Application of Magnetic Resonance (MR) Imaging for the Development and Validation of Computational Fluid Dynamic (CFD) Models of the Rat Respiratory System

Computational fluid dynamic (CFD) models of the respiratory system provide a quantitative, biological basis for extrapolating the localized dosimetry of inhaled materials and improving human health risk assessments based upon inhalation studies conducted in animals. Nevertheless, model development and validation have historically been tedious and time-consuming tasks that have traditionally limited CFD's wider utilization for inhalation research. In recognition of this we previously reported on the use of proton (1H) Magnetic Resonance (MR) imaging for visualizing nasal-sinus passages in the rat, and on the use of three-dimensional (3D) image data for speeding computational mesh generation. Here, detailed 3D 1H MR imaging of pulmonary casts is reported, mesh generation is described in more detail, simulated gas-flows in nasal-sinus airways are presented, and the feasibility of validating CFD predictions with MR is tested by imaging the dynamics of hyperpolarized 3He at physiological flow rates in a straight pipe with a diameter comparable to the rat trachea. Results show that measured laminar flow structure is significantly blurred by rapid 3He diffusion but that the degree of blurring is generally predictable from the diffusion equation. Findings therefore support the notion that MR imaging is not only useful for defining airway architecture but also rapid CFD validation, and in this context, progress towards applications involving live animals and airway models is described