Since the MAR algorithm may damage the overall CT image, a study of the accuracy of the digital models produced with MAR-applied CT data is necessary. However, no research has yet analyzed its influence on STL formatted digital models produced from MAR-applied CT data. The accuracy of MAR-applied CT image has been studied 9, 10, 11. This process effectively removes data that have been corrupted by metal artifact, but may lead to minor deformations in the entire CT data 8. After repeated execution of the overall process, the finalized projection data form an axial CT image 5, 6, 7. The estimated data is interpolated with the original data to produce metal artifact removed data. Then, an appropriate estimate of the corrupted data is predicted based on the uncorrupted data of the original projection. Basically, the algorithm identifies and segments the corrupted data by metal artifact. This means that the MAR algorithm may modify the non-artifact image data while processing the artifact area. However, the MAR process alters the projection data, which are the primary data stored on the workstation of the CT console. Furthermore, it is advantageous for clinicians, because CT data with MAR algorithm enables them to save time and to avoid the laborious work needed to manipulate and refine the digital models before 3D printing. In this way, digital model producing is much easier and simpler to use for surgical simulations or patient education. Thus, digital model in STL format can be generated as smooth without spicules when it is based on the CT data applied with MAR algorithm. These algorithms have advanced considerably, and effectively recover images corrupted with metal artifact. Metal artifact reduction (MAR) algorithms can be applied to CT images affected with metal artifact.
DIGITAL ARTIFACT MEANING REGISTRATION
If a dental scanner and registration system are not accessible, the spicules due to metal artifact around the dental arch in a digital model should be removed manually on the computer-aided design (CAD) software. However, doing so requires additional work and a registration program. Previous studies have attempted to solve this problem by integrating CT and other digital dental scan data 4. The artifact also appears as spicule-shaped area that disrupt generated digital models 3. Metal artifact corrupt the entire axial image section that includes the prosthesis. However, dental prostheses cause metal artifact in images, preventing the development of smooth and satisfactory 3D digital models.
Generating precise and fine digital models in standard tessellation language (STL) from Digital Imaging and Communications in Medicine data (DICOM) has been a useful technique in maxillofacial region 1, 2. Three-dimensional (3D) digital models produced from computed tomography (CT) data have played an increasingly important role in patient education, planning, simulation, and navigation surgery in the oral and maxillofacial region. The MAR algorithm can be used regardless of the amount of metal artifact, which are generated by dental prostheses, for the quick and convenient manipulation of dental digital models.
MAR-applied CT is a convenient source for digital modeling with clinically acceptable accuracy. The amount of artifact did not significantly influence the accuracy of the digital models. The overall mean deviation of the MAR-applied models was 0.0868 mm, with no significant difference according to the reference plane. The MAR algorithm reduced metal artifact in all cases. Statistical analyses were performed to compare deviations and to assess correlations between the amount of artifact and deviation. Paired digital models were superimposed and shape deviation in planar surface was measured at 10 points in 4 planes. Digital models were generated from the original and the MAR-applied CT data. By subtracting the original and MAR-applied CT images, the amount of metal artifact was quantified. Thirty maxillofacial CT scans were randomly selected and a MAR algorithm was applied. This study investigated whether metal artifact reduction (MAR) applied computed tomography (CT) scans could be used to generate precise digital models and explored possible correlations between the amount of metal artifact and model accuracy.
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