title: Positive contrast magnetic resonance imaging of cells labeled with magnetic nanoparticles.
abstract: Contrast agents incorporating superparamagnetic iron-oxide nanoparticles have shown promise as a means to visualize labeled cells using MRI. Labeled cells cause significant signal dephasing due to the magnetic field inhomogeneity induced in water molecules near the cell. With the resulting signal void as the means for detection, the particles behave as a negative contrast agent, which can suffer from partial-volume effects. In this paper, a new method is described for imaging labeled cells with positive contrast. Spectrally selective RF pulses are used to excite and refocus the off-resonance water surrounding the labeled cells so that only the fluid and tissue immediately adjacent to the labeled cells are visible in the image. Phantom, in vitro, and in vivo experiments show the feasibility of the new method. A significant linear correlation (r = 0.87, P < 0.005) between the estimated number of cells and the signal was observed.
authors.affiliation: Department of Electrical Engineering, Stanford University, California, USA. chuck.cunningham@stanford.edu
authors.forename: Charles H
authors.initials: CH
authors.lastname: Cunningham
authors.forename: Takayasu
authors.initials: T
authors.lastname: Arai
authors.forename: Phillip C
authors.initials: PC
authors.lastname: Yang
authors.forename: Michael V
authors.initials: MV
authors.lastname: McConnell
authors.forename: John M
authors.initials: JM
authors.lastname: Pauly
authors.forename: Steven M
authors.initials: SM
authors.lastname: Conolly
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003287:Contrast Media / Q000378:metabolism*; D003911:Dextrans; D004622:Embryo, Mammalian; D005240:Feasibility Studies; D052203:Ferrosoferric Oxide; D066298:In Vitro Techniques; D007501:Iron / Q000378:metabolism*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D058185:Magnetite Nanoparticles; D051379:Mice; D010087:Oxides / Q000378:metabolism*; D019047:Phantoms, Imaging; D013234:Stem Cells / Q000378:metabolism*
chemical_list: D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; D010087:Oxides; D007501:Iron; C065507:ferumoxides; D052203:Ferrosoferric Oxide