Oelze Michael L, O'Brien William D
Bioacoustic Research Laboratory, Department of Electrical and Computer Engineering, University of Illinois, 405 North Mathews, Urbana, Illinois 61801, USA.
J Acoust Soc Am. 2002 Dec;112(6):3053-63. doi: 10.1121/1.1517064.
The frequency dependence of RF signals backscattered from random media (tissues) has been used to describe the microstructure of the media. The frequency dependence of the backscattered RF signal is seen in the power spectrum. Estimates of scatterer properties (average scatterer size) from an interrogated medium are made by minimizing the average squared deviation (MASD) between the measured power spectrum and a theoretical power spectrum over an analysis bandwidth. Estimates of the scatterer properties become increasingly inaccurate as the average signal to noise ratio (SNR) over the analysis bandwidth becomes smaller. Some frequency components in the analysis bandwidth of the measured power spectrum will have smaller SNR than other frequency components. The accuracy of estimates can be improved by weighting the frequency components that have the smallest SNR less than the frequencies with the largest SNR in the MASD. A weighting function is devised that minimizes the noise effects on the estimates of the average scatterer sizes. Simulations and phantom experiments are conducted that show the weighting function gives improved estimates in an attenuating medium. The weighting function is applied to parametric images using scatterer size estimates of a rat that had developed a spontaneous mammary tumor.
从随机介质（组织）反向散射的射频（RF）信号的频率依赖性已被用于描述介质的微观结构。反向散射RF信号的频率依赖性在功率谱中可见。通过在分析带宽上最小化测量功率谱与理论功率谱之间的平均平方偏差（MASD），来对被检测介质的散射体特性（平均散射体大小）进行估计。随着分析带宽上的平均信噪比（SNR）变得更小，散射体特性的估计会变得越来越不准确。在测量功率谱的分析带宽中，一些频率成分的SNR会比其他频率成分小。通过在MASD中对SNR最小的频率成分赋予比SNR最大的频率成分更小的权重，可以提高估计的准确性。设计了一种加权函数，可将噪声对平均散射体大小估计的影响降至最低。进行的模拟和体模实验表明，该加权函数在衰减介质中能给出更好的估计。该加权函数应用于使用患有自发性乳腺肿瘤的大鼠的散射体大小估计的参数图像。
