CBCT Image Artefacts: A Referring Clinician’s Guide to Recognition and Clinical Impact

Every referring clinician who requests a CBCT scan will encounter CBCT image artefacts at some point. These artefacts can obscure anatomy, mimic pathology, or reduce diagnostic confidence. Therefore, understanding their causes and clinical impact helps anyone who refers patients for cone beam computed tomography.

This guide covers the most common types of CBCT image artefacts. It explains their origins in practical terms and offers advice on when to request a rescan or alternative modality.

Quick Answer: Why Do CBCT Image Artefacts Matter?

CBCT image artefacts matter because they directly affect clinical decisions. For example, metal scatter around an existing implant may mask adjacent bone loss. Similarly, motion blur can obscure the inferior alveolar nerve canal and make implant planning unreliable. Consequently, recognising these artefacts helps referring clinicians interpret reports with greater confidence.

According to Schulze et al. (2011), artefacts in CBCT fall into three broad categories. First, physics-based artefacts arise from the nature of X-ray imaging. Second, patient-related artefacts come from movement or anatomy. Third, scanner-related artefacts stem from hardware or software limitations. Each category demands a different clinical response.

Metal Scatter and Beam Hardening: The Most Common CBCT Image Artefacts

Metal scatter represents the single most frequent source of CBCT image artefacts. When the X-ray beam passes through dense metallic objects, it produces bright streaks and dark bands. Indeed, amalgam restorations, cast metal crowns, implants, and orthodontic brackets all trigger this effect.

Beam hardening occurs through a closely related mechanism. Dense materials absorb lower-energy photons first. This leaves the remaining beam “harder” and alters attenuation values. As a result, cupping artefacts appear, where the centre of a dense object looks darker than its edges. In addition, streak artefacts form between two metallic objects.

For the referring clinician, the practical impact matters greatly. In implant planning, metal artefacts from an existing restoration can obscure the cortical plate. This leads to inaccurate bone width measurements. Similarly, in endodontic assessment, a post-and-core may produce scatter that masks a periapical lesion.

Therefore, clinicians should note metallic restorations on the referral form. The radiologist can then select the most appropriate field of view and exposure parameters to minimise their effect.

Motion Artefacts in CBCT Imaging

Patient movement during the scan produces blurring, ghosting, or doubling of structures. Even movements of 1 to 2 millimetres can significantly degrade image quality. Notably, this creates particular challenges because CBCT scan rotations typically take 10 to 40 seconds.

Certain patient groups show greater susceptibility to motion artefacts. For instance, children, elderly patients, and individuals with tremors move more during acquisition. Furthermore, swallowing during the scan shifts the hyoid bone and soft tissues. This can affect airway analysis and posterior mandible assessment.

Recognising motion artefact proves generally straightforward. Look for doubled cortical outlines, blurred root apices, or misaligned structures across slices. When motion compromises the diagnostic region of interest, clinicians should request a rescan. At 3Beam, our radiographers use chin rests and head stabilisation to minimise movement. However, some rescans remain unavoidable.

Truncation Artefacts and Field of View

Truncation artefacts occur when anatomy extends beyond the selected field of view. The scanner cannot capture complete projection data for structures outside the FOV. As a result, the reconstruction algorithm fills in missing data with estimated values. This produces bright bands or distorted edges at the image boundary.

In particular, this artefact type affects orthodontic cases frequently. For instance, if the clinician selects a narrow FOV for impacted canine localisation, adjacent teeth may show distortion. Similarly, in TMJ assessment, a small FOV centred on one condyle may clip the other side.

The solution lies in careful FOV selection. As noted in the FGDP Selection Criteria for Dental Radiography, the FOV should cover the clinical question without unnecessary exposure. Indeed, clear clinical information on the referral form helps the imaging centre choose correctly.

Ring and Band Artefacts

Ring artefacts appear as concentric circles in axial CBCT slices. They arise from miscalibrated detector elements. When a single detector pixel records incorrect values, the algorithm maps that error as a ring. In contrast, band artefacts present as horizontal or vertical lines across the image.

Both types represent scanner-related issues. Referring clinicians cannot prevent them. However, recognising them matters greatly. In particular, a ring artefact through a periapical lesion could mimic pathology. Alternatively, it could obscure genuine anatomy.

If ring artefacts appear prominently, clinicians should notify the imaging centre. Quality assurance protocols, as recommended by the European Academy of DentoMaxilloFacial Radiology, mandate regular phantom testing. This detects calibration issues before they affect clinical images.

