Reproducibility and Radiation Effect of High-Resolution In Vivo Micro Computed Tomography Imaging of the Mouse Lumbar Vertebra and Long Bone

A moderate radiation dose, in vivo µCT scanning protocol was developed and validated for long-term monitoring of multiple skeletal sites (femur, tibia, vertebra) in mice. A customized, 3D printed mouse holder was designed and utilized to minimize error associated with animal repositioning, resulting in good to excellent reproducibility in most cortical and trabecular bone microarchitecture and density parameters except for connectivity density. Repeated in vivo µCT scans of mice were performed at the right distal femur and the 4th lumbar vertebra every 3 weeks until euthanized at 9 weeks after the baseline scan. Comparing to the non-radiated counterparts, no radiation effect was found on trabecular bone volume fraction, osteoblast and osteoblast number/surface, or bone formation rate at any skeletal site. However, trabecular number, thickness, and separation, and structure model index were sensitive to ionizing radiation associated with the µCT scans, resulting in subtle but significant changes over multiple scans. Although the extent of radiation damage on most trabecular bone microarchitecture measures are comparable or far less than the age-related changes during the monitoring period, additional considerations need to be taken to minimize the confounding radiation factors when designing experiments using in vivo µCT imaging for long-term monitoring of mouse bone.