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(a) Side view of a CT-based airway model. The rm is the radius of the mouthpiece. (b) The left to right lung (L/R) particle ratio as a function of the particle normalized release location at the mouth piece in (a) (the shaded area). rc=(ri+ro)/2. He, helium; He23, helium with a ventilation ratio of 2:3; He-O2, helium-oxygen; Xe-O2, xenon-oxygen mixture. 68
