Objectives: Regenerative studies on model animals often require invasive techniques such as tissue sampling and histology for visualisation of regenerative processes. These interactions are avoided using non invasive imaging techniques. The internalisation of very small super paramagnetic iron oxide particles (VSOP) in animal cells enable non invasive cell tracking using magnetic resonance imaging (MRI) and can prove useful, when visualising regenerative processes. This study examines the possibility of labelling limited numbers of axolotl blastema cells (aBC) and pig endothelial progenitor cells (pEPC) with VSOP and detecting these in vitro and in vivo using a traditional clinical 1.5 T scanner.
Methods: aBC and pEPG were incubated with VSOP C200 Vitro (Ferropharm) at different concentrations. T1- and T2*-weighted MRI was applied to labelled and control cells in vitro and to cells implanted in live axolotl tail and dead porcine heart, respectively. Cellular iron uptake was determined using inductively coupled plasma optical emission spectrometry (ICP-OES).
Results: T2*-weighted 2D gradient-echo sequences on samples of 10˄5 cells yielded at significant linear correlations between labelling concentration and signal decrease (F-ratio = 36.52, p < 0.0001, R˄2 = 0.16) in vitro. Implanted cells were easily distinguishable as dark spots with negative contrast relative to surrounding tissue. Applying a T1-weighted 2D spin-echo sequence on samples of 10˄6 cells yielded a significant increase in signal intensity of 9.0 % at low concentrations, 8.2 pg Fe/cell, (F-ratio = 30.88, p < 0.0001) in vitro. In vivo, cells labelled at low concentration appeared bright with positive contrast, whereas cells labelled at higher concentration again appeared dark.
Conclusion: aBC and pEPG labelled with VSOP can be detected in 1.5 T MRI. Cells labelled at relatively high concentrations appear dark with less contrast, whereas labelling at low concentrations induces positive contrast.