Comments on “Ensuring safety of implanted devices under MRI using reversed polarization”

Abstract

In the work titled ‘‘Ensuring Safety of Implanted Devices Under MRI Using Reversed RF Polarization,’’ the authors propose a method based on reversed polarization, which can be used as a prescan technique for patients with implants. In their work, to visualize qualitatively the induced radiofrequency (RF) currents on a metallic lead inside the patient, they propose to reverse the RF polarization for the transmit and/or the receive procedure. They performed simulations and experiments to investigate the performance of this technique and correctly identified the dangerous coupling currents that may cause risk to the patients. They formulated the RF field that is generated by an induced current on a straight wire, and they calculated its effect on the image intensity in both the forward and the reversed polarization cases. They compared these analytical test results with the experiments and showed that the results accurately match. They claim that the coupling currents can be visualized with better sensitivity when reversed polarization is used. According to the authors, the transmit polarization reversal provides better background suppression, making it easier to distinguish signal variation in the vicinity of the lead from variations due to anatomy. With polarization reversal, they claim that better wire-signal accuracy is provided. Although using reversed polarization to visualize the coupling currents is an innovative idea and could enhance the safety of patients with implants who are undergoing MRI, with this letter we would like to note that there may be certain situations where the proposed method may not work efficiently to accurately visualize the induced currents. In these specific cases, the RF safety of the patient could still be under question.