2.1 |. PET imaging

At baseline (0 h) and 20 h, ¹³NN-saline PET scans were acquired for assessment of regional ventilation and perfusion, as previously described.^16–19 Briefly, each dynamic PET scan started during a breath-hold at mean airway pressure simultaneously with the central injection of a 30-40 mL of bolus of ¹³NN-saline solution (10 mL/s). After 60 s of apnea, mechanical ventilation was restarted. The total imaging sequence lasted 4 min, including 8 × 2.5 s, 4 × 10 s, 6 × 10 s, and 4 × 30 s images (frames). Each image consisted of 15 transverse slices of 6.5 mm thickness, 128 × 128×15 voxels of 2.0 × 2.0 × 6.5 mm each, covering a 9.7 cm-long field of view (~70% of the total sheep lung volume).¹⁹ The resulting effective resolution after spatial filtering was ~2.2 cm³.