[Magnetic resonance imaging of single SPIO labeled mesenchymal stem cells at 3 Tesla]

To assess the detectability of single magnetically labeled mesenchymal stem cells (MSC) in-vitro on a clinical 3T MR scanner using a small animal volume coil.

GFP-transfected MSC were magnetically labeled with superparamagnetic iron oxide particles (SPIO) while applying different dosages of iron (56 vs. 560 microg Fe/ml). The cellular iron content was determined with atomic absorption spectrometry (AAS). Single labeled MSC were displayed in a culture flask using MR imaging and microscopy. Special cell phantoms were designed to examine the detection of labeled MSC with MR imaging in a spatial model. A T2*-weighted 3D gradient echo sequence with isotropic spatial resolution of 150 to 500 microm (3) was used for image acquisition. The detection of labeled MSC in the cell phantoms was quantitatively evaluated using an automated image analysis. Statistical analysis was performed with a significance level of p < 0.05.

The labeling of MSC yielded a mean cellular iron content of 1.5 +/- 0.17 pg Fe/cell (56 microg Fe/ml) and 8.3 +/- 1.85 pg Fe/cell (560 microg Fe/ml). Examination of the culture flasks showed single magnetically labeled MSC centered in much larger MR signal voids. The detection and quantification of single MSC in cell phantoms were feasible for spatial resolutions of 150 microm and 200 microm. Cells with a lower SPIO content (1.5 +/- 0.17 pg Fe/cell) were detected in 14.2 +/- 4.2 % (150 microm) and 7.7 +/- 3.8 % (200 microm). MSC with a higher cellular SPIO content (8.3 +/- 1.85 pg Fe/cell) revealed significantly higher occurrences at both spatial resolutions with 81.4 +/- 5.8 % (150 microm) and 59.9 +/- 12.4 % (200 microm), respectively. Regarding the spatial resolution (150 vs. 200 microm), significantly different detection rates were determined only for MSC with the higher SPIO content (8.3 +/- 1.85 pg Fe/cell).

Detection of single magnetically labeled MSC is feasible on a clinical 3T MR scanner with a small animal volume coil at isotropic spatial resolutions of 150 microm and 200 microm. The number of detected cells is influenced by the cellular iron content and the spatial resolution.