Characterization of oligodendrogliomas using short echo time 1H MR spectroscopic imaging

Differential metabolic alterations in IDH1 mutant vs. wildtype glioma cells promote epileptogenesis through distinctive mechanisms

Glioma-related epilepsy (GRE) is a hallmark clinical presentation of gliomas with significant impacts on patient quality of life. The current standard of care for seizure management is comprised of anti-seizure medications (ASMs) and surgical resection. Seizures in glioma patients are often drug-resistant and can often recur after surgery despite total tumor resection. Therefore, current research is focused on the pro-epileptic pathological changes occurring in tumor cells and the peritumoral environment. One important contribution to seizures in GRE patients is metabolic reprogramming in tumor and surrounding cells. This is most evident by the significantly heightened seizure rate in patients with isocitrate dehydrogenase mutated (IDHmut) tumors compared to patients with IDH wildtype (IDHwt) gliomas. To gain further insight into glioma metabolism in epileptogenesis, this review compares the metabolic changes inherent to IDHmut vs. IDHwt tumors and describes the pro-epileptic effects these changes have on both the tumor cells and the peritumoral environment. Understanding alterations in glioma metabolism can help to uncover novel therapeutic interventions for seizure management in GRE patients.

Optimized multi-voxel TE-averaged PRESS for glutamate detection in the human brain at 3T

PURPOSE

To optimize possible combinations of echo times (TE) for multi-voxel TE-averaged Point RESolved Spectroscopy (PRESS) while reducing the total number of TEs required to separate glutamate (Glu) and glutamine (Gln) within a clinically feasible scan time.

METHODS

General Approach to Magnetic resonance Mathematical Analysis (GAMMA) was used to implement 2D J-resolved PRESS technique, and the spectra of 14 individual brain metabolites were simulated at 64 different TEs. Monte Carlo simulations were used for selecting the best TE combinations to separate Glu and Gln using TE-averaged PRESS with a total number of two, three, four and five TEs. Single-voxel 1H-MRS data were acquired using 64 different TEs from a healthy volunteer on a clinical 3T MR scanner to validate the echo time combinations selected with simulations. Additionally, 2D 1H-MRSI data of eight healthy volunteers were acquired on a clinical 3T MR scanner using four different TEs that were determined by Monte Carlo simulations. Optimized TE-averaged PRESS spectra were created by averaging the spectra acquired at selected TEs. LCModel was used for spectral quantification. A Wilcoxon signed-rank test was used to detect statistically significant differences in Glu/Gln ratios between 35 ms PRESS and optimized TE-averaged PRESS data.

RESULTS

Glu could be clearly separated from Gln at 2.35 ppm, using optimized TE-averaged PRESS with only four TEs (35, 37, 40, and 42 ms) that were selected through Monte Carlo simulations. Glu/Gln ratios were significantly higher in the optimized TE-averaged PRESS data of healthy volunteers than in the 35 ms PRESS data (P = 0.008).

CONCLUSION

Optimized multi-voxel TE-averaged PRESS enabled faster and unobstructed quantification of Glu at multiple voxels in the human brain in vivo at 3T.

Spatial metabolic heterogeneity of oligodendrogliomas at single-cell resolution

Oligodendrogliomas are a type of rare and incurable gliomas whose metabolic profiles have yet to be fully examined. The present study examined the spatial differences in metabolic landscapes underlying oligodendrogliomas and should provide unique insights into the metabolic characteristics of these uncommon tumors. Single-cell RNA-sequencing expression profiles from 4044 oligodendroglioma cells derived from tumors resected from four locations frontal, temporal, parietal, and frontotemporoinsular) and in which 1p/19q co-deletion and IDH1 or IDH2 mutations were confirmed were computationally analyzed through a robust workflow to elucidate relative differences in metabolic pathway activities among the different locations. Dimensionality reduction using metabolic expression profiles exhibited clustering corresponding to each location subgroup. From the 80 metabolic pathways examined, over 70 pathways had significantly different activity scores between location subgroups. Further analysis of metabolic heterogeneity suggests that mitochondrial oxidative phosphorylation accounts for considerable metabolic variation within the same locations. Steroid and fatty acid metabolism pathways were also found to be major contributors to heterogeneity. Oligodendrogliomas display distinct spatial metabolic differences in addition to intra-location metabolic heterogeneity.

Memantine in the Prevention of Radiation-Induced Brain Damage: A Narrative Review

Simple Summary

Decline in cognitive function is a major problem for patients undergoing whole-brain radiotherapy (WBRT). Scientific interest has increased due to the high dropout rate of patients in the first months after WBRT and the early onset of cognitive decline. Therefore, the study of antiglutamatergic pharmacological prophylaxis and hippocampal-sparing WBRT techniques has been deepened based on the knowledge of the mechanisms of hyperglutamatergic neurotoxicity and the role of some hippocampal areas in cognitive decline. In order to provide a summary of the evidence in this field, and to foster future research in this setting, this literature review presents current evidence on the prevention of radiation-induced cognitive decline and particularly on the role of memantine.

Abstract

Preserving cognitive functions is a priority for most patients with brain metastases. Knowing the mechanisms of hyperglutamatergic neurotoxicity and the role of some hippocampal areas in cognitive decline (CD) led to testing both the antiglutamatergic pharmacological prophylaxis and hippocampal-sparing whole-brain radiotherapy (WBRT) techniques. These studies showed a relative reduction in CD four to six months after WBRT. However, the failure to achieve statistical significance in one study that tested memantine alone (RTOG 0614) led to widespread skepticism about this drug in the WBRT setting. Moreover, interest grew in the reasons for the strong patient dropout rates in the first few months after WBRT and for early CD onset. In fact, the latter can only partially be explained by subclinical tumor progression. An emerging interpretation of the (not only) cognitive impairment during and immediately after WBRT is the dysfunction of the limbic and hypothalamic system with its immune and hormonal consequences. This new understanding of WBRT-induced toxicity may represent the basis for further innovative trials. These studies should aim to: (i) evaluate in greater detail the cognitive effects and, more generally, the quality of life impairment during and immediately after WBRT; (ii) study the mechanisms producing these early effects; (iii) test in clinical studies, the modern and advanced WBRT techniques based on both hippocampal-sparing and hypothalamic-pituitary-sparing, currently evaluated only in planning studies; (iv) test new timings of antiglutamatergic drugs administration aimed at preventing not only late toxicity but also acute effects.

Investigation of metabolic kinetics in different brain regions of awake rats using the [1H-13C]-NMR technique

Energy metabolism and neurotransmission are necessary for sustaining normal life activities. Hence, neurological or psychiatric disorders are always associated with changes in neurotransmitters and energy metabolic states in the brain. Most studies have only focused on the most important neurotransmitters, particularly GABA and Glu, however, other metabolites such as NAA and aspartate which are also very important for cerebral function are rarely investigated. In this study, most of the metabolic kinetics information of different brain regions was investigated in awake rats using the [¹H-¹³C]-NMR technique. Briefly, rats (n = 8) were infused [1-¹³C] glucose through the tail vein for two minutes. After 20 min of glucose metabolism, the animals were sacrificed and the brain tissue was extracted and treated. Utilizing the ¹H observed/¹³C-edited nuclear magnetic resonance (POCE-NMR), the enrichment of neurochemicals was detected which reflected the metabolic changes in different brain regions and the metabolic connections between neurons and glial cells in the brain. The results suggest that the distribution of every metabolite differed from every brain region and the metabolic rate of NAA was relatively low at 8.64 ± 2.37 μmol/g/h. In addition, there were some correlations between several ¹³C enriched metabolites, such as Glu₄-Gln₄ (p = 0.062), Glu₄-GABA₂ (p < 0.01), Glx₂-Glx₃ (p < 0.001), Asp₃-NAA₃ (p < 0.001). This correlativity reflects the signal transmission between astrocytes and neurons, as well as the potential interaction between energy metabolism and neurotransmission. In conclusion, the current study systematically demonstrated the metabolic kinetics in the brain which shed light on brain functions and the mechanisms of various pathophysiological states.

