Dynamic multiscan CT during artificial respiration: Comparison of different density ranges in healthy lungs and in a lavage ARDS model.

Purpose: In this animal study, density ranges for CT-based quantification o f ventilated lung area were determined. Healthy lungs and ARDS lungs were c ompared during artificial respiration. Material and Methods: CT-scans were performed in 5 anesthetized pigs using a dynamic multiscan CT option on a p redefined transverse slice (slice thickness 1 mm; effective temporal resolu tion, 250 ms). During continuous CT acquisition, airway pressure was increa sed or decreased in a stepwise manner. In all images, areas of defined HU r anges were determined planimetrically. The lower threshold was set to -910 HE in all images. The upper threshold was varied from -800 HE to -200 HE in steps of 100 HE. Results: During inspiration in healthy lungs the HU-range of -910 to -700 HU showed the largest increase in area. During inspiration in ARDS lungs the HU range from -910 to -300 HU allowed the most sensitive assessment of area changes. These findings can be explained by recruitment of atelectases (HU-range >-300 HU) and their transition to a HU range from -700 to -300 HU. Conclusion: Dynamic multiscan CT acquisitions are a usefu l method to determine changes of ventilated lung area during a respiratory cycle. Different HU-ranges are required to access volume changes in healthy lungs and in ARDS lungs.