In vivo visualization of cells labeled with superparamagnetic iron oxides by a sub-millisecond gradient echo sequence
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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.
Materials and 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.
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.
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.
KeywordsVariable echo time 3T MRI SPIO Pancreatic islets Diabetes Positive contrast
The study was supported by the grant project (Ministry of Health, Czech Republic) for development of research organization 00023001 (IKEM, Prague, Czech Republic)—Institutional support and by grant ENCITE—Seventh EU Framework Program, number 201842 and by the Ministry of education, youth and sports of the Czech Republic, IC 7E08102 and by the grant IGA NT/13099 from Ministry of Health of the Czech Republic. This work was supported by Bayer Schering Pharma, of Switzerland. The study sponsor played no role in matters of design, collection, analysis, interpretation of data, and writing of the report. We thank Nicolin Hainc for reading and commenting on the paper.
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