51 research outputs found
Metabolite-specific echo-planar imaging of hyperpolarized [1-- 13 C]pyruvate at 4.7 T
Although hyperpolarization (HP) greatly increases the sensitivity o
Hyperpolarized 13C Spectroscopic Evaluation of Oxidative Stress in a Rodent Model of Steatohepatitis.
Nonalcoholic fatty liver disease (NAFLD) has become highly prevalent, now considered the most common liver disease in the western world. Approximately one-third of patients with NASH develop non-alchoholic steatohepatitis (NASH), histologically defined by lobular and portal inflammation, and accompanied by marked oxidative stress. Patients with NASH are at increased risk for cirrhosis and hepatocellular carcinoma, and diagnosis currently requires invasive biopsy. In animal models of NASH, particularly the methionine-choline deficient (MCD) model, profound changes are seen in redox enzymes and key intracellular antioxidants. To study antioxidant status in NASH non-invasively, we applied the redox probe hyperpolarized [1-13C] dehydroascorbic acid (HP DHA), which is reduced to Vitamin C (VitC) rapidly in the normal liver. In MCD mice, we observed a significant decrease in HP DHA to VitC conversion that accompanied hepatic fat deposition. When these animals were subsequently placed on a normal diet, resonance ratios reverted to those seen in control mice. These findings suggest that HP DHA, a potentially clinically translatable imaging agent, holds special promise in imaging NASH and other metabolic syndromes, to monitor disease progression and response to targeted therapies
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Imaging glutathione depletion in the rat brain using ascorbate-derived hyperpolarized MR and PET probes.
Oxidative stress is a critical feature of several common neurologic disorders. The brain is well adapted to neutralize oxidative injury by maintaining a high steady-state concentration of small-molecule intracellular antioxidants including glutathione in astrocytes and ascorbic acid in neurons. Ascorbate-derived imaging probes for hyperpolarized 13C magnetic resonance spectroscopy and positron emission tomography have been used to study redox changes (antioxidant depletion and reactive oxygen species accumulation) in vivo. In this study, we applied these imaging probes to the normal rat brain and a rat model of glutathione depletion. We first studied hyperpolarized [1-13C]dehydroascorbate in the normal rat brain, demonstrating its robust conversion to [1-13C]vitamin C, consistent with rapid transport of the oxidized form across the blood-brain barrier. We next showed that the kinetic rate of this conversion decreased by nearly 50% after glutathione depletion by diethyl maleate treatment. Finally, we showed that dehydroascorbate labeled for positron emission tomography, namely [1-11C]dehydroascorbate, showed no change in brain signal accumulation after diethyl maleate treatment. These results suggest that hyperpolarized [1-13C]dehydroascorbate may be used to non-invasively detect oxidative stress in common disorders of the brain
Imaging Renal Urea Handling in Rats at Millimeter Resolution using Hyperpolarized Magnetic Resonance Relaxometry
\textit{In vivo} spin spin relaxation time () heterogeneity of
hyperpolarized \textsuperscript{13}C urea in the rat kidney was investigated.
Selective quenching of the vascular hyperpolarized \textsuperscript{13}C signal
with a macromolecular relaxation agent revealed that a long- component of
the \textsuperscript{13}C urea signal originated from the renal extravascular
space, thus allowing the vascular and renal filtrate contrast agent pools of
the \textsuperscript{13}C urea to be distinguished via multi-exponential
analysis. The response to induced diuresis and antidiuresis was performed
with two imaging agents: hyperpolarized \textsuperscript{13}C urea and a
control agent hyperpolarized
bis-1,1-(hydroxymethyl)-1-\textsuperscript{13}C-cyclopropane-.
Large increases in the inner-medullar and papilla were observed with the
former agent and not the latter during antidiuresis suggesting that
relaxometry may be used to monitor the inner-medullary urea transporter (UT)-A1
and UT-A3 mediated urea concentrating process. Two high resolution imaging
techniques - multiple echo time averaging and ultra-long echo time sub-2 mm
resolution 3D imaging - were developed to exploit the particularly long
relaxation times observed
Current Methods for Hyperpolarized [1-13C]pyruvate MRI Human Studies
MRI with hyperpolarized (HP) 13C agents, also known as HP 13C MRI, can
measure processes such as localized metabolism that is altered in numerous
cancers, liver, heart, kidney diseases, and more. It has been translated into
human studies during the past 10 years, with recent rapid growth in studies
largely based on increasing availability of hyperpolarized agent preparation
methods suitable for use in humans. This paper aims to capture the current
successful practices for HP MRI human studies with [1-13C]pyruvate - by far the
most commonly used agent, which sits at a key metabolic junction in glycolysis.
The paper is divided into four major topic areas: (1) HP 13C-pyruvate
preparation, (2) MRI system setup and calibrations, (3) data acquisition and
image reconstruction, and (4) data analysis and quantification. In each area,
we identified the key components for a successful study, summarized both
published studies and current practices, and discuss evidence gaps, strengths,
and limitations. This paper is the output of the HP 13C MRI Consensus Group as
well as the ISMRM Hyperpolarized Media MR and Hyperpolarized Methods &
Equipment study groups. It further aims to provide a comprehensive reference
for future consensus building as the field continues to advance human studies
with this metabolic imaging modality
Detection of localized changes in the metabolism of hyperpolarized gluconeogenic precursors 13Câlactate and 13Câpyruvate in kidney and liver
Hyperpolarized [13C]ketobutyrate, a molecular analog of pyruvate with modified specificity for LDH isoforms
Directly detected (55)Mn MRI: application to phantoms for human hyperpolarized (13)C MRI development.
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Hardware and software developments for high field (>=3T) MRI
Key engineering challenges associated with realizing the full potential of high field MRI are the design of phased array RF coils, the development of parallel imaging techniques for rapid imaging, and the determination of optimal acquisition parameters for various clinical applications. Parallel imaging techniques, which are enabled by phased array RF coils, take advantage of higher MRI field strengths by trading the higher SNR for imaging speed. I constructed a novel eight-channel non-overlapping phased array RF coil with capacitive decoupling for imaging of the brain and the hip, which was designed to minimize reconstruction-related SNR losses in parallel imaging. The design was aided by high frequency electromagnetic simulations that I programmed, and the coil was tested in various clinical applications, demonstrating quantitative performance improvements over a commercial eight-channel head coil. Higher field strengths improve the capability of intracranial time-of-flight MR angiography, an important fully non-invasive angiographic technique, due to the higher baseline SNR and the improved background suppression that is a result of longer T1 relaxation times. I optimized the acquisition protocol for 7T intracranial MRA, relying on a combination of simulations and experiments, and quantitatively verified the performance improvements over 3T. Using GRAPPA-based parallel imaging acquisition and reconstruction techniques that I developed, I designed a very high resolution (0.146mm3) protocol for 7T imaging of volunteers and patients with vascular disease. These techniques produced angiograms free from artifacts in all subjects, and correctly identified vascular pathology in patients
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