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Communication Dans Un Congrès Année : 2020

Cortical bone characterization using backscatter statistics of the signals through measurements of Shannon entropy

Résumé

The structural changes of cortical bone such as increase in porosity as a result of changes in pore diameter (Ct.Po.Dm.) and density (Ct.Po.Dn.) are closely associated with osteoporosis and risk of fracture. In the present numerical study, finite difference time domain simulations are executed on 301 2D images of human femoral cortical specimens obtained from CT scans. A plane wave at 5MHz is transmitted into the medium and the backscattered signals are received on a linear array transducer. Each backscattered signal is then truncated into half-overlapping 0.2μs time-windows corresponding to one signal period. Shannon entropy as a measure of uncertainties in the system is defined as the negative of the logarithm of the backscattered probability distribution of the signal. In the past, microstructure-dependent backscatter statistics of the signals has been exploited to characterize heterogeneous media like liver[1] using Shannon entropy. This parameter is measured for each time-window resulting in an entropy map for each cortical bone structure. The average entropy value over the whole region of interest is plotted against cortical porosity, average pore diameter and pore density. The entropy demonstrates strong correlations with porosity (R=0.83, p<0.0001) and average pore diameter (R=0.78, p<0.0001) such that an increase in either parameter would lead to an increase in entropy. Plotting entropy versus pore density for all structures does not result in a monotonous trend due to large variations in pore diameter which ranges from 51.9 to 157.4μm. Limiting this parameter by using the structures with 71.7μm<Ct.Po.Dm<80.6μm (N=75) leads to a better correlation between Ct.Po.Dn. and entropy (R=0.55, p<0.0001). To summarize, the present study has successfully used Shannon entropy as a statistical tool to quantify microstructural changes of cortical bone. Use of backscattered signals is especially desired in case of clinical applications on accessible sites like tibia bone.
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Dates et versions

hal-03240339 , version 1 (28-05-2021)

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Yasamin Karbalaeisadegh, Quentin Grimal, Marie Muller. Cortical bone characterization using backscatter statistics of the signals through measurements of Shannon entropy. Forum Acusticum, Dec 2020, Lyon, France. pp.1079-1079, ⟨10.48465/fa.2020.0873⟩. ⟨hal-03240339⟩
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