DECOUPLING CIRCUIT OF SURFACE COIL FOR MRI

PURPOSE:To prevent resonance to a high frequency magnetic field by connecting a diode circuit wherein 2 or more diodes are connected in reverse parallel with a capacitor connected with a surface coil for MRI and connecting it between a signal line of a cable at a position where the length from a connecting part of the surface coil for MRI with the cable is an odd times of 1/4 of the MR wave length and an earth line. CONSTITUTION:A resonance circuit is constituted of a surface coil 2, capacitors 4 and 5, impedance of the surface coil 2, and a coaxial cable 7 is matched by means of the capacitors 4 and 5. A diode circuit 6 is made by connecting 2 or more PIN diodes in reverse parallel and is connected with the capacitor 5 in parallel. As a resonance preventing coil is not used, the ratio of electric voltage charged on the diode circuit 6 becomes higher and it results in a short circuit of the capacitor 5 and prevention of resonance. As a diode circuit 8 inserted at a position of a length of lambda/4 of the coaxial cable 7 makes a short circuit to a loop of a wave with a wave length of lambda, resonance to a high frequency magnetic field at transmitting can be prevented.