Research On Image Reconstruction Algorithm For Intravascular Photoacoustic Imaging

Intravascular photoacoustic(IVPA) imaging is a newly developed intravascular endoscopic imaging technique, which overcomes the deficiencies of the existing intravascular imaging modalities. It can directely detect the morphological and pathological changes of the vessel wall and the composition of vulnerable plaques. It has potential value for clinical application in diagnosis and interventional treatment of vascular diseases.In this dissertation, the imaging principle of IVPA and the physical properties of the photoacoustic signals generated by the vessel wall tissues are analyzed. The ill-posed problem of deconvolution in removing the infulence of the detecter pluse response is solved with a regularization method. Consequently, the photoacoustic signals generated by the tissues can be restored effectively.Image reconstruction from the collected and pre-processed photoacoustic signals is an essential problem of IVPA imaging. The image quality highly depends on the proper reconstruction algorithm. In this dissertation, current reconstruction algorithms for vitro photoacoustic imaging are overviewed. Then, two image reconstruction methods for IVPA imaging system equipped with a single-element ultrasonic transducer are presented,which are based on, respectively, filtered back-projection and time-reversal algorithm.The validity and effectiveness of the methods are demonstrated with a computer-generated vessel phantom. A comparison between the reconstruction results of the two methods is performed and the adavantage and limits are discussed. Also, the influences of sparse sampling and limit-angle sampling on reconstructed IVPA images are discussed. Finally, a conculison that the tissue boundaries can be correctly reconstructed only when their normal lines pass the detector sampling location is drawn.