Because of the observational study design, the degree of inspiration during CT could not be controlled: www.selleckchem.com/products/chir-99021-ct99021-hcl.html Reference spontaneous patients were asked to hold their breath after inspiration (without checking for compliance) during CT. Reference ventilated and ALI patients were scanned during uninterrupted mechanical ventilation, which is current clinical practice in our institution. Calibration of the CT scanners was performed using air and the manufacturer’s standard phantom.Quantitative CT analysisThe lung parenchyma was segmented manually in CT images covering the entire lungs (Osiris software; University Hospital Geneva, Geneva, Switzerland) . Window levels and widths appropriate for the lung parenchyma (-500/1,500 HU) or the mediastinum (50/250 HU) were used.
Major hilar vessels and bronchi, pneumothoraces, pleural fluids and gross motion artefacts were manually excluded. Only in aerated lung regions did we use a threshold (-350 HU)-based segmentation technique in an attempt to guide and standardize the manual exclusion of partial volume effects close to the thoracic wall, mediastinum, heart or diaphragm. To do so, window level and width were set to (-350/0 HU), and the segmentation line was drawn at the black-white interface [32-34]. Opacified lung regions were segmented manually using anatomical landmarks.The total lung volume (Vlung), the total lung mass (Mlung) and the masses of differently aerated lung compartments were calculated voxel-by-voxel using customized software as previously described [9,10,12,25,35].
Mlung and Vlung values were calculated on the basis of all lung voxels within the -1,000 to +100 HU range. The following HU ranges were used to separate differently aerated lung compartments: nonaerated, -100 to +100 HU; poorly aerated, -101 to -500 HU; normally aerated, -501 to -900 HU; and hyperaerated, -901 to -1,000 HU. The masses of differently aerated lung compartments were calculated as percentages of Mlung. Although it was calculated, we omitted between-group comparison of the hyperaerated compartment because two different CT scanners and image reconstruction protocols were used, and such comparison was not required for the present study .The validity of our analytical method was reviewed in 27 patients by placing a water-filled plastic bottle next to the thorax. We then selected an arbitrary region of interest (ROI) within this bottle in the CT image and compared the weight resulting from our voxel-by-voxel analysis method with that obtained by simply multiplying the volume of interest (ROI area �� slice thickness) by the volumetric mass density of water (approximately 997.77 kg/m3 at Brefeldin_A 22��C).Statistical analysisData are given as medians with interquartile ranges unless specified otherwise.