Model-based Iterative Reconstruction Compared to Adaptive Statistical Iterative Reconstruction and Filtered Back-projection in CT of the Kidneys and the Adjacent Retroperitoneum Eric W. Olcott, MD, Lewis K. Shin, MD, Graham Sommer, MD, Ian Chan, MD, Jarrett Rosenberg, PhD, F. Lior Molvin, RT, F. Edward Boas, MD, PhD, Dominik Fleischmann, MD Rationale and Objectives: To prospectively evaluate the perceived image quality of model-based iterative reconstruction (MBIR) compared to adaptive statistical iterative reconstruction (ASIR) and filtered back-projection (FBP) in computed tomography (CT) of the kid- neys and retroperitoneum. Materials and Methods: With investigational review board and Health Insurance Portability and Accountability Act compliance, 17 adults underwent 31 contrast-enhanced CT acquisitions at constant tube potential and current (range 30–300 mA). Each was reconstructed with MBIR, ASIR (50%), and FBP. Four reviewers scored each reconstruction’s perceived image quality overall and the perceived image quality of seven imaging features that were selected by the authors as being relevant to imaging in the region and pertinent to the evaluation of high-quality diagnostic CT. Results: MBIR perceived image quality scored superior to ASIR and FBP both overall (P < .001) and for observations of the retroperitoneal fascia (99.2%), corticomedullary differentiation (94.4%), renal hilar structures (96.8%), focal renal lesions (92.5%), and mitigation of streak artifact (100.0%; all, P < .001). MBIR achieved diagnostic overall perceived image quality with approximately half the radiation dose required by ASIR and FBP. The noise curve of MBIR was significantly lower and flatter (P < .001). Conclusions: Compared to ASIR and FBP, MBIR provides superior perceived image quality, both overall and for several specific imaging features, across a broad range of tube current levels, and requires approximately half the radiation dose to achieve diagnostic overall perceived image quality. Accordingly, MBIR should enable CT scanning with improved perceived image quality and/or reduced radiation exposure. Key Words: Computed tomography; image reconstruction; radiation protection; tomography scanners; x-ray computed; kidney. ªAUR, 2014 I terative image reconstruction algorithms, such as the orig- inal algebraic reconstruction technique, (ART) were used in the early days of transmission computed tomography (CT) (1,2) but were quickly superseded by much faster analytical methods such as filtered back-projection (FBP) (3). Significant disadvantages exist with FBP, however, including its assumption that data are exact when in reality they are not, and the operation of the FBP filter which typically amplifies noise in the projection data. Iterative techniques, in contrast, can include models of features such as noise that improve the image during each iteration. This produces much better image quality than FBP does, when the signal-to-noise ratio is low, although this occurs at the expense of substantially increased computation time (4,5). Owing to substantial increases in computational power, iterative image reconstruction algorithms have recently re-emerged and are now available on commercial CT scanners manufactured by all major vendors (6). The recent literature appears to confirm the expected dose saving potential of Acad Radiol 2014; 21:774–784 From the Department of Radiology, Stanford University School of Medicine, 300 Pasteur Drive, H1307, Stanford, CA 94305-5105 (E.W.O., L.K.S., G.S., I.C., J.R., F.L.M., F.E.B., D.F.) and Veterans Affairs Palo Alto Health Care System, Palo Alto, CA (E.W.O., L.K.S.). Received October 8, 2013; accepted February 10, 2014. Address correspondence to: E.W.O. e-mail: eolcott@ stanford.edu ªAUR, 2014 http://dx.doi.org/10.1016/j.acra.2014.02.012 774