|Titre||RF heating reduction associated to an MR endoluminal coil at 3T|
|Publication Type||Conference Paper|
|Authors||Verret, J-M, Pilleul, F, Rabrait, C, Beuf, O|
|Full Text|| |
Purpose / 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 . 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 . 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. Subjects and Methods Experiments were performed on a GE DVMR750 3T system (General Electric Medical Systems). Endoluminal coil is a double loop coil prototype (60 mm length, 6 mm width) developed at CREATIS and was placed in 1.5 % agar gel phantom, an adequate medium for heat propagation. Four optic fiber probes were taped on the endoluminal coil: 3 at the distal extremity and 1 at the proximal base and connected to a temperature measurement device (Opsens Tempsens: 0.1 °C resolution, 0.357 Hz sampling rate). A FIESTA was performed with Acquisition Time: 1min36, 35°flip angle ; FOV :48*48 cm2, matrix 128*128, 250 KHz Bandwidth, TE/TR : 0.988/2.7ms. The receiver cable was an RG 58 coaxial cable 225cm long incorporating between0 and 5 RF traps. Inside the MRI bore, the receiver cable path passed through the maxima of the electric field, located with an electric dipole associated to a LED (Agilent HLMP 4015) Results Maximum temperature elevations measured at different locations in function of the number of traps are summarized in Table1.
Discussion/Conclusion RF heating is a local phenomenon which occurs mostly at distal extremity. Without RF traps, observed maximum temperature increase was 14.66 ± 1°C which would cause necrosis. In the worst case scenario, 5 RF traps efficiently suppressed heating for a cable length of 225 cm References  Pilleul, F, 2005, Lyon 1 Thesis  C. Armenean et al., 2004, Magn Reson Med 1200-1206
RF heating reduction associated to an MR endoluminal coil at 3T