Author: Victor B. Kassey, Maciej M. Kmiec, Periannan Kuppusamy, Ryan C. O'Connell, Sergey V. Petryakov, Conner Ubert 👨🔬
Affiliation: Dartmouth College 🌍
Purpose: High-resolution magnetic field uniformity is essential for quantitative and pre-clinical MRI research. Imaging uniformity is affected by the B0 field, which can be corrected using manual or automatic shimming, and the B1 field, which is partly adjustable through tuning and matching capacitors but largely depends on the design of the RF coil. Our lab has developed a capacitor-free, mechanically tunable ceramic volume coil for pre-clinical MRI with excellent B1 field uniformity to address this need.
Methods: The coil is made of a ceramic material with a high dielectric constant and tuned to resonate at 400 MHz (9.4T). Two parallel opposing resonators feed the ceramic bore and are mechanically adjustable to tune the coil to the correct frequency while under load. Finite element analysis eigenmode simulation assessed the field uniformity and performance of the coil. An in-vivo experiment with a mouse validated its practical application.
Results: Numerical simulations indicate a high relative B1 field strength throughout the entire coil volume, with substantial uniformity over approximately 80% of the coil volume. In-vitro experiments using a DI water phantom (27 mm diameter) showed a signal-to-noise ratio (SNR) greater than 222 across the sample volume, compared to about 50 for a 20 mm industrial surface coil. A B1 profile assessment exhibited excellent uniformity over the central slice of the coil, with deviations of a fraction of a Gauss (± 0.1G), primarily due to imperfect loop placement of the prototype.
Conclusion: These preliminary results show that pre-clinical soft-tissue imaging is accessible without needing expensive, difficult-to-construct industrial birdcage or phased-array volume coils. The simple construction contributes to a high SNR by reducing electronic noise sources. Further research is required for optimization, but this prototype shows excellent potential as a cost-effective alternative to marketed pre-clinical RF volume coils.