When typical symptoms and signs of lung cancer appear, it is often at an advanced stage and 80% have lost the chance of surgical treatment, with a long-term survival rate of less than 10%. Therefore, early diagnosis of lung cancer is very important, but most patients do not have any symptoms, so lung cancer screening is advocated for high-risk groups, and the only proven effective means is low-dose CT screening for lung cancer. On the other hand, most diseases in the lung present with symptoms such as cough, sputum, hemoptysis and chest pain, and it is difficult to make an accurate diagnosis of lung diseases through clinical manifestations. Therefore, imaging examinations are very important. In most cases, the imaging doctor’s discerning eye is able to determine the diagnosis of lung cancer and, more importantly, to exclude the diagnosis of lung cancer, saving patients from psychological burden and surgery. Diseases that are easily confused with lung cancer include the following categories: neoplastic: malignant tumors include solitary lung metastases, malignant lymphoma, and malignant mesenchymal tissue tumors of the lung; low-grade malignant tumors include inflammatory myofibroblastoma; benign tumors include mismatched tumors, sclerosing hemangioma, endobronchial papilloma, and benign mesenchymal tissue-derived tumors. Infectious and granulomatous lesions (benign): tuberculosis; spherical pneumonia, lung abscess, and mechanized pneumonia; fungal infections; nodular disease; and right middle lung syndrome. A variety of rheumatic immune diseases can cause intrapulmonary lesions, such as rheumatoid nodules, Caplan’s syndrome, Wegener’s granulomatosis, etc. Developmental abnormalities: bronchial/pulmonary cysts; pulmonary isolation disease; arteriovenous fistulas. Others: endobronchial mucus plug from postoperative chest and abdominal pain, respiratory depressants, chronic bronchitis, etc.; bronchial foreign bodies; bronchiectasis; pulmonary amyloidosis; spherical pulmonary atelectasis, etc. For intrapulmonary lesions that are difficult to identify, diagnostic imaging physicians generally start from the following aspects: 1. High-quality imaging data: Most patients will think that high-end examination equipment must bring high-quality imaging data, which is incomplete. High-quality imaging data cannot be separated from high-end equipment, but what is more important is the level of the physicians operating these devices, i.e., the method of scanning. High level hospitals generally use thin layer enhanced CT and CT multiplanar reconstruction as a routine application. CT multiplanar reconstruction can view the lesion from multiple angles and provide help for differential diagnosis. For difficult cases, individualized scanning protocols are also needed based on various clinical and available imaging data clues, such as enhancement scans with different phases, dynamic enhancement scans, perfusion scans, 3D volume imaging, etc. If there is still doubt, the imaging physician will also recommend further tests such as PET-CT, fiberoptic bronchoscopy, etc. Sometimes invasive tests such as CT-guided puncture biopsy, ultrasound bronchoscopy-guided transbronchial puncture biopsy (EBUS-TBNA), thoracoscopy or open-chest biopsy are also used. 2. Clinical data: Respiratory diseases have few specific symptoms. For more difficult cases, patients should take the initiative to cooperate with the physician and provide as detailed a medical history as possible. For example, the repeated occurrence of intrapulmonary infections in the same area should pay special attention to whether they are caused by tumor obstruction; some paraneoplastic syndromes such as skin paraneoplastic syndrome and proliferative osteoarthropathy can suggest the diagnosis of lung cancer; infectious lesions similar to tumors can appear in the lungs when the blood sugar of diabetes is not well controlled, etc. For example, in one case of suspected lung cancer, CT showed that there appeared to be bone-like high-density material in the bronchial lesion in the upper lobe of the left lung, and after questioning the patient, the patient recalled that he had a severe choking cough when he ate mackerel one month ago, followed by intermittent coughing symptoms, so we suspected that there might be mackerel bone in the lesion and suggested performing Bronchoscopy was performed, and the mackerel bone was indeed removed bronchoscopically, and the patient was cured with antimicrobial treatment. Previous imaging data is also very important, even if it is not of high quality, it may help the imaging doctor to make a correct diagnosis. We often encounter patients who have a very strange mentality, as if to test the imaging doctor, deliberately withholding medical history and previous examinations, thinking that the imaging doctor is a “film reader”, “just look at what is on the film”, this idea is very wrong. It is very common to see different images of the same disease and different diseases, and it is necessary to combine clinical manifestations, medical history and other examinations such as bronchoscopy to make the most correct diagnosis or provide information on the next step of examination or treatment. 3.Follow-up: that is, the same examination is repeated over a period of time. There are usually two types of follow-up examinations in the diagnostic process. One is when the diagnosis is relatively clear, such as the diagnosis of pneumonia or tuberculosis, which requires follow-up examinations after treatment to observe the efficacy and verify the diagnosis; another is when the diagnosis of benign tumor requires follow-up examinations for a period of time to completely exclude the diagnosis of lung cancer. Another situation is that the diagnosis is difficult at present and requires waiting for a period of time before making the diagnosis, during which experimental treatment, such as antibacterial and anti-tuberculosis drugs, may be needed; or it may just be waiting without further examination and treatment measures. Patients are often more worried about whether the malignant tumor will progress during this time. This concern is normal, but the growth of tumor is a long-term process, and the impact of short-term follow-up is minimal. The imaging doctor will follow up the lesion, usually at 1~3 months, and make another diagnosis according to the growth of the lesion. Some lung cancers grow extremely slowly, taking more than 8 years for the diameter to grow by a factor of 1. Patients over 70 years old can be followed up for a long time without any treatment. Therefore, follow-up imaging is both a diagnostic method and an important part of treatment.