Reconstruction of the Human Airways - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 64

3.4.3 Oral Cavity

It is rare to find existing scans that have the oral cavity opened. Typically a patient
undergoing a scan for other medical purposes has their mouth closed and therefore
this region is not shown in the scans. In addition the shape of the oral cavity during
breathing can differ during inhalation, exhalation, high exertion activities such as
running, or smoking. An alternative is to obtain an imprint such as those made from
the dentists that provide a physical model. This model can then undergo reverse-
engineering techniques by scanning the model and importing the data into a CAD
software for clean up and to create a volume by closing the model. As an alternative
method, the following example will make use of existing data found in the literature.
2D cross-sections of the oral cavity at 0.3 cm intervals are shown in Fig. 3.14 .

Fig. 3.14 Coronal sections of the oral cavity at 0.3 cm intervals extending from the lips to the
oropharynx. The distance from the oral entrance (denoted as the origin) is given under each cross-
section. This data is taken from Cheng et al. (1997)

The figure is taken from the work of Cheng et al. (1997) which also provide
perimeters and cross-sectional areas of each coronal cross-section. Using CAD or any
specialised 3D-graphic design software, the outline from each cross-section is laid
out in 3D space separated by 0.3 cm intervals. The outline of each slice then needs to
be stitched together to form a surface shell, or to apply 3D volume-rendering methods.
The accuracy of this technique is heavily reliant on the interpolating function that is
used to stitch the outlines together. Furthermore a smaller interval distance between
each cross-section would improve the accuracy of the model greatly.
Figure 3.15 shows some the process used in this reconstruction technique.