Magnetostatic Susceptibility Tomography: Experimental Feasibility Toward a Noncontact and Fast 3-D Mapping of Virtually Nonmagnetic and Inhomogeneous Bodies

The strategic goal is a magnetostatic susceptibility mapping or tomography through the volume of inhomogeneous and nonmagnetic bodies, where susceptibility imaging in magnetic resonance imaging (MRI) is also not well applicable. Ultrasound imaging or microwave radiation could also be hindered, for example, by strong scattering from the inhomogeneous interior. Objects of interest here are diamagnetic and/or paramagnetic materials with low susceptibility (by amount) and low or no electrical conductivity. These can be minerals or plastics, but might also be organics and humid materials, or liquid flows. Adaptions to metals are also briefly described. The noncontact measurements here are fast (less than a second) and direct. A disadvantage would be the rather modest resolution compared to susceptibility imaging in MRI. Technical basis of the magnetostatic susceptibility tomography (MST) approach is a permanent magnetic field through which the object under investigation passes quickly. Small field deformations (pT...nT) due to weakening (diamagnetic compartments) or enhancement (paramagnetic) are detected by induction coils, which also leads to a favorable spatial derivation for signaling. The theoretical forward description for the weakly coupling targets can be used here as purely linear and straight, advantageous over the typically nonlinear signaling of related electromagnetic tomography methods. In practice, small signals not far above the thermal noise floor are challenging because they are also subject to electromagnetic interference and/or mechanical vibration. For time being, the signaling (the forward behavior of MST) depending on spatial material accumulation in theory and practice is presented here; further maturation is recommended for 3-D mapping (the inverse problem). However, the path to get there seems clear.