DECOUPLING WITH RF COIL PAIR EXPNDED OF MRI IN RF TUNING OF RF TRANSMISSION COIL FOR MRI

摘要

PURPOSE: To achieve the expanded decoupling and detuning of a reception coil by providing a step for impressing a forward bias to a varactor diode element connected to the RF reception coil of MRI in the manner of circuit. CONSTITUTION: Varactor diodes Di-D"7 are arranged so as to apply a coupling/ matching capacitance Cs and a parallel tuning capacitance Cp to be combined with a reception coil 14. They are insulated from RF by a resistor R in which a suitable DC bias control circuit is arranged as well. The contact of a relay K1 and a switch S1 is connected to a varactor at a backward bias voltage of which the level can be usually regulated by potentiometers 62 and 64 (a minimum tuning bias is determined by resistors 62' and 64' and in this case, it becomes the minimum tuning bias of about 3 volts.) When the relay coil K1 is operated by a detune instruction from a control computer, in this case, the contact of the switch S1 supplies the forward bias of 24 volts from a battery 70 to the varactor.