If there is reason to suspect that you have lung cancer, your doctor will use one or more of these methods to clarify the diagnosis of lung cancer. If these tests have identified lung cancer, additional tests should be performed to clarify how far the cancer has spread. There are many tests that we are exposed to during the consultation and treatment process. The following are some of the commonly used methods in the diagnosis of lung cancer. 1. X-ray diagnosis: It is the most common means of lung cancer diagnosis, and its positive detection rate can reach over 90%. It includes fluoroscopy, plain film, body layer, chest computer-aided body layer (CT), magnetic resonance imaging (MRI), bronchography and other methods. The principle in clinical practice is to perform examinations in the above order from simple to complicated and from less to more costly. CT has been widely used in the diagnosis of lung cancer since the 1970s. It is superior to X-ray in understanding the location of lesions, the relationship with surrounding organs, small pleural implantation or small amount of effusion, segmental atelectasis, enlarged lymph nodes in the mediastinum and small metastases in the lung, but it also has its limitations. Because enlarged lymph nodes are not always equal to metastases, we often encounter inflammatory lymph nodes that are more than 1.5 cm in diameter and cancerous metastatic lymph nodes that are less than 0.5 cm in diameter. Of course, if the lymph nodes have fused into a mass, the diagnosis of metastasis should be confirmed. The CT of abdomen is very helpful to observe whether there are metastases in abdominal organs such as liver, kidney and adrenal gland. Early X-ray manifestations of lung cancer: a. isolated spherical shadows or irregular small infiltrations; b. limited emphysema during expiratory phase; c. mediastinal oscillation during deep breathing; d. if lung cancer progresses to block segment or lobe bronchus, the distal gas of blockage will be gradually absorbed and segmental atelectasis will appear, and such atelectasis will form pneumonia or lung abscess if it is complicated by infection. In addition to a clearer view of the shape, density, location, hilar and mediastinal lymph node enlargement of the mass, a plain body layer film can also reveal the blockage, stenosis, external pressure and intra-tubular masses of the larger bronchi (above the lung segment). More advanced lung cancer can be seen as: huge mass nodules in the lung fields or hilum, lobar in shape, generally uniform in density, with burrs at the edges and sometimes liquefied in the center, appearing as thick-walled, eccentric, and unevenly lined cavities. When the mass blocks the lobe or the common bronchus, there is lobar or whole lung atelectasis, and a large amount of pleural fluid is seen when the pleura is involved, and rib destruction is seen when the chest wall is invaded. Alveolar cell carcinoma, also called fine bronchoalveolar carcinoma, is less common and is more common in women. Isolated type often shows small infiltration and slow growth, but it is still easy to be misdiagnosed as tuberculosis. 2.Magnetic resonance imaging (MRI): It is a new diagnostic imaging technology compared with CT. In the diagnosis and regular diagnosis of lung cancer, it can show the relationship between central tumor and surrounding organs and blood vessels more clearly, it does not need contrast agent and can determine whether the tumor invades blood vessels or compresses and encircles blood vessels. MRI can also show clearly when the tumor invades soft tissue. 3.Bone imaging or emission tomography (ECT): It can detect the lesion 3-6 months earlier than ordinary X-ray, so bone imaging can detect the bone metastasis earlier. 4. Positron emission tomography (PET): whole-body PET can detect unexpected extrathoracic metastases. There is no false positive rate in cases of extrathoracic metastases, but there are false positive findings on PET in intradistinal granulomas or other inflammatory lymph node lesions. This case needs to be confirmed by cytology or biopsy. However, there is no doubt that PET can make preoperative lung cancer screening more accurate. Fiberoptic bronchoscopy: The positive detection rate is 60%-80%, and the positive detection rate is much better than that of rigid bronchoscopy due to the magnification of the image by optical fiber illumination. During the examination, attention is paid to the degree of vocal cord activation, the shape and mobility of the bulge, and changes in the bronchial opening at all levels (generally up to 4-5) such as swelling, stenosis, ulceration, etc., as well as smear cytology, bite biopsy, and local irrigation. This examination, which is generally more complete, has also been reported to be complicated by bleeding after 9%-29% of biopsies. Encountering tumors suspected to be carcinoid and rich in intuitive blood flow should be done with caution, and it is best to avoid biopsy trauma. 2.Percutaneous pulmonary puncture: it is suitable for peripheral lesions and not suitable for open-chest cases for various reasons, and is mostly used in internal medicine. The current tendency is to use a fine needle, which is safer to operate and has fewer complications. The positive rate is 74%-96% in malignant tumors and 50%-74% in benign tumors. Complications include pneumothorax 20%-35% (about 1/4 of them need to be treated), small amount of hemoptysis 3%, fever 1.3%, air embolism 0.5%. 3.Mediastinoscopy: The current consensus is that mediastinoscopy should be performed when the lymph nodes in the anterior, parasternal and inferior ramus of the trachea (2, 4, 7) groups are enlarged as seen in CT. The operation is performed under general anesthesia and has a mortality rate of approximately 0.04% and complications of 1.2%. Complications include pneumothorax, paralysis of the recurrent laryngeal nerve, hemorrhage, fever, etc. C. Screening methods: Sputum exfoliative cytology: easy to perform, but the positive detection rate is only 50%-80%, and there is a false positive rate of 1%-2%. This method is suitable for confirming the diagnosis in high-risk groups. In order to increase the detection rate, attention should be paid from the beginning of sputum production, firstly, the patient should cough up real sputum from the “deep” part of the lung, not just saliva, and if necessary, stimulate the sputum with drugs. Secondly, the sample should be picked and fixed when the sputum is fresh, and then stained and read.