Cortical Bone Assessment Using Ultrasonic Guided Waves: Towards a Robust Clinical Measurement

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Osteoporosis is a skeletal disease leading to bone fragility and increasing the risk of fractures and still remains a major public health problem worldwide. Therefore it is crucial to prevent severe fractures responsible for excess of mortality and considerable morbidity. Patient at risk of fractures are currently identified as having osteoporosis using Dual-energy X-ray Absorptiometry (DXA), assessing the areal or projected Bone Mineral Density (aBMD g.cm-2). In Chile, the hip fracture occurrence is very similar to the international incidence. Due to the demographic and epidemiological transition, the number of hip fracture for patient older than 50 year, is expected to severely increase from about 6.500 (2007) to 30.000 (2050) without adequate preventive and / or therapeutic measures. Even if DXA remains the current gold standard, it is limited by the difficulty to set a threshold in the BMD distribution for osteoporosis diagnosis. Moreover, some medical conditions (chronic kidney disease, diabetes) or drugs (glucocorticoids) are associated with an increase of fracture risk without a BMD decrease. Quantitative ultrasound (QUS) have the advantages of portability, low cost, absence of radiation and need for a radiographic technologist or designated room, and are sensitive to both elasticity and geometry of the medium explored by the waves. Among QUS techniques, axial transmission (AT) is a technique for which transducers are aligned along the bone axis. Measured ultrasonic guided waves, associated with an appropriate waveguide model have the potential to yield estimates of material and/or geometrical cortical properties. In vivo combined estimation of both cortical thickness and porosity has been proposed using bidirectional axial transmission (BDAT). BDAT measurement has been recently validated on ex vivo specimen (radius and tibia) and has been tested in a pilot clinical study, in which cortical porosity measured at the one-third distal radius has been found as discriminant of low trauma fractures as DXA. Cortical porosity is increasingly recognized as a major contributor to bone fragility. The hypothesis underlying this project are that (1) it is possible to obtain robust and accurate estimates of cortical thickness and porosity using an improved BDAT device and (2) these estimates are of clinical interest in the context of osteoporosis in elderly. Moreover, novel parameters obtained from automatic classification tools will be tested.

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