A deformable template method for describing and averaging the anatomical variation of the human nasal cavity

Abstract

BackgroundUnderstanding airflow through human airways is of importance in drug delivery and development of assisted breathing methods. In this work, we focus on development of a new method to obtain an averaged upper airway geometry from computed tomography (CT) scans of many individuals. This geometry can be used for air flow simulation. We examine the geometry resulting from a data set consisting of 26 airway scans. The methods used to achieve this include nasal cavity segmentation and a deformable template matching procedure.MethodsThe method uses CT scans of the nasal cavity of individuals to obtain a segmented mesh, and coronal cross-sections of this segmented mesh are taken. The cross-sections are processed to extract the nasal cavity, and then thinned (‘skeletonized’) representations of the airways are computed. A reference template is then deformed such that it lies on this thinned representation. The average of these deformations is used to obtain the average geometry. Our procedure tolerates a wider variety of nasal cavity geometries than earlier methods.ResultsTo assess the averaging method, key landmark points on each of the input scans as well as the output average geometry are located and compared with one another, showing good agreement. In addition, the cross-sectional area (CSA) profile of the nasal cavities of the input scans and average geometry are also computed, showing that the CSA of the average model falls within the variation of the population.ConclusionsThe use of a deformable template method for aligning and averaging the nasal cavity provides an improved, detailed geometry that is unavailable without using deformation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12880-016-0154-8) contains supplementary material, which is available to authorized users.

Rapid maxillary expansion effects of nasal airway in children with cleft lip and palate using computational fluid dynamics

“…Nasal septum deviation was measured by calculating the differences between the right and left nasal chamber width in coronal and axial sections at the level of maximal septum deviation . Nasal cross‐sectional areas (CSAs) were measured at the anterior and posterior regions of the nasal airway. Anterior CSA 1 was defined as lying in the frontal plane through the ANS; posterior CSA 2 was defined as lying in the frontal plane through 15 mm posterior to the ANS.…”

Strategies for Segmenting the Upper Airway in Cone-Beam Computed Tomography (CBCT) Data

“…A representative airway tem-plate is needed for this method. A population average or mean representative geometry, such as that of [27], may be used as a shape template to match to the airway image being segmented.…”

“…The nasal passages are narrow (often comparable to pixel size) and intricate and the adjacent paranasal sinuses are particularly susceptible to over-or under-segmentation, when the segmentation result is too fine or too coarse respectively, when using global thresholding. This often results in nasal passages and sinuses being merged and requires laborious and tedious manual slice-by-slice editing to obtain anatomically accurate airway segmentation [27]. Under-segmentation is preferred as it simplifies manual editing in post-processing.…”

“…To make the models, or CFD meshes, shape data for both patient-specific and population-averaged airways are needed. Population-averaged airways have been generated by superimposing aligned individual patient-specific airway geometries [25], by averaging images of the airways slice-by-slice [26], by using used thin-plate spline deformations [27], or by applying a Fourier descriptor method to decompose airway shapes into morphological feature descriptors which can be averaged [12] [28]. Whichever method is followed, to generate airways representative of the population requires the segmentation of large numbers of scans, which is time consuming if done manually.…”

Nasal Internal and External Aerodynamics for Healthy and Blocked Cavities

“…Flow visualisation based on the Schlieren method indicated the possible existence of a universal angle of the external air stream,where this method of flow visualisation can be used on patients. However, more statistical studies on the variation in the population is required where methods as of statistically averaging CT scans can be of use31 . Such statistical studies will advance the TRL of this approach beyond the fundamentals of this study and should be able to provide clinical instructions of the flow visualizations similar to what was performed in the lab and illustrated inFig 17a.…”