Reduction of Artifact of Metallic Implant in Magnetic Resonance Imaging by Coating of Diamagnetic Material

Metallic implants composed of paramagnetic materials, such as stainless steel (SUS), Ti, Co-Cr-Mo alloy, etc., are widely used as artificial hip joints or aneurysm clips. When the metallic implant is placed in a uniform magnetic field of a magnetic resonance scanner, a magnetic disturbance is created due to its magnetization. This magnetic disturbance distorts the image of the metallic implant and body tissues in the magnetic resonance imaging (MRI). In order to overcome this problem, a method of coating the metallic implant with diamagnetic material has been proposed as the magnetic disturbance created by the metallic implant can be removed by the cancellation of the respective magnetizations of the paramagnetic and diamagnetic materials. But the optimal thickness of the diamagnetic coating has been obtained only for a sphere model by mathematical modeling. In this paper, the effects of a straight cylindrical hip joint model and an aneurysm clip model on the magnetic disturbance are investigated by using the magnetic field analysis of the finite element method (FEM). First, the magnetic disturbances generated by the two models made of paramagnetic material are calculated and compared with measured results. Moreover, the associations of susceptibilities chi_par and chi_dia of the paramagnetic and diamagnetic materials and the optimal thicknesses of the diamagnetic coating when the magnetic disturbances can be reduced for the two models are shown.