Computational Imaging Group, Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
Magn Reson Med. 2024 Jul;92(1):226-235. doi: 10.1002/mrm.30052. Epub 2024 Feb 7.
To demonstrate the feasibility and robustness of the Magnetic Resonance Spin TomogrAphy in Time-domain (MR-STAT) framework for fast, high SNR relaxometry at 7T.
To deploy MR-STAT on 7T-systems, we designed optimized flip-angles using the BLAKJac-framework that incorporates the SAR-constraints. Transmit RF-inhomogeneities were mitigated by including a measured -map in the reconstruction. Experiments were performed on a gel-phantom and on five volunteers to explore the robustness of the sequence and its sensitivity to inhomogeneities. The SNR-gain at 7T was explored by comparing phantom and in vivo results to MR-STAT at 3T in terms of SNR-efficiency.
The higher SNR at 7T enabled two-fold acceleration with respect to current 2D MR-STAT protocols at lower field strengths. The resulting scan had whole-brain coverage, with 1 x 1 x 3 mm resolution (1.5 mm slice-gap) and was acquired within 3 min including the -mapping. After -correction, the estimated T and T in a phantom showed a mean relative error of, respectively, 1.7% and 4.4%. In vivo, the estimated T and T in gray and white matter corresponded to the range of values reported in literature with a variation over the subjects of 1.0%-2.1% (WM-GM) for T and 4.3%-5.3% (WM-GM) for T. We measured a higher SNR-efficiency at 7T (R = 2) than at 3T for both T and T with, respectively, a 4.1 and 2.3 times increase in SNR-efficiency.
We presented an accelerated version of MR-STAT tailored to high field (7T) MRI using a low-SAR flip-angle train and showed high quality parameter maps with an increased SNR-efficiency compared to MR-STAT at 3T.
展示磁共振自旋层析时域（MR-STAT）框架在 7T 下快速、高 SNR 弛豫测量的可行性和稳健性。
为了在 7T 系统上部署 MR-STAT，我们使用 BLAKJac 框架设计了优化的翻转角，该框架结合了 SAR 约束。通过在重建中包含测量的 - 映射来减轻发射 RF 不均匀性。在凝胶体模和五名志愿者上进行了实验，以探索序列的稳健性及其对不均匀性的敏感性。通过比较体模和体内结果与 3T 时的 MR-STAT 的 SNR 效率，探索了 7T 时的 SNR 增益。
7T 时的更高 SNR 使得相对于较低场强下的当前 2D MR-STAT 协议，能够实现两倍的加速。得到的扫描具有全脑覆盖，分辨率为 1×1×3mm（1.5mm 切片间隙），包括 - 映射在内，在 3 分钟内完成。经过 - 校正后，体模中估计的 T 和 T 的平均相对误差分别为 1.7%和 4.4%。在体内，灰质和白质中估计的 T 和 T 与文献中报道的值范围相对应，T 的受试者间变化为 1.0%-2.1%（WM-GM），T 的变化为 4.3%-5.3%（WM-GM）。我们测量了 7T 时的 SNR 效率（R=2）高于 3T 时的 SNR 效率（R=2），T 和 T 的 SNR 效率分别提高了 4.1 倍和 2.3 倍。
我们使用低 SAR 翻转角序列为高场（7T）MRI 定制了 MR-STAT 的加速版本，并展示了高质量的参数图，与 3T 时的 MR-STAT 相比，具有更高的 SNR 效率。
