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CT Depiction of Pulmonary Emboli: Display Window Settings¹

¹ From the Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 S Kingshighway Blvd, St Louis, MO 63110. Received September 8, 2004; revision requested November 15; revision received November 24; accepted December 21. Address correspondence to K.T.B. (e-mail: baet{at}mir.wustl.edu).

View larger version (85K): [in a new window]   Figure 1a. Patient 3. Transverse CT images obtained with the (a) standard mediastinal (window width, 400 HU; window center, 30 HU), (b) modified (window width, 416 HU; window center, 208 HU), and (c) double-half (window width, 748 HU; window center, 187 HU) window settings. (d) Transverse CT image obtained with the mean value of the personal window setting for all observers (window width, 628 HU; window center, 175 HU). A subtle nonocclusive PE (arrow) in the right upper lobe PA is obscured by apparent intensely enhanced blood, and it becomes invisible at the standard mediastinal window setting. PE is apparent at other window settings.

View larger version (49K): [in a new window]   Figure 1b. Patient 3. Transverse CT images obtained with the (a) standard mediastinal (window width, 400 HU; window center, 30 HU), (b) modified (window width, 416 HU; window center, 208 HU), and (c) double-half (window width, 748 HU; window center, 187 HU) window settings. (d) Transverse CT image obtained with the mean value of the personal window setting for all observers (window width, 628 HU; window center, 175 HU). A subtle nonocclusive PE (arrow) in the right upper lobe PA is obscured by apparent intensely enhanced blood, and it becomes invisible at the standard mediastinal window setting. PE is apparent at other window settings.

View larger version (95K): [in a new window]   Figure 1c. Patient 3. Transverse CT images obtained with the (a) standard mediastinal (window width, 400 HU; window center, 30 HU), (b) modified (window width, 416 HU; window center, 208 HU), and (c) double-half (window width, 748 HU; window center, 187 HU) window settings. (d) Transverse CT image obtained with the mean value of the personal window setting for all observers (window width, 628 HU; window center, 175 HU). A subtle nonocclusive PE (arrow) in the right upper lobe PA is obscured by apparent intensely enhanced blood, and it becomes invisible at the standard mediastinal window setting. PE is apparent at other window settings.

View larger version (91K): [in a new window]   Figure 1d. Patient 3. Transverse CT images obtained with the (a) standard mediastinal (window width, 400 HU; window center, 30 HU), (b) modified (window width, 416 HU; window center, 208 HU), and (c) double-half (window width, 748 HU; window center, 187 HU) window settings. (d) Transverse CT image obtained with the mean value of the personal window setting for all observers (window width, 628 HU; window center, 175 HU). A subtle nonocclusive PE (arrow) in the right upper lobe PA is obscured by apparent intensely enhanced blood, and it becomes invisible at the standard mediastinal window setting. PE is apparent at other window settings.

View larger version (119K): [in a new window]   Figure 2a. Patient 23. Transverse CT images obtained with the (a) standard mediastinal (window width, 400 HU; window center, 30 HU), (b) modified (window width, 454 HU; window center, 227 HU), and (c) double-half (window width, 820 HU; window center, 205 HU) window setting. (d) Transverse CT image obtained with the mean value of the personal window setting for all observers (window width, 688 HU; window center, 192 HU). A focal embolus (arrowhead) in the right lower lobe PA is well demarcated from the enhanced blood at all four window settings; however, both the embolus and the lung parenchyma were equally dark and were not separable at the modified window setting, thereby potentially affecting the conspicuity and detection of PE. The pulmonary valve (arrow) is obscured and invisible at the mediastinal window setting, but it is well depicted at the other window settings.

View larger version (79K): [in a new window]   Figure 2b. Patient 23. Transverse CT images obtained with the (a) standard mediastinal (window width, 400 HU; window center, 30 HU), (b) modified (window width, 454 HU; window center, 227 HU), and (c) double-half (window width, 820 HU; window center, 205 HU) window setting. (d) Transverse CT image obtained with the mean value of the personal window setting for all observers (window width, 688 HU; window center, 192 HU). A focal embolus (arrowhead) in the right lower lobe PA is well demarcated from the enhanced blood at all four window settings; however, both the embolus and the lung parenchyma were equally dark and were not separable at the modified window setting, thereby potentially affecting the conspicuity and detection of PE. The pulmonary valve (arrow) is obscured and invisible at the mediastinal window setting, but it is well depicted at the other window settings.

