Image Artifacts

An artifact is described as any image distortion that is not related to the patient’s anatomical structures.¹³ There are several types of artifacts that may interfere with the image quality. It is important that the clinician knows how to differentiate these artifacts to avoid misinterpretation.

The most common artifacts are beam hardening artifacts. Metallic restorations or objects, orthodontic appliances, and endodontic materials are the main cause of beam hardening in CBCT data volumes. Due to the high density of these materials, it creates an area of undersampling where information cannot be recorded. Beam hardening artifacts reduce the image quality in the axial plane; it presents as white streaks and black bands. (Figure 9).¹ To limit artifacts, reduction of the FOV may avoid inclusion of metallic restorations. Placing cotton rolls between the arches during the acquisition may also be appropriate to decrease the beam hardening artifact from opposing arch restorations. CBCT manufacturing companies continue to develop computer metal artifact reduction algorithms to reduce the number of artifacts visualized in a CBCT data volume.

Figure 9. Beam hardening artifacts with white streaks and black bands.

Figure 9. Beam hardening artifacts with white streaks and black bands.

Another artifact related to technique is called “aliasing.” It is created when too few basis images are acquired due to a fast scan technique; therefore, a reduced data set leads to a noisier image and it appears as small lines throughout the scan.

Patient-related artifacts are typically due to motion during the acquisition of the data volume, such as pronounced respiration, eye motion, or tremors. Movement artifact ranges from blurring to double contours of bony outlines (Figure 10). Evaluation and consideration on how much the movement artifact prevents the visualization of the region of interest should be made prior to rescanning. Head straps and chin cups are utilized to avoid motion artifact during the acquisition phase. In addition, by using as short a scan time as possible can minimize motion artifact and also reduce radiation dose associated with CBCT imaging.

Figure 10. Patient motion artifacts with double contour of bony outlines.

Figure 10. Patient motion artifacts with double contour of bony outlines.

“Ring” artifact may appear consistently in studies acquired in a machine in which the detector is not properly calibrated. It is visualized in the axial plane as a black or white circular artifact normally located in the center or at the edges of the data volume.¹³ Periodic realignment/calibration of CBCT unit is needed based on manufacture’s recommendation.