title: Quantifying iron-oxide nanoparticles at high concentration based on longitudinal relaxation using a three-dimensional SWIFT Look-Locker sequence.
abstract: OBJECTIVE
  Iron-oxide nanoparticles (IONPs) have proven utility as contrast agents in many MRI applications. Previous quantitative IONP mapping has been performed using mainly T2 * mapping methods. However, in applications requiring high IONP concentrations, such as magnetic nanoparticles based thermal therapies, conventional pulse sequences are unable to map T2 * because the signal decays too rapidly. In this article, sweep imaging with Fourier transformation (SWIFT) sequence is combined with the Look-Locker method to map T1 of IONPs in high concentrations.
  
  
  METHODS
  T1 values of agar containing IONPs in different concentrations were measured with the SWIFT Look-Locker method and with inversion recovery spectroscopy. Precisions of Look-Locker and variable flip angle (VFA) methods were compared in simulations.
  
  
  RESULTS
  The measured R1 (=1/T1 ) has a linear relationship with IONP concentration up to 53.6 mM of Fe. This concentration exceeds concentrations measured in previous work by almost an order of magnitude. Simulations show SWIFT Look-Locker method is also much less sensitive to B1 inhomogeneity than the VFA method.
  
  
  CONCLUSIONS
  SWIFT Look-Locker can accurately measure T1 of IONP concentrations ≤53.6 mM. By mapping T1 as a function of IONP concentration, IONP distribution maps might be used in the future to plan effective magnetic nanoparticle hyperthermia therapy.
authors.affiliation: Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA; School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Jinjin
authors.initials: J
authors.lastname: Zhang
authors.forename: Ryan
authors.initials: R
authors.lastname: Chamberlain
authors.forename: Michael
authors.initials: M
authors.lastname: Etheridge
authors.forename: Djaudat
authors.initials: D
authors.lastname: Idiyatullin
authors.forename: Curtis
authors.initials: C
authors.lastname: Corum
authors.forename: John
authors.initials: J
authors.lastname: Bischof
authors.forename: Michael
authors.initials: M
authors.lastname: Garwood
mesh_terms: D005583:Fourier Analysis; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D058185:Magnetite Nanoparticles / Q000032:analysis / Q000737:chemistry*; D019047:Phantoms, Imaging; D014867:Water / Q000737:chemistry
chemical_list: D058185:Magnetite Nanoparticles; D014867:Water
keywords: Look-Locker; SWIFT; T1 mapping; iron-oxide nanoparticles; magnetic hyperthermia; positive contrast