| Real-Time 3D ultrasound would be an invaluable tool for many medical applications. To obtain medical quality 3D images, frame rates of 500 2D images per second must be achieved, while maintaining −60dB side lobes. Conventional focused aperture systems are too slow to reach these frame rates. Synthetic aperture beamforming can achieve these rates, but has high processing requirements and poor noise performance. In this thesis I propose a new beamforming approach, called Multi-Transmit Synthetic Aperture (MTSA) that trades off some of the speed of synthetic aperture to gain computational simplicity and signal to noise performance. In this approach multiple simultaneous beams are spread evenly across the imaged region, using a subset of elements to form each beam. This provides a speed increase equal to the number of beams, and signal to noise ratio improvement proportional to the number of elements contributing to each beam. The beamformer was implemented for an 143 element array using four Field Programmable Gate Arrays (FPGA). An approximation algorithm was developed to simplify the beamforming mathematics, and reduce the RAM requirements to conform with FPGA limitations. Linear interpolation was used to limit time quantization effects. The entire design was tested by comparing computer simulations of the gate array design with a theoretical model of the beamformer. The results of both simulations were identical. |
