Sehgal C M
Department of Radiology, University of Pennsylvania, Philadelphia 19104-6086.
J Acoust Soc Am. 1993 Oct;94(4):1944-52. doi: 10.1121/1.407517.
This study establishes quantitative laws by which the magnitude of ultrasonic scatter is related to the gross chemical composition of tissues, viz., water, fat, and collagen. Tissues are modeled as immiscible mixtures, the constituents of which are uniformly dispersed over the volume. Each component of the mixture causes the ultrasonic velocity of the medium to fluctuate about the mean value. Such localized variations in the refractive index of a medium cause propagating sound waves to scatter. It is proposed that the contribution of each component to the total fluctuation is in proportion to its volume fraction. The analysis shows that the scatter of ultrasound exhibits a complex nonlinear dependence on the concentrations of the individual components. From the knowledge of sound speed of individual components, total velocity fluctuations are determined for binary and three-component models of the tissue. Comparison of these values, with those estimated from scatter measurements, shows a close correlation between the two sets. Collagen, although present in relatively small amounts in soft tissues, contributes a significant portion of the total scatter. However, both fat and collagen fractions must be taken into consideration to account for the major fraction of the observed scatter. In conclusion, there is a direct relationship between tissue composition and scatter from tissues. Such dependence must also be taken into consideration, in addition to the correlation function and correlation lengths to explain backscatter or loss in a transmitted signal due to scatter from tissues.
本研究建立了定量规律，通过这些规律，超声散射的大小与组织的总体化学成分相关，即水、脂肪和胶原蛋白。组织被建模为不混溶的混合物，其成分在整个体积中均匀分散。混合物的每个成分都会使介质的超声速度围绕平均值波动。介质折射率的这种局部变化会导致传播的声波散射。有人提出，每个成分对总波动的贡献与其体积分数成正比。分析表明，超声散射对各个成分的浓度表现出复杂的非线性依赖关系。根据各个成分的声速知识，确定了组织的二元和三元模型的总速度波动。将这些值与从散射测量估计的值进行比较，结果表明两组值之间存在密切相关性。胶原蛋白虽然在软组织中的含量相对较少，但却占总散射的很大一部分。然而，必须同时考虑脂肪和胶原蛋白的比例，才能解释观察到的散射的主要部分。总之，组织成分与组织散射之间存在直接关系。除了相关函数和相关长度之外，在解释由于组织散射导致的背向散射或透射信号损失时，也必须考虑这种依赖关系。
