title: In vivo visualization of cells labeled with superparamagnetic iron oxides by a sub-millisecond gradient echo sequence.
abstract: OBJECTIVE
  In vivo magnetic resonance imaging (MRI) of iron-labeled pancreatic islets (PIs) transplanted into the liver is still challenging in humans. The aim of this study was to develop and evaluate a double contrast method for the detection of PIs labeled with superparamagnetic iron oxide (SPIO) nanoparticles.
  
  
  METHODS
  A double-echo three-dimensional (3D) spoiled gradient echo sequence was adapted to yield a sub-millisecond first echo time using variable echo times and highly asymmetric Cartesian readout. Positive contrast was achieved by conventional and relative image subtraction. Experiments for cell detection efficiency were performed in vitro on gelatin phantoms, in vivo on a Lewis rat and on a patient 6 months after PI transplantation.
  
  
  RESULTS
  It was demonstrated that the proposed method can be used for the detection of transplanted PIs with positive contrast in vitro and in vivo. For all experiments, relative subtraction yielded comparable and in some cases better contrast than conventional subtraction. For the first time, positive contrast imaging of transplanted human PIs was performed in vivo in patients.
  
  
  CONCLUSIONS
  The proposed method allows 3D data acquisition within a single breath-hold and yields enhanced contrast-to-noise ratios of transplanted SPIO labeled pancreatic islets relative to negative contrast images, therefore providing improved identification.
authors.affiliation: Division of Radiological Physics, Department of Radiology, Clinic of Radiology and Nuclear Medicine, University of Basel Hospital, Petersgraben 4, 4031, Basel, Switzerland, xeni.deligianni@unibas.ch.
authors.forename: Xeni
authors.initials: X
authors.lastname: Deligianni
authors.forename: Daniel
authors.initials: D
authors.lastname: Jirák
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Berková
authors.forename: Milan
authors.initials: M
authors.lastname: Hájek
authors.forename: Klaus
authors.initials: K
authors.lastname: Scheffler
authors.forename: Oliver
authors.initials: O
authors.lastname: Bieri
mesh_terms: D000818:Animals; D003287:Contrast Media / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D005780:Gelatin / Q000737:chemistry; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007515:Islets of Langerhans / Q000166:cytology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics; D008297:Male; D053758:Nanoparticles; D019047:Phantoms, Imaging; D051381:Rats; D011917:Rats, Inbred Lew
chemical_list: D003287:Contrast Media; D005290:Ferric Compounds; C000499:ferric oxide; D005780:Gelatin