Reduction of Acquisition time using Partition of the sIgnal Decay in Spectroscopic Imaging technique (RAPID-SI)

To overcome long acquisition times of Chemical Shift Imaging (CSI), a new Magnetic Resonance Spectroscopic Imaging (MRSI) technique called Reduction of Acquisition time by Partition of the sIgnal Decay in Spectroscopic Imaging (RAPID-SI) using blipped phase encoding gradients inserted during signal acquisition was developed. To validate the results using RAPID-SI and to demonstrate its usefulness in terms of acquisition time and data quantification; simulations, phantom and in vivo studies were conducted, and the results were compared to standard CSI. The method was based upon the partition of a magnetic resonance spectroscopy (MRS) signal into sequential sub-signals encoded using blipped phase encoding gradients inserted during signal acquisition at a constant time interval. The RAPID-SI technique was implemented on a clinical 3 T Siemens scanner to demonstrate its clinical utility. Acceleration of data collection was performed by inserting R (R = acceleration factor) blipped gradients along a given spatial direction during data acquisition. Compared to CSI, RAPID-SI reduced acquisition time by the acceleration factor R. For example, a 2D 16x16 data set acquired in about 17 min with CSI, was reduced to approximately 2 min with the RAPID-SI (R = 8). While the SNR of the acquired RAPID-SI signal was lower compared to CSI by approximately the factor √R, it can be improved after data pre-processing and reconstruction. Compared to CSI, RAPID-SI reduces acquisition time, while preserving metabolites information. Furthermore, the method is flexible and could be combined with other acceleration methods such as Parallel Imaging.为解决化学位移成像（Chemical Shift Imaging, CSI）采集时间过长的问题，本研究开发了一种新型磁共振波谱成像（Magnetic Resonance Spectroscopic Imaging, MRSI）技术——通过将波谱成像中的信号衰变分区以缩短采集时间（Reduction of Acquisition time by Partition of the Signal Decay in Spectroscopic Imaging, RAPID-SI），该技术通过在信号采集过程中插入跳变相位编码梯度实现。为验证RAPID-SI的有效性并评估其在缩短采集时间与数据定量分析层面的实用性，研究团队开展了仿真实验、体模实验与活体实验，并将所得结果与标准CSI进行对照。该方法的核心原理为将磁共振波谱（Magnetic Resonance Spectroscopy, MRS）信号按恒定时间间隔分割为若干连续子信号，通过在信号采集期间沿指定空间方向插入R个跳变相位编码梯度（R为加速因子）实现数据采集加速。本研究在3特斯拉西门子临床扫描仪上完成了RAPID-SI技术的实现，以验证其临床应用价值。相较于标准CSI，RAPID-SI的采集时间可缩短至原加速因子R的倒数倍。举例而言，采用标准CSI采集一幅2D 16×16数据集约需17分钟，而采用RAPID-SI（加速因子R=8）时仅需约2分钟。尽管RAPID-SI采集得到的信号信噪比（Signal-to-Noise Ratio, SNR）相较于CSI约降低了√R倍，但可通过数据预处理与重建流程对其进行优化改善。与标准CSI相比，RAPID-SI在保留代谢物信息的前提下缩短了采集时间。此外，该方法具备良好的灵活性，可与并行成像（Parallel Imaging）等其他加速技术结合使用。