Clinical value of N-acetyl mucinous compounds and lipid peaks in differentiating benign and malignant ovarian mucinous tumors by MR spectroscopy

PURPOSE

To retrospectively evaluate the clinical significance of the peaks of N-acetyl mucinous compounds (NAMC) at 2 ppm and lipid at 1.3 ppm in in-vivo proton magnetic resonance (MR) spectroscopy for distinguishing benign and malignant mucinous tumors in patients with ovarian masses.

METHODS

MR spectroscopy was performed in patients with pathologically diagnosed mucinous ovarian tumors at 3 T MRI system. The peaks of NAMC, lipid, and total choline compounds (tCho) were classified into three classes in comparison with the noise level by visual estimation. The NAMC concentration was quantified relative to unsuppressed water by using LCModel analysis.

RESULTS

A total of 27 ovarian mucinous tumors in 27 patients were included in this study. The NAMC peak was observed in all 27 mucinous tumors, and the lipid peak was observed in 14 of 27 tumors: 1 of 9 benign tumors (11%), and 13 of 18 malignant tumors (11 borderline malignancies and 7 carcinomas) (72%). The presence of the lipid peak for the diagnosis of malignant mucinous tumor showed generally better diagnostic ability than MR imaging, with a sensitivity of 72%, specificity of 89%, accuracy of 78%, PPV of 93%, and NPV of 62%. The concentration of the NAMC in malignant mucinous tumors tended to be higher than that in benign mucinous tumors, but there was no statistically significant difference.

CONCLUSIONS

The bimodal peaks of NAMC and lipid are suggestive of malignant mucinous tumors, and the presence of the lipid peak may be useful in distinguishing benign from malignant ovarian mucinous tumors.

Targeting Glutamine Addiction in Gliomas

The most common malignant brain tumors are those of astrocytic origin, gliomas, with the most aggressive glioblastoma (WHO grade IV) among them. Despite efforts, medicine has not made progress in terms of the prognosis and life expectancy of glioma patients. Behind the malignant phenotype of gliomas lies multiple genetic mutations leading to reprogramming of their metabolism, which gives those highly proliferating cells an advantage over healthy ones. The so-called glutamine addiction is a metabolic adaptation that supplements oxidative glycolysis in order to secure neoplastic cells with nutrients and energy in unfavorable conditions of hypoxia. The present review aims at presenting the research and clinical attempts targeting the different metabolic pathways involved in glutamine metabolism in gliomas. A brief description of the biochemistry of glutamine transport, synthesis, and glutaminolysis, etc. will forego a detailed comparison of the therapeutic strategies undertaken to inhibit glutamine utilization by gliomas.

Glutamate weighted imaging contrast in gliomas with 7 Tesla magnetic resonance imaging

Introduction

Diffuse gliomas are incurable malignancies, which undergo inevitable progression and are associated with seizure in 50–90% of cases. Glutamate has the potential to be an important glioma biomarker of survival and local epileptogenicity if it can be accurately quantified noninvasively.

Methods

We applied the glutamate-weighted imaging method GluCEST (glutamate chemical exchange saturation transfer) and single voxel MRS (magnetic resonance spectroscopy) at 7 Telsa (7 T) to patients with gliomas. GluCEST contrast and MRS metabolite concentrations were quantified within the tumour region and peritumoural rim. Clinical variables of tumour aggressiveness (prior adjuvant therapy and previous radiological progression) and epilepsy (any prior seizures, seizure in last month and drug refractory epilepsy) were correlated with respective glutamate concentrations. Images were separated into post-hoc determined patterns and clinical variables were compared across patterns.

Results

Ten adult patients with a histo-molecular (n = 9) or radiological (n = 1) diagnosis of grade II-III diffuse glioma were recruited, 40.3 +/− 12.3 years. Increased tumour GluCEST contrast was associated with prior adjuvant therapy (p = .001), and increased peritumoural GluCEST contrast was associated with both recent seizures (p = .038) and drug refractory epilepsy (p = .029). We distinguished two unique GluCEST contrast patterns with distinct clinical and radiological features. MRS glutamate correlated with GluCEST contrast within the peritumoural voxel (R = 0.89, p = .003) and a positive trend existed in the tumour voxel (R = 0.65, p = .113).

Conclusion

This study supports the role of glutamate in diffuse glioma biology. It further implicates elevated peritumoural glutamate in epileptogenesis and altered tumour glutamate homeostasis in glioma aggressiveness. Given the ability to non-invasively visualise and quantify glutamate, our findings raise the prospect of 7 T GluCEST selecting patients for individualised therapies directed at the glutamate pathway. Larger studies with prospective follow-up are required.

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7 T GluCEST glioma imaging is feasible, producing high quality quantifiable images.

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Increased peritumoural GluCEST contrast correlates with drug resistant epilepsy.

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Increased tumour GluCEST contrast is associated with prior adjuvant therapy.

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Two GluCEST patterns were identified with distinct clinico-radiological features.

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GluCEST contrast correlates with MRS glutamate in peritumoural regions.

In Vivo 1H Magnetic Resonance Spectroscopy

In vivo Magnetic Resonance Spectroscopy (MRS) allows the non-invasive detection and quantification of a number of metabolites from localized volumes within a living organism. MRS localization techniques can be divided into two main groups, single voxel and multi-voxel. Single voxel techniques provide the metabolic profile from a specific small volume, whereas multi-voxel techniques are used to obtain the spatial distribution of metabolites throughout a large volume subdivided into small contiguous voxels. This chapter describes standard protocols for the acquisition and processing of in vivo single voxel¹H MRS data from the rodent brain.

Targeting nitric oxide and NMDA receptor-associated pathways in treatment of high grade glial tumors. Hypotheses for nitro-memantine and nitrones

Glioblastoma multiforme (GBM) is a devastating brain cancer with no curative treatment. Targeting Nitric Oxide (NO) and glutamatergic pathways may help as adjunctive treatments in GBM. NO at low doses promotes tumorigenesis, while at higher levels (above 300 nM) triggers apoptosis. Gliomas actively secrete high amounts of glutamate which activates EGR signaling and mediates degradation of peritumoral tissues via excitotoxic injury. Memantine inhibits NMDA-subtype of glutamate receptors (NMDARs) and induces autophagic death of glioma cells in vitro and blocks glioma growth in vivo. Nitro-memantines may exert further benefits by limiting NMDAR signaling and by delivery of NO to the areas of excessive NMDAR activity leading NO-accumulation at tumoricidal levels within gliomas. Due to the duality of NO in tumorigenesis, agents which attenuate NO levels may also act beneficial in treatment of GBM. Nitrone compounds including N-tert-Butyl-α-phenylnitrone (PBN) and its disulfonyl-phenyl derivative, OKN-007 suppress free radical formation in experimental cerebral ischemia. OKN-007 failed to show clinical efficacy in stroke, but trials demonstrated its high biosafety in humans including elderly subjects. PBN inhibits the signaling pathways of NF-κB, inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX). In animal models of liver cancer and glioblastoma, OKN-007 seemed more efficient than PBN in suppression of cell proliferation, microvascular density and in induction of apoptosis. OKN-007 also inhibits SULF2 enzyme, which promotes tumor growth via versatile pathways. We assume that nitromemantines may be more beneficial concomitant with chemo-radiotherapy while nitrones alone may act useful in suppressing basal tumor growth and angiogenesis.

