Dynamic T2* relaxometry of hyperpolarized [1‐13C]pyruvate MRI in the human brain and kidneys.

Purpose: This study aimed to quantify T2*$$ {T}_2^{\ast } $$ for hyperpolarized [1‐13C]pyruvate and metabolites in the healthy human brain and renal cell carcinoma (RCC) patients at 3 T. Methods: Dynamic T2*$$ {T}_2^{\ast } $$ values were measured with a metabolite‐specific multi‐echo spiral sequence. The dynamic T2*$$ {T}_2^{\ast } $$ of [1‐13C]pyruvate, [1‐13C]lactate, and 13C‐bicarbonate was estimated in regions of interest in the whole brain, sinus vein, gray matter, and white matter in healthy volunteers, as well as in kidney tumors and the contralateral healthy kidneys in a separate group of RCC patients. T2*$$ {T}_2^{\ast } $$ was fit using a mono‐exponential function; and metabolism was quantified using pyruvate‐to‐lactate conversion rate maps and lactate‐to‐pyruvate ratio maps, which were compared with and without an estimated T2*$$ {T}_2^{\ast } $$ correction. Results: The T2*$$ {T}_2^{\ast } $$ of pyruvate was shown to vary during the acquisition, whereas the T2*$$ {T}_2^{\ast } $$ of lactate and bicarbonate were relatively constant through time and across the organs studied. The T2*$$ {T}_2^{\ast } $$ of lactate was similar in gray matter (29.75 ± 1.04 ms), white matter (32.89 ± 0.9 ms), healthy kidney (34.61 ± 4.07 ms), and kidney tumor (33.01 ± 2.31 ms); and the T2*$$ {T}_2^{\ast } $$ of bicarbonate was different between whole‐brain (108.17 ± 14.05 ms) and healthy kidney (58.45 ± 6.63 ms). The T2*$$ {T}_2^{\ast } $$ of pyruvate had similar trends in both brain and RCC studies, reducing from 75.56 ± 2.23 ms to 22.24 ± 1.24 ms in the brain and reducing from 122.72 ± 9.86 ms to 57.38 ± 7.65 ms in the kidneys. Conclusion: Multi‐echo dynamic imaging can quantify T2*$$ {T}_2^{\ast } $$ and metabolism in a single integrated acquisition. Clear differences were observed in the T2*$$ {T}_2^{\ast } $$ of metabolites and in their behavior throughout the timecourse. [ABSTRACT FROM AUTHOR]