A valid transfer function measurement bench is described. Magn Reson Med 79:1766-1772, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Purpose To develop a fast and easy‐to‐use electrical properties tomography (EPT) method based on a single MR scan, avoiding both the need of a B1‐map and transceive phase assumption, and that is robust against noise. Theory Derived from Maxwell’s equations, conductivity, and permittivity are reconstructed from a new partial differential equation involving the product of the RF fields and its derivatives. This also allows us to clarify and revisit the relevance of common assumptions of MREPT. Methods Our new governing equation is solved using a 3D finite‐difference scheme and compared to previous frameworks. The benefits of our method over selected existing MREPT methods are demonstrated for different simulation models, as well as for both an inhomogeneous agar phantom gel and in vivo brain data at 3T. Results Simulation and experimental results are illustrated to highlight the merits of the proposed method over existing methods. We show the validity of our algorithm in versatile configurations, with many transition regions notably. Complex admittivity maps are also provided as a complementary MR contrast. Conclusion Because it avoids time‐consuming RF field mapping and generalizes the use of standard MR image for electrical properties reconstruction, this contribution is promising as a new step forward for clinical applications.

A very simple displacement sensor is presented with nanometric resolution over centimetric travel range. The compact system is composed of a laser-diode module and a photodiode array leading to a non-contact sensor. With a corner cube configuration, it is not sensitive to most of main mechanical defects of the mobile platform. The use of an optical fiber and a normalization process inspired from classical fourquadrant detectors allows high repeatability and minimal drifts. This paper exposes the setup, simulations and experimental results. Several displacements over millimeters range with a resolution of 1.2 nm sustain the simulations.

we present a reduced-order model of the squeezed-film damping phenomenon which is valid for flexible structures, large displacements (with respect to the gap) and small pressure variations (with respect to the ambient pressure). This reduced-order model is obtained by transforming the Reynolds equation into a form more amenable to modal projection techniques. Our approach is validated by comparison to simulated and experimental data. Moreover, we show that in several practical cases the "small pressure" hypothesis is not limitative, even when the gap becomes very small.

Numerical simulation is an essential tool for MRI safety testing of medical devices. The main issues remain the accuracy of simulations compared to real life and the studies of complex devices; but as the research field is constantly evolving, some promising ideas are now under investigation to take up the challenges.

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A low-cost method for the active alignment of twodimensional bundles of optical single mode fibres is described in this article. Submicron translational alignment accuracy is being implemented by this method. High positioning accuracy can be realised by combining electrostatic movement and monitoring of the insertion losses in a closed loop feedback alignment system.

Purpose: Multiple medical-device leads implanted next to each other are often encountered in clinical practice. The aim of this work is to study a coupled transfer function model to evaluate the safety of these coupled leads submitted to the RF field of a 1.5T MRI scanner for a constant distance between both leads. Methods: The effect of coupling on the heating of 2 cables with different termination conditions is evaluated experimentally. The coupled and single transfer functions are determined experimentally and used to predict the relative temperature increases of both cables alone and coupled. Two different coupled models, an additive model and a global model, are proposed. The coupled transfer functions are also simulated. Results: The coupling between cables has a strong influence on the resulting heating at the electrodes. The coupled additive transfer function model is a relevant tool to evaluate the heating of coupled leads separated by a constant distance. The global model underestimates the heating in one of the coupled cases by about 30%. The measured coupled transfer functions coincide with the simulated models. Conclusion: It is necessary to take into account the coupling effect between leads to evaluate the safety of implanted devices. This work shows that, in the case of 2 cables separated by a constant distance, that an experimentally determined coupled transfer function allows estimation of the heating of the 2 electrodes for a given incident field. Further work should take into account the in vivo varying distance between the 2 cables. K E Y W O R D Scables coupling, heating, MRI safety, pacemaker leads, radiofrequency, transfer function | INTRODUCTIONMagnetic resonance imaging is an essential imaging modality for soft tissue imaging. The main applications, among others, are cancer, musculoskeletal system, and neurologic disorders diagnostics. The number of MRI scans worldwide has increased considerably in the past few years, reaching 95 million a year. 1 The number of new implantations of pacing devices (pacemakers and defibrillators) is more than 750 000 a year worldwide. 2 The probability of needing an MRI scan doubles after the age of 65 years. 3 This is the same population that is most likely to have an implanted device.The pacing devices may interact with the strong static field of the MRI (torque, force, and electronics), the low-frequency 992 | KABIL et AL.How to cite this article: Kabil J, Felblinger J, Vuissoz P-A, Missoffe A. Coupled transfer function model for the evaluation of implanted cables safety in MRI. Magn Reson Med. 2020;84:991-999.