The dual-mode dipole: A new array element for 7T body imaging with reduced SAR

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Radiofrequency (RF) Engineering
• Biomedical Engineering

Background:

• High-field MRI at 7 Tesla (T) offers enhanced signal-to-noise ratio (SNR) but faces challenges with radiofrequency (RF) power deposition (SAR) and B1+ field uniformity.
• Existing RF coil designs often struggle to balance SAR reduction with adequate B1+ efficiency for body imaging.

Purpose of the Study:

• To design and evaluate a novel dual-mode dipole RF coil for 7T body imaging.
• To improve SAR efficiency while maintaining comparable B1+ field performance to conventional coils.

Main Methods:

• A dual-mode dipole RF coil utilizing two orthogonal eigenmodes (even and odd) was designed and simulated.
• Numerical simulations were performed using homogeneous phantoms and a voxel body model.
• The dual-mode dipole was compared against a fractionated dipole and surface loop coil in a 7T MRI system using phantoms and a human volunteer.

Main Results:

• The dual-mode dipole's even mode achieved a 70% SAR reduction compared to the fractionated dipole with equivalent B1+ in the prostate region.
• The odd mode demonstrated comparable SAR and B1+ efficiency to a surface loop coil.
• Imaging results showed comparable SNR and prostate imaging quality between the dual-mode dipole array and the reference array, but with lower SAR.

Conclusions:

• The dual-mode dipole RF coil array provides equivalent imaging performance and SNR to reference arrays at 7T.
• The proposed coil design achieves significantly lower SAR due to a smoother current distribution, enhancing safety for body imaging.