Patient safety concept for multichannel transmit coils

Area of Science:

• Medical Imaging
• Electromagnetics
• Biophysics

Background:

• Multichannel transmit coils in MRI offer advanced capabilities but introduce new safety challenges.
• Current radio frequency (RF) safety protocols may not adequately address the complexities of these systems.

Purpose of the Study:

• To propose and validate a novel safety concept for multichannel transmit coils in MRI.
• To utilize finite-differences time-domain (FDTD) simulations and experimental measurements for this purpose.

Main Methods:

• FDTD simulations were performed to model specific absorption rate (SAR) distributions in an agarose phantom.
• RF driving conditions, including amplitude and phase, were systematically varied for a four-element coil array.
• MRI was used to measure transmit field distributions and temperature rise.

Main Results:

• Simulated and measured field distributions showed quantitative agreement, validating the FDTD modeling approach.
• Varying the RF phase between coil elements resulted in a significant (approx. 15-fold) variation in maximum SAR distribution.
• This highlights the critical impact of phase settings on localized RF power deposition.

Conclusions:

• Existing RF safety measures are insufficient for multichannel transmit coils.
• A new safety concept is proposed, involving systematic exploration of RF phase and amplitude parameter space.
• This approach enables identification of driving conditions that maximize local SAR, informing MRI system safety.