Permanent magnet desktop magnetic resonance imaging system with microfabricated multiturn gradient coils for microflow imaging in capillary tubes

摘要

A prototype for a desktop high-resolution magnetic resonance imaging (MRI) velocimetry instrument to characterize flow fields in a capillary tube is demonstrated. This inexpensive compact system is achieved with a 0.6 T permanent magnetic configuration (Larmor frequency of 25 MHz) and temperature compensation using off-the-shelf NdFeB permanent magnets. A triaxial gradient module with microfabricated copper coils using a lithographic fabrication process has been developed. This gradient module is capable of generating fast-switching gradients (<100 μs) with amplitudes up to 1.7 T/m using custom made current amplifiers, and was optimized for microflow imaging. The radio frequency probe is integrated with the gradient module and is driven by custom electronics. A two-dimensional (2D) cross-sectional static image of the inside of a capillary tube with an inner diameter of 1.67 mm is acquired at an in-plane spatial resolution of better than 40 μm. Time-of-flight flow measurements were also obtained using this MRI system to measure the velocity profile of water flowing at average velocities of above 50 mm/s. The flow profile for slower flow velocities was obtained using phase-encoded techniques, which provides quantitative velocity information in 2D. © 2010 American Institute of Physics Article Outline INTRODUCTION EXPERIMENTAL SETUP Permanent magnet Triaxial gradient module Design of the gradient coils Simulation of the gradient fields for multiturn coils Fabrication of gradient coils rf coil and electronics Probe rf electronics RESULTS AND DISCUSSION Characterization of the gradient coils Imaging Fourier-based static imaging Microflow velocity imaging in a capillary tube TOF technique Phase encoding technique CONCLUSIONS AND DISCUSSIONS