title: Spin-lock MR enhances the detection sensitivity of superparamagnetic iron oxide particles.
abstract: OBJECTIVE
  To evaluate spin-lock MR for detecting superparamagnetic iron oxides and compare the detection sensitivity of quantitative T1ρ with T2 imaging.
  
  
  METHODS
  In vitro experiments were performed to investigate the influence of iron oxide particle size and composition on T1ρ . These comprise T1ρ and T2 measurements (B0 = 1.41T) of agar (2%) with concentration ranges of three different iron oxide nanoparticles (IONs) (Sinerem, Resovist, and ION-Micelle) and microparticles of iron oxide (MPIO). T1ρ dispersion was measured for a range of spin-lock amplitudes (γB1 = 6.5-91 kHz). Under relevant in vivo conditions (B0 = 9.4T; γB1 = 100-1500 Hz), T1ρ and T2 mapping of the liver was performed in seven mice pre- and 24 h postinjection of Sinerem.
  
  
  RESULTS
  Addition of iron oxide nanoparticles decreased T1ρ as well as the native T1ρ dispersion of agar, leading to increased contrast at high spin-lock amplitudes. Changes of T1ρ were highly linear with iron concentration and much larger than T2 changes. MPIO did not show this effect. In vivo, a decrease of T1ρ was observed with no clear influence on T1ρ dispersion.
  
  
  CONCLUSIONS
  By suppression of T1ρ dispersion, iron oxide nanoparticles cause enhanced T1ρ contrast compared to T2 . The underlying mechanism appears to be loss of lock. Spin-lock MR is therefore a promising technique for sensitive detection of iron oxide contrast agents.
authors.affiliation: Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
authors.forename: Rik P M
authors.initials: RP
authors.lastname: Moonen
authors.affiliation: Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.|Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Pieternel
authors.initials: P
authors.lastname: van der Tol
authors.affiliation: Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
authors.forename: Stefanie J C G
authors.initials: SJ
authors.lastname: Hectors
authors.affiliation: Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
authors.forename: Lucas W E
authors.initials: LW
authors.lastname: Starmans
authors.affiliation: Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
authors.forename: Klaas
authors.initials: K
authors.lastname: Nicolay
authors.affiliation: Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.|Biomedical Engineering and Physics, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Gustav J
authors.initials: GJ
authors.lastname: Strijkers
mesh_terms: D003287:Contrast Media / Q000032:analysis / Q000737:chemistry; D003911:Dextrans / Q000032:analysis* / Q000737:chemistry / Q000648:ultrastructure*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D058185:Magnetite Nanoparticles / Q000032:analysis* / Q000737:chemistry / Q000648:ultrastructure*; D008422:Materials Testing; D057054:Molecular Imaging / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013113:Spin Labels
chemical_list: D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; D013113:Spin Labels; C097921:ferumoxtran-10
keywords: Spin-lock MR; T1ρ contrast agent; T1ρ dispersion; iron oxide nanoparticles; rotating frame relaxation; superparamagnetic iron oxide particles