Brain Health Imaging Centre, Centre for Addiction and Mental Health, Toronto, Ontario M5T 1R8, Canada; Department of Psychiatry, University of Toronto, Toronto, Ontario M5T 1R8, Canada.
Brain Health Imaging Centre, Centre for Addiction and Mental Health, Toronto, Ontario M5T 1R8, Canada.
Magn Reson Imaging. 2021 Apr;77:88-98. doi: 10.1016/j.mri.2020.12.009. Epub 2020 Dec 15.
Large consistent differences have been observed between maps of the flip angle correction factor (commonly called "B-maps") produced with different fast methods in the human brain. We present an empirical procedure for first-order multiplicative bias correction that can be applied when more than one B-mapping method is available. We use a B-map measurement in a calibration phantom as a reference and the voxel-wise histogram mode between ratios of B-maps produced from different methods to calculate determine the bias as a multiplicative correcting scale factor. Institutional implementations of four common methods of B-mapping were assessed: Method of Slopes, FSE and EPI double angle methods (DAM), and Bloch-Siegert. In human subjects, the multiplicative bias used to correct for each of the four methods was: Method of Slopes = 1.005, FSE-DAM = 0.956, EPI-DAM = 1.080, and Bloch-Siegert = 1.128. Scaling to remove this bias between methods produces more consistent B-maps which enable more consistent values for any computations requiring flip angle correction. In addition, we present evidence that the corrected B maps, using our calibration method, are also more accurate.
在人脑的不同快速方法产生的翻转角校正因子（通常称为“B 图”）之间，已经观察到了很大的一致差异。我们提出了一种用于一阶乘法偏差校正的经验程序，当有多种 B 映射方法可用时，可以应用该程序。我们使用校准体模中的 B 映射测量值作为参考，并使用来自不同方法的 B 映射比值的体素直方图模式来计算确定偏差作为乘法校正比例因子。评估了四种常见 B 映射方法的机构实现：斜率法、FSE 和 EPI 双角度方法（DAM）以及 Bloch-Siegert。在人体受试者中，用于校正这四种方法的乘法偏差分别为：斜率法=1.005、FSE-DAM=0.956、EPI-DAM=1.080 和 Bloch-Siegert=1.128。缩放以消除方法之间的这种偏差会产生更一致的 B 图，从而为任何需要翻转角校正的计算提供更一致的值。此外，我们还提供了证据表明，使用我们的校准方法校正后的 B 图也更准确。
