title: [Field perturbations by magnetic dipoles as a model for magnetically labelled cells in MRI].
abstract: Due to the creation of intense local magnetic fields, iron oxide nanoparticles are used as a contrast agent to produce signal loss in Magnetic Resonance Imaging (MRI) in regions where labelled cells have migrated.
  
  
  OBJECTIVE
  To study effects of the intracellular distribution of magnetic moments on the extracellular magnetic field by means of numerical simulations.
  
  
  METHODS
  Various geometries of intracellular particle distributions were scrutinized and the extracellular field distortions were computed. The total magnetic moment of a labelled cell was assigned to various magnetic subcompartments. The implications on the intravoxel frequency distribution and the static MR signal decay were assessed.
  
  
  RESULTS
  The extracellular field perturbation was affected by the intracellular particle distribution only in close proximity to the labelled cell. With increasing distance from the labelled cell, the effects of the intracellular particle distribution were less pronounced. The intravoxel frequency distribution induced by a single labelled cell was non-lorentzian.
  
  
  CONCLUSIONS
  The magnetic fields created by an iron loaded cell are sensitive to the intracellular distribution of nanoparticles only in close proximity to the cell. Far from the cell the field perturbation cannot be distinguished from the magnetic dipole field produced by a magnetic sphere with the same total magnetic moment.
authors.affiliation: Sektion für Experimentelle Radiologie, Abteilung für Radiologische Diagnostik, Universitätsklinikum Tübingen. Joerg.Pintaske@med.uni-tuebingen.de
authors.forename: Jörg
authors.initials: J
authors.lastname: Pintaske
authors.forename: Bernd
authors.initials: B
authors.lastname: Müller-Bierl
authors.forename: Fritz
authors.initials: F
authors.lastname: Schick
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics; D008854:Microscopy, Electron; D013347:Subcellular Fractions / Q000648:ultrastructure*