CALCULATION OF CROSS-SECTIONAL GEOMETRY OF BONE FROM CT IMAGES WITH APPLICATION IN POSTMENOPAUSAL WOMEN

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.