Intravascular imaging on high-frequency ultrasound combined with optical modalities

Atherosclerosis is a complex syndrome characterized by plaques build up on the inner lining of arteries, which is the leading cause of morbidity in developed countries. Conventional gold standard for diagnosing the vulnerability of plaques is intravascular ultrasound (IVUS) imaging working in the 20∼40 MHz range. At this range, the resolution (∼100 µm) is insufficient for detecting a number of critical microstructures that are in the scope of less than 65 µm. Driving the working frequency above 80 MHz could be a feasible solution for improving IVUS resolution. Meanwhile, intravascular Optical Coherence Tomography (OCT) is a new imaging modality recently approved for clinical use. OCT features high resolution (10∼30 µm) but limited penetration depth (∼1 mm). The other emerging optical modality: Intravascular Photoacoustic (IVPA) is based on the tissue optical absorption properties and has been proved to offer better contrast of tissue composition. In this dissertation, three intravascular imaging modalities have been investigated: integrated IVUS-OCT imaging, very high frequency IVUS, and IVPA imaging, which aim to overcome the limitations in resolution, penetration and imaging contrast of current technologies. Imaging systems and different types of ultrasonic or optical-ultrasonic hybrid probes have been designed and fabricated for using in each modality. In vitro and in vivo studies have been carried out to validate these new imaging concepts. The imaging results successfully support the enhancements brought by the new modalities. The complementary synergy of ultrasonic and optical modalities provides extra diagnosing information. This research suggests a bright future for multi-modality imaging that combines the conventional IVUS and new optical technologies.