| Popis: |
Conventional ultrasound medical imaging systems use simple high voltage pulses of around 200V peak to drive the ultrasound transducer to emit short ultrasonic pulses and multiple multi-bit analog to digital converters (ADC) to digitize the return echo signals, thus making it extremely challenging to integrate the transmit and receive electronic circuits onto a single chip. With coded excitation techniques, the necessary drive voltage can be reduced if the duration of the drive signal (coded signal in this case) is increased. Pulse compression techniques are used to compress the returned signal to achieve the high resolution needed for imaging. Oversampling sigma delta ADCs have much smaller silicon area compared to the equivalent multi-bit ADCs. The motivation of the project is to realize an efficient front-end transmit and receive system for medical ultrasound imaging, which takes advantage of the low drive voltage of the coded excitation method and the hardware efficiency of the sigma delta ADC, for possible single-chip implementation. An introduction of conventional ultrasound imaging systems was presented with details on the front-end transmit and receive electronics. Both time and frequency domain beamforming techniques were reviewed. Basic theory of the coded excitation system showing the possibility of low drive voltage without sacrificing signal to noise ratio and resolution were presented. Various applicable codes and pulse compression techniques were reviewed. The pre-compression method, which requires multiple compressor channels in parallel to compress the returned signals prior to beamforming, is capable of generating high quality artifact free images. The post-compression method, which uses only a single compression channel to compress the signal after beamforming, is more hardware efficient but gives rise to image artifacts in dynamic focusing. A two-stage compression technique, which can significantly reduce the post-compression artifacts in dynamic focusing, was proposed. Both simulation and phantom results were presented to show that the proposed technique in capable of producing artifact-free images. Doctor of Philosophy |
