Department of Radiology, University of Wisconsin, Madison, Wisconsin 53705, USA.
J Magn Reson Imaging. 2013 Mar;37(3):717-26. doi: 10.1002/jmri.23851. Epub 2012 Oct 10.
To investigate R2* mapping robustness in the presence of fat using in-phase echoes, without and with spectral modeling of fat (single-peak and multipeak models, respectively), using varying numbers of echoes.
Data from 88 volunteers (men/women: 52/36, ages: 55.4 ± 12.2) were randomly chosen according to magnetic resonance imaging (MRI) liver fat-fraction (%), and classified into six fat-fraction groups (1: 20 cases, 0%-<10%; 2: 20 cases, 10%-<20%; 3: 20 cases, 20%-<30%; 4: 20 cases, 30%-<40%; 5: 8 cases >40% liver fat; 6: subcutaneous fat from all cases). R2* maps obtained from five in-phase echoes (echo times: 4.8-23.8 msec) were retrospectively reconstructed using single-peak and multipeak fat modeling. R2* maps were also calculated using different numbers (2-5) of echoes.
Multipeak fat corrected R2* mapping is feasible from in-phase echoes, with noise performance comparable to single-peak R2* when using ≥ 4 echoes. Single-peak R2* showed poor robustness to varying echo time combinations in the presence of fat, where using few echoes resulted in large errors. These errors can be reduced using more echoes, or fully corrected using multipeak fat modeling. The mean R2* increased significantly with increasing fat-fraction when using single-peak R2* for any TE combination (P < 0.001), but did not vary when using multipeak R2* for any TE combination (P ≥ 0.158).
R2* mapping uncorrected for spectral complexity of fat contains protocol and fat-dependent errors (lack of robustness) in tissues with high fat content. Accounting for complex fat spectrum improves robustness and accuracy of signal fitting, with modest noise performance loss.
使用同相位回波，在不进行和进行脂肪频谱建模（单峰和多峰模型，分别）的情况下，研究 R2* 映射在脂肪存在下的稳健性，使用不同数量的回波。
根据磁共振成像（MRI）肝脏脂肪分数（%），随机选择 88 名志愿者的数据（男性/女性：52/36，年龄：55.4±12.2），并将其分为六个脂肪分数组（1：20 例，0%-<10%；2：20 例，10%-<20%；3：20 例，20%-<30%；4：20 例，30%-<40%；5：8 例>40%肝脏脂肪；6：所有病例的皮下脂肪）。使用单峰和多峰脂肪建模，从五个同相位回波（回波时间：4.8-23.8 msec）中回顾性重建 R2* 图。也使用不同数量（2-5）的回波计算 R2*图。
多峰脂肪校正 R2* 映射从同相位回波中是可行的，在使用≥4 个回波时，噪声性能与单峰 R2相当。单峰 R2 在存在脂肪的情况下，对不同的回波时间组合的稳健性较差，使用少量回波会导致较大的误差。这些误差可以通过使用更多的回波来减小，或者使用多峰脂肪建模来完全校正。当使用任何 TE 组合的单峰 R2时，R2值随脂肪分数的增加而显著增加（P<0.001），但当使用任何 TE 组合的多峰 R2时，R2值没有变化（P≥0.158）。
未校正脂肪光谱复杂性的 R2*映射在脂肪含量高的组织中包含协议和脂肪依赖性误差（缺乏稳健性）。考虑到复杂的脂肪频谱可以提高信号拟合的稳健性和准确性，同时略有噪声性能损失。
