Assessment of bone micro-structure using ultrasonic methods

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Osteoporosis is increasingly prevalent. It modifies microarchitecture and bone density and the assessment of both is required to predict bone competence accurately. Several studies have demonstrated the relationship between bone micro-architecture and bone strength. However, the current gold standard for fracture risk assessment relies on the X-ray characterization of bone mineral density alone. A quantitative, non-invasive and non-ionizing characterization of bone micro-architecture is currently not possible in vivo. There is therefore an unmet need. We propose to address this need by developing a novel technique for the assessment of bone micro- architecture using multiple scattering of ultrasound. We hypothesize that when multiple scattering occurs there is a measureable relationship between ultrasonic parameters, such as the scattering mean free path, and micro-architectural parameters, such as anisotropy, connectivity and trabecular separation. Our approach is based on the following two-fold paradigm: First: Combining the characterization of bone micro-architecture to the currently available assessment of bone mineral density would improve the diagnosis of fracture risk. Second: Ultrasound waves in the MHz range are subjected to multiple scattering by the micro-structure during propagation in bone. The resulting ultrasonic signals are complex and embed information on the micro- architecture. We will have the following specific aims: SA.1 Using numerical simulations, we will establish a quantitative relationship between bone micro- architecture and ultrasound parameters. We will create bone-like numerical media in which we will vary the micro-architectural and material properties independently, to study their individual influence on ultrasound propagation. SA.2 Using 3D printing, we will create bone phantoms with arbitrary and fully controlled micro-architecture. The relationship between the micro-architecture and ultrasound parameters will be experimentally studied in vitro in phantoms and real specimen. SA.3 Using mechanical testing, we will investigate the relationship between ultrasound parameters, micro- architecture and mechanical competence. If successful, this research will lead to a quantitative and non-ionizing ultrasound-based method to characterize bone micro-architecture. Ultimately, the methods developed will be used for screening, diagnosis and monitoring of osteoporosis. This research aims at limiting the use of ionizing and costly techniques for the diagnosis of osteoporosis.