Cavernous hemangiomas: dipolar susceptibility artifacts at MR imaging.

A misleading susceptibility artifact was originally encountered at magnetic resonance imaging in a patient with multiple cavernous hemangiomas. By using a gradient-recalled echo sequence, the artifact appeared on axial sections as a single ring of enhanced signal intensity within the expected signal void around many of the individual lesions. It was hypothesized and confirmed through phantom experiments with ferromagnetic samples that hemosiderin deposits within each lesion behaved like a point magnetic dipole, causing the intravoxel signal interference patterns that appeared as a ring of enhanced signal intensity. The artifact was therefore found to be entirely susceptibility-induced. Knowledge of the origin and appearance of this new artifact will aid radiologists in the interpretation of susceptibility images and help them avoid misinterpreting a single lesion as multiple contiguous lesions.