论文标题
单个B值数据中的免费水DTI估计似乎是合理的，但必须谨慎解释
Free water DTI estimates from single b-value data might seem plausible but must be interpreted with care
论文作者
论文摘要
目的：游离水扩散张量成像（FWE-DTI）已被广泛用于区分自由水的增加（FW）部分体积的影响与组织在健康衰老和退化性疾病中的扩散。由于FWE-DTI拟合仅适用于多壳采集，因此提出了一种正则化梯度下降（RGD）方法，以启用适用于单壳数据，在诊所中更常见。但是，RGD方法的有效性评估不佳。这项研究旨在量化FWE-DTI程序在单壳数据和多壳数据上的特异性。方法：在体内扩散数据集以及单壳和多壳合成信号（包括RGD和标准的非线性最小二乘（NLS）方法）上测试了不同的FWE-DTI拟合程序。进行单素模拟以比较初始化方法。进行多素幻影模拟，以评估方法之间的空间正则化影响。为了测试算法的特异性，模拟了具有两种不同类型病变的幻象：平均扩散率（MD）增加或FW增加。结果：通过从体内数据中的单壳中获得的RGD获得了合理的参数图。这些地图的合理性证明是由初始化确定的。插入体内数据中的模拟病变的测试表明，与NLS算法相反，RGD方法无法将FW与组织MD的改变区分开。结论：RGD FWE-DTI具有有限的特异性，因此，应仔细解释其来自单壳数据的结果。如果可能的话，应该首选多壳采集和NLS方法。
Purpose: Free water elimination diffusion tensor imaging (FWE-DTI) has been widely used to distinguish increases of free water (FW) partial volume effects from tissue's diffusion in healthy ageing and degenerative diseases. Since the FWE-DTI fitting is only well posed for multi-shell acquisitions, a regularized gradient descent (RGD) method was proposed to enable application to single-shell data, more common in the clinic. However, the validity of the RGD method has been poorly assessed. This study aims to quantify the specificity of FWE-DTI procedures on single- and multi-shell data. Methods: Different FWE-DTI fitting procedures were tested on an open-source in vivo diffusion dataset and single- and multi-shell synthetic signals, including the RGD and standard non-linear least squares (NLS) methods. Single-voxel simulations were carried out to compare initialization approaches. A multi-voxel phantom simulation was performed to evaluate the impact of spatial regularization when comparing between methods. To test the algorithms' specificity, phantoms with two different types of lesions were simulated: with increased mean diffusivity (MD) or with increased FW. Result: Plausible parameter maps were obtained with RGD from single-shell in vivo data. The plausibility of these maps was shown to be determined by the initialization. Tests with simulated lesions inserted into the in vivo data revealed that the RGD approach cannot distinguish FW from tissue MD alterations, contrarily to the NLS algorithm. Conclusion: RGD FWE-DTI has limited specificity and, thus, its results from single-shell data should be carefully interpreted. When possible, multi-shell acquisitions and the NLS approach should be preferred instead.
