Isolated pulmonary nodules (SPN) are round or round-like lesions with a diameter of <3 cm in the lung, without pulmonary atelectasis, satellite foci and local lymph node enlargement, and the qualitative diagnosis of SPN has been a hot topic of research in the imaging field for more than a decade. Before the application of spiral CT in clinical practice, SPN studies were mostly analyzed morphologically and achieved good results, but some patients were still not correctly diagnosed preoperatively, and the rate of misdiagnosis and leakage of early lung cancer was high. Percutaneous lung aspiration biopsy is a good method to obtain pathological diagnosis in a minimally invasive manner, but <2em nodule puncture is more difficult. The correct diagnosis rate is relatively low. In recent years, with the attention to early lung cancer, there is an urgent need to fundamentally solve the problem of differential diagnosis of SPN. The birth of GE's 64-row spiral CT (Light Speed VCT) provides us with a better diagnostic tool, which uses 64 rows of 0.625mm wide detectors with completely equal width, fast scanning speed, short scanning interval, large coverage in Z-axis direction, and small radiometric measurement, which is more conducive to various evaluations of lung nodules. At present, most researchers of enhanced CT classify SPN into three categories: (1) various types of lung cancer and lung metastases, collectively referred to as malignant nodules; (2) benign tumors (mainly malignant tumors), various types of chronic inflammatory nodules and tuberculosis spheres, collectively referred to as benign nodules; (3) acute inflammatory nodules, also referred to as active inflammatory nodules, or inflammatory nodules. The advantage of single-layer dynamic scanning technology is that it scans the same level, so the CT value changes before and after enhancement measured in the corresponding area of the same level of the nodule are more accurate, the disadvantage is that SPN is prone to artifacts, and is easily affected by partial volume effect and level Repeatability is poor. Some scholars also use spiral scanning, and they believe that this method can reduce or eliminate the formation of artifacts and missed lesions. The amount of contrast should be determined by body weight, and the amount of contrast should increase with increasing body weight. In both dynamic and spiral scans, the patient needs to be trained to hold his or her breath before the examination, as consistency at multiple scan levels is essential for a successful examination. Generally, it is easy to control the breath hold by calm breathing at the end of inspiration or expiration, and oxygen can be given to ensure the breath hold time. There are 3 main methods of CT value measurement: (1) Measurement at the nodal center level, the area of interest should include all the nodules except the edges of 1 to 2 mm or at least 60% of the short diameter of the nodules. (2) For nodule center level measurement, 3 to 4 area values were measured and the average was taken. (3) If the difference between the CT values of 3 levels is greater than 10HU, the median value is taken. If the difference between the CT values of 3 levels is within 10HU, the CT value of the nodule is averaged. If there is necrosis or calcification within the lesion, the area of interest should avoid the necrosis or calcification area. 2. The CT enhancement characteristics of SPN are mainly analyzed from three aspects: the size of enhancement, time-density curve and morphological characteristics of enhancement (1) Size of enhancement The degree of enhancement is divided into four categories according to the size of enhancement: (1) No enhancement: enhancement value <5HU. (2) Mild enhancement: enhancement value >30HU. (3) Moderate enhancement: enhancement value >50HU. (4) Significant enhancement: enhancement value >70HU. ＞The degree of enhancement of SPN is not related to its diameter but to its histological type, and the magnitude of enhancement is an important basis for the qualitative diagnosis of SPN. Swensen et al. reported that the degree of enhancement of peripheral lung cancer is significantly higher than that of benign nodules. 20 HU was used as the lower limit for determining the degree of enhancement of malignant nodules, with a sensitivity of 100% and specificity of 76.9%, but A small number of benign and malignant nodules had enhancement values within the range of 20±5 HU. Therefore, nodules with enhancement values between 16 and 24 HU were considered indeterminate nodules, and nodules with enhancement values >25 HU were highly suspected to be lung cancer. Yamashita et al. reported that the enhancement values of peripheral type lung cancer were lower than those of inflammatory nodules and higher than those of benign tumors and tuberculosis spheres, and enhancement values between 20 and 60 HU were diagnostic indicators of malignant nodules. There were also differences in the enhancement values for different histological types of peripheral lung cancer, with adenocarcinoma generally having higher enhancement values than squamous and large cell carcinomas, but there were no statistically significant differences. This suggests that the enhancement values of SPN are not only related to its histological type but also to other factors. Using the SPN/AO value (the ratio of the peak enhancement of SPN to the CT value of the aorta at the corresponding moment) as the enhancement index of SPN can reduce or eliminate the error caused by the difference in cardiac output between individuals. The SPN/AO value of malignant nodules is significantly higher than that of benign nodules, and when the SPN/AO value is >6%, malignant nodules should be highly suspected. Some scholars have also used the CT enhancement rate (the ratio of nodal enhancement value to the plain CT value) as an evaluation index of the degree of SPN enhancement, and an enhancement rate of 