Extracellular matrix mineralization and its heterogeneity near donor eGFP⁺ and host eGFP⁻ osteocytes measured by confocal Raman microspectroscopy. The measurements of extracellular matrix mineralization (A) and its heterogeneity (B) were performed near 96 cells in 20 different sections of femur cortical bone from the same animal with 1.9% engraftment in bone marrow. Consistent results were obtained for another 1.9%-engraftment animal. The mineralization was evaluated from the intensity ratio of mineral phosphate (ν₁PO₄³⁻) to organic CH Raman peaks, mean (± standard error [SE]). The mineralization heterogeneity was defined as the coefficient of variation of the ratio, COV = 100% SD/mean; the mean square errors of COV (mse) were calculated from the mean square error for the unbiased variance estimator.⁵¹