Magnetic field gradient imaging for material classification by magnetic resonance imaging

In a uniform magnetic field, objects with different magnetic susceptibility may cause magnetic field distortion that can be detected by magnetic resonance imaging (MRI). Conventional MRI techniques focus on magnitude image that shows dark signals at non-uniform magnetic field. However, it is difficult to obtain the magnetic susceptibility information just from the magnitude of signal. A post-processing method is proposed to measure the magnetic field gradient induced by the sample object. Both the polarity and strength of magnetic field gradient can be calculated by this method. The method is proved by MRI experiments with paramagnetic material iron oxide particles at different concentrations, copper, and diamagnetic material graphite.