Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada.
Magn Reson Med. 2012 Jun;67(6):1803-14. doi: 10.1002/mrm.23157. Epub 2011 Oct 19.
We propose a multicomponent fitting algorithm for multiecho T(2) data which allows for correction of T(2) distributions in the presence of stimulated echoes. Tracking the population of spins in many coherence pathways via the iterated method of the Extended Phase Graph algorithm allows for accurate quantification of echo magnitudes. The resulting decay curves allow for correction of errors due to nonideal refocusing pulses as a result of inhomogeneities in the B(1) transmit field. Non-Negative Least Squares fitting is used to quantify the magnitude of T(2) components at various T(2) values. This method, allowing calculation of the T(2) distribution with simultaneous extraction of the refocusing pulse flip angle, requires no change to image acquisition procedures and no extra data input. Validation by means of both simulations and in vivo data shows excellent interscan reproducibility while vastly improving the accuracy of extracted T(2) parameters in voxels where poor B(1) homogeneity leads to refocusing pulse flip angles significantly less than 180°. Most notably, myelin water fraction values in these regions are found to have increased consistency and accuracy.
我们提出了一种用于多回波 T(2) 数据的多分量拟合算法，该算法允许在存在受激回波的情况下校正 T(2) 分布。通过扩展相位图算法的迭代方法跟踪许多相干路径中的自旋群体，可实现回波幅度的准确量化。所得的衰减曲线可校正由于 B(1) 发射场不均匀性导致的非理想聚焦脉冲引起的误差。非负最小二乘拟合用于量化在各种 T(2) 值下 T(2) 分量的幅度。该方法允许在不改变图像采集程序且无需额外数据输入的情况下计算 T(2) 分布并同时提取聚焦脉冲翻转角。通过模拟和体内数据验证，该方法在显著提高聚焦脉冲翻转角显著小于 180°的体素中提取的 T(2) 参数的准确性的同时，还具有出色的扫描间可重复性。值得注意的是，在这些区域中，髓鞘水分数值的一致性和准确性得到了提高。
