MR imagingにおける金属ア-チファクトの研究

抄録

Magnetic resonance imaging is becoming ever more essential in stomatognathic examination and diagnosis. MR images, however, may be affected by artifacts caused by certain dental mate-rials. To analyze possible metal-induced artifacts developed in dental MR images, quantitative analyses were done in a basic experiment using a medium intensity magnetic field (0.3 tesla). To simplify the relationship between the skull and dental restorations, we prepared metal (6 types: Nickel-chromium alloys, Cobalt-chromium alloys, Titanium alloys, Au alloys, Ag-Pd-Cu-Au alloys, silver) as well as acrylic resin specimens as 5 mm cubes and as a phantom. MR images of each metal specimens were compared to those of acrylic resin specimens. Imaging conditions were fast spin echo T2 weight, spin echo T2 weight, spin echo proton density weight, spin echo Ti weight and gradient echo T2*, and imaging directions were transverse, sagittal and coronal. Therefore, 645 different combinations were possible. The area of each resulting image was calculated. Nickel-chromium alloys, Cobalt-chromium alloys and Titanium alloys showed artifacts when compared with the acrylic resin control. Au alloys, Ag-Pd-Cu-Au alloys and silver did not show a consistent tendency, and images obtained tended to differ from those of the acrylic resin control depending on imaging conditions and direction. The order of artifact development range was Nickelchromium alloys, Cobaltchromium alloys, Titanium al-loys, Ag-Pd-Cu- Au alloys, Au alloys and silver. The strongest and weakest artifacts were ob-served under the condition of spin echo T2 weight and spin echo Ti weight, respectively. There was no consistent tendency observed among imaging directions: in Nickel-chromium alloys, Cobalt-chromium alloys and Titanium alloys, the artifact area increased in proportion to the increase in the number of specimens. In silver, Au alloys and Ag-Pd-Cu-Au alloys, the artifact area increased in proportion to the increase in the number of specimens, but only when speci-mens were arranged parallel to the imaging direction. In Nickel-chromium alloys, Cobalt-chro-mium alloys and Titanium alloys, artifacts were larger in the horizontal imaging direction than in the vertical direction. This finding was reversed in silver, Au alloys and Ag-Pd-Cu-Au al-loys. Quantitative artifact analysis revealed that the artifact area differed depending on the type of metal, imaging condition and direction. It is important to be aware that metal artifacts can create misleading images, so careful attention should be paid to the interpretation of raw dental MR images.