Abstract：
Free-breathing abdominal chemical exchange saturation transfer (CEST) has great potential for clinical application, but its technical implementation remains challenging. This study aimed to propose and evaluate a free-breathing abdominal CEST sequence. The proposed sequence employed respiratory gating (ResGat) to synchronize the data acquisition with respiratory motion and performed a water presaturation module before the CEST saturation to abolish the influence of respiration-induced repetition time variation. In vivo experiments were performed to compare different respiratory motion-control strategies and B0 offset correction methods, and to evaluate the effectiveness and necessity of the quasi-steady-state (QUASS) approach for correcting the influence of the water presaturation module on CEST signal. ResGat with a target expiratory phase of 0.5 resulted in a higher structural similarity index and a lower coefficient of variation on consecutively acquired CEST S0 images than breath-holding (BH) and respiratory triggering (all p < 0.05). B0 maps derived from the abdominal CEST dataset itself were more stable for B0 correction, compared with the separately acquired B0 maps by a dual-echo time scan and B0 maps derived from the water saturation shift referencing approach. Compared with BH, ResGat yielded more homogeneous magnetization transfer ratio asymmetry maps at 3.5 ppm (standard deviation: 3.96% vs. 3.19%, p = 0.036) and a lower mean squared difference between scan and rescan (27.52‱ vs. 16.82‱, p = 0.004). The QUASS approach could correct the water presaturation-induced CEST signal change, but its necessity for in vivo scanning needs further verification. The proposed free-breathing abdominal CEST sequence using ResGat had an acquisition efficiency of approximately four times that using BH. In conclusion, the proposed free-breathing abdominal CEST sequence using ResGat and water presaturation has a higher acquisition efficiency and image quality than abdominal CEST using BH.
摘要：
自由呼吸腹部化学交换饱和转移(CEST)具有巨大的临床应用潜力,但其技术实施仍然具有挑战性。本研究旨在提出和评估自由呼吸腹部CEST序列。所提出的序列采用呼吸门控（ResGat）来使数据采集与呼吸运动同步，并在CEST饱和之前执行水预饱和模块，以消除呼吸引起的重复时间变化的影响。进行了体内实验，以比较不同的呼吸运动控制策略和B0偏移校正方法，并评估准稳态（QUASS）方法校正水预饱和模块对CEST信号影响的有效性和必要性。与屏气（BH）和呼吸触发相比，在连续采集的CESTS0图像上，目标呼气相位为0.5的ResGat导致更高的结构相似性指数和更低的变异系数（所有p<0.05）。从腹部CEST数据集本身得出的B0图对于B0校正更稳定，与通过双回波时间扫描分别获取的B0图和从水饱和度偏移参考方法得出的B0图进行比较。与BH相比,ResGat在3.5ppm时产生了更均匀的磁化转移比不对称图（标准偏差：3.96％与3.19%，p=0.036），扫描和重新扫描之间的均方差较低（27.52/vs.16.82，p=0.004)。QUASS方法可以校正水的预饱和引起的CEST信号变化，但其在体内扫描的必要性需要进一步验证。使用ResGat提出的自由呼吸腹部CEST序列的采集效率约为使用BH的四倍。总之,与使用BH的腹部CEST相比,所提出的使用ResGat和水的预饱和的自由呼吸腹部CEST序列具有更高的采集效率和图像质量。
