Osteoporosis management: translating research into optimal fracture protection II

Automated cortical bone segmentation for multirow-detector CT imaging with validation and application to human studies

PURPOSE

Cortical bone supports and protects human skeletal functions and plays an important role in determining bone strength and fracture risk. Cortical bone segmentation at a peripheral site using multirow-detector CT (MD-CT) imaging is useful for in vivo assessment of bone strength and fracture risk. Major challenges for the task emerge from limited spatial resolution, low signal-to-noise ratio, presence of cortical pores, and structural complexity over the transition between trabecular and cortical bones. An automated algorithm for cortical bone segmentation at the distal tibia from in vivo MD-CT imaging is presented and its performance and application are examined.

METHODS

The algorithm is completed in two major steps-(1) bone filling, alignment, and region-of-interest computation and (2) segmentation of cortical bone. After the first step, the following sequence of tasks is performed to accomplish cortical bone segmentation-(1) detection of marrow space and possible pores, (2) computation of cortical bone thickness, detection of recession points, and confirmation and filling of true pores, and (3) detection of endosteal boundary and delineation of cortical bone. Effective generalizations of several digital topologic and geometric techniques are introduced and a fully automated algorithm is presented for cortical bone segmentation.

RESULTS

An accuracy of 95.1% in terms of volume of agreement with manual outlining of cortical bone was observed in human MD-CT scans, while an accuracy of 88.5% was achieved when compared with manual outlining on postregistered high resolution micro-CT imaging. An intraclass correlation coefficient of 0.98 was obtained in cadaveric repeat scans. A pilot study was conducted to describe gender differences in cortical bone properties. This study involved 51 female and 46 male participants (age: 19-20 yr) from the Iowa Bone Development Study. Results from this pilot study suggest that, on average after adjustment for height and weight differences, males have thicker cortex (mean difference 0.33 mm and effect size 0.92 at the anterior region) with lower bone mineral density (mean difference -28.73 mg/cm(3) and effect size 1.35 at the posterior region) as compared to females.

CONCLUSIONS

The algorithm presented is suitable for fully automated segmentation of cortical bone in MD-CT imaging of the distal tibia with high accuracy and reproducibility. Analysis of data from a pilot study demonstrated that the cortical bone indices allow quantification of gender differences in cortical bone from MD-CT imaging. Application to larger population groups, including those with compromised bone, is needed.

A New Algorithm for Cortical Bone Segmentation with Its Validation and Applications to In Vivo Imaging

Cortical bone supports and protects our skeletal functions and it plays an important in determining bone strength and fracture risks. Cortical bone segmentation is needed for quantitative analyses and the task is nontrivial for in vivo multi-row detector CT (MD-CT) imaging due to limited resolution and partial volume effects. An automated cortical bone segmentation algorithm for in vivo MD-CT imaging of distal tibia is presented. It utilizes larger contextual and topologic information of the bone using a modified fuzzy distance transform and connectivity analyses. An accuracy of 95.1% in terms of volume of agreement with true segmentations and a repeat MD-CT scan intra-class correlation of 98.2% were observed in a cadaveric study. An in vivo study involving 45 age-similar and height-matched pairs of male and female volunteers has shown that, on an average, male subjects have 16.3% thicker cortex and 4.7% increased porosity as compared to females.

Intra and interobserver reliability and agreement of semiquantitative vertebral fracture assessment on chest computed tomography

Objectives

To evaluate the reliability of semiquantitative Vertebral Fracture Assessment (VFA) on chest Computed Tomography (CT).

Methods

Four observers performed VFA twice upon sagittal reconstructions of 50 routine clinical chest CTs. Intra- and interobserver agreement (absolute agreement or 95% Limits of Agreement) and reliability (Cohen's kappa or intraclass correlation coefficient(ICC)) were calculated for the visual VFA measures (fracture present, worst fracture grade, cumulative fracture grade on patient level) and for percentage height loss of each fractured vertebra compared to the adjacent vertebrae.

Results

Observers classified 24–38% patients as having at least one vertebral fracture, giving rise to kappa's of 0.73–0.84 (intraobserver) and 0.56–0.81 (interobserver). For worst fracture grade we found good intraobserver (76–88%) and interobserver (74–88%) agreement, and excellent reliability with square-weighted kappa's of 0.84–0.90 (intraobserver) and 0.84–0.94 (interobserver). For cumulative fracture grade the 95% Limits of Agreement were maximally ±1,99 (intraobserver) and ±2,69 (interobserver) and the reliability (ICC) varied from 0.84–0.94 (intraobserver) and 0.74–0.94 (interobserver). For percentage height-loss on a vertebral level the 95% Limits of Agreement were maximally ±11,75% (intraobserver) and ±12,53% (interobserver). The ICC was 0.59–0.90 (intraobserver) and 0.53–0–82 (interobserver). Further investigation is needed to evaluate the prognostic value of this approach.

Conclusion

In conclusion, these results demonstrate acceptable reproducibility of VFA on CT.

Osteoporosis management: impact of fracture type on cost and quality of life in patients at risk for fracture I

BACKGROUND

Osteoporosis is a major and costly global public health problem. It is a chronic disease in which fracture is the main outcome, and the impact of these fractures can vary depending on the age of the individual and the severity of the fracture.

SCOPE

Using literature review, this paper discusses and summarizes the information available regarding the individual and socio-economic consequences associated with the several types of osteoporotic fractures.

FINDINGS

Different types of osteoporotic fractures are generally associated with different age groups. The health-economic impact of vertebral and hip fractures has been extensively explored and it is well known that these fractures are associated with morbidity/disability and increased mortality; they also account for a substantial portion of the direct fracture costs. However, to accurately estimate the individual and socio-economic burden of the disease, further research is needed on the morbidity/disability, mortality, and costs associated with non-hip, nonvertebral fractures, which account for more than half of the total fractures. More data are also required on the indirect costs associated with all fracture types.

CONCLUSIONS

Understanding the socio-economic consequences of each fracture type will be important to fully estimate the burden of osteoporosis and may help clinicians tailor management plans for individual patients.