Günther M, Bock M, Schad L R
Deutsches Krebsforschungszentrum (DKFZ), Forschungsschwerpunkt Radiologische Diagnostik und Therapie (E0201), Heidelberg, Germany.
Magn Reson Med. 2001 Nov;46(5):974-84. doi: 10.1002/mrm.1284.
Arterial spin labeling (ASL) permits quantification of tissue perfusion without the use of MR contrast agents. With standard ASL techniques such as flow-sensitive alternating inversion recovery (FAIR) the signal from arterial blood is measured at a fixed inversion delay after magnetic labeling. As no image information is sampled during this delay, FAIR measurements are inefficient and time-consuming. In this work the FAIR preparation was combined with a Look-Locker acquisition to sample not one but a series of images after each labeling pulse. This new method allows monitoring of the temporal dynamics of blood inflow. To quantify perfusion, a theoretical model for the signal dynamics during the Look-Locker readout was developed and applied. Also, the imaging parameters of the new ITS-FAIR technique were optimized using an expression for the variance of the calculated perfusion. For the given scanner hardware the parameters were: temporal resolution 100 ms, 23 images, flip-angle 25.4 degrees. In a normal volunteer experiment with these parameters an average perfusion value of 48.2 +/- 12.1 ml/100 g/min was measured in the brain. With the ability to obtain ITS-FAIR time series with high temporal resolution arterial transit times in the range of -138 - 1054 ms were measured, where nonphysical negative values were found in voxels containing large vessels.
动脉自旋标记（ASL）无需使用磁共振造影剂即可对组织灌注进行定量分析。使用诸如血流敏感交替反转恢复（FAIR）等标准ASL技术时，在磁标记后的固定反转延迟时间测量来自动脉血的信号。由于在此延迟期间不采集图像信息，FAIR测量效率低下且耗时。在这项工作中，将FAIR准备与Look-Locker采集相结合，以便在每个标记脉冲后采集一系列而非一幅图像。这种新方法允许监测血液流入的时间动态变化。为了对灌注进行定量分析，开发并应用了Look-Locker读出期间信号动态变化的理论模型。此外，使用计算得到的灌注方差表达式对新的ITS-FAIR技术的成像参数进行了优化。对于给定的扫描仪硬件，参数如下：时间分辨率100毫秒，23幅图像，翻转角25.4度。在使用这些参数的正常志愿者实验中，测得大脑的平均灌注值为48.2±12.1毫升/100克/分钟。由于能够以高时间分辨率获得ITS-FAIR时间序列，测量到的动脉通过时间范围为-138至1054毫秒，在包含大血管的体素中发现了非物理意义上的负值。
