RF shimming in the cervical spinal cord at 7 T

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Neuroimaging
• Biomedical Engineering

Background:

• 7 Tesla (7 T) MRI development is vital for diagnosing neurodegenerative diseases and traumas.
• Transmit field inhomogeneity is a major challenge in 7 T MRI, especially for cervical spinal cord imaging.
• Inhomogeneity compromises image quality and elevates specific absorption ratio (SAR).

Purpose of the Study:

• To explore and evaluate various radiofrequency (RF) shimming techniques for improving transmit field and signal homogeneity in the cervical spinal cord at 7 T.
• To address the challenges posed by transmit field inhomogeneity in high-field MRI of the spinal cord.

Main Methods:

• A multisite study involving 5 participants at two 7 T MRI sites.
• Utilized a custom 8Tx/20Rx parallel transmission coil.
• Compared two vendor-based and four open-source RF shimming approaches.

Main Results:

• Circularly polarized (CP), coefficient of variation (CoV), and SAR efficiency shim modes exhibited the highest B1+ efficiency.
• Vendor-based "patient" and "volume" modes showed the lowest B1+ efficiency.
• The CoV method yielded the highest CSF/spinal cord contrast (1.27 ± 0.03) on T2*-weighted scans with minimal superior-inferior variation.

Conclusions:

• RF shimming holds significant potential to enhance the clinical utility of 7 T MRI for central nervous system imaging.
• Achieving more homogenous and efficient spinal cord imaging is possible with optimized RF shimming.
• The study provides a reproducible Jupyter Notebook, promoting transparency and peer verification.