1. A composition comprising a cavity-forming shell structure, wherein said shell structure includes a medicament, and said composition is associated with at least one contrast agent, and where said shell structure is capable of releasing its contents into the outer space under the influence of an external stimulus, and said the contrast agent contains magnetic particles consisting of Fe, Co, Ni, Zn or Mn or from their alloys or oxides of any of these metals or alloys, and more preferably from FeO or Fe O, which can be detected by magnetic particle imaging (HMF), where at least more than 5% (w / w) of the magnetic particles contained in said contrast medium have a magnetic moment of at least 10 m · A, and where at least more than 5 wt.% of said magnetic particles have a magnetization reversal time of less than 10 milliseconds per particle. The composition according to claim 1, wherein said contrast agent is associated with external or internal parts of said shell structure, or with said drug, or is encapsulated in a cavity of said shell structure. The composition according to claim 1, wherein said shell structure is a part of a liposome, a polymersome, a nanocapsule or any mixtures thereof, and preferably contains a heat-sensitive material or a material that is sensitive to pressure increase. The composition of claim 1, wherein said external stimulus is capable of causing pore formation and / or decomposition of said shell structure. The composition of claim 4, wherein said external stimulus is an increase in temperature, a decrease in temperature,1. Композиция, содержащая полость-образующую оболочечную структуру, где указанная оболочечная структура включает лекарственное средство, а указанная композиция связана по меньшей мере с одним контрастным веществом, и где указанная оболочечная структура способна высвобождать свое содержимое во внешнее пространство под действием внешнего стимула, а указанное контрастное вещество содержит магнитные частицы, состоящие из Fe, Co
