Metabolic Magnetic Resonance Imaging Research Articles

13C MRI of hyperpolarized pyruvate at 120 µT

Nuclear spin hyperpolarization increases the sensitivity of magnetic resonance dramatically, enabling many new applications, including real-time metabolic imaging. Parahydrogen-based signal amplification by reversible exchange (SABRE) was employed to hyperpolarize [1-13C]pyruvate and demonstrate 13C imaging in situ at 120 µT, about twice Earth’s magnetic field, with two different signal amplification by reversible exchange variants: SABRE in shield enables alignment transfer to heteronuclei (SABRE-SHEATH), where hyperpolarization is transferred from parahydrogen to [1-13C]pyruvate at a magnetic field below 1 µT, and low-irradiation generates high tesla (LIGHT-SABRE), where hyperpolarization was prepared at 120 µT, avoiding magnetic field cycling. The 3-dimensional images of a phantom were obtained using a superconducting quantum interference device (SQUID) based magnetic field detector with submillimeter resolution. These 13C images demonstrate the feasibility of low-field 13C metabolic magnetic resonance imaging (MRI) of 50 mM [1-13C]pyruvate hyperpolarized by parahydrogen in reversible exchange imaged at about twice Earth’s magnetic field. Using thermal 13C polarization available at 120 µT, the same experiment would have taken about 300 billion years.

In Vivo Metabolic Imaging of [1-13 C]Pyruvate-d3 Hyperpolarized By Reversible Exchange With Parahydrogen.

Metabolic magnetic resonance imaging (MRI) using hyperpolarized (HP) pyruvate is becoming a non-invasive technique for diagnosing, staging, and monitoring response to treatment in cancer and other diseases. The clinically established method for producing HP pyruvate, dissolution dynamic nuclear polarization, however, is rather complex and slow. Signal Amplification By Reversible Exchange (SABRE) is an ultra-fast and low-cost method based on fast chemical exchange. Here, for the first time, we demonstrate not only in vivo utility, but also metabolic MRI with SABRE. We present a novel routine to produce aqueous HP [1-13 C]pyruvate-d3 for injection in 6 minutes. The injected solution was sterile, non-toxic, pH neutral and contained ≈30 mM [1-13 C]pyruvate-d3 polarized to ≈11 % (residual 250 mM methanol and 20 μM catalyst). It was obtained by rapid solvent evaporation and metal filtering, which we detail in this manuscript. This achievement makes HP pyruvate MRI available to a wide biomedical community for fast metabolic imaging of living organisms.

Cover Image, Volume 36, Issue 7

The cover image is based on the Research Article A new deuterium-labeled compound [2,3,4,6,6’-2H5]-D-glucose for deuterium magnetic resonance metabolic imaging by Chao Zou et al., https://doi.org/10.1002/nbm.4890.

A new deuterium-labeled compound [2,3,4,6,6'-2 H5 ]-D-glucose for deuterium magnetic resonance metabolic imaging.

Deuterium (2 H) magnetic resonance imaging is an emerging approach for noninvasively studying glucose metabolism in vivo, which is important for understanding pathogenesis and monitoring the progression of many diseases such as tumors, diabetes, and neurodegenerative diseases. However, the synthesis of 2 H-labeled glucose is costly because of the expensive raw substrates and the requirement for extreme reaction conditions, making the 2 H-labeled glucose rather expensive and unaffordable for clinic use. In this study, we present a new deuterated compound, [2,3,4,6,6'-2 H5 ]-D-glucose, with an approximate 10-fold reduction in production costs. The synthesis route uses cheaper raw substrate methyl-α-D-glucopyranoside, relies on mild reaction conditions (80°C), and has higher deuterium labeling efficiency. Magnetic resonance spectroscopy (MRS) and mass spectroscopy experiments confirmed the successful deuterium labeling in the compound. Animal studies demonstrated that the substrate could describe the glycolytic metabolism in a glioma rat model by quantifying the downstream metabolites through 2 H-MRS on an ultrahigh field system. Comparison of the glucose metabolism characteristics was carried out between [2,3,4,6,6'-2 H5 ]-D-glucose and commercial [6,6'-2 H2 ]-D-glucose in the animal studies. This cost-effective compound will help facilitate the clinical translation of deuterium magnetic resonance imaging, and enable this powerful metabolic imaging modality to be widely used in both preclinical and clinical research and applications.

