Comparison of hyperpolarized ¹³C and non-hyperpolarized deuterium MRI approaches for imaging cerebral glucose metabolism at 4.7 T

Purpose: The purpose of this study was to directly compare two isotopic metabolic imaging approaches, hyperpolarized (HP) ¹³C MRI and deuterium metabolic imaging (DMI), for imaging specific closely related segments of cerebral glucose metabolism at 4.7 T. Methods: Comparative HP-¹³C and DMI neuroimaging experiments were conducted consecutively in normal rats during the same scanning session. Localized conversions of [1-¹³C]pyruvate and [6,6-²H₂]glucose to their respective downstream metabolic products were measured by spectroscopic imaging, using an identical 2D-CSI sequence with parameters optimized for the respective experiments. To facilitate direct comparison, a pair of substantially equivalent 2.5-cm double-tuned X/¹H RF surface coils was developed. For improved results, multidimensional low-rank reconstruction was applied to denoise the raw DMI data. Results: Localized conversion of HP [1-¹³C]pyruvate to [1-¹³C]lactate, and [6,6-²H₂]glucose to [3,3-²H₂]lactate and Glx-d (glutamate and glutamine), was detected in rat brain by spectroscopic imaging at 4.7 T. The SNR and spatial resolution of HP-¹³C MRI was superior to DMI but limited to a short time window, whereas the lengthy DMI acquisition yielded maps of not only lactate, but also Glx production, albeit with relatively poor spectral discrimination between metabolites at this field strength. Across the individual rats, there was an apparent inverse correlation between cerebral production of HP [1-¹³C]lactate and Glx-d, along with a trend toward increased [3,3-²H₂]lactate. Conclusion: The HP-¹³C MRI and DMI methods are both feasible at 4.7 T and have significant potential for metabolic imaging of specific segments of glucose metabolism.