Abstract
In this work, we present the synthesis and evaluation of magnetic resonance (MR) properties of novel phosphorus/iron-containing probes for dual (31)P and (1)H MR imaging and spectroscopy (MRI and MRS). The presented probes are composed of biocompatible semitelechelic and multivalent phospho-polymers based on poly(2-methacryloyloxyethyl phosphorylcholine) (pMPC) coordinated with small paramagnetic Fe(3+) ions or superparamagnetic maghemite (γ-Fe(2)O(3)) nanoparticles via deferoxamine group linked to the end or along the polymer chains. All probes provided very short (1)H T(1) and T(2) relaxation times even at low iron concentrations. The presence of iron had a significant impact on the shortening of (31)P relaxation, with the effect being more pronounced for probes based on γ-Fe(2)O(3) and multivalent polymer. While the water-soluble probe having one Fe(3+) ion per polymer chain was satisfactorily visualized by both (31)P-MRS and (31)P-MRI, the probe with multiple Fe(3+) ions could only be detected by (31)P-MRS, and the probes consisting of γ-Fe(2)O(3) nanoparticles could not be imaged by either technique due to their ultra-short (31)P relaxations. In this proof-of-principle study performed on phantoms at a clinically relevant magnetic fields, we demonstrated how the different forms and concentrations of iron affect both the (1)H MR signal of the surrounding water molecules and the (31)P MR signal of the phospho-polymer probe. Thus, this double contrast can be exploited to simultaneously visualize body anatomy and monitor probe biodistribution.