The invention provides MRI detectable species of formula (I): Dp-Sn-Nm, wherein D is a MRI detectable moiety; S is a spacer; N is a molecule of a nutrient or pseudo-nutrient; n is 0 or an integer; m is an integer and p is an integer. These compounds are useful for internalising into tumor cells an amount of the MRI detectable moiety that is distinguishably higher than the amount internalised in normal healthy cells thus allowing the diagnosis of tumors. The internalisation of the MRI detectable moiety involves the nutrients or pseudo-nutrients transporting system. Preferred compounds of formula (I) are those wherein D is the chelated complex of a paramagnetic metal ion.