Backscattered Electron Imaging: The Role in Calcified Tissue and Implant Analysis

Backscattered electron (BSE) imaging is being developed into an accurate and useful technique for determining changes in bone morphology, histometry, and mineral content. BSE is currently used as a tool for quantifying the response of mineralized tissue to biomaterials. This paper briefly discusses the physics of BSE imaging and its application to mineralized tissue and biomaterials research. Original research is reported which better defines the errors that are imposed by changes in specimen working distance and tilt. Two parameters, the backscattered electron profile and the weighted mean graylevel, were introduced and developed so that BSE imaging could be used as a reproducible, quantitative technique for studying mineral content changes in bone. Results demonstrated that the working distance to a cortical bone surface can vary up to 300 μm or tolerate a tilt of up to 10 degrees without altering weighted mean graylevel values by more than 2 percent. Calibration of the BSE signal would allow for reproducible, quantitative mineral content analysis to be conducted on bone and bone/implant interfaces. Bone substitutes and pure metals were investigated to determine their potential as BSE graylevel calibration standards. Pure metals appear to be the most promising materials for standardizing BSE graylevels, due to their greater homogeneity. Finally, interrelationships between compressive strength and stiffness, histometry, and mineral content of individual trabecula in cancellous bone are investigated. Failure site trabecular thickness and minimum trabecular thickness, two new histometric parameters defined in this study, were found to statistically correlate with cancellous bone strength and stiffness.