CRYSTAL SIZE AND PROPERTIES OF SUPERPARAMAGNETIC IRON-OXIDE (SPIO) PARTICLES

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, na turally occurring glycosaminoglycan, Fractionation of the HEP-SPIO sus pension showed the existence of colloidally stable particles ranging f rom approx, 100 nm down to single crystal sizes, The small (<20 nm) pa rticles represented the major number fraction of particles present, bu t only approx, 2% of the total iron oxide mass, The volume weighted av erage diameter of the individual iron oxide crystals forming the multi crystal agglomerates was found to be 11-12 nm using transmission elect ron microscopy and vibrating sample magnetometry (VSM) techniques, Com parable results were obtained with X-ray diffraction and Mossbauer spe ctroscopy, A number of additional SPIO properties could also be determ ined on a routine VSM, such as the distribution standard deviation for the log-normal distribution of crystal sizes, the magnetic susceptibi lity, the magnetic remanence, and the intrinsic magnetization (magneti c moment) of the iron oxide, These parameters are useful tools for eva luation of the magnetic characteristics and contrast efficacy of SPIO contrast agents, (C) 1997 Elsevier Science Inc.