Department of Biomedical Engineering, School of Basic Medical Science, Central South University, Changsha, Hunan, 410083, China.
Department of Biomedical Engineering, College of Biology, Hunan University, Changsha, Hunan, 410082, China.
Med Phys. 2021 Jun;48(6):3011-3021. doi: 10.1002/mp.14880. Epub 2021 May 10.
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.
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.
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.
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.
在基于环形扫描的光声断层成像（PAT）中，有限换能器孔径的影响尚未得到有效解决。本文的目的是提出一种实用的重建方法，考虑有限换能器孔径，以提高横向分辨率。
我们首次提出在正向模型中计算所使用的有限尺寸换能器的时空响应（STR），然后在反向投影方法的框架中补偿换能器的时间延迟和方向灵敏度。通过模拟和体模实验来评估所提出方法的横向分辨率提高效果。通过计算平均图像梯度来评估该新方法对复杂目标成像的性能。
模拟结果表明，使用这种新方法，离中心目标的横向分辨率可以与中心目标一样好。体模实验结果表明，该新方法可以将离旋转中心约 5mm 的点目标的横向分辨率提高两倍以上。体模实验结果还表明，新方法很好地恢复了离中心区域的叶片静脉的许多模糊精细结构，平均图像梯度提高了约 1.3 倍。
所提出的新方法可以有效地考虑均匀声学介质中基于环形扫描的 PAT 中有限换能器孔径的影响。该新方法还具有稳健性和计算效率，因此是基于环形扫描或球形扫描的 PAT 中传统反向投影算法的理想替代品。该新方法对于环形扫描或球形扫描的 PAT 系统的设计具有重要意义。
