  Accurate spine segmentation allows for improved identification and
quantitative characterization of abnormalities of the vertebra, such as
vertebral fractures. However, in existing automated vertebra segmentation
methods on computed tomography (CT) images, leakage into nearby bones such as
ribs occurs due to the close proximity of these visibly intense structures in a
3D CT volume. To reduce this error, we propose the use of joint vertebra-rib
atlases to improve the segmentation of vertebrae via multi-atlas joint label
fusion. Segmentation was performed and evaluated on CTs containing 106 thoracic
and lumbar vertebrae from 10 pathological and traumatic spine patients on an
individual vertebra level basis. Vertebra atlases produced errors where the
segmentation leaked into the ribs. The use of joint vertebra-rib atlases
produced a statistically significant increase in the Dice coefficient from 92.5
$\pm$ 3.1% to 93.8 $\pm$ 2.1% for the left and right transverse processes and a
decrease in the mean and max surface distance from 0.75 $\pm$ 0.60mm and 8.63
$\pm$ 4.44mm to 0.30 $\pm$ 0.27mm and 3.65 $\pm$ 2.87mm, respectively.
