|Title:||Development of novel imaging systems and techniques for micro-ultrasound|
Hong Kong Polytechnic University -- Dissertations
|Department:||Interdisciplinary Division of Biomedical Engineering|
|Pages:||xxiv, 147 leaves : ill. ; 30 cm.|
|Abstract:||High resolution and non-invasive visualization of living tissues is an enormous demand in the field of medical and biological study. Micro-ultrasound is able to delineate small structures with fine spatial resolution on the order of tens of microns. It has been extensively applied for ophthalmology, dermatology, cardiovascular diseases, and small animal studies. Individual study is unique and requires different utilization of the micro-ultrasound system to accommodate different transducer characteristics, data acquisition strategies, signal processing, and image reconstruction methods. One critical technical challenge of micro-ultrasound is to generate high-voltage pulsed signal to effectively excite the transducer for high signal-to-noise ratio (SNR). A multi-functional, reconfigurable pulse generator was developed in this thesis for micro-ultrasound. It could produce high-voltage unipolar pulses, bipolar pulses, or arbitrary pulses for B-mode imaging, Doppler measurement, and modulated excitation imaging. An open system was developed for flexible micro-ultrasound imaging to allow users to customize the system for various studies and have full access to experimental data. It was based on high speed field programmable technology in a compact printed circuit board (PCB) to achieve flexible applications. Thus, the system architecture could be easily modified by users for customized applications. In addition, a novel digital quadrature demodulation algorithm based on Hilbert transform was implemented to achieve fast and accurate pulsed-wave (PW) Doppler profiling. Phantom and in vivo imaging experiments were conducted and results demonstrated good system performance.|
The application of the developed open system for intravascular ultrasound (IVUS) was presented in this thesis. Since the open system was based on electronic components and field programmable technology, it could achieve reconfigurable hardware implementation, programmable image processing algorithms, and flexible imaging control, which supported various strategies including multi-modality imaging. Testing results showed that the open system could offer good hardware performance for IVUS applications. Phantom imaging, in vitro vessel imaging, and multi-modality imaging combining IVUS with photoacoustics were conducted to demonstrate the performance of the open system. A novel modulated excitation imaging scheme with high programmability and flexibility was proposed to improve the penetration depth of micro-ultrasound. It incorporated the developed open system with arbitrary waveform generator and programmable imaging receiver for real-time image formation. Test results showed that the proposed modulated excitation imaging scheme could acquire up to 20dB SNR improvement and 83% increase of penetration depth in contrast with traditional short pulse imaging method. In vivo experiment on the dorsal skin of a human hand demonstrated good performance of the proposed scheme. Finally, a flexible annular array imaging system was developed to improve the depth of field (DOF) of micro-ultrasound. It supported multi-channel dynamic beamforming technique for large DOF imaging. Real-time imaging was achieved by fast processing algorithms and high speed data transfer interface. The system utilized PCB scheme incorporating state-of-the-art electronics for compactness and cost effectiveness. Extensive tests including hardware, algorithms, wire phantom, and tissue phantom measurements were conducted to demonstrate the system performance.
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