High-resolution 7 Tesla magnetic resonance metabolic imaging in epilepsy patients

High-resolution 7 Tesla magnetic resonance metabolic imaging in epilepsy patients

NIMG-36. VISUALIZATION OF TUMOR HETEROGENEITY AND PREDICTION OF ISOCITRATE DEHYDROGENASE MUTATION STATUS FOR HUMAN GLIOMAS BY USING MULTIPARAMETRIC PHYSIOLOGIC AND METABOLIC MRI

Abstract Preoperative prediction of isocitrate dehydrogenase mutation status is clinically meaningful, but remains challenging. This study aimed to predict the isocitrate dehydrogenase (IDH) status of gliomas by using the machine learning voxel-wise clustering method of multiparametric physiologic and metabolic magnetic resonance imaging (MRI) and to show the association of the created cluster labels with the glucose metabolism status of the tumors. Sixty-nine patients with diffuse glioma were scanned by pH-sensitive MRI, diffusion-weighted imaging, fluid-attenuated inversion recovery, and contrast-enhanced T1-weighted imaging at 3 T. An unsupervised two-level clustering approach, including the generation of a self-organizing map followed by the K-means clustering, was used for voxel-wise feature extraction from the acquired images. The logarithmic ratio of the labels in each class within tumor regions was applied to a support vector machine to differentiate IDH mutation status. Bootstrapping and leave-one-out cross-validation were used to calculate the area under the curve (AUC) of receiver operating characteristic curves, accuracy, sensitivity, and specificity for evaluating performance. Targeted biopsies were performed for 14 patients to explore the relationship between clustered labels and the expression of key glycolytic proteins determined using immunohistochemistry. The highest prediction performance to differentiate IDH status was found for 10-class clustering, with a mean AUC, accuracy, sensitivity, and specificity of 0.94, 0.91, 0.90, and 0.91, respectively. The tissues with labels 7 + 8 + 9 + 10 showed high expression levels of hypoxia-inducible factor 1-alpha, glucose transporter 3, and hexokinase 2, which are typical of IDH wild-type glioma, whereas those with labels 1 showed low expression of these proteins. Our machine learning model successfully predicted the IDH mutation status of gliomas, and the resulting clusters properly reflected the metabolic status of the tumors.

Rapid hyperpolarization and purification of the metabolite fumarate in aqueous solution

Hyperpolarized fumarate is a promising biosensor for carbon-13 magnetic resonance metabolic imaging. Such molecular imaging applications require nuclear hyperpolarization to attain sufficient signal strength. Dissolution dynamic nuclear polarization is the current state-of-the-art methodology for hyperpolarizing fumarate, but this is expensive and relatively slow. Alternatively, this important biomolecule can be hyperpolarized in a cheap and convenient manner using parahydrogen-induced polarization. However, this process requires a chemical reaction, and the resulting solutions are contaminated with the catalyst, unreacted reagents, and reaction side-product molecules, and are hence unsuitable for use in vivo. In this work we show that the hyperpolarized fumarate can be purified from these contaminants by acid precipitation as a pure solid, and later redissolved to a desired concentration in a clean aqueous solvent. Significant advances in the reaction conditions and reactor equipment allow for formation of hyperpolarized fumarate at 13C polarization levels of 30-45%.

Water and Collagen Content Are High in Pancreatic Cancer: Implications for Quantitative Metabolic Imaging

In magnetic resonance metabolic imaging, signal from the water content is frequently used for normalization to derive quantitative or semi-quantitative values of metabolites in vivo or ex vivo tumors and tissues. Ex vivo high-resolution metabolic characterization of tumors with magnetic resonance spectroscopy (MRS) provides valuable information that can be used to drive the development of noninvasive MRS biomarkers and to identify metabolic therapeutic targets. Variability in the water content between tumor and normal tissue can result in over or underestimation of metabolite concentrations when assuming a constant water content. Assuming a constant water content can lead to masking of differences between malignant and normal tissues both in vivo and ex vivo. There is a critical need to develop biomarkers to detect pancreatic cancer and to develop novel treatments. Our purpose here was to determine the differences in water content between pancreatic tumors and normal pancreatic tissue as well as other organs to accurately quantify metabolic differences when using the water signal for normalization. Our data identify the importance of factoring the differences in water content between tumors and organs. High-resolution proton spectra of tumors and pancreatic tissue extracts normalized to the water signal, assuming similar water content, did not reflect the significantly increased total choline observed in tumors in vivo without factoring the differences in water content. We identified significant differences in the collagen 1 content between Panc1 and BxPC3 pancreatic tumors and the pancreas that can contribute to the differences in water content that were observed.

