Bøe S, Kristoffersen K
Department of Informatics, University of Oslo, Norway.
IEEE Trans Biomed Eng. 1995 Mar;42(3):260-8. doi: 10.1109/10.364512.
Analog to digital conversion in multigate Doppler ultrasound systems for blood velocity measurements is a technological challenge. The echoes must be digitized at a rate determined by the system bandwidth (typically 2 MHz), and the dynamic range is large (16 bits or more) due to the presence of strong, low-frequency Doppler clutter echoes originating from slowly moving tissue. Off-the-shelf A/D converters do not meet these requirements with the transducer configuration employed by contemporary Doppler systems. Analysis reveals a 5-b reduction in required wordlength for an A/D converter in a predictive feedback loop when the maximum clutter frequency is about 1.5% of the pulse repetition frequency. The prediction error filter is recursive. Alternatively, first- and second-order DPCM (Differential Pulse Code Modulation) yield 4 and 6 b, respectively. With short input segments (from a high-resolution Color Flow Mapper), the results are, in the above order, 4, 4, and 5 b. The results are verified by processing an experimental Doppler signal.
用于血流速度测量的多门控多普勒超声系统中的模数转换是一项技术挑战。回波必须以由系统带宽（通常为2MHz）确定的速率进行数字化，并且由于存在源自缓慢移动组织的强低频多普勒杂波回波，动态范围很大（16位或更多）。现成的A/D转换器无法满足当代多普勒系统所采用的换能器配置的这些要求。分析表明，当最大杂波频率约为脉冲重复频率的1.5%时，预测反馈回路中的A/D转换器所需字长可减少5位。预测误差滤波器是递归的。另外，一阶和二阶DPCM（差分脉冲编码调制）分别产生4位和6位。对于短输入段（来自高分辨率彩色血流映射器），结果按上述顺序分别为4位、4位和5位。通过处理实验多普勒信号对结果进行了验证。
