Rubert Nicholas, Varghese Tomy
IEEE Trans Ultrason Ferroelectr Freq Control. 2013 Jun;60(6):1061-73. doi: 10.1109/TUFFC.2013.2670.
It has been hypothesized that estimates of mean scatterer spacing are useful indicators for pathological changes to the liver. A commonly employed estimator of the mean scatterer spacing is the location of the maximum of the collapsed average of coherence of the ultrasound radio-frequency signal. To date, in ultrasound, estimators for this quantity have been calculated with a single taper. Using frequency-domain Monte Carlo simulations, we demonstrate that multi-taper estimates of coherence are superior to single-taper estimates for predicting mean scatterer spacing. Scattering distributions were modeled with Gamma-distributed scatterers for fractional standard deviations in scatterer spacings of 5, 10, and 15% at a mean scatterer spacing of 1 mm. Additionally, we demonstrate that we can distinguish between ablated liver tissue and unablated liver tissue based on signal coherence. We find that, on the average, signal coherence is elevated in the liver relative to signal coherence of received echoes from thermally ablated tissue. Additionally, our analysis indicates that a tissue classifier utilizing the multi-taper estimate of coherence has the potential to distinguish between ablated and unablated tissue types better than a single-taper estimate of coherence. For a gate length of 5 mm, we achieved an error rate of only 8.7% when sorting 23 ablated and 23 unablated regions of interest (ROIs) into classes based on multi-taper calculations of coherence.
据推测，平均散射体间距的估计值是肝脏病理变化的有用指标。一种常用的平均散射体间距估计器是超声射频信号相干性折叠平均值最大值的位置。迄今为止，在超声领域，该量的估计器一直是用单一窗函数计算的。通过频域蒙特卡罗模拟，我们证明了相干性的多窗函数估计在预测平均散射体间距方面优于单一窗函数估计。在平均散射体间距为1毫米时，对于散射体间距分数标准偏差为5%、10%和15%的情况，用伽马分布的散射体对散射分布进行了建模。此外，我们证明了基于信号相干性能够区分消融的肝组织和未消融的肝组织。我们发现，平均而言，相对于热消融组织接收到的回波的信号相干性，肝脏中的信号相干性有所提高。此外，我们的分析表明，利用相干性多窗函数估计的组织分类器比相干性单一窗函数估计更有潜力区分消融和未消融的组织类型。对于5毫米的门长，当基于相干性的多窗函数计算将23个消融的和23个未消融的感兴趣区域（ROI）分类时，我们实现的错误率仅为8.7%。
