Sumino Y, Waag R C
Department of Electrical Engineering, University of Rochester, New York 14627.
J Acoust Soc Am. 1991 Dec;90(6):2924-30. doi: 10.1121/1.401766.
The influence of propagation medium inhomogeneities on pulsatile ultrasonic fields has been investigated experimentally. The study employed a special curved transducer to produce a hemispherical wave pulse and a linear array to measure the resulting field along a line in a plane. Translation of the array in the elevation direction yielded data over a two-dimensional aperture. Time delay across the aperture was calculated by adding delay differences obtained by cross-correlating signals on adjacent elements and noting the position of the cross-correlation peaks. Received waveforms were shifted an amount given by the difference between the actual arrival time and a calculated geometric delay to isolate arrival time differences due to propagation path inhomogeneities. Waveform and time delay difference plots as well as histograms and statistics derived from them for propagation through a water path and for propagation through five specimens of human abdominal wall indicate that arrival time fluctuations in the presence of human abdominal wall specimens are significantly greater than for a water path and that degradation in focusing through human abdominal wall can be expected in ultrasonic imaging systems that operate in the low megahertz range and employ a relatively large aperture.
已经通过实验研究了传播介质不均匀性对脉动超声场的影响。该研究使用了一个特殊的弯曲换能器来产生半球形波脉冲，并使用线性阵列来测量平面中沿一条线的所得声场。阵列在仰角方向上的平移产生了二维孔径上的数据。通过将相邻元件上信号互相关获得的延迟差相加并记录互相关峰值的位置，计算出孔径上的时间延迟。将接收波形移动一个由实际到达时间与计算出的几何延迟之间的差值给出的量，以分离由于传播路径不均匀性引起的到达时间差。通过水路传播以及通过五个人类腹壁标本传播的波形和时间延迟差图以及从中得出的直方图和统计数据表明，在存在人类腹壁标本的情况下，到达时间波动明显大于水路传播，并且在工作于低兆赫兹范围且采用相对较大孔径的超声成像系统中，可以预期通过人类腹壁聚焦会退化。
