In vivo quantification of magnetically labelled cells by MRI relaxometry

Cellular MRI, which visualizes magnetically labelled cells (cells*), is an active research field for in vivo cell therapy and tracking. The simultaneous relaxation rate measurements (R2*, R2, R1) are the basis of a quantitative cellular MRI method proposed here. U937 cells were labelled with Molday ION Rhodamine B, a bi‐functional superparamagnetic and fluorescent nanoparticle (U937*). U937* viability and proliferation were not affected in vitro. In vitro relaxometry was performed in a cell concentration range of [2.5 × 104–108] cells/mL. These measurements show the existence of complementary cell concentration intervals where these rates vary linearly. The juxtaposition of these intervals delineates a wide cell concentration range over which one of the relaxation rates in a voxel of an in vivo image can be converted into an absolute cell concentration. The linear regime was found at high concentrations for R1 in the range of [106– 2 × 108] cells/mL, at intermediate concentrations for R2 in [2.5 × 105– 5 × 107] cells/mL and at low concentrations for R2* in [8 × 104– 5 × 106] cells/mL. In vivo relaxometry was performed in a longitudinal study, with labelled U937 cells injected into a U87 glioma mouse model. Using in vitro data, maps of in vivo U937* concentrations were obtained by converting one of the in vivo relaxation rates to cell concentration maps. MRI results were compared with the corresponding optical images of the same br...

Source: Contrast Media and Molecular Imaging - August 31, 2016 Category: Radiology Authors: Ulysse Gimenez, H élène Lajous, Michèle El Atifi, Marie Bidart, Vincent Auboiroux, Pascal Henry Fries, François Berger, Hana Lahrech Tags: Full paper Source Type: research