准连续性动脉自旋标记技术在磁共振系统上的序列实现和参数优化

准连续性动脉自旋标记技术(pCASL)是一种新兴的动脉自旋标记脑灌注成像技术(ASL)：一方面，它克服了连续性动脉自旋标记技术(CASL)需要独立发射线圈的硬件限制；另一方面，也避免了脉冲式动脉自旋标记技术(PASL)带来的标记效率低的影响．为了在 1.5 T 磁共振系统上开发一款可稳定应用于临床扫描的 pCASL 序列；并使用该序列准确获得反
应灌注功能的局部脑血流量值(Regional Cerebral Blood Flow， rCBF)．该文利用水模测试pCASL 序列，验证了标记部分的标记性能并通过人体实验，优化了协议中标记位置中心到成像层面中心的距离和标记部分结束点到成像脉冲开始前的等待时间这两项参数．基于优化了参数的 pCASL 协议，扫描 12 组正常志愿者，观测灌注信号分布情况，并对特定灰质区域定量计算，对比不同个体该区域的 rCBF 值．通过人体实验，经验性地确定了延迟时间为 1 200 ms、标记距离为 70 mm 时灌注图像的信噪比达到最优．将两项优化后的参数存入协议中，并使用协议扫描，共获取 12 组结果，其中的 10 组都表明灌注信号稳定均匀，并且灰质区域的 CBF 值同经验结果一致．该工作在1.5 T 的磁共振系统上成功实现了 pCASL序列，经优化参数后的协议扫描，可以获得准确稳定的脑部灌注信号．

Sequence Development and Parameter Optimization for A Pseudo-Continuous Arterial Spin Labeling Method on 1.5 T Clinical Magnetic Resonance Imaging Systems

Pseudo-continuous arterial spin labeling (pCASL) is perfusion imaging technique that combines the advantages of continuous arterial spin labeling (CASL) and pulsed arterial spin labeling (PASL). In this study, we implemented a pCASL sequence on uMR560 1.5 T MRI systems developed by United Imaging Healthcare Cooperation. Experiments were performed to demonstrate the stability of the pCASL sequence implemented and the accuracy of perfusion quantification. The tagging efficiency was first measured through phantom experiments. In order to achieve the highest signal-to-noise ratio, post-labeling delay time and labeling distance were optimized empirically to be approximately 70 mm blow the imaging slab and 1 200 ms, respectively. Lastly, perfusion-weighted signal intensity and absolute cerebral blood flow (CBF) were measured from 12 normal volunteers using the pCASL sequence implemented, with satisfactory results obtained from 10 subjects. In summary, the pCASL sequence implemented on the uMR560 1.5 T MRI systems can be used for perfusion imaging on human brain, with reasonable stability and accuracy.