Superparamagnetic iron oxide contrast agents: physicochemical characteristics and applications in MR imaging

Abstract

Superparamagnetic iron oxide MR imaging contrast agents have been the subjects of extensive research over the past decade. The iron oxide particle size of these contrast agents varies widely, and influences their physicochemical and pharmacokinetic properties, and thus clinical application. Superparamagnetic agents enhance both T1 and T2/T2* relaxation. In most situations it is their significant capacity to reduce the T2/T2* relaxation time to be utilized. The T1 relaxivity can be improved (and the T2/T2* effect can be reduced) using small particles and T1-weighted imaging sequences. Large iron oxide particles are used for bowel contrast [AMI-121 (i.e. Lumirem and Gastromark) and OMP (i.e. Abdoscan), mean diameter no less than 300 nm] and liver/spleen imaging [AMI-25 (i.e. Endorem and Feridex IV, diameter 80-150 nm); SHU 555A (i.e. Resovist, mean diameter 60 nm)]. Smaller iron oxide particles are selected for lymph node imaging [AMI-227 (i.e. Sinerem and Combidex, diameter 20-40 nm)], bone marrow imaging (AMI-227), perfusion imaging [NC100150 (i.e. Clariscan, mean diameter 20 nm)] and MR angiography (NC100150). Even smaller monocrystalline iron oxide nanoparticles are under research for receptor-directed MR imaging and magnetically labeled cell probe MR imaging. Iron oxide particles for bowel contrast are coated with insoluble material, and all iron oxide particles for intravenous injection are biodegradable. Superparamagnetic agents open up an important field for research in MR imaging.

Superparamagnetic Iron Oxide Nanoparticle Probes for Molecular Imaging

“…Larger diameters are available and are useful in such enterprises as cell tracking 134,58 and separation, 73 cell rheology and membrane deformation, 38,151 and as contrast agents for the gastrointestinal tract, 54 but have limited functionality in molecular imaging applications due to their limited accessibility to the neo-and microvasculature. Categories of SPIO, based on their overall diameter (including iron oxide core and hydrated coating), are noted in the literature 152 as oral-SPIO at between 300 nm and 3.5 µm; standard SPIO (SS-PIO) at approximately 60-150 nm; ultrasmall SPIO (US-PIO) of approximately 10-40 nm 156 ; and monocrystalline iron oxide nanoparticles (MION-a subset of USPIO 34 ) of approximately 10-30 nm. 135,158 MION nanoparticles are so named to underline the single crystal nature of their core.…”

Bifunctional Gold Nanoshells with a Superparamagnetic Iron Oxide−Silica Core Suitable for Both MR Imaging and Photothermal Therapy

“…Since SPIO nanoparticles are effective T 2 MRI contrast agents 7 , 8 , we evaluated the T 2 relaxation of SPIO-Au nanoshells. The relaxivity data measured at 4.7T in water showed a high r 2 value of 152 S -1 per mM of Fe 2 O 3 , a very low r 1 value of 0.65 S -1 mM -1 , and thus a high r 2 /r 1 ratio of 234.…”

“…Another class of inorganic nanoparticles, superparamagnetic iron oxide (SPIO) nanoparticles, have shown great promise in magnetic resonance imaging (MRI) 7 , 8 . SPIO nanoparticles have a high transverse relaxivity, r 2 , which results in negative contrast on T 2 -weighted images.…”

In vivo tracking of genetically engineered, anti-HER2/neu directed natural killer cells to HER2/neu positive mammary tumors with magnetic resonance imaging

“…Ferumoxides (Endorem ® ; Laboratoire Guerbet, Aulnay-sous-Bois, France and Ferridex ™ ; Berlex Laboratories, USA) are colloid based superparamagnetic iron oxide particles (SPIO) with an R2/R1 relaxivity ratio (L x mmol -1 x sec -1 ) of 160/40 and a diameter of 120-180 nm, mean 150 nm (29)(30)(31).…”