In Vivo Dynamic MRI Tracking of Rat T‐Cells Labeled with Superparamagnetic Iron‐Oxide Particles

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Abstract
Dynamic MRI tracking of rat T‐cells in vivo is performed in rat testicles after labeling isolated rat T‐cells in vitro with superparamagnetic dextran‐coated iron‐oxide particles, BMS180549. Tissue inflammation induced by the local injection of the calcium ionophore, A23187, is used to attract labeled T‐cells. Gradient‐echo MR images of rat testicles show a statistically significant decrease (4%) of the signal intensity in areas of injection of A23187 as early as 30 min after intravenous infusion of 2 x 108 labeled T‐cells. The signal change reaches its maximum (6–7% decrease) at about 60–120 min after cell infusion. T2‐mapping also shows a decrease of T2 in the areas with A23187. Image quantitation, which includes a chemical‐shift effect, significantly enhances the sensitivity for detection of superparamagnetically labeled T‐cells. Localization of labeled T‐cells in rat testicles has been verified by fluorescence microscopy studies of T‐cells co‐labeled with a lipophilic fluorescent carbocyanine dye, 1,1‐dioctadecyl‐3,3,3',3'‐tetramethyl‐lindocarbocyanine perchlorate. These results represent the first successful demonstration of dynamic tracking of specific cells in vivo using MRI.