The present invention relates to a composition comprising a shell structure forming a cavity,wherein said shell structure comprises a drug and wherein said composition is associated with at least one contrast agent wherein said shell structure is capable of releasing its contents into the exterior upon the application of an external stimulus and wherein said contrast agent comprises magnetic particles which are capable of being detected by Magnetic Particle Imaging (MPI), wherein at least more than 5% (w/w) of the magnetic particles comprised in said contrast agent have a magnetic moment of at least -18 m 2 A, 10 wherein said magnetic particles are preferably composed of Fe, Co, Ni, Zn or Mn or alloys thereof or oxides of any of these. The present invention further relates to the use of such a composition or a composition comprising a shell structure forming a cavity,wherein said shell structure comprises a drug and wherein said composition is associated with at least one contrast agent, wherein said contrast agent is capable of being detected by MPI and wherein said shell structure is capable of releasing its contents into the exterior upon the application of an external stimulus as a carrier for a controlled delivery of a drug, as well as to a method of data acquisition for the control ofa drug delivery process comprising the detection or localization via MPI of such compositions. In a further aspect the present invention relates to such compositions for treating a pathological condition, wherein the treatment comprises the release of the drug by the application of a stimulus.La présente invention concerne une composition qui comprend une structure denveloppe formant une cavité, ladite structure denveloppe comprenant un médicament et ladite composition étant associée avec au moins un agent de contraste ladite structure denveloppe étant capable de libérer son contenu dans lextérieur lors de lapplication dun stimulus externe et ledit agent de contraste compre
