서강대학교

초록/요약

Intravascular ultrasound (IVUS) imaging is the most common minimally invasive imaging method for evaluating atherosclerosis based on morphological information about blood vessels. A clear identification of vulnerable plaque indicators such as lumen and lipid core size, degree of stenosis, and thickness of fibrous cap is required for accurate diagnosis of atherosclerosis. For this purpose, it is essential to develop an IVUS transducer with high spatial and contrast resolutions. To enhance the spatial resolution, the center frequency of ultrasound and aperture size should be increased and the focal point should be on the imaging region of interest. Contrast resolution can be improved using tissue harmonic imaging and frequency compounding. However, conventional IVUS transducers have limitations in enhancing spatial and contrast resolutions due to its flat aperture (i.e., nonfocusing), relatively low center frequency, small aperture size, and narrow spectral bandwidth. These limitations of conventional IVUS transducers are mainly due to their unique imaging environment; an IVUS transducer is inserted into blood vessels with an inner diameter of approximately 2 mm. To improve spatial and contrast resolutions, in this dissertation, new IVUS transducer are proposed, designed, and fabricated: IVUS focused transducer and dual-frequency IVUS focused transducer. Especially, the dual-frequency IVUS focused transducer facilities tissue harmonic imaging and frequency compounded imaging, thus further improving contrast resolution as well as spatial resolution. The characteristics and imaging performance of the developed IVUS transducer were evaluated through in vitro and ex vivo experiments using wire targets, tissue-mimicking phantoms, stent-deployed phantoms, and resected pig arteries. The experimental results demonstrated that the new IVUS transducers, proposed and developed in this dissertation, have the ability to significantly improve spatial and contrast resolution of IVUS imaging and thus high potential to increase diagnostic accuracy of atherosclerosis.