68 CLINICAL UTILITY OF RADIOGRAPHIC TEXTURE ANALYSIS PERFORMED ON DENSITOMETRIC CALCANEAL IMAGES. (2007)

<h3>Background</h3> Currently, the major challenge in osteoporosis research and clinical practice is to improve the assessment of fracture risk. Bone fragility is determined by bone quantity measured as bone mineral density (BMD) and by bone quality or structure that cannot be easily assessed using currently available methods. Radiographic texture analysis (RTA) is an image-based noninvasive method of evaluating bone structure through computerized analysis of trabecular pattern of bone radiographs. We have applied RTA to calcaneal images obtained using a portable densitometer. RTA yields the following features: RMS (root mean square variation, a measure of the variability in the radiographic texture pattern, the relative difference in the contrast between light and dark areas with higher values corresponding to the strong rich trabecular pattern), and its directional measure, sdRMS (standard deviation of RMS), which is a measure of anisotropy of the trabecular pattern, with higher values corresponding to the more directional texture pattern, and Minkowski fractal (MINK), a measure of roughness-smoothness of the trabecular pattern. In this study of patients referred for BMD testing at the University of Chicago, we examined (1) which biologic factors influence RTA and (2) how well RTA differentiates subjects with high and low bone fragility. <h3>Methods</h3> In 837 patients (age 19-95 years, 759 women), BMD was measured at the lumbar spine, proximal femur, and calcaneus; clinical risk factors were obtained using a questionnaire; and RTA was performed on densitometric heel images. Fragility was defined as the presence of vertebral fractures detected on VFA (vertebral fracture assessment - densitometric spine image). The association of RTA with biologic factors or with prevalent vertebral fractures was examined using regression analysis. <h3>Results</h3> (1) Relationship between RTA and biologic factors: In a multivariate regression analysis, significant predictors of sdRMS were BMI (<i>p</i> &lt; .001), gender (<i>p</i> &lt; .001), age (<i>p</i> = .001), race (<i>p</i> = .004), and heel BMD (<i>p</i> = .009). For MINK, the only significant predictors were BMI (<i>p</i> &lt; .001) and heel BMD (<i>p</i> &lt; .001). (2) Utility of RTA in assessing fragility was examined in a subset of 333 postmenopausal women who had no secondary causes of and were not receiving therapy for osteoporosis. In a univariate logistic regression analysis with the presence of prevalent vertebral fractures as a binary outcome, the separations between 49 women with and 284 without vertebral fractures using RTA and using BMD measurement were similar (<i>p</i> = .002 and <i>p</i> &lt; .001 for sdRMS and MINK, respectively; <i>p</i> = .01, <i>p</i> = .003, and <i>p</i> &lt; .001 for spine, heel, and hip BMD, respectively). In a multivariate logistic regression, there was a significant association of vertebral fractures with RTA, BMD, and age with odds ratio (OR) of having a vertebral fracture of 2.0 for each decade increase in age (<i>p</i> &lt; .001), OR = 1.8 for a 1-unit decrease in hip BMD T-score (<i>p</i> = .003), and OR = 1.7 for a 1 SD decrease in sdRMS (<i>p</i> = .003) or MINK (<i>p</i> = .008). <h3>Conclusion</h3> These results suggest that RTA of heel images obtained using a portable densitometer characterizes bone properties not measured by BMD. Specifically, RTA provides assessment of fragility that is not captured by the currently used measurements such as BMD and clinical risk factors (age). Addition of RTA to BMD and clinical risk factors can improve the stratification of fracture risk. Further studies are needed to determine whether RTA would be useful in selecting patients for different forms of osteoporosis therapy.