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首页> 外文期刊>IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control >Nonlinear Imaging of Microbubble Contrast Agent Using the Volterra Filter: In Vivo Results
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Nonlinear Imaging of Microbubble Contrast Agent Using the Volterra Filter: In Vivo Results

机译：使用Volterra滤波器对微泡造影剂进行非线性成像：体内结果

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摘要

A nonlinear filtering approach to imaging the dynamics of microbubble ultrasound contrast agents (UCAs) in microvessels is presented. The approach is based on the adaptive third-order Volterra filter (TVF), which separates the linear, quadratic, and cubic components from beamformed pulse-echo ultrasound data. The TVF captures polynomial nonlinearities utilizing the full spectral components of the echo data and not from prespecified bands, e.g., second or third harmonics. This allows for imaging using broadband pulse transmission to preserve the axial resolution and the SNR. In this paper, we present the results from imaging the UCA activity in a 200- μm cellulose tube embedded in a tissue-mimicking phantom using a linear array diagnostic probe. The contrast enhancement was quantified by computing the contrast-to-tissue ratio (CTR) for the different imaging components, i.e., B-mode, pulse inversion (PI), and the TVF components. The temporal mean and standard deviation of the CTR values were computed for all frames in a given data set. Quadratic and cubic images, referred to as QB-mode and CB-mode, produced higher mean CTR values than B-mode, which showed improved sensitivity. Compared with PI, they produced similar or higher mean CTR values with greater spatial specificity. We also report in vivo results from imaging UCA activity in an implanted LNCaP tumor with heterogeneous perfusion. The temporal means and standard deviations of the echogenicity were evaluated in small regions with different perfusion levels in the presence and absence of UCA. The in vivo measurements behaved consistently with the corresponding calculations obtained under microflow conditions in vitro. Specifically, the nonlinear VF components produced larger increases in the temporal mean and standard deviation values compared with B-mode in regions with low to relatively high perfusion. These results showed that polynomial filters such as the TVF can provide an important tool for imaging UCA activity in regions with heterogeneous perfusion as is the case in some tumors and ischemic tissues.
机译：提出了一种非线性滤波方法来对微血管中微泡超声造影剂（UCA）的动力学进行成像。该方法基于自适应三阶Volterra滤波器（TVF），该滤波器将线性，二次和三次分量与波束形成的脉冲回波超声数据分开。 TVF利用回波数据的全部频谱分量而不是从预先规定的频段（例如二次或三次谐波）中捕获多项式非线性。这允许使用宽带脉冲传输进行成像以保留轴向分辨率和SNR。在本文中，我们介绍了使用线性阵列诊断探针对嵌入在模仿组织模型中的200μm纤维素管中的UCA活性进行成像的结果。通过计算不同成像成分（即B模式，脉冲反转（PI）和TVF成分）的组织对比度（CTR）来量化对比度增强。计算给定数据集中所有帧的CTR值的时间平均值和标准偏差。二次和三次图像（称为QB模式和CB模式）产生的平均CTR值比B模式更高，显示出更高的灵敏度。与PI相比，他们产生的相似或更高的平均CTR值具有更高的空间特异性。我们还报告了异种灌注植入LNCaP肿瘤中的UCA活性成像的体内结果。在存在和不存在UCA的情况下，在不同灌注水平的小区域中评估回声性的时间平均值和标准偏差。体内测量与在体外微流条件下获得的相应计算结果一致。具体而言，在低或相对较高的灌注区域中，与B模式相比，非线性VF分量在时间平均值和标准偏差值上产生了更大的增加。这些结果表明，多项式过滤器（例如TVF）可以提供一种重要的工具，用于对异质性灌注区域中的UCA活性进行成像，就像某些肿瘤和局部缺血组织中的情况一样。

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