1). selleckchem Ivacaftor The transfer rate constant k3 in this model characterizes 18F-FDG phosphorylation to 18F-FDG-6-phosphate (metabolic compartment), which is proportional to hexokinase activity and has been associated with cellular metabolic activity [16,29]. The 18F-FDG net uptake rate is computed as Ki = Fe �� k3, where Fe is the distribution volume of 18F-FDG as a fraction of lung volume [13,20,30].Figure 1Sokoloff model for 18F-fluorodeoxyglucose tracer kinetics [13]. The three compartments of the model describe the activity concentration of 18F-fluorodeoxyglucose (18F-FDG) in plasma (Cp(t)), the region of interest (ROI) concentration of extravascular …
To account for potential effects of lung inflation and blood volume on regional Ki, we also standardized Ki by lung tissue fraction, thus computing a specific Ki as follows: Kis = Ki/ftissue, where ftissue = (1 ? fgas ? fblood) and fblood is the fractional volume of the blood compartment obtained from the Sokoloff model. Kis is proportional to 18F-FDG uptake per gram of lung tissue. The Patlak two-compartment model [31] was used to compute 18F-FDG net uptake rate at the voxel level (KiP) to calculate the spatial heterogeneity of 18F-FDG uptake using the standard deviation (SD(KiP)) and to construct parametric images [20].Experimental protocolEach sheep was placed supine in the PET scanner with the caudal end of the field of view just superior to the dome of the diaphragm. Physiological data and transmission and 13NN emission scans were acquired both at the start and after 2 h of mechanical ventilation, and the 18F-FDG scan was performed at the end of the study.
After the initial set of scans, all sheep received a continuous infusion of endotoxin (Escherichia coli O55:B5, 10 ng/kg/min intravenously; List Biological Laboratories Inc, Campbell, CA, USA).Histological analysisLungs were excised at the end of the experiment and fixed with Trump’s fixative (BBC Biochemical, Mt Vernon, WA, USA) at a pressure of 25 cmH2O. Blocks of lung tissue were sampled from ventral and dorsal regions and embedded in paraffin. Sections of 5-��m thickness were cut, mounted and stained with hematoxylin and eosin for light microscopy. Lung neutrophil counts and semiquantitative ALI scores [32] were assessed in 40 randomly selected high-power (��400 magnification) fields per animal (10 per region, 2 regions per lung) by two investigators (NP and MT) who were blinded to the group assignment. This procedure included two steps. First, a JPEG picture was obtained for each field Brefeldin_A and analyzed using dedicated software (Image-Pro Plus version 6.0; MediaCybernetics, Rockville, MD, USA). Each neutrophil was tallied and marked independently by investigators, and an overlay image was created.