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There are currently
more than 15 third-party DICOM viewers mainly for orthodontics, implantology,
and oral and maxillofacial surgery are available commercially. Although the
reliability, repeatability and accuracy of CBCT machines have been evaluated,
testing the reliability of CBCT-related software has not gone further as they
differ in terms of the statistical test used.

In this study, 2 commercially
available CBCT-software programs that use automatic segmentation to calculate
airway volumes were tested. From the t-test analysis, the p-value is equal to
0.914 for both quantity measured. This means that there is no significant
different between two software for the airway volume and minimum area. While
for ICC test, the intrarater value is more than 0.90 indicating excellent
agreement. According to 15, the ICC value of 0.50 to 0.74 was good and 0.75
and above is considered as excellent 15. So, the correlation values obtained
from this study indicate that they are reproducible. The results obtained are
supported by other studies 2, 3, 4 and 7. Reference 16 had use Romexis
software to measure the airway volume to find the correlation between 3D airway
and 2D. They found that the correlation value between area in 2D and volume in
3D are very high correlation 16. While for Invivo software, 10 had used
this software to measure pharyngeal airway volumes in healthy children with
retrognathic mandible and those with normal craniofacial growth.

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The measurement
from these two software differs slightly due to the fact that this 2 software
programs did not use the same methods for calculation of the airway volume and
the minimum area. In Invivo5, the segmentation of the airway base on the point
the user click on the airway space and the upper and lower level are follows
the shape of the airway. However, in Romexis, the segmentation was done base on
the region growing in a cube, thus the upper and lower level does not follow
the shape of the airway. This gives a slightly vary measurement for both
software. The Invivo5 software allows more control where the user can “sculpt
out” the desired airway volume from the rest of the 3D structures. User also
can adjust the brightness and opacity values, clean out the unwanted voxels
before calculating the final airway volume. The software also lets the user to
change the threshold values to obtain a solid airway volume. This also might be
the reason to why the measurement of volume using Invivo5 software is more
variable than Romexis software.

For automatic
segmentation, volume measurements should be done with proper technique and
diligence. This is because the measurement changes depend on the image threshold
chosen. This is proved by 2. The proper technique also important as different
position will significantly increase or decrease the measurement 11. A study
had proved that the CBCT-based 3D analysis gives a better picture of the
anatomical characteristics of the upper airways and therefore can lead to an
improvement of the diagnosis 4. The automatic segmentation of the airway
imaged using CBCT is feasible and this method can be used to evaluate airway
cross-section and volume comparable to measurements extracted using manual
segmentation 5. Reference
3 had suggested
that the three-dimensional CBCT digital measurements of the airway volume and
the most constricted area of the airway are reliable and accurate. The use of
CBCT imaging for the assessment of the airway can provide clinically useful
information in orthodontics and for assessing the airway after surgery. This is
proved by 17 where they conclude that the use of point-based analysis (from
3D CBCT) measures are better explained the changes in clinical symptoms
compared to conventional measures.

 The Bland & Altman plot are created to compare the two
measurements that each provides some errors in their measure. The plot also
allows the identification of any systematic difference between the measurements
or possible outliers. The dotted horizontal lines represent the 95% confidence
limits (limits of agreement). Thus, if the differences between methods were
distributed normally, 95% of the differences from the bias in the sample are
expected to be between upper and lower limit of agreement. As the confidence
limits are not exceeded, it can be concluded that the repeatability of the
method is acceptable and the
two methods are considered to be in agreement and may be used interchangeably.


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