Improvements of the echo PIV technique in system development, theory, methods and applications

The quantification and characterization of local blood flow information such as velocity vectors, mechanical wall shear stress, recirculation and local vortex patterns are critical for the early diagnosis of many cardiovascular diseases since they are closely associated with the initiation and progression of thrombus, intimal hyperplasia, plaque rupture, atherosclerosis and left ventricular dysfunction. Nowadays ultrasound Doppler and phase-contrast MRI (PC-MRI) are two basic techniques that have been widely adopted in the clinical measurements of human hemodynamics. However, even though ultrasound Doppler is cheap and fast, it has the inherent limitations of angle-dependence, aliasing and difficulties in providing multi-component flow velocity information; PC-MRI has exceptional performance in accurate and multi-dimensional, three-component flow measurement, but still suffers from the costs in time and expense as well as the temporal resolution.;Echo Particle Image Velocimetry (Echo PIV) is a newly developed technique for non-invasive, real-time, multi-component and high-resolution flow visualization in arteries and opaque flows, and may be especially useful for vascular profiling in human carotid arteries. It is an integrative method combing the existing technologies of ultrasound brightness mode (B-mode) contrast imaging and digital particle image velocimetry (Digital PIV), and has been well developed and validated both in vivo and in vitro through post-processing of radio-frequency (RF) raw backscatter data.;The objectives of this work are primary on the improvements of the Echo PIV technique in theory, algorithms, and feasibility. The specific aspects are presented as follows: (1) Understand microbubble response to high-frequency ultrasound excitation, with specific focus on determining the frequency ranges which affect higher-order scattering modes, liquid compressibility and gas inertial effects; (2) Develop a swept scanning ultrasound imaging system as the first step toward a customized Micro Echo PIV system, and demonstrate the feasibility of Echo PIV applications in the micro scale; (3) Reexamine post-processing algorithms for Echo PIV including the one-quarter rule derived from Digital PIV, with specific examination of new rules for qualitative and quantitative assessments of blood flow using ultrasound-based Echo PIV techniques; (4) Develop new algorithms for DICOM-based Echo PIV analysis to make Echo PIV platform independent and validate these new algorithms using experimental investigations on various flow models; (5) Develop and prototype a novel intra-vascular ultrasound-based Echo PIV (IVUS Echo PIV) to study vascular profiling for coronary artery models. These studies should pave the way to extend Echo PIV into new application areas.