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Fig. 5 Automatic detection,
identi cation, and
segmentation of the vertebrae
in routine thoracic and
abdominal MDCT images.
Note the automatically
detected osteoporotic
vertebral fracture of L1
vertebrae are not analyzed, since inclusion of the endplate will cause overestimation
of BMD.
DXA is the most common technique to measure BMD [ 45 ]. It is usually per-
formed at the forearm, spine, and hip (Fig. 6 ). BMD is measured as areal value in
g/cm 2 calcium hydroxyapatite. Compared with alternative bone densitometry
techniques, DXA-based BMD results of the spine and hip are the only ones which
can be interpreted using the WHO T-score de
nition of osteoporosis. The T-score is
calculated by comparing the measured BMD value of the subject with the mean
BMD value of a reference population consisting of healthy young adult women:
measured BMD subject mean BMD reference population
standard deviation BMD reference population
T-score
ΒΌ
Subjects with T-scores between
2.5 and
1.0 are classi
ed as osteopenic and
βˆ’
βˆ’
those with T-scores <
2.5 as osteoporotic [ 10 ]. The Z-score expresses the com-
parison of the measured BMD value of the subject with the mean BMD value of an
age-matched reference population:
βˆ’
 
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