Algebraic Decomposition of Fat and Water in MRI
Algebraic Decomposition of Fat and Water in MRI
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DOI：
10.1109/tmi.2008.927344
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发表时间：
2009-02-01
影响因子：
10.6
通讯作者：
Sutton, Bradley P.
中科院分区：
文献类型：
--
作者：
Jacob, Mathews;Sutton, Bradley P.
磁共振成像(MRI)数据的分解生成水和脂肪图像在医学成像中有几个应用，包括脂肪抑制和内脏脂肪的量化。我们引入了一种新的算法来克服当前分析和迭代分解方案中的一些问题。与传统的分析方案相比，我们的方法足够通用，可以容纳任何均匀的回声位移模式、任何数量的代谢物和信号样本。与使用光滑场映射初始化来解决理想算法的模糊性的区域增长方法不同，我们提出在最终的场映射估计上使用显式光滑度约束。为此，在求根之前，我们估计所有体素的可行解的数目。这种方法使算法能够计算所有的可行根，从而避免收敛到错误的解。该估计过程基于对谐波恢复(HR)框架的修改，以考虑频率中的化学位移依赖。与标准的线性HR框架相比，我们得到了频移作为一组二次方程的公根。在大多数具有多个可行解的像素上，可以通过对解的简单排序来识别正确的解。我们使用区域合并算法来解决剩余的歧义和相位包裹。实验结果表明，该算法在不影响噪声性能的前提下，消除了现有算法的大部分困难。此外，所提出的算法在计算上也更加高效。
The decomposition of magnetic resonance imaging (MRI) data to generate water and fat images has several applications in medical imaging, including fat suppression and quantification of visceral fat. We introduce a novel algorithm to overcome some of the problems associated with current analytical and iterative decomposition schemes. In contrast to traditional analytical schemes, our approach is general enough to accommodate any uniform echo-shift pattern, any number of metabolites and signal samples. In contrast to region-growing method that use a smooth field-map initialization to resolve the ambiguities with the IDEAL algorithm, we propose to use an explicit smoothness constraint on the final fieldmap estimate. Towards this end, we estimate the number of feasible solutions at all the voxels, prior to the evaluation of the roots. This approach enables the algorithm to evaluate all the feasible roots, thus avoiding the convergence to the wrong solution. The estimation procedure is based on a modification of the harmonic retrieval (HR) framework to account for the chemical shift dependence in the frequencies. In contrast to the standard linear HR framework, we obtain the frequency shift as the common root of a set of quadratic equations. On most of the pixels with multiple feasible solutions, the correct solution can be identified by a simple sorting of the solutions. We use a region-merging algorithm to resolve the remaining ambiguity and phase-wrapping. Experimental results indicate that the proposed algebraic scheme eliminates most of the difficulties with the current schemes, without compromising the noise performance. Moreover, the proposed algorithm is also computationally more efficient.