11 research outputs found
A robust broadband fat suppressing phaser T2 preparation module for cardiac magnetic resonance imaging at 3T
Purpose: Designing a new T2 preparation (T2-Prep) module in order to
simultaneously provide robust fat suppression and efficient T2 preparation
without requiring an additional fat suppression module for T2-weighted imaging
at 3T. Methods: The tip-down RF pulse of an adiabatic T2 preparation (T2-Prep)
module was replaced by a custom-designed RF excitation pulse that induces a
phase difference between water and fat, resulting in a simultaneous T2
preparation of water signals and the suppression of fat signals at the end of
the module (now called a phaser adiabatic T2-Prep). Using numerical
simulations, in vitro and in vivo ECG-triggered navigator gated acquisitions of
the human heart, the blood, myocardium and fat signal-to-noise ratio and right
coronary artery (RCA) vessel sharpness using this approach were compared
against previously published conventional adiabatic T2-Prep approaches Results:
Numerical simulations predicted an increased fat suppression bandwidth and
decreased sensitivity against transmit magnetic field inhomogeneities using the
proposed approach, while preserving the water T2 preparation capabilities. This
was confirmed by the tissue signals acquired on the phantom and the in vivo
MRA, which show similar blood and myocardium SNR and CNR and significantly
reduced fat SNR compared to the other methods tested. As a result, the RCA
conspicuity was significantly increased and the motion artifacts were visually
decreased. Conclusion: A novel fat-suppressing T2-preparation method was
developed and implemented that demonstrated robust fat suppression and
increased vessel sharpness compared with conventional techniques, while
preserving its T2 preparation capabilities.Comment: 23 pages, 5 figures, submitted to Magnetic Resonance in Medicin
Radical-free hyperpolarized MRI using endogenously-occurring pyruvate analogues and UV-induced nonpersistent radicals
It was demonstrated that nonpersistent radicals can be generated in frozen
solutions of metabolites such as pyruvate by irradiation with ultraviolet (UV)
light, enabling radical-free dissolution DNP. Although pyruvate is endogenous,
an excess of additional pyruvate may perturb metabolic processes, making it
potentially unsuitable as a polarizing agent when studying fatty acids or
carbohydrate metabolism. Therefore, the aim of the study was to characterize
solutions containing endogenously-occurring alternatives to pyruvate as
UV-induced nonpersistent radical precursors for in vivo hyperpolarized MRI. The
metabolites alpha-ketovalerate (AKV) and alpha-ketobutyrate (AKB) are analogues
of pyruvate and were chosen as potential radical precursors. Sample
formulations containing AKV and AKB were studied with UV-visible spectroscopy,
irradiated with UV light, and their nonpersistent radical yields were
quantified with ESR and compared to pyruvate. The addition of 13C labeled
substrates to the sample matrix altered the radical yield of the precursors.
Using AKB increased the 13C-labeled glucose liquid state polarization to 16.3
+/- 1.3% compared with 13.3 +/- 1.5% obtained with pyruvate, and 8.9 +/- 2.1%
with AKV. For [1-13C]butyric acid, polarization levels of 12.1 +/- 1.1% for AKV
and 12.9 +/- 1.7% for AKB were achieved. Hyperpolarized [1-13C]butyrate
metabolism in the heart revealed label incorporation into
[1-13C]acetylcarnitine, [1-13C]acetoacetate, [1-13C]butyrylcarnitine,
[5-13C]glutamate and [5-13C]citrate. This study demonstrates the potential of
AKV and AKB as endogenous polarizing agents for in vivo radical-free
hyperpolarized MRI. UV-induced, nonpersistent radicals generated in endogenous
metabolites enable high polarization without requiring radical filtration, thus
simplifying the quality-control tests in clinical applications.Comment: 38 pages, 5 Tables, 8 Figures, Submitted to NMR in Biomedicin
[13C]bicarbonate labelled from hyperpolarized [1-13C]pyruvate is an in vivo marker of hepatic gluconeogenesis in fasted state.
Funder: EC | EC Seventh Framework Programm | FP7 People: Marie-Curie Actions (FP7-PEOPLE - Specific Programme "People" Implementing the Seventh Framework Programme of the European Community for Research, Technological Development and Demonstration Activities (2007 to 2013)); Grant(s): 264780Hyperpolarized [1-13C]pyruvate enables direct in vivo assessment of real-time liver enzymatic activities by 13C magnetic resonance. However, the technique usually requires the injection of a highly supraphysiological dose of pyruvate. We herein demonstrate that liver metabolism can be measured in vivo with hyperpolarized [1-13C]pyruvate administered at two- to three-fold the basal plasma concentration. The flux through pyruvate dehydrogenase, assessed by 13C-labeling of bicarbonate in the fed condition, was found to be saturated or partially inhibited by supraphysiological doses of hyperpolarized [1-13C]pyruvate. The [13C]bicarbonate signal detected in the liver of fasted rats nearly vanished after treatment with a phosphoenolpyruvate carboxykinase (PEPCK) inhibitor, indicating that the signal originates from the flux through PEPCK. In addition, the normalized [13C]bicarbonate signal in fasted untreated animals is dose independent across a 10-fold range, highlighting that PEPCK and pyruvate carboxylase are not saturated and that hepatic gluconeogenesis can be directly probed in vivo with hyperpolarized [1-13C]pyruvate