Page 72 - Cellular Imaging in Regenerative Medicine, Cancer and Osteoarthritis

Chapter 3
Conclusion
Our results suggest that in vitro relaxivity calibrations can be applied to in vivo measurements only under special circumstances. We can conclude that the cell-to-cell variations play an important role in transversal relaxation rates. We demonstrated that samples of labeled cells of the same type at the same cell density at a given iron concentration can exhibit different R2* and R2' relaxation rates, depending on the cell-to-cell variations in the labeling particle content. Unless there is only one, well-defined, dominant process in the investigated volume, iron content cannot be determined by relaxation measurement. During cell mixing, cell densities can be derived from relaxation values, even if iron concentration remains ambiguous. When cell division is the dominant process, despite labeling variations, iron content and also cell densities can be determined from re- laxation rates. Cell death can be identified by the simultaneous increase in R2 and decrease in R2'.
Acknowledgement
Our study was supported by the ENCITE (European Network for Cell Imaging and Tracking Expertise) project Cooperation Health-2007-1.2-4 In Vivo Image-guidance for Cell Therapy, Large-scale Integrating Project (IP).
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