Evidence of multiexponential T2 in rat glioblastoma

The aim of this study was to characterize multiexponential T(2) (MET(2)) relaxation in a rat C6 glioblastoma tumor model. To do this, rats (n = 11) were inoculated with the C6 cells via stereotaxic injection into the brain. Ten days later, MET(2) measurements were performed in vivo using a single-slice, multi-echo spin-echo sequence at 7.0 T. Tumor signal was biexponential in eight animals with a short-lived T(2) component (T(2) = 20.7 +/- 5.4 ms across samples) representing 6.8 +/- 6.2% of the total signal and a long-lived T(2) component (T(2) = 76.4 +/- 9.3 ms) representing the remaining signal fraction. In contrast, signal from contralateral grey matter was consistently monoexponential (T(2) = 48.8 +/- 2.3 ms). Additional ex vivo studies (n = 3) and Monte Carlo simulations showed that the in vivo results were not significantly corrupted by partial volume averaging or noise. The underlying physiological origin of the observed MET(2) components is unknown; however, MET(2) analysis may hold promise as a non-invasive tool for characterizing tumor microenvironment in vivo on a sub-voxel scale.