[Signal loss in magnetic resonance imaging caused by intraoral anchored dental magnetic materials].
OBJECTIVE
To measure the maximum extent of the signal loss areas in the center of the susceptibility artifacts generated by ferromagnetic dental magnet attachments using three different sequences in the 1.5 and 3.0 Tesla MRI.


METHODS
Five different pieces of standard dental magnet attachments with volumes of 6.5 to 31.4 mm(3) were used: a NdFeB magnet with an open magnetic field, a NdFeB magnet with a closed magnetic field, a SmCo magnet with an open magnetic field, a stainless steel keeper (AUM-20) and a PdCo piece. The attachments were placed between two cylindrical phantoms and examined in 1.5 and 3.0 Tesla MRI using gradient echo and T1- and T2-weighted spin echoes. We measured the maximum extent of the generated signal loss areas parallel and perpendicular to the direction of B (O).


RESULTS
In gradient echoes the artifacts were substantially larger and symmetrically adjusted around the object. The areas with total signal loss were mushroom-like with a maximum extent of 7.4 to 9.7 cm parallel to the direction of B (O) and 6.7 to 7.4 cm perpendicular to B (O). In spin echoes the signal loss areas were obviously smaller, but not centered. The maximum values ranged between 4.9 and 7.2 cm (parallel B (O)) and 3.6 and 7.0 cm (perpendicular B (O)). The different ferromagnetic attachments had no clinically relevant influence on the signal loss neither in 1.5 T nor 3.0 T MRI.


CONCLUSIONS
Ferromagnetic materials used in dentistry are not intraorally standardized. To ensure, that the area of interest is not affected by the described artifacts, the maximum extent of the signal loss area should be assumed: a radius of up to 7 cm in 1.5 and 3.0 T MRI by T1 and T2 sequences, and a radius of up to 10 cm in T2* sequences. To decide whether magnet attachments have to be removed before MR imaging, physicians should consider both the intact retention of the keepers and the safety distance between the ferromagnetic objects and the area of interest.
Blankenstein
F H
FH
Zentrum für Zahnmedizin (CVK), Charité--Universitätsmedizin Berlin. felix.blankenstein@charite.de
Truong
B
B
Thomas
A
A
Schröder
R J
RJ
Naumann
M
M
D016477:Artifacts; D003764:Dental Materials; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics / Q000295:instrumentation*; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D003764:Dental Materials