Lightspeed 16

To make the lung volume consistent with MRI acquisition, a CT scan was also performed after 1 L of air was inhaled by each patient. The CT scan was done on a 16‐slice multi‐detector CT scanner (LightSpeed 16, GE Healthcare, Chicago, IL). Scanning parameters used included pitch 1.75: 1, in‐plane resolution = 1 × 1 mm², thickness = 5 mm. CT was acquired on the same day as MRI scans.

All CT scans were performed on a Lightspeed 16 or VCT (General Electric Healthcare, Milwaukee, WI, USA) with patients in the supine position, and the parameters for imaging tests were as follows: tube voltage = 100–120 kVp, matrix = 512 × 512, slice thickness = 1.00–1.25 mm, and FOV = 350 mm × 350 mm. The single collimation width of the reconstructed images was 0.50–1.25 mm, and the tube current was regulated through an automatic exposure modulation system.

The CT examinations were performed in clinical stability and no CT during acute exacerbation was evaluated. Most of the CT examinations were performed in our Radiology Department. CT examinations were obtained with a 64 row MDCT (Lightspeed VCT, GE Healthcare, Milwaukee, WI, USA) or a 16 row MDCT (Lightspeed 16, GE Healthcare, Milwaukee, WI, USA). All CT data were acquired volumetrically using a standard dose protocol with 120 kV and 100 mAs. CT data were reconstructed with a slice collimation of 1.25 mm and an interval of 1 mm. Intravenous contrast medium was used if it was required for the particular clinical situation. Thirty-seven CT examinations were performed externally in patients with PCD using differing protocols and a slice thickness varying from 1.25 mm to 5 mm. CT with insufficient quality due to a slice thickness >5mm or to severe motion artifacts were excluded.

Computed tomography scans were performed by using a 16-slice or 64-slice multidetector-row CT scanner (Lightspeed 16 or Lightspeed 64; GE Medical Systems Milwaukee, Wis). Images were reconstructed at slice thickness and interval ranging from 3 to 5 mm. Contrast enhanced CT was performed after the intravenous injection of iohexol (Omnipaque 300 or 350; Amersham, Shanghai, China) at an injection volume of 90 to 120 ml and an injection rate of 3 to 4 ml/s. As for the contrast enhanced CT, 7 patients underwent imaging both in the arterial phase and the portal venous phase; the other 11 patients underwent imaging only in the portal venous phase.

Abdominal adiposity was assessed using a 16-slice multidetector CT scanner (LightSpeed 16; GE Healthcare, Milwaukee, WI) in the supine position (120 kVp, 400 mAs, slice thickness of 5 mm). Image analysis software (ImageJ, version 1.44; National Institutes of Health, Bethesda, MD) was used to quantify the subcutaneous and visceral adipose fat areas, on one cross-sectional scan obtained at the level of umbilicus and expressed in millimeters squared. [11] (link) After applying threshold with an attenuation range of –50 to –250 Hounsfield units, a fat-density mask was generated. A total fat mask was created after manual exclusion of non-adipose area (such as the CT table, air-object interface or fecal material) from the fat-density mask (Figure 1). The visceral fat area was determined by cutting areas other than visceral fat, and the subcutaneous fat area was calculated with the total fat area subtracted by the visceral fat area. The visceral fat area was further divided into peritoneal and retroperitoneal areas along the boundary comprised of posterior surface of small bowel, ascending colon, descending colon, mesenteric vessels and gonadal veins (Figure 1). The interfascial plane could be visualized as a thin line in some participants and this could help outline of the boundary.