Emory National Primate Research Center, Emory University, Atlanta, Georgia, USA.
Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia, USA.
Magn Reson Med. 2023 Dec;90(6):2400-2410. doi: 10.1002/mrm.29810. Epub 2023 Aug 1.
To integrate 3D CEST EPI with an unevenly segmented RF irradiation module and preliminarily demonstrate it in the clinical setting.
A CEST MRI with unevenly segmented RF saturation was implemented, including a long primary RF saturation to induce the steady-state CEST effect, maintained with repetitive short secondary RF irradiation between readouts. This configuration reduces relaxation-induced blur artifacts during acquisition, allowing fast 3D spatial coverage. Numerical simulations were performed to select parameters such as flip angle (FA), short RF saturation duration (Ts2), and the number of readout segments. The sequence was validated experimentally with data from a phantom, healthy volunteers, and a brain tumor patient.
Based on the numerical simulation and l-carnosine gel phantom experiment, FA, Ts2, and the number of segments were set to 20°, 0.3 s, and the range from 4 to 8, respectively. The proposed method minimized signal modulation in the human brain images in the k direction during the acquisition and provided the blur artifacts-free CEST contrast over the whole volume. Additionally, the CEST contrast in the tumor tissue region is higher than in the contralateral normal tissue region.
It is feasible to implement a highly accelerated 3D EPI CEST imaging with unevenly segmented RF irradiation.
将三维 CEST EPI 与不均匀分段射频辐射模块集成，并初步在临床环境中进行演示。
实现了具有不均匀分段射频饱和的 CEST MRI，包括诱导稳态 CEST 效应的长初始 RF 饱和，在读取之间用重复的短二次 RF 辐射维持。这种配置减少了采集过程中弛豫引起的模糊伪影，允许快速的三维空间覆盖。进行了数值模拟，以选择参数，如翻转角（FA）、短 RF 饱和持续时间（Ts2）和读出段数。该序列通过来自体模、健康志愿者和脑肿瘤患者的数据进行了实验验证。
基于数值模拟和 l-肌肽凝胶体模实验，将 FA、Ts2 和段数分别设置为 20°、0.3s 和 4 到 8 的范围。所提出的方法在采集过程中最小化了在 k 方向上的人脑图像中的信号调制，并提供了整个体积内无模糊伪影的 CEST 对比。此外，肿瘤组织区域的 CEST 对比高于对侧正常组织区域。
在不均匀分段射频辐射下实现高度加速的三维 EPI CEST 成像具有可行性。