In vivo Metabolic Profiles as Determined by 31P and short TE 1H MR-Spectroscopy : No Difference Between Patients with IDH Wildtype and IDH Mutant Gliomas

PURPOSE

Previous ex vivo spectroscopic data from tissue samples revealed differences in phospholipid metabolites between isocitrate dehydrogenase mutated (IDHmut) and IDH wildtype (IDHwt) gliomas. We investigated whether these changes can be found in vivo using ¹H-decoupled ³¹P magnetic resonance spectroscopic imaging (MRSI) with 3D chemical shift imaging (CSI) at 3 T in patients with low and high-grade gliomas.

METHODS

The study included 33 prospectively enrolled, mostly untreated patients who met spectral quality criteria according to the World Health Organization (WHO II n = 7, WHO III n = 17, WHO IV n = 9; 25 patients IDHmut, 8 patients IDHwt). The MRSI protocol included ¹H decoupled ³¹P MRSI with 3D CSI (3D ³¹P CSI), 2D ¹H CSI and a ¹H single voxel spectroscopy sequence (TE 30 ms) from the tumor area. For ¹H MRS, absolute metabolite concentration values were calculated (phantom replacement method). For ³¹P MRS, metabolite intensity ratios were calculated for the choline (C) and ethanolamine (E)-containing metabolites.

RESULTS

In our patient cohort we did not find significant differences for the ratio of phosphocholine (PC) and phosphoethanolamine (PE), PC/PE, (p = 0.24) for IDHmut compared to IDHwt gliomas. Furthermore, we found no elevated ratios of glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE), GPC/GPE, (p = 0.68) or GPC/PE (p = 0.12) for IDHmut gliomas. Even the ratio (PC+GPC)/(PE+GPE) showed no significant differences with respect to mutation status (p = 0.16). Nonetheless, changes related to tumor grade regarding intracellular pH (pH_i) and phospholipid metabolism as well as absolute metabolite concentrations of co-registered 2D ¹H CSI data for tumor and control tissue showed the anticipated results.

CONCLUSION

Using 3D-CSI data acquisition, in vivo ³¹P MR spectroscopic measurement of phospholipid metabolites could not distinguish between IDHmut and IDHwt.

Magnetic Resonance Spectroscopy and its Clinical Applications: A Review

In vivo NMR spectroscopy is known as magnetic resonance spectroscopy (MRS). MRS has been applied as both a research and a clinical tool in order to detect visible or nonvisible abnormalities. The adaptability of MRS allows a technique that can probe a wide variety of metabolic uses across different tissues. Although MRS is mostly applied for brain tissue, it can be used for detection, localization, staging, tumour aggressiveness evaluation, and tumour response assessment of breast, prostate, hepatic, and other cancers. In this article, the medical applications of MRS in the brain, including tumours, neural and psychiatric disorder studies, breast, prostate, hepatic, gastrointestinal, and genitourinary investigations have been reviewed.

Adult Brain Tumors: Clinical Applications of Magnetic Resonance Spectroscopy

Proton magnetic resonance spectroscopy (H-MRS) may be helpful in suggesting tumor histology and tumor grade and may better define tumor extension and the ideal site for biopsy compared with conventional magnetic resonance (MR) imaging. A multifunctional approach with diffusion-weighted imaging, perfusion-weighted imaging, and permeability maps, along with H-MRS, may enhance the accuracy of the diagnosis and characterization of brain tumors and estimation of therapeutic response. Integration of advanced imaging techniques with conventional MR imaging and the clinical history help to improve the accuracy, sensitivity, and specificity in differentiating tumors and nonneoplastic lesions.

Memantine Induces NMDAR1-Mediated Autophagic Cell Death in Malignant Glioma Cells

Objective

Autophagy is one of the key responses of cells to programmed cell death. Memantine, an approved anti-dementia drug, has an antiproliferative effect on cancer cells but the mechanism is poorly understood. The aim of the present study was to test the possibility of induction of autophagic cell death by memantine in glioma cell lines.

Methods

Glioma cell lines (T-98 G and U-251 MG) were used for this study.

Results

The antiproliferative effect of memantine was shown on T-98 G cells, which expressed N-methyl-D-aspartate 1 receptor (NMDAR1). Memantine increased the autophagic-related proteins as the conversion ratio of light chain protein 3-II (LC3-II)-/LC3-I and the expression of beclin-1. Memantine also increased formation of autophagic vacuoles observed under a transmission electron microscope. Transfection of small interfering RNA (siRNA) to knock down NMDAR1 in the glioma cells induced resistance to memantine and decreased the LC3-II/LC3-I ratio in T-98 G cells.

Conclusion

Our study demonstrates that in glioma cells, memantine inhibits proliferation and induces autophagy mediated by NMDAR1.

Human astrocytes in the diseased brain

Astrocytes are key active elements of the brain that contribute to information processing. They not only provide neurons with metabolic and structural support, but also regulate neurogenesis and brain wiring. Furthermore, astrocytes modulate synaptic activity and plasticity in part by controlling the extracellular space volume, as well as ion and neurotransmitter homeostasis. These findings, together with the discovery that human astrocytes display contrasting characteristics with their rodent counterparts, point to a role for astrocytes in higher cognitive functions. Dysfunction of astrocytes can thereby induce major alterations in neuronal functions, contributing to the pathogenesis of several brain disorders. In this review we summarize the current knowledge on the structural and functional alterations occurring in astrocytes from the human brain in pathological conditions such as epilepsy, primary tumours, Alzheimer's disease, major depressive disorder and Down syndrome. Compelling evidence thus shows that dysregulations of astrocyte functions and interplay with neurons contribute to the development and progression of various neurological diseases. Targeting astrocytes is thus a promising alternative approach that could contribute to the development of novel and effective therapies to treat brain disorders.

Refined modelling of the short-T2 signal component and ensuing detection of glutamate and glutamine in short-TE, localised, (1) H MR spectra of human glioma measured at 3 T

Short-TE (1) H MRS has great potential for brain cancer diagnostics. A major difficulty in the analysis of the spectra is the contribution from short-T2 signal components, mainly coming from mobile lipids. This complicates the accurate estimation of the spectral parameters of the resonance lines from metabolites, so that a qualitative to semi-quantitative interpretation of the spectra dominates in practice. One solution to overcome this difficulty is to measure and estimate the short-T2 signal component and to subtract it from the total signal, thus leaving only the metabolite signals. The technique works well when applied to spectra obtained from healthy individuals, but requires some optimisation during data acquisition. In the clinical setting, time constraints hardly allow this. Here, we propose an iterative estimation of the short-T2 signal component, acquired in a single acquisition after measurement of the full spectrum. The method is based on QUEST (quantitation based on quantum estimation) and allows the refinement of the estimate of the short-T2 signal component after measurement. Thus, acquisition protocols used on healthy volunteers can also be used on patients without further optimisation. The aim is to improve metabolite detection and, ultimately, to enable the estimation of the glutamine and glutamate signals distinctly. These two metabolites are of great interest in the characterisation of brain cancer, gliomas in particular. When applied to spectra from healthy volunteers, the new algorithm yields similar results to QUEST and direct subtraction of the short-T2 signal component. With patients, up to 12 metabolites and, at least, seven can be quantified in each individual brain tumour spectrum, depending on the metabolic state of the tumour. The refinement of the short-T2 signal component significantly improves the fitting procedure and produces a separate short-T2 signal component that can be used for the analysis of mobile lipid resonances. Thus, in brain tumour spectra, distinct estimates of signals from glutamate and glutamine are possible. Copyright © 2016 John Wiley & Sons, Ltd.

