Paramagnetic nanoparticles as potential MRI contrast agents: characterization, NMR relaxation, simulations and theory
Paramagnetic nanoparticles, mainly rare earth oxides and hydroxides, have been produced these last few years for use as MRI contrast agents. They could become an interesting alternative to iron oxide particles. However, their relaxation properties are not well understood.
Materials and methods
Magnetometry, 1H and 2H NMR relaxation results at different magnetic fields and electron paramagnetic resonance are used to investigate the relaxation induced by paramagnetic particles. When combined with computer simulations of transverse relaxation, they allow an accurate description of the relaxation induced by paramagnetic particles.
For gadolinium hydroxide particles, both T1 and T2 relaxation are due to a chemical exchange of protons between the particle surface and bulk water, called inner sphere relaxation. The inner sphere is also responsible for T1 relaxation of dysprosium, holmium, terbium and erbium containing particles. However, for these latter compounds, T2 relaxation is caused by water diffusion in the field inhomogeneities created by the magnetic particle, the outer-sphere relaxation mechanism. The different relaxation behaviors are caused by different electron relaxation times (estimated by electron paramagnetic resonance).
These findings may allow tailoring paramagnetic particles: ultrasmall gadolinium oxide and hydroxide particles for T1 contrast agents, with shapes ensuring the highest surface-to-volume ratio. All the other compounds present interesting T2 relaxation performance at high fields. These results are in agreement with computer simulations and theoretical predictions of the outer-sphere and static dephasing regime theories. The T2 efficiency would be optimum for spherical particles of 40–50 nm radius.
KeywordsNanoparticles Paramagnetic Contrast agents MRI Relaxation Simulation Relaxation theory
- 6.Arrais A, Botta M, Avedano S, Giovenzana GB, Gianolio E, Boccaleri E, Stanghellini PL, Aime S (2008) Carbon coated microshells containing nanosized Gd(III) oxidic phases for multiple bio-medical applications. Chem Commun (45):5936–5938Google Scholar
- 21.Petoral RM, Söderlind F, Klasson A, Suska A, Fortin MA, Abrikossova N, Selegård L, Käll P-O, Engström M, Uvdal K (2009) Synthesis and characterization of Tb3+-doped Gd2O3 nanocrystals: a bifunctional material with combined fluorescent labeling and MRI contrast agent properties. J Phys Chem C 113:6913–6920CrossRefGoogle Scholar
- 30.Néel L (1948) Magnetic properties of ferrites: ferrimagnetism and antiferromagnetism. Ann Phys Paris 3:137–198Google Scholar
- 32.Cheung ENM, Alvares RDA, Oakden W, Chaudhary R, Hill ML, Pichaandi J, Mo GCH, Yip C, Macdonald PM, Stanisz GJ, van Veggel FCJM, Cheung RSP (2010) Polymer-stabilized lanthanide fluoride nanoparticle aggregates as contrast agents for magnetic resonance imaging and computed tomography. Chem Mater 22:4728–4739CrossRefGoogle Scholar
- 35.Park JH, Baek MJ, Choi ES, Woo S, Kim JH, Kim TJ, Jung JC, Chae KS, Chang Y, Lee GH (2009) Paramagnetic ultrasmall gadolinium oxide nanoparticles as advanced T1 MRI contrast agent: account for large longitudinal relaxivity, optimal particle diameter, and in vivo T1 MR images. ACS Nano 3:3663–3669PubMedCrossRefGoogle Scholar
- 44.(1977) Handbook of chemistry and physics. CRC Press, ClevelandGoogle Scholar
- 46.Mc Connel J (1987) The theory of nuclear magnetic relaxation in liquids. Cambridge university press, CambridgeGoogle Scholar
- 56.Abragam A, Bleaney B (1970) Electron paramagnetic resonance. Clarendon press, OxfordGoogle Scholar