The present invention relates to a particle composition for use as a contrasting agent in medical imaging such as Magnetic Resonance Imaging (MRI), the particle composition comprising: a metal containing compound comprises at least one metal complexed with at least one metal chelating agent wherein the metal chelating agent is adapted to bind to one or more protein molecules to thereby allow or enhance visibility of the protein molecules under the medical imaging. The present invention further relates to a diagnostic agent for use in magnetic resonance imaging (MRI) comprising the above described particle composition and a method of preparing thereof.
