Geração e Controle de Pulsos de Radiofrequência para um Protótipo de Imagem por Ressonância Magnética

Abstract

Magnetic Resonance Imaging is a non-invasive, high-resolution imaging technique widely used in medicine for its ability to differentiate soft tissues without the use of ionizing radiation. However, there is a significant inequality in access to such equipment across Brazil, with large regions showing limited or no availability of MRI exams. The development of national MRI equipment represents an alternative to reduce costs and expand access, promoting technological autonomy. In this context, the CNPEM has been developing expertise in this field and currently has a 0.4 T MRI prototype partially developed at the center, except for the gradient amplifiers, power amplifiers, and console. This work marks the beginning of the console development, focusing on the RF transmission system. The objective was to design and validate a digital RF pulse generator implemented on a Field-Programmable Gate Array (FPGA), using the Red Pitaya development board and the VHSIC Hardware Description Language (VHDL). The methodology employed the Direct Digital Synthesis (DDS) technique for generating sine and cosine carriers through a Numerically Controlled Oscillator (NCO), combined with quadrature (IQ) modulation. The digital design was developed in VHDL and validated through testbenches in a simulation environment using Vivado software. Simulation results demonstrated the correct integration of the modules and the generation of the pulse with frequency matching the control parameter. This behavior validated the frequency-controlled signal generation using the DDS technique and pulse modulation. Bench tests showed a modulated pulse on the oscilloscope consistent with the simulations, confirming the correct FPGA implementation for RF pulse generation, with experimental values close to those obtained in simulation. This work contributed to the team’s technical training and served as an initial step in the development of the conceptual console. The results obtained in this process can be further optimized and improved to support CNPEM’s goal of developing a fully national MRI system in the future.