Crystal size and properties of superparamagnetic iron oxide (SPIO) particles

• Published in: Magnetic resonance imaging Vol. 15; no. 1; pp. 55 - 67
• Main Authors: Sjögren, Carl E., Johansson, Christer, Nævestad, Anne, Sontum, Per C., Briley-Sæbø, Karen, Fahlvik, Anne K.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 1997; Elsevier Science
• Subjects: Biological and medical sciences; Chemical Fractionation; Colloids - chemistry; Contrast Media - chemistry; Crystal size; Crystallography; Ferric Compounds - chemistry; Ferrosoferric Oxide; Heparin - chemistry; Investigative techniques, diagnostic techniques (general aspects); Iron - analysis; Iron - chemistry; Iron oxides; Laser-Doppler Flowmetry; Magnetic Resonance Imaging; Magnetics; Materials Testing; Medical sciences; Microscopy, Electron; Miscellaneous. Technology; Models, Chemical; MR contrast agent; Oxides - chemistry; Radiodiagnosis. Nmr imagery. Nmr spectrometry; Spectrophotometry, Infrared; Spectroscopy, Mossbauer; Sulfur - analysis; Superparamagnetism; Vibration; X-Ray Diffraction; Crystal size; Superparamagnetism; Iron oxides; MR contrast agent; Moessbauer effect; Parameter estimation; Iron oxide; Vibrating sample magnetometer; X ray diffraction; Nuclear magnetic resonance imaging; Magnetization curve; Transmission electron microscopy; Efficiency; Size effect; Medical imagery; Contrast media; Crystalline structure
• ISSN: 0730-725X; 1873-5894
• DOI: 10.1016/S0730-725X(96)00335-9

The properties of a superparamagnetic iron oxide (SPIO) model contrast agent have been studied. The test material, HEP-SPIO, contained iron oxide multicrystal agglomerates coated with heparin, a polyanionic, naturally occurring glycosaminoglycan. Fractionation of the HEP-SPIO suspension showed the existence of colloidally stable particles ranging from approx. 100 nm down to single crystal sizes. The small (<20 nm) particles represented the major number fraction of particles present, but only approx. 2% of the total iron oxide mass. The volume weighted average diameter of the individual iron oxide crystals forming the multicrystal agglomerates was found to be 11–12 nm using transmission electron microscopy and vibrating sample magnetometry (VSM) techniques. Comparable results were obtained with X-ray diffraction and Mössbauer spectroscopy. A number of additional SPIO properties could also be determined on a routine VSM, such as the distribution standard deviation for the log-normal distribution of crystal sizes, the magnetic susceptibility, the magnetic remanence, and the intrinsic magnetization (magnetic moment) of the iron oxide. These parameters are useful tools for evaluation of the magnetic characteristics and contrast efficacy of SPIO contrast agents.