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.