The Effects of Magnetic Attachment Keepers on MRI Examination

Objectives: To evaluate the MRI artifacts induced by keepers of magnetic attachment system, and analyze the obscured anatomic structures within human's brain, neck and orofacial region. Methods: In in-vitro part, keepers of MAGFIT EX 400, MAGFIT EX 600 and MAGNEDISC 800 magnetic attachment systems were cast into standard root-caps with different alloy respectively, including nickel-chromium alloy and gold-palladiu alloy. To analyze the artifact range and shape, a phantom filled with purified-water was established. Then the phantom with keeper specimens was imaged with a 1.5-T MRI scanner. Extent of the artifacts in every slice was measured. In in-vivo part, volunteers with keepers in different position and amount were included, all of whom were imaged with 1.5-T MRI scanner, using SE sequence and GRE sequence, respectively. Extent of the artifacts in every slice was measured. The magnitude of the artifacts and the distortion of the anatomic structures were compared. Results: All kinds of keepers being studied produced obvious MRI artifacts. The extent of MRI artifacts induced by MAGFIT EX 400 keepers showed the minimum values (153.84mm), while MAGNEDISC 800 keepers showed the maximum values (173.00mm). The kind of casting alloys had no significant influence on the artifacts. The images of mental region, tongue, palate, jawbone and sinus were evidently obscured by artifacts in all cases. When keeper was put in the molar region, the keeper-related MRI artifact may obscure the imaging of brain, spinal cord, pharynx, parotid and condyle. SE sequence was more desirable in MRI for the patients with magnetic attachment keepers. Conclusion: Keepers of magnetic attachment system do induce considerable MRI artifacts in human's orofacial region, even in brain and spinal cord region. The extent of the artifacts and obscured anatomic structures depend on the type, amount and position of keepers, and also on MR imaging parameters.