Magnetic Resonance Imaging Contrast Agents Based on Iron Oxide Superparamagnetic Ferrofluids

Abstract

Novel systems based on suspensions of colloidal magnetic nanoparticles have been investigated as perspective superparamagnetic contrast agents (CA) for magnetic resonance imaging (MRI). The nanostructures that we have studied contain surfactant-capped magnetite (Fe3O4) inorganic cores with different controlled sizes, ranging from 5.5 to 12 nm. The as-synthesized nanostructures are passivated by hydrophobic surfactants and thus are fully dispersible in nonpolar media. The magnetic nanocrystals have been transferred into aqueous media by a procedure based on the surface intercalation and coating with an amphiphilic polymer shell. The MRI efficiency in contrasting images, i.e., the NMR relaxivities r1 and r2, have been compared with Endorem and Sinerem, commercial superparamagnetic MRI contrast agents. We found that our nanostructures exhibit r1 and r2 relaxivities comparable to those of commercial CA over the whole frequency range. The MRI efficiency of our samples was related to their microstructural and magnetic properties. The transverse relaxivity r2, leading the contrast in “negative” superparamagnetic agents, was found to improve as the diameter of the inorganic core is increased. The NMR relaxometry profile confirmed the nature of the physical mechanisms inducing the increase of the nuclear relaxation rates at low (magnetic anisotropy) and high (Curie relaxation) fields.

Colloidal magnetic nanocrystal clusters: variable length-scale interaction mechanisms, synergetic functionalities and technological advantages

“…In view of the above, the SLP of the aforementioned amine-capped nanocluster system has been found enhanced (1175 W/g, under a field of 21.5 kAm -1 , at 700 kHz) [18] compared to the superparamagnetic commercial product Endorem ® (115 W/g, under a field of 37.3 kA/m, at 500 kHz) [149]. Interestingly, the heating efficiency of the latter is shown to be much reduced compared to superparamagnetic iron oxide nanocrystals, a consequence of its broad size distribution and poorer crystallinity, both originating from its synthesis protocol [150,151].…”

Colloidal assemblies of oriented maghemite nanocrystals and their NMR relaxometric properties

“…19,20 To develop new magnetic compounds for improved MR-based diagnostics, it is desirable to adjust the magnitude of the particle's net magnetic moment μ (because R 2 = 1/T 2  μ 2 , where R 2 is the transverse relaxation rate and T 2 is the spin-spin relaxation time) by controlling the structural characteristics of the nano-object, i.e. the nanoparticle's size, shape, composition and crystallinity.…”

Influence of structural and magnetic properties in the heating performance of multicore bioferrofluids

“…Its structure is similar to our samples with a maghemite core diameter of 5.7 nm and a hydrodynamic size of the beads of 290 nm. 25 Chemicell's FluidMag-UC (labeled as 50 nm by the manufacturer) is a highly concentrated colloidal suspension of magnetite uncoated nanoparticles with mean size 8 nm and agglomerates with mean hydrodynamic size 32 nm. 26 The frequency dependence of the SLP is almost linear for all investigated ferrofluids.…”