Spatial and contrast resolution of ultralow dose dentomaxillofacial CT imaging using iterative reconstruction technology

OBJECTIVE: The objective of this study was to determine how iterative reconstruction technology (IRT) influences contrast and spatial resolution in ultralow dose dentomaxillofacial computed tomography (CT) imaging. METHODS: A polymethyl methacrylate phantom with various inserts was scanned using a reference protocol at CTDIvol 36.56 mGy, a sinus protocol at 18.28 mGy, and ultralow dose protocols at 4.17, 2.36, 0.99, and 0.53 mGy. All datasets were reconstructed using filtered back projection (FBP) and the following IRTs: adaptive statistical iterative reconstructions (ASIR-50, ASIR-100), and model-based iterative reconstruction (MBIR). Inserts containing line pair patterns and contrast-detail patterns for three different materials were scored by three observers. Observer agreement was analyzed using Cohen's kappa and difference in performance between the protocols and reconstruction was analyzed with Dunn's test at α=0.05. RESULTS: Inter-observer agreement was acceptable with a mean kappa value of 0.59. Compared with the reference protocol using FBP, similar scores were achieved at 2.36 mGy using MBIR. MIBR reconstructions showed the highest noise suppression as well as good contrast even at the lowest doses. Overall, ASIR reconstructions did not outperform FBP. CONCLUSIONS: Ultralow dose protocols and MBIR at a dose reduction of more than 90% may show no significant differences in spatial and contrast resolution compared to a reference protocol and FBP. Ultralow dose CT and IRT should be further explored in clinical studies.status: publishe