An improved method to measure transfer functions using MRI.

Area of Science:

• Medical Imaging
• Electromagnetics
• Biophysics

Background:

• Current MRI transfer function assessment relies on the transceive phase assumption (TPA).
• TPA limits applicability to shorter leads and lower field strengths.
• A more generalizable method is needed for diverse MRI applications.

Purpose of the Study:

• To develop a novel MRI-based method for transfer function assessment.
• To overcome limitations of the transceive phase assumption (TPA).
• To enhance applicability for longer leads and higher magnetic field strengths.

Main Methods:

• Determined background electric fields from both B1+ and B1- field distributions.
• Utilized spoiled gradient echo multiflip angle acquisition for B1 field mapping.
• Employed a magnitude squared least squares approach for B1 field modeling.
• Validated the method using EM-simulated data, phantom experiments, and bench measurements.

Main Results:

• Accurate reconstruction of B1 fields, currents, and incident electric fields in simulations.
• Experimental transfer function determination showed high similarity to simulations.
• Experimental results demonstrated accurate transfer function determination despite minor field model deviations.
• The method proved effective for copper wire lengths up to 40 cm.

Conclusions:

• A more generally applicable MRI-based transfer function assessment method is presented.
• The new method avoids phase assumptions, expanding use to longer objects and higher field strengths.
• Improvements in B1 mapping and the solution algorithm enhance the method's robustness.