Design of RF Transmitter with high speed for Magnetic Resonance Imaging (MRI) using 8-Core DDS System of FPGA
Abstract
An overall goal of the research is to investigate a new approach to the MRI RF Transmitter. Design a highspeed MRI RF transmitter. The goal is to explore the potential of a built-in DDS core of an FPGA chip to generate a dualchannel output at a 1 GHz sampling frequency of each. This output will be processed by a dual-input DAC chip for a total of 2 GHz sampling rate. The entire system should be able to generate the output signal ranging from 100 kHz to 750MHz. To accomplish this goal, it is necessary to study and to investigate the structures of these features to see how they could be utilized as a main core in a pulse generator
According to the datasheet provided by Xilinx, a DDS core has a single sine or/ and cosine output signal. The DDS core can operate at a maximum clock of 250 MHz. A 250 MHz clock speed is insufficient to generate outputs at 1 GHz sampling frequency. Consequently, the proposed custom DDS system is expected to quadruple the clock speed of the system by implementing multiple DDS core modules within the system.
Keywords
Download Options
Introduction
1.1 Introduction of Magnetic Resonance Imaging
MRI spectroscopy is a technique used to study the physical, chemical and biological properties of materials by probing the nuclear dipole moments in the material. It was found and measured using molecular beams by Isidor Rabi in 1938. He received the Noble Prize in Physics in 1944 for his work. Two years later, Felix Bloch and Edward Mills Purcell expanded the technique to liquids and solids. They used it as an analytical tool in chemistry and physics in 1946.
An overall goal of the research is to investigate a new approach to the MRI RF Transmitter. The detail research objectives are as below:
Design a high-speed MRI RF transmitter: The goal is to explore the potential of a built-in DDS core of an FPGA chip to generate a dual-channel output at a 1 GHz sampling frequency of each. This output will be processed by a dual-input DAC chip for a total of 2 GHz sampling rate. The entire system should be able to generate the output signal ranging from 100 kHz to 750MHz. To accomplish this goal, it is necessary to study and to investigate the structures of these features to see how they could be utilized as a main core in a pulse generator. However, due to the limitations of FPGA to go beyond an allowable clock speed in DDS, the challenges of this problem lead to four objectives as below:
a) Design a new topology for an MRI RF transmitter by using Matlab-Simulink. The Simulink is used to design the structures of a high-speed RF transmitter. The structures are verified through the Matlab-Simulink simulation.
b) Simulate the designs in 1.3(a) above in the register-transfer level (RTL-level) simulation by using the Xilinx Verilog compiler. The simulations in Matlab do not consider the timing constraints within the DDS system. Matlab simulations are used to verify the functionality of the design and to analyze the flow from input to output. Therefore, it is necessary to simulate the design in RTL-level to ensure the behavioral structures meet the timing constraints.
c) Design a new methodology to run a dual-output DDS module at 1 GHz each. The 1GHz frequency is beyond the clock limitation of an internal DDS core in an FPGA chip.
Conclusion
The RF Transmitter for Magnetic Resonance Imaging (MRI) is designed using 8-Core DDS System by Simulink Block set and Xilinx Block set. The System Generator tool converted the design into Verilog HDL. All these designs are simulated by using Xilinx ISE Simulator and then Synthesized by using Xilinx Synthesis Tool. All these designs are prototyped on Virtex5 LX110T FPGA board. The RF Transmitter for Magnetic Resonance Imaging (MRI) is designed using 8-Core DDS System by Matlab Simulink Library and System Generator Tool. The design is simulated for functionality by using Xilinx ISE simulator tool.
The synthesized RF Transmitter for Magnetic Resonance Imaging (MRI) using 8-Core DDS System has 1099 LUT slices, 719 slice registers and 2 buffers. Timing analysis results show that the critical path is 3.091 ns i.e., the maximum clock frequency is 323.520MHz. The synthesized RF Transmitter for Magnetic Resonance Imaging (MRI) using 8-Core DDS System was successfully implemented on Xilinx Virtex 5 FPGA.
The RF Transmitter for Magnetic Resonance Imaging (MRI) can be extended to multi-frequency RF Generator. The design can cover the frequency range from 100 KHz to 750MHz.