Tracking of Labelled Stem Cells Using Molecular MR Imaging in a Mouse Burn Model in Vivo as an Approach to Regenerative Medicine.

Therapies based on stem cell transplants offer significant potential in the field of regenerative medicine. Monitoring the fate of the transplanted stem cells in a timely manner is considered one of the main limitations for long-standing success of stem cell transplants. Imaging methods that visualize and track stem cells in vivo non-invasively in real time are helpful towards the development of successful cell transplantation techniques. Novel molecular imaging methods which are non-invasive particularly such as MRI have been of great recent interest. Hence, mouse models which are of clinical relevance have been studied by injecting contrast agents used for labelling cells such as super-paramagnetic iron-oxide (SPIO) nanoparticles for cellular imaging. The MR techniques which can be used to generate positive contrast images have been of much relevance recently for tracking of the labelled cells. Particularly when the off-resonance region in the vicinity of the labeled cells is selectively excited while suppressing the signals from the non-labeled regions by the method of spectral dephasing. Thus, tracking of magnetically labelled cells employing positive contrast in vivo MR imaging methods in a burn mouse model in a non-invasive way has been the scope of this study. The consequences have direct implications for monitoring labeled stem cells at some stage in wound healing. We suggest that our approach can be used in clinical trials in molecular and regenerative medicine.

Understanding cross-polarization (CP) NMR experiments through dipolar truncation.

A theoretical model based on the phenomenon of dipolar truncation is proposed to explain the nuances of polarization transfer from abundant to less-abundant nuclei in cross-polarization (CP) NMR experiments. Specifically, the transfer of polarization from protons to carbons (in solids) in strongly coupled systems is described in terms of effective Hamiltonians based on dipolar truncation. Through suitable model spin systems, the important role of dipolar truncation in the propagation of spin polarization in CP experiments is outlined. We believe that the analytic theory presented herein provides a convenient framework for modeling polarization transfer in strongly coupled systems.