Magnetic resonance spectroscopy - Revisiting the biochemical and molecular milieu of brain tumors

Background

Magnetic resonance spectroscopy (MRS) is an established tool for in-vivo evaluation of the biochemical basis of human diseases. On one hand, such lucid depiction of ‘live biochemistry’ helps one to decipher the true nature of the pathology while on the other hand one can track the response to therapy at sub-cellular level. Brain tumors have been an area of continuous interrogation and instigation for mankind. Evaluation of these lesions by MRS plays a crucial role in the two aspects of disease management described above.

Scope of review

Presented is an overview of the window provided by MRS into the biochemical aspects of brain tumors. We systematically visit each metabolite deciphered by MRS and discuss the role of deconvoluting the biochemical aspects of pathologies (here in context of brain tumors) in the disease management cycle. We further try to unify a radiologist's perspective of disease with that of a biochemist to prove the point that preclinical work is the mother of the treatment we provide at bedside as clinicians. Furthermore, an integrated approach by various scientific experts help resolve a query encountered in everyday practice.

Major conclusions

MR spectroscopy is an integral tool for evaluation and systematic follow-up of brain tumors. A deeper understanding of this technology by a biochemist would help in a swift and more logical development of the technique while a close collaboration with radiologist would enable definitive application of the same.

General significance

The review aims at inciting closer ties between the two specialists enabling a deeper understanding of this valuable technology.

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Magnetic resonance spectroscopy is an established technology for non-invasive assessment of pathological tissue.

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Good understanding of the physical principles of the technique can help one exploit it maximally.

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An array of information from the technique is available and needs deep understanding of the results.

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Newer variations of this technology are being invented to evaluate different aspects of pathologies in a more refined manner.

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We also discuss the limitations of this technology and possible solutions there-off.

Functional MR Imaging in Gynecologic Cancer

Dynamic-contrast enhanced (DCE) and diffusion-weighted (DW) MR imaging are invaluable in the detection, staging, and characterization of uterine and ovarian malignancies, for monitoring treatment response, and for identifying disease recurrence. When used as adjuncts to morphologic T2-weighted (T2-W) MR imaging, these techniques improve accuracy of disease detection and staging. DW-MR imaging is preferred because of its ease of implementation and lack of need for an extrinsic contrast agent. MR spectroscopy is difficult to implement in the clinical workflow and lacks both sensitivity and specificity. If used quantitatively in multicenter clinical trials, standardization of DCE- and DW-MR imaging techniques and rigorous quality assurance is mandatory.

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.

Parallel reconstruction in accelerated multivoxel MR spectroscopy

PURPOSE

To develop the simultaneous acquisition of multiple voxels in localized MR spectroscopy (MRS) using sensitivity encoding, allowing reduced total scan time compared to conventional sequential single voxel (SV) acquisition methods.

METHODS

Dual volume localization was used to simultaneously excite voxels in both hemispheres. Receiver coil sensitivity profiles were used to unfold the data. To demonstrate the method, MRS voxels in the left and right hippocampus were measured at 3 tesla (T) and the left and right motor cortices at 7T. Spectra were compared to conventional SV acquisitions. Spectra were also recorded from the lesion and contralateral hemisphere of a patient with a low-grade oligodendroglioma at 7T.

RESULTS

It was possible to generate signal in two voxels simultaneously and separate the signal originating from the different locations, with spectral results almost identical to those observed using conventional single voxel methods. The method results in an increased chemical shift displacement artifact, which might be improved by advanced pulse designs, and a noise increase due to the unfolding g-factor, which was larger at 3T than 7T.

CONCLUSION

The simultaneous acquisition of voxels for MRS is possible by using modulated slice-selective pulses and receive coil sensitivity profiles to unfold the resulting signals.

SLC7A11 expression is associated with seizures and predicts poor survival in patients with malignant glioma

Glioma is the most common malignant primary brain tumor. Its rapid growth is aided by tumor-mediated glutamate release, creating peritumoral excitotoxic cell death and vacating space for tumor expansion. Glioma glutamate release may also be responsible for seizures, which complicate the clinical course for many patients and are often the presenting symptom. A hypothesized glutamate release pathway is the cystine/glutamate transporter System xc (-) (SXC), responsible for the cellular synthesis of glutathione (GSH). However, the relationship of SXC-mediated glutamate release, seizures, and tumor growth remains unclear. Probing expression of SLC7A11/xCT, the catalytic subunit of SXC, in patient and mouse-propagated tissues, we found that ~50% of patient tumors have elevated SLC7A11 expression. Compared with tumors lacking this transporter, in vivo propagated and intracranially implanted SLC7A11-expressing tumors grew faster, produced pronounced peritumoral glutamate excitotoxicity, induced seizures, and shortened overall survival. In agreement with animal data, increased SLC7A11 expression predicted shorter patient survival according to genomic data in the REMBRANDT (National Institutes of Health Repository for Molecular Brain Neoplasia Data) database. In a clinical pilot study, we used magnetic resonance spectroscopy to determine SXC-mediated glutamate release by measuring acute changes in glutamate after administration of the U.S. Food and Drug Administration-approved SXC inhibitor, sulfasalazine (SAS). In nine glioma patients with biopsy-confirmed SXC expression, we found that expression positively correlates with glutamate release, which is acutely inhibited with oral SAS. These data suggest that SXC is the major pathway for glutamate release from gliomas and that SLC7A11 expression predicts accelerated growth and tumor-associated seizures.

Fast spectroscopic multiple analysis (FASMA) for brain tumor classification: a clinical decision support system utilizing multi-parametric 3T MR data

INTRODUCTION

A clinical decision support system (CDSS) for brain tumor classification can be used to assist in the diagnosis and grading of brain tumors. A Fast Spectroscopic Multiple Analysis (FASMA) system that uses combinations of multiparametric MRI data sets was developed as a CDSS for brain tumor classification.

METHODS

MRI metabolic ratios and spectra, from long and short TE, respectively, as well as diffusion and perfusion data were acquired from the intratumoral and peritumoral area of 126 patients with untreated intracranial tumors. These data were categorized based on the pathology, and different machine learning methods were evaluated regarding their classification performance for glioma grading and differentiation of infiltrating versus non-infiltrating lesions. Additional databases were embedded to the system, including updated literature values of the related MR parameters and typical tumor characteristics (imaging and histological), for further comparisons. Custom Graphical User Interface (GUI) layouts were developed to facilitate classification of the unknown cases based on the user's available MR data.

RESULTS

The highest classification performance was achieved with a support vector machine (SVM) using the combination of all MR features. FASMA correctly classified 89 and 79% in the intratumoral and peritumoral area, respectively, for cases from an independent test set. FASMA produced the correct diagnosis, even in the misclassified cases, since discrimination between infiltrative versus non-infiltrative cases was possible.

CONCLUSIONS

FASMA is a prototype CDSS, which integrates complex quantitative MR data for brain tumor characterization. FASMA was developed as a diagnostic assistant that provides fast analysis, representation and classification for a set of MR parameters. This software may serve as a teaching tool on advanced MRI techniques, as it incorporates additional information regarding typical tumor characteristics derived from the literature.

