For a device to be used in an MR environment, it needs to be evaluated for magnetic deflection and torque. A commonly used acceptance criterion is the magnetic induced deflection and torque as compared to forces and torque due to gravity. For magnetic deflection, if the magnetic force is less than the force due to gravity, then the deflection angle will be less than or equal to 45 degrees. This is very conservative and some devices may exhibit more deflection than this and still may be safe and pose acceptable risk to patients in the MRI environment.
What do you do?
To assess magnetic induced deflection at MED Institute, we test the device at a location of a known static magnetic field (i.e., static field and spatial gradient). If the device is expected to deflect more than 45 degrees in the desired static magnetic field we perform additional evaluation to determine if the magnetic induced force causes damage to adjacent tissue, leads to device migration, or otherwise adversely affects the performance of the device.
MR safety labeling is important, because a device that deflects too much under MR scanning can migrate within the body or cause trauma to tissue. Accurately determining a device’s MR safety requires more than merely placing the device in an MR scanner and measuring its deflection.
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