Disclosed herein are methods, kits, and compositions for medical imaging relating to fluorescent dyes entrapped in erythrocytes. Also disclosed therein are methods, and compositions further comprising erythrocytes entrapping at least one therapeutically active agent, as well as methods for releasing the entrapped therapeutically active agent(s). Disclosed herein also are methods for preparation of the cells entrapping dye and therapeutically active agent(s) in a freeze-dried form that makes them readily available and easy to use in a clinical environment.