Technical Note: A deuterated 13 C-urea reference for clinical multiparametric MRI prostate cancer studies including hyperpolarized pyruvate.

Metabolic magnetic resonance imaging (MRI) using hyperpolarized [1-13 C]-pyruvate offers unprecedented new insight into disease and response to therapy. 13 C-enriched reference standards are required to enable fast and accurate calibration for 13 C studies, but care must be taken to ensure that the reference is compatible with both 13 C and 1 H acquisitions. The goal of this study was to optimize the composition of a 13 C-urea reference for a dual-tuned 13 C/1 H endorectal coil and minimize imaging artifacts in metabolic and multiparametric MRI studies involving hyperpolarized [1-13 C]-pyruvate. Due to a high amount of Gd doping for the purpose of reducing the spin-lattice relaxation time (T1 ) of urea, the 1 H signal produced by a reference of 13 C-urea in normal water was rapidly relaxed, resulting in severe artifacts in heavily T1 -weighted images. Hyperintense ringing artifacts in 1 H images were mitigated by reducing the 1 H concentration in a 13 C-urea reference via deuteration and lyophilization. Several references were fabricated and their SNR was compared using 1 H and 13 C imaging sequences on a 3T MRI scanner. Finally, 1 H prostate phantom imaging was conducted to compare image quality and 1 H signal intensity of normal and deuterated urea references. The deuterated 13 C-urea reference provides strong 13 C signal for calibration and an attenuated 1 H signal that does not interfere with heavily T1 -weighted scans. Deuteration and lyophilization were fundamental to the reduction in 1 H signal and hyperintense ringing artifacts. There was a 25-fold reduction in signal intensity when comparing the nondeuterated reference to the deuterated reference, while the 13 C signal was unaffected. A deuterated reference reduced hyperintense ringing artifacts in 1 H images by reducing the 1 H signal produced from the 13 C-urea in the reference. The deuterated reference can be used to improve anatomical image quality in future clinical 1 H and hyperpolarized [1-13 C]-pyruvate MRI prostate imaging studies.

Effect of a multicomponent exercise intervention on brain metabolism: A randomized controlled trial on Alzheimer's pathology (Dementia-MOVE).

BackgroundPhysical activity has shown a positive impact on aging and neurodegeneration and represents a possible treatment option in cognitive decline. However, its underlying mechanisms and influences on brain pathology remain unclear. Dementia‐MOVE (Multi‐Objective Validation of Exercise) is a randomized‐controlled pilot trial, including 50 patients with amnestic cognitive impairment associated with Alzheimer's pathology, aiming to analyze the effect of physical activity and fitness on disease progression.MethodsDementia‐MOVE is divided into two arms, of either an intervention comprising physical activity, for at least twice a week, combined with a psychoeducational program, or a sole psychoeducational program. Physical activity intervention includes a supervised and unsupervised multimodal concept combining resistance, endurance, coordinative, and aerobic training. The primary outcome is the change of brain metabolism due to physical interventional treatment. Besides metabolic magnetic resonance imaging (MRI) including sodium and phosphorus imaging, resting state functional MRI, T1‐, T2‐weighted and fluid‐attenuated inversion recovery (FLAIR), as well as diffusion‐weighted imaging (DWI) of the brain and whole‐body fat MRI are performed before and after intervention, and will be compared in their sensitivity for the detection of intervention effects. We further assess cognitive performance, neuropsychiatric symptoms, quality of life, fitness, and sleep via questionnaires/interviews and/or fitness trackers, as well as microbiome, under the aspect of Alzheimer's pathology.DiscussionThe aim of Dementia‐MOVE is to investigate the effect of a multimodal exercise program on Alzheimer's pathology under different aspects of the disease. In this context, one of the main aims is the comparison of different MRI methods regarding their responsiveness for the detection of alterations induced by physical activity. As an underlying goal, new treatment and diagnostic options, as well as the exploration of fitness effects on brain structure and metabolism within a whole‐body perspective of Alzheimer's disease are envisaged.

Assessing Therapeutic Efficacy in Real-time by Hyperpolarized Magnetic Resonance Metabolic Imaging.

