title: Magnetorelaxometry procedures for quantitative imaging and characterization of magnetic nanoparticles in biomedical applications.
abstract: BACKGROUND
  Quantitative knowledge about the spatial distribution and local environment of magnetic nanoparticles (MNPs) inside an organism is essential for guidance and improvement of biomedical applications such as magnetic hyperthermia and magnetic drug targeting. Magnetorelaxometry (MRX) provides such quantitative information by detecting the magnetic response of MNPs following a fast change in the applied magnetic field.
  
  
  METHODS
  In this article, we review our MRX based procedures that enable both the characterization and the quantitative imaging of MNPs in a biomedical environment.
  
  
  RESULTS
  MRX characterization supported the selection of an MNP system with colloidal stability and suitable cellular MNP uptake. Spatially resolved MRX, a procedure employing multi-channel MRX measurements allowed for in-vivo monitoring of the MNP distribution in a pre-clinical carcinoma animal model. Extending spatially resolved MRX by consecutive magnetization of distinct parts of the sample led to a demonstration of MRX tomography. With this tomography, we reconstructed the three dimensional MNP distribution inside animal sized phantoms with a sensitivity of milligrams of MNPs per cm3. In addition, the targeting efficiency of MNPs in whole blood was assessed using a flow phantom and MRX quantification.
  
  
  CONCLUSIONS
  These MRX based measurement and analysis procedures have substantially supported the development of MNP based biomedical applications.
authors.forename: Maik
authors.initials: M
authors.lastname: Liebl
authors.forename: Frank
authors.initials: F
authors.lastname: Wiekhorst
authors.forename: Dietmar
authors.initials: D
authors.lastname: Eberbeck
authors.forename: Patricia
authors.initials: P
authors.lastname: Radon
authors.forename: Dirk
authors.initials: D
authors.lastname: Gutkelch
authors.forename: Daniel
authors.initials: D
authors.lastname: Baumgarten
authors.forename: Uwe
authors.initials: U
authors.lastname: Steinhoff
authors.forename: Lutz
authors.initials: L
authors.lastname: Trahms
mesh_terms: D003287:Contrast Media / Q000737:chemistry; D007089:Image Enhancement / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D058185:Magnetite Nanoparticles / Q000737:chemistry* / Q000528:radiation effects / Q000648:ultrastructure*; D057054:Molecular Imaging / Q000379:methods*; D010316:Particle Size; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D003287:Contrast Media; D058185:Magnetite Nanoparticles