[Visualization of the enzymatic activity in living systems using activated NMR contrast agents]

New approaches to the development and some applications of novel paramagnetic "sensing" contrast agents designed for specific visualization of the enzymatic activity in living systems are reviewed. The activation of the above sensing agents includes either the cleavage or the synthesis of reactive precursor compounds that recombine with macromolecules with the formation of immobilized or rotationally inhibited paramagnetic cations. This effect results in strong changes of water proton relaxivity. The need in such agents is justified by efforts to utilize magnetic resonance imaging (MRI) for the visualization of fine structures in the living tissue as well as for increasing the molecular specificity of MRI. The review also contains information regarding recent efforts of increasing the sensitivity of MRI to the presence of paramagnetic cations in living systems.