Node-Link and Containment Methods in Ontology Visualization

A method and apparatus for correcting ghost artifacts that are related to orthogonal perturbation magnetic fields is disclosed. The technique includes acquiring MR data and an MR reference scan, each in the presence of orthogonal perturbation magnetic fields. However, the region of interest for the MR reference scan is limited to a relatively narrow band within the imaging subject. Preferably, the narrow band is selected in the vicinity of the magnet iso-center and parallel to the readout direction. Alternatively, the narrow band can also be selected in the limited region where the orthogonal perturbation fields are either minimal or constant along the phase encoding direction, and parallel to the readout direction. The selection of the relatively narrow band is accomplished by either spatially saturating surrounding regions, or using a two-dimensional spatially selective RF pulse. Phase correction values can then be calculated from a more accurately defined slope and intercept of the phase of the MR reference scan and used to correct the MR data. A reconstructed MR image using this technique has reduced ghost artifacts otherwise caused by the adverse effects of the orthogonal perturbation fields in the phase correction process.