View larger version (132K): [in a new window]   Figure 2c. Patient 23. Transverse CT images obtained with the (a) standard mediastinal (window width, 400 HU; window center, 30 HU), (b) modified (window width, 454 HU; window center, 227 HU), and (c) double-half (window width, 820 HU; window center, 205 HU) window setting. (d) Transverse CT image obtained with the mean value of the personal window setting for all observers (window width, 688 HU; window center, 192 HU). A focal embolus (arrowhead) in the right lower lobe PA is well demarcated from the enhanced blood at all four window settings; however, both the embolus and the lung parenchyma were equally dark and were not separable at the modified window setting, thereby potentially affecting the conspicuity and detection of PE. The pulmonary valve (arrow) is obscured and invisible at the mediastinal window setting, but it is well depicted at the other window settings.

View larger version (135K): [in a new window]   Figure 2d. Patient 23. Transverse CT images obtained with the (a) standard mediastinal (window width, 400 HU; window center, 30 HU), (b) modified (window width, 454 HU; window center, 227 HU), and (c) double-half (window width, 820 HU; window center, 205 HU) window setting. (d) Transverse CT image obtained with the mean value of the personal window setting for all observers (window width, 688 HU; window center, 192 HU). A focal embolus (arrowhead) in the right lower lobe PA is well demarcated from the enhanced blood at all four window settings; however, both the embolus and the lung parenchyma were equally dark and were not separable at the modified window setting, thereby potentially affecting the conspicuity and detection of PE. The pulmonary valve (arrow) is obscured and invisible at the mediastinal window setting, but it is well depicted at the other window settings.

View larger version (13K): [in a new window]   Figure 3. Graph shows mean ratings of the seven observers for the 25 patients. A score of 1 indicates the most preferred window setting, and a score of 3 indicates the least preferred window setting. To better illustrate the distribution of data points, they are spread horizontally to minimize overlapping. The horizontal lines across the diamonds represent the mean value of the group, and the vertical spans of the diamonds represent 95% confidence intervals. If the horizontal lines within the diamonds drawn above and below the mean lines overlap, group means are not significantly different at the 95% confidence interval. The horizontal spans of the diamonds are proportional to the sample sizes of the groups.

View larger version (16K): [in a new window]   Figure 4a. Box plots of window (a) width and (b) center ratios for the double-half and modified window settings and for the seven observers on the basis of their personal settings. To better illustrate the distribution of the data points, they are spread horizontally to minimize overlapping. The ends of the boxes are the 25th and 75th quartiles. The lines across the middle of the boxes indicate the median values. The interquartile range is the difference between the quartiles. The lines extend from the boxes to the outermost points that fall within the interquartile range.

View larger version (18K): [in a new window]   Figure 4b. Box plots of window (a) width and (b) center ratios for the double-half and modified window settings and for the seven observers on the basis of their personal settings. To better illustrate the distribution of the data points, they are spread horizontally to minimize overlapping. The ends of the boxes are the 25th and 75th quartiles. The lines across the middle of the boxes indicate the median values. The interquartile range is the difference between the quartiles. The lines extend from the boxes to the outermost points that fall within the interquartile range.

View larger version (21K): [in a new window]   Figure 5a. Graphs show regression curves of the window (a) width and (b) center ratios for mean PA attenuation values (measured in Hounsfield units), as measured by observer 2. Of the regression curves of the seven observers, those of observer 2 had the highest r2 values for width ratios (r2 = 0.59, P < .001) and center ratios (r2 = 0.40, P < .001). Each point corresponds to one of the 25 cases. The 95% confidence intervals are included in each plot.

View larger version (23K): [in a new window]   Figure 5b. Graphs show regression curves of the window (a) width and (b) center ratios for mean PA attenuation values (measured in Hounsfield units), as measured by observer 2. Of the regression curves of the seven observers, those of observer 2 had the highest r2 values for width ratios (r2 = 0.59, P < .001) and center ratios (r2 = 0.40, P < .001). Each point corresponds to one of the 25 cases. The 95% confidence intervals are included in each plot.