  The purpose of this study is to correct the movement errors that may occur
because of the patients' movement during the CT scanning and thus, to obtain
more precise CT images, additionally to investigate the possible use of
Parallel Beam CT in the dental treatment. An extracted human tooth was scanned
with PBCT and the possible movement errors that patients may cause during the
CT scan were intentionally assigned. The maximum width of errors was designed
to reach 0.1 mm. The trajectory of the fixed point was traced in the sinogram
that includes the fixed point. The part deviated from the sinusoidal curve was
modified using the Virtual Alignment Method. The quality of reconstructed image
was remarkably degraded when the movement errors were given. A radiopaque part
inside the tooth was used as a fixed point. The errors were corrected by
shifting the fixed point to the center of sinogram and this relocation of fixed
point did not cause any distortion of image or change of size. The movement
errors were corrected with the fixed point inside the tooth. The more precise
CT images obtained through this method are expected to be of extensive
application in the area of dental treatment using CAD/CAM.
