Quantification of injected MSC viability using the IVIS system. The luciferase reporter MSCs (500,000 or 2,500,000 cells/10 μL PBS; five mice per group) were injected into bone marrow at femurs. Cell viability was evaluated using IVIS every 2 days for 28 days. (a) Summary of experiment design. (b) The IVIS images at day 0, 14 and 28. (c) Quantification results of MSC viability during 4 weeks of experiments (p/s/cm2/sr). p=photon, sr=surface radiance.