13.2% as the lower limit of enhancement value for malignant nodules, with a sensitivity of 87.5% and specificity of 95.5%. It is worth noting that a few benign nodules can be significantly enhanced, while a few malignant nodules have a CT enhancement value of <20 HU due to improper scanning technique or low blood supply. (2) Time-density curve The time-density curve reflects the trend of nodule enhancement value, which is mainly determined by the hemodynamics of the nodule, and is also affected by the amount of contrast agent or whether oxygen is administered. The time-density curve of lung cancer is obviously different from that of benign nodules, which mostly shows a parabolic pattern, with the enhancement value of nodules increasing progressively after contrast injection and then decreasing slowly after reaching the peak. Swensen et al. reported that the peak enhancement value of lung cancer peaked within 2 min after contrast injection and then gradually decreased, while Yamashita et al. suggested that the peak value peaked after 5 min and Zhang et al. suggested that 1 min was the peak arrival time. This may be related to the histological type of the selected cases and the different dosage and speed of the contrast agent. Because the peak enhancement arrival time was not the same for different histological types of lung cancer, adenocarcinoma and large cell carcinoma enhanced faster than squamous carcinoma. Benign tumors or nodular bulbs do not enhance or enhance slightly and appear as a nearly horizontal straight line. Inflammatory nodules show a rapid increase in enhancement value after contrast injection, and the speed is higher than that of malignant nodules, with a mild decrease after reaching the peak, followed by a rise to the original peak state, which results in a plateau period, so the time-density curve has a small serrated or irregular shape. (3) Morphological characteristics of enhancement The enhancement pattern of SPN is generally divided into 5 types: (1) non-enhanced: enhancement value <5HU. (2) uniform enhancement: no density inhomogeneous area discernible to the naked eye after enhancement. (3) Uneven enhancement: dotted strips or sheets of non-enhancement or more prominent areas of enhancement are visible within the lesion after enhancement. (4) Peripheral strengthening: the peripheral part is strengthened but the central part is not strengthened. (5) Envelope-like intensification: only the edge of the lesion is envelope-like intensified, while the rest of the lesion is not intensified. Lung cancers smaller than 3 cm are mostly uniformly intensified, and a few can be unevenly intensified, while lung cancers larger than 3 cm are mostly unevenly intensified and can also be peripherally intensified due to necrosis in the center, and the surrounding solid parts are very irregular. The enhancement pattern of different histological types of lung cancer also differs. The peripheral part of adenocarcinoma tumor may show strip-like uneven enhancement, which is a characteristic of adenocarcinoma. Squamous carcinoma is prone to coagulative necrosis, which is difficult to identify on plain scan. Non-enhancing or envelope-like intensification mostly suggests tuberculoma, and a few tuberculomas may show central curve-like intensification or uniform intensification. Malignant pseudotumors are generally non-enhancing, but in a few cases, dense intervals may appear within the tumor, and these intervals may show mild enhancement after enhancement. The reinforcement pattern of inflammatory pseudotumor is various. In the seven cases of inflammatory pseudotumor reported by Zhang et al, one case showed uniform reinforcement, two cases showed inhomogeneous reinforcement, and four cases showed peripheral reinforcement, and the peripheral part of reinforcement was more irregular than that of malignant nodules. (4) Tumor vascular sign Through CT and pathology control study, it was found that the thin layer magnification image of enhanced CT could show the heterogeneous expansion and thickening of tumor vessels in cancer, which was called "heterogeneous vascular intensification sign" by Zhang Zhenfeng et al. and "CT tumor vascular imaging" by Sli Yanqing et al. This is called "heterogeneous vascular enhancement sign" by Zhang Zhenfeng et al. On the CT image, it appears as dotted or striped hyperintensities (enhancement value >60HU), radial vascular clusters, or disordered vascular network around the tumor body, whose width varies from that of normal vessels and is more rigid and different from the extension of normal vessels in the lesion. The former believes that the sign starts to be displayed 60s after contrast injection and is fully displayed around 2min, while the latter believes that it is displayed during the arterial phase (20-40s). The author believes that the reason for this difference may be related to the observer’s point of view and the different contrast flow rates. This sign is mostly seen in adenocarcinoma, followed by fine bronchoalveolar carcinoma, while other types of lung cancer and benign lesions are rare, with a high diagnostic specificity of 91.3% to 100%, but its sensitivity and its positive and negative predictive values still need to be tested in large samples. 3, pulmonary function tests and lung nodule analysis Computer-aided diagnosis is applied to automatically analyze and record the results of the first examination, and the growth rate and multiplication time of lung nodules can be automatically calculated when the examination is repeated, which provides an objective basis for judging the benignity and malignancy of nodules. The CT scan of the lung is performed at the end of deep inspiration and deep expiration respectively, and the lung function indexes can be measured quickly and accurately in the AW workstation, which is of great clinical significance for the evaluation of pulmonary ventilation function in patients with COPD.