Design Of RF Circuit For MRI

This research contains three parts of MRI system which are Ultra-low Noise Preamplifier for receiver. Power Amplifier for transmitter, and RF Power Switch between receiver and transmitter.Pre-amplifier as one of the most important part of MRI receiver placed between the signal and the second part of amplifier. It has always been designed for the weak signal from MRI probes. The noise of pre-amplifier can directly influence the performance of MRI system. Considering that the noise will be impossible to remove from the output signal if we cannot filter some kinds of noise in the first receiver’s stage, we integrate the BPF filter and the Ultra-low noise amplifier IC to suppress the noise and hope to limit it at a very low level which was necessary for our system to keep an excellent SNR.RF Power Amplifier is a crucial device in MRI system which is usually placed at the end of MRI transmitter. The function of this kind of device is to transmit the power signal through the probes and make sure it can be used to fulfill different requirements. For the proposal of this power amplifier, we prefer to apply it for some portable devices more than some fixable instruments. Therefore, its power has been restrained by10W. Furthermore, a series of functions, which consist of power-supply supervisory system, Input/output power supervisory system and trigger supervisory system, have also been included in our design for self-protection.RF Switch-Power we designed consists of a Power-Outputs board and a Power-control board. The outputs board generates stable and continuously current with six channels and one external channel. In this board, we use the analog circuit because the ripple needs to be restrained in a short range. In Power-control board, we combine analog and logic circuit to control the PIN diode. The analog circuit will restrict the noise at a low level while the logic circuit will contribute to a high-speed work. At the end of the board, a low-resistance RF switch, which can prevent from too much heat, is set in each channel for a higher efficiency. Finally, this RF Switch-Power can work with30KHz. lOus rise-time and5A (MAX) load capacity.