| Author: | Su, Min |
| Title: | Novel intravascular ultrasound transducers |
| Advisors: | Sun, Lei (BME) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Intravascular ultrasonography Blood-vessels -- Ultrasonic imaging Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Biomedical Engineering |
| Pages: | xxx, 142 pages : color illustrations |
| Language: | English |
| Abstract: | Cardiovascular disease (CVD) is accountable for majority of the global mortality and is primarily attributable to atherosclerotic plaques (APs). Intravascular ultrasound (IVUS) is currently among the most crucial imaging technologies for AP diagnosis. However, poor spatial resolution is the main drawback of conventional IVUS. To address this limitation, we proposed two novel ultrasound transducers were developed to enhance the lateral resolution of IVUS imaging. In one study, a Fresnel zone plate (FZP) layer was prepared and introduced on the IVUS transducer surface. This FZP layer enhances the transducer’s focusing effect, thereby improving the lateral imaging resolution. The structure of the transducer is designed based on theoretical calculations. The acoustic beam and other important parameters of the transducer are optimized using COMSOL software. The transducer has an ultrasonic element (dimension: 0.778 × 0.9 mm2). FZP and planar IVUS transducers were fabricated and compared in the study. The FZP transducer demonstrates a center frequency (Fc) of 52.5 MHz and a −6 dB relative bandwidth (BW) of 42%. The planar transducer, on the other hand, has a center frequency of 51.3 MHz and a −6 dB relative bandwidth of 58%. To evaluate the imaging performance of the fabricated transducers, imaging experiments with the house made wire phantom and swine artery sample were conducted. The FZP and planar transducers achieved axial imaging resolutions of 47 and 44 μm and lateral imaging resolutions of 184 and 314 μm, respectively. The study results indicate that the inclusion of the FZP layer enhances the lateral imaging resolution of the transducer for IVUS applications. The other study presents a novel approach for enhancing the spatial resolution of IVUS imaging by proposing a geometrically focused IVUS transducer that uses PIN-PSN-PT piezoelectric ceramic with a larger aperture compared with conventional geometrically focused transducers. The selected PIN-PSN-PT ceramic has a favorable dielectric constant, allowing a suitable electrical impedance (50 Ω) at a larger element aperture of 0.6 × 0.6 mm. Acoustic beams and spatial resolutions were simulated using Field II program. Geometrically focused and planar transducers were manufactured accordingly. The focused and planar transducers had a center frequency of 42 and 41 MHz and a−6 dB relative bandwidth of 71% and 68%, respectively. The designed transducers were characterized by conducting imaging experiments of wire phantom and ex-vivo porcine artery. The focused transducer exhibited superior spatial resolution, with values of 45 µm axially and 208 µm laterally, to the planar transducer with resolutions of 48 µm axially and 282 µm laterally, respectively. These results indicate the potential of the focused transducer, utilizing PIN-PSN-PT ceramic, to enhance the lateral resolution in IVUS imaging applications. Non-uniform rotational distortion (NURD) encountered in mechanically rotating catheters hampers accurate image acquisition. We here proposed a dual-element IVUS catheter to address this concern. In the catheter, two elements with similar frequencies and other properties are assembled in a back-to-back configuration. In the presence of NURD during imaging, the abnormal image portion obtained from one element can be modified by the corresponding regular ultrasound image acquired by another element in the catheter. This allows the reconstruction of an image without NURD. In addition, the catheter can obtained two images in a single rotation, effectively doubling the imaging frame rate compared to a single-element configuration. Wire phantom imaging was performed for evaluating the imaging resolution of these two elements. Additionally, the feasibility and overall imaging performance of the proposed protocol were verified using a tissue phantom and by performing porcine artery vascular imaging. The results indicate that the novel strategy has substantial potential for application in clinical settings. |
| Rights: | All rights reserved |
| Access: | open access |
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