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Magnetic Resonance Visualization of Pancreatic Islets Labeled by PARACEST Contrast Agents at 4.7 T

 Andrea Gálisová, Daniel Jirák, Tereza Krchová, Vít Herynek, Eva Fábryová, Jan Kotek and Milan Hájek  

Introduction: Monitoring of Pancreatic Islets (PIs) after their transplantation could provide important data related to diabetes treatment; however their visualization is conditioned by the contrast agent use. The aim of this study was to label and visualize PIs labeled by the contrast agents based on Chemical Exchange Saturation Transfer (CEST) owing an advantage of contrast switching on/off and simultaneous visualization of differently treated cell population in one MR experiment.
1.2 Material and methods: Two paramagnetic chelates with europium Eu-DO3A-ae and ytterbium Yb-DO3A-ae were tested for labeling of PIs by pinocytosis and microporation. The toxicity, labeling efficacy and detection threshold were assessed for each agent. In vitro MR imaging of the labeled islets was performed on a 4.7 T scanner using a modified turbo spin-echo (RARE) sequence.
1.3 Results: The sufficient labeling efficacy was observed only by using high agent concentration compromising islet viability. The microporation procedure was not effective for islet labeling because of its invasive nature. The islets labeled by pinocytosis were visualized in a phantom by CEST imaging, however, after a long acquisition time at 4.7 T.
1.4 Conclusion: The low sensitivity of detection and impaired cellular viability of the pancreatic islets labeled by the novel CEST contrast agents represent a challenge for the further implementation of these probes as exogenous cellular labels.