Creation of an idealized nasopharynx geometry for accurate computational fluid dynamics simulations of nasal airflow in patient‐specific models lacking the nasopharynx anatomy

• Published in: International journal for numerical methods in biomedical engineering 2017-05, Vol.33 (5), p.n/a
• Main Authors: A.T. Borojeni, Azadeh, Frank‐Ito, Dennis O., Kimbell, Julia S., Rhee, John S., Garcia, Guilherme J.M.
• Format: Article
• Language: English
• Subjects: Air flow; Airway management; Anatomy; Boundary conditions; Computational fluid dynamics; computational fluid dynamics (CFD); Computed tomography; Computer applications; Computer Simulation; Cross-sections; Exposure; Fluid dynamics; Geometry; Humans; Hydrodynamics; idealized nasopharynx; Medical imaging; nasal airway obstruction; Nasal Cavity - anatomy & histology; Nasal Cavity - physiology; Nasal Cavity - surgery; Nasal Obstruction - physiopathology; Nasal Obstruction - surgery; nasal resistance; nasal surgery; Nasopharynx; Nasopharynx - anatomy & histology; Nasopharynx - physiology; Nasopharynx - surgery; Nose; Nose - anatomy & histology; Nose - physiology; Nose - surgery; patient‐specific numerical simulation; Radiation effects; Respiration; Respiratory tract; Simulation; Sinusitis; Surgical outcomes
• ISSN: 2040-7939; 2040-7947
• DOI: 10.1002/cnm.2825

Virtual surgery planning based on computational fluid dynamics (CFD) simulations has the potential to improve surgical outcomes for nasal airway obstruction patients, but the benefits of virtual surgery planning must outweigh the risks of radiation exposure. Cone beam computed tomography (CT) scans represent an attractive imaging modality for virtual surgery planning due to lower costs and lower radiation exposures compared with conventional CT scans. However, to minimize the radiation exposure, the cone beam CT sinusitis protocol sometimes images only the nasal cavity, excluding the nasopharynx. The goal of this study was to develop an idealized nasopharynx geometry for accurate representation of outlet boundary conditions when the nasopharynx geometry is unavailable. Anatomically accurate models of the nasopharynx created from 30 CT scans were intersected with planes rotated at different angles to obtain an average geometry. Cross sections of the idealized nasopharynx were approximated as ellipses with cross‐sectional areas and aspect ratios equal to the average in the actual patient‐specific models. CFD simulations were performed to investigate whether nasal airflow patterns were affected when the CT‐based nasopharynx was replaced by the idealized nasopharynx in 10 nasal airway obstruction patients. Despite the simple form of the idealized geometry, all biophysical variables (nasal resistance, airflow rate, and heat fluxes) were very similar in the idealized vs patient‐specific models. The results confirmed the expectation that the nasopharynx geometry has a minimal effect in the nasal airflow patterns during inspiration. The idealized nasopharynx geometry will be useful in future CFD studies of nasal airflow based on medical images that exclude the nasopharynx. An idealized nasopharynx geometry was developed for accurate representation of outlet boundary conditions in nasal airflow simulations when the nasopharynx anatomy is not available. We demonstrated that the nasopharynx geometry has a negligible effect on nasal airflow patterns during inspiration, which means that the anatomically accurate nasopharynx can be replaced by an idealized geometry without significantly affecting airflow estimates in the main nasal cavity.