Development of Intravascular Ultrasound/Photoacoustic Imaging System and Probe
Date Issued
2012
Date
2012
Author(s)
Hsieh, Bao-Yu
Abstract
Photoacoustic (PA) imaging combines good ultrasonic resolution with high optical contrast. In this thesis, integration of intravascular ultrasound (IVUS) and photoacoustic (IVPA) imaging was proposed for diagnosis of cardiovascular diseases. The hypothesis is that ultrasound (US) provide anatomical details of vessels, while the atherosclerotic and normal vessels can be differentiated by the photoacoustic (PA) techniques. In the first part of the thesis, we constructed a dual-modality imaging system for IVUS/IVPA imaging. A high-speed pulsed laser was used to increase the imaging frame rate for real-time IVUS/IVPA imaging. An optical fiber with an axicon-like distal tip was designed for omni-directional excitation, eliminating the need of fiber rotation. The imaging frame rate can reach 19 frames per second. Phantom and ex vivo experiments show that the lateral and axial resolution of US is 2.56° and 62.4μm at -6 dB, respectively. The PA resolution is 3.76° laterally and 91.5μm axially. In the second part, we developed two types of integrated imaging probes. One is an imaging scanhead with piezoelectric ring-shaped transmitter and the other is an all-optical IVUS/IVPA transducer. Both can be made sufficiently small for intravascular applications and a polymer microring was used for acoustic detection. Note that the all-optical design is suitable for one-time, disposable use. In the first all-optical design, the US signal is induced by impinging the laser energy on the substrate of the microring. A subband imaging method is subsequently applied to separate the PA signals from the US signals. In the second all-optical design, a dichroic filter is located at the outlet of the optical fiber to switch between US and PA imaging modes. The green laser pulse was absorbed by the red dichroic filter to induce an acoustic signal for US transmission, while the red laser light penetrated through the dichroic filter and illuminated the sample directly for PA imaging. The image resolution and the contrast can be further improved by applying the SAFT. The axial and lateral resolutions of this imaging system are 125μm and 2.52°, respectively. In summary, the thesis has realized effective IVUS/IVPA imaging methods for cardiovascular diseases diagnosis. The contributions include development of a dual-modality imaging system and various kinds of integrated imaging probes. Future works include high-frame-rate imaging techniques to achieve real-time 2D and 3D IVUS/IVPA imaging by integration of omni-directional excitation with a ring array transducer.
Subjects
atherosclerotic plaque
intravascular ultrasound (IVUS)
intravascular photoacoustic (IVPA) imaging
all-optical US/PA imaging scanhead
SDGs
Type
thesis
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