Department of Biomedical Engineering, University of Alberta, Edmonton, Canada.
Magn Reson Med. 2013 Nov;70(5):1340-6. doi: 10.1002/mrm.24568. Epub 2013 Jan 16.
Transverse relaxation (T2 ) mapping has many applications, including imaging of iron accumulation in grey matter. Using the typical multiecho spin-echo sequence with long echo trains, stimulated echo compensation can enable T2 fitting under conditions of variable radio frequency homogeneity arising from slice profile and in-plane radio frequency variation. Substantial reduction in the number of refocusing pulses could enable use at high magnetic fields where specific absorption rate is a major limitation, and enable multislice use with reduced incidental magnetization transfer at all field strengths. We examine the effect of reduced echo train lengths and multislice imaging on T2 fitting using stimulated echo compensation applied to iron-rich subcortical grey matter in human brain at 4.7 T. Our findings indicate that reducing from 20 echoes to as few as four echoes can maintain consistent T2 values when using stimulated echo compensation in grey and white matter, but not for cerebrospinal fluid. All territories produce marginal results when using standard exponential fitting. Savings from reduced echoes can be used to substantially increase slice coverage. In multislice mode, the resulting incidental magnetization transfer decreased brain signal but had minimal effect on measured T2 values.
横向弛豫（T2）映射有许多应用，包括脑灰质中铁积累的成像。使用具有长回波链的典型多回波自旋回波序列，通过刺激回波补偿，可以在由于切片轮廓和平面射频变化引起的射频不均匀性条件下进行 T2 拟合。减少重聚焦脉冲的数量可以在特定吸收率是主要限制的高磁场中使用，并在所有场强下使用减少偶然磁化转移的多切片。我们研究了减少回波链长度和多切片成像对使用刺激回波补偿的 T2 拟合的影响，该补偿应用于 4.7T 人脑富含铁的皮质下灰质。我们的发现表明，在灰质和白质中使用刺激回波补偿时，从 20 个回波减少到 4 个回波可以保持一致的 T2 值，但对于脑脊液则不行。所有领域在使用标准指数拟合时都产生了边缘结果。减少回波的节省可以用于大大增加切片覆盖范围。在多切片模式下，产生的偶然磁化转移会降低脑信号，但对测量的 T2 值影响最小。
