Figure 1.

a, Viable cell counts from in vitro assay of either unlabeled MSCs (control) or MSCs labeled with increasing doses of ¹¹¹In oxine ranging from 5 to 30 μCi per million MSCs determined 1 to 7 days after labeling. Cells were initially plated in a T-25 flask at a density of 2 × 10⁶ MSCs. Cell counts were determined every other day in alternate flasks. Cell counts remained constant after adhering ≈48 hours after seeding. b, MTS assay measuring absorption of different doses of ¹¹¹In oxine–labeled MSCs and unlabeled MSCs (control) at 1 to 8 days after labeling. At 6 days after labeling, unlabeled MSCs showed an increased metabolic activity relative to labeled cells (*P < 0.001). However, no dose-dependent change in metabolic activity was noted between different amounts of MSC radiolabeling.