Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany.
Working Group on Cardiovascular Magnetic Resonance, Experimental and Clinical Research Center, A Joint Cooperation between the Charité Medical Faculty and the Max-Delbrück Center for Molecular Medicine, Berlin, Germany.
Magn Reson Med. 2024 Oct;92(4):1496-1510. doi: 10.1002/mrm.30137. Epub 2024 May 10.
To address the limitations of spinal cord imaging at ultra-high field (UHF) due to time-consuming parallel transmit (pTx) adjustments. This study introduces calibration-free offline computed universal shim modes that can be applied seamlessly for different pTx RF coils and spinal cord target regions, substantially enhancing spinal cord imaging efficiency at UHF.
A library of channel-wise relative maps for the cervical spinal cord (six datasets) and thoracic and lumbar spinal cord (nine datasets) was constructed to optimize transmit homogeneity and efficiency for these regions. A tailored B shim was optimized for the cervical spine to enhance spatial magnetic field homogeneity further. The performance of the universal shims was validated using absolute saturation based mapping and high-resolution 2D and 3D multi-echo gradient-recalled echo (GRE) data to assess the image quality.
The proposed universal shims demonstrated a 50% improvement in efficiency compared to the default (zero phase) shim mode. homogeneity was also improved by 20%. The optimized universal shims achieved performance comparable to subject-specific pTx adjustments, while eliminating the need for lengthy pTx calibration times, saving about 10 min per experiment.
The development of universal shims represents a significant advance by eliminating time-consuming subject-specific pTx adjustments. This approach is expected to make UHF spinal cord imaging more accessible and user-friendly, particularly for non-pTx experts.
解决超高场（UHF）下脊髓成像因并行发射（pTx）调整耗时而受限的问题。本研究引入了无需校准的离线计算通用匀场模式，可无缝应用于不同的 pTx RF 线圈和脊髓靶区，显著提高 UHF 下的脊髓成像效率。
构建了用于颈椎（六个数据集）和胸腰椎脊髓（九个数据集）的通道相对图库，以优化这些区域的发射均匀性和效率。针对颈椎，优化了定制的 B 匀场，以进一步提高空间磁场均匀性。使用基于绝对饱和的映射和高分辨率 2D 和 3D 多回波梯度回波（GRE）数据来评估图像质量，验证了通用匀场的性能。
与默认（零相位）匀场模式相比，所提出的通用匀场提高了 50%的效率。均匀性也提高了 20%。优化后的通用匀场达到了与个体特异性 pTx 调整相当的性能，同时消除了耗时的 pTx 校准时间，每个实验节省了约 10 分钟。
通用匀场的开发通过消除耗时的个体特异性 pTx 调整取得了重大进展。该方法有望使 UHF 下的脊髓成像更加普及和用户友好，特别是对于非 pTx 专家。
