Spatial Variation of Resolution and Noise in Multi–Detector Row Spiral CT 1 John F. Meinel, Jr, BSE, Ge Wang, PhD, Ming Jiang, PhD, Troy Frei, Michael Vannier, MD, Eric Hoffman, PhD Rationale and Objectives. The authors performed this study to evaluate an approach for measuring the variations of three-dimensional spatial resolution and image noise throughout a field of view imaged with multi– detector row spiral computed tomographic (CT) scanners. Materials and Methods. The authors designed a phantom (diameter, 320 mm) that contained 37 metallic spheres (diame- ter, approximately 0.8 mm) positioned between two disks made of a material with attenuation being that of water. One sphere was located at the isocenter of the phantom, and the rest were evenly spaced in three concentric rings with diame- ters of 100, 200, and 300 mm, respectively. The phantom was imaged with two widely used multi– detector row CT scan- ners by using a standard protocol and four variations of that protocol. Because a recently developed theory holds that im- age resolution should be proportional to the square root of the trace of the covariance matrix of a point spread function, the authors developed a software package to segment high-attenuation spheres from the CT image volume and compute point spread functions from blurred images of the spheres. Three-dimensional spatial resolution and image noise were cal- culated as a function of radial distance within the field of view. Results. Resolution and noise were quantified in the resultant CT image volumes and found to be nonisotropic, with worse resolution and less noise occurring at the periphery of the field of view. Conclusion. The method enabled measurement of variations in spatial resolution and of their distribution on images ob- tained with multi– detector row CT scanners. These findings may contribute to the development of an improved algorithm for image reconstruction. Key Words. Computed tomography (CT), image quality; computed tomography, multi– detector row; computed tomogra- phy (CT), quantitative. © AUR, 2003 During the past few years, rapid progress has been made in computed tomographic (CT) theory, technology, and applications, and multi– detector row CT has become a standard modality of medical imaging. Objective, quanti- tative, CT image– based measures are gaining acceptance in the clinical setting as diagnostic aids for characterizing pathologic processes and as predictors of therapeutic out- comes. Image quality is thus of primary concern. Exten- sive studies of various methods for quantitative and quali- tative assessment of CT image quality have produced many valuable results (1–5). A number of factors contribute to image quality, in- cluding the choice of a CT scanner and scanning proto- col. In this study, we investigated various parameters that affect spatial resolution and image noise. Previous re- search studies of image quality were focused mainly on the center of the field of view, and most were concerned Acad Radiol 2003; 10:607–613 1 From the Departments of Biomedical Engineering (J.F.M., G.W., E.H.) and Radiology (G.W., T.F., M.V., E.H.), University of Iowa College of Medicine, 200 Hawkins Dr, Iowa City, IA 52242; and the School of Mathematics, Pe- king University, Beijing, China (M.J.). Supported in part by National Insti- tutes of Health, Bioengineering Research Partnership grants R01-HL- 064368 and R01-DC-03590. Received January 21, 2003; revision requested February 6; revision received and accepted February 18. Address corre- spondence to G.W. © AUR, 2003 607