Recent technological developments in magnetic resonance (MR) hardware and contrast agents have enabled high resolution of the soft brain tissue in living subjects at the anatomical, functional and molecular levels. MRI is a relatively safe technology that has excellent depth of penetration. Nanoparticle-enhanced MR imaging (MRI) is highly sensitive and it can track neural progenitor cells in vivo after stem cell therapy in preclinical and perhaps clinical disease models. MRI measures the relaxation time of proton spins in tissue water when a magnetic field (B0) is applied; the presence of a contrast agent in the tissue alters the longitudinal (T1) and transverse (T2) relaxation times, or rate of relaxivity (R1 or R2, respectively), and the resulting MR image shows the difference of these parameters.
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