Artefacts in cone beam CT

Artifacts can seriously degrade the quality of computed tomographic (CT) images, sometimes to the point of making them diagnostically unusable. To optimize image quality, it is necessary to understand why artifacts occur and how they can be prevented or suppressed. CT artifacts originate from a range of sources. Physics-based artifacts result from the physical processes involved in the acquisition of CT data. Patient-based artifacts are caused by such factors as patient movement or the presence of metallic materials in or on the patient. Scanner-based artifacts result from imperfections in scanner function. Helical and multisection technique artifacts are produced by the image reconstruction process. Design features incorporated into modern CT scanners minimize some types of artifacts, and some can be partially corrected by the scanner software. However, in many instances, careful patient positioning and optimum selection of scanning parameters are the most important factors in avoiding CT artifacts. (c) RSNA, 2004.

The purpose of this study was to use cone-beam computed tomography to quantitatively evaluate skeletal expansion and alveolar tipping of the maxilla at the maxillary canine (C1), first premolar (P1), second premolar (P2), and first molar (M1) after rapid maxillary expansion (RME). The transverse effects to the maxillary suture, nasal width, and maxillary sinus were also assessed. Thirty consecutive patients (17 boys, 13 girls; mean age, 13.8 +/- 1.7 years) who required RME with Hyrax appliances as part of their comprehensive orthodontic treatment were studied. Measurements before and after RME of palatal and buccal maxillary widths, palatal alveolar angle, nasal width, nasal floor width, and maxillary sinus width at C1, P1, P2, and M1 were compared by using Wilcoxon signed rank, Kruskal-Wallis, and Wilcoxon rank sum tests. Pearson correlation analyses were also performed (* = .05). Skeletal expansion of the maxilla had a triangular pattern with a wider base in the anterior region, accounting for 55% of total expansion at P1, 45% at P2, and 38% at M1. Alveolar bending or tipping accounted for 6% of total expansion at P1, 9% at P2, and 13% at M1. The remaining orthodontic (dental tipping) portions of total expansion were 39% at P1, 46% at P2, and 49% at M1. RME produces a statistically significant increase in nasal width and a decrease in maxillary sinus width (P 0.05).