(A) study on the implementation of the ultrasonic B-scan imaging system based on the bandwidth sampling techniques

Abstract

B-scan imaging is the most widely used modality in current medical vltrasound imaging. The quality of the ultrasonic B-scan image is primarily determined by the spatial resolution which is mainly dependent on the focusing capability. In all the commercial B-scan equipments using analogue delay line for focusing, however, the poor resolution has known to be the major factor to limit the image quality. In order to overcome this drawback, digital focusing technologies have received a great deal of attention. However, digital focusing using sampled RF data and subsequent envelope detection directly from the focused RF data are not easy tasks. Furthermore, digital circuitry for focusing must be consisted of a large amount of memory and high speed devices. In other words, the cost of the system should go up. These difficulties can be alleviated by employing one of the bandwidth sampling techniques. If we apply quadrature sampling technique to the ultrasound imaging system using an array transducer, unwanted phase terms appear in the expressions of he inphase and quadrature components of the baseband signal when an appropriate delay time is introduced to each channel signal for the purpose of focusing. In this thesis these unwated terms are derived and analyzed in detail from a viewpoint of focusing, and a new scheme to eliminate the unwanted phase terms is proposed. The resulting phase-error-free quadrature sampling technique(PEFQST) is applied to the synthetic focusing system. Its system block diagram with the simulation and experimental results are presented. And, the application of analytic-signal sampling to the ultrasound imaging system is described in this thesis. This has not the unwanted phase terms and hence does not need the phase compensation logic. Therefore we can apply the analytic-signal sampling to the non-synthetic focusing system as well as the synthetic focusing system. Especially, the analytic-signal sampling applied to the pipelined-sampled-delay...