A Numerical Alternative to MR Thermometry for Safety Validation of Multi-Channel RF Transmit Coils

Area of Science:

• Medical Imaging
• Biophysics
• Electromagnetism

Background:

• Patient safety in MRI requires adherence to specific absorption rate (SAR) limits.
• Electromagnetic simulations are crucial for predicting SAR in parallel transmit systems but need experimental validation.
• Existing validation methods, like Magnetic Resonance Thermography (MRT), face technical challenges, necessitating alternative approaches.

Purpose of the Study:

• To propose and validate a numerical technique for estimating peak local SAR uncertainty in multi-channel RF coils.
• To offer an alternative to experimental temperature and electric-field measurements for safety validation.
• To enable human studies at ultra-high field strengths (10.5T) by improving SAR estimation.

Main Methods:

• The technique propagates errors from experimentally acquired B1+ distributions to simulated peak local SAR uncertainty using Monte-Carlo simulations.
• It bypasses the need for MRT by comparing experimental and numerical B1+ maps.
• Validation was performed using 16-channel and 8-channel RF coils at 10.5T.

Main Results:

• The proposed numerical technique provides more conservative SAR error quantification than MRT-based methods.
• It facilitated regulatory approval for human head imaging using three state-of-the-art head coils at 10.5T.
• High-quality diffusion and functional MRI results were achieved at 10.5T.

Conclusions:

• The technique enables SAR prediction uncertainty estimation through experimental B1+ map acquisition and comparison with simulations.
• It was successfully applied to multi-channel transmit and receive arrays for in vivo imaging.
• This method enhances the safety validation process for advanced MRI systems at ultra-high fields.