MR “in vivo” preclinical molecular and cellular imaging

In respect to other molecular imaging modalities such as PET or SPECT, the low sensitivity is the main limitation of the Magnetic Resonance-Molecular Imaging (MRMI) approach. To overcome this limitation the imaging probe for MRMI applications must identify the target with high specificity and should provide sufficiently intense signal enhancement within the imaged volume to be easily distinguishable from un-enhanced tissue. Therefore, the success of a MRMI protocol strongly relies on the amplification effects associated to the accumulation of the agents at the cells of interest. A general route to get this goal consists of using nano-sized systems such as liposome, micelles, microemulsions, polymers etc… able to carry a huge payload of Gd complexes. A straightforward extension of this approach involves the use of naturally occurring nanosized aggregates such as apoferritin and lipoproteins (LDL, HDL). The nanocarriers are then functionalized with the suitable vectors that provide the overall particles with the required recognition capabilities towards the selected cellular target. MRI, with its high spatial resolution is also the technique of choice for the visualization of grafted cells (i.e. stem cells, pancreatic insule, T cells, etc.) in cell-based therapies. Examples of labeling strategies with MRI contrast agents are reported.