Abstract
ObjectivesTo assess how modifying multiple protocol parameters affects the dose and diagnostic performance of a neck CT protocol using patient-mimicking phantoms and task-based methods.MethodsSix patient-mimicking neck phantoms containing hypodense lesions of 1 cm diameter and 30 HU contrast and one non-lesion phantom were examined with 36 CT protocols. All possible combinations of the following parameters were investigated: 100- and 120-kVp tube voltage; tube current modulation (TCM) noise levels of SD 7.5, 10, and 14; pitches of 0.637, 0.813, and 1.388; filtered back projection (FBP); and iterative reconstruction (AIDR 3D). Dose-length products (DLPs) and lesion detectability (assessed by 14 radiologists) were compared with the clinical standard protocol (120 kVp, TCM SD 7.5, 0.813 pitch, AIDR 3D).ResultsThe DLP of the standard protocol was 25 mGy•cm; the area under the curve (AUC) was 0.839 (95%CI: 0.790–0.888). Combined effects of tube voltage reduction to 100 kVp and TCM noise level increase to SD 10 optimized protocol performance by improving dose (7.3 mGy•cm) and detectability (AUC 0.884, 95%CI: 0.844–0.924). Diagnostic performance was significantly affected by the TCM noise level at 120 kVp (AUC 0.821 at TCM SD 7.5 vs. 0.776 at TCM SD 14, p = 0.003), but not at 100-kVp tube voltage (AUC 0.839 at TCM SD 7.5 vs. 0.819 at TCM SD 14, p = 0.354), the reconstruction method at 100 kVp (AUC 0.854 for AIDR 3D vs. 0.806 for FBP, p < 0.001), but not at 120-kVp tube voltage (AUC 0.795 for AIDR 3D vs. 0.793 for FBP, p = 0.822), and the tube voltage for AIDR 3D reconstruction (p < 0.001), but not for FBP (p = 0.226).ConclusionsCombined effects of 100-kVp tube voltage, TCM noise level of SD 10, a pitch of 0.813, and AIDR 3D resulted in an optimal neck protocol in terms of dose and diagnostic performance. Protocol parameters were subject to complex interactions, which created opportunities for protocol improvement.Key Points• A task-based approach using patient-mimicking phantoms was employed to optimize a CT system for neck imaging through systematic testing of protocol parameters.• Combined effects of 100-kVp tube voltage, TCM noise level of SD 10, a pitch of 0.813, and AIDR 3D reconstruction resulted in an optimal protocol in terms of dose and diagnostic performance.• Interactions of protocol parameters affect diagnostic performance and should be considered when optimizing CT techniques.
Highlights
Computed tomography (CT) acquisition protocols should provide diagnostic image quality at the lowest possible dose in line with the ALARA principle
The reference protocol had a Dose-length products (DLPs) of 25 mGycm with a mean area under the curve (AUC) across all readers of 0.839
A higher tube current modulation (TCM) noise level resulted in inferior detectability when combined with 120-kVp tube voltage while detectability was unchanged when combined with a reduced tube voltage of 100 kVp
Summary
Computed tomography (CT) acquisition protocols should provide diagnostic image quality at the lowest possible dose in line with the ALARA principle (as low as reasonably achievable). Prior efforts to optimize protocols harmonized dose exposure across CT facilities through protocol revision by expert panels and best practice sharing [5, 6] Such programs were shown to be valuable in reducing dose and identifying dose outliers. They were not intended to assess diagnostic image quality, which means that they could neither exclude unacceptable image quality nor identify optimal protocols that strike the best balance between dose and image quality. Protocol optimization for such purposes can be defined in terms of determining how to better use a system’s imaging capabilities for obtaining adequate diagnostic information at the lowest possible dose
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
