ENDOLUMINAL MR RECEIVER COIL BASED ON ELECTRO-OPTICAL CONVERSION AND ACTIVE OPTICAL DECOUPLING
Résumé
The use of endoluminal coil in magnetic resonance imaging (MRI) located close to the region of interest enhances image spatial/temporal resolution using the local signal-to-noise ratio (SNR) gain. Wall bowel analysis could be then performed and wall layer could be distinguished for a better diagnosis and characterization of inflammation and lesions [1]. Conventionally, coaxial cables connecting the MRI console and the receiver endoluminal coil are used to transmit the NMR signal and the DC bias current used for active decoupling. However, patient safety can be compromised by heating of tissues located in proximity of these cables. In fact, the electric field accompanying the radiofrequency (RF) magnetic field B1 induces high-frequency currents along the metallic wire and thus increases the specific absorption rate (SAR) by the tissues lying nearby [2]. To ensure full patient safety, an optical fiber was chosen as an alternative solution to transfer optically the RMN and the DC decoupling signal. Both electrical signals are converted into optical signals: the conversion of NMR signal is based on Pockels effect ensured by an electro-optical (EO) crystal which its refractive indexes change according to an applied electric field. While DC signal is converted by the use of optoelectronic devices. The electro-optical (EO) conversion and the active optical-base decoupling were demonstrated and proven separately in previous works [3], [4]. In the following, the results of these previous works are presented and a novel type of endoluminal receiver coil combining both optical transmission and active optical decoupling was designed.
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