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Phase unwrapping for magnetic resonance imaging near metal prostheses

Magnetic resonance imaging (MRI) has the potential to be the best technique for assessing complications in patients with metal orthopedic implants. However, the performance of existing fat suppression techniques is inadequate near metal, due to large variations induced in the magnetic field by the implant. The Dixon method can suppress fat in the presence of magnetic field inhomogeneities, but it requires a robust phase unwrapping algorithm. Current phase unwrapping methods are unable to resolve the large field variations produced by metal implants. This paper presents a new phase unwrapping technique which uses prior knowledge of the implant to aid the unwrapping. Initial simulation-based results are shown using a model which is offset in location and size from the simulated `true' implant. The proposed technique is able to successfully unwrap the phase extracted from simulated images with a signal-to-noise ratio of 10 dB.