Relaxation times and contrast of Mn-labeled MNCs.
(A) R1 and R2 calculated for the in vitro samples are presented. The pelleted 0.1 mM Mn-labeled MNCs showed larger R1 and R2 in comparison to the saline control. It was not possible to calculate the R1 and R2 values for the MNCs with 0.25 mM Mn-labeling and over (N/A) because the T2 was too short due to the large susceptibility effect. The R1s of the MnCl2 solutions were approximately linearly correlated with the Mn concentration. The R1 and R2 for the supernatant fluid were approximately independent of the initial Mn labeling concentration. (B) T1-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 MnCl2-labeling showed partial signal enhancement in the T1-weighted 7 T MRI (arrow). The pelleted MNCs with MnCl2-labeling over 0.25 mM lost signal in comparison with the unlabeled (0 mM) control due to the very short T2 and the T2* susceptibility effect at 7 T. In the 0.2 T MRI, the the 0.1, 0.25 and 0.5 mM MnCl2-labeled MNCs showed positive contrast, although there may have been some signal loss at the base of the 0.5 mM sample.
