Centricity 2

CT images were reconstructed using IMR (IMR-level 1; Philips Healthcare, Cleveland, Ohio, U.S.A.) in Group A and hybrid IR (iDose⁴-level 5) in Group B. The images were then transferred to a picture archiving and communication system (PACS; Centricity 2.0, GE Medical Systems, Mount Prospect, IL, U.S.A.). The reconstruction parameters were the following: 0.9-mm slice thickness, 0.45-mm increment, 512 × 512 pixel image matrix, XCC kernel, and a 15–23 cm field of view. Post-processing and reconstruction were performed for qualitative evaluation with multi-planar and curved-planar reformatted images, using commercially available software (Aquarius Workstation V3.6, TeraRecon, San Mateo, CA, U.S.A.).

CT scans were performed using one of two multi-detector scanners: a 16-slice (Somatom Sensation 16; Siemens Medical Solutions, Erlangen, Germany) or a 64-slice (Somatom Sensation 64; Siemens Medical Solutions, Erlangen, Germany) device. Scanning was performed during inspiration in patients assuming a supine position. The scanning range was from apex of lung to adrenal gland. After obtaining a scout image to determine the field of view, conventional CT scanning was performed in the mediastinal window setting using a 1–2.5-mm reconstruction interval. The scanning parameters were as follows: voltage, 120 kVp; current, 100–200 mA; slice thickness 1–2.5 mm. CT images were reconstructed using the scanner's workstation. All CT images were retrieved from a picture archiving and communication system (Centricity 2.0, GE Medical Systems, Mt Prospect, IL, USA).

All CT scans were performed with a 256-row multi-detector CT scanner (Revolution CT, General Electric, Boston, MA, US). Chest CT was performed using a helical technique and a mediastinal window setting with the following exposure parameters: Three tube voltages of 80, 100, and 120 kVp in combination with five tube currents of 25, 50, 100, 200, and 400 mA. The data were reconstructed with three slice thicknesses of 0.625, 1.25, and 2.5 mm; four different reconstruction algorithms of adaptive statistical iterative reconstruction (ASIR-V) of 30, 60, and 90% on the scanner workstation. Each of the variables was determined by dividing the parameters in the clinically available range into 3~5 sections. All CT images were transferred to the picture archiving and communication system (Centricity 2.0; GE Medical Systems) and CAD system for analysis.

CT scans were performed using one of three scanners: a 16-slice multidetector CT (MDCT) scanner (Somatom Sensation 16; Siemens Medical Solutions, Erlangen, Germany), a 64-slice MDCT scanner (Somatom Sensation 64; Siemens Medical Solutions), or a 128-slice MDCT scanner (Somatom Definition AS+; Siemens Medical Solutions). Scanning was performed in the supine position from the lung apices to the level of the adrenal glands during inspiration. After acquiring the scout image to determine the field of view, conventional CT scanning was performed without contrast enhancement using a helical technique, with a 3 mm or 5 mm reconstruction interval in the mediastinal window setting. The exposure parameters for the CT scans were as follows: 80–100 kVp, 50–130 mA, slice thickness, 1 mm or 5 mm, and a reconstruction increment of 3 mm or 5-mm. Image reconstruction for conventional CT scans was performed on the scanner’s workstation. All CT images were retrieved on an image archiving and communication system (Centricity 2.0; GE Medical Systems, Mt Prospect, IL, USA) and then analyzed using the mediastinal window settings (level, 50 HU; width, 400 HU).

Chest CT images were obtained with an 80- (LightSpeed Ultra; GE Healthcare, Mt. Prospect, IL, USA) or 16- (LightSpeed16; GE Healthcare) detector row CT scanner using the following parameters: detector collimation, 0.625 mm; field of view, 34.5 cm; beam pitch, 1.35 or 1.375; gantry speed, 0.6 s per rotation; 120 kVp; 150 to 200 mA; and section thickness, 1.25 mm for transverse images. Chest CT data were interfaced directly to a picture archiving and communication system (Path-Speed or Centricity 2.0; GE Healthcare) that displayed all of the image data on two monitors (1536 × 2048 matrix, 8-bit viewable grayscale, 60-foot-lambert luminescence). The monitors were adapted to view both mediastinal (width, 400 HU; level, 20 HU) and lung (width, 1500 HU; level, −700 HU) window images. A pure GGN was defined as a discrete pulmonary nodular abnormality with homogeneous attenuation that was not as high as that of the surrounding soft-tissue structures. A part-solid GGN was defined as a lesion containing both GGO and solid soft-tissue attenuation components. In all of the cases, the maximum diameter of the tumors (maxD) and the largest dimension perpendicular (perD) to maxD using both the lung and mediastinal windows were measured and the tumor disappearance rate and its quantification were calculated to assess tumor volume and the proportion of pure GGO (Supplementary Fig. S1)^{40 (link)}.