Evaluation of the static magnetic field interactions for a newly developed magnetic ophthalmic implant at 3 Tesla MRI

Abstract

Purpose The purpose of this study is to analyze the static magnetic field interactions for an ophthalmic-magnetic shunt implant with a ferromagnetic steel plate in a thin silicon layer. The plate is used for opening of a valve flap. Ten different sizes of this steel plate were investigated to characterize the relationship between the size of the metal and the magnetic forces of the static magnetic field of a 3.0 T MRI.

Materials and Methods The magnetic translation force F_z was quantified by determining the deflection angle using the deflection angle test (ASTM F 2052). The torque was qualitatively estimated by using a 5-point grading scale (0: no torque; + 4: very strong torque) according to Sommer et al. [11]. For the visual investigation of the function of the metal plate both prototypes were positioned at the magnetic field’s spatial gradient and at the magnet’s isocenter. The stitches were exposed to the thousandfold of the translational force by a dynamometer.

Results The translational force was found to be 10 times greater than the weight of a single plate. The plates were exposed to a high torque (grade 3 to 4). The seams and the tissue withstood more than a thousandfold of the determined translational force. No spontaneous, uncontrolled opening of the valve flap was visible in the MRI, as a result of which the intraocular pressure could decrease considerably.

Conclusion Due to the small size of the plates the translational force and the torque will be compensated by the silicon layer and also by the fixation in the eye.

Key points: 

• Magnetic forces will be compensated by silicon layer and fixation in the eye.

• The magnetic-ophthalmological implant is not restricted in its function by the MRI magnetic field.

• The ophthalmic magnetic shunt implant can be considered conditionally MRI-safe.

Citation Format

• Bodenstein A, Lüpke M, Seiler C et al. Evaluation of the static magnetic field interactions for a newly developed magnetic ophthalmic implant at 3 Tesla MRI. Fortschr Röntgenstr 2019; 191: 209 – 215

Key words

ophthalmologic implant - magnetic resonance imaging - MRI safety - magnetic forces

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