Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
Mannheim Institute for Intelligent Systems in Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
Magn Reson Med. 2024 Oct;92(4):1440-1455. doi: 10.1002/mrm.30132. Epub 2024 May 10.
To develop a new sequence to simultaneously acquire Cartesian sodium (Na) MRI and accelerated Cartesian single (SQ) and triple quantum (TQ) sodium MRI of in vivo human brain at 7 T by leveraging two dedicated low-rank reconstruction frameworks.
The Double Half-Echo technique enables short echo time Cartesian Na MRI and acquires two k-space halves, reconstructed by a low-rank coupling constraint. Additionally, three-dimensional (3D) Na Multi-Quantum Coherences (MQC) MRI requires multi-echo sampling paired with phase-cycling, exhibiting a redundant multidimensional space. Simultaneous Autocalibrating and k-Space Estimation (SAKE) were used to reconstruct highly undersampled Na MQC MRI. Reconstruction performance was assessed against five-dimensional (5D) CS, evaluating structural similarity index (SSIM), root mean squared error (RMSE), signal-to-noise ratio (SNR), and quantification of tissue sodium concentration and TQ/SQ ratio in silico, in vitro, and in vivo.
The proposed sequence enabled the simultaneous acquisition of fully sampled Na MRI while leveraging prospective undersampling for Na MQC MRI. SAKE improved TQ image reconstruction regarding SSIM by 6% and reduced RMSE by 35% compared to 5D CS in vivo. Thanks to prospective undersampling, the spatial resolution of Na MQC MRI was enhanced from mm to mm while reducing acquisition time from min to min.
The proposed sequence, coupled with low-rank reconstructions, provides an efficient framework for comprehensive whole-brain sodium MRI, combining TSC, T2*, and TQ/SQ ratio estimations. Additionally, low-rank matrix completion enables the reconstruction of highly undersampled Na MQC MRI, allowing for accelerated acquisition or enhanced spatial resolution.
利用两个专用的低秩重建框架，开发一种新的序列，以便在 7T 下同时获取体内人脑的笛卡尔钠离子（Na）MRI 和加速笛卡尔单（SQ）和三重量子（TQ）Na 磁共振成像。
双半回波技术可实现短回波时间笛卡尔 Na MRI，并采集两个 k 空间的一半，由低秩耦合约束重建。此外，三维（3D）Na 多量子相干（MQC）MRI 需要多回波采样与相位编码配对，表现出冗余的多维空间。同时自校准和 k 空间估计（SAKE）用于重建高度欠采样的 Na MQC MRI。重建性能通过五维（5D）CS 进行评估，评估结构相似性指数（SSIM）、均方根误差（RMSE）、信噪比（SNR）以及体内、体外和体内组织钠浓度和 TQ/SQ 比的定量。
所提出的序列能够在利用前瞻性欠采样进行 Na MQC MRI 的同时获取完全采样的 Na MRI。与 5D CS 相比，SAKE 在体内提高了 TQ 图像重建的 SSIM 约 6%，降低了 RMSE 约 35%。由于前瞻性欠采样，Na MQC MRI 的空间分辨率从 mm 提高到了 mm，同时将采集时间从 min 减少到了 min。
所提出的序列与低秩重建相结合，为全面的全脑钠 MRI 提供了一个高效的框架，结合 TSC、T2* 和 TQ/SQ 比估计。此外，低秩矩阵完成可以实现高度欠采样的 Na MQC MRI 的重建，从而实现加速采集或增强空间分辨率。
