Representative CT sections of upper and lower lobes obtained at baseline and day 7 in a patient with acute respiratory distress syndrome. Computed tomography (CT) sections at baseline and day 7 are at the same lung region as attested by the anatomical landmarks present on the rough images at baseline and day 7 (aortic arch and vascular divisions for upper lobe CT sections and vascular divisions for the lower lobe CT sections). As previously described , poorly and nonaerated lung areas of right and left upper and lower lobes are manually delineated (dashed line) at baseline (before HL-10 administration) with the aid of the software Lungview) that identifies poorly and nonaerated lung areas in light gray and red, respectively. Delineation performed at baseline is manually 'transposed' to the CT section corresponding to the same anatomical level obtained at day 7. Surfactant-induced lung reaeration is defined as the increase in gas volume within the delineated zone between day 7 and baseline. The same process is repeated on each CT section in order to assess overall surfactant-induced lung reaeration.