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    ASBMR 2010 Annual Meeting

    Improved Evaluation of Hip Structure using High Resolution Cortical Thickness Measurement from Clinical CT Data

    Category: Bone Biomechanics and Quality (Clinical)

    Poster Sessions, Presentation Number: FR0037
    Session: Welcome Reception and Plenary Poster Session
    Friday, October 15, 2010 5:45 PM - 7:00 PM, Metro Toronto Convention Centre, South Building, South Building: Hall E

    Poster Sessions, Presentation Number: SA0037
    Session: Poster Session I and Poster Tours
    Saturday, October 16, 2010 11:30 AM - 1:30 PM, Metro Toronto Convention Centre, South Building, South Building: Hall E

    Graham M Treece, University of Cambridge, United Kingdom, Andrew H Gee, University of Cambridge, United Kingdom, * Paul Mayhew, University of Cambridge, UNITED KINGDOM, Kenneth Poole, University of Cambridge, UNITED KINGDOM

    The distribution of cortical bone in the proximal femur is believed to be critical in determining fracture resistance. Ageing leads to thinning of femoral neck cortical bone, which can become as thin as an egg-shell by the eighth decade in critical areas (0.3mm). In current clinical practice, hip bone mineral density estimates made with 2-dimensional dual-energy x-ray absorptiometry ('DXA') are specific for predicting hip fracture but have low sensitivity. Recent studies have instead utilised multi-detector computed tomography (MDCT) to examine femoral neck cortical thickness and 3-D structure and its potential for in vivo hip fracture prediction. However, existing CT technology is limited in its ability to measure cortical thickness, especially in the sub-millimetre range which lies within the point spread function of today's clinical scanners. We present a novel analysis technique that is capable of producing unbiased cortical thickness estimates down to 0.3mm, considerably outperforming previous methods (referred to here as simple thresholding, and 50% relative threshold). The technique relies on a mathematical model of the anatomy and the imaging system, which is fitted to the data at a large number of sites around the proximal femur, producing around 17,000 independent thickness estimates per specimen. In a series of experiments on sixteen cadaveric femurs, estimation errors were  measured as -0.01±0.58mm (mean ± 1 std. dev.) for cortical thicknesses in the range 0.3mm to 4mm. This compares with 0.25±0.69mm for simple thresholding and 0.90±0.92mm for a variant of the 50% relative threshold method. In the clinically relevant sub-millimetre range, thresholding increasingly fails to detect the cortex at all, whereas the new technique continues to perform well. The many cortical thickness estimates can be displayed as a colour map painted onto the femoral surface. Computation of the surfaces and colour maps is rapid and largely automatic. The technique is ideally suited to the evaluation of cortical bone structure in life, in clinical fracture prediction, and in assessing the structural response of the hip to interventions.

     

    Disclosures: None

    * Presenting Authors(s): Paul Mayhew, University of Cambridge, UNITED KINGDOM

    Attachments

    Comparing the high res C.Th map (upper) with low res thresholding (middle) and new technique (lower)