Scanning Acoustic Microscopy of human and canine cortical bone microstructure at high frequencies

An Olympus UH3 Scanning Acoustic Microscope (Tokyo, Japan) has been used in the burst mode at 400 and 600 MHz to study the elastic properties of osteons and osteonic lamellae in both canine and human compact cortical bone. The nominal resolution at each frequency is within the width of an individual lamella. Three important new observations have been made regarding the acoustic properties of individual lamellae. Firstly, the acoustic impedance, as measured by shade of gray levels, of the outer most lamellae of adjacent osteons interdigitate (blend) although the structures, as determined by backscatter scanning electron microscopy, are seen to be quite separate. Secondly, in almost every osteon observed in this study, the shade of gray level for individual lamellae appear to alternate-dark, light etc.-translating to alternating compliant, stiff lamellar units respectively. Thirdly, the outermost lamella of each osteon appears to be the most compliant (darkest gray level). A preliminary SAM study of sheep femoral trabecular bone has shown the some alternation of lamellar gray levels as observed in osteonic lamellae.