Magnetic resonance spectroscopy in intracranial tumours of glial origin

BACKGROUND AND PURPOSE

To determine in vivo magnetic resonance spectroscopy (MRS) characteristics of intracranial glial tumours and to assess MRS reliability in glioma grading and discrimination between different histopathological types of tumours.

MATERIAL AND METHODS

Analysis of spectra of 26 patients with glioblastomas, 6 with fibrillary astrocytomas, 4 with anaplastic astrocytomas, 2 with pilocytic astrocytoma, 3 with oligodendrogliomas, 3 with anaplastic oligodendrogliomas and 17 control spectra taken from healthy hemispheres.

RESULTS

All tumours' metabolite ratios, except for Cho/Cr in fibrillary astrocytomas (p = 0.06), were statistically significantly different from the control. The tumours showed decreased Naa and Cr contents and a high Cho signal. The Lac-Lip signal was high in grade III astrocytomas and glioblastomas. Reports that Cho/Cr ratio increases with glioma's grade whereas Naa/Cr decreases were not confirmed. Anaplastic astrocytomas compared to grade II astrocytomas had a statistically significantly greater mI/Cr ratio (p = 0.02). In pilocytic astrocytomas the Naa/Cr value (2.58 ± 0.39) was greater, whilst the Cho/Naa ratio was lower (2.14 ± 0.64) than in the other astrocytomas. The specific feature of oligodendrogliomas was the presence of glutamate/glutamine peak Glx. However, this peak was absent in two out of three anaplastic oligodendrogliomas. Characteristically, the latter tumours had a high Lac-Lip signal.

CONCLUSIONS

MRS in vivo cannot be used as a reliable method for glioma grading. The method is useful in discrimination between WHO grade I and WHO grade II astrocytomas as well as oligodendrogliomas from other gliomas.

Glutamate and glutamine: a review of in vivo MRS in the human brain

Our understanding of the roles that the amino acids glutamate (Glu) and glutamine (Gln) play in the mammalian central nervous system has increased rapidly in recent times. Many conditions are known to exhibit a disturbance in Glu-Gln equilibrium, and the exact relationships between these changed conditions and these amino acids are not fully understood. This has led to increased interest in Glu/Gln quantitation in the human brain in an array of conditions (e.g. mental illness, tumor, neuro-degeneration) as well as in normal brain function. Accordingly, this review has been undertaken to describe the increasing number of in vivo techniques available to study Glu and Gln separately, or pooled as 'Glx'. The present MRS methods used to assess Glu and Gln vary in approach, complexity, and outcome, thus the focus of this review is on a description of MRS acquisition approaches, and an indication of relative utility of each technique rather than brain pathologies associated with Glu and/or Gln perturbation. Consequently, this review focuses particularly on (1) one-dimensional (1)H MRS, (2) two-dimensional (1)H MRS, and (3) one-dimensional (13)C MRS techniques.

N-acetylaspartate (NAA) and N-acetylaspartylglutamate (NAAG) promote growth and inhibit differentiation of glioma stem-like cells

Metabolic reprogramming is a pathological feature of cancer and a driver of tumor cell transformation. N-Acetylaspartate (NAA) is one of the most abundant amino acid derivatives in the brain and serves as a source of metabolic acetate for oligodendrocyte myelination and protein/histone acetylation or a precursor for the synthesis of the neurotransmitter N-acetylaspartylglutamate (NAAG). NAA and NAAG as well as aspartoacylase (ASPA), the enzyme responsible for NAA degradation, are significantly reduced in glioma tumors, suggesting a possible role for decreased acetate metabolism in tumorigenesis. This study sought to examine the effects of NAA and NAAG on primary tumor-derived glioma stem-like cells (GSCs) from oligodendroglioma as well as proneural and mesenchymal glioblastoma, relative to oligodendrocyte progenitor cells (Oli-Neu). Although the NAA dicarboxylate transporter NaDC3 is primarily thought to be expressed by astrocytes, all cell lines expressed NaDC3 and, thus, are capable of NAA up-take. Treatment with NAA or NAAG significantly increased GSC growth and suppressed differentiation of Oli-Neu cells and proneural GSCs. Interestingly, ASPA was expressed in both the cytosol and nuclei of GSCs and exhibited greatest nuclear immunoreactivity in differentiation-resistant GSCs. Both NAA and NAAG elicited the expression of a novel immunoreactive ASPA species in select GSC nuclei, suggesting differential ASPA regulation in response to these metabolites. Therefore, this study highlights a potential role for nuclear ASPA expression in GSC malignancy and suggests that the use of NAA or NAAG is not an appropriate therapeutic approach to increase acetate bioavailability in glioma. Thus, an alternative acetate source is required.

3 Tesla magnetic resonance spectroscopy: cerebral gliomas vs. metastatic brain tumors. Our experience and review of the literature

The aim of the present study is to report about the value of magnetic resonance spectroscopy (MRS) in differentiating brain metastases, primary high-grade gliomas (HGG) and low-grade gliomas (LGG). MRI (magnetic resonance imaging) and MRS were performed in 60 patients with histologically verified brain tumors: 32 patients with HGG (28 glioblastomas multiforme [GBM] and 4 anaplastic astrocytomas), 14 patients with LGG (9 astrocytomas and 5 oligodendrogliomas) and 14 patients with metastatic brain tumors. The Cho/Cr (choline-containing compounds/creatine-phosphocreatine complex), Cho/NAA (N-acetyl aspartate) and NAA/Cr ratios were assessed from spectral maps in the tumoral core and peritumoral edema. The differences in the metabolite ratios between LGG, HGG and metastases were analyzed statistically. Lipids/lactate contents were also analyzed. Significant differences were noted in the tumoral and peritumoral Cho/Cr, Cho/NAA and NAA/Cr ratios between LGG, HGG and metastases. Lipids and lactate content revealed to be useful for discriminating gliomas and metastases. The results of this study demonstrate that MRS can differentiate LGG, HGG and metastases, therefore diagnosis could be allowed even in those patients who cannot undergo biopsy.

Glutamate and tumor-associated epilepsy: glial cell dysfunction in the peritumoral environment

Seizures are a serious and debilitating co-morbidity of primary brain tumors that affect most patients, yet their etiology is poorly understood. In many CNS pathologies, including epilepsy and brain injury, high levels of extracellular glutamate have been implicated in seizure generation. It has been shown that gliomas release neurotoxic levels of glutamate through their high expression of system xc-. More recently it was shown that the surrounding peritumoral cortex is spontaneously hyperexcitable. In this review, we discuss how gliomas induce changes in the surrounding environment that may further contribute to elevated extracellular glutamate and tumor-associated seizures. Peritumoral astrocytes become reactive and lose their ability to remove glutamate, while microglia, in response to signals from glioma cells, may release glutamate. In addition, gliomas increase blood brain barrier permeability, allowing seizure-inducing serum components, including glutamate, into the peritumoral region. These factors, working together or alone, may influence the frequency and severity of tumor-associated epilepsy.

Immunoexcitatory mechanisms in glioma proliferation, invasion and occasional metastasis

There is increasing evidence of an interaction between inflammatory cytokines and glutamate receptors among a number of neurological diseases including traumatic brain injuries, neurodegenerative diseases and central nervous system (CNS) infections. A number of recent studies have now suggested a strong relation between inflammatory mechanisms and excitatory cascades and these may play a role in glioma invasiveness and proliferation.

