A method for improving the magnetic resonance imaging contrast of a selected portion of a sample. A selected ferrimagnetic constituent is associated with the sample portion, by molecular or biological attachment or by some other means, so that the sample portion is distinguished from other adjacent portions of the sample that do not have the selected ferrimagnetic constituent associated therewith. Alternatively, the sample portion is suspected, but not yet confirmed, to have the selected ferrimagnetic constituent associated with it. Ferromagnetic resonance imaging is performed on the sample portion, and at least one resonance frequency ω0 of the sample portion is provided. At least one material parameter of the sample portion is measured at or near the frequency ω0, with enhanced imaging contrast relative to adjacent portions of the sample that do not have the selected ferrimagnetic constituent in association. Alternatively, the measured value is compared with a corresponding reference value for the selected ferrimagnetic constituent. If (and only if) the measured and corresponding reference values substantially agree, the selected ferrimagnetic constituent is present in association with the selected sample portion. Other parameters of the selected ferrimagnetic consituent can also be measured.