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ects both the fully
quantitative nature of the method and the improved visualisation of syndesmophytes
using CT. Exploiting the 3D imaging capability of CT, we were able to quantitate
syndesmophytes along the entire vertebral body rim. It has been suggested that
magnetic resonance imaging (MRI) could also be used to image the spine tomo-
graphically and with less exposure for patients. Several rating systems for structural
chronic damage inAShave been proposed [
63
The higher sensitivity to change of our computed volumes re
fl
66
]. However, few longitudinal studies
tracking syndesmophyte growth inMRI have been published [
67
]. In [
62
], it was found
that computed volumes in CTwere muchmore sensitive to change thanMRI readings.
Cortical bone is poorly visualised on MRI because its water content is similar to the
water content of surrounding tissues. Scoring systems based on MRI are semiquan-
titative, which also may limit their sensitivity to change. In addition, higher resolution
can be achieved in CT and long acquisition time for MRI causes motion artefacts.
A major criticism of the work has centered on the radiation exposure associated
with a CT scan. With the protocol used in the study, patients received an average
radiation dose of 8.01 mSv compared with 2.59 mSv for lateral radiographs of the
cervical and lumbar spine (as would be used in a complete mSASSS assessment)
[
56
,
62
]. However, the question of radiation exposure has to be considered in close
relation with the information obtained. Although the radiation exposure of CT is
substantially higher than the radiation exposure of radiographs, each CT scan
provides complete information on syndesmophytes, and, in our study, none needed
to be discarded because of poor visualisation. The advantages of low radiation
exposure need to be weighed by the usefulness of the information gathered by that
exposure. It should be stressed that scanner technology is improving fast and, with
the introduction of iterative reconstruction, dose reduction of 50 % or more has
been achieved with minimal loss in image quality [
68
,
69
]. The reliability of the
algorithm has to be evaluated using such dose saving methods.
Because the algorithm visualizes and quantitates syndesmophytes in their real
3D environment for the
-
first time, it opens the door to new research possibilities.
For instance, the distribution of the syndesmophytes around the rim of the vertebral
end plates, if not random, could shed some light on the drivers of osteoproliferation,
which are still unknown. The testing of drugs that can potentially halt or slow
syndesmophyte progression will bene
t from the greatly improved sensitivity and
reliability of the new method. Similarly, studies that seek to associate syndesmo-
phyte progression with gene expression, biomarkers and lifestyle risk factors (such
as smoking or lack of exercise for example) should use a method that can capture
syndesmophytes in their totality and quantitatively.
6 Conclusion
To improve the low sensitivity to change associated radiographic reading, we have
designed a quantitative measurement of syndesmophytes in CT scans. The method
has very good reliability. In a 2-year longitudinal study, the algorithm could detect