Chronic inflammation appears to be a major initiating mechanism in most human cancers, involving cell-signaling pathways, which are responsible for cell cycling, cancer cell migration, invasion, tumor aggressiveness, and angiogenesis. It is less well appreciated that glutamate receptors also play a significant role in both proliferation and especially glioma invasion. There is some evidence that sustained elevations in glutamate may play a role in initiating certain cancers and new studies demonstrate an interaction between inflammation and glutamate receptors that may enhance tumor invasion and metastasis by affecting a number of cell-signaling mechanisms. These mechanisms are discussed in this paper as well as novel treatment options for reducing immune-glutamate promotion of cancer growth and invasion.

Brain proton magnetic resonance spectroscopy: introduction and overview

Magnetic resonance (MR) spectroscopy offers a noninvasive means of assessing in vivo brain metabolites that shed light on cellular concentrations, cell function and dysfunction, cellular energetics, presence of ischemia, and presence of necrosis, among others. Studies obtained at higher field strengths are evolving toward sampling of smaller tissue volumes, greater signal-to-noise ratio, and higher metabolic spatial resolution. This article discusses the usefulness, from the clinical standpoint, of MR spectroscopy in various disorders. However, to be valid and significant the results of MR spectroscopy should always be correlated with their imaging counterparts.

Blood glutamate scavengers prolong the survival of rats and mice with brain-implanted gliomas

L-Glutamate (Glu) plays a crucial role in the growth of malignant gliomas. We have established the feasibility of accelerating a naturally occurring brain to-blood Glu efflux by decreasing blood Glu levels with intravenous oxaloacetate, the respective Glu co-substrate of the blood resident enzyme humane glutamate–oxaloacetate transaminase(hGOT). We wished to demonstrate that blood Glu scavenging provides neuroprotection in the case of glioma.We now describe the neuroprotective effects of blood Glu scavenging in a fatal condition such as brain-implanted C6 glioma in rats and brain-implanted human U87 MG glioma in nude mice. Rat (C-6) or human (U87) glioma cells were grafted stereotactically in the brain of rats or mice. After development of tumors, the animals were drinking oxaloacetate with or without injections of hGOT. In addition, mice were treated with combination treatment, which included drinking oxaloacetate with intracutaneous injections of hGOT and intraperitoneal injection of Temozolomide. Animals drinking oxaloacetate with or without injections of hGOT displayed a smaller tumor volume, reduced invasiveness and prolonged survival than control animals drinking saline. These effects were significantly enhanced by Temozolomide in mice, which increased survival by 237%. This is the first demonstration of blood Glu scavenging in brain cancer, and because of its safety, is likely to be of clinical significance for the future treatment of human gliomas. As we demonstrated, the blood glutamate scavenging treatment in combination with TMZ could be a good candidate or as an alternative treatment to the patients that do not respond to TMZ.

Imaging hypoxia in gliomas

Hypoxia plays a central role in tumour development, angiogenesis, growth and resistance to treatment. Owing to constant developments in medical imaging technology, significant advances have been made towards in vitro and in vivo imaging of hypoxia in a variety of tumours, including gliomas of the central nervous system. The aim of this article is to review the literature on imaging approaches currently available for measuring hypoxia in human gliomas and provide an insight into recent advances and future directions in this field. After a brief overview of hypoxia and its importance in gliomas, several methods of measuring hypoxia will be presented. These range from invasive monitoring by Eppendorf polarographic O(2) microelectrodes, positron electron tomography (PET) tracers based on 2-nitroimidazole compounds [(18)F-labelled fluoro-misonidazole ((18)F-MISO) or 1-(2-[((18))F]fluoro-1-[hydroxymethyl]ethoxy)methyl-2-nitroimidazole (FRP-170)], (64)Cu-ATSM Cu-diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) or (99m)Tc- and (68)Ga-labelled metronidazole (MN) agents to advanced MRI methods, such as blood oxygenation level dependent (BOLD) MRI, oxygen-enhanced MRI, diffusion-weighted MRI (DWI-MRI), dynamic contrast-enhanced MRI (DCE-MRI) and (1)H-magnetic resonance spectroscopy.

Biology, genetics and imaging of glial cell tumours

Despite advances in therapy, gliomas remain associated with poor prognosis. Clinical advances will be achieved through molecularly targeted biological therapies, for which knowledge of molecular genetic and gene expression characteristics in relation to histopathology and in vivo imaging are essential. Recent research supports the molecular classification of gliomas based on genetic alterations or gene expression profiles, and imaging data supports the concept that molecular subtypes of glioma may be distinguished through non-invasive anatomical, physiological and metabolic imaging techniques, suggesting differences in the baseline biology of genetic subtypes of infiltrating glioma. Furthermore, MRI signatures are now being associated with complex gene expression profiles and cellular signalling pathways through genome-wide microarray studies using samples obtained by image guidance which may be co-registered with clinical imaging. In this review we describe the pathobiology, molecular pathogenesis, stem cells and imaging characteristics of gliomas with emphasis on astrocytomas and oligodendroglial neoplasms.

Spectroscopic evaluation of glioma grading at 3T: the combined role of short and long TE

Purpose. To evaluate the diagnostic value of 3T ¹H-MRS in grading cerebral gliomas using short and long echo times. Methods. 1H-MRS was performed on 71 patients with untreated cerebral gliomas. Metabolite ratios of NAA/Cr, Cho/Cr, Cho/NAA, and mI/Cr were calculated for short and long TE and compared between low and high grade gliomas. Lipids were qualitatively evaluated. ROC analysis was performed to obtain the cut-off values for the metabolic ratios presenting statistical difference between the two glioma grades. Results. Intratumoral Cho/Cr at both TEs and long TE Cho/NAA were significantly different between low and high grade gliomas. Peritumoral NAA/Cr of both TEs, as well as long TE Cho/Cr and Cho/NAA ratios, significantly differentiated the two tumor grades. Diagnostic sensitivity of peritumoral short TE NAA/Cr proved to be superior over the other metabolic ratios, whereas intratumoral short TE Cho/Cr reached the highest levels of specificity and accuracy. Overall, short TE 1H-MRS reached higher total sensitivity in predicting glioma grade, over long TE. Conclusion. An advantage was found in using short TE over long TE 1H-MRS in the discrimination of low versus high grade gliomas. Moreover, the results suggested that the peritumoral area of gliomas may be more valuable in predicting glioma grade than using only the intratumoral area.

Human glioma cells induce hyperexcitability in cortical networks

PURPOSE

Patients with gliomas frequently present with seizures, but the factors associated with seizure development are still poorly understood. In this study, we assessed peritumoral synaptic network activity in a glioma animal model and tested the contribution of aberrant glutamate release from gliomas on glioma-associated epileptic network activity.

METHODS

In vitro brain slices were made from glioma-implanted mice. Using extracellular field recordings, we analyzed peritumoral epileptiform activity induced by Mg(2+)-free medium in slices from tumor-bearing animals and sham-operated controls. We assessed the effect of sulfasalazine (SAS), a blocker of system and glutamate release, on spontaneous and evoked activity in tumor-associated slices.

KEY FINDINGS

Tumor-associated cortical networks were hyperexcitable. The onset latency of Mg(2+)-free-induced epileptiform activity was significantly shorter in tumor-bearing slices, and the incidence of Mg(2+)-free-induced ictal-like events was higher. Block of glutamate release from system decreased the response area of evoked activity and completely blocked Mg(2+)-free-induced ictal-like, but not interictal-like events.

