Ta. Corcoran et al., CALCULATION OF CROSS-SECTIONAL GEOMETRY OF BONE FROM CT IMAGES WITH APPLICATION IN POSTMENOPAUSAL WOMEN, Journal of computer assisted tomography, 18(4), 1994, pp. 626-633
Objective: The objectives of this study were to develop a software pro
gram that calculates bone cross-sectional area (CSA) and moments of in
ertia from digital images, test the computations for accuracy, and imp
lement the software in a study of longitudinal changes in bone propert
ies in a large group of postmenopausal women. Materials and Methods: A
program called SLICE was adapted to use computed tomography (CT) bone
images as input. The main outcome variables of the resulting program,
SLICE_CT, were bone CSA, areal moments of inertia, and mass-weighted
moments of inertia. SLICE_CT was tested for accuracy using representat
ive arrays of CT numbers that approximate cross-sections of cortical b
one. Then the technique was applied to images from a 3 year longitudin
al study of the radius in 86 postmenopausal women who underwent quanti
tative CT of the dominant radius at 30% the distance from the wrist to
the elbow. The mean age of the subjects at entry into the study was 5
7 years. Images at baseline and at 3 years were analyzed, and the null
hypothesis of no change in cross-sectional geometry was tested by a p
aired difference two-tailed t test. Results: The error of SLICE_CT was
<1% with proper segmentation, using half-maximal height as the thresh
old. In the longitudinal study of postmenopausal women, the mean chang
e of CSA of the radius was - 1.4% (SD = 3.0%; p < 0.001). However, the
re was a compensatory 2.4% increase in the cross-sectional second pola
r moment of inertia (SD = 3.7%; p < 0.001). Conclusion: SLICE_CT is an
accurate method with which to determine cross-sectional geometry of d
igital images and can be used to detect changes in cross-sectional geo
metry of the radius with age in postmenopausal women. The results indi
cate that the radius remodels to compensate for bone loss and decreasi
ng material properties of bone associated with aging.