Microwave/Thermal Analyses for Human Bone Characterization

Abstract

A novel imaging approach utilizing microwave scattering was proposed in order to analyze various properties of bone. Microwave frequencies of 900 MHz, 1 GHz, and 2.4 GHz were used during this study. This investigation’s objectives were to emphasize characteristics of abnormalities in human bones and to detect fine fractures through contrasts in bone density. The finite element method (FEM) presented here is generated from COMSOL software at different frequencies. The study identified the optimum transmission directed at the interface layers from an external microwave source. It was found that approximately 900 MHz microwave power was ideal for this application. This can be attributed to the penetration depth where the power dissipation is analyzed based on bone condition. The microwave energy was generated from an exterior antenna that was interfaced, via catheter, to skeletal bone. The power transmitted to bone was converted into thermal energy, and has led to a visible temperature distribution pattern, which reflects the bone density level, and accordingly, the type of bone under investigation. The electrical and thermal properties, including the dielectric permittivity, thermal conductivity, and heat flux absorption through the bone substance, have great implications on the FEM distribution. The boundary conditions using tangential matching of field components at the tissue-bone interface were incorporated into the finite element method. The average power from the electromagnetic fields (estimated from the Poynting’s vector, P = E*H), was assumed to be fully absorbed as heat due to the conductivity of the bone material. Furthermore, microwave energy was applied as a delta function and the thermal distributions have been analyzed in order to distinguish between normal healthy bone and bones with structural or metabolic abnormalities. The latter was emulated by different bone density to contrast normal bone anatomy. The FEM simulation suggests that thermography microwave imaging could be a good tool for bone characterization in order to detect skeletal abnormalities. This approach could be advantageous over other existing methods such as X-ray imaging.