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首页> 外文期刊>Physics in medicine and biology. >An automatic differentiation-based gradient method for inversion of the shear wave equation in magnetic resonance elastography: specific application in fibrous soft tissues
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An automatic differentiation-based gradient method for inversion of the shear wave equation in magnetic resonance elastography: specific application in fibrous soft tissues

机译：一种基于微分的自动梯度法，用于磁共振弹性成像中剪切波方程的反演：在纤维软组织中的特定应用

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摘要

Quantitative and accurate measurement of in vivo mechanical properties using dynamic elastography has been the scope of many research efforts over the past two decades. Most of the shear-wave-based inverse approaches for magnetic resonance elastography (MRE) make the assumption of isotropic viscoelasticity. In this paper, we propose a quantitative gradient method for inversion of the shear wave equation in anisotropic media derived from a full waveform description using analytical viscoelastic Green formalism and automatic differentiation. The abilities and performances of the proposed identification method are first evaluated on numerical phantoms calculated in a transversely isotropic medium, and subsequently on experimental MRE data measured on an isotropic hydrogel phantom, on an anisotropic cryogel phantom and on an ex vivo fibrous muscle. The experiments are carried out by coupling circular shear wave profiles generated by acoustic radiation force and MRE acquisition of the wave front. Shear modulus values obtained by our MRE method are compared to those obtained by rheometry in the isotropic hydrogel phantom, and are found to be in good agreement despite non-overlapping frequency ranges. Both the cryogel and the ex vivo muscle are found to be anisotropic. Stiffness values in the longitudinal direction are found to be 1.8 times and 1.9 times higher than those in the transverse direction for the cryogel and the muscle, respectively. The proposed method shows great perspectives and substantial benefits for the in vivo quantitative investigation of complex mechanical properties in fibrous soft tissues.
机译：在过去的二十年中，使用动态弹性成像技术定量准确地测量体内机械性能一直是许多研究工作的范围。磁共振弹性成像（MRE）的大多数基于剪切波的逆方法都假设各向同性粘弹性。在本文中，我们提出了一种定量梯度方法，用于各向异性介质中剪切波方程的反演，该方法使用解析粘弹性格林形式和自动微分从完整的波形描述中得出。首先对在横向各向同性介质中计算出的数字体模进行评估，然后对在各向同性水凝胶体模，各向异性冷冻凝胶体模和离体纤维肌上测量的实验MRE数据进行评估，从而对所提出的识别方法的能力和性能进行评估。通过耦合由声辐射力产生的圆形剪切波剖面和波前的MRE采集来进行实验。通过我们的MRE方法获得的剪切模量值与在各向同性水凝胶体模中通过流变法获得的剪切模量值进行了比较，尽管频率范围不重叠，但发现它们具有很好的一致性。发现冷冻凝胶和离体肌肉都是各向异性的。对于冷冻凝胶和肌肉，纵向的刚度值分别是横向的1.8倍和1.9倍。所提出的方法显示出广阔的前景，并为体内定量研究纤维软组织的复杂机械性能带来了巨大的好处。

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