Date of Award

1-1997

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Medical Physics

Supervisor

C.E. Webber

Abstract

Loss of bone mass has long been recognized as a major factor which makes bones brittle and susceptible to fracture. Currently bone mass is measured using a dual energy photon transmission technique, and a fracture risk is derived from comparison with reference normal values. Although the risk of fracture increases as bone mass decreases, variations in trabecular bone architecture can also affect strength. Consequently, trabecular bone architecture is often cited as a factor which might contribute significantly to fracture risk. Currently, estimates of trabecular bone structure are derived from biopsy studies. Such studies are invasive, destructive, cannot be used routinely in patients ar volunteers, and certainly cannot be repeated at the same site to obtain longitudinal measurements. If routine clinical assessments of architecture are to be made, it is necessary to determine which imaging modality best reveals structure in a non-invasive manner. It is also necessary to determine how the competence of the structure can best be expressed quantitatively. This work has examined ways of assessing trabecular bone structure at the distal radius in-vivo to better understand the contribution of architecture to fracture risk. To this end, it proceeded on four major fronts. First, images of sufficient resolution were acquired using a commercial pQCT scanner and a clinical MR imager. Second, the image processing software necessary to segment the imaged trabecular structure was developed. Third, two indices were proposed to quantify the connectivity of the segmented structure. One index was derived from the application of trabecular strut analysis to a skeletonized representation of the bone network. The other quantified the marrow space by deriving a mean hole area and maximum hole area of the bone structure as it appears in two dimensions. The clinical value of these indices was tested by conducting pilot studies which examined the ability of the indices to discriminate a small group of Colles fracture patients from the normal population and to reflect normal age related changes in structure. The proposed structural parameters better discriminated Colles' fracture patients than did measures of bone mineral density. The fourth and last stage of this work examined the proportion of the variance in compressive strength of a group of radius bones that can be accounted for by bone mineral density and bone architecture. In seeking the features that were the most reliable indicators of bone strength, a combination of the mean hole area and maximum hole area had the highest correlation with peak load at fracture. This held true whether these two variables were derived from pQCT or MR images. Therefore, these structural indices may represent a potentially exciting and promising means of discriminating fracture outcomes and monitoring changes in trabecular bone structure.

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