From complex B(1) mapping to local SAR estimation for human brain MR imaging using multi-channel transceiver coil at...

Area of Science:

• Medical Physics
• Biomedical Engineering
• Radiology

Background:

• Ultra-high-field (UHF) magnetic resonance imaging (MRI) offers enhanced signal-to-noise ratio but poses safety concerns due to elevated specific absorption rate (SAR).
• Accurate local SAR calculation is crucial for UHF MRI safety, requiring knowledge of electric fields and tissue properties.
• Current numerical simulations for SAR estimation are time-consuming and lack subject-specific anatomical and electrical property data.

Purpose of the Study:

• To develop and validate a novel method for estimating local, voxel-wise, and subject-specific SAR in UHF MRI.
• To utilize measurable radio-frequency magnetic fields (B1) to predict SAR, overcoming limitations of conventional methods.
• To assess the accuracy of the proposed SAR estimation technique in numerical simulations and experimental studies.

Main Methods:

• Mathematical deduction from measurable B1 fields to estimate local SAR.
• Multi-channel transceiver array coil utilized for RF transmission.
• Validation through numerical simulations with human head models.
• Experimental verification using a physical phantom and human subjects at 7T.

Main Results:

• Demonstrated the feasibility of estimating subject-specific SAR from B1 field measurements.
• Achieved voxel-wise SAR estimation for individual coil elements.
• Experimental results at 7T corroborated the simulation findings.

Conclusions:

• The proposed method enables accurate, subject-specific SAR prediction in UHF MRI using multi-channel RF transmission.
• This approach addresses the limitations of traditional SAR estimation techniques.
• Improved SAR assessment is vital for enhancing the safety of advanced UHF MRI applications.