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We describe a novel method of estimating reduced bone mineral density (BMD) from dental panoramic tomograms (DPTs), which show the entire mandible. Careful expert width measurement of the inferior mandibular cortex has been shown to be predictive of BMD in hip and spine osteopenia and osteoporosis. We have implemented a method of automatic measurement of the width by active shape model search, using as training data 132 DPTs of female subjects whose BMD has been established by dual-energy X-ray absorptiometry. We demonstrate that widths measured after fully automatic search are significantly correlated with BMD, and exhibit less variability than manual measurements made by different experts. The correlation is highest towards the lateral region of the mandible, in a position different from that previously employed for manual width measurement. An receiver-operator characterstic (ROC) analysis for identifying osteopenia (T < -1: BMD more than one standard deviation below that of young healthy females) gives an area under curve (AUC) value of 0.64. Using a minimal interaction to initiate active shape model (ASM) search, the measurement can be made at the optimum region of the mandible, resulting in an AUC value of 0.71. Using an independent test set, AUC for detection of osteoporosis (T < -2.5) is 0.81.

There is consensus to use the bone mineral density (BMD) for the operational definition of the degree of osteoporosis and the risk of osteoporotic fractures. Dual X-ray absorptiometry (DXA) is the common technique to determine BMD. Because of high costs and limited availability of DXA equipment it is worthwhile to look for alternative diagnostic techniques. As part of a larger study, the Osteodent project, we investigated if the trabecular pattern on dental radiographs can be used to predict BMD and to identify the subjects with osteoporosis and increased risk of osteoporotic fractures. In four clinical centers 671 women with an average age of 55 years were recruited. BMD values were measured by DXA equipment at the femoral neck, total hip, and spine. One panoramic and two intraoral radiographs were made. From 525 women a complete set of BMD values and radiographs was obtained. Four regions of interest on the radiographs were selected manually and then processed automatically. On all regions of interest mean and standard deviation of the gray values were measured and several features describing the shape of the binarized trabecular pattern. Multiple regression was used to predict BMD of total hip and spine by means of the radiographic measurements combined with age. It was found that age accounts for 10% of the variation in total hip BMD and 14% of the variation in spinal BMD. When all measurements on the dental radiographs are used the explained variation increases to 22% and 23%. The areas under the ROC curves are comparable to those of commonly used screening instruments for osteoporosis. It is concluded that prediction of DXA measurements of BMD by means of quantitative analysis of the trabecular pattern on dental radiographs is feasible.

The high precision and stable calibration of dual X-ray absorptiometry (DXA) scanners have led to their widespread use in longitudinal studies for research and the follow-up of individual patients who are receiving treatment for osteoporosis. However, difficulties in maintaining the continuity of the bone mineral density (BMD) calibration scale can arise when an old DXA system is replaced by a newer model. We report the results of an in vivo cross-calibration study performed when a GE-Lunar Prodigy fan-beam system replaced a DPX-L pencil-beam scanner. Lumbar spine and hip DXA scans were performed in 133 patients (104 female, 29 male) attending long-term BMD monitoring. On average, lumbar spine BMD measurements on the two systems agreed closely, with Prodigy values 1% lower than those on the DPX-L. However, after allowing for this difference, the root mean square error (RMSE) of 0.037 g/cm2 was larger than in previous cross-calibration studies reported in the literature, and was 3 times the value expected from the precision of the BMD measurements. Mean femoral neck BMD also agreed closely between the two systems, although for Prodigy, the spread of measurements was 10% smaller than that for the DPX-L. For the trochanter and Ward's triangle regions, mean BMD was 4% and 6% lower, respectively, on the Prodigy system, and the results were affected by a similar compression of the range of values. RMSE values were 0.037 g/cm2, 0.044 g/cm2, and 0.044 g/cm2, respectively, for the femoral neck, trochanter, and Ward's triangle sites. When the high value of the RMSE was investigated, it was found that for lumbar spine BMD, patient body weight and the difference between the two systems in the percentage fat reported in the soft tissue reference region explained 40% of the variance. This enabled equations to be developed that significantly improved the agreement between scans performed on the two systems. Smaller improvements were obtained for the femur BMD measurements.

The study assessed the precision, sensitivity, and specificity of a recently developed peripheral dual-energy X-ray absorptiometry (DXA) scanner, applied to the calcaneus, in the identification of individuals with osteoporosis at axial sites by DXA. Two hundred and two women, aged 55.2 +/- l3.7 years (mean +/- SD), participated in the study. The precisions (coefficient of variation) of measurements in vitro (0.48%) and in vivo (1.40%) were very good. The in vivo precision was independent of the operator, foot size, foot width, weight, height, and body mass index. Calcaneus BMD correlated moderately (r = 0.494-0.690, P <0.001) with axial BMD measurements by DXA. Using the World Health Organization (WHO) criterion for defining osteoporosis (T score ? -2.5) the specificity of the calcaneus to identify patients with osteoporosis at total hip, femoral neck, spine, or any of these axial sites was excellent (97.0%, 97.0%, 96.5%, and 97.1%, respectively); however, the sensitivity was poor (58.8%, 36.4%, 21.8%, and 20.3%, respectively). Therefore, the WHO criterion is not appropriate for DXA calcaneus. Based on femoral neck BMD for detection of osteoporosis, a more appropriate calcaneus T score threshold would be -1.4 by analyses of receiver-operator characteristic curves; this might serve to select those patients who might appropriately be referred for axial DXA.