published_or_final_version / Physics / Master / Master of Philosophy

Thesis (M. Phil.)--University of Hong Kong, 1994. / Includes bibliographical references (leaves 137-140).

Thesis--University of Wisconsin--Madison. / Typescript. Vita. Includes bibliographical references.

The primary focus of the work was to evaluate the capability of intravascular photoacoustic (IVPA) imaging in combination with intravascular ultrasound (IVUS) to detect and differentiate atherosclerotic plaques. The composition rather than structural narrowing of the arteries is a major indicator of the propensity of a vascular lesion to rupture. Consequently, intravascular imaging of these high-risk plaques is required to exactly determine the vulnerable plaque constituents for appropriate follow-up therapy. Our multi-modality imaging approach aims to utilize the high resolution structural assessment abilities of IVUS and the optical contrast of IVPA imaging and is capable of differentiating the lipid, fibrous and fibro-cellular components of an inflammatory lesion. To test the hypothesis, we developed an IVUS catheter based laboratory prototype of a combined IVUS/IVPA imaging system. The performance of the synergistic combination of IVUS and IVPA imaging was evaluated through tissue mimicking phantom studies. Further, to test the ability of the combined imaging to detect plaques, excised samples of an aorta were utilized from a specifically designed animal model of atherosclerosis. Ex-vivo IVPA imaging studies were performed using a 532 nm laser excitation to detect the lipids in the plaque. In addition, multi-wavelength spectroscopic IVPA imaging studies were evaluated to differentiate plaques. Finally, an ultrasound based temperature estimation method was utilized to demonstrate and confirm safety of IVPA imaging for clinical intravascular applications. Upon analysis of the results of our investigation, we believe that IVPA imaging offer numerous potential advantages when integrated with clinical IVUS imaging. The IVUS imaging system with integrated IVPA imaging capability could play a major role in interventional cardiology. / text

published_or_final_version / Physics / Master / Master of Philosophy

Thesis (M. Phil.)--University of Hong Kong, 1995. / "9th September 1994." Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Neuromodulation plays a crucial role in facilitating research into brain function and enabling treatments for neurological and psychiatric disorders. In brain research, current non-invasive tools face challenges when studying brain sub-regions due to their limited spatial resolution, which can barely reach a scale of 100 μm. Moreover, precise control over the volume of tissue activated (VTA) is needed to effectively target diverse-shaped brain regions, such as ocular dominance columns. Similarly, in disease treatment, the lack of sufficient spatial resolution poses obstacles in restoring normal vision using existing FDA-approved retina prostheses for retinitis pigmentosa. To address these challenges, my thesis work focuses on the development of optically-generated ultrasound devices for non-invasive brain stimulation and implantable retina prostheses. Firstly, to meet the need for non-invasive neuromodulation with ultrahigh precision, we have developed an optically-generated focused ultrasound device. By embedding candle soot nanoparticles in a curved polydimethylsiloxane pad, this device generates a transcranial ultrasound focus at 15 MHz with an ultrahigh lateral resolution of 83 μm. This resolution is two orders of magnitude smaller than conventional transcranial-focused ultrasound, enabling successful submillimeter transcranial stimulation in vivo targeting the mouse motor cortex. Addressing the requirement for a customized VTA in specific brain sub-regions, we have developed an optically-generated Bessel beam ultrasound device. This device was specifically designed to target brain columns with an elongated acoustic focus, and it successfully achieved a VTA with a lateral resolution of 152 μm and an axial resolution of 1.93 mm. The stimulation capability of the device has been confirmed through immunofluorescence imaging, which showed that the stimulation depth in mouse brains reached up to 2.2 mm. Furthermore, in order to address the need for an ultrahigh spatial resolution in retina prosthesis, we have developed an optically-generated ultrasound film as a subretinal prosthesis. In proof-of-concept experiments using blind rat retina, this film has successfully achieved retina stimulation ex vivo. In conclusion, optically-generated ultrasound devices offer promising opportunities for brain science research and disease treatments. They revolutionize non-invasive brain stimulation with ultrahigh precision and customized VTA for studying brain sub-regions. Additionally, they hold the potential for enhancing spatial resolution in retina prostheses, bringing hope to individuals with retinal disorders. / 2024-09-08T00:00:00Z

Call number: LD2668 .T4 1985 V464 / Master of Science

Call number: LD2668 .T4 1986 E34 / Master of Science / Physics