Coils for large standoff relaxometry with unilateral magnets

Area of Science:

• Physics
• Engineering
• Chemistry

Background:

• Maximizing standoff distance and signal-to-noise ratio (SNR) is crucial for unilateral Nuclear Magnetic Resonance (NMR).
• Traditional surface coils face challenges with eddy current shielding when placed on conductive magnet surfaces.
• Unilateral magnets require specialized radio frequency (rf) coil designs for effective application.

Purpose of the Study:

• To introduce and characterize two novel rf coil designs, "simple fringe" and "split fringe coils," for linear array unilateral magnets.
• To enable direct placement of rf coils on magnet surfaces, overcoming limitations of conventional designs.
• To enhance the performance of unilateral NMR by maximizing standoff distance and SNR.

Main Methods:

• Design of solenoid coils with rectangular cross-sections, either continuous or center-split, with axes parallel to the magnet surface.
• Utilizing ANSYS™ finite element modeling software to simulate and characterize the spatial homogeneity of the rf fields.
• Construction and experimental characterization of the designed coils using magnetic resonance imaging (MRI).

Main Results:

• The designed "simple fringe" and "split fringe" coils demonstrated enhanced rf field generation in the sample region outside the solenoid.
• Finite element modeling predicted homogeneous, surface-displaced rf fields for the proposed coil geometries.
• Experimental characterization confirmed the performance of the constructed coils, enabling large standoff relaxation measurements.

Conclusions:

• The developed fringe coils effectively overcome the limitations of traditional surface coils on conductive magnet surfaces.
• These novel rf coil designs significantly improve the standoff distance and SNR for unilateral NMR.
• The study successfully demonstrates the application of these coils for advanced NMR measurements, such as large standoff relaxation studies.