Cardiac T2∗ measurement of hyperpolarized ¹³C metabolites using metabolite-selective multi-echo spiral imaging

Purpose: Noninvasive imaging with hyperpolarized (HP) pyruvate can capture in vivo cardiac metabolism. For proper quantification of the metabolites and optimization of imaging parameters, understanding MR characteristics such as (Formula presented.) s of the HP signals is critical. This study is to measure in vivo cardiac (Formula presented.) s of HP [1-¹³C]pyruvate and the products in rodents and humans. Methods: A dynamic ¹³C multi-echo spiral imaging sequence that acquires [¹³C]bicarbonate, [1-¹³C]lactate, and [1-¹³C]pyruvate images in an interleaved manner was implemented for a clinical 3 Tesla system. (Formula presented.) of each metabolite was calculated from the multi-echo images by fitting the signal decay of each region of interest mono-exponentially. The performance of measuring (Formula presented.) using the sequence was first validated using a ¹³C phantom and then with rodents following a bolus injection of HP [1-¹³C]pyruvate. In humans, (Formula presented.) of each metabolite was calculated for left ventricle, right ventricle, and myocardium. Results: Cardiac (Formula presented.) s of HP [1-¹³C]pyruvate, [1-¹³C]lactate, and [¹³C]bicarbonate in rodents were measured as 24.9 ± 5.0, 16.4 ± 4.7, and 16.9 ± 3.4 ms, respectively. In humans, (Formula presented.) of [1-¹³C]pyruvate was 108.7 ± 22.6 ms in left ventricle and 129.4 ± 8.9 ms in right ventricle. (Formula presented.) of [1-¹³C]lactate was 40.9 ± 8.3, 44.2 ± 5.5, and 43.7 ± 9.0 ms in left ventricle, right ventricle, and myocardium, respectively. (Formula presented.) of [¹³C]bicarbonate in myocardium was 64.4 ± 2.5 ms. The measurements were reproducible and consistent over time after the pyruvate injection. Conclusion: The proposed metabolite-selective multi-echo spiral imaging sequence reliably measures in vivo cardiac (Formula presented.) s of HP [1-¹³C]pyruvate and products.