Accuracy of 2-hydroxyglutarate quantification by short-echo proton-MRS at 3 T: a phantom study

The diagnostic efficiency of integration of 2HG MRS and IVIM versus individual parameters for predicting IDH mutation status in gliomas in clinical scenarios: A retrospective study

PURPOSE

Currently, there remains a scarcity of established preoperative tests to accurately predict the isocitrate dehydrogenase (IDH) mutation status in clinical scenarios, with limited research has explored the potential synergistic diagnostic performance among metabolite, perfusion, and diffusion parameters. To address this issue, we aimed to develop an imaging protocol that integrated 2-hydroxyglutarate (2HG) magnetic resonance spectroscopy (MRS) and intravoxel incoherent motion (IVIM) by comprehensively assessing metabolic, cellular, and angiogenic changes caused by IDH mutations, and explored the diagnostic efficiency of this imaging protocol for predicting IDH mutation status in clinical scenarios.

METHODS

Patients who met the inclusion criteria were categorized into two groups: IDH-wild type (IDH-WT) group and IDH-mutant (IDH-MT) group. Subsequently, we quantified the 2HG concentration, the relative apparent diffusion coefficient (rADC), the relative true diffusion coefficient value (rD), the relative pseudo-diffusion coefficient (rD*) and the relative perfusion fraction value (rf). Intergroup differences were estimated using t-test and Mann-Whitney U test. Finally, we performed receiver operating characteristic (ROC) curve and DeLong's test to evaluate and compare the diagnostic performance of individual parameters and their combinations.

RESULTS

64 patients (female, 21; male, 43; age, 47.0 ± 13.7 years) were enrolled. Compared with IDH-WT gliomas, IDH-MT gliomas had higher 2HG concentration, rADC and rD (P < 0.001), and lower rD* (P = 0.013). The ROC curve demonstrated that 2HG + rD + rD* exhibited the highest areas under curve (AUC) value (0.967, 95%CI 0.889-0.996) for discriminating IDH mutation status. Compared with each individual parameter, the predictive efficiency of 2HG + rADC + rD* and 2HG + rD + rD* shows a statistically significant enhancement (DeLong's test: P < 0.05).

CONCLUSIONS

The integration of 2HG MRS and IVIM significantly improves the diagnostic efficiency for predicting IDH mutation status in clinical scenarios.

Application of 7T MRS to High-Grade Gliomas

MRS, including single-voxel spectroscopy and MR spectroscopic imaging, captures metabolites in high-grade gliomas. Emerging evidence indicates that 7T MRS may be more sensitive to aberrant metabolic activity than lower-field strength MRS. However, the literature on the use of 7T MRS to visualize high-grade gliomas has not been summarized. We aimed to identify metabolic information provided by 7T MRS, optimal spectroscopic sequences, and areas for improvement in and new applications for 7T MRS. Literature was found on PubMed using "high-grade glioma," "malignant glioma," "glioblastoma," "anaplastic astrocytoma," "7T," "MR spectroscopy," and "MR spectroscopic imaging." 7T MRS offers higher SNR, modestly improved spatial resolution, and better resolution of overlapping resonances. 7T MRS also yields reduced Cramér-Rao lower bound values. These features help to quantify D-2-hydroxyglutarate in isocitrate dehydrogenase 1 and 2 gliomas and to isolate variable glutamate, increased glutamine, and increased glycine with higher sensitivity and specificity. 7T MRS may better characterize tumor infiltration and treatment effect in high-grade gliomas, though further study is necessary. 7T MRS will benefit from increased sample size; reductions in field inhomogeneity, specific absorption rate, and acquisition time; and advanced editing techniques. These findings suggest that 7T MRS may advance understanding of high-grade glioma metabolism, with reduced Cramér-Rao lower bound values and better measurement of smaller metabolite signals. Nevertheless, 7T is not widely used clinically, and technical improvements are necessary. 7T MRS isolates metabolites that may be valuable therapeutic targets in high-grade gliomas, potentially resulting in wider ranging neuro-oncologic applications.

