Sensitivity of Susceptibility-Weighted Imaging in Detecting Superparamagnetic Iron Oxide-Labeled Mesenchymal Stem Cells: A Comparative Study

BACKGROUND Susceptibility-weighted imaging (SWI) is extremely sensitive in the detection of superparamagnetic iron oxide (SPIO) nanoparticle-labeled cells. However, no study has compared molecular imaging for stem cell detection using SWI and other MRI pulse sequences. OBJECTIVES This study aims to assess the sensitivity of SWI in detecting SPIO nanoparticle-labeled, human bone marrow-derived mesenchymal stem cells (SPIO-hMSCs) compared with that of T2- and T2*-weighted imaging (T2WI and T2*WI, respectively) in a phantom and in vivo study in rats. MATERIALS AND METHODS A phantom was prepared with various cell concentrations. In one normal rat, SPIO-hMSCs were implanted directly through burr holes into both caudate putamens, while in three rats without and six rats with photothrombotic infarction, 2.5 × 10(5)/ml SPIO-hMSCs were infused into the ipsilateral internal carotid artery (ICA). T2WI, T2*WI, and SWI findings were compared for dark regions representing SPIO-hMSCs. RESULTS SWI and T2*WI detected 15 µL of 13 SPIO-hMSCs/µL and 15 µL of 27 SPIO-hMSCs/µL in the phantom, respectively and 3 µL of 333 SPIO-hMSCs/µL and 3 µL of 167 SPIO-hMSCs/µL in the normal rat brain (direct implantation). In the normal rat brain (ICA infusion), one of the three cases showed numerous foci of dark regions dispersed throughout the brain on T2*WI and SWI. Dark regions surrounded the infarcts in all six infracted rat brains. The dark region was most prominent on SWI, followed by T2*WI and T2WI in all six rats (P = 0.002). Implanted SPIO-hMSCs were confirmed using Prussian blue staining. CONCLUSIONS SWI is the most sensitive in the detection of SPIO-hMSCs, with the dark regions representing SPIO-hMSCs being more prominent on SWI than on T2*WI and T2WI.