The Design And Development Of High-resolution Intravascular Photoacoustic System

The rupture of vulnerable plaques is the major cause of acute cardiovascular disease, which kills more than 3.5 million people annually in China. Several imaging techniques including coronary angiography, intravascular ultrasound(IVUS) and intravascular optical coherence tomography(IVOCT), are commonly used in clinics, which can provide the structural information of the plaque. However, none of the above techniques can reveal the chemical composition of the plaque, which is a critical factor closely related to the vulnerability of the plaques. The newly emerging photoacoustic imaging technology has showed great potential to identify the plaque composition. However, due to the large probe size, low spatial resolution and low imaging speed, the current intravascular photoacoustic(IVPA) imaging systems are insufficient to identify the microstructures of the plaque. Therefore, it is of great significance to develop high-resolution IVPA imaging system, which can improve the identification efficiency of vulnerable plaques.In the theoretical section, the theoretical analysis of photoacoustic imaging was conducted from the perspective of the mechanism of photoacoustic effect, the properties of acoustic propagation in tissues and the method of photoacoustic signal reception. The theory introduction will contribute to the design of the IVPA imaging system.In the system development section, the design of the imaging system was discussed from both the hardware and software aspects. For the hardware part, the overall system design schematic was given based on the system goals. By solving a series of key challenges including optical focusing in small space, photoacosutic detection as well as precise assembly, the imaging probe with spatial resolution of 20 micrometers, diameter of 0.9 millimeters and combined IVPA/IVUS imaging was successfully built. After that, a single-mode fiber coupling system was also designed, which is composed of four modules including beam shaping, beam collimating, beam focusing and fiber coupling. For the software control part, the system control interface with Lab VIEW program by drawing the flow chart of main program and data acquisition program was developed. With the completion of all above work, a high-resolution intravascular photoacoustic system was finished, with an imaging speed up to1 frame per second.In the experimental research section, a series of photoacoustic imaging experiments was designed to test the performance of new system. Firstly, the signal-to-noise ratio(SNR) and resolution of imaging were measured. Secondly, a heart stent was scanned with the system to obtain the 3D photoacoustic and ultrasound images. Finally, the lipid phantom was imaged to validate the feasibility of the system for identifying plaque composition. The results showed that the system can detect the photoacoustic signal from lipid.The high-resolution intravascular photoacoustic imaging system was designed and built up in this dissertation, and based on that, the 3D photoacoustic/ultrasound images of the stent as well as the photoacoustic signal from lipid phantom were obtained. It can be seen that this work will help to improve the diagnosis of vulnerable plaques as well as decrease the incidents of cardiovascular diseases.