5 research outputs found
Radical-induced hetero-nuclear mixing and low-field C relaxation in solid pyruvic acid
Radicals serve as a source of polarization in dynamic nuclear polarization, but may also act as polarization sink, in particular at low field. Additionally, if the couplings between the electron spins and different nuclear reservoirs are stronger than any of the reservoirs’ couplings to the lattice, radicals can mediate hetero-nuclear polarization transfer. Here, we report radical-enhanced C relaxation in pyruvic acid doped with trityl. Up to 40 K, we find a linear carbon field dependence between 5 mT and 2 T. We model the dependence quantitatively, and find that the presence of trityl accelerates direct hetero-nuclear polarization transfer at low fields, while at higher fields C relaxation is diffusion limited. Measurements of hetero-nuclear polarization transfer up to 600 mT confirm the predicted radical-mediated proton–carbon mixing
Radical-Induced Low-Field 1H Relaxation in Solid Pyruvic Acid Doped with Trityl-OX063
In dynamic nuclear polarization (DNP), radicals such as trityl provide a source for high nuclear spin polarization. Conversely, during the low-field transfer of hyperpolarized solids, the radicals’ dipolar or Non-Zeeman reservoir may act as a powerful nuclear polarization sink. Here, we report the low-temperature proton spin relaxation in pyruvic acid doped with trityl, for fields from 5 mT to 2 T. We estimate the heat capacity of the radical Non-Zeeman reservoir experimentally and show that a recent formalism by Wenckebach yields a parameter-free, yet quantitative model for the entire field range
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Deuterium Metabolic Imaging of Alzheimer Disease at 3-T Magnetic Field Strength: A Pilot Case-Control Study
Background: Impaired glucose metabolism is characteristic of several dementia types, preceding cognitive symptoms and structural brain changes. Reduced glucose uptake detection in specific brain regions using 18F-fluorodeoxyglucose-PET (18F-FDG-PET) is a valuable diagnostic marker in Alzheimer’s disease (AD). However, 18F-FDG-PET use in clinical practice may be limited by equipment availability and high cost.
Purpose: To test the feasibility of using MRI-based deuterium metabolic imaging (DMI) at a clinical magnetic-field strength (3 T) to detect and localize changes in glucose and its metabolites in patients with a clinical diagnosis of AD.
Materials and Methods: Participants were recruited for this prospective case‒control pilot study between March 2021 and February 2023. DMI was performed at 3 T using a custom birdcage head coil following oral administration of deuterium-labeled glucose (0.75 g/kg). Unlocalized whole-brain magnetic resonance spectroscopy (MRS) and 3D magnetic resonance spectroscopic images (MRSI, cubic 3.2 cm voxel) were acquired. Ratios of 2H-glucose, 2H-glutamate/glutamine (2H-Glx) and 2H-lactate spectroscopic peak signals to 2H-water peak signal were calculated for the whole-brain MRS, and for individual MRSI voxels.
Results: A total of 19 participants, including 10 participants with AD (mean age, 68 years ±5 [SD]; 8 males) and 9 cognitively healthy control participants (mean age, 70 years ± 6 [SD]; 6 males) were evaluated. Whole-brain spectra demonstrated a reduced ratio of the peak 2H-Glx to 2H-glucose signals in participants with AD compared with control participants (0.41±0.09 vs. 0.58±0.20, P=.04), suggesting an impairment of oxidative glucose metabolism in AD. However, there was no evidence of localization of these changes to the expected regions of metabolic impairment on MRSI presumably due to insufficient spatial resolution.
Conclusion: DMI at 3 T demonstrated impairment of oxidative glucose metabolism in patients with Alzheimer’s disease but no evidence of regional signal differences.Evelyn Trus
Radical-induced Hetero-Nuclear Mixing and Low-field C Relaxation in Solid Pyruvic Acid
Radicals serve as source in dynamic nuclear polarization, but may also act as
polarization sink. If the coupling between the electron spins and different
nuclear reservoirs is stronger than any of the reservoirs' couplings to the
lattice, radicals can mediate hetero-nuclear mixing. Here, we report
radical-enhanced C relaxation in pyruvic acid doped with trityl. We find
a linear dependence of the carbon on field between 5 mT and 2 T. We
extend a model, employed previously for protons, to carbon, and predict
efficient proton-carbon mixing via the radical Non-Zeeman reservoir, for fields
from 20 mT to beyond 1 T. Discrepancies between the observed carbon relaxation
and the model are attributed to enhanced direct hetero-nuclear mixing due to
trityl-induced linebroadening, and a field-dependent carbon diffusion from the
radical vicinity to the bulk. Measurements of hetero-nuclear polarization
transfer up to 600 mT confirm the predicted mixing as well as both effects
inferred from the relaxation analysis.Comment: 6 pages, 3 figure
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Deuterium metabolic imaging and hyperpolarized 13C-MRI of the normal human brain at clinical field strength reveals differential cerebral metabolism.
Deuterium metabolic imaging (DMI) and hyperpolarized 13C-pyruvate MRI (13C-HPMRI) are two emerging methods for non-invasive and non-ionizing imaging of tissue metabolism. Imaging cerebral metabolism has potential applications in cancer, neurodegeneration, multiple sclerosis, traumatic brain injury, stroke, and inborn errors of metabolism. Here we directly compare these two non-invasive methods at 3 T for the first time in humans and show how they simultaneously probe both oxidative and non-oxidative metabolism. DMI was undertaken 1-2 h after oral administration of [6,6'-2H2]glucose, and 13C-MRI was performed immediately following intravenous injection of hyperpolarized [1-13C]pyruvate in ten and nine normal volunteers within each arm respectively. DMI was used to generate maps of deuterium-labelled water, glucose, lactate, and glutamate/glutamine (Glx) and the spectral separation demonstrated that DMI is feasible at 3 T. 13C-HPMRI generated maps of hyperpolarized carbon-13 labelled pyruvate, lactate, and bicarbonate. The ratio of 13C-lactate/13C-bicarbonate (mean 3.7 ± 1.2) acquired with 13C-HPMRI was higher than the equivalent 2H-lactate/2H-Glx ratio (mean 0.18 ± 0.09) acquired using DMI. These differences can be explained by the route of administering each probe, the timing of imaging after ingestion or injection, as well as the biological differences in cerebral uptake and cellular physiology between the two molecules. The results demonstrate these two metabolic imaging methods provide different yet complementary readouts of oxidative and reductive metabolism within a clinically feasible timescale. Furthermore, as DMI was undertaken at a clinical field strength within a ten-minute scan time, it demonstrates its potential as a routine clinical tool in the future