Figure 2
Image processing and analysis for sequential lung [18F]F-FDG SUR determination: The acquired X-ray and PET-CT image data sets were processed for flat and dark current normalization, reconstruction, co-registration (MI Labs software) and preliminary quantification by Pmod (pmod.com). As all the time-points, before and after O3 exposure, were acquired through the same imaging protocol, the [18F]F-FDG counts were decay corrected in order to plot tissue [18F]F-FDG uptake or elimination, and not decay, for the 30 min imaging time. Thereafter, the image sequences were quantified and analyzed on Image J (https://fiji.sc/#). The image stacks from X-ray CT were threshold-selected to segment out the lungs. The selected lung regions of interest (ROIs) were then copied on to the corresponding [18F]F-FDG PET image slices across multiple frames (F0–F4). The ROIs, from X-ray CT as well as the PET images, were simultaneously quantified for the various image parameters such as the area, perimeter, mean, median, mode, standard deviation (S.D.), range and integrated counts. After exporting the data to excel file (https://doi.org/10.6084/m9.figshare.12233576), data was sorted, filtered and analyzed for corresponding mouse time-points, frames and/or CT parameters. Finally, a SUM of the same full-body parameters of Z-stacks were analyzed for every frame in order to calculate the [18F]F-FDG SUV. After [18F]F-FDG SUV is quantified for lung slice(s) as well as the full-body, the ratio of these values, termed as the Standard Uptake Ratio (SUR), is computed. The lung CT grey values were plotted against “lung [18F]F-FDG SUR” or “lung [18F]F-FDG S.D.” which was overlaid for multiple frames on the same graph. These plots were then smoothened using the second polynomial function (Savistsky-Golay), in order to compute trends in final lung [18F]F-FDG SUR or S.D. and subsequently, % increase in lung [18F]F-FDG post-O3 exposure (https://doi.org/10.6084/m9.figshare.12233576).
