Fresnel beamforming for low-cost, portable ultrasound systems.

摘要

The contributions of this dissertation are proposing, evaluating, and refining a novel beamforming method that can reduce the size and cost of ultrasound imaging systems while providing image quality comparable to that of conventional systems. This method, called Fresnel beamforming, has a delay profile with a shape similar to a physical Fresnel lens. This method uses a unique combination of analog and digital beamforming methods. The advantage of Fresnel beamforming is that a system with 4 transmit and 2 receive channels with a network of single-pole/single-throw switches can be used to focus an array with 64 to 128 elements. The main trade-off of this method is the presence of focal errors, leading to image degradation. Several techniques are presented in this dissertation for overcoming the trade-off of Fresnel beamforming. These techniques include 1) integrating a novel side-lobe suppression method, called dual apodization with cross-correlation (DAX); 2) implementing harmonic imaging; 3) the gated transmit beamforming technique; and 4) the modular Fresnel receive beamforming technique. These techniques helps improve the performance of Fresnel beamforming, making it a suitable alternative beamforming method for various transducer arrays even in the presence of aberration, where differences in sound speed induce additional focal errors in Fresnel beamforming. In summary, this dissertation demonstrates the suitability and robustness of Fresnel beamforming in providing ultrasound imaging systems, not only with reduced cost and size but also with comparable image quality to that of conventional harmonic imaging systems.