title: Cone beam CT image artefacts related to head motion simulated by a robot skull: visual characteristics and impact on image quality.
abstract: OBJECTIVE
  The aim of this study was to assess artefacts and their impact on cone beam CT (CBCT) image quality (IQ) after head motion simulated by a robot skull.
  
  
  METHODS
  A fully dentate human skull incorporated into a robot simulated pre-determined patient movements. Ten head motion patterns were selected based on the movement of the C-arm of the CBCT units (no motion as reference). Three CBCT units were used [a three-dimensional eXam (K) (KaVo Dental GmbH, Biberach, Germany), a Promax 3D MAX (P) (Planmeca Oy, Helsinki, Finland) and a Scanora(®) 3D (S) (Soredex Oy, Tuusula, Finland)]. Axial images were qualitatively assessed at three levels: mental foramen (MF), infraorbital foramen and supraorbital foramen, and artefacts characterized as stripe-like, double contours, unsharpness or ring-like. A 100 mm visual analogue scale (VAS) was used to quantitatively assess IQ. Cross-sectional images of the lower third molar and MF bilaterally were also evaluated by VAS. Four blinded examiners assessed the images.
  
  
  RESULTS
  For all units and motion patterns, stripe-like artefacts were the most common. The four observers agreed on the presence of at least one artefact type in 90% of the images. Axial images showed lower overall IQ after motion (VAS = 72.4 ± 24.0 mm) than reference images (VAS = 97.3 ± 2.6 mm). The most severe artefacts were seen at the MF level. For cross-sectional images, IQ was lowest after tremor. The mean IQ range was 74-89 and 57-90 for isolated (tilting, rotation and nodding) and combined (nodding + tilting and rotation + tilting) movements, respectively. IQ for MF was lower than for third molar for any movement except tremor.
  
  
  CONCLUSIONS
  Head motion of any type resulted in artefacts in CBCT images. The impact on IQ depended on the region and level in the skull.
authors: Oral Radiology, Department of Dentistry, Aarhus University, Denmark. rsn@odont.au.dk
authors: R
authors: R
authors: Spin-Neto
authors: J
authors: J
authors: Mudrak
authors: L H
authors: LH
authors: Matzen
authors: J
authors: J
authors: Christensen
authors: E
authors: E
authors: Gotfredsen
authors: A
authors: A
authors: Wenzel
mesh_terms: D019412:Anatomy, Cross-Sectional; D016477:Artifacts; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008334:Mandible / Q000000981:diagnostic imaging; D008953:Models, Anatomic; D008964:Molar, Third / Q000000981:diagnostic imaging; D009915:Orbit / Q000000981:diagnostic imaging; D011856:Radiographic Image Enhancement / Q000379:methods*; D019252:Radiography, Dental, Digital / Q000379:methods; D012371:Robotics; D012399:Rotation; D012886:Skull