Disclosed are CEST paramagnetic agents comprising a substrate (SH) containing mobile protons bonded to a paramagnetic chelate (SR) containing a metal selected from iron (11) (high-spin configuration), iron (111), cobalt (11), rhodium (11), copper (11), nickel (11), cerium (111), praseodymium (111), neodymium (111), dysprosium (111), erbium (111), terbium (111), holmium (111), thulium (III), ytterbium (III) and europium (111).