Authors

Isabelle Saniour, Anne-Laure Perrier, Gwenaël Gaborit, Jean Dahdah, Lionel Duvillaret, Olivier Beuf

Abstract

In magnetic resonance imaging (MRI), the real time measurement of RF electrical field E associated with the RF magnetic field B1 is important to quantify the energy absorbed by the tissues and to assess possible safety hazards due to local heating phenomenon. E-field could effectively increase the temperature in the tissues nearby by inducing RF currents in any implant or metallic cables used for signal transmission and placed inside the transmit body-coil (1, 2). For the measurement of the intensities and the distribution of E-field, the adequate probe should be non-magnetic and non-perturbative regarding the E-field and must have a large working frequency range depending on B0. The commonly used probes have either a metallic structure or a large dimension which limits their bandwidth (3, 4) and may disturb the electromagnetic field with bias measurements. Others optical probes do not measure directly the E-field (5). In the following, the E-field measurement experiment using a sub-cm electro-optical (EO) probe in a preclinical 4.7-T MR system is presented.

Introduction

The specific absorption rate (SAR) has become a standard parameter to evaluate the energy absorbed by the tissues during the magnetic resonance imaging (MRI) examination. The measurement of the electrical field which is associated with the radiofrequency (RF) magnetic field could be used as a method to determine the SAR-values. In addition, real time assessment and tracking of the E-field is important in identifying and avoiding any possible safety hazards due to local heating phenomenon (1,2) especially in the presence of external coils or implants inside the patient’s body. For E-field measurements, there are basically two types of probes: metal-based probes (monopole, diode loaded dipole,…) and electro-optical (EO) probes. The latter is more appropriate for MR applications because it has the advantage of being non-magnetic and non-perturbative as regards the orientation and the magnitude of the E-field….

Reference

ISMRM 2016, May 2016, Singapour, Singapore

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