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

Abstract

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 T2∗s of the HP signals is critical. This study is to measure in vivo cardiac T2∗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. T2∗ 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 T2∗ 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, T2∗ of each metabolite was calculated for left ventricle, right ventricle, and myocardium. Results Cardiac T2∗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, T2∗ of [1‐13C]pyruvate was 108.7 ± 22.6 ms in left ventricle and 129.4 ± 8.9 ms in right ventricle. T2∗ 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. T2∗ 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 T2∗s of HP [1‐13C]pyruvate and products.

Dual‐phase imaging of cardiac metabolism using hyperpolarized pyruvate

“…The HP 13 C data were reconstructed and analyzed using MATLAB (R2020a; MathWorks, Natick, MA) as previously described. 11 Regions of interest of the heart and myocardium at ES and ED were selected from the corresponding multiphase 1 H MRI. The HP signals and ratios of products were quantified in the myocardial regions of interest.…”

“…After positioning the participant in the magnet, a series of multiphase 1 H images with expiration breath‐hold were conducted (FOV = 400 mm, spatial resolution = 2.08 × 2.08 mm, slice thickness = 8 mm, flip angle = 50°, TE/TR = 1.2 ms/3.4 ms, 30 cardiac phases). For HP 13 C imaging, a time‐resolved metabolite‐interleaved dual‐phase imaging sequence that consists of a spectral‐spatial RF pulse 11 and single‐shot spiral readouts was applied for [ 13 C]bicarbonate, [1‐ 13 C]lactate, [1‐ 13 C]alanine, and [1‐ 13 C]pyruvate at ES and ED in an interleaved manner every 1 R‐R, as described in Figure 1 (FOV = 400 mm, spatial resolution = 10 × 10 mm, slice thickness = 30 mm, TE/TR = 21.6 ms/101.6 ms, 2 cardiac phases). For imaging HP products, a variable flip‐angle scheme (, i = 1, 2) was applied to maintain the same effective flip angle between the ES and ED imaging (flip angles = 45° for ES, 90° for ED) 12 .…”

“…A SPINlab system (GE Healthcare) was used to produce HP [1‐ 13 C]pyruvate. The general polarization procedure and targeted pyruvate dose were similar to previous human HP studies 6,11 . For hyperpolarization, each [1‐ 13 C]pyruvate sample was prepared in a clinical fluid path (GE Healthcare).…”

Initial Experience on Hyperpolarized [1-13C]Pyruvate MRI Multicenter Reproducibility—Are Multicenter Trials Feasible?

“…However, the T 2 *-estimation from non-localized spectra introduced additional variation from field inhomogeneities, including from outside the brain, as it only provided global estimates. For future studies, local T 2 * values may be estimated with multi-echo or chemical shift 13 C-imaging [30] or extrapolated from the proton B 0 maps. This would allow more accurate estimation of T 2 * and local corrections.…”

“…However, when comparing different protocols, corrections may be needed, as further underlined by the lower apparent k PL observed in a previous study in healthy volunteers [ 4 ]. In this study, echo time correction was needed to avoid confounding of the metabolic metrics by the different T 2 * of lactate and pyruvate [ 29 , 30 ]. The correction allowed comparison of single and variable resolution data obtained with different readouts and echo times.…”