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Digital Mammography: Effects of Reduced Radiation Dose on Diagnostic Performance¹

¹ From the Duke Advanced Imaging Laboratories, Department of Radiology (E.S., R.S.S., J.A.B.), and Division of Breast Imaging, Department of Radiology (J.A.B.), Duke University Medical Center, 2424 Erwin Rd, Suite 302, Durham, NC 27705; and Departments of Physics (E.S., R.S.S.), Biomedical Engineering (E.S.), and Biostatistics and Bioinformatics (D.M.D.), and Medical Physics Graduate Program (E.S.), Duke University, Durham, NC. Received June 19, 2006; revision requested August 21; revision received November 3; final version accepted December 11. Supported in part by grants from the National Institutes of Health (R21-CA95308) and U.S. Army Medical Research and Materiel Command (W81XWH-04-1-0323). Address correspondence to E.S. (e-mail: samei{at}deckard.duhs.duke.edu).

View larger version (187K): [in this window] [in a new window] [Download PPT slide]   Figure 1: Mammograms obtained with full dose (left column), half dose (center column), and quarter dose (right column) in the observer experiment show microcalcification distributions (arrows in top row) and malignant (arrows in middle row) and benign (arrows in bottom row) masses.

View larger version (15K): [in this window] [in a new window] [Download PPT slide]   Figure 2: Contingency table used to deduce performance results. This table was used to detect malignant masses. B = benign mass, C = microcalcification, M = malignant mass, N = normal.

View larger version (24K): [in this window] [in a new window] [Download PPT slide]   Figure 3a: Contingency tables at (a) full dose, (b) half dose, and (c) quarter dose averaged across observers indicate the fraction of which the observers scored the images of a given class. The scale to the right of each table shows the fraction of images from a given truth category that were rated in a given category. B = benign mass, C = microcalcification, M = malignant mass, N = normal.

View larger version (22K): [in this window] [in a new window] [Download PPT slide]   Figure 3b: Contingency tables at (a) full dose, (b) half dose, and (c) quarter dose averaged across observers indicate the fraction of which the observers scored the images of a given class. The scale to the right of each table shows the fraction of images from a given truth category that were rated in a given category. B = benign mass, C = microcalcification, M = malignant mass, N = normal.

View larger version (19K): [in this window] [in a new window] [Download PPT slide]   Figure 3c: Contingency tables at (a) full dose, (b) half dose, and (c) quarter dose averaged across observers indicate the fraction of which the observers scored the images of a given class. The scale to the right of each table shows the fraction of images from a given truth category that were rated in a given category. B = benign mass, C = microcalcification, M = malignant mass, N = normal.

View larger version (31K): [in this window] [in a new window] [Download PPT slide]   Figure 4: Bar graph shows variation in the overall accuracy, representing an average over all diagnostic tasks involved, as a function of dose level for individual observers and the average across observers. The variance for each observer was calculated by using bootstrap analysis, with error bars representing one standard error. This graph shows that for each observer and across all observers, overall accuracy was reduced as radiation dose was decreased.

View larger version (31K): [in this window] [in a new window] [Download PPT slide]   Figure 5: Bar graph shows the effect of dose level on the detection of microcalcifications and the detection and discrimination of malignant and benign masses. Data correspond to averages for all observers, with standard errors (error bars) calculated in a fashion similar to the manner in which data were calculated in Figure 4. With the reduction from a full dose to a quarter dose, there was a significant decrease in microcalcification detection (P < .01) and mass discrimination (P < .05). Detection of malignant masses was reduced only with a quarter dose, and detection of benign masses changed little when radiation dose was reduced.

View larger version (45K): [in this window] [in a new window] [Download PPT slide]   Figure 6: Bar graph shows the potential effect of bias in the detection of microcalcifications. Bias could be potentially due to the multiplicity of observer grading tasks; therefore, this graph shows the raw detection results and the detection results adjusted to remove any potential bias. Error bars represent one standard error. Nearly identical results were found for the two scoring schemes (ie, categorical and two task) and thus showed that categorical scoring introduced minimal or no bias.

View larger version (17K): [in this window] [in a new window] [Download PPT slide]   Figure 7: Graph shows the number of unrated images at a given time. The three lines show the reading times for images with signal-to-noise ratios that reflect full, half, and quarter doses. A significant relationship was found between radiation dose and observer interpretation time.