Table 1. Parameters for propagation-based phase-contrast X-ray imaging of small animals.

The field of view was typically 2000 pixels across. The pixel size used for imaging the trachea depends on whether the images aim to capture the whole width of the airway (e.g. to observe mucociliary clearance) or a single airway surface (e.g. to measure airway surface liquid depth).

Animal	Breathing rate (breaths min−1)	Imaging region	Exposure time (ms)	Energy (keV)	Propagation distance (m)	Pixel size (um)
Mouse	90–200	Nose	100	25	∼0.4	∼0.5
		Trachea	∼25	25	∼0.4	∼0.18–0.5
		Lungs	∼10 (<30)†	25	∼2–4	∼10
Rat	∼80	Trachea	∼50	25	∼0.4	∼0.36–1
		Lungs	∼20 (<50)	25	∼3–4	∼13–20
Pig	∼15	Trachea	∼100	55	∼4	∼7.6

^†When using X-ray sources that have less flux than a synchrotron, a ventilator can be configured to briefly slow the respiratory rate so that exposure times for lung imaging can be extended up to 200 ms (Gradl et al., 2018 ▸).