Synthesis of [1-13 C-5-12 C]-alpha-ketoglutarate enables noninvasive detection of 2-hydroxyglutarate

Isocitrate dehydrogenase 1 (IDH1) mutations that generate the oncometabolite 2-hydroxyglutarate (2-HG) from α-ketoglutarate (α-KG) have been identified in many types of tumors and are an important prognostic factor in gliomas. 2-HG production can be determined by hyperpolarized carbon-13 magnetic resonance spectroscopy (HP-¹³ C-MRS) using [1-¹³ C]-α-KG as a probe, but peak contamination from naturally occurring [5-¹³ C]-α-KG overlaps with the [1-¹³ C]-2-HG peak. Via a newly developed oxidative-Stetter reaction, [1-¹³ C-5-¹² C]-α-KG was synthesized. α-KG metabolism was measured via HP-¹³ C-MRS using [1-¹³ C-5-¹² C]-α-KG as a probe. [1-¹³ C-5-¹² C]-α-KG was synthesized in high yields, and successfully eliminated the signal from C5 of α-KG in the HP-¹³ C-MRS spectra. In HCT116 IDH1 R132H cells, [1-¹³ C-5-¹² C]-α-KG allowed for unimpeded detection of [1-¹³ C]-2-HG. ¹² C-enrichment represents a novel method to circumvent spectral overlap, and [1-¹³ C-5-¹² C]-α-KG shows promise as a probe to study IDH1 mutant tumors and α-KG metabolism.

In vivo characterization of physiological and metabolic changes related to isocitrate dehydrogenase 1 mutation expcression by multiparametric MRI and MRS in a rat model with orthotopically grafted human-derived glioblastoma cell lines

The physiological mechanism induced by the isocitrate dehydrogenase 1 (IDH1) mutation, associated with better treatment response in gliomas, remains unknown. The aim of this preclinical study was to characterize the IDH1 mutation through in vivo multiparametric MRI and MRS. Multiparametric MRI, including the measurement of blood flow, vascularity, oxygenation, permeability, and in vivo MRS, was performed on a 4.7 T animal MRI system in rat brains grafted with human-derived glioblastoma U87 cell lines expressing or not the IDH1 mutation by the CRISPR/Cas9 method, and secondarily characterized with additional ex vivo HR-MAS and histological analyses. In univariate analyses, compared with IDH1-, IDH1+ tumors exhibited higher vascular density (p < 0.01) and better perfusion (p = 0.02 for cerebral blood flow), but lower vessel permeability (p < 0.01 for time to peak (TTP), p = 0.04 for contrast enhancement) and decreased T1 map values (p = 0.02). Using linear discriminant analysis, vascular density and TTP values were found to be independent MRI parameters for characterizing the IDH1 mutation (p < 0.01). In vivo MRS and ex vivo HR-MAS analysis showed lower metabolites of tumor aggressiveness for IDH1+ tumors (p < 0.01). Overall, the IDH1 mutation exhibited a higher vascularity on MRI, a lower permeability, and a less aggressive metabolic profile. These MRI features may prove helpful to better pinpoint the physiological mechanisms induced by this mutation.

Association of preoperative seizures with tumor metabolites quantified by magnetic resonance spectroscopy in gliomas

Seizures are common in patients with gliomas; however, the mechanisms of epileptogenesis in gliomas have not been fully understood. This study hypothesized that analyzing quantified metabolites using magnetic resonance spectroscopy (MRS) might provide novel insights to better understand the epileptogenesis in gliomas, and specific metabolites might be indicators of preoperative seizures in gliomas. We retrospectively investigated patient information (gender, age at diagnosis of tumor, their survival time) and tumor information (location, histology, genetic features, and metabolites according to MRS) in patients with gliomas. The data were correlated with the incidence of seizure and analyzed statistically. Of 146 adult supratentorial gliomas, isocitrate dehydrogenase (IDH) mutant tumors significantly indicated higher incidence of preoperative seizures than IDH wild-type gliomas. However, MRS study indicated that glutamate concentration in IDH wild-type gliomas was higher than that in IDH mutant gliomas. Glutamate was not associated with high frequency of preoperative seizures in patients with gliomas. Instead, increased total N-acetyl-L-aspartate (tNAA) was significantly associated with them. Moreover, multivariable analysis indicated that increased level of tNAA was an independent predictor of preoperative seizures. According to MRS analysis, tNAA, rather than glutamate, might be a useful to detect preoperative seizures in patient with supratentorial gliomas.

