Homogeneous B₁⁺ for bilateral breast imaging at 7 T using a five dipole transmit array merged with a high density...

Area of Science:

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

Background:

• High-field MRI (7 Tesla) offers potential for improved signal-to-noise ratio and spectral resolution.
• Breast MRI at 7T faces challenges with B1 field inhomogeneity and limited penetration depth.
• Advanced RF coil designs are crucial for optimizing performance and safety at ultra-high fields.

Purpose of the Study:

• To evaluate a multi-transmit setup using five meandering dipole antennas for 7T breast MRI.
• To assess the coil's ability to improve penetration depth and B1 field homogeneity.
• To investigate RF safety, antenna performance, and in vivo imaging capabilities.

Main Methods:

• Design and simulation (Finite Difference Time Domain) of a five-meandering dipole transmit array.
• Integration with a 30-loop receive array for parallel imaging at 7 Tesla.
• Measurement of scattering parameters, inter-element coupling, and noise correlation.
• In vivo imaging including B1 mapping, T1-weighted, and T2-weighted sequences with RF shimming.

Main Results:

• Maximum local Specific Absorption Rate (SAR10g) was 7.0 W/kg at 5x1W accepted power, meeting safety limits.
• Excellent antenna performance with reflection < -11.8 dB and inter-element coupling < -14.2 dB.
• Low coupling between transmit antennas and receive loops (< -18.2 dB) and manageable noise correlation (7.83 ± 8.69%).
• In vivo scans demonstrated an extended field of view reaching the axilla and high transmit efficiency.
• Acquisition of T1-weighted images with 0.7 mm3 isotropic resolution and uniformly contrasted T2-weighted images.

Conclusions:

• The developed multi-transmit coil system significantly improves B1 field homogeneity and penetration depth for 7T breast MRI.
• The system demonstrates excellent RF safety, coil performance, and in vivo imaging capabilities, including high-resolution anatomical imaging.
• This coil design represents a promising advancement for clinical applications of ultra-high field breast MRI.