Recently, the CT.MR room of our hospital has officially launched low-dose CT examination of the chest for early screening of lung cancer. And it has been generally recognized by hospital leaders, clinicians and patients. It is reported that the radiation dose of low-dose CT examination of chest is only 1/4 of that of conventional CT scan, which greatly reduces the radiation dose to the examinees and provides health protection for them. As we all know, lung cancer is the cancer with the highest incidence rate in China, with about 400,000 new cases every year. Since early lung cancer often lacks clinical symptoms, most patients are already in the middle or late stage when they are diagnosed. Lung cancer with diameter less than 2cm usually has no distant and lymph node metastasis and has a good prognosis for surgical resection, with a five-year survival rate of up to 70%. Therefore, early detection, early diagnosis and early treatment are the keys to improve the survival rate of lung cancer. One important way to detect lung cancer early is lung cancer screening, which includes people over 40 years old, long-term smoking history and family history of lung cancer. Current screening methods include chest radiography, sputum cytology, molecular oncology and immunohistochemical examination, spiral CT examination, etc. Although chest radiography has the advantages of convenience, low cost, time saving and low radiation dose, its diagnostic sensitivity for small lung cancer is low, its diagnostic role for early lung cancer has gradually decreased, and chest radiography has not changed the mortality rate of lung cancer patients. Sputum cytology test is more sensitive only for squamous carcinoma involving large bronchi, but it cannot provide information for the detection of most other lung cancers, thus its application value is also limited. Low-dose CT of the chest is not only effective in reducing the radiation dose to the subject, but also has less overlapping lung images, higher density resolution, and higher sensitivity, specificity, and accuracy than chest radiographs. Most studies have confirmed that low-dose CT scanning technology has been able to meet the diagnostic requirements of chest CT plain scan, and has been able to be consistent with conventional dose CT scanning in the detection and characterization of disease. Low-dose spiral CT images have not reduced the image quality of parenchymal, diffuse lung lesions and have not reduced the density resolution of CT images. Therefore, the use of low-dose spiral CT for lung cancer screening meets the diagnostic requirements of the images (its lung cancer detection rate is about 10 times higher than that of chest radiographs), while reducing the X-ray radiation dose. It meets the requirements of the International Commission on Radiological Protection (ICRP) for radiation protection justification and optimization, greatly reduces the mortality rate of lung cancer patients, and effectively reduces the risk of malignant lesions caused by radiation of medical origin. Although there are some limitations of low-dose spiral CT for lung cancer screening, such as the low detection rate of central lung cancer and the false-positive rate, which leads to anxiety and psychological burden of the patient, low-dose spiral CT scan is still the best screening method for early lung cancer screening. In addition, this technology can also be used for routine chest examination, regular follow-up of nodular lesions in the lung, regular examination of interstitial lung lesions, traumatic lung, asbestosis, etc.