| Peripheral artery disease (PAD) is associated with a high level of morbidity and is estimated to affect 8 to 12 million Americans though the diagnosis of patients with PAD is relatively low. Associated with PAD is the development of vascular wall buildups known as stenoses that introduce a disruption to the normal blood flow. In this work, proof-of-concept has been established for an instrument that synergistically combines sonic and ultrasonic modalities for the detection, localization, and characterization of vascular stenoses.; A 15 element, 2-D acoustic array sensor is developed that is conformable to the skin surface and sensitive to subsurface, turbulence-induced acoustic sources. The sensor pad is combined with a commercial ultrasound device used for subsurface structural detection. A magnetic position and orientation probe is used for accurate spatial reconstruction of the obtained data.; The data obtained by this multi-mode instrument is used to produce a composite image of subsurface structures determined ultrasonically with the stenosis-induced acoustic field determined using Owsley and Hull's Multiple Auscultation Point (MAP) beamformer. Overall 3-D vascular structure is successfully determined ultrasonically and the instrument is tested on a flow model simulating a stenosis for Reynolds numbers consistent with in situ stenosis observations. The acoustic detection and localization capability has been shown to be accurate at Re=1100 and with reduced accuracy at Re=550 (Reynolds number calculated based on unstenosed vessel) for a 75 percent area reduction stenosis, thus implying potential for the early detection of PAD. Findings beyond technological innovation include improvement to the MAP beamformer by using a Blackman-Tukey spectral estimate to derive the cross spectral density matrix. Additionally, acoustic field reconstruction at approximately 100 Hz is shown to clearly indicate the presence of a stenosis by a strong acoustic intensity though not spatially accurately, while reconstruction at approximately 150 Hz is shown to spatially locate a stenosis more accurately though at a reduced acoustic intensity. |
