Magnetic resonance imaging (MRI) is a leading technique enabling medical imaging of the whole body and soft tissues. Cardiovascular related diseases are the first cause of human death worldwide. Better visualization of the blood vascular system could help early diagnosis, better follow up, and treatment adjustment for these diseases. Blood pool contrast agents (BPCAs) that stay for a prolonged period of time in the vascular compartment are needed to enable accurate interpretation of the MR scans of the vasculature. This medical need and lack of BPCAs on the market need to be filled in the following years. In this thesis, three micellar systems have been developed, fully characterized, and tested in vitro and in vivo, intended as BPCAs. Two types of Gadolinium-based micelles were formed with a single multifunctional building block and the third one as mixed micelles system, self-assembled with four building blocks in water. The two first formulations significantly enhanced the signal of the blood vessels in vivo in a mouse model. The third formulation contained a fibrin-targeted moiety for the specific molecular imaging of fibrin clots. Efficient targeting was demonstrated in vitro. The sum of the results warrants further development of Gadolinium-based supramolecular assemblies as contrast agent for MRI and other imaging applications.