title: The Effect of Inversion Time on the Relationship Between Iron Oxide Nanoparticles Concentration and Signal Intensity in T1-Weighted MR Images.
abstract: BACKGROUND
  Magnetic nanoparticles have been widely applied in recent years for biomedical applications. Signal intensity (SI) of magnetic resonance (MR) images depends on the concentration of nanoparticles. It is important to find the minimum concentration of iron oxide nanoparticles that produces maximum SI and determines the minimum injection dose for clinical studies.
  
  
  OBJECTIVE
  This study was performed to determine the relationship between the iron oxide nanoparticle concentration and SI using inversion recovery (IR) sequence in T1-weighted MR images.
  
  
  METHODS
  Different concentrations of carboxydextran-coated iron oxide nanoparticles 20 nm in size were prepared. In vitro MR imaging was performed with inversion times (TI) of 100-400 ms (interval of 20 ms) and IR Turbo-FLASH (Turbo fast low angle shot) pulse sequence using a 1.5 T MRI system. Then the SI produced by each concentration of nanoparticles was measured and the minimum nanoparticle concentration that led to the maximum SI was determined. Coil non-uniformity was also considered for measuring the accurate SI of each image.
  
  
  RESULTS
  The results indicate that SI depended on the concentration of nanoparticles and TI. In addition, SI increased by increasing the TIs ranging from 200 to 400 ms for all studied concentrations. The linear relationship between the nanoparticle concentrations and SI that gave a square correlation coefficient (R(2)) equal to 0.99 was seen up to 76.83 µmol Fe/L in 400 ms for long TI and 239.16 µmol Fe/L in 200 ms for short TI.
  
  
  CONCLUSIONS
  TI is an important parameter to consider in the relationship between SI and nanoparticle concentrations. An increase in TI leads to a decrease in the range of linearity.
authors.affiliation: Department of Medical Physics, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran ; Student Research Committee, School of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran.
authors.forename: Hodaiseh
authors.initials: H
authors.lastname: Saharkhiz
authors.affiliation: Department of Radiology, School of Paramedicine, Tabriz University of Medical Sciences, Tabriz, Iran.
authors.forename: Nahideh
authors.initials: N
authors.lastname: Gharehaghaji
authors.affiliation: Department of Radiology, School of Paramedicine, Tabriz University of Medical Sciences, Tabriz, Iran.
authors.forename: Mahmood
authors.initials: M
authors.lastname: Nazarpoor
authors.affiliation: Department of Medical Physics, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran.
authors.forename: Asghar
authors.initials: A
authors.lastname: Mesbahi
authors.affiliation: Department of Radiology, School of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran.
authors.forename: Masoud
authors.initials: M
authors.lastname: Pourissa
keywords: Ferrosoferric Oxide; Inversion Recovery; Magnetic Resonance Imaging; Nanoparticles