CT scans can be used to visualize the lungs, mediastinum, trachea, bronchi and large blood vessels, and are most effective in areas that are not easily visualized on plain chest films, such as subpleural, near-transverse and parasternal lesions. GE LightSpeed VCT is superior to single-row CT and multi-row CT in identifying lesions that are not detected on plain films. If you want to observe vascular lesions, such as aortic coarctation aneurysm, aortitis, pulmonary artery embolism, or to distinguish small mediastinal masses or enlarged lymph nodes, etc., and need to observe their contrast enhancement effect, you can do the enhancement scan directly. (A) General scan 1. Scanning technique: The chest scan is performed in the supine position with the hands raised above the head to reduce the scanning artifacts of the shoulders and both upper limbs on the chest. The sternoclavicular intersection is used as the localization mark, and the orthopantomogram of the chest is taken before the scan, and the scanning range from the lung tip to the septal angle is selected on the localization film. Generally, the scan has a layer thickness of 5 mm and an interval of 5 mm, and a set of thin layer images with a layer thickness and interval of 1.25 mm at the same time. The scan is performed using a spiral scan with inspiration followed by breath holding. The general whole lung scan is about 3-5 seconds. 2, image display: chest CT images should be observed with two different window widths and window positions, namely the lung window and mediastinal window, the lung window has a window width of 1000-1600 and a window position of -600-800; the mediastinal window has a window width of 300-500 and a window position of about 30. The window width of the mediastinal window is 300-500, and the window position is generally taken to be about 30. Both axial and coronal images are given, and sagittal images are given as appropriate. (ii) Enhancement scan 1. Preparation before the examination: fasting 4-6 h before the scan, and negative iodine allergy test. Train the patient to follow instructions to inhale and hold the breath. Remove the chest ornaments with iron to avoid artifacts. 2. Scanning technique: After selecting the scan area including the pulmonary apex and septum on the localization film, inject 80-100 mL of intravenous contrast agent at a flow rate of 3-3.5 mL/s. Layer thickness is 5 mm, interval is 5 mm, and sweep the whole lung in one breath-hold. For vascular cases such as entrapment aneurysms, the images obtained are reconstructed in multiple planes to assist in the diagnosis, with excellent results. (iii) Pulmonary CTA angiography technique is suitable for pulmonary artery embolism, pulmonary tumor blood supply situation, etc. 1. Preparation before examination: same as pulmonary enhancement scan. 4-6h fasting and negative iodine allergy test. 2. Scanning technique: on the basis of the general lung scan, select the scanning range. Depending on the size of the lesion, a scan layer thickness of 1.25- 5mm with an interval of 1.25-5mm was selected, and the reconstruction interval was as thin as 0.625mm,. After the injection of 80-100mL of intravenous contrast agent at a flow rate of 3-4s, the spiral scan is performed after the drug injection (intelligent tracking or empirical value can be selected). 3.Image display: The original CTA image obtained, after post-processing (MPR, MIP, MinP, VR, 3D, etc.) can clearly show the tumor blood supply, as well as pulmonary artery embolism, pulmonary vascular malformation, etc. (D) Lung simulation endoscopy scan Suitable for central type lung tumor cases, to observe the relationship between trachea and its surrounding tumor. 1.Scanning technique: The scanning method is the same as pulmonary plain scan, and the scanning range is selected on the localization film from the bifurcation of trachea to the end of the lesion area. 2.Image display: The obtained images can be simulated by endoscopic technique to observe the invasion of tumor in or outside the trachea, and the effect is the same as that of bronchoscopy. The disadvantage is that biopsy cannot be performed.