Characterization and compensation of inhomogeneity artifact in spiral hyperpolarized 13 C imaging of the human heart

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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.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Chen

Reed

et al. 2021

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Dual‐phase imaging of cardiac metabolism using hyperpolarized pyruvate

Malloy

Peña

et al. 2021

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Purpose: Previous cardiac imaging studies using hyperpolarized (HP) [1- 13 C] pyruvate were acquired at end-diastole (ED). Little is known about the interaction between cardiac cycle and metabolite content in the myocardium. In this study, we compared images of HP pyruvate and products at end-systole (ES) and ED.Methods: A dual-phase 13 C MRI sequence was implemented to acquire two sequential HP images within a single cardiac cycle at ES and ED during successive R-R intervals in an interleaved manner. Each healthy volunteer (N = 3) received two injections of HP [1-13 C]pyruvate for the dual-phase imaging on the shortaxis and the vertical long-axis planes. Spatial distribution of HP 13 C metabolites at each cardiac phase was correlated to multiphase 1 H MRI to confirm the mechanical changes. Ratios of myocardial HP metabolites were compared between ES and ED. Segmental analysis was performed on the midcavity short-axis plane. Results:In addition to mechanical changes, metabolic profiles of the heart detected by HP [1-13 C]pyruvate differed between ES and ED. The myocardial signal of [ 13 C]bicarbonate relative to [1-13 C]lactate was significantly smaller at ED than the ratio at ES (p < .05), particularly in mid-anterior and mid-inferoseptal segments. The distinct metabolic profiles in the myocardium likely reflect the technical aspects of the imaging approach such as the coronary flow in addition to the cyclical changes in metabolism. Conclusion:The study demonstrates that metabolic profiles of the heart, measured by HP [1-13 C]pyruvate, are affected by the cardiac cycle in which that the data are acquired.

Considerations for hyperpolarized ¹³C MR at reduced field: Comparing 1.5T versus 3T

Traechtler

Füetterer

Albannay

et al. 2023

In contrast to conventional MR, signal-to-noise ratio (SNR) is not linearly dependent on field strength in hyperpolarized MR, as polarization is generated outside the MR system. Moreover, field inhomogeneity-induced artifacts and other practical limitations associated with field strengths ≥3T are alleviated at lower fields. The potential of hyperpolarized 13 C spectroscopy and imaging at 1.5T versus 3T is demonstrated in silico, in vitro, and in vivo for applications on clinical MR systems. Theory and Methods: Theoretical noise and SNR behavior at different field strengths are investigated based on simulations. A thorough field comparison between 1.5T and 3T is performed using thermal and hyperpolarized 13 C spectroscopy and imaging. Cardiac in vivo data is obtained in pigs using hyperpolarized [1-13 C]pyruvate spectroscopy and imaging at 1.5T and 3T.Results: Based on theoretical considerations and simulations, the SNR of hyperpolarized MR at identical acquisition bandwidths is independent of the field strength for typical coil setups, while adaptively changing the acquisition bandwidth proportional to the static magnetic field allows for net SNR gains of up to 40% at 1.5T compared to 3T. In vitro 13 C data verified these considerations with less than 7% deviation. In vivo feasibility of hyperpolarized [1-13 C]pyruvate dynamic metabolic spectroscopy and imaging at 1.5T is demonstrated in the pig heart with comparable SNR between 1.5T and 3T while B 0 artifacts are noticeably reduced at 1.5T. Conclusion:Hyperpolarized 13 C MR at lower field strengths is favorable in terms of SNR and off-resonance effects, which makes 1.5T a promising alternative to 3T, especially for clinical cardiac metabolic imaging.