DEVELOPMENT OF ADVANCED BEAMFORMING METHODS FOR HIGH-FREQUENCY ULTRAFAST AND 3D ULTRASOUND IMAGING

Abstract

A key defining feature in clinical ultrasound systems is the ability to acquire images in real-time. A perception of instantaneous feedback from a diagnostic imaging system is especially critical in a surgical setting where tissue is being removed. Neurosurgery to remove a glioblastoma tumor, an extremely aggressive an infiltrative cancer can benefit heavily from the use of real-time ultrasound imaging. Specifically, an endoscopic ultrasound probe capable of high-resolution imaging coupled with high-resolution blood vessel detection. However, the use of high-resolution ultrasound imaging and blood vessel imaging significantly increases computational requirements often preventing real-time imaging. To improve the clinical viability of this endoscopic ultrasound probe, two studies in this thesis pursued designing an ultrasound system capable of handling the increased computational demand. Another study introduces a novel 3D imaging technique that could further aid surgeons by acquiring a volume rather than a single image slice. The first study created an ultrasound imaging system capable of performing conventional focused imaging and ultrafast defocused imaging. Conventional imaging acquired a high-resolution ultrasound image, while ultrafast imaging acquired a series of low-quality images enabling the generation of a power Doppler image. Power Doppler imaging is useful for detecting blood vessels, including micro-vasculature that often surrounds tumors. The performance of this system was validated by acquiring ultrasound images and micro-vasculature images of a rat brain in-vivo at a 3 Hz frame-rate. The second study validated a new 3D imaging technique on an electrostrictive row-column-array. This technique replaces a fixed focus lens with a reconfigurable digital lens. While, not implemented in this study this technique allows the reconfigurable lens to be multiplexed across an aperture to acquire a volume. This technique was validated by confirming the digital lens functioned comparable to conventional focused imaging. The third study built on study one by increasing the size of the micro-vasculature image while optimizing the ultrasound system. This allowed new in-vivo images of a rat brain to be collected at a 5 Hz frame-rate thanks to hardware and software improvements. This study also laid the groundwork for further improvements in the obtainable frame-rate.