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Published online before print May 23, 2007, 10.1148/radiol.2441060977
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(Radiology 2007;244:130-137.)
© RSNA, 2007

Experimental Studies

Detection of Simulated Microcalcifications in a Phantom with Digital Mammography: Effect of Pixel Size1

Sankararaman Suryanarayanan, PhD, MBA, Andrew Karellas, PhD, Srinivasan Vedantham, PhD, Ioannis Sechopoulos, MS, and Carl J. D'Orsi, MD

1 From the Winship Cancer Institute and Department of Radiology, Emory University School of Medicine, 1701 Uppergate Dr, Bldg C, Suite 5018, Atlanta, GA 30322 (S.S., A.K., S.V., I.S., C.J.D.); and Wallace H. Coulter Department of Biomedical Engineering at Georgia Institute of Technology and Emory University, Atlanta, Ga (S.S., A.K., I.S.). Received June 6, 2006; revision requested August 7; revision received September 8; accepted October 5; final version accepted November 15. Supported in part by National Institutes of Health (NIH) grants (RO1-CA88792 and RO1-EB002123) from the National Cancer Institute (NCI) and the National Institute of Biomedical Imaging and Bioengineering (NIBIB). Supported in part by an infrastructure grant from the Georgia Cancer Coalition (GCC). Address correspondence to A.K. (e-mail: akarell{at}emory.edu).

Purpose: To evaluate the effect of pixel size on the detection of simulated microcalcifications in a phantom with digital mammography.

Materials and Methods: A high-spatial-resolution prototype imager that yields variable pixel size (39 and 78 µm) and a clinical full-field digital mammography (FFDM) system that yields a 100-µm pixel size were used. Radiographic images of a contrast-detail (CD) phantom were obtained to perform four-alternative forced-choice observer experiments. Polymethylmethacrylate was added to obtain phantom thicknesses of 45 and 58 mm, which are typical breast thicknesses encountered in mammography. Phantom images were acquired with both systems under nearly identical exposure conditions by using an antiscatter grid. Twelve images were acquired for each phantom thickness and pixel size (for a total of 72 images), and six observers participated in this study. Observer responses were used to compute the fraction of correctly detected disks. A signal detection model was used to fit the recorded data from which CD characteristics were obtained. Repeated-measures analyses with mixed-effects linear models were performed for each of the six observers. All statistical tests were two sided and unadjusted for multiple comparisons. A P value of .05 or less was considered to indicate a significant difference.

Results: Statistical analysis revealed significantly better CD characteristics with 39- and 78-µm pixel sizes compared with 100-µm pixel size for all disk diameters and phantom thicknesses (P < .001). Increase in phantom thickness degraded CD characteristics regardless of pixel size (P < .001).

Conclusion: On the basis of the conditions of this study, reducing pixel size below 100 µm with low imaging system noise enhances the visual perception of small objects that correspond to typical microcalcifications.

© RSNA, 2007