A method to approximate maximum local SAR in multichannel transmit MR systems without transmit phase information.

Area of Science:

• Medical Physics
• Magnetic Resonance Imaging (MRI)
• Electromagnetic Field Theory

Background:

• Accurate local specific absorption rate (SAR) calculation in MRI requires knowledge of both amplitude and phase of transmit signals.
• Existing methods for SAR estimation can be overly conservative or require complex phase information, limiting their applicability.

Purpose of the Study:

• To develop a method for deriving a conservative upper bound of local SAR without requiring knowledge of transmit channel phases.
• To improve the accuracy and safety margin of SAR estimations in MRI systems.

Main Methods:

• The proposed method utilizes virtual observation points (VOPs).
• Correction factors are calculated for VOPs to prevent underestimation of local SAR when using fixed phases.
• This approach allows estimation based on power measurements, bypassing the need for phase monitoring.

Main Results:

• The proposed method offers a superior alternative to worst-case calculations based on maximum eigenvalue.
• It successfully reduces the mean overestimation of local SAR across various coil setups.
• In tested scenarios, overestimation was reduced from a factor of 3.3 to 1.7, ensuring no underestimation of maximum local SAR.

Conclusions:

• The developed method provides a fast and reliable estimation of local SAR.
• It is particularly beneficial for MRI systems lacking the capability to monitor transmit phases.
• Facilitates enhanced SAR monitoring and safety compliance in diverse MRI applications.