Image acquisition
CT scans of the chest were acquired on 16- to 64-multidector CT scanners (Philips Brilliant 16, Philips Healthcare; GE LightSpeed 16, GE Healthcare; GE VCT LightSpeed 64, GE Healthcare; Somatom Sensation 64, Siemens Healthcare; Somatom AS, Siemens Healthcare; Somatom Spirit, Siemens Healthcare; GE Optima 680, GE Healthcare). The CT parameters were as follows: 120 kVp, current intelligent control (auto mA) of 30–300 mA, and slice thickness reconstructions of 0.6–3.0 mm. All CT examinations were performed without intravenous contrast material.