A paramagnetic Solid Lipid Nanoparticle (pSLN) comprising: a lipid core solid up to 55°C, comprising at least a glyceride selected in the group consisting of: a monoglyceride, diglyceride and triglyceride, or mixtures thereof, having a C 12 -C 24 saturated or unsaturated linear and branched alkyl chain, where in the case of a di- and tri-glyceride the alkyl chain can be the same or different, optionally further comprising a saturated or unsaturated fatty acid C 12 -C 22, a fatty acid ester, and mixtures thereof, said solid lipid core surrounded by an amphiphilic component comprising an amphiphilic paramagnetic metal chelating moiety selected from: a diazepine derivative of Formula I and a tetraazocyclododecane of Formula II or salts thereof: wherein: Y is a group of formula Y'-NH- or (Y') 2 -N-, where Y' is selected in the group consisting of: a linear or branched saturated or insaturated C 8 -C 16 alkyl group; a C 1 -C 10 alkyl group interrupted by a phosphate group -O-(HO-P=O)-O- optionally substituted by one or more groups selected from: hydroxy -OH, carboxy -COOR 1, oxycarbonil-(C 8 -C 16)alkyl and oxycarbonil -(C 8 -C 16)alkenyl; where R 1 is hydrogen H or a C 1 -C 4 linear or branched alkyl group; or Y' is a monophosphate ester of a substituted or partially substituted glycerol, having at least one functional group of said glycerol esterified with an aliphatic fatty acid with saturated or unsaturated carbon chains, and the phosphoric acid function is either free or salified with a alkali or earth alkali metal; L is a bivalent linker selected from: aliphatic C 3 -C 10 cyclic and heterocyclic and a C 1 -C 6 alkyl, C 2 -C 6 alkenyl or alkynil, linear or branched group optionally substituted or interrupted with an atom or group selected from: carbonyl -C=O, thiocarbonyl -C=S, amino -NR 1 -, carboxy -COO-, oxy-carbonyl -OCO-, amido -NR 1 CO- or -CONR 1 -, oxygen -O- and sulphur -S-, wherein R 1 is as defined above; R I-IV and R I-III are each, independently a -(C 1 -C 3)alkylcarboxy group, wherein said chelating moiety thereof is complexed to a paramagnetic metal ion selected from the group consisting of: Gd, Mn, Cr, Cu, Fe, Pr, Nd, Sm, Tb, Yb, Dy, Ho and Er, or a salt thereof. a lipid core solid up to 55°C, comprising at least a glyceride selected in the group consisting of: a monoglyceride, diglyceride and triglyceride, or mixtures thereof, having a C 12 -C 24 saturated or unsaturated linear and branched alkyl chain, where in the case of a di- and tri-glyceride the alkyl chain can be the same or different, optionally further comprising a saturated or unsaturated fatty acid C 12 -C 22, a fatty acid ester, and mixtures thereof, said solid lipid core surrounded by an amphiphilic component comprising an amphiphilic paramagnetic metal chelating moiety selected from: a diazepine derivative of Formula I and a tetraazocyclododecane of Formula II or salts thereof: wherein: Y is a group of formula Y'-NH- or (Y') 2 -N-, where Y' is selected in the group consisting of: a linear or branched saturated or insaturated C 8 -C 16 alkyl group; a C 1 -C 10 alkyl group interrupted by a phosphate group -O-(HO-P=O)-O- optionally substituted by one or more groups selected from: hydroxy -OH, carboxy -COOR 1, oxycarbonil-(C 8 -C 16)alkyl and oxycarbonil -(C 8 -C 16)alkenyl; where R 1 is hydrogen H or a C 1 -C 4 linear or branched alkyl group; or Y' is a monophosphate ester of a substituted or partially substituted glycerol, having at least one functional group of said glycerol esterified with an aliphatic fatty acid with saturated or unsaturated carbon chains, and the phosphoric acid function is either free or salified with a alkali or earth alkali metal; L is a bivalent linker selected from: aliphatic C 3 -C 10 cyclic and heterocyclic and a C 1 -C 6 alkyl, C 2 -C 6 alkenyl or alkynil, linear or branched group optionally substituted or interrupted with an atom or group selected from: carbonyl -C=O, thiocarbonyl -C=S, amino -NR 1 -, carboxy -COO-, oxy-carbonyl -OCO-, amido -NR 1 CO- or -CONR 1 -, oxygen -O- and sulphur -S-, wherein R 1 is as defined above; R I-IV and R I-III are each, independently a -(C 1 -C 3)alkylcarboxy group, Y is a group of formula Y'-NH- or (Y') 2 -N-, where Y' is selected in the group consisting of: a linear or branched saturated or insaturated C 8 -C 16 alkyl group; a C 1 -C 10 alkyl group interrupted by a phosphate group -O-(HO-P=O)-O- optionally substituted by one or more groups selected from: hydroxy -OH, carboxy -COOR 1, oxycarbonil-(C 8 -C 16)alkyl and oxycarbonil -(C 8 -C 16)alkenyl; where R 1 is hydrogen H or a C 1 -C 4 linear or branched alkyl group; or Y' is a monophosphate ester of a substituted or partially substituted glycerol, having at least one functional group of said glycerol esterified with an aliphatic fatty acid with saturated or unsaturated carbon chains, and the phosphoric acid function is either free or salified with a alkali or earth alkali metal; L is a bivalent linker selected from: aliphatic C 3 -C 10 cyclic and heterocyclic and a C 1 -C 6 alkyl, C 2 -C 6 alkenyl or alkynil, linear or branched group optionally substituted or interrupted with an atom or group selected from: carbonyl -C=O, thiocarbonyl -C=S, amino -NR 1 -, carboxy -COO-, oxy-carbonyl -OCO-, amido -NR 1 CO- or -CONR 1 -, oxygen -O- and sulphur -S-, wherein R 1 is as defined above; R I-IV and R I-III are each, independently a -(C 1 -C 3)alkylcarboxy group,