Multi-Channel Rf Generator Ciriuit Design For High Field Magnetic Resonance Imaging

Magnetic Resonance Imaging (MRI) has been widely used in clinical medicine with the rapid development of MRI technology all around the world. In the MRI system, spectrometer is the core equipment of the MRI system. The radio frequency (RF) generator circuit is an important component of the spectrometer. With the running of sequence controller, it can generate the RF pulse whose frequency, phase, amplitude, waveform and pulse width can be controlled, to generate the Bi field for MRI. With the popularity of high field MRI system (1.5 T and above system), because RF pulse wavelength is close to the size of human tissue, the RF pulse for the image uniformity and the RF power deposition has a significant impact particularly. Therefore, using multi-channel parallel transmission technology to improve image quality and reduce the RF power deposition value plays an important role in the high field MRI system.This article is designed by multi-channel RF generator circuit firstly in China based on ARM and field-programmable gate array (FPGA), which can flexibly achieve the generation of multi-channel RF pulse. The circuit of RF is used for high field Nuclear Magnetic Resonance (NMR) system, and the frequency for output of RF signal can be up to 127.74 MHz, and it is suitable for 1.5 T to 3 T high-filed system. The data communication between external sequence controller and ARM (STM32F205) is realized. The parameters and data of FPGA are configured through the local parallel bus to control Direct Digital Synthesizer (DDS) operation. Those make the design more flexible and efficient. The frequency, phase, amplitude, and the parameters of soft pulse which are waveform length line, waveform data and time precision, can be controlled. Through the FPGA module design, the time precision of the soft pulse soft pulse time precision is improved significantly, which can reach 0.1 us. The design implements eight-channel generator circuit of 3 T system and dual-channel generator circuit of 1.5 T system, which reduced the development costs and the RF generator circuit has characteristics of compact volume and convenient debugging by adopting the above hardware technology solutions.