Electromagnetic fields inside a lossy, multilayered spherical head phantom excited by MRI coils: models and methods

Area of Science:

• Medical Imaging
• Electromagnetism
• Computational Physics

Background:

• Accurate electromagnetic field (EMF) evaluation is crucial for designing high-field Magnetic Resonance Imaging (MRI) systems.
• Traditional homogeneous head phantoms offer limited accuracy in simulating complex electromagnetic interactions within biological tissues.
• Understanding EMF distribution is key to optimizing MRI performance and safety.

Purpose of the Study:

• To propose and validate a multilayered dielectric spherical head model for improved EMF evaluation in high-field MRI.
• To compare the efficacy of Debye Potential (DP) and Dyadic Green's Function (DGF) methods for EMF calculation in this model.
• To offer a computationally efficient alternative to complex models for rapid prototyping of MRI hardware.

Main Methods:

• Development of Debye Potential (DP) solutions for symmetric sources (circular loop) and Dyadic Green's Function (DGF) solutions for arbitrary RF coils.
• Modeling a head-sized, stratified sphere with realistic radial conductivity and permittivity profiles.
• Utilizing the method of moments to evaluate RF coil current distributions for DGF calculations.

Main Results:

• The proposed multilayered spherical model accurately calculates EMF distributions within a human head analog.
• Both DP and DGF methods provide effective solutions for EMF computation across a wide frequency range.
• The model demonstrates significantly reduced computation times compared to finite difference time domain (FDTD) methods for complex models.

Conclusions:

• The multilayered spherical head model provides a valuable tool for precise EMF evaluation in high-field MRI.
• This approach facilitates rapid prototyping and design optimization for RF coils and gradient systems.
• The methods presented offer a balance between accuracy and computational efficiency for MRI system development.