A recent study, published in the current issue of Cell Transplantation, showed that using the , FDA-approved, 
contrast agent Indocyanine Green (ICG) for labeling human, embryonic stem cell-derived, cardiomyocytes (hESC-CMs) would significantly enhance efforts carried out to optically track stem cells after transplantation into cardiac tissues. The study was performed by the Departments of Radiology at the University of California and the Technical University of Munich.
Dr. Sophie E. Boddington of the UCSF Department of Radiology, said "We found that hESC-CMs labeled with ICG show a significant fluorescence up to 48 hours and can be visualized with optical imaging," she added "Once more, the labeling procedure did not impair the viability or functional integrity of the cells." Based on the study, developing an efficient stem cell delivery technique was always a challenge. A lot of stem cells when aimed at myocardial regeneration were "washed away" into non-cardiac tissues or even die soon. A 10% survival rate for hESC-CMs has been commonly reported. Researchers mentioned that a better way for visualization of the transplanted stem cells was required in order to help direct stem cell delivery. They also added that the materials used for labeling the cells had to show maximum fluorescence and yet not confirming the viability of the cells.
Dr. Boddington said "We found the ICG-labeling technique advantageous because it is cost effective, straightforward and rapid," she added "Its most noticeable advantage is that it can be used with iron oxide-based nano-particles for use with MRIs, as it increases single cell sensitivity. This is important because of the unpredictable migrational dynamics of the cells." Moreover, the study said that despite PET techniques are showing more single cell sensitivity than MRI, PET is associated with radiation exposure and therefore more risks. Yet, optical imaging applying the MRI is rapidly, less expensive, of easier performance, and noninvasive procedure. Dr. Boddington added that another advantage of the ICG is that it is quickly excreted and this indicates safe elimination.
Dr. Boddington concluded "Our data suggests that hESCs labeled with ICG may be useful in assessing delivery routes to improve the engraftment of transplanted hESC-CMs or other stem cell progenitors," While Dr. Dwaine Emerich, section editor for Cell Transplantation, confirmed that the study was significant. He said "These studies are an important step forward in the quest for techniques to label and visualize stem cells in vivo," he added "The ICG-labeling technique described by Boddington and colleagues provides several advantages including its straight forward simplicity, reliability, and the fact that the technique can be easily combined with other developing imaging technologies."