Abstract
ObjectiveWe investigated the variability in diagnostic information inherent in computed tomography (CT) images acquired at 68 different CT units, with the selected acquisition protocols aiming to answer the same clinical question.MethodsAn anthropomorphic abdominal phantom with two optional rings was scanned on 68 CT systems from 62 centres using the local clinical acquisition parameters of the portal venous phase for the detection of focal liver lesions. Low-contrast detectability (LCD) was assessed objectively with channelised Hotelling observer (CHO) using the receiver operating characteristic (ROC) paradigm. For each lesion size, the area under the ROC curve (AUC) was calculated and considered as a figure of merit. The volume computed tomography dose index (CTDIvol) was used to indicate radiation dose exposure.ResultsThe median CTDIvol used was 5.8 mGy, 10.5 mGy and 16.3 mGy for the small, medium and large phantoms, respectively. The median AUC obtained from clinical CT protocols was 0.96, 0.90 and 0.83 for the small, medium and large phantoms, respectively.ConclusionsOur study used a model observer to highlight the difference in image quality levels when dealing with the same clinical question. This difference was important and increased with growing phantom size, which generated large variations in patient exposure. In the end, a standardisation initiative may be launched to ensure comparable diagnostic information for well-defined clinical questions. The image quality requirements, related to the clinical question to be answered, should be the starting point of patient dose optimisation.Key Points• Model observers enable to assess image quality objectively based on clinical tasks.• Objective image quality assessment should always include several patient sizes.• Clinical diagnostic image quality should be the starting point for patient dose optimisation.• Dose optimisation by applying DRLs only is insufficient for ensuring clinical requirements.
Highlights
In diagnostic radiology, computed tomography (CT) contributes to a major part of the public radiation dose exposure, which leads to public concern over potential cancer induction risks [1,2,3,4]
Model observers enable to assess image quality objectively based on clinical tasks
Dose optimisation by applying diagnostic reference levels (DRLs) only is insufficient for ensuring clinical requirements
Summary
In diagnostic radiology, computed tomography (CT) contributes to a major part of the public radiation dose exposure, which leads to public concern over potential cancer induction risks [1,2,3,4]. The introduction of diagnostic reference levels (DRLs) allowed, to a certain extent, a reduction in the heterogeneity of the delivered dose exposure from one institution to another [5]. Technological developments, such as the automatic tube current modulation (ATCM), using dynamic beam collimation with less over-ranging have been proposed to drastically reduce patient exposure [6]. In the last 10 years, iterative reconstruction (IR) techniques have become increasingly popular as a mechanism to reduce CT dose exposure while ensuring image quality. IR techniques allow drastic noise reductions while maintaining a reasonable spatial resolution compared to traditional filtered back-projection (FBP) techniques [7,8,9,10,11,12]
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