Image quality assessment of chest CT scans used in Functional Respiratory Imaging

Aim: To study the impact of the CT scan protocol for Functional Respiratory Imaging (as developed by Fluidda, Belgium) and, where possible, suggest a scan protocol that provides consistent results over different scanners. Methods: In a first step, 76 CT scans have been realized of Kyoto Kagaku's Lungman, all with different exposure and/or reconstruction settings on two CT scanners. In a second step, all scans were processed to collect pulmonary blood vessel volume using the blood segmentation algorithm of the software platform of Fluidda (Kontich, Belgium). The relative fraction of the blood vessel volume from vessels smaller than 5 mm2 in cross-sectional area (BV5) were compared among the scans, and the variability was calculated. Results: In general, tube current and tube voltage have only a very small influence on BV5. The reconstruction method on the other hand affects the results significantly. The differences between minimal and maximal value per acquisition procedure reach up to 11 % for the proportional BV5 values. The results for the reconstruction methods that make the images smoother than suggested deviate from the other reconstructions. Conclusion: The impact of scan parameters on quantitative data should be verified with a sufficiently dense sample of scan protocols to ensure consistent data. Anthropomorphic phantoms should be developed with gold standard parameters (such as total blood vessel volume) and include all structures of interest. When smooth reconstructions are avoided, consistent data between scanners and acquisition methods can be obtained for the Lungman phantom.