To sample the posterior thorax, subjects were seated close to the gamma camera detector (Starcam 3200 AC/T GE Medical Systems, Little Chalfont, Buckinghamshire, UK) with an acquisition of 300 s with a matrix of 256 × 256 pixel. The scanner was repositioned to scan the anterior upper airway/face, followed by a scan of device components (nebulizer, humidifier chamber, tubing, cannula, mask, and filter) [21 (link)].
Both pulmonary and extrapulmonary regions of interest (ROI) were delimited using the Xeleris 3 Functional Imaging Workstation (GE Healthcare, Milwaukee, WI, USA). The radiation count of each compartment (lungs, upper respiratory tract, stomach, device, and filter) was determined for each ROI, with a mass balance expressed as a percentage of the sum of the counts (primary outcomes) [22 (link)]. Attenuation and tissue absorption correction factors for lungs, stomach, and oropharynx were applied as described by Lee [23 (link)]. Correction factors of 2.27 were specifically applied to the lung and stomach counts, and 2.37 for the upper airway, with no correction applied to device components and filters.
Both pulmonary and extrapulmonary regions of interest (ROI) were delimited using the Xeleris 3 Functional Imaging Workstation (GE Healthcare, Milwaukee, WI, USA). The radiation count of each compartment (lungs, upper respiratory tract, stomach, device, and filter) was determined for each ROI, with a mass balance expressed as a percentage of the sum of the counts (primary outcomes) [22 (link)]. Attenuation and tissue absorption correction factors for lungs, stomach, and oropharynx were applied as described by Lee [23 (link)]. Correction factors of 2.27 were specifically applied to the lung and stomach counts, and 2.37 for the upper airway, with no correction applied to device components and filters.