Interpretation Basics of Cone Beam Computed Tomography. Группа авторов

Multiplanar reformation, or MPR, is a view of three different directional 2D images (axial, coronal, and sagittal planes) (Figure 1.7). Within this view, the images may be manipulated in the thickness of data, and direction of viewing can be altered. Reconstructed pantomographs and lateral cephalometric skulls (Figures 1.8 and 1.9) are possible without distortion from standard 2D radiography. The dataset may also be manipulated to create cross‐sectional (orthogonal) views of the jaws and condyles (Figures 1.10 and 1.11).

Figure 1.7. Axial (A), coronal (C), sagittal (S), and reconstructed 3D views.

Figure 1.8. Reconstructed pantomograph from a CBCT scan.

Figure 1.9. Reconstructed lateral cephalometric skull.

Figure 1.10. Cross‐sectional slices with axial view and reconstructed pantomograph.

Figure 1.11. Temporomandibular joint view with rotated sagittal cross‐sectional slices.

      3D Rendering

The most common form of 3D rendering offered in CBCT software is indirect volume rendering, which determines the grays of the voxels to create a 3D image (Figure 1.12). Another form of 3D rendering is referred to as direct volume rendering, where the highest attenuation value for each voxel is used creating a maximum intensity projection (MIP) (Figure 1.13).

Figure 1.12. (a) 3D rendered view with teeth setting. (b) 3D rendered view with bone setting.

Figure 1.13. Maximum Intensity Projection (MIP) view.

Artifacts

      Streak Artifacts/Undersampling

Streak artifacts occur when an object with high density (such as metallic restorations) creates areas of undersampling where no viable information is recorded. These present as white streaks (Figure 1.14) radiating from the high‐density object. Beam hardening artifact is caused when low energy x‐rays are absorbed by high‐density objects creating an increase in x‐ray beam energy, which “hardens” the beam. This results as increased density (black) lines radiating from the high‐density object (Figure 1.14). Care should be taken not to interpret anything in the streak artifacts and beam hardening. Aliasing is another form of undersampling, when too few images are acquired and appear as small lines throughout a scan (Figure 1.15).

Figure 1.14. (a) Axial view showing streak artifact (black arrow) and beam hardening (white arrow) due to metallic restorations. (b) Coronal view showing streak artifact (black arrow) and beam hardening (white arrow) due to metallic restorations.

Figure 1.15. Axial view with metallic streak artifact (black arrow), beam hardening (white arrow), and aliasing of scan as linear radiolucent lines (white dotted arrow) throughout the entire image.

      Motion Artifacts

Motion artifacts occur due to either normal pathophysiological movement or when the patient moves during a scan. This presents as double bony borders to ill‐defined bony borders (Figures 1.16 and 1.17). This can be minimized by restraining the patient’s head and using as short a scan time as possible.

Figure 1.16. (a) Sagittal view showing motion artifact of the cervical vertebrae (black arrow). (b) Axial view showing motion artifact of the cervical vertebrae (black arrow).

Figure 1.17. Axial (A), coronal (C), and sagittal (S) views with motion artifact (black arrows) throughout the jaws.

      Ring Artifacts

Ring artifacts present as white or black circular artifacts. They typically indicate poor calibrations and imperfections in the scanner detection (Figure