Local perturbation in magnetic field due to differences in magnetic susceptibility of tissues within the patient or between the patient and surrounding air. The abnormalities are similar to those produced by ferromagnetic implants but less severe. Depending on the imaging sequence and parameters, they may manifest as geometric distortion, signal loss due to intravoxel dephasing or mismapping of signals, signal summation at edges of area of distortion, impaired chemical fat saturation, and “blooming” (the apparent enlargement on GRE sequences of structures, such as vetebral bone, with large susceptibility effects).