Experimental study on T2 relaxation time of protons in water suspensions of iron-oxide nanoparticles: Cases of composite nanospheres

The experimental transverse relaxivity r2,expr2,exp of protons in water suspensions of spherical SiO2 shelled γ‐Fe2O3γ‐Fe2O3 nanoparticle clusters of different sizes is analyzed based on existing models. It is shown that r2,expr2,exp can be significantly larger than the modelling relaxivity, which may be attributed to nanosphere aggregations.

► The negligible contribution of the fluctuation of the magnetic moments to r2r2 is argued for the case of clusters.
► Several errors in the author's previous publications are corrected.
► Practically, the over-low r2r2 for suspensions of large clusters is still a problem to be resolved.