Detecting response of rat C6 glioma tumors to radiotherapy using hyperpolarized [1-¹³C]pyruvate and ¹³C magnetic resonance spectroscopic imaging

We show here that hyperpolarized [1-¹³C]pyruvate can be used to detect treatment response in a glioma tumor model; a tumor type where detection of response with ¹⁸fluoro-2-deoxyglucose, using positron emission tomography, is limited by the high background signals from normal brain tissue. ¹³C chemical shift images acquired following intravenous injection of hyperpolarized [1-¹³C]pyruvate into rats with implanted C6 gliomas showed significant labeling of lactate within the tumors but comparatively low levels in surrounding brain.Labeled pyruvate was observed at high levels in blood vessels above the brain and from other major vessels elsewhere but was detected at only low levels in tumor and brain.The ratio of hyperpolarized ¹³C label in tumor lactate compared to the maximum pyruvate signal in the blood vessels was decreased from 0.38 ± 0.16 to 0.23 ± 0.13, (a reduction of 34%) by 72 h following whole brain irradiation with 15 Gy.