Assessment of task-based image quality for abdominal CT protocols linked with national diagnostic reference levels

Abstract

Objectives To assess task-based image quality for two abdominal protocols on various CT scanners. To establish a relationship between diagnostic reference levels (DRLs) and task-based image quality. Methods A protocol for the detection of focal liver lesions was used to scan an anthropomorphic abdominal phantom containing 8- and 5-mm low-contrast (20 HU) spheres at five CTDIvol levels (4, 8, 12, 16, and 20 mGy) on 12 CTs. Another phantom with high-contrast calcium targets (200 HU) was scanned at 2, 4, 6, 10, and 15 mGy using a renal stones protocol on the same CTs. To assess the detectability, a channelized Hotelling observer was used for low-contrast targets and a non-prewhitening observer with an eye filter was used for high contrast targets. The area under the ROC curve and signal to noise ratio were used as figures of merit. Results For the detection of 8-mm spheres, the image quality reached a high level (mean AUC over all CTs higher than 0.95) at 11 mGy. For the detection of 5-mm spheres, the AUC never reached a high level of image quality. Variability between CTs was found, especially at low dose levels. For the search of renal stones, the AUC was nearly maximal even for the lowest dose level. Conclusions Comparable task-based image quality cannot be reached at the same dose level on all CT scanners. This variability implies the need for scanner-specific dose optimization. Key Points • There is an image quality variability for subtle low-contrast lesion detection in the clinically used dose range. • Diagnostic reference levels were linked with task-based image quality metrics. • There is a need for specific dose optimization for each CT scanner and clinical protocol.

Photon-Counting Detector CT With Quantum Iterative Reconstruction

“…The potential for radiation dose reduction without impairment in lesion detection was computed for the QIR strength level with the highest AUC compared with EID-CT VMIs and LBIs for each of the 3 radiation doses. By fitting the curve between AUC and radiation dose, we evaluated the radiation dose for which PCD-CT would achieve the same AUC as EID-CT applying the steps described in a previous study 38 …”

“…By fitting the curve between AUC and radiation dose, we evaluated the radiation dose for which PCD-CT would achieve the same AUC as EID-CT applying the steps described in a previous study. 38…”