Determining mineral content variations in bone using backscattered electron imaging

The mechanical properties of bones are greatly influenced by the ratio of organic constituents to mineral. Determination of bone mineral content on a macroscopic scale is straightforward, but microscopic variations, which can yield new insights into remodelling activities, mechanical strength, and integrity, are profoundly more difficult to measure. Measurement of microscopic mineral content variations in bone material has traditionally been performed using microradiography. Backscattered electron (BSE) imaging is a technique with significantly better resolution than microradiography with demonstrated consistency, and it does not suffer from projection-effect errors. We report results demonstrating the applicability of quantitative BSE imaging as a tool for measuring microscopic mineral content variations in bones representing a broad range of mineralization. Bones from ten species were analyzed with Fourier-transformed infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectrometry, ash measurements, and BSE imaging. BSE image intensity (graylevel) had a very strong positive correlation to mineral (ash) content. Compositional and crystallographic variations among bones had negligible influence on backscattered electron graylevels. The present study confirms the use of BSE imaging as a tool to measure the microscopic mineral variability in a broad range of mineralized tissues.