Noise and Scatter in CBCT Scans

Image noise appears as a grainy texture that reduces contrast resolution. In CBCT, noise levels tend to run higher than in medical CT. This occurs because dental CBCT units use lower radiation doses and flat-panel detectors.

Scatter radiation contributes additional noise. When X-rays interact with tissue, some photons change direction and reach the detector at incorrect positions. Notably, this effect grows more pronounced with larger FOVs. A large-FOV scan of the entire skull shows more noise than a focused single-tooth scan.

For the referring clinician, noise affects subtle density differences. In periodontology, for example, early furcation bone loss may prove difficult to detect on a noisy scan. In such cases, a structured radiologist report becomes especially valuable. Indeed, the reporting radiologist applies windowing and contrast adjustments that standard images do not show.

Partial Volume Averaging and Aliasing

Partial volume averaging occurs when a single voxel contains multiple tissue types. The scanner then assigns an average attenuation value to that voxel. Consequently, this can blur the boundary between bone and soft tissue.

Aliasing artefacts result from insufficient projection data during the scan rotation. Fine structures such as thin cortical plates may appear stepped or jagged. However, modern CBCT scanners have largely addressed aliasing through higher frame rates.

In clinical practice, partial volume averaging affects thin-structure measurements most. For example, a buccal bone plate of 0.5 mm may appear thicker or thinner, depending on voxel size. Therefore, for implant planning in the aesthetic zone, the referring clinician should discuss this limitation with their radiologist.

How to Minimise CBCT Image Artefacts: Tips for Referrers

Referring clinicians cannot control scanner hardware. However, they can significantly influence image quality through the information they provide.

Complete the referral form thoroughly. List all metallic restorations in the region of interest. Also mention removable prostheses, orthodontic wires, or piercings. The imaging centre can then ask patients to remove what they can.

Specify the clinical question clearly. A precise question allows optimal FOV and voxel size selection. For instance, “assess bone volume at UR6 for implant” proves far more useful than “CBCT upper jaw.” As highlighted in our guide to incidental findings, a well-targeted scan also reduces reporting complications.

Flag patient factors. If the patient feels anxious, has a movement disorder, or cannot stay still, note this on the referral. The imaging centre can then allow extra time for positioning and reassurance.

Ask about post-processing. Modern CBCT software includes metal artefact reduction (MAR) algorithms. At 3Beam, our reporting radiologists routinely apply MAR when they detect metalwork. Indeed, this forms part of the structured reporting process.

When to Request a Rescan or Alternative Imaging

Not every artefact warrants a rescan. Clinicians can safely ignore a minor metal streak outside the diagnostic region. However, they should consider a rescan in specific situations.

First, the artefact directly obscures relevant anatomy. For example, motion blur affecting the IAN canal in a nerve proximity case demands a repeat scan. Second, the artefact creates false findings. A cupping artefact around a metal post could mimic a periapical radiolucency.

In some situations, an alternative modality works better. Conventional intraoral radiography may suffice for simple endodontic questions. For complex maxillofacial pathology requiring soft tissue contrast, medical CT or MRI may prove more appropriate instead.

Frequently Asked Questions

Q: Can clinicians completely eliminate CBCT image artefacts?
A: No. Some artefacts occur inherently in cone beam geometry. However, proper patient preparation, optimal scan parameters, and MAR algorithms significantly reduce their impact.

Q: Do all CBCT scanners produce the same artefacts?
A: Different scanners use different detectors and reconstruction algorithms. As a result, artefact patterns vary between manufacturers. Notably, flat-panel detectors show greater susceptibility to scatter but offer superior spatial resolution.

Q: How does field of view affect CBCT image artefacts?
A: A smaller FOV generally produces fewer scatter artefacts and lower noise. However, a FOV that shrinks too much risks truncation. Our FOV selection guide explains the balance in detail.

Q: Should patients remove all metal before a CBCT scan?
A: Yes. Patients should always remove dentures, retainers, piercings, and spectacles. Clinicians cannot remove fixed metalwork, but noting it on the referral form allows proper planning.

Q: Does 3Beam use metal artefact reduction?
A: Yes. Our reporting radiologists apply MAR routinely when they detect metalwork. This forms a standard part of the comprehensive reporting process at 3Beam.

The Bottom Line on CBCT Image Artefacts

CBCT image artefacts represent an unavoidable part of cone beam imaging. They arise from X-ray physics, patient movement, and scanner limitations. For the referring clinician, the key skill involves recognising them and understanding their clinical significance.

A thorough referral form and a clear clinical question remain the most effective tools for minimising artefact-related uncertainty. When artefacts do affect quality, a structured radiologist report provides the interpretation needed to guide treatment decisions with confidence.