Precisely measuring tumor-associated alterations in metabolism clinically will enable the efficient assessment of therapeutic responses. Advances in imaging technologies can exploit the differences in cancer-associated cell metabolism as compared to normal tissue metabolism, linking changes in target metabolism to therapeutic efficacy. Metabolic imaging by Positron Emission Tomography (PET) employing 2-fluoro-deoxy-glucose ([18F]FDG) has been used as a routine diagnostic tool in the clinic. Recently developed hyperpolarized Magnetic Resonance (HP-MR), which radically increases the sensitivity of conventional MRI, has created a renewed interest in functional and metabolic imaging. The successful translation of this technique to the clinic was achieved recently with measurements of 13C-pyruvate metabolism. Here, we review the potential clinical roles for metabolic imaging with hyperpolarized MRI as applied in assessing therapeutic intervention in different cancer systems.

Metabolic MRI for In Vivo Detection of Graft-Versus-Host Disease in a Pre-Clinical Model

Chronic graft-versus-host disease (cGVHD) remains a prominent barrier preventing successful allogeneic hematopoietic stem cell transplantation (AHSCT). Diagnosis of cGVHD is challenging since biopsies of the involved tissues are associated with bleeding and infection risks. In the absence of biopsy specimens, clinicians rely on subjective clinical scoring for cGVHD diagnosis and monitoring of therapeutic responses. Our previous studies in the pre-clinical cGVHD mouse model demonstrated that the primary cellular mediators of cGVHD, alloreactive donor-derived CD4+ T cells, are distributed to target rather than lymphoid organs. This is in direct contrast to syngeneic HSCT recipients (matched host and donor pairings) where T cells are primarily localized to lymphoid organs. Our prospective metabolic screening and ex vivo metabolic profiling of CD4+ T cell subsets indicated that effector memory T cells (Tem) preferentially utilize aerobic glycolysis. Thus, we hypothesized that visualization of tissues exhibiting high rates of glycolysis could allow in vivo detection of cGVHD in the affected organs since they are infiltrated by alloreactive glycolytic Tem cells. In order to test this, we initiated metabolic magnetic resonance imaging (MRI) in the minor antigen mismatched HSCT mouse model. Following administration of 13C-pyruvate, we measured the conversion of the glycolytic end product, pyruvate, into lactate as a means of evaluating glycolytic rates in target organs. Indeed, hyperpolarized 13C-pyruvate MRI of the liver and gut distinguished allogeneic versus syngeneic HSCT recipients, prior to the development of clinically evident cGVHD. This imaging approach is amenable to clinical translation to potentially allow for cGVHD diagnosis and disease monitoring in patients.

Abstract 370: Hyperpolarized magnetic resonance metabolic imaging in pancreatic cancer research: Early detection, assessing aggressiveness and real-time monitoring treatment response

Abstract Pancreatic cancer is on pace to become the second leading cause of cancer-related death. The high mortality rate results from a lack of methods for early detection and the inability to successfully treat patients once diagnosed. Pancreatic cancer cells have extensively reprogrammed metabolism, which is driven by oncogene-mediated pathways and the unique physiology of the tumor microenvironment. In our research, we are interrogating reprogrammed metabolism in pancreatic cancer. We have employed hyperpolarized metabolic imaging to measure noninvasively the metabolic plasticity as the diseases initiate, evolve and respond to the drugs. Genetically engineered mouse (GEM) model with progression of pancreatic intraepithelial neoplasm (PanIN) lesions has been used for early detection, patient-derived xenografts (PDX) model to assess aggressiveness, and orthotopic pancreatic cancer model for monitoring metabolically targeted therapeutic response. Hyperpolarization of pyruvate and in-vivo 13C MRS were performed using Hypersense (Oxford Instruments) and 7T MRI scanner with a dual tuned 1H/13C volume coil (Bruker), respectively. Tissue alanine and lactate concentrations were determined using a Bruker 500 MHz NMR spectrometer coupled with cryoprobe. Histology and immunohistochemistry were performed on excised tissue samples. Hyperpolarized pyruvate metabolism in PDX tumor was well captured in real time. Pyruvate was readily metabolized to lactate and alanine in vivo. The quantitative flux ratios lactate-to-pyruvate (Lac/Pyr) and alanine-to-lactate were determined. The most aggressive tumors showed the highest value of Lac/Pyr ratio. GEM model such as P48Cre;LSLKrasG12D mice were used for detection of early and advanced PanIN, which usually develop in these mice between 20 and 25 weeks. The imaging experiments were performed at the different stages of the disease. Progression of disease from tissue containing predominantly low-grade PanIN to tissue with high-grade PanIN showed a decreasing alanine/lactate concentration ratio as measured by 1H-NMR metabolomics. These results demonstrate that there are significant alterations of alanine transaminase (ALT) and lactate dehydrogenase (LDH) activities that favor the transformation of aggressive pancreatic cancer from PanIN lesion. The efficacy of a metabolically targeted drug was monitored in orthotopic pancreatic cancer mice by measuring flux ratio of Lac/Pyr after injecting hyperpolarized pyruvate before the tumor shrinkage. Metabolic imaging with hyperpolarized pyruvate and NMR metabolomics enabled detection and monitoring of the progression of pancreatic cancer lesions. Translation of this HP-MRI technique to the clinic has the potential to improve early detection and the management of patients' care. Citation Format: Prasanta Dutta, Erick Riquelme Sanchez, Yu Zhang, Travis Salzillo,, Priyank Raj, Jaehyuk Lee, Niki Millward, Anirban Maitra, Florencia McAllister, Pratip Bhattacharya. Hyperpolarized magnetic resonance metabolic imaging in pancreatic cancer research: Early detection, assessing aggressiveness and real-time monitoring treatment response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 370.