In vivo 2-hydroxyglutarate-proton magnetic resonance spectroscopy (3 T, PRESS technique) in treatment-naïve suspect lower-grade gliomas: feasibility and accuracy in a clinical setting

Isocitrate dehydrogenase 1/2 (IDH1/2) mutations are often detected in lower-grade gliomas (LGG) and result into 2-hydroxyglutarate (2HG) synthesis. Prior studies showed that 2HG can be detected in vivo using magnetic resonance spectroscopy (MRS), but its accuracy and translational impact are still under investigation.

PURPOSE

To investigate the clinical feasibility of MRS for in vivo detection and quantification of 2HG on consecutive treatment-naïve suspect LGG patients and to compare MRS accuracy with tissue IDH1/2 analysis.

METHODS

MRS spectra at 3 T were acquired with 1H-MRS single-voxel PRESS 2HG-tailored sequences with TE 30 (group 1) or TE 97 (groups 2A and B). Voxel sizes were 1.5 × 1.5 × 1.5 cm³ for group 1 (n = 13) and group 2A (n = 14) and 2 × 2 × 2 cm³ for group 2B (n = 32). Multiple metabolites' concentrations were analyzed with LCModel. Tumors were assessed for IDH status and main molecular markers. 2HG levels in urine/blood were measured by liquid chromatography-mass spectrometry.

RESULTS

The larger voxel TE 97 sequence resulted in highest specificity (100%), sensitivity (79%), and accuracy (87%). Urine and blood 2HG did not result predictive.

CONCLUSION

Our data confirm that 2 × 2 × 2-cm³ voxel TE 97 MRS shows high accuracy for 2HG detection, with good sensitivity and 100% specificity in distinguishing IDH mutant gliomas. Main limits of the technique are small tumor volume and low cellularity. Integrating 2HG-MRS with other metabolites may help non-invasive diagnosis of glioma, prognostic assessment, and treatment planning in clinical setting.

Quantitative analysis of neurite orientation dispersion and density imaging in grading gliomas and detecting IDH-1 gene mutation status

Background and purpose

Neurite orientation dispersion and density imaging (NODDI) is a new diffusion MRI technique that has rarely been applied for glioma grading. The purpose of this study was to quantitatively evaluate the diagnostic efficiency of NODDI in tumour parenchyma (TP) and peritumoural area (PT) for grading gliomas and detecting isocitrate dehydrogenase-1 (IDH-1) mutation status.

Methods

Forty-two patients (male: 23, female: 19, mean age: 44.5 y) were recruited and underwent whole brain NODDI examination. Intracellular volume fraction (icvf) and orientation dispersion index (ODI) maps were derived. Three ROIs were manually placed on TP and PT regions for each case. The corresponding average values of icvf and ODI were calculated, and their diagnostic efficiency was assessed.

Results

Tumours with high icvf_TP (≥0.306) and low icvf_PT (≤0.331) were more likely to be high-grade gliomas (HGGs), while lesions with low icvf_TP (<0.306) and high icvf_PT (>0.331) were prone to be low-grade gliomas (LGGs) (P < 0.001). A multivariate logistic regression model including patient age and icvf values in TP and PT regions most accurately predicted glioma grade (AUC = 0.92, P < 0.001), with a sensitivity and specificity of 92% and 89%, respectively. However, no significant differences were found in NODDI metrics for differentiating IDH-1 mutation status.

