**4. Future perspectives**

In the new era of molecular imaging, MRI faces major challenges in accomplishing detection of molecular probes with increased sensitivity and specificity, comparable to other diagnostic techniques (such as PET/SPECT). Currently, 10-100 μmolar sensitivity is attained by MRI in contrast to the established nano- and picomolar sensitivity of PET and SPECT. While a new generation of contrast agents is anticipated to extend current limits shedding new light into cellular and molecular mechanisms, current efforts focus primarily on stem cell technology, cellular tracking, and construction of hybrid PET/MRI systems, as discussed below.
