Oosterveld B J, Thijssen J M, Verhoef W A
Ultrason Imaging. 1985 Apr;7(2):142-60. doi: 10.1177/016173468500700204.
B-mode echograms were simulated by employing the impulse response method in transmission and reception using a discrete scatterer tissue model, with and without attenuation. The analytic signal approach was used for demodulation of the RF A-mode lines. The simulations were performed in 3-D space and compared to B-mode echograms obtained from experiments with scattering tissue phantoms. The average echo amplitude appeared to increase towards the focus and to decrease beyond it. In the focal zone, the average amplitude increased proportionally to the square root of the scatterer density. The signal to noise ratio (SNR) was found to be independent of depth, i.e., 1.91 as predicted for a Rayleigh distribution of gray levels, although a minimum was found in the focal zone at relatively low scatterer densities. The SNR continuously increased with increasing scatterer density and reached the limit of 1.91 at relatively high densities (greater than 10(4) cm-3). The lateral full width at half maximum (FWHM) of the two dimensional autocovariance function of the speckle increased continuously from the transducer face to far beyond the focus and decreased thereafter due to the diffraction effect. The lateral FWHM decreased proportionally to the logarithm of the scatterer density at low densities and reached a limit at high densities. Introduction of attenuation in the simulated tissue resulted in a much more pronounced depth dependence of the texture. The axial FWHM was independent of the distance to the transducer to a first approximation and decreased slightly with increasing scatterer density until a limit was reached at densities larger than 10(3) cm-3. This limit was in agreement with theory. The experiments confirmed the simulations and it can be concluded that the presented results are of great importance to the understanding of B-mode echograms and to the potential use of the analysis of B-mode texture for tissue characterization.
使用离散散射体组织模型，通过发射和接收中的脉冲响应方法，在有衰减和无衰减的情况下模拟了B型超声图。采用解析信号方法对射频A模式线进行解调。模拟在三维空间中进行，并与从散射组织体模实验获得的B型超声图进行比较。平均回波幅度似乎朝着焦点增加，并在焦点之外减小。在聚焦区，平均幅度与散射体密度的平方根成正比增加。发现信噪比（SNR）与深度无关，即对于灰度的瑞利分布预测为1.91，尽管在相对较低的散射体密度下在聚焦区发现了最小值。信噪比随着散射体密度的增加而持续增加，并在相对较高的密度（大于10⁴ cm⁻³）下达到1.91的极限。散斑二维自协方差函数的横向半高全宽（FWHM）从换能器表面到远超过焦点处持续增加，此后由于衍射效应而减小。在低密度下，横向FWHM与散射体密度的对数成比例减小，并在高密度下达到极限。在模拟组织中引入衰减导致纹理的深度依赖性更加明显。轴向FWHM在一阶近似下与到换能器的距离无关，并且随着散射体密度的增加而略有减小，直到在密度大于10³ cm⁻³时达到极限。该极限与理论一致。实验证实了模拟结果，可以得出结论，所呈现的结果对于理解B型超声图以及B型纹理分析在组织表征中的潜在应用非常重要。
