The effect on precision and T1 bias comparing two flip angles when estimating muscle fat infiltration using fat-referenced chemical shift-encoded imaging,NMR in Biomedicine

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The effect on precision and T1 bias comparing two flip angles when estimating muscle fat infiltration using fat-referenced chemical shift-encoded imaging
NMR in Biomedicine ( IF 2.7 ) Pub Date : 2021-07-07 , DOI: 10.1002/nbm.4581
Anette Karlsson _{1,

2} , Anneli Peolsson _{2,

3} , Thobias Romu ₄ , Olof Dahlqvist Leinhard _{2,

4,

5} , Anna-Clara Spetz Holm ₆ , Sofia Thorell ₆ , Janne West _{1,

2,

4} , Magnus Borga _{1,

2,

4}

Affiliation

Investigation of the effect on accuracy and precision of different parameter settings is important for quantitative MRI. The purpose of this study was to investigate T1 bias and precision for muscle fat infiltration (MFI) measurements using fat-referenced chemical shift MFI measurements at flip angles of 5° and 10°. The fat-referenced measurements were compared with fat fractions, which is a more commonly used measure of MFI. This retrospective study was performed on data from a clinical intervention study including 40 postmenopausal women. Test and retest images were acquired with a 3-T scanner using four-point 3D spoiled gradient multiecho acquisition. Postprocessing included T2* correction and fat-referenced calibration, where the fat signal was calibrated using adipose tissue as reference. The mean MFI was calculated in six different muscle regions using both the fat-referenced fat signal and the fat fraction, defined as the fat signal divided by the sum of the fat and water signals. Both methods used the same fat and water images as input. The variance of the difference between mean MFI from test and retest was used as the measure of precision. The signal-to-noise ratio (SNR) characteristics were analyzed by measuring the full width at half maximum (FWHM) of the fat signal distribution. There was no difference in the mean MFI at different flip angles for the fat-referenced technique (p = 0.66), while the measured fat fractions were 3.3 percentage points larger for 10° compared with 5° (p < 0.001). No significant difference in the precision was found in any of the muscles analyzed. However, the FWHM of the fat signal distribution was significantly (p = 0.01) lower at 10°. This strenghtens the hypothesis that fat-referenced MFI is insensitive to flip angle-induced T1 bias in CSE-MRI, enabling usage of a higher and more SNR-effective flip angle. The lower FWHM in fat-referenced MFI at 10° indicates that high flip angle acquisition is advantageous even although no significant differences in precision were observed comparing 5° and 10°.

中文翻译：

使用脂肪参考化学位移编码成像估计肌肉脂肪浸润时比较两个翻转角对精度和 T1 偏差的影响

研究不同参数设置对准确性和精度的影响对于定量 MRI 很重要。本研究的目的是使用 5° 和 10° 翻转角的脂肪参考化学位移 MFI 测量来研究肌肉脂肪浸润 (MFI) 测量的 T1 偏差和精度。脂肪参考测量值与脂肪分数进行了比较，脂肪分数是更常用的 MFI 测量方法。这项回顾性研究是根据一项临床干预研究的数据进行的，该研究包括 40 名绝经后妇女。使用四点 3D 破坏梯度多回波采集的 3-T 扫描仪采集测试和重新测试图像。后处理包括 T2* 校正和脂肪参考校准，其中脂肪信号使用脂肪组织作为参考进行校准。使用脂肪参考脂肪信号和脂肪分数计算六个不同肌肉区域的平均 MFI，定义为脂肪信号除以脂肪和水信号的总和。两种方法都使用相同的脂肪和水图像作为输入。测试和重新测试的平均 MFI 之间的差异的方差用作精度的度量。通过测量脂肪信号分布的半峰全宽 (FWHM) 来分析信噪比 (SNR) 特性。对于脂肪参考技术，不同翻转角度的平均 MFI 没有差异（测试和重新测试的平均 MFI 之间的差异的方差用作精度的度量。通过测量脂肪信号分布的半峰全宽 (FWHM) 来分析信噪比 (SNR) 特性。对于脂肪参考技术，不同翻转角度的平均 MFI 没有差异（测试和重新测试的平均 MFI 之间的差异的方差用作精度的度量。通过测量脂肪信号分布的半峰全宽 (FWHM) 来分析信噪比 (SNR) 特性。对于脂肪参考技术，不同翻转角度的平均 MFI 没有差异（p = 0.66），而 10° 测量的脂肪分数比 5° 高 3.3 个百分点（p < 0.001）。在所分析的任何肌肉中都没有发现精确度的显着差异。然而，脂肪信号分布的 FWHM在 10°时显着降低 ( p = 0.01)。这加强了脂肪参考 MFI 对 CSE-MRI 中翻转角引起的 T1 偏差不敏感的假设，从而能够使用更高和更有效的 SNR 翻转角。脂肪参考 MFI 在 10° 时的 FWHM 较低表明高翻转角采集是有利的，即使在比较 5° 和 10° 时没有观察到显着的精度差异。

更新日期：2021-07-07

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