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Cubic specimens (N equals 26, 12 mm multiplied by 12 mm multiplied by 12 mm) of human vertebrae were cut along three orthogonal anatomical orientations, i.e. superior-inferior (SI), medial-lateral (MI) and anterior-posterior (AP). Contact radiographs of the bone cubes along these orientations were obtained and digitized using a laser scanner with a pixel size of 50 mm. A standardized digital image processing procedure was designed to assess trabecular bone structure. Global gray level thresholding and local thresholding algorithms were used to extract the trabecular bone network. Apparent trabecular bone fraction (ABV/TV), apparent trabecular thickness (I.Th), mean intercept separation (I.Sp), and number of nodes (N.Nd) were measured from the extracted trabecular network. Box counting based fractal dimension (Fr.D) of the trabecular bone pattern was also measured. Quantitative computed tomography (QCT) was then used to obtain bone mineral density (BMD). The specimens were further tested in compression along the same orthogonal orientations, and the corresponding Young's modulus (YM) were calculated. Paired t-test showed that the mean value of texture parameters (except ABV/TV) and YM along the SI orientation were significantly different (p less than 0.05) from those along the ML and AP orientations. In comparison, the mean values along ML and AP orientations were not significantly different. Correlation coefficients from linear regression and non-parametric correlation between YM, BMD and texture parameters showed a wide range, but they differed depending on the orthogonal plane of radiographic projection and the direction of biomechanical testing. In conclusion, trabecular texture parameters correlated significantly with BMD and YM. Trabecular texture parameters reflect the anisotropy or trabecular structure.
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