Making sense of metal artifacts

Turn it down

Image noise in cone beam computed tomography (CBCT) radiography is the unwanted distribution of signal disturbance which obscures present information.[ii] A high level of noise is expected and reported in CBCT use,ⁱⁱ especially in comparison to conventional CT imaging, as there is a relatively high amount of electric noise in the detector, amongst other factors.ⁱ

Noise appears in an image as an indiscriminate mottle which, at its most intense, can severely impede the differentiation of low-density tissue.[iii] Scatter, caused by the diffraction of photons from a designated path following an interaction with matter, will also affect the density values of all tissue, and appears as streak artifacts throughout the image.ⁱⁱ

There is an imperative balance to strike with CBCT radiography to minimise noise whilst maintaining patient safety. Studies have observed that noise increases at a lower tube current-exposure time (mAs).[iv] However, dental professionals should take care to justify any increases in radiation, as the ALARP principle means clinicians should optimise X-rays with doses that are “as low as reasonably practicable”.[v] With current CBCT solutions, clinicians can follow a manufacturers guide to find the lowest necessary exposure for a variety of patient groups, whilst avoiding image noise creation – though the literature has shown that, in some cases, an even lower dose than recommended may produce acceptable results.^iv

Awareness around metal

Patients who have received restorations in the past may have disfigured radiograph results due to metal artifacts. Amalgam fillings, dental implants, and other metal materials that can be used for crowns are high-density compared to the surrounding dentition and maxillofacial structures. These objects can cause scatter and beam hardening, which may severely obscure the radiographic result at the site of a restoration, in the surrounding anatomy, or even throughout the entire image.[vi]

Beam hardening is the result most commonly associated with metal artifact interference. As an X-ray beam – which is composed of individual photons with a range of energies – passes through an object, the lower-energy photons are absorbed rapidly, increasing the mean energy of the beam, creating the process referred to as hardening.ⁱⁱ Metals, in particular, are high-absorbing materials, and therefore create a more intense hardening effect. Whilst these structures may appear bright and solid in the radiographic image, the surrounding areas absorb a minimised volume of X-rays in comparison. In turn, reconstruction algorithms can misinterpret these as being completely radiolucent, leading to inaccurately dark areas.ⁱ Dark streaks might also appear as a result of beam hardening.ⁱⁱ

Metal objects that are present in the dentition can prompt false positive diagnoses of problems such as dental caries or root fracture, though roots may also be completely obscured by metal posts in the case of dental implants.^v

Change your approach

Reducing the instance of metal artifact creation in dental radiography is difficult, but not impossible. Adjustments to settings such as mA do not improve the appearance of a radiograph featuring metal objects enough,ⁱ but there are other workarounds. A CBCT scanner with modifiable fields of view may help clinicians focus on a limited area of the dentition where a metal object is not present. This can minimise the impact of artifacts, though is not entirely helpful if the area that needs to be assessed is close to an amalgam filling, dental implant, or other such restoration.

The CS 9600 CBCT Scanner from Carestream Dental, an advanced radiographic imaging solution for practices that strive for perfection, offers exceptional solutions. Exclusive CS MAR (Metal Artifact Reduction) reduces the impact of metal artifacts effectively, creating clearer results for dynamic comparisons. Plus, beam hardening is reduced through an intelligent filtration system and a 120 kV X-ray tube that maximises the number of high-energy photons that are used to create an image. Whilst other systems only offer 120 kV, the CS 9600 features a dynamic filtration system that can work dependent on your needs.

Understanding how artifacts can affect radiographic results is essential for all dental professionals and radiologists. Working to reduce noise and metal artifacts is also key to optimise accurate diagnoses and support patients whilst following the ALARP principle.

For more information on Carestream Dental visit www.carestreamdental.co.uk

For the latest news and updates, follow us on Facebook and Instagram @carestreamdental.uk

Author:

Nimisha Nariapara is the Trade Marketing Manager at Carestream Dental covering the UK, Middle East, Nordics, South Africa, Russia and CIS regions. She has worked at Carestream Dental for the past 7 years, where she has developed her marketing skills and industry knowledge to bring the core values and philosophy of the company to the market.

[i] Pauwels, R., Araki, K., Siewerdsen, J. H., & Thongvigitmanee, S. S. (2015). Technical aspects of dental CBCT: state of the art. Dentomaxillofacial Radiology, 44(1), 20140224.

[ii] Nagarajappa, A. K., Dwivedi, N., & Tiwari, R. (2015). Artifacts: The downturn of CBCT image. Journal of International Society of Preventive and Community Dentistry, 5(6), 440-445.

[iii] Kazimierczak, W., Kędziora, K., Janiszewska-Olszowska, J., Kazimierczak, N., & Serafin, Z. (2024). Noise-Optimized CBCT Imaging of Temporomandibular Joints—The Impact of AI on Image Quality. Journal of Clinical Medicine, 13(5), 1502.

[iv] Pauwels, R., Seynaeve, L., Henriques, J. C. G., de Oliveira-Santos, C., Souza, P. C., Westphalen, F. H., … & Jacobs, R. (2015). Optimization of dental CBCT exposures through mAs reduction. Dentomaxillofacial Radiology, 44(9), 20150108.

[v] Public Health England, Faculty of General Dental Practice, (2020). Guidance Notes for Dental Practitioners on the Safe Use of X-ray Equipment. 2^nd Edition. (Online) Available at: https://www.rqia.org.uk/RQIA/files/44/449bdd1c-ccb0-4322-b0df-616a0de88fe4.pdf

[vi] Pauwels, R., Stamatakis, H., Manousaridis, G., Walker, A., Michielsen, K., Bosmans, H., … & SEDENTEXCT Project Consortium. (2011). Development and applicability of a quality control phantom for dental cone‐beam CT. Journal of Applied Clinical Medical Physics, 12(4), 245-260.