Gai Neville D, Butman John A
Radiology and Imaging Sciences, National Institutes of Health, Bethesda, Maryland, USA.
J Magn Reson Imaging. 2009 Sep;30(3):640-8. doi: 10.1002/jmri.21842.
To demonstrate a modification of the Look-Locker (LL) technique that enables rapid high resolution T1 mapping over the physiologic range of intracranial T1 values, ranging from white matter to cerebrospinal fluid (CSF). This is achieved by use of a three-dimensional (3D) balanced steady-state free precession (b-SSFP) acquisition (for high signal-to-noise and resolution) along with variable repetition time to allow effective full recovery of longitudinal magnetization.
Two modifications to the Look-Locker technique were made to realize high resolution imaging in a clinically reasonable scan time. The 3D b-SSFP acquisition after an initial inversion pulse was followed by a variable repetition time. This technique makes it possible to image a volume of thin contiguous slices with high resolution and accuracy using a simple fitting procedure and is particularly useful for imaging long T1 species such as CSF. The total scan time is directly proportional to the number of slices to be acquired. The scan time was reduced by almost half when the repetition time was modified using a predesigned smooth function. Phantoms and volunteers were imaged at different resolutions on a 3 Tesla scanner. Results were compared with other accepted techniques.
T1 values in the brain corresponded well with full repetition time imaging as well as inversion recovery spin echo imaging. T1 values for white matter, gray matter, and CSF were measured to be 755 +/- 10 ms, 1202 +/- 9 ms, and 4482 +/- 71 ms, respectively. Scan times were reduced by approximately half over full repetition time measurements.
High resolution T1 maps can be obtained rapidly and with a relatively simple postprocessing method. The technique is particularly well suited for long T1 species. For example, changes in the composition of proteins in CSF are linked to various pathologies. The T1 values showed excellent agreement with values obtained from inversion recovery spin-echo imaging.
展示一种对Look-Locker（LL）技术的改进方法，该方法能够在颅内T1值的生理范围内（从白质到脑脊液（CSF））实现快速高分辨率T1映射。这是通过使用三维（3D）平衡稳态自由进动（b-SSFP）采集（用于高信噪比和分辨率）以及可变重复时间来实现的，以便纵向磁化有效完全恢复。
对Look-Locker技术进行了两项改进，以在临床合理的扫描时间内实现高分辨率成像。在初始反转脉冲后进行3D b-SSFP采集，随后是可变重复时间。该技术使用简单的拟合程序就能够以高分辨率和准确性对一系列薄的连续切片进行成像，对于成像诸如脑脊液等长T1物质特别有用。总扫描时间与要采集的切片数量成正比。当使用预先设计的平滑函数修改重复时间时，扫描时间减少了近一半。在3特斯拉扫描仪上对体模和志愿者进行了不同分辨率成像。将结果与其他公认技术进行了比较。
大脑中的T1值与全重复时间成像以及反转恢复自旋回波成像结果吻合良好。白质、灰质和脑脊液的T1值分别测量为755±10毫秒1202±9毫秒和±71毫秒。扫描时间比全重复时间测量减少了约一半。
可以通过相对简单的后处理方法快速获得高分辨率T1映射。该技术特别适用于长T1物质。例如，脑脊液中蛋白质组成的变化与各种病理状况相关。T1值与从反转恢复自旋回波成像获得的值显示出极好的一致性。
