Phase-contrast MRI and CFD modeling of apparent 3He gas flow in rat pulmonary airways

Abstract

Phase-contrast (PC) magnetic resonance imaging (MRI) with hyperpolarized 3He is potentially useful for developing and testing patient-specific models of pulmonary airflow. One challenge, however, is that PC-MRI provides apparent values of local 3He velocity that not only depend on actual airflow but also on gas diffusion. This not only blurs laminar flow patterns in narrow airways but also introduces anomalous airflow structure that reflects gas-wall interactions. Here, both effects are predicted in a live rat using computational fluid dynamics (CFD), and for the first time, simulated patterns of apparent 3He gas velocity are compared with in-vivo PC-MRI. Results show 1) that correlations (R2) between measured and simulated airflow patterns increase from 0.23 to 0.79 simply by accounting for apparent 3He transport, and 2) that remaining differences are mainly due to uncertain airway segmentation and partial volume effects stemming from relatively coarse MRI resolution. Higher-fidelity testing of pulmonary airflow predictions should therefore be possible with future imaging improvements.

Airflow and Particle Deposition Simulations in Health and Emphysema: From In Vivo to In Silico Animal Experiments

“…Airflow 17,18,32 and particle deposition 13,25,35 in the lung were shown to be highly dependent on geometry and flow asymmetry 8 . Boundary conditions that describe the upstream and downstream mechanics outside of the 3D domain must be defined on the inlets and outlets for all CFD simulations.…”

“…Traditionally, constant pressure 17 or flow rate 11,26 boundary conditions have been applied at the mouth or trachea. Constant pressure 17,26,46 or flow rate 11,32 boundary conditions are typically implemented at the distal airway outlets. However, as the flow patterns change in time, CFD simulations should model the breathing unsteadiness, to determine airflow 30 and particle 13 deposition patterns in the lung.…”

“…Despite their extensive use in toxicology 52 and therapeutic studies 1 relatively few studies have simulated airflow 32 and particle deposition in the rat lung. In a recent study, CFD and MRI steady flow measurements agreed well in the conducting airways.…”

In vivo measurement of gas flow in human airways with hyperpolarized gas MRI and compressed sensing

“…To date, airflow measurement with PCV MRI has been performed in human airways with 3 He in a single axial slice of the trachea using a radial sequence (10). More recently, Minard et al (11) measured velocity fields in rat pulmonary airways with a 3D radial sequence, HP 3 He and an acquisition time of 14 min. Similar to 3 He, HP 129 Xe can also be used as a tracer gas for lung MRI (12) and PCV-MRI in vitro (13) and in vivo (14).…”

Molecular Binding Contributes to Concentration Dependent Acrolein Deposition in Rat Upper Airways: CFD and Molecular Dynamics Analyses

“…The influences of tidal breathing [30,31,32], dynamic airways [33,34,35,36], polydisperse aerosols [37,38], hygroscopic growth [39,40,41], electric charges [42,43], and intersubjective variability [44,45,46] on acrolein deposition are also important and should be considered in future studies. Imaging techniques such as phase-contrast MRI (magnetic resonance imaging) with hyperpolarized 3 He can be used to visualize respiratory flows [47,48]. It is acknowledged that MD and CFD simulations were conducted separately, without coupling, in this study, as two distinct methods for understanding the experimentally observed concentration-dependent acrolein deposition in rats.…”