Speckle Tracking for Cardiac Strain Imaging in Ultrasound Imaging and Constrast Enchancement in Photoacoustic Imaging.

Ultrasound (US) and photoacoustic (PA) imaging, as coherent imaging modalities, are characterized by the appearance of speckle. Speckle formation is related to the specifics of the imaging system and underlying tissue microstructure. Speckle tracking (ST) is a technique to measure speckle motion, providing a foundation for non-invasive and quantitative image-based disease diagnosis. This dissertation has demonstrated ST’s application to cardiac strain imaging in US imaging and contrast enhancement in PA imaging. In cardiac strain imaging, the accuracy of tissue Doppler imaging (TDI) and 2-dimensional (2-D) ST estimates of instantaneous and accumulated axial normal strains were compared using a simulated heart model. An isolated rabbit heart model of acute ischemia produced by left anterior descending (LAD) artery ligation was used to evaluate the performance of the two methods in detecting abnormal cardiac wall motion. A well-controlled 2-D cardiac elasticity imaging technique was then introduced using two coplanar and orthogonal linear probes simultaneously imaging an isolated retroperfused rabbit heart. Acute ischemia was generated by LAD artery ligation. Single probe detection demonstrated that directional changes in the in-plane principal deformation axes can locate an ischemic cardiac wall bulging area due to LAD ligation, and strains based on principal stretches can characterize heart muscle contractility. These two findings were further validated using symmetric displacement accuracy derived from two probe data. To evaluate 3-D ST on controlled complex 3-D heart motion, a left ventricular (LV) phantom was constructed using Polyvinyl alcohol cryogel and integrated with a pulsatile pump in combination with a pressure meter. A commercial 2-D phased array (Sonos 7500, Philips) was used to acquire 3-D radiofrequency data with increased effective frame rate. 2-D and 3-D ST algorithms were tested on this 3D data set. LV contraction and out-of-plane motion were also simulated and tracked using a computer model of cardiac imaging. In PA imaging, ST can be used to increase specific contrast by identifying regions moved by manipulating Au-shell-encapsulated magnetic nanoparticles and then suppressing unwanted background PA signals without motion. Magnetomotive PA imaging can potentially also be used for tissue elasticity imaging, such as measuring the relaxation time constant of tissue.PhDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/77928/1/cxjia_1.pd