Cone beam CT image artefacts related to head motion simulated by a robot skull: visual characteristics and impact on image quality

Abstract

Objectives: 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.

Figure 1

Sketch of skull illustrating the planes of movement and the foramina with radio-opaque markers: supraorbital foramen (a), infraorbital foramen (b) and mental foramen (c)

Figure 2

Examples of axial images, generated using a Scanora 3D (Soredex Oy, Tuusula, Finland). First row (a,b,c) shows reference images without motion artefacts. Second row (d,e,f) shows images with tremor artefacts. (a,d) Mental foramen; (b,e) infraorbital foramen; (c,f) supraorbital foramen

Figure 3

Examples of cross-sectional images of the lower third molar region, generated using three-dimensional eXam (KaVo Dental GmbH, Biberach, Germany). (a) Reference image; (b) image with motion (tremor) artefacts

Figure 4

Examples of cross-sectional images of the mental foramen region, generated using ProMax 3D MAX (Planmeca Oy, Helsinki, Finland). (a) Reference image; (b) image with motion (tremor) artefacts