Fig. 4. Time-elapsed MR images of photothrombotic cerebral infarction and superparamagnetic iron oxide (SPIO)-labeled stem cells in rat model.

MR images were obtained on day 2 after photothrombotic cerebral infarction (pre, 1 day before cell injection) and on days 1, 3, 7, and 14 after internal carotid arterial injection of SPIO-labeled human bone marrow-derived mesenchymal stem cells. As time progressed, high signal intensity of infarction (⊚) was reduced in size and intensity, and dark signal region (arrowheads) appeared by encircling infarction from day 1 until day 14, indicating engraftment of stem cells to infarction. Dark regions were large and prominent in susceptibility-weighted images (SWI), followed by T2^*-weighted images (T2^*WI), and then by T2-weighted images (T2WI).