The authors have performed many MR examinations for patients with magnetic keepers fixed in the mouth as part of a dental magnetic attachment system, who had been refused MR examinations because of the risk of heating the keeper as a result of exposure to RF radiation. The purpose of this study was to evaluate the risk of RF heat associated with MR imaging procedures. In this study, the RF heat of the keeper in a simulated phantom head was measured with a fiber optic temperature measurement system and 1.5-Tesla MR equipment. Measurement revealed that the RF heat of the keeper in the phantom was a maximum of 0.3℃. The authors concluded from this result that the RF heat of keepers fixed in the mouth does not exceed 1℃ during clinical MR imaging procedures of the brain. In this study, however, the risk of burn in the mouth caused by RF heat was not directly estimated. Therefore, it is important to exercise caution in performing MR examinations on patients with magnetic keepers.
