Patent ID: 8013609

Claim:
A magnetic resonance imaging system having a transmit phase and a receive phase, the system comprising: a) a main magnetic field generator for generating a main magnetic field through an imaging region; b) a gradient field generator for generating magnetic field gradients across the main magnetic field; c) a radio frequency transmitter coil for selectively transmitting an RF transmit pulse having a resonance frequency spectrum through the imaging region during the transmit phase, exciting nuclei in the imaging region to generate magnetic resonance signals in the resonance frequency spectrum; d) an RF receive coil, adapted to resonate in the resonant frequency spectrum, for receiving magnetic resonance signals during the receive phase; and e) a detuning circuit for detuning the RF receive coil during the transmit phase, the detuning circuit including e1) a resonance circuit including a detuning capacitor and a detuning inductor; e2) a PIN diode coupled in series to said detuning inductor and together with said detuning inductor in parallel communication with said detuning capacitor for enabling or disabling the resonance circuit; e3) a bias current generating circuit for generating a DC bias current through the PIN diode during the transmit phase including: e31) a rectifier coupled, with the same serial polarity, in parallel to the PIN diode, e32) a current limiting circuit coupled in series to said rectifier and together with said rectifier in parallel communication with said detuning capacitor for passing a small current through the rectifier, and e33) a reactive circuit coupled between the common node of the detuning inductor and the PIN diode and the common node of the rectifier and the current limiting circuit for passing a DC current between said common nodes.