Research On Two-Dimensional Photoacoustic Tomography Algorithm Based On Sound Field Response

In two-dimensional circular scanning based photoacoustic tomography,system and image reconstruction algorithm are the two major factors affecting the quality and resolution of imaging.The conventional back projection algorithm is developed on the basis of "ideal point transducers",and the non-focusing transducer with large detection area is usually used in the system.The model mismatch will result in a decrease in the lateral resolution of the reconstructed image,ie,when the target moves further from the scanning center,the target image will be elongated in the lateral direction with a lateral resolution equal to the transducer size at the detection boundary.This is called the "finite aperture effect." The essential cause of this effect is the introd uction of time delay errors and detection angle limitations due to the spatial temporal impulse response(STR)of the planar transducer.To solve this problem,this paper attempts to calculate the STR of a finite-size planar transducer using a forward model,and compensates for the error in the back projection reconstruction using the precise time delay extracted from the STR.This paper has also tried to compensate the signal loss due to the detector angle effect of the transducer during reconstruction.Finally,the new algorithm is used to reconstruct the simulated data and experimental data,and compared with the results of the conventional method to evaluate the proposed method.The results show that the application of time delay correction and signal sensitivity compensation can effectively restore the lateral resolution of the image.At the same time,in order to avoid low-space sampling in the scanning,all targets should be well captured at each transducer position,and our proposed method is used to compensate the time delay and signal strength compensation in the back-projection reconstruction to improve the lateral resolution.