Relaxation times and contrast of Mn-labeled MNCs.

<p>(A) R<sub>1</sub> and R<sub>2</sub> calculated for the <i>in vitro</i> samples are presented. The pelleted 0.1 mM Mn-labeled MNCs showed larger R<sub>1</sub> and R<sub>2</sub> in comparison to the saline control. It was not possible to calculate the R<sub>1</sub> and R<sub>2</sub> values for the MNCs with 0.25 mM Mn-labeling and over (N/A) because the T<sub>2</sub> was too short due to the large susceptibility effect. The R<sub>1</sub>s of the MnCl<sub>2</sub> solutions were approximately linearly correlated with the Mn concentration. The R<sub>1</sub> and R<sub>2</sub> for the supernatant fluid were approximately independent of the initial Mn labeling concentration. (B) T<sub>1</sub>-weighted sagittal images of pelleted MNCs after suspension in 0, 0.1, 0.25, and 0.5 mM Mn solutions. The pelleted MNCs at 0.1 mM MnCl<sub>2</sub>-labeling showed partial signal enhancement in the T<sub>1</sub>-weighted 7 T MRI (arrow). The pelleted MNCs with MnCl<sub>2</sub>-labeling over 0.25 mM lost signal in comparison with the unlabeled (0 mM) control due to the very short T<sub>2</sub> and the T<sub>2</sub>* susceptibility effect at 7 T. In the 0.2 T MRI, the the 0.1, 0.25 and 0.5 mM MnCl<sub>2</sub>-labeled MNCs showed positive contrast, although there may have been some signal loss at the base of the 0.5 mM sample.</p>

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