Imaging the femoral cortex: Thickness, density and mass from clinical CT

[Display omitted] ► Focal thinning of cortical bone in the proximal femur predisposes a hip to fracture. ► Thinning is difficult to detect in CT since the cortex may be narrower than the PSF. ► We present a model-fitting technique to estimate cortical thickness, density and mass. ► Evaluation on cadaveric femurs confirms accurate measurement of mass and peak density. ► Thickness errors do not exceed 20% and are confined to regions of thin cortex. There is growing evidence that focal thinning of cortical bone in the proximal femur may predispose a hip to fracture. Detecting such defects in clinical CT is challenging, since cortices may be significantly thinner than the imaging system’s point spread function. We recently proposed a model-fitting technique to measure sub-millimetre cortices, an ill-posed problem which was regularized by assuming a specific, fixed value for the cortical density. In this paper, we develop the work further by proposing and evaluating a more rigorous method for estimating the constant cortical density, and extend the paradigm to encompass the mapping of cortical mass (mineral mg/cm2) in addition to thickness. Density, thickness and mass estimates are evaluated on sixteen cadaveric femurs, with high resolution measurements from a micro-CT scanner providing the gold standard. The results demonstrate robust, accurate measurement of peak cortical density and cortical mass. Cortical thickness errors are confined to regions of thin cortex and are bounded by the extent to which the local density deviates from the peak, averaging 20% for 0.5mm cortex.