| Popis: |
Pre-delay reconstruction sigma-delta beamformer (SDBF) was proposed in recent years to achieve a higher level of integration in ultrasound imaging systems. The high-order reconstruction filter used in each channel of SDBF makes the beamformer highly complex. The beamformer can be simplified by reconstructing the signal only after the delay-and-sum process. It requires only one reconstruction filter for the entire beamformer. However, this post-delay reconstruction-based beamformer degrades the image quality when dynamic focusing is performed. This thesis studied the cause of the dynamic focusing artifact problem suffered by the sigma-delta beamformer. It was found that the degree of the problem is related to the pre-delay quantization noise that is present in the signal. Hence, similar performance to the conventional pre-delay reconstruction SDBF can be achieved by simply employing a simple pre-delay filter, as long as the pre-delay filter provides the required pre-delay signal-to-quantization noise ratio (SQNR). Based on this finding, a cascaded reconstruction beamformer was developed that utilizes a boxcar filter as the pre-delay filter in each channel to achieve the required pre-delay SQNR value. Simulations using real phantom data demonstrated that the proposed cascaded reconstruction beamforming method can achieve a contrast resolution comparable to that of the pre-delay reconstruction beamforming method. In addition, the savings on hardware and power can be as much as 85% and 68% respectively, as compared to the pre-delay reconstruction SDBF. DOCTOR OF PHILOSOPHY (EEE) |
