An indirect method for in vivo T2 mapping of [1‐13C] pyruvate using hyperpolarized 13C CSI

An indirect method for in vivo T2 mapping of 13C–labeled metabolites using T2 and T2* information of water protons obtained a priori is proposed. The T2 values of 13C metabolites are inferred using the relationship to T2′ of coexisting 1H and the T2* of 13C metabolites, which is measured using routine hyperpolarized 13C CSI data. The concept is verified with phantom studies. Simulations were performed to evaluate the extent of T2 estimation accuracy due to errors in the other measurements. Also, bias in the 13C T2* estimation from the 13C 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 13C T2 values within typical experimental settings. The in vivo studies found that the estimated T2 of [1-13C] 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 T2 relaxation times from multiple voxels using conventional hyperpolarized 13C CSI and can potentially be used with time resolved fast CSI.