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

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 $$ s of the HP signals is critical. This study is to measure in vivo cardiac $$ s of HP [1-¹³ C]pyruvate and the products in rodents and humans.

A dynamic ¹³ C multi-echo spiral imaging sequence that acquires [¹³ C]bicarbonate, [1-¹³ C]lactate, and [1-¹³ C]pyruvate images in an interleaved manner was implemented for a clinical 3 Tesla system. $$ of each metabolite was calculated from the multi-echo images by fitting the signal decay of each region of interest mono-exponentially. The performance of measuring $$ using the sequence was first validated using a ¹³ C phantom and then with rodents following a bolus injection of HP [1-¹³ C]pyruvate. In humans, $$ of each metabolite was calculated for left ventricle, right ventricle, and myocardium.

Cardiac $$ s of HP [1-¹³ C]pyruvate, [1-¹³ C]lactate, and [¹³ C]bicarbonate in rodents were measured as 24.9 ± 5.0, 16.4 ± 4.7, and 16.9 ± 3.4 ms, respectively. In humans, $$ of [1-¹³ C]pyruvate was 108.7 ± 22.6 ms in left ventricle and 129.4 ± 8.9 ms in right ventricle. $$ of [1-¹³ C]lactate was 40.9 ± 8.3, 44.2 ± 5.5, and 43.7 ± 9.0 ms in left ventricle, right ventricle, and myocardium, respectively. $$ of [¹³ C]bicarbonate in myocardium was 64.4 ± 2.5 ms. The measurements were reproducible and consistent over time after the pyruvate injection.

The proposed metabolite-selective multi-echo spiral imaging sequence reliably measures in vivo cardiac $$ s of HP [1-¹³ C]pyruvate and products.