ABSTRACT
PURPOSE: The aim of this work was to implement, validate, and compare two procedures for routine image quality (IQ) assurance in dental cone-beam computed tomography (CBCT): 1. the German standard DINâ6868â-â161 introduced in 2013 and 2. the established standard IEC 61,223â-â3-5 for clinical CT x-ray equipment referenced as "DIN" and "IEC" below. MATERIALS AND METHODS: The approximated in-plane modulation transfer function (MTF), the contrast-to-noise indicator (CNI), and the uniformity indicator (UI*) were determined in accordance with DIN. Image noise, the uniformity index (UI), the contrast-to-noise ratio (CNR), and the 3âD MTF were measured according to IEC 61,223â-â3-5 using a previously proposed quality assurance (QA) framework. For this, a modular phantom was used. All experiments were performed on a clinical dental CBCT unit. The severity of image artefacts was measured at different z-positions. A dedicated computer program was implemented to allow for automated QA procedure. RESULTS: The position and orientation of the phantoms were detected automatically in all of the measurements providing a reproducible placement of the evaluation regions and volumes. 50â% and 10â% in-plane MTF values of the approximated and the exact MTF calculation procedure were in agreement to within 5â%. With increasing axial distance from the isocentre, UI* and CNI dropped by 30â% and 19â%, respectively. Conventional IQ parameters showed higher sensitivity to image artefacts; i.âe., UI and CNR were reduced by about 197â% and 37â%. CONCLUSION: The implemented automated QA routines are compatible with both the DINâand the IEC approach and offer reliable and quantitative tracking of imaging performance in dental CBCT for clinical practice. However, there is no equivalence between the DINâand the IEC metrics. In addition, direct measurements of physical IQ parameters such as image contrast and noise, uniformity, and axial resolution are not supported by the new concept according to DIN. KEY POINTS: The new DINâ6868â-â161 is not equivalent to the established IEC 61â223â-â3-5. Noise, uniformity, and contrast are well-suited to assess image artefacts. The implemented automated quality assurance program fits clinical routine.