Identifying Voxels at Risk for Progression in Glioblastoma Based on Dosimetry, Physiologic and Metabolic MRI.

Despite the longstanding role of radiation in cancer treatment and the presence of advanced, high-resolution imaging techniques, delineation of voxels at-risk for progression remains purely a geometric expansion of anatomic images, missing subclinical disease at risk for recurrence while treating potentially uninvolved tissue and increasing toxicity. This remains despite the modern ability to precisely shape radiation fields. A striking example of this is the treatment of glioblastoma, a highly infiltrative tumor that may benefit from accurate identification of subclinical disease. In this study, we hypothesize that parameters from physiologic and metabolic magnetic resonance imaging (MRI) at diagnosis could predict the likelihood of voxel progression at radiographic recurrence in glioblastoma by identifying voxel characteristics that indicate subclinical disease. Integrating dosimetry can reveal its effect on voxel outcome, enabling risk-adapted voxel dosing. As a system example, 24 patients with glioblastoma treated with radiotherapy, temozolomide and an anti-angiogenic agent were analyzed. Pretreatment median apparent diffusion coefficient (ADC), fractional anisotropy (FA), relative cerebral blood volume (rCBV), vessel leakage (percentage recovery), choline-to-NAA index (CNI) and dose of voxels in the T2 nonenhancing lesion (NEL), T1 post-contrast enhancing lesion (CEL) or normal-appearing volume (NAV) of brain, were calculated for voxels that progressed [NAV→NEL, CEL (N = 8,765)] and compared against those that remained stable [NAV→NAV (N = 98,665)]. Voxels that progressed (NAV→NEL) had significantly different (P < 0.01) ADC (860), FA (0.36) and CNI (0.67) versus stable voxels (804, 0.43 and 0.05, respectively), indicating increased cell turnover, edema and decreased directionality, consistent with subclinical disease. NAV→CEL voxels were more abnormal (1,014, 0.28, 2.67, respectively) and leakier (percentage recovery = 70). A predictive model identified areas of recurrence, demonstrating that elevated CNI potentiates abnormal diffusion, even far (>2 cm) from the tumor and dose escalation >45 Gy has diminishing benefits. Integrating advanced MRI with dosimetry can identify at voxels at risk for progression and may allow voxel-level risk-adapted dose escalation to subclinical disease while sparing normal tissue. When combined with modern planning software, this technique may enable risk-adapted radiotherapy in any disease site with multimodal imaging.

