Objective: Dental materials can produce metal artifacts during magnetic resonance imaging（MRI）, which can be problematic in clinical practice. Recently, the use of MRI for disease diagnosis in patients with dental implants has increased. Concurrently, the range of sizes of dental implants has also expanded. However, there are few reports comparing the metal artifacts produced on MR images by dental implants of different sizes. The purpose of this study was to investigate the metal artifacts caused by pure titanium-based dental implants of various sizes（3.5mm×8.0mm, 3.5mm×9.5mm, 3.5mm×11.0mm, and 4.5mm×8.0mm）using a phantom.
Methods: The phantom used in our study was composed of a hollow cylinder with an outer diameter of 20cm, and a removable rod of 1.0cm in diameter was placed along the phantom’s central axis. MRI was performed with a 1.5 T MRI machine（Philips Co. Intera Achieva 1.5T）, using a SENSE head 8-channel coil. The imaging conditions included spin echo（SE） T1-weighted imaging, Turbo SE（TSE）T2-weighted imaging, short TI（inversion time）inversion recovery（STIR）, and diffusion-weighted imaging（DWI）. The TR/TE remained constant during the DWI and the b-value, field of view（FOV）, rectangular field of view（RFOV）, SENSE factor, frequency direction, and phase direction were changed. ImageJ was used to measure the changes in the gray values on coronal images. Gray value changes of up to 30% were evaluated depending on the imaging conditions.
Results: All of the pure titanium-based dental implants studied produced similar metal artifacts on SE T1, TSE T2, and STIR images. The largest（in dimension）metal artifacts were seen on the DW images. This study showed that the size of metal artifacts depends on changes in the FOV, RFOV, SENSE factor, frequency direction, and phase direction for DW images.
Conclusions: In the SE T1, TSE T2, and STIR imaging conditions, pure titanium-based dental implants produced small metal artifacts of similar size and intensity regardless of their size. On DWI, the implants produced larger metal artifacts than were seen on the SE T1, TSE T2, and STIR images.
