An automatic differentiation-based gradient method for inversion of the shear wave equation in magnetic resonance elastography: specific application in fibrous soft tissues
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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DOI：
10.1088/0031-9155/61/13/5000
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发表时间：
2016-07-07
影响因子：
3.5
通讯作者：
Vappou, Jonathan
中科院分区：
文献类型：
--
作者：
Chatelin, Simon;Charpentier, Isabelle;Vappou, Jonathan
在过去的二十年里，利用动态弹性成像对体内力学性能进行定量和精确的测量已经成为许多研究工作的范围。大多数基于剪切波的磁共振弹性成像反演方法都假定各向同性粘弹性。在本文中，我们提出了一种定量梯度方法来反演各向异性介质中横波方程，该方法是利用分析粘弹性格林形式和自动微分的全波形描述导出的。首先在横向各向同性介质中计算的数值模型上对所提出的识别方法的能力和性能进行了评估，然后在各向同性水凝胶模型、各向异性低温凝胶模型和离体纤维肌肉上测量的实验MRE数据上进行了评估。实验采用声辐射力产生的圆横波剖面与波前的MRE采集相耦合的方法进行。我们的MRE方法获得的剪切模量值与流变法在各向同性水凝胶幻影中获得的剪切模量值进行了比较，发现尽管频率范围不重叠，但它们的一致性很好。低温凝胶和离体肌肉都具有各向异性。研究发现，低温凝胶和肌肉的纵向刚度值分别是横向刚度值的1.8倍和1.9倍。所提出的方法为纤维软组织复杂力学性能的体内定量研究显示了很大的前景和实质性的好处。
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.