Abstract 4215: Hyperpolarized magnetic resonance metabolic imaging and NMR metabolomics to assess the progression and aggressiveness of patient-derived pancreatic cancer xenografts

Abstract Pancreatic cancer, the most lethal of solid tumors is an aggressive disease that develops relatively symptom-free. The absence of early symptoms has created a critical need for identifying and developing new noninvasive biomarkers and therapeutic intervention to improve the survival rate of pancreatic cancer patients. Our goal is to identify metabolic biomarkers for early detection with an understanding of pancreatic cancer progression from benign lesions to a malignant state. Hyperpolarized magnetic resonance imaging (HP-MRI) provides a &amp;gt;10,000-fold signal enhancement for detecting of endogenous metabolic substrates to monitor metabolic fluxes through the multiple key biochemical pathways including glycolysis and citric acid cycle. In particular, conversion between hyperpolarized 13C-labeled pyruvate and lactate, catalyzed by lactate dehydrogenase (LDH), has been shown to have a number of potential applications such as diagnosis, staging tumor grade and monitoring therapy response. Genetic mutation is evident in causing tumorigenesis and often time these mutations trigger the signaling pathways that are associated with “metabolic transformations. There is currently tremendous research interest in dissecting the mechanisms of metabolic transformation as the cancers progress. In this effort, we are applying high-resolution NMR (nuclear magnetic resonance) metabolomics and the real-time hyperpolarized metabolic imaging of patient-derived xenograft tumors for probing the underlying mechanism of altered-metabolism and correlate with pancreatic cancer progression and its aggressiveness. The protocol detailing heterotopic engraftment of pancreatic cancer patient tumors into immunodeficient mice and expansion of direct xenograft tumors was recently reported elsewhere. These patient-derived xenografts (PDX) were well annotated with original patient tumors. For the NMR metabolomics study, the fresh-frozen tumor samples were homogenized, lyophilized, and resuspended in D2O and 1-D proton NMR spectroscopy was employed to characterize the water-soluble portion of the metabolome. These data suggest that elevated glycolysis (production of high lactate) and alterations in choline metabolism may arise in pancreatic cancer development. Also, the metabolite concentrations were significantly higher in aggressive tumors compare to non-aggressive one. The real-time metabolic imaging shows the immediate conversion of lactate after injection (i.v.) of hyperpolarized 13C pyruvate and probe the upregulated LDH activity as the cancer progress. The basic genomic profiling of these tumors is in progress. This model may provide an excellent platform where mutational status of these patient tumors can be correlated with both high resolution and hyperpolarized dynamical metabolomics data for characterizing individual tumor phenotypes. Citation Format: Prasanta Dutta, Mayrim Rios Perez, Travis Cole Salzillo, Michael Pratt, Yaan Kang, Niki Zacharias, Anirban Maitra, Jason B. Fleming, Pratip Bhattacharya. Hyperpolarized magnetic resonance metabolic imaging and NMR metabolomics to assess the progression and aggressiveness of patient-derived pancreatic cancer xenografts. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4215.

Science to Practice: Hyperpolarized Metabolic MR Imaging--The Light at the End of the Tunnel for Clinical (13)C MR Spectroscopy?

Hyperpolarized metabolic magnetic resonance (MR) imaging offers greatly enhanced sensitivity to multinuclear MR spectroscopy, opening up a new tool with which to noninvasively assess metabolic changes in the diseased heart. In this issue of Radiology, O h-Ici et al ( 1 ) have demonstrated this ability by exploring the metabolic changes that occur in the setting of ischemia-reperfusion. They have shown the acute metabolic alterations that occur immediately after reperfusion (increased anaerobic and decreased oxidative metabolism) that then normalize over the following 60 minutes. This demonstration paves the way for the use of hyperpolarized metabolic MR imaging in the assessment of coronary artery disease in humans and shows the potential for this new tool to aid in the assessment of the diseased heart.

Hyperpolarized Metabolic MR Imaging of Acute Myocardial Changes and Recovery after Ischemia-Reperfusion in a Small-Animal Model.

