Research And Realization For Gradient Controller In MRI Spectrum Console

MRI ( Magnetic Resonance Imaging) is a new and high-tech production which combines with physics computer technology elec-tronic technology machine manufacture and fine chemical. As a new medical diagnosis method, MRI has been shown out its amplitude ap-plication foreground. As a kernel of the MRI, spectrum console con-trols the operation of the MRI. It generates three gradient fields direc-ting X Y and Z respectively and emits pulse sequence to the emitting coil. It can also receive and process the magnetic resonance signal (FID, free inducing decay or ECHO, echo sequence) caused by the phenomena of magnetic resonance. According to the intension of the magnetic resonance signal, it can be used to format image applied to medical diagnosis.In this paper, I pay my emphases on analyzing the theory and structure of the Gradient Control system under the introducing MRI general theory and structure and also present realization method in de-tail. At the same time, I provide the theory base for calculating varies of parameters and final design result.Gradient control system controlled by the computer provides a gradient field that can be switched quickly and has well linearity. Stat-ic field can be modified automatically and spatial position of voxel ( volume element) can be provided. In imaging process, the computer samples homologous waveform of gradient current according to the scansequence and store pulse sequence in a file. When initial sequence start the pulse sequence values are stored in memory. When the scan is started address counters are operated and gradient data store are se-lected orderly . The computer generates timing and logic gradient of the X,Y and Z - axis according to the scan sequence and calculates rotation angles of space - oriented . Then it is transferred to gradient waveform generator to calculate the transformation matrices by multi-plier . The transformation matrices assign gradient rotation, gradient linearity and phase encode orientation .In my paper, gradient control system communicates with the com-puter through ISA interface. The waveforms stored in gradient control system adopted higher - speed dual port RAM receive logic values of gradient waveform from the computer. We use a TMS320C5402as a DSP and a FPGA ( XC2S150PQ208 - 5 ). The multiplied values are actual gradient control signal values. These values are stored in FIFO, then are sent to D/AC under controlling by gradient control system. The values are converted to analogue signal which is sent to gradient power amplifier. In this design , the D/AC input is 16bits binary val-ue.In the circuit, it consists of waveform store , matrix multipliers , matrix calculator and sequencers . This paper also provides many structure diagrams, simulation wave figures and some VHDL codes. It also gives selective standard and offset analysis for D/AC . The experi-ment process and stimulator results indicate that this design is correct and plan is available . The testing result indicates that this design can meet the need of the project.Because the room is limited, I pay more emphases on researching and analyzing the principle and structure of all parts. The detail DSPsequence list, VHDL sequence list , hardware principle scheme and PCB scheme are not in this paper.