Research On Methods Of Quantitative Intravascular Photoacoustic Tomography And Optical Coherence Tomography

Intravascular optical coherence tomography(IVOCT)is a catheter-based imaging technique with the highest resolution among the current intravascular imaging modalities.However,its main drawback is the low penetration depth due to the nature of pure optical imaging.Moreover,atherosclerotic plaques with complex components cannot be identified and characterized accurately based on the structural images at the early stage of their occurence.A comparison mechanism of physiological information in addition to morphological structures is required to obtain parameters with clinical diagnostic value that aid the differentiation of tissue components along with the determination of plaque vulnerability.Intravascular photoacoustic(IVPA)is a newly developed functional imaging technique which combines the high optical absorption contrast of optical imaging and high resolution of ultrasonic detection.However,some information of weakly absorbing structures may be lost.The dual-modal imaging by combining IVPA and IVOCT is able to acquire the images of optical absorption and scattering simultaneously based on the complementary characteristics of both imaging modalities.The main work of this thesis involves two aspects.First,a method based on depth resolved analysis and an error minimization method are designed to quantitatively estimate the spatial distribution of optical attenuation coefficients on the vascular cross sections from IVOCT gray-scale images to realize quantitative imaging.Second,a model physically describing IVPA-OCT dual-modal quantitative imaging is established based on the electromagnetic theory,with which the electrical polarization and thermal expansion coefficient(i.e.Grüneisen coefficient)of the tissues can be reconstructed simultaneously from IVPA and OCT measurements.The methods have been demonstrated by using computer-simulated phantoms mimicking coronary arterial vessels and clinically acquired images.The simulation experiments aim for evaluating the accuracy of estimating optical attenuation coefficients from IVOCT images and validating the numerical simulation of IVPA-OCT dual-modal imaging based on the electromagnetic theory as well.The experiments with clinical images aim for demonstrating the validity of estimating optical attenuation coefficients of different tissue types with the proposed methods.The results suggest that the images representing the maps of optical attenuation coefficient distribution can effectively improve the contrast between the normal and atherosclerotic tissues in comparison with IVOCT structural images.It provides a useful tool for identifying and characterizing the arterial tissues with different compositions.By utilizing the physical model of IVPA-OCT imaging based on the electromagnetic theory,the dual-modal imaging can be made possible by using the complementarity of the two imaging modalities to their full potential.The images representing the initial pressure and optical scattering on vascular cross section can be obtained simultaneously with which the tissues with different components and unstable plaques can be differentiated with high accuracy.