SAR and temperature: simulations and comparison to regulatory limits for MRI

Area of Science:

• Medical Physics
• Biomedical Engineering
• Electromagnetics

Background:

• Monitoring local specific absorption rate (SAR) and temperature during MRI is challenging.
• Existing methods for calculating SAR and temperature are continually improving.
• Interpreting these calculated results against regulatory limits requires careful consideration.

Purpose of the Study:

• To present numerical calculations of SAR and temperature in the human head during MRI.
• To compare these calculated values against established regulatory limits.
• To discuss the implications of these findings for MRI safety guidelines.

Main Methods:

• Numerical simulations of SAR and temperature distributions in the human head.
• Utilized a volume coil for MRI simulations at various frequencies.
• Analyzed the ratio of maximum local SAR to whole-head average SAR.

Main Results:

• SAR and temperature distributions are highly dependent on the B(1) field frequency.
• The ratio of maximum local SAR to average SAR significantly exceeds regulatory limits.
• Local SAR limits are likely to be reached before average SAR limits.

Conclusions:

• Local SAR and temperature distributions vary considerably with MRI frequency.
• Temperature distributions do not consistently correlate with SAR distributions.
• Regulatory limits for local temperature may be less restrictive than those for local SAR.