Fig. 2.

a, b Workflow for MRI measurement of retainers and subsequent quantification of artifact volumes. a Retainers were embedded in agar in plastic boxes. These boxes were then placed into a 16-channel multipurpose coil for in vitro MRI measurement at 3 T. b The primary image dataset is shown on the left, in which signal loss artifacts as well as the retainer itself appear hypointense (dark), and pile-up artifacts appear hyperintense (bright). After image acquisition, 3D volumes of hypointense (blue) and hyperintense regions (red) were defined by segmentation, as shown in the volume rendering on the right. Finally, the artifact volume was obtained by adding the volumes of hypointense and hyperintense areas and subtracting the retainer volume. MRI, magnetic resonance imaging; CAD/CAM, computer-aided design/computer-aided manufacturing