Contrast Agents for Micro-Computed Tomography of Microdamage in Bone

Accumulation of microdamage during fatigue can lead to increased fracture susceptibilityin bone. Current techniques for imaging microdamage in bone are inherently destructiveand two-dimensional. Therefore, the objective of this study was to image the accumulationof fatigue microdamage in cortical bone using micro-computed tomography (micro-CT)with a barium sulfate (BaSO4) contrast agent. Two symmetric notches were machined onthe tensile surface of bovine cortical bone beams in order to generate damage ahead ofthe stress concentrations during four-point bending fatigue. Specimens were loaded to aspecified number of cycles or until one notch fractured, such that the other notch exhibitedthe accumulation of microdamage prior to fracture. Microdamage ahead of the notch wasstained in vitro by precipitation of BaSO4 and imaged using micro-CT. Reconstructed imagesshowed a distinct region of bright voxels around the notch tip or along propagating cracksdue to the presence ofBaSO4, which was verified by backscattered electron imaging andenergy dispersive spectroscopy. The shape of the stained region ahead of the notch tipwas consistent with principal strain contours calculated by finite element analysis. Therelative volume of the stained region was correlated with the number of loading cycles bynon-linear regression using a power law. This study demonstrates new methods for thenon-destructive and three-dimensional detection of fatigue microdamage accumulation incortical bone in vitro, which may be useful to gain further understanding into the role ofmicrodamage in bone fragility.c© 2007 Elsevier Ltd. All rights reserved.