The tracing of in vivo distribution after stem cell transplantation can be accomplished by examining markers of stem cells, reporter gene transfection and Y chromosome markers. However, these methods cannot be used for dynamic observation and in vivo tracing of the introduced stem cells, and are therefore not available for clinical research. With the development of molecular imaging in recent years, MRI technology has become widely used for in vivo tracing of stem cells. Studies have shown that MRI can reveal the survival and migration of iron oxide-labeled stem cells through intracranial injection in focal cerebral infarction models. Other research has shown that feridex and poly-L-lysine complexes have been successfully used to label mesenchymal stem cells in mammals.  
A comprehensive understanding of distribution following transplantation of stem cells using a radiographic approach is now a hot topic in related research fields. Included in this issue are four papers that describe dynamic observation and in vivo tracing of transplanted stem cells using various techniques and imaging markers.

? Bone marrow mesenchymal stem cell transplantation for treatment of spinal cord injury: an in vivo magnetic resonance imaging tracking study
Neural Regen Res. 2010;6(13):978-982. 
       
? Migration of Resovist-labeled neural stem cells towards focal rat cerebral ischemic regions as determined by in vivo tracking and magnetic resonance imaging
Neural Regen Res. 2010;5(13):970-974.

? Feridex-labeled bone marrow stromal cells for analysis of sciatic nerve defects in rabbits
Neural Regen Res. 2010;5(11):846-852.

? Magnetic resonance imaging tracing of transplanted bone marrow mesenchymal stem cells in a rat model of cardiac arrest-induced global brain ischemia
Neural Regen Res. 2009;4(9):645-653.