In this dissertation work, scan conversion algorithm for compound scanning, variable rate sampling clock generator and multi-gate Doppler system has been studied.
This dissertation work may be divided into three parts. First, scanconversion algorithm for compount scanner has been studied. Input data in spatial domain are sampled by concentric square raster sampling(CSRS) method, and the diplay pixel data is interpolated by one-directional interpolation. The reconstruction error of the proposed algorithm is much smaller than the existed algorithms, because only one-dimensional interpolation rather than the complex two-dimensional interpolation is involved. The proposed algorithm can be applied to the spatial compound scanner where two or more transducers are arranged in linear or circular fashion. The implemention of this algorithm seems to be quite easy compare to the previous algorithms.
Second, variable rate sampling clock generator is studied. A new clock generator satisfy the general requirements of sampling clock generators; fast transition time, precise frequency resolution, and phase coherency. The proposed method reduces the accumulated error below the half period of the master clock by accumulated error correction. The clock is generated by dividing a high frequency master clock with proper division value stored in look-up table ROM. The look-up table is divided into base value and bitencoded correction value to reduce the storage size and the required access time of table ROM. access time of table ROM.
Finally, multi-gate pulsed Doppler system is investigated. Pulsed ultrasonic Doppler system is a useful diagnostic instrument to measure blood velocity and volume blood flow. This system is more powerful compare with 2-dimensional image. A system has been developed and is being evaluted using TMS32010 DSP. We use this DSP for the purpose of spectrum analyzer in singlegate pulsed Doppler system and for the serial comb filter and zero crossing counter in multigate plused Doppler system. The Doppler shift of the back-scattered signals is sensed in a phase detector. This Doppler signal corresponds to the mean velocity over a some region in space defined by the ultrasonic beam dimensions, transmitted pulse duration, and transducer bandwidth. Multigate pulsed Doppler system enable the transcutaneous and simultaneous assessment of the velocities in a number of adjacent sample volumes as a continuous function of time. A multigate pulsed Doppler system processing the information originating from 16 sample volumes in a sequential way is presented. Serial data processing is achieved by digitizing the range and timedependent phase signal and performing the required signal processing (serial comb filtering and zero crossing counting) in digital form.
본 논문에서는 초음파 B-Scan이 가지고 있는 문제점들을 해결하기 위해 사용하는 compound scan에 대해 설명하고, 둥글게 배열된 여러개의 트랜스듀서를 가진 compound scanner에 사용되는 새로운 scan conversion 알고리즘을제시했다. 극좌표계에서 샘플된 데이타를 직각 좌표계에 표시되는 여러가지 알고리즘이 발표되고 현재 사용되고 있으나 이들에는 변환과정의 복잡성도 따르고 변환된 영상은 reconstruction error를 포함하고 있다. 본 논문에서는 샘플링시의 한 좌표축을 직각좌표계의 한 축과 일치시켜 한쪽 축만을 1-D linear interpolation으로 하여 좌표축 변환과정에서 발생하는 영상의 찌그러짐을 대폭 감소시키고 hardware의 구성을 간단히 할 수 있어 real-time compound의 실현을 가능하게 하는 새로운 알고리즘을 제시하고 기존의 방법과 비교하여 성능의 우위성을 입증하고 있다.
제시된 새로운 알고리즘을 실현하기 위해 스위칭 시간이 짧고, 해상도가 높고, 출발위상의 일관성을 갖는 샘플링 클럭 발생기가 요구된다. 이를 위해 누적 오차 수정에 의한 새로운 샘플링 클럭 발생기를 제안하고 구현하여 앞에 서술한 compound scan conversion 알고리즘의 실현 가능성을 보여 주었다.
마지막으로 고속의 DSP(Digital Signal Processor)를 이용하여 혈관전체나 심장 판막부근의 혈류 방향 및 속도 분포를 알 수 있는 16CH multi-gate Doppler 시스템의 구현과 FFT를 하여 방향을 갖는 Doppler 신호의 스펙트럼을 color로 보여주는 시스템의 구현에 대해 설명했다.
