Effects of Anatomical Differences on Electromagnetic Fields, SAR, and Temperature Change

Area of Science:

• Medical Physics
• Biomedical Engineering
• Electromagnetics

Background:

• Electromagnetic field simulations are crucial for ensuring patient safety during MRI scans.
• Accurate patient tissue properties are often unknown, necessitating the use of models.
• Transmit magnetic field (B1+) distribution agreement is frequently used to infer heating distribution agreement.

Purpose of the Study:

• To investigate the impact of anatomical variations on B1+ distribution, Specific Absorption Rate (SAR), and temperature change (ΔT).
• To evaluate the reliability of using B1+ distribution agreement for RF safety validation in MRI.

Main Methods:

• Numerical simulations were conducted using various phantoms and human body models with a surface coil.
• Experimental validation was performed on a bovine phantom using MR thermometry and B1+ mapping.
• Comparative analysis of B1+ distributions, SAR, and ΔT across different geometries.

Main Results:

• B1+ field distributions showed good correlation across different samples and geometries.
• Significant differences were observed in maximum SAR and ΔT values despite B1+ correlation.
• Simulations and experiments highlighted discrepancies between B1+ correlation and thermal outcomes.

Conclusions:

• Relying solely on B1+ field distribution agreement for MRI RF safety validation is insufficient and potentially misleading.
• Anatomical variations pose challenges for accurate RF safety assessment in MRI.
• Caution is advised when using B1+ distributions to validate simulations or experiments for safety assurance in different subjects.