Feasibility study of subject-specific, brain specific-absorption-rate maps retrieved from MRI data

Area of Science:

• Medical Imaging
• Biophysics
• Magnetic Resonance Imaging

Background:

• Specific Absorption Rate (SAR) is vital for monitoring radiofrequency power absorption in MRI.
• Current numerical simulations for SAR distribution are time-consuming and impractical for real-time, patient-specific assessments.
• This limitation hinders immediate clinical application of SAR data.

Purpose of the Study:

• To confirm the feasibility of deriving in vivo, subject-specific, image-based SAR and 10-g SAR maps directly from MRI data.
• To establish a practical method for real-time SAR assessment during MRI examinations.
• To provide an alternative to traditional simulation-based SAR calculations.

Main Methods:

• Complex B1+ maps were generated using a combination of XFL magnitude and balanced steady-state free precession phase sequences.
• Anatomical information and tissue masking were obtained from T1-weighted imaging.
• Electrical conductivity maps were derived from balanced steady-state free precession phase, and whole-brain SAR maps were created from 3T MRI data acquired with a 32-channel head coil.
• A correction factor was applied to account for B1+ underestimation, and results were compared with simulation-based SAR distributions.

Main Results:

• Multi-slice, image-based brain SAR maps were generated in 12 minutes (9-minute acquisition, 3-minute reconstruction).
• In vitro experiments validated B1+ distribution and electrical conductivity values, which were within reference ranges for both in vitro and in vivo experiments.
• Image-based SAR and 10-g SAR maps demonstrated a distribution similar to simulation-based maps (r=0.5) after applying a correction factor.

Conclusions:

• This study confirms the feasibility of generating inline, subject-specific SAR and 10-g SAR maps using standard clinical brain MRI sequences.
• Image-based SAR mapping presents a practical and efficient alternative to simulations for intra-exam SAR assessment.
• This method enhances the potential for real-time, patient-specific safety monitoring during MRI procedures.