The invention relates to a pharmaceutically acceptable colloidal suspension, which comprises a microcapsule, which is enclosed by a container (“double container”), wherein the microcapsules comprise magnetic particles in a colloidal solution. The invention further relates to the use of said pharmaceutically acceptable colloidal suspension as an oral contrast medium for the diagnostic investigation of the gastrointestinal tract and the use of the contrast medium to diagnose proliferative diseases, inflammatory and autoimmune diseases, infectious diseases and hormonal and hereditary diseases in the gastrointestinal tract.
