Multi-Slice-Computertomographie an der distalen Radiusmetaphyse

We explore the relationship of region-specific densitometric and geometry-based (cortical) parameters at the distal radial metaphysis with gender, age, and osteoporotic status, using multislice computed tomography (CT). We specifically test the hypothesis that these parameters can improve the prediction of mechanical strength of the distal radius vs bone mass (bone mineral content [BMC]). The BMC was determined in 56 forearm specimens with peripheral dual-energy X-ray absorptiometry (DXA). Trabecular and cortical density and geometric properties of the metaphyseal cortex were determined using multislice CT and proprietary image analysis software. Specimens were tested to failure in a fall simulation, maintaining the integrity of the elbow joint and hand. Women displayed significantly lower failure strength (-34%), BMC (-35%), trabecular density (-26%), and cortical area (-12%) than men. The reduction of trabecular density with age and osteoporotic status was stronger than that of cortical density or thickness. DXA explained approx 50% (r2) of the variability in bone failure loads. This proportion was slightly increased (55%) when adding geometry-based parameters. The study suggests that high-resolution tomographic measurements with current clinical imaging methodology can marginally improve the prediction of mechanical failure strength. Further efforts are required to improve spatial resolution for determining metaphyseal cortical properties clinically

Sources of entropy in dynamic representative agent models

We propose two data-based performance measures for asset pricing models and apply them to models with recursive utility and habits. Excess returns on risky securities are reflected in the pricing kernel's dispersion and riskless bond yields are reflected in its dynamics. We measure dispersion with entropy and dynamics with horizon dependence, the difference between entropy over several periods and one. We compare their magnitudes to estimates derived from asset returns. This exercise reveals tension between a model's ability to generate one-period entropy, which should be large, and horizon dependence, which should be small