3D Image Registration Is Critical to Ensure Accurate Detection of Longitudinal Changes in Bone Microstructure and Mineral Density Measurements in Rats by In Vivo Micro Computed Tomography

Introduction In the recent decade, in vivo micro computed tomography (μCT) scanners have become available to monitor longitudinal bone changes in rodents. With an isotropic image voxel size up to 10.5 μm, changes in geometry and microstructural properties of rodent bone in response to either disease or treatment can be visualized and quantified over time. In order to detect longitudinal changes, it is critical to understand the precision of in vivo μCT measurements. Although reproducibility of ex vivo μCT at various volumes of interest (VOI) and resolutions have been reported, influences of movement and repositioning of animals, which are associated with in vivo scans, have not been well studied. Nishiyama et al reported that by 3D image registration, reproducibility can be significantly improved in microstructural measurements at 12.5 μm resolution (precision ~1-5% in rats). However, in their study the followup scans were within 2 days where changes to the bone microstructure are negligible. The first objective of the current study was to investigate the short-term reproducibility and long-term precision of bone microstructure and density measurements in the rat tibia by in vivo μCT scans at the highest achievable voxel size (10.5 μm). The second objective was to test whether a 3D image registration technique can improve shortand long-term precision.