Design of digital beamformers for high -frequency ultrasound transducer arrays using field-programmable gate array (FPGA)

Ultrasound imaging is a well-established and widely used clinical technique that shows the cross-sectional image of human tissues. Conventional ultrasound systems are targeted at imaging the heart or abdominal organs and the spatial resolution at this frequency range is on the order of a few millimeter. An ultrasound system will be capable of providing a better spatial resolution if higher frequencies are used. High frequency ultrasonic imaging (>20 MHz) using single element transducers has been shown to be clinically useful in ophthalmology, dermatology, small animal and intravascular imaging. In recent years, more studies have been carried out on the development of high frequency array transducers.;Due to the fact that beamforming electronics is not yet commercially available for the high frequency arrays, prototypical digital beamformers for the annular and linear arrays were specifically developed for the purpose of testing the annular array and linear array developed at the NIH Transducer Resource Center at University of Southern California (USC). Field Programmable Gate Arrays (FPGAs) have been demonstrated to be an ideal platform for beamformer development. They provide the processing speed necessary for real-time beamformer with high frequency array transducers. Two digital beamformers were developed for the 8-element annular array and 64-element linear arrays.;An imaging system composed of an annular array transducer, an eight-channel analog front-end, a field programmable gate array (FPGA) based beamformer, and a DSP microprocessor based scan converter was developed. A PC computer is used as the interface for image display. The beamformer that applies delays to the echoes for each channel is implemented with the strategy of combining the coarse and fine delays. The coarse delays that are integer multiples of the clock periods are achieved by using a First-In-First-Out (FIFO) structure and the fine delays are obtained with a Fractional Delay (FD) filter. Using this principle, dynamic receive focusing is achieved. The image from a wire phantom obtained with the imaging system was compared to that from a single element transducer using one channel of the system. The improved lateral resolution and depth of field from the wire phantom image were observed. Images from an excised rabbit eye sample were also obtained, and fine anatomical structures were discerned. (Abstract shortened by UMI.).