SIGNIFICANCE

Control of seizures in patients with gliomas is an essential component of clinical management; therefore, understanding the origin of seizures is vital. This work provides evidence that peritumoral synaptic network activity is disrupted by tumor masses resulting in network excitability. We show that blocking glutamate release via system with SAS, a drug already approved by the U.S. Food and Drug Administration (FDA), can inhibit Mg(2+)-free-induced ictal-like epileptiform events similar to other chemicals used to decrease seizure activity. We, therefore, suggest that further studies should consider SAS a promising agent to aid in the treatment of seizures associated with gliomas.

Blood glutamate scavengers prolong the survival of rats and mice with brain-implanted gliomas

L-Glutamate (Glu) plays a crucial role in the growth of malignant gliomas. We have established the feasibility of accelerating a naturally occurring brain to-blood Glu efflux by decreasing blood Glu levels with intravenous oxaloacetate, the respective Glu co-substrate of the blood resident enzyme humane glutamate-oxaloacetate transaminase (hGOT). We wished to demonstrate that blood Glu scavenging provides neuroprotection in the case of glioma. We now describe the neuroprotective effects of blood Glu scavenging in a fatal condition such as brain-implanted C6 glioma in rats and brain-implanted human U87 MG glioma in nude mice. Rat (C-6) or human (U87) glioma cells were grafted stereotactically in the brain of rats or mice. After development of tumors, the animals were drinking oxaloacetate with or without injections of hGOT. In addition, mice were treated with combination treatment, which included drinking oxaloacetate with intracutaneous injections of hGOT and intraperitoneal injection of Temozolomide. Animals drinking oxaloacetate with or without injections of hGOT displayed a smaller tumor volume, reduced invasiveness and prolonged survival than control animals drinking saline. These effects were significantly enhanced by Temozolomide in mice, which increased survival by 237%. This is the first demonstration of blood Glu scavenging in brain cancer, and because of its safety, is likely to be of clinical significance for the future treatment of human gliomas. As we demonstrated, the blood glutamate scavenging treatment in combination with TMZ could be a good candidate or as an alternative treatment to the patients that do not respond to TMZ.

Proton MR spectroscopy-detectable major neurotransmitters of the brain: biology and possible clinical applications

Neurotransmitters are chemical substances that, by definition, allow communication between neurons and permit most neuronal-glial interactions in the CNS. Approximately 80% of all neurons use glutamate, and almost all interneurons use GABA. A third neurotransmitter, NAAG, modulates glutamatergic neurotransmission. Concentration changes in these molecules due to defective synthetic machinery, receptor expression, or errors in their degradation and metabolism are accepted causes of several neurologic disorders. Knowledge of changes in neurotransmitter concentrations in the brain can add useful information in making a diagnosis, helping to pick the right drug of treatment, and monitoring patient response to drugs in a more objective manner. Recent advances in (1)H-MR spectroscopy hold promise in providing a more reliable in vivo detection of these neurotransmitters. In this article, we summarize the essential biology of 3 major neurotransmitters: glutamate, GABA, and NAAG. Finally we illustrate possible applications of (1)H-MR spectroscopy in neuroscience research.

Improved spatial coverage for brain 3D PRESS MRSI by automatic placement of outer-volume suppression saturation bands

PURPOSE

To develop a technique for optimizing coverage of brain 3D (1) H magnetic resonance spectroscopic imaging (MRSI) by automatic placement of outer-volume suppression (OVS) saturation bands (sat bands) and to compare the performance for point-resolved spectroscopic sequence (PRESS) MRSI protocols with manual and automatic placement of sat bands.

MATERIALS AND METHODS

The automated OVS procedure includes the acquisition of anatomic images from the head, obtaining brain and lipid tissue maps, calculating optimal sat band placement, and then using those optimized parameters during the MRSI acquisition. The data were analyzed to quantify brain coverage volume and data quality.

RESULTS

3D PRESS MRSI data were acquired from three healthy volunteers and 29 patients using protocols that included either manual or automatic sat band placement. On average, the automatic sat band placement allowed the acquisition of PRESS MRSI data from 2.7 times larger brain volumes than the conventional method while maintaining data quality.

CONCLUSION

The technique developed helps solve two of the most significant problems with brain PRESS MRSI acquisitions: limited brain coverage and difficulty in prescription. This new method will facilitate routine clinical brain 3D MRSI exams and will be important for performing serial evaluation of response to therapy in patients with brain tumors and other neurological diseases.

Multiparametric characterization of grade 2 glioma subtypes using magnetic resonance spectroscopic, perfusion, and diffusion imaging

BACKGROUND AND PURPOSE

The purpose of this study was to derive quantitative parameters from magnetic resonance (MR) spectroscopic, perfusion, and diffusion imaging of grade 2 gliomas according to the World Health Organization and to investigate how these multiple imaging modalities can contribute to evaluating their histologic subtypes and spatial characteristics.

MATERIALS AND METHODS

MR spectroscopic, perfusion, and diffusion images from 56 patients with newly diagnosed grade 2 glioma (24 oligodendrogliomas, 18 astrocytomas, and 14 oligoastrocytomas) were retrospectively studied. Metabolite intensities, relative cerebral blood volume (rCBV), and apparent diffusion coefficient (ADC) were statistically evaluated.

RESULTS

The 75th percentile rCBV and median ADC were significantly different between oligodendrogliomas and astrocytomas (P < .0001) and between oligodendrogliomas and oligoastrocytomas (P < .001). Logistic regression analysis identified both 75th percentile rCBV and median ADC as significant variables in the differentiation of oligodendrogliomas from astrocytomas and oligoastrocytomas. Group differences in metabolite intensities were not significant, but there was a much larger variation in the volumes and maximum values of metabolic abnormalities for patients with oligodendroglioma compared with the other tumor subtypes.

CONCLUSIONS

Perfusion and diffusion imaging provide quantitative MR parameters that can help to differentiate grade 2 oligodendrogliomas from grade 2 astrocytomas and oligoastrocytomas. The large variations in the magnitude and spatial extent of the metabolic lesions between patients and the fact that their values are not correlated with the other imaging parameters indicate that MR spectroscopic imaging may provide complementary information that is helpful in targeting therapy, evaluating residual disease, and assessing response to therapy.

Five-Year Longitudinal MRI Follow-up and (1)H Single Voxel MRS in 14 patients with Gliomatosis Treated with Temodal, Radiotherapy and Antiangiogenic Therapy

Gliomatosis cerebri (GC) is a challenging tumor, considered to have a poor prognosis and poor response to treatments. The purpose of this study is to better understand glial tumor metabolism and post chemotherapy, radiotherapy and antiangiogenic variations in a longitudinal study to determine cerebral variation in MRS area, amplitude, and ratios of metabolites and spectral profiles during a five year longitudinal follow-up in 14 patients with gliomatosis without initial hyperperfusion and treated with chemotherapy (Temozolomide (Temodal(®))), radiotherapy and subsequent antiangiogenic therapy. The study also aimed to detect changes in infiltration, proliferation, lipids or glycolytic metabolism, as these changes could be monitored longitudinally in humans with glial brain tumors (low and high grade) after therapy, using conventional magnetic resonance imaging (MRI), spectroscopy (MRS) and MR perfusion. Most patients had first initial clinical and MRS improvement and stable MRI. After 12 to 24 chemotherapy treatment cycles MRS usually showed an increase in the Cho/Cr ratio (proliferation) and sometimes contrast enhancements. Later, the patients showed clinical deterioration and radiotherapy was started. There was an improvement with radiotherapy that lasted nine to 18 months. This was followed by a worsening that led to try antiangiogenic therapy. Later in the evolution for three patients with hyperperfusion this symptom disappeared, but proliferation, infiltration and glycolytic metabolism remained at a high level. Spectroscopic and metabolic changes often occur well before clinical deterioration and sometimes before improvement. Therefore, MRS could be more sensitive and could detect changes earlier than MRI and is sometimes predictive. Despite the difficulty, the variability and unknown factors, these repeated measurements give us a better insight into the nature of the different processes, tumor progression and could lead to better understanding of therapeutic response.

