CT image acquisition
All scans were performed with the patient in the supine position during end-inspiration without intravenous contrast on two CT scanners, uCT 760 and uMI 780 scanners (United Imaging). The scanning range was from the apex to lung base. All images were obtained with a standard dose scanning protocol, reconstructed at 1.0 mm slice thickness, with 1 mm increment, 512 mm × 512 mm, and a sharp reconstruction kernel (B_VSHARP_B). Lung window setting was with a window level of − 600 Hounsfield units (HU) and window width of 1500 HU.