Ultrasound Speckle Image Velocimetry: Studies on System Performance and Application to Cardiovascular Fluid Dynamics

Citation

Lin, Ben Albert (2018) Ultrasound Speckle Image Velocimetry: Studies on System Performance and Application to Cardiovascular Fluid Dynamics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z998856J. https://resolver.caltech.edu/CaltechTHESIS:08152017-194113650

Abstract

Knowledge of detailed blood flow characteristics can be extremely valuable in a variety of settings. Examples range from studying disease processes such as atherosclerosis to aiding in the design of medical devices such as prosthetic cardiac valves. For in vivo and optically inaccessible in vitro flows, accurate measurements of velocity fields and shear stresses can be difficult to obtain. Doppler ultrasound and magnetic resonance imaging are the most commonly used techniques, but have important limitations. Recently, there has been increased interest in the application of particle image velocimetry principles towards tracking of ultrasound speckle patterns to determine multidimensional flow velocities with increased temporal resolution. We refer to our implementation as ultrasound speckle image velocimetry (USIV). In this research project, our first objective was to obtain a detailed characterization of the factors unique to ultrasound imaging that can influence the accuracy of velocity measurements. By conducting in vitro experiments with uniform speckle phantom translation as well as steady tube flow, we have shown that characteristics such as transducer focal depth and beam sweep speed as well as particle motion direction and velocity can all influence USIV results. Our second objective was to demonstrate the utility of USIV for analyzing in vivo blood flows. After administering ultrasound contrast agent to anesthetized pigs, we were able to obtain detailed images of both left ventricular flow and abdominal aortic flow. Velocity profiles were measured during both left ventricular filling and ejection. Our most interesting finding was the presence in certain cases of highly asymmetric retrograde flow in the infrarenal aorta. The factors that lead to such flows may have relevance to the development of atherosclerosis and abdominal aneurysms. USIV is likely to be very useful for further studies both in vivo and with in vitro elastic aorta models.

Thesis Files