An indirect method for in vivo T-2 mapping of [1-C-13] pyruvate using hyperpolarized C-13 CSI

Abstract

An indirect method for in vivo T-2 mapping of C-13-labeled metabolites using T-2 and T-2* information of water protons obtained a priori is proposed. The T-2 values of C-13 metabolites are inferred using the relationship to T-2 of coexisting H-1 and the T-2* of C-13 metabolites, which is measured using routine hyperpolarized C-13 CSI data. The concept is verified with phantom studies. Simulations were performed to evaluate the extent of T-2 estimation accuracy due to errors in the other measurements. Also, bias in the C-13 T-2* estimation from the C-13 CSI data was studied. In vivo experiments were performed from the brains of normal rats and a rat with C6 glioma. Simulation results indicate that the proposed method provides accurate and unbiased C-13 T-2 values within typical experimental settings. The in vivo studies found that the estimated T-2 of [1-C-13] pyruvate using the indirect method was longer in tumor than in normal tissues and gave values similar to previous reports. This method can estimate localized T-2 relaxation times from multiple voxels using conventional hyperpolarized C-13 CSI and can potentially be used with time resolved fast CSI.