Effect of Voxel Size on Finite-Element Analysis of Micro-CT Derived Bone Sample

Abstract

Introduction: Bone strength is dependent on the structural parameters of thetrabecular micro-architecture1. A method to estimate bone strength is finite element(FE) analysis of the bone micro-architecture2. Quantification of structural parameters3and FE analysis results are dependent on the image resolution2. This study used microcomputedtomography (micro-CT) to investigate how voxel size affects the accuracy oftrabecular bone measurements, particularly regarding how it relates to FE modelingprediction of bone strength.Methods: Cadaveric bovine cubic bones were imaged at an isotropic voxel sizeof 20mm using a micro-CT scanner (Micro-CT35). Images were segmented using athreshold based technique and re-scaled to voxel sizes 2-4 times larger (40mm-80mm)than the original images. Three-dimensional analyses of trabecular bone propertieswere quantified within the images of the bone cubes. Image voxels were converted tohexahedral elements for FE analysis. Uniaxial 1% compression test was performed onall data (FAIM 5.4). Nodes on the bottom surface were fixed while the top surface wassubjected to compression. No constraints were applied to the x and y directions.Results: Trabecular number (TbN) measurements increased linearly with increasingresolution. There was a 22.11% difference between trabecular number values at20mm versus 80mm. All other structural parameters were not statistically significantbetween different image resolutions (p > 0.05). For FE analysis, there was a 3.05%percent difference for mean von-Mises Stress at 20mm versus 80mm. Total reactionforce between 20mm and 80mm differed by 0.484%. Maximum von-Mises stress wasstatistically significantly different between 20mm and 80mm.Conclusion: All structural parameters except TbN measured at 20mm are comparableto 80mm. Similarly, bone strength estimates through FE analysis at 20mm arecomparable to 80mm. It is unlikely that TbN influenced the bone strength estimates.These results will allow for non-invasive estimate of bone strength with advancedclinical CT scanners.