An oil-in-water nanoemulsion composition for RM, comprising: - an aqueous phase, representing 70 to 90% by weight of the composition, advantageously 75 to 85%, more advantageously 78 to 82% - a lipid phase that it comprises an oil, which represents from 9.5 to 29.5% by weight of the composition, advantageously from 14 to 25%, more advantageously from 17 to 21%, - a surfactant at the interface between the aqueous and lipid phases, the surfactant comprising at least a chelate of an amphiphilic paramagnetic metal, at least one amphiphilic identification ligand and possibly an amphiphilic lipid； - the total surfactant content being comprised by weight with respect to the oil between 4 and 10%, advantageously between 5 and 8%； - the total surfactant content being comprised by weight with respect to the composition between 0.35 and 2.95%, advantageously between 0.5 and 2%； - the oil comprising at least 70%, advantageously at least 80%, advantageously at least 95% by weight, particularly at least 97%, of saturated C6-C18 fatty acids, advantageously C6-C14, more advantageously C6-C10.Composición de nanoemulsión de aceite en agua para RM, que comprende: - una fase acuosa, que representa del 70 al 90 % en peso de la composición, ventajosamente del 75 al 85 %, más ventajosamente del 78 al 82 % - una fase lipídica que comprende un aceite, que representa del 9.5 al 29.5 % en peso de la composición, ventajosamente del 14 al 25 %, más ventajosamente del 17 al 21 %, - un tensioactivo en la interfase entre las fases acuosa y lipídica, comprendiendo el tensioactivo al menos un quelato de un metal paramagnético anfifílico, al menos un ligando de identificación anfifílico y eventualmente un lípido anfifílico； - estando comprendido el contenido total en tensioactivo en peso con respecto al aceite entre el 4 y el 10 %, ventajosamente entre el 5 y el 8 %； - estando comprendido el contenido total en tensioactivo en peso con respecto a la composición entre el 0.35 y el 2.95 %, ventajosament
