Oh Joonmi, Han Eric T, Pelletier Daniel, Nelson Sarah J
Department of Radiology, Center for Molecular and Functional Imaging, University of California, San Francisco, CA 94107, USA.
Magn Reson Imaging. 2006 Jan;24(1):33-43. doi: 10.1016/j.mri.2005.10.016. Epub 2005 Dec 19.
The objective of this study was to implement a clinically relevant multi-slice multi-echo imaging sequence in order to quantify multi-component T2 relaxation times for normal volunteers at both 1.5 and 3 T. Multi-echo data were fitted using a nonnegative least square algorithm. Twelve echo data with nonlinear echo sampling were acquired using a receive-only eight-channel phased array coil and volume head coil for phantoms and normal volunteers, and compared to 32-echo data with linear echo sampling. It was observed that the performance of the 180 degrees refocusing trains was more spatially uniform for the receive-only eight-channel phased array coil than for the head coil, particularly at 3 T. The phantom study showed that the estimated T2 relaxation times were accurate and reproducible for both single- and multi-slice acquisition from a commercial phantom with known T2 relaxation times. Short T2 components (T2 <50 ms) were mainly observed within the white matter for normal volunteers, and the fraction of short T2 water components (i.e., myelin water) was 7-12% of total water. It was observed that the calculated myelin water fraction map from the nonlinearly sampled 12-echo data was comparable with that from the linearly sampled 32-echo data. Quantification of T2 relaxation times from multi-slice images was accomplished with a clinically acceptable scan times (16 min) for normal volunteers by using a nonselective T2 prep imaging sequence. The use of the eight-channel head coil involved more accurate quantification of T2 relaxation times particularly when the number of echoes was limited.
本研究的目的是实施一种临床相关的多层多回波成像序列，以便对1.5T和3T场强下的正常志愿者进行多组分T2弛豫时间的定量分析。多回波数据采用非负最小二乘算法进行拟合。使用仅接收的八通道相控阵线圈和容积头部线圈，针对体模和正常志愿者采集了具有非线性回波采样的12个回波数据，并与具有线性回波采样的32个回波数据进行比较。结果发现，对于仅接收的八通道相控阵线圈，180°重聚焦序列的性能在空间上比头部线圈更均匀，尤其是在3T场强时。体模研究表明，对于具有已知T2弛豫时间的商用体模，单切片和多切片采集的估计T2弛豫时间准确且可重复。在正常志愿者的白质中主要观察到短T2成分（T2<50ms），短T2水成分（即髓磷脂水）占总水的比例为7-12%。结果发现，从非线性采样的12个回波数据计算得到的髓磷脂水分数图与从线性采样的32个回波数据计算得到的髓磷脂水分数图相当。通过使用非选择性T2预脉冲成像序列，在正常志愿者可接受的扫描时间（16分钟）内完成了多层图像T2弛豫时间的定量分析。使用八通道头部线圈尤其在回波数量有限时能更准确地定量T2弛豫时间。
