CT image acquisition
tumor, obstructive inflammation
PRIMARY TUMOR, TUMOR, CAVITY
For all patients, contrast-enhanced chest CT scans were conducted with a 256-multidetector CT scanner (Discovery CT 750 HD Revolution, GE Medical Systems, Milwaukee, Wisconsin, USA). Before scanning, the patients were trained to breathe and hold their breath at the end of inspiration to obtain the scans. The patients were placed in the supine position with both arms raised to reduce scanning artifacts. The locational marker was the sternoclavicular joint, and the range included the thoracic inlet to the lung bases. The scanning parameters were as follows: tube voltage 120 kV, tube current 200 mAs, reconstruction layer thickness 1.25 mm, matrix ​​512 × 512, and pitch 1.2. The reconstruction algorithm adopts the lung algorithm. After the plain scan was completed, 70–90 ml of nonionic contrast agent iohexol or ioversol (300 mg·I/ml) was injected via a bolus through the cubital vein with a high-pressure syringe at a flow rate of 3 ml/s. Arterial phase and venous phase dual-phase enhanced scans were performed 30 s and 90 s after the injection of the contrast agent, respectively. The other parameters were the same as those for the plain scans. After scanning, the raw data were uploaded to a postprocessing workstation for multiplanar reconstruction (MPR) [Image feature analysis was performed by two board-certified thoracic group radiologists (with 6 and 12 years of experience in chest CT imaging, respectively) who were blinded to the clinical and histological findings. The mediastinal window (window width 400 HU; window level 40 HU) and lung window (window width 1200 HU; window level − 600 HU) were set. The CT image features recorded in the image analysis were as follows: (1) primary tumor location (left and right lungs, upper, middle and lower lobes); (2) tumor size (maximum diameter), mean CT value (plain scan, venous phase), ΔCTV (the difference in the mean CT value of the venous phase and the mean CT value of the plain scan), and edge (lobular, blur); (3) internal features of the tumor: the presence or absence of cavities or vacuoles; and (4) external features of the tumor: the presence or absence of satellite lesions around the nodules. The mean CT values of the nodules on the plain scan and the venous scan were measured. The cavity and vacuole were defined as a gaseous density with a maximum diameter greater than 5 mm and less than 5 mm, respectively. The satellite lesions were defined as ≥ 1 miliary nodule surrounding each nodule (within 3.0 cm), apart from one miliary nodule distal to each nodule (possible obstructive inflammation). All CT image features were independently recorded by two radiologists, and any discrepancies in assessments were consistently resolved [