Radiosafe micro-computed tomography for longitudinal evaluation of murine disease models

Implementation of in vivo high-resolution micro-computed tomography (μCT), a powerful tool for longitudinal analysis of murine lung disease models, is hampered by the lack of data on cumulative low-dose radiation effects on the investigated disease models. We aimed to measure radiation doses and effects of repeated μCT scans, to establish cumulative radiation levels and scan protocols without relevant toxicity. Lung metastasis, inflammation and fibrosis models and healthy mice were weekly scanned over one-month with μCT using high-resolution respiratory-gated 4D and expiration-weighted 3D protocols, comparing 5-times weekly scanned animals with controls. Radiation dose was measured by ionization chamber, optical fiberradioluminescence probe and thermoluminescent detectors in a mouse phantom. Dose effects were evaluated by in vivo μCT and bioluminescence imaging readouts, gold standard endpoint evaluation and blood cell counts. Weekly exposure to 4D μCT, dose of 540–699 mGy/scan, did not alter lung metastatic load nor affected healthy mice. We found a diseaseindependent decrease in circulating blood platelets and lymphocytes after repeated 4D μCT. This effect was eliminated by optimizing a 3D protocol, reducing dose to 180–233 mGy/scan while maintaining equally high-quality images. We established μCT safety limits and protocols for weekly repeated whole-body acquisitions with proven safety for the overall health status, lung, disease process and host responses under investigation, including the radiosensitive blood cell compartment.