NMR imaging with shorted coaxial line probes

Area of Science:

• Physics
• Electrical Engineering
• Biomedical Imaging

Background:

• Coaxial lines are traditionally used in CW-Electron Paramagnetic Resonance (EPR) below 1 GHz.
• Samples are typically placed at maximum B1 field in short-circuited coaxial lines.

Purpose of the Study:

• To demonstrate that removing the coaxial line shield near the truncated end minimally perturbs RF properties.
• To enable local imaging capabilities in Magnetic Resonance Imaging (MRI) using modified coaxial lines.
• To explore the potential for tailored B1 field shaping and image aperture control.

Main Methods:

• Modified coaxial line sections by removing the shield in the truncated end region.
• Contoured inner conductors and outer shields to shape B1 fields.
• Varied shield cutout shapes to control image aperture.
• Tested probes with shield diameters ranging from 2 mm to 10 cm.
• Investigated both resonant and nonresonant probe configurations.

Main Results:

• Excellent separation of B and E fields achieved by removing the shield.
• Demonstrated local imaging in MRI with custom-shaped probes.
• Imaging depth was found to be limited to 3-4 times the probe's outer radius.
• Achieved sharp RF cutoff at millimeter depths by controlling shield removal and RF power.
• Nonresonant probes exhibited broad bandwidth, suitable for FT-EPR and FT-EPR imaging.

Conclusions:

• Modified coaxial lines offer a versatile platform for EPR and MRI.
• The ability to shape fields and control apertures opens new possibilities for localized measurements.
• Nonresonant truncated line probes are promising for time-domain EPR techniques, minimizing dead times.