Simultaneous Reconstruction Of Optical Absorption Properties And Sound Speed In Endoscopic Photoacoustic Tomography

Endoscopic photoacoustic tomography(EPAT)is a newly emerged functional imaging modality based on the photoacoustic effect of biological tissues.The prior knowledge of the distribution of speed of sound(SOS)in tissues is usually unavailable before imaging.The ideal assumption of a constant SOS may lead to acoustic distortion,artifacts,blurring and target dislocation in the reconstructed images.This thesis focuses on the simultaneous reconstruction of the distribution map of the SOS,optical absorption and optical absorption coefficient on the luminal cross-sections from the time series of photoacoustic pressure measured by the detectors from inside the lumen.The joint reconstruction is implemented by alternately minimizing the error function relating to the photoacoustic measurements and the theoretical photoacoustic signals obtained by forward simulation.The images of the optical absorption distribution display the morphological structures on the luminal cross-sections.The SOS and optical absorption coefficient distribution images present the quantitative information of the acoustic and optical characteristics.Also,the accuracy of image reconstruction is improved by reducing the influence of the variations in the SOS.The validity of the methods was numerically demonstrated by utilizing the computer-simulated phantoms of arterial vessels.The experiments comparing the proposed methods with the the reconstruction based on a constant SOS were also performed.The results show that the quality of the optical absorption distribution images can be improved through joint reconstruction of the SOS and optical absorption.The artifacts and distortion caused by the heterogeneously distributed SOS are effectively reduced.The advantages of the proposed algorithm were verified by the quantitative analysis of the optical absorption energy distribution map which was reconstructed by the alternating optimization algorithm and the time-reversal algorithm,and the optical absorption coefficient distribution map which was reconstructed by the alternating optimization algorithm and the two-step algorithm.