Study of MRI Susceptibility Artifacts for Nanomedical Applications

This article deals with the exploitation of magnetic susceptibility artifacts in magnetic resonance imaging (MRI) for the recognition of metallic delivery capsules. The targeted application is a closed-loop position control of magnetic objects implemented using the components of a clinical MRI scanner. Actuation can be performed by switching the magnetic gradient fields, whereas object locations are detected by an analysis of the MRI scans. A comprehensive investigation of susceptibility artifacts with a total number of 108 experimental setups has been performed in order to study scaling laws and the impact of object properties and imaging parameters. In addition to solid metal objects, a suspension of superparamagnetic nanoparticles has been examined. All 3D scans have been segmented automatically for artifact quantification and location determination. Analysis showed a characteristic shape for all three base types of sequences, which is invariant to the magnetic object shape and material. Imaging parameters such as echo time and flip angle have a moderate impact on the artifact volume but do not modify the characteristic artifact shape. The nanoparticle agglomerates produce imaging artifacts similar to the solid samples. Based on the results, a two-stage recognition/tracking procedure is proposed.