Scanning acoustic microscopy studies of cortical and trabecular bone in the femur and mandible

Abstract

Scanning acoustic microscopy (SAM) has been used to study the micromechanical properties of cortical and trabecular bone in both the human femur and mandible. SAM images vary in gray level reflecting the variations in reflectivity of the material under investigation. The reflection coefficient, r=(Z2−Z1)/(Z2+Z1), where the acoustic impedance (AI), Z=dv, d is the materials local density and v is the speed of sound at the focal point; Z2 represents the AI of the material, Z1 that of the fluid coupling the acoustic wave from the lens to the material. Femoral cortical bone consists of haversian systems (secondary osteons) and interstitial lamellae, both of which show systematic variations of high and low AI from lamella to lamella. The lamellar components defining the edges of trabecular cortical bone exhibit the same lamellar variations as seen in cortical bone. Mandibular bone, while oriented perpendicular to the direction of gravitational attraction, exhibits the same cortical and trabecular structural organizations as found in the femur. It also exhibits the same systematic alternations in lamellar AI as found in femoral bone. Both femoral and mandibular cortical bone have transverse isotropic symmetry. Thus, modeling elastic properties requires only five independent measurements.