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目的：分析ＣＴ双窗技术的原理以及其优点与限度。方法：在３０例胸部ＣＴ检查发现病变的病例常规扫描后，分别在纵隔窗（窗位０－５０Ｈｕ，窗宽５００Ｈｕ），肺窗（窗位－５００至－８００Ｈｕ）和双窗下（第１窗位－８００Ｈｕ，第１窗宽１２００，第２窗位５Ｈｕ，第２窗宽５００）摄片。采用双盲法分别阅读肺窗、纵隔窗和双窗位像，比较使用双窗前后的诊断结果。结果：使用双窗前，有５例（１６．７％）误诊或诊断不确定。应用双窗后，诊断完全正确（误诊０％），二组结果相差显著（Ｐ＜０．０１）。设置双窗后，二个窗的交界处形成明亮的交界线，如肺的边缘，支气管管壁与管腔。正常情况下这种交界线光滑锐利。当有病时，也可见到这种交界线，其光滑程度受病变部位和病变性质的影响，一般肺内病变与正常的肺组织间的交界线较模糊，毛糙。相反单纯的肺外病变（胸壁、胸膜、纵隔），只要不侵犯肺，由于脏层胸膜的缘故，肺内和肺外的ＣＴ值相差很大，病变与肺的交界线光滑、锐利。另外使用双窗可以在一张图像上同时显示肺组织和胸壁、纵隔软组织，显示病变比较直观。双窗的限度在于不能根据灰度来估计ＣＴ值。结论：应用双窗使病变显示更直观，有利于胸部疾病的定位诊断，在一定程度上对定性诊断也?
OBJECTIVE: To analyze the principle, advantages and limitations of CT double window technique. Methods: Thirty cases of thoracic CT were examined under the condition of mediastinal window (0-50Hu, 500Hu), lung window (-500 to -800Hu) and double window Window level -800Hu, the first window width 1200, the second window level 5Hu, the second window width 500) radiography. Double-blind method were used to read the lung window, mediastinum window and double window images, compared with the double window before and after the diagnosis. Results: Five patients (16.7%) were misdiagnosed or diagnosed before using dual window. After applying double windows, the diagnosis was correct (misdiagnosis 0%), and the difference between the two groups was significant (P <0.01). After setting the double window, the two windows form a bright boundary at the junction, such as the edge of the lung, the bronchial wall and the lumen. Under normal circumstances, this borderline is smooth and sharp. When sick, can also see this kind of boundary line, the smooth degree is affected by the lesion site and the nature of the lesion, the general lung lesions and the normal lung tissue borderline is fuzzy, rough. On the contrary pure extrapulmonary lesions (chest wall, pleura, mediastinum), as long as no invasion of the lungs, due to the visceral pleura, lung and lung CT values vary greatly, the lesion and lung border line smooth and sharp. In addition to the use of double windows in an image on both lung and chest wall, mediastinal soft tissue, showing lesions more intuitive. The limit of the double window is that the CT value can not be estimated from the gray level. Conclusion: The application of double-window display of lesions more intuitive, is conducive to the diagnosis of chest disease localization, to a certain extent, the qualitative diagnosis also?