C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom.
Magn Reson Med. 2019 Jun;81(6):3734-3744. doi: 10.1002/mrm.27692. Epub 2019 Mar 3.
The goal of this study was to achieve high temporal resolution, multi-time point pseudo-continuous arterial spin labeling (pCASL) MRI in a time-efficient manner, while maintaining whole-brain coverage.
A Hadamard 8-matrix was used to dynamically encode the pCASL labeling train, thereby providing the first source of temporal information. The second method for obtaining dynamic arterial spin labeling (ASL) signal consisted of a Look-Locker (LL) readout of 4 phases that are acquired with a flip-angle sweep to maintain constant sensitivity over the phases. To obtain whole-brain coverage in the short LL interval, 4 slices were excited simultaneously by multi-banded radiofrequency pulses. After subtraction according to the Hadamard scheme, the ASL signal was corrected for the use of the flip-angle sweep and background suppression pulses. The BASIL toolkit of the Oxford Centre for FMRIB was used to quantify the ASL signal.
By combining a time-encoded pCASL labeling scheme with an LL readout and simultaneous multi-slice acquisition, 28 time points of 16 slices with a 75- or 150-ms time resolution were acquired in a total scan time of 10 minutes 20 seconds, from which cerebral blood flow (CBF) maps, arterial transit time maps, and arterial blood volume could be determined.
Whole-brain ASL images were acquired with a 75-ms time resolution for the angiography and 150-ms resolution for the perfusion phase by combining the proposed techniques. Reducing the total scan time to 1 minute 18 seconds still resulted in reasonable CBF maps, which demonstrates the feasibility of this approach for practical studies on brain hemodynamics.
本研究旨在以高效的方式实现高时间分辨率、多时间点伪连续动脉自旋标记（pCASL）MRI，同时保持全脑覆盖。
使用 Hadamard 8 矩阵动态编码 pCASL 标记列车，从而提供时间信息的第一个来源。获取动态动脉自旋标记（ASL）信号的第二种方法由 4 个相位的 Look-Locker（LL）读出组成，采用翻转角扫描来保持各相位的恒定灵敏度。为了在短 LL 间隔内获得全脑覆盖，通过多带射频脉冲同时激发 4 个切片。根据 Hadamard 方案进行减影后，ASL 信号会根据翻转角扫描和背景抑制脉冲进行校正。牛津大学磁共振成像研究中心的 BASIL 工具包用于量化 ASL 信号。
通过将时间编码的 pCASL 标记方案与 LL 读出和同时多切片采集相结合，在总共 10 分 20 秒的扫描时间内，采集了 16 个切片的 28 个时间点，时间分辨率分别为 75 或 150ms，从中可以确定脑血流量（CBF）图、动脉转运时间图和动脉血容量图。
通过结合提出的技术，以 75ms 的时间分辨率获取血管造影图，以 150ms 的分辨率获取灌注期图像，实现了全脑 ASL 图像的采集。将总扫描时间减少到 1 分 18 秒仍能得到合理的 CBF 图，证明了该方法在脑血液动力学实际研究中的可行性。
