Ayman M. Mostafa

Comparative investigation of bone mineral density using CT and DEXA in a canine femoral model

Bone density measurements using computed tomography (CT) instead of dual‐energy X‐ray absorptiometry (DEXA) are currently of great interest in human and veterinary medical research as it would be beneficial to use CT scans obtained for other indications also for determining bone density. For Hounsfield units (HU) measured with CT in specific regions of interests (ROIs) in one or several slice/s a correlation with bone mineral density (BMD) measured by DEXA in humans and dogs of between 0.44 and 0.77 is reported in the literature. In the present study, instead certain volumes of interest (VOIs) obtained by CT scan and the corresponding HU to the respective VOIs were compared with the bone mineral density of the corresponding areas measured by DEXA. The aim of the study was to investigate whether this procedure gives more accurate information about bone density of the bones as three‐dimensional objects of the respective patient. Correlation between measured HU in the respective VOI and BMD measured with DEXA in the corresponding ROI showed a very good correlation of 0.93. Linear regression with R2 = 0.85 (p = 0.0262) was calculated. Except for VOI5, similar distribution of values and significant differences (p < 0.0001–0.0087) between ROIs/VOIs were detected. Determining HU for assessing bone mineral density in a certain volume provides more accurate results than those previously reported from two‐dimensional (2D) CT measurements.

Nonlinear Wave-Induced Instability in a Caisson-Type Breakwater Having a Multi-Layered Base

A study has been conducted to investigate the stability of a caisson-type breakwater constructed over a multi-layered base in a nonlinear wave field. The nonlinear interactions among waves, caisson-type breakwater and the multi-layered high base have been considered. The problem has been simulated numerically by two models, BEM-FEM model and poro-elastic FEM model. The latter models are developed to simulate the nonlinear wave field and its interactions with the porous media. Modifications have been made in the models to account for the multi-layered base and applications have been made to various configurations and properties of the breakwater. It has been found that the nonlinear effects become more significant in case of a high base and the fine material of the base may suffer from tensile stresses. The base may also fail at smaller wave heights than that needed for causing failure in the caisson.