Molecular magnetic resonance imaging (mMRI) enables the detection of a protein of interest in vivo, in a noninvasive manner. The general concept of mMRI is to target a contrast agent to a protein of interest, and to perform a contrast-sensitive MRI sequence. Typically, contrast agents are made of a "contrastophore" (the part of the construct responsible for the contrast on the images) and a targeting moiety ("pharmacophore"). Recently, the development of a new family of contrastophore carrying a high payload of iron oxide (micro-sized particles of iron oxide, MPIO) has led to a dramatic increase in the sensitivity of mMRI. Here, we describe the production of targeted MPIO using commercially available reagents and the MRI protocols to allow their detection in vivo.