Proton magnetic resonance spectroscopy in differentiating glioblastomas from primary cerebral lymphomas and brain metastases

OBJECTIVE

To differentiate glioblastomas, primary cerebral lymphomas (PCLs), and brain metastases using multivoxel proton magnetic resonance (MR) spectroscopic imaging.

METHODS

A total of 56 patients with brain neoplasms underwent MR imaging and proton MR spectroscopic imaging. The data were analyzed from contrast-enhancing and peritumoral regions (PTR). N-acetylaspartate/creatine (Cr), choline (Cho)/Cr, glutamate+glutamine/Cr, myo-inositol/Cr, and lipids+lactate/Cr ratios were computed, and pairwise comparisons between neoplasms were made using Mann-Whitney U tests.

RESULTS

The PTR demonstrated most significant differences in metabolite ratios. The Cho/Cr ratio in glioblastomas (0.46 [0.01]) was significantly higher than that in metastases (0.38 [0.02], P = 0.01). Significantly elevated Cho/Cr levels were also noted in PCLs (0.48 [0.03]) compared with those in metastases (P = 0.04). In addition, PCLs also demonstrated significantly higher lipids+lactate/Cr levels (11.83 [2.59]) compared with glioblastomas (4.50 [0.59], P = 0.003) and metastases (2.79 [0.33], P = 0.001).

CONCLUSIONS

Proton MR spectroscopic imaging from PTR may assist in the differentiation of glioblastomas, metastases, and PCLs.

Clinical pitfalls related to short and long echo times in cerebral MR spectroscopy

MR-spectroscopy (MRS) is a multiparameter diagnostic tool and modification of each parameter results in spectrum morphology changes. In particular, changing the echo time (TE) represents a useful tool to highlight different diagnostic elements, but also has significant impact on the spectrum morphology. Diagnostic errors can result if the role of TE is not properly considered. This article reviews the four most common TE-related pitfalls of MRS interpretation. Clinical practical methods to avoid such pitfalls are also suggested.

Glutamate and the biology of gliomas

Several important and previously unrecognized roles for the neurotransmitter glutamate in the biology of primary brain tumors have recently been elucidated. Glutamate is produced and released from glioma cells via the system x(c) (-) cystine glutamate transporter as a byproduct of glutathione synthesis. Glutamate appears to play a central role in the malignant phenotype of glioma via multiple mechanisms. By binding to peritumoral neuronal glutamate receptors, glutamate is responsible for seizure induction and similarly causes excitotoxicity, which aids the expansion of tumor cells into the space vacated by destroyed tissue. Glutamate also activates ionotropic and metabotropic glutamate receptors on glioma cells in a paracrine and autocrine manner. α-Amino-3-hydroxy-5-methyl-4-isoaxazolepropionate acid (AMPA) glutamate receptors lack the GluR2 subunit rendering them Ca(2+) permeable and capable of activating the AKT and MAPK pathways. Furthermore, these receptors are critical in aiding the invasion of glioma cells into normal brain. AMPA-Rs accumulate at focal adhesion sites where they may indirectly mediate interactions between the extracellular matrix and integrins. Glutamate receptor stimulation results in activation of focal adhesion kinase, which is critical to the regulation of growth factor and integrin-stimulated cell motility and invasion. The multitude of effects of glutamate on glioma biology supports the rationale for pharmacological targeting of glutamate receptors and transporters. Several ongoing and recently completed clinical trials are exploring the therapeutic potential of interrupting glutamate-mediated brain tumor growth.

Role of proton magnetic resonance spectroscopy in differentiating oligodendrogliomas from astrocytomas

BACKGROUND AND PURPOSE

Preoperative differentiation of astrocytomas from oligodendrogliomas is clinically important, as oligodendrogliomas are more sensitive to chemotherapy. The purpose of this study was to assess the role of proton magnetic resonance spectroscopy in distinguishing astrocytomas from oligodendrogliomas.

METHODS

Forty-six patients [astrocytomas (n= 17) and oligodendrogliomas (n= 29)] underwent magnetic resonance imaging and multi voxel proton magnetic resonance spectroscopic imaging before treatment. Peak areas for N-acetylaspartate (NAA), creatine (Cr), choline (Cho), myo-inositol (mI), glutamate/glutamine (Glx), and lipids + lactate (Lip+Lac) were analyzed from voxels that exhibited hyperintensity on fluid-attenuated inversion recovery images and were normalized to Cr from each voxel. The average metabolite/Cr ratios from these voxels were then compared between astrocytomas and oligodendrogliomas. Receiver-operating curve analyses were used as measures of differentiation accuracy of metabolite ratios. A threshold value for a metabolite ratio was estimated by maximizing the sum of sensitivity and specificity.

RESULTS

A significant difference in mI/Cr was observed between astrocytomas and oligodendrogliomas (.50 +/- .18 vs. 0.66 +/- 0.20, P < .05). Using a threshold value of .56 for mI/Cr ratio, it was possible to differentiate oligodendrogliomas from astrocytomas with a sensitivity of 72.4% and specificity of 76.4%.

CONCLUSION

These results suggest that mI/Cr might aid in distinguishing oligodendrogliomas from astrocytomas.

Molecular mechanisms of necrosis in glioblastoma: the role of glutamate excitotoxicity

Glioblastomas continue to rank among the most lethal primary human tumors. Despite treatment with the most rigorous surgical interventions along with the most optimal chemotherapeutic and radiation regimens, the median survival is just 12-15 mo for patients with glioblastoma. Among the histological hallmarks of glioblastoma, necrosis has been demonstrated to be a powerful predictor of poor patient prognosis. Over the years, there have been many advances in our understanding of the molecular mechanisms underlying glioblastoma formation, yet the mechanisms that lead to tumor necrosis remain unclear. One pathway that may lead to necrosis in glioblastoma involves the neurotransmitter, glutamate, which has been shown to accumulate in the peritumoral fluid as a result of decreased cellular uptake by glioblastoma cells. This accumulation leads to subsequent glutamate excitotoxicity and probable necrosis through a massive elevation of intracellular Ca(2+) and reduction in cellular ATP levels. We propose that a pathway involving tumor necrosis factor-alpha (TNFalpha), astrocyte-elevated gene-1 (AEG-1) and nuclear factor-kappaB (NFkappaB) leads to decreased glutamate uptake through coordinated downregulation of the excitatory amino acid transporter 2 (EAAT2), the glutamate transporter responsible for the majority of glutamate uptake in the human brain. In addition, we suggest that AEG-1 signaling, loss of phosphatase and tensin homolog (PTEN), and ionotropic glutamate receptor activity lead to AKT pathway activation, which results in nutrient overconsumption and necrosis. Together, these pathways provide a new perspective on glioblastoma necrosis involving the process of glutamate excitotoxicity. Future research should address the components of these molecular pathways in order to better understand the mechanism of necrosis in glioblastoma and to begin to develop targeted therapies that may improve patient prognosis in the future.