A hardware reconstruction system for real-time magnetic resonance imaging via 2D FFT or filtered backprojection

Abstract

A "real-time" hardware reconstruction system for Magnetic Resonance Imaging (MRI) has been designed, constructed, and demonstrated. Here, "real-time" corresponds to frame rates of 30 or more per second (i.e., video rate). The system is capable of reconstructing images via either the 2D FFT algorithm or the filtered backprojection algorithm. The 2D FFT hardware reconstructs 256 x 256 images from complex-valued data (on a rectilinear grid) at a rate of 30 frames/sec while the filtered backprojection hardware is capable of reconstructing 64 x 64 images from complex-valued data (on a polar grid) at a rate of 37 frames/sec. Real-time MRI may be achieved by interfacing the reconstruction system to MR scanners with ultra-fast acquisition capabilities, such as echo-planar imaging (EPI) for rectilinear data or spiral-scan for polar data. The reconstruction system consists of a number of circuit boards plugged into the bus of a personal computer (PC). The circuit boards are configured by the PC, and thereafter, communicate with each other through ribbon cables independent of the PC operation. Three of the circuit boards are common in both reconstruction methods. They are an analog-to-digital convertor board (ADC), an interface memory board (IM), and a display processor board (DP). In the 2D FFT method a fourth circuit board referred to as the Fourier processor board (FP) is utilized. In the filtered backprojection method two additional circuit boards, a projection filter board (PF) and a backprojection board (BP) are used. The basic theory of the two reconstruction methods as well as design and implementation of the digital-electronic hardware are described in this dissertation. Real-time reconstructed images by both methods are presented to demonstrate the capabilities of the digital-electronic system.