title: Response to Commentary on "The influence of lung airways branching structure and diffusion time on measurements and models of short-range 3He gas MR diffusion".
abstract: Our extensive investigation of the cylinder model theory through numerical modelling and purpose-designed experiments has demonstrated that it does produce inaccurate estimates of airway dimensions at all diffusion times currently used. This is due to a variety of effects: incomplete treatment of non-Gaussian effects, finite airway size, branching geometry, background susceptibility gradients and diffusion time dependence of the (3)He MR diffusion behaviour in acinar airways. The cylinder model is a good starting point for the development of a lung morphometry technique from (3)He diffusion MR but its limitations need to be understood and documented in the interest of reliable clinical interpretation.
authors.affiliation: Unit of Academic Radiology, University of Sheffield, United Kingdom. Electronic address: j.parra-robles@sheffield.ac.uk.
authors.forename: Juan
authors.initials: J
authors.lastname: Parra-Robles
authors.affiliation: Unit of Academic Radiology, University of Sheffield, United Kingdom.
authors.forename: Jim M
authors.initials: JM
authors.lastname: Wild
mesh_terms: D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006371:Helium; D006801:Humans; D008168:Lung / Q000033:anatomy & histology* / Q000378:metabolism*
chemical_list: D006371:Helium
keywords: (3)He Diffusion MR; Lung morphometry; model validation