An inverse methodology for high-frequency RF coil design for MRI with de-emphasized B1 fields

Area of Science:

• Biomedical Engineering
• Electromagnetics
• Medical Imaging

Background:

• High-frequency radio-frequency (RF) coils in Magnetic Resonance Imaging (MRI) can suffer from field/tissue interactions, leading to central overemphasis in images.
• Designing RF coils to mitigate these effects, especially at higher field strengths (e.g., 4 Tesla), is crucial for image quality.

Purpose of the Study:

• To develop and validate an inverse methodology for designing biologically loaded RF coils for MRI.
• To reduce the central overemphasis artifact in head images acquired at high field strengths (170 MHz and above).

Main Methods:

• Utilized free space time-harmonic electromagnetic Green's functions to calculate current density on a coil cylinder.
• Employed de-emphasized B1 target fields in the RF transverse plane to guide current distribution.
• Used an in-house finite-difference time-domain (FDTD) routine to evaluate B1 field and signal intensity in phantom and human head models.
• Compared the performance against a conventional RF birdcage coil.

Main Results:

• Calculated the current distribution for a head coil operating at 4 T (170 MHz) using the inverse methodology.
• Demonstrated that the designed coil can reduce the central bright region artifact observed in conventional coils.
• Evaluated B1 field and signal intensity within homogenous and human head models.

Conclusions:

• The inverse methodology with de-emphasized B1 target fields provides an effective approach for designing RF coils.
• This method shows promise for improving image quality in high-field MRI by mitigating field/tissue interaction artifacts.
• The findings are particularly relevant for head imaging at 170 MHz and higher frequencies.