title: Positive contrast with therapeutic iron nanoparticles at 4.7 T.
abstract: OBJECTIVE
  The purpose of the study was to show the feasibility of a positive contrast technique GRadient echo Acquisition for Superparamagnetic particles with Positive contrast (GRASP), for a specific type of magnetic particles, designed for tumor treatment under MRI monitoring.
  
  
  METHODS
  A simulation study was performed to estimate field inhomogeneity intensities induced by increasing concentrations of particles at different static fields. The GRASP sequence was setup on a 4.7 T Bruker system during an in vitro study. Six mice, included in the in vivo study received particles in the left calf muscle and contrast enhancement values, were measured over three time points, for both negative and positive contrast images.
  
  
  RESULTS
  Comparing values obtained by simulation at 1.5, 3, and 4.7 T, the strongest susceptibility effect was obtained at 4.7 T. Based on simulation and in vitro data, gradient settings were chosen for in vivo imaging. GRASP resulted in bright regions at and around the injection site, and higher enhancement values, compared to standard GRE imaging. Both contrasts were useful for longitudinal follow-up, with a faster decay over time for GRASP.
  
  
  CONCLUSIONS
  The magnetic nanoparticles for drug delivery can be detected using positive contrast. Combining imaging sequences, i.e., negative contrast and susceptibility methods, increased imaging specificity of large magnetic particles and enabled their follow-up for theranostic applications.
authors: CREATIS-LRMN, UMR CNRS 5220, U630 INSERM, Lyon-1 University, Lyon, France. monica.sigovan1@gmail.com
authors: Monica
authors: M
authors: Sigovan
authors: Misara
authors: M
authors: Hamoudeh
authors: Achraf
authors: A
authors: Al Faraj
authors: Delphine
authors: D
authors: Charpigny
authors: Hatem
authors: H
authors: Fessi
authors: Emmanuelle
authors: E
authors: Canet-Soulas
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