Yokoo Takeshi, Yuan Qing, Sénégas Julien, Wiethoff Andrea J, Pedrosa Ivan
Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
J Magn Reson Imaging. 2015 Dec;42(6):1544-59. doi: 10.1002/jmri.24948. Epub 2015 May 21.
To compare Rician and non-Rician noise models for quantitative R2 * magnetic resonance imaging (MRI), in a simulation, phantom, and human study.
Synthetic 12-echo spoiled GRE (SGRE) datasets were generated with various R2 * rates (0-2000 sec(-1) ) at a signal-to-noise ratio (SNR) of 50, 20, 10, and 5. Phantoms of different MnCl2 concentrations (0-25 mM) were constructed and imaged using a 12-echo 3D SGRE sequence at 1.5T. Increasing levels of synthetic noise was added to the original data to simulate sequentially lower SNR conditions. Sixteen patients with suspected or known iron overload were imaged using 12-echo 3D SGRE at 1.5T. Various R2 * quantification methods, based on Rician and non-Rician noise models, were compared in the simulation, phantom, and human datasets.
Non-Rician R2 * estimates were variably inaccurate in the high R2 * range (>500 sec(-1) ), with SNR-dependent linear goodness-of-fit statistic (R(2) ) of 0.373-0.999. Rician R2 * estimates were accurate even in the high R2 * range, with high R(2) of 0.940-0.999 regardless of SNR. Non-Rician R2 * estimates were variably nonlinear at high MnCl2 concentrations, with SNR-dependent R(2) of 0.345-0.994. Rician R2 * estimates were linear even at high MnCl2 concentrations, with high R(2) of 0.923-0.994 regardless of SNR. Between-method agreement of the R2 * estimates was excellent in patients with low ferritin but poor in patients with high ferritin. Rician R2 * estimates had excellent correlation with ferritin (r = 0.966 P < 0.001).
Rician R2 * estimates were most consistent in the high R2 * conditions and under varying SNR, and may be more reliable when high iron load is suspected.
在模拟、体模和人体研究中比较用于定量R2 *磁共振成像（MRI）的莱斯噪声模型和非莱斯噪声模型。
生成了合成的12回波扰相梯度回波（SGRE）数据集，其具有各种R2 *率（0 - 2000秒^(-1)），信噪比（SNR）分别为50、20、10和5。构建了不同MnCl2浓度（0 - 25 mM）的体模，并使用1.5T的12回波3D SGRE序列进行成像。向原始数据中添加逐渐增加水平的合成噪声，以依次模拟更低的SNR条件。对16例疑似或已知铁过载的患者使用1.5T的12回波3D SGRE进行成像。在模拟、体模和人体数据集中比较了基于莱斯噪声模型和非莱斯噪声模型的各种R2 *定量方法。
在高R2 *范围（＞500秒^(-1)）内，非莱斯R2 *估计值存在不同程度的不准确，信噪比相关的线性拟合优度统计量（R(2)）为0.373 - 0.999。即使在高R2 *范围内，莱斯R2 *估计值也很准确，无论信噪比如何，R(2)都高达0.940 - 0.999。在高MnCl2浓度下，非莱斯R2 *估计值存在不同程度的非线性，信噪比相关的R(2)为0.345 - 0.994。即使在高MnCl2浓度下，莱斯R2 *估计值也是线性的，无论信噪比如何，R(2)都高达0.923 - 0.994。在低铁蛋白患者中，R2 *估计值的方法间一致性良好，但在高铁蛋白患者中较差。莱斯R2 *估计值与铁蛋白具有极好的相关性（r = 0.966，P ＜ 0.001）。
莱斯R2 *估计值在高R2 *条件下以及不同信噪比情况下最为一致，当怀疑有高铁负荷时可能更可靠。
