Reina Aydé, Gwenaël Gaborit, Pierre Jarrige, Lionel Duvillaret, Raphaël Sablong, Anne-Laure Perrier, and Olivier Beuf
In this paper, we demonstrate the use of a LiTaO3 crystal associated with a typical nuclear magnetic resonant loop coil to perform an optically remote radio frequency magnetic-field characterization. The whole transduction scheme is theoretically and experimentally studied. The measurement dynamics reaches 60 dB. The minimum detectable magnetic field is lower than 1 nT, which corresponds to an induced inner crystal electric field as low as 30 mV/m. To evaluate the spatial potentialities of the sensor, a 1-D mapping of the field along an asymmetric butterfly-shaped loop coil is performed. The result is in good agreement with finite-difference time-domain simulations and demonstrates the vectorial behavior of the sensor device.
Magnetic Resonance Imaging (MRI) is based on a spatial characterization of the nuclear magnetization. Recording the variation of the nuclear magnetization is often realized with a MRI external surface coil. However, spatial resolution and image quality achievable with external surface coils are limited in the case of thin internal organs, e.g. bowel. On the other hand, the use of an endoluminal MRI coil located close to the area of interest could provide both high contrast to noise ratio (CNR) and high spatial resolution images leading, in turn, to a good evaluation of biological diseases , . Since metallic coaxial cables are mainly used with endoluminal coils, also located within the MRI transmit RF coil, heating phenomena may occur inside biological media . Optical fibre link can be used to overcome heating problem, thus ensuring patients safety , . Direct modulation of a laser diode remains invasive because its biasing requires a DC power supply . Furthermore, the achieved realizations including active devices may also be disturbed by the static magnetic field , , .
IEEE SENSORS JOURNAL, VOL. 13, NO. 4, APRIL 2013