been proposed recently, and the spatial-temporal response (STR)-based back-projection method (STR-BP) is one such method, which is [19]:…”

“…This assumes a focused transducer scanned over N positions, with a step size of Δx. The detected photoacoustic pressure at an arbitrary point can be expressed with the following Fresnel integral over the transducer surface S [19]: This assumes a focused transducer scanned over N positions, with a step size of ∆x. The detected photoacoustic pressure at an arbitrary point can be expressed with the following Fresnel integral over the transducer surface S [19]:…”