Advances in synthetic aperture, compounded plane wave, and spatially encoded excitation techniques for fast ultrasonography

Ultrasonography offers subcutaneous imaging at a fraction of the cost of magnetic resonance imaging (MRI) and without the ionizing radiation of X-ray or computed tomography (CT) imaging. In addition, ultrasound imaging machines are compact and portable, and do not require any sort of specialized environment to function. Ultrasonography is, however, limited by the relatively slow speed of sound and standard beamforming can only achieve low imaging frame rates (20 - 80 frames per second). This restricts its use in a number of applications that would otherwise benefit greatly from its use. For example, transient elastography, 3-dimensional volumetric imaging, and Doppler sonography would all benefit from higher frame rates. This thesis presents two new variations of fast imaging methods. The first is by combining two existing fast-imaging techniques, plane wave (PW) and synthetic aperture (SA), using an adaptive weighting algorithm to compound images generated from the techniques individually. This method improves image resolution and signal-to-noise ratio (SNR) without losing the higher frame rate of each, which is successfully demonstrated through experiments on a physical commercial ultrasound system. The second method for increasing frame rate involves two extensions on a spatial encoding technique proposed by Fredrik Gran and Jørgen Arendt Jensen in 2008; these extensions entailed implementing a compressed sensing algorithm to reduce the code length requirement presented in their paper and removing the non-imagable “deadzone” region that their method produces. These extensions are applicable for scenarios requiring high definition for a small set of high-reflectivity points in an otherwise dark region, such as intra-spinal needle guidance, and are demonstrated using the Field II ultrasound simulation software.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat