MRI-based transfer function determination through the transfer matrix by jointly fitting the incident and scattered
Janot P Tokaya1,2, Alexander J E Raaijmakers1,2,3, Peter R Luijten4
1Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
Magnetic Resonance in Medicine
|October 22, 2019
Summary
A new experimental method determines the transfer function (TF) for MRI implants using only MR-measurable data. This technique accurately assesses radiofrequency heating potential, advancing safety assessments for medical devices.
Area of Science:
- Biomedical Engineering
- Medical Imaging Physics
- Electromagnetics
Background:
- Radiofrequency (RF) heating of medical implants during MRI is a significant safety concern.
- Current methods for assessing RF heating potential, such as phantom-based assessments, have limitations in realistic scenarios.
- Transfer functions (TFs) quantify the relationship between incident RF fields and implant response, crucial for predicting heating.
Purpose of the Study:
- To present a purely experimental method for determining the transfer function (TF) of linear implants using MRI.
- To enable TF assessment solely from MR-measurable quantities, specifically B1+ and transceive phase distributions.
- To move beyond phantom-based assessments towards more realistic, MR-based TF evaluations.
Main Methods:
- Utilized a transfer matrix (TM) model to derive an analytical description of B1+ magnitude and transceive phase distributions around wire-like implants.
- Employed a superposition of spherical and cylindrical harmonics to model the background field.
- Parameterized the TM using a previously introduced attenuated wave model.
Main Results:
- Successfully determined TFs for mock-up implants (bare and insulated copper wires) across various trajectories.
- Achieved high correlation (coefficients > 0.96) between measured TFs, simulated references, and independent experiments.
- Demonstrated low maximum deviations (9.4% and 12.2%) in estimated tip fields compared to simulations for bare and insulated wires, respectively.
Conclusions:
- Developed and validated an MRI-based experimental method for accurate TF measurement of medical implants.
- The technique, by jointly fitting B1+ distributions with the TM-based analytical model, eliminates the need for simulated data.
- This MR-based approach holds potential for TF assessment in more realistic settings, including preclinical (animal) and post-mortem studies.
