Enhanced detection of paramagnetic contrast agents in magnetic resonance images via phase image cross-correlation analysis

Metal-ion based magnetic resonance imaging (MRI) contrast agents can be used to non-invasively track cells, target specific molecules, and watch gene expression in vivo. However, it is often difficult to detect and interpret the subtle image contrast changes produced by these agents if the biodistribution is not known a priori. Sensitive post-processing methods are needed to help identify localized accumulations of contrast agent and to minimize false positives and negatives. Towards these goals, we apply image cross-correlation methods to MRI phase images to highlight the characteristic magnetic susceptibility pattern created by magnetic dipoles in a magnetic field. We show that this method is very effective in highlighting localized paramagnetic deposits. We investigate the detection limits of this cross-correlation method, and we find that it can be used even for images with a very low signal-to-noise ratio (< 4). This method can be used alongside existing magnitude MRI methods, requires no extra scan time, and can be applied retrospectively to previously acquired data.