Fleysher Roman, Fleysher Lazar, Liu Songtao, Gonen Oded
Department of Radiology, NYU School of Medicine, New York, NY 10016, USA.
Magn Reson Imaging. 2008 Jul;26(6):781-9. doi: 10.1016/j.mri.2008.01.024. Epub 2008 May 22.
Fast, high-resolution, longitudinal relaxation time (T1) mapping is invaluable in clinical and research applications. It has been shown that two spoiled gradient recalled echo (SPGR) images acquired in steady state with variable flip angles is an attractive alternative to the multi-image sets previously acquired with inversion or saturation recovery. The known sensitivity of the two-point method to transmit radiofrequency field (B1) inhomogeneity exacerbated at 3 T and above, however, mandates its combination with an additional, time-consuming and possibly specific-absorption-rate-intensive B1 measurement, preventing direct migration of the method to these fields. To address this, we introduce a method designed to be free of systematic errors caused by B1 inhomogeneity in which the value of T1 is extracted from three SPGR images acquired with echo planar imaging (EPI) readout. The precision of the T1 maps produced is found to be comparable to the two-point method, while the accuracy is greatly improved in the same time and spatial resolution. A welcome byproduct of the method is a map of B1 that can be used to correct other acquisitions in the same session. Tables of the optimal acquisition protocols are provided for several total imaging times.
快速、高分辨率的纵向弛豫时间（T1）映射在临床和研究应用中具有重要价值。研究表明，通过可变翻转角在稳态下采集的两幅扰相梯度回波（SPGR）图像，是之前通过反转或饱和恢复采集的多幅图像集的一种有吸引力的替代方法。然而，两点法对发射射频场（B1）不均匀性的已知敏感性在3 T及以上时会加剧，这就要求将其与额外的、耗时且可能特定吸收率较高的B1测量相结合，从而阻碍了该方法直接应用于这些场强。为了解决这个问题，我们引入了一种旨在消除由B1不均匀性引起的系统误差的方法，该方法从通过回波平面成像（EPI）读出采集的三幅SPGR图像中提取T1值。结果发现，所生成的T1图的精度与两点法相当，但在相同的时间和空间分辨率下，准确性有了很大提高。该方法一个受欢迎的副产品是一幅B1图，可用于校正同一扫描过程中的其他采集。针对几种总成像时间，提供了最佳采集协议表。