To implement hyperpolarized magnetic resonance (MR) imaging in an animal model of ischemia-reperfusion and to assess in vivo the regional changes in pyruvate metabolism within the 1st hour and at 1 week after a brief episode of coronary occlusion and reperfusion. All animal experiments were performed with adherence to the Swiss Animal Protection law and were approved by the regional veterinary office. A closed-chest rat model was implemented by using an inflatable balloon secured around the left coronary artery. Animals were placed in an MR system 5-7 days after surgery. [1-(13)C]pyruvate was polarized by using a home-built multisample hyperpolarizer. Hyperpolarized pyruvate was injected at five stages: at baseline; at reperfusion after 15 minutes of coronary occlusion; and at 30 minutes, 60 minutes, and 1 week after ischemia reperfusion. The conversion of pyruvate into lactate and bicarbonate was imaged by using dedicated MR sequences alongside wall motion and delayed enhancement imaging. After imaging, the heart was removed and stained to delineate the area at risk (AAR). Differences between AAR and remote myocardium were assessed by using a repeated measures analysis of variance and a post hoc Bonferroni multiple comparison test. Data were collected in 12 animals. Occlusion led to hypokinesia of the anterior or anterolateral segments of the myocardium. At reperfusion, the average lactate-to-bicarbonate ratio increased in the AAR relative to that at baseline (from 1.93 ± 0.48 to 3.01 ± 0.74, P < .001) and was significantly higher when compared with that in the remote area (1.91 ± 0.38, P < .001). In the 60 minutes after occlusion, the lactate-to-bicarbonate ratio in the AAR recovered but was still elevated relative to that in the remote area. One week after ischemia-reperfusion, no difference between AAR and remote area could be detected. Hyperpolarized metabolic MR imaging can be used to successfully detect acute changes in [1-(13)C]pyruvate metabolism after ischemia-reperfusion, thereby enabling in vivo monitoring of the metabolic effects of reperfusion strategies.

Magnetic Resonance (MR) Metabolic Imaging in Glioma.

This review is focused on describing the use of magnetic resonance (MR) spectroscopy for metabolic imaging of brain tumors. We will first review the MR metabolic imaging findings generated from preclinical models, focusing primarily on in vivo studies, and will then describe the use of metabolic imaging in the clinical setting. We will address relatively well-established (1) H MRS approaches, as well as (31) P MRS, (13) C MRS and emerging hyperpolarized (13) C MRS methodologies, and will describe the use of metabolic imaging for understanding the basic biology of glioma as well as for improving the characterization and monitoring of brain tumors in the clinic.

Dynamic nuclear polarization and optimal control spatial-selective 13C MRI and MRS

Aimed at 13C metabolic magnetic resonance imaging (MRI) and spectroscopy (MRS) applications, we demonstrate that dynamic nuclear polarization (DNP) may be combined with optimal control 2D spatial selection to simultaneously obtain high sensitivity and well-defined spatial restriction. This is achieved through the development of spatial-selective single-shot spiral-readout MRI and MRS experiments combined with dynamic nuclear polarization hyperpolarized [1-13C]pyruvate on a 4.7T pre-clinical MR scanner. The method stands out from related techniques by facilitating anatomic shaped region-of-interest (ROI) single metabolite signals available for higher image resolution or single-peak spectra. The 2D spatial-selective rf pulses were designed using a novel Krotov-based optimal control approach capable of iteratively fast providing successful pulse sequences in the absence of qualified initial guesses. The technique may be important for early detection of abnormal metabolism, monitoring disease progression, and drug research.

Detection of radiation-induced lung injury using hyperpolarized13C magnetic resonance spectroscopy and imaging

Radiation-induced lung injury limits radiotherapy of thoracic cancers. Detection of radiation pneumonitis associated with early radiation-induced lung injury (2–4 weeks postirradiation) may provide an opportunity to adjust treatment, before the onset of acute pneumonitis and/or irreversible fibrosis. In this study, localized magnetic resonance (MR) spectroscopy and imaging of hyperpolarized 13C-pyruvate (pyruvate) and 13C-lactate (lactate) were performed in the thorax and kidney regions of rats 2 weeks following whole-thorax irradiation (14 Gy). Lactate-to-pyruvate signal ratio was observed to increase by 110% (P < 0.01), 57% (P < 0.02), and 107% (P < 0.01), respectively, in the thorax, lung, and heart tissues of the radiated rats compared with healthy age-matched rats. This was consistent with lung inflammation confirmed using cell micrographs of bronchioalveolar lavage specimens and decreases in arterial oxygen partial pressure (paO2), indicative of hypoxia. No statistically significant difference was observed in either lactate-to-pyruvate signal ratios in the kidney region (P = 0.50) between the healthy (0.215 ± 0.100) and radiated cohorts (0.215 ± 0.054) or in blood lactate levels (P = 0.69) in the healthy (1.255 ± 0.247 mmol/L) and the radiated cohorts (1.325 ± 0.214 mmol/L), confirming that the injury is localized to the thorax. This work demonstrates the feasibility of hyperpolarized 13C metabolic MR spectroscopy and imaging for detection of early radiation-induced lung injury. Magn Reson Med 70:601–609, 2013. © 2012 Wiley Periodicals, Inc.