Bauman Grzegorz, Afshari Roya, Bieri Oliver
Department of Biomedical Engineering, University of Basel, Allschwil, Switzerland; Department of Radiology, Division of Radiological Physics, University Hospital Basel, Basel, Switzerland.
Department of Biomedical Engineering, University of Basel, Allschwil, Switzerland; Department of Radiology, Division of Radiological Physics, University Hospital Basel, Basel, Switzerland.
Z Med Phys. 2025 Feb;35(1):78-86. doi: 10.1016/j.zemedi.2024.12.001. Epub 2025 Jan 17.
This study aims to evaluate the feasibility of structural sub-millimeter isotropic brain MRI at 0.55 T using a 3D half-radial dual-echo balanced steady-state free precession sequence, termed bSTAR and to assess its potential for high-resolution magnetization transfer imaging.
Phantom and in-vivo imaging of three healthy volunteers was performed on a low-field 0.55 T MR-system with isotropic bSTAR resolution settings of 0.87 × 0.87 × 0.87 mm and 0.69 × 0.69 × 0.69 mm. Furthermore, off-resonance mapping was performed using 3D double-echo spoiled gradient imaging. For magnetization transfer (MT) MRI, the RF pulse duration of the 0.87 mm bSTAR scan was modified. Data were reconstructed using a GPU-accelerated compressed sensing algorithm. Magnetization transfer ratio (MTR) maps were calculated from two bSTAR scans with and without RF pulse prolongation. The MTR scan took 5 minutes and the reproducibility was assessed through repeated scans.
Off-resonance mapping revealed that bSSFP brain imaging with TR < 5ms is essentially free of off-resonance-related artifacts even near the nasal cavities. Phantom and in-vivo scans demonstrated the feasibility of sub-millimeter isotropic bSTAR imaging. MTR maps obtained with high isotropic resolution bSTAR showed contrast between white and gray matter in agreement with expectations from high-field studies. The MTR measurements were highly reproducible with an average inter-scan MTR peak value of 43.3 ± 0.3 percent units.
This study demonstrated the potential of sub-millimeter and artifact-free morphologic brain imaging at 0.55 T using bSTAR leveraging the advantages of low-field MRI, such as reduced susceptibility artifacts and improved radio-frequency field homogeneity. Furthermore, MT-sensitized bSTAR brain MRI enabled whole-brain MTR assessment within clinically feasible times and with high reproducibility.
本研究旨在评估使用称为bSTAR的3D半径向双回波平衡稳态自由进动序列在0.55 T场强下进行亚毫米各向同性脑MRI的可行性，并评估其在高分辨率磁化传递成像方面的潜力。
在一台低场0.55 T MR系统上对三个健康志愿者进行了体模和活体成像，各向同性bSTAR分辨率设置为0.87×0.87×0.87 mm和0.69×0.69×0.69 mm。此外，使用3D双回波扰相梯度成像进行了失谐映射。对于磁化传递（MT）MRI，对0.87 mm bSTAR扫描的射频脉冲持续时间进行了修改。使用GPU加速压缩感知算法对数据进行重建。根据两次分别具有和不具有射频脉冲延长的bSTAR扫描计算磁化传递率（MTR）图。MTR扫描耗时5分钟，并通过重复扫描评估其可重复性。
失谐映射显示，即使在鼻腔附近，TR<5 ms的bSSFP脑成像基本没有与失谐相关的伪影。体模和活体扫描证明了亚毫米各向同性bSTAR成像的可行性。具有高各向同性分辨率bSTAR获得的MTR图显示白质和灰质之间的对比度与高场研究的预期一致。MTR测量具有高度可重复性，扫描间MTR峰值的平均单位为43.3±0.3%。
本研究证明了使用bSTAR在0.55 T场强下进行亚毫米且无伪影的形态学脑成像的潜力，利用了低场MRI的优势，如减少的磁化率伪影和改善的射频场均匀性。此外，MT敏感的bSTAR脑MRI能够在临床可行的时间内进行全脑MTR评估，且具有高可重复性。
