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

An indirect method for in vivo T 2 mapping of 13 C–labeled metabolites using T 2 and T 2 * information of water protons obtained a priori is proposed. The T 2 values of 13 C metabolites are inferred using the relationship to T 2 ′ of coexisting 1 H and the T 2 * of 13 C metabolites, which is measured using routine hyperpolarized 13 C 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 13 C T 2 * estimation from the 13 C 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 13 C T 2 values within typical experimental settings. The in vivo studies found that the estimated T 2 of [1‐ 13 C] 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 13 C CSI and can potentially be used with time resolved fast CSI.