Iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL): Application with fast spin-echo imaging
Iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL): Application with fast spin-echo imaging
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DOI：
10.1002/mrm.20624
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发表时间：
2005-09-01
影响因子：
3.3
通讯作者：
Pelc, NJ
中科院分区：
文献类型：
--
作者：
Reeder, SB;Pineda, AR;Pelc, NJ
基于化学位移的方法通常被用来实现均匀的水-脂肪分离，这对细菌的不均质性不敏感。许多自旋回波(SE)或快速自旋回波(FSE)方法获得围绕SE对称移动的三个回波，产生由水-脂肪化学位移引起的随时间变化的相移。这项工作表明，对称获取的回波会造成图像质量下降的伪影。从理论上讲，任何一种水脂分离方法的噪声性能都取决于体素中水和脂肪的比例，以及回波相对于SE的位置。为了解决这个问题，我们提出了一种名为“回波不对称最小二乘估计迭代分解水和脂肪”的方法(理想)。该技术将非对称采集的回波与迭代最小二乘分解算法相结合，以最大限度地提高噪声性能。理论计算表明，当回波的相对相位被2pi/3分开，中间回波中心位于pi/2+pi k(k=任意整数)，即(-pi/6+pi k，pi/2+pi k，7pi/6+pi k)时，最佳回波组合出现。只有有了这些回声组合，噪声性能才能达到最大可能，并且不依赖于水和脂肪的比例。油水模型的理论计算结果与实验结果吻合较好，表明迭代最小二乘分解法是一种有效的估计器。
Chemical shift based methods are often used to achieve uniform water-fat separation that is insensitive to B. inhomogeneities. Many spin-echo (SE) or fast SE (FSE) approaches acquire three echoes shifted symmetrically about the SE, creating time-dependent phase shifts caused by water-fat chemical shift. This work demonstrates that symmetrically acquired echoes cause artifacts that degrade image quality. According to theory, the noise performance of any water-fat separation method is dependent on the proportion of water and fat within a voxel, and the position of echoes relative to the SE. To address this problem, we propose a method termed "iterative decomposition of water and fat with echo asymmetric and least-squares estimation" (IDEAL). This technique combines asymmetrically acquired echoes with an iterative least-squares decomposition algorithm to maximize noise performance. Theoretical calculations predict that the optimal echo combination occurs when the relative phase of the echoes is separated by 2 pi/3, with the middle echo centered at pi/2+pi k (k = any integer), i.e., (-pi/6+pi k, pi/2+pi k, 7 pi/6+pi k). Only with these echo combinations can noise performance reach the maximum possible and be independent of the proportion of water and fat. Close agreement between theoretical and experimental results obtained from an oil-water phantom was observed, demonstrating that the iterative least-squares decomposition method is an efficient estimator.