RF heating reduction associated to an MR endoluminal coil at 3T

International audiencePurpose/Introduction: MR endoluminal coils increase the Signal-to-Noise Ratio (SNR), allowing better distinction of the layers of the bowel: a crucial criterion for diagnosis of bowel diseases [1]. But they present a risk of burn for the patient. Radio Frequency (RF) electric field may cause important heating due to local concentrations of the E-field along the conductive cable and coil [2]. In this paper, the efficiency of RF traps toward heating suppression was assessed. The particular case of a 225 cm long receiver cable was with a cable path configuration tested to be in the worst case scenario

Réalisation de capteurs endoluminaux en Imagerie de par Résonance Magnétique à 3T: performances et sécurité

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A susceptibility matched endorectal coil design suited for the MRS examination of the rectal wall

International audienceA susceptibility matched endorectal coil was tested and compared against a classical endorectal coil design. For different phantom angulations, it enabled a significant decrease (~30%) of the FWHM of spectra acquired on in vitro NMR tubes. These promising results and the restricted FWHM observed suggest the interest of this new coil for the acquisition of in vivo spectra especially for the characterization of the colorectal cancer

assessment of RF heating reduction devices for endoluminal MR imaging at T

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Assessment of miniaturized RF traps for RF heating reduction and reception coil sensitivity profile restoration

International audienceTo reduce RF-induced heating, standard passive RF traps are known to be efficient. Novel miniaturized RF traps are as efficient as standard ones for this purpose. Furthermore, it is demonstrated that RF traps enable a restoration of the signal intensity pattern of the coil. It is thus possible to perform a MR endoscopy of deeper regions of the bowel (after left colonic flexure for instance) since the coaxial cable incorporating miniaturized RF traps now may be inserted through the rectum with limited discomfort for the patient

Distribution of RF Traps to Reduce RF Heating with Endoluminal Coils: An Experimental Study

International audienceThere are many techniques considered in the literature to reduce RF heating. A small number of passive RF traps incorporated in the reception cable present excellent results in the case of an endoluminal coil at 3T. The historical design of RF trap such as LC filters is efficient. Due to the distribution of induced currents in the cable, a close attention should be paid to the location of the RF traps along the cable. Optimal placememt can also narrow down the number of RF traps to a minimum

Optimization of intra-voxel incoherent motion imaging at 3.0 Tesla for fast liver examination.

International audienceBACKGROUND: Optimization of multi b-values MR protocol for fast intra-voxel incoherent motion imaging of the liver at 3.0 Tesla. METHODS: A comparison of four different acquisition protocols were carried out based on estimated IVIM (DSlow , DFast , and f) and ADC-parameters in 25 healthy volunteers. The effects of respiratory gating compared with free breathing acquisition then diffusion gradient scheme (simultaneous or sequential) and finally use of weighted averaging for different b-values were assessed. An optimization study based on Cramer-Rao lower bound theory was then performed to minimize the number of b-values required for a suitable quantification. The duration-optimized protocol was evaluated on 12 patients with chronic liver diseases RESULTS: No significant differences of IVIM parameters were observed between the assessed protocols. Only four b-values (0, 12, 82, and 1310 s.mm(-2) ) were found mandatory to perform a suitable quantification of IVIM parameters. DSlow and DFast significantly decreased between nonadvanced and advanced fibrosis (P < 0.05 and P < 0.01) whereas perfusion fraction and ADC variations were not found to be significant. CONCLUSION: Results showed that IVIM could be performed in free breathing, with a weighted-averaging procedure, a simultaneous diffusion gradient scheme and only four optimized b-values (0, 10, 80, and 800) reducing scan duration by a factor of nine compared with a nonoptimized protocol. Preliminary results have shown that parameters such as DSlow and DFast based on optimized IVIM protocol can be relevant biomarkers to distinguish between nonadvanced and advanced fibrosis. J. Magn. Reson. Imaging 2014. © 2014 Wiley Periodicals, Inc

Characterization of a dedicated double loop, endoluminal coil for anal sphincter MR imaging at 1.5 T and 3 T

International audienceMRI has proven its usefulness in the prediction of surgical anterior anal repair that cannot be done with the reference endosonographic exam. Conventional endorectal coils are often based on a single loop coil design and do not possess satisfactory radial uniformity which could impede the correct assessment of the anal sphincter. In this study, several double loop endorectal coils were designed, built, and assessed in simulations, on phantoms and in vivo. The optimum was found for a 50°–70° double loop endorectal coil which presents a better radial uniformity especially at close distance from the coil where the SNR is the highest. First in vivo experiments proved enhanced readability of the MR exam for the radiologist