Department of Prosthodontics, Geriatric Dentistry and Craniomandibular Disorders, Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin and Berlin Institute of Health, Aßmannshauser Str. 4-6, 14197, Berlin, Germany.
Branch office Stendal, Clinic for Radio oncology, Johanniter Ltd., Wendstraße 31, 39576, Stendal, Germany.
J Orofac Orthop. 2023 Jul;84(4):252-263. doi: 10.1007/s00056-021-00360-9. Epub 2021 Nov 4.
Metal dental products lack precautionary statements regarding MR compatibility due to an exemption in the labelling obligation. Hence, it is difficult for radiologists to decide whether to remove fixed metal objects in patients prior to MRI. A solution could be the direct determination of the magnetic permeability (µ) as a decisive material-related predictor of artifact formation and other interactions. Thus, the applicability of an industrially used measurement device as a screening instrument and the relevance of the manufacturer's application restrictions in vitro and in vivo were tested.
Precision and trueness were tested using self-made test objects with different dimensions and different permeability. To clarify whether the measurement results are affected by the remanence (B) induced in the objects, 28 brackets of different materials were exposed to a weak and a strong external magnetic field and the magnetic flux density before and after these exposures was compared. The clinical test was performed on a volunteer with an orthodontic appliance experimentally composed of brackets with different levels of magnetic permeability (µ). Validity and intra- and interrater reliability were calculated using two rater groups consisting of four dentists and four medical-technical radiology assistants (MTRA), respectively.
With coefficients of variation below 0.14%, precision was excellent regardless of object surface and size. Trueness was high on objects with µ ≤ 1.002, and decreased with increasing µ, for which size-dependent correction factors were calculated. Intra- and interrater reliability and validity were excellent and independent of professional intraoral manipulation experience.
The permeability measurement allows for a valid and reliable determination of the magnetizability of intraoral metal objects. When used as a screening tool to detect nonartifact-causing objects, no correction factor needs to be calculated. For the first time, it offers radiologists a decision support for the selective removal of only the highly permeable components of the multiband apparatus.
由于标签义务的豁免，金属牙科产品缺乏关于磁共振兼容性的预防声明。因此，放射科医生很难决定在进行 MRI 检查前是否需要移除患者体内的固定金属物体。一种解决方案可以是直接确定磁导率（µ），作为预测伪影形成和其他相互作用的决定性材料相关因素。因此，测试了一种工业用测量设备作为筛选仪器的适用性以及制造商在体外和体内的应用限制的相关性。
使用具有不同尺寸和不同磁导率的自制测试对象测试精度和准确度。为了阐明测量结果是否受到物体中感应剩磁（B）的影响，将 28 个不同材料的托槽暴露于弱磁场和强磁场中，并比较暴露前后的磁通密度。在一名志愿者身上进行了临床测试，该志愿者的正畸装置由具有不同磁导率（µ）的托槽组成。使用由四名牙医和四名医疗技术放射科助理（MTRA）组成的两个评估员组，计算有效性和组内和组间可靠性。
无论物体表面和尺寸如何，变异系数均低于 0.14%，精度均非常出色。µ≤1.002 的物体的准确度较高，而µ增加时准确度降低，为此计算了尺寸相关的校正系数。组内和组间可靠性和有效性均非常出色，并且与专业的口腔内操作经验无关。
渗透率测量允许对口腔内金属物体的磁化率进行有效和可靠的确定。当用作检测无伪影物体的筛选工具时，无需计算校正系数。它首次为放射科医生提供了一种决策支持，用于选择性地仅去除多频段设备中高渗透性的组件。
