Evaluation of the effects of positioning and configuration on contrast-to-noise ratio in the quality control of a 3D Accuitomo 170 dental CBCT system.

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This study evaluated the effect of phantom positioning and the configuration of phantom inserts on the measurement of contrast-to-noise ratio (CNR) in dental CBCT. The work aimed to make pragmatic suggestions for the remedial tolerances for CNR measurements in the routine quality control (QC) of a three-dimensional Accuitomo 170 dental CBCT system (J Morita, Kyoto, Japan). Images of the SEDENTEXCT (safety and efficacy of a new and emerging dental X-ray modality) IQ (image quality) dental CBCT phantom (Leeds Test Objects Ltd, Boroughbridge, UK) were acquired and measurements of CNR were obtained in three configurations of inserts and in six phantom orientations for one of the configurations. Five consecutive images were acquired in each case, to assess the reproducibility of measurements. Reproducibility of measurements ranged from 1.8% to 4.6%. For the CNR measurements in the three phantom configurations, the ratio of the measured CNR to the minimum value was 2.1 ± 0.2 times the minimum value for Delrin(®) (DuPont UK Ltd, Stevenage, UK). For aluminium, there was no significant variation between configurations and for the other three materials, the ratio ranged from 20% to 50%. Significant variations in CNR with phantom position were observed, with differences between the maximum and minimum values ranging from 10% to 60%. Absolute differences in CNR from the minimum value ranged from <0.1 to 2.1 with phantom configuration and from 1.2 to 4.5 with phantom position. The effects of phantom configuration and positioning on CNR measurements for dental CBCT QC were investigated and possible remedial tolerances suggested.