Conclusions

The quantitative NODDI metrics in the TP and PT regions are highly valuable for glioma grading. A multivariate logistic regression model using the patient age and the icvf values in TP and PT regions showed very high predictive power. However, the utility of NODDI metrics for detecting IDH-1 mutation status has not been fully explored, as a larger sample size may be necessary to uncover benefits.

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Neurite orientation dispersion and density imaging (NODDI) is a new diffusion MRI technique

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Quantitative NOODI metrics in TP and PT area could help grading gliomas

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Age, icvf in TP and PT area were significantly associated with glioma grading

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The utility of NODDI in detecting IDH-1 mutation status has not been fully explored

Imaging Correlates of Adult Glioma Genotypes

Primary brain tumors, most commonly gliomas, are histopathologically typed and graded as World Health Organization (WHO) grades I-IV according to increasing degrees of malignancy. These grades provide prognostic information and guidance on treatment such as radiation therapy and chemotherapy after surgery. Despite the confirmed value of the WHO grading system, results of a multitude of studies and prospective interventional trials now indicate that tumors with identical morphologic criteria can have highly different outcomes. Molecular markers can allow subtypes of tumors of the same morphologic type and WHO grade to be distinguished and are, therefore, of great interest in personalization of brain tumor treatment. Recent genomic-wide studies have resulted in a far more comprehensive understanding of the genomic alterations in gliomas and provide suggestions for a new molecularly based classification. Magnetic resonance (MR) imaging phenotypes can serve as noninvasive surrogates for tumor genotypes and can provide important information for diagnosis, prognosis, and, eventually, personalized treatment. The newly emerged field of radiogenomics allows specific MR imaging phenotypes to be linked with gene expression profiles. In this article, the authors review the conventional and advanced imaging features of three tumoral genotypes with prognostic and therapeutic consequences: (a) isocitrate dehydrogenase mutation; (b) the combined loss of the short arm of chromosome 1 and the long arm of chromosome 19, or 1p19q codeletion; and (c) methylguanine methyltransferase promoter methylation. ^© RSNA, 2017.

Clinical Applications of Contrast-Enhanced Perfusion MRI Techniques in Gliomas: Recent Advances and Current Challenges

Gliomas possess complex and heterogeneous vasculatures with abnormal hemodynamics. Despite considerable advances in diagnostic and therapeutic techniques for improving tumor management and patient care in recent years, the prognosis of malignant gliomas remains dismal. Perfusion-weighted magnetic resonance imaging techniques that could noninvasively provide superior information on vascular functionality have attracted much attention for evaluating brain tumors. However, nonconsensus imaging protocols and postprocessing analysis among different institutions impede their integration into standard-of-care imaging in clinic. And there have been very few studies providing a comprehensive evidence-based and systematic summary. This review first outlines the status of glioma theranostics and tumor-associated vascular pathology and then presents an overview of the principles of dynamic contrast-enhanced MRI (DCE-MRI) and dynamic susceptibility contrast-MRI (DSC-MRI), with emphasis on their recent clinical applications in gliomas including tumor grading, identification of molecular characteristics, differentiation of glioma from other brain tumors, treatment response assessment, and predicting prognosis. Current challenges and future perspectives are also highlighted.

2-Hydoxyglutarate: D/Riving Pathology in gLiomaS

Common pathways and mechanisms can be found in both cancers and inborn errors of metabolism. 2-Hydroxyglutarate (2-HG) acidurias and isocitrate dehydrogenase (IDH) 1/2 mutant tumors are examples of this phenomenon. 2-HG can exist in two chiral forms, D(R)-2-HG and L(S)-2-HG, which are elevated in D- and L-acidurias, respectively. D-2-HG was subsequently discovered to be synthesized in IDH 1/2 mutant tumors including ∼70% of intermediate-grade gliomas and secondary glioblastomas (GBM). Recent studies have revealed that L-2-HG is generated in hypoxia in IDH wild-type tumors. Both 2-HG enantiomers have similar structures as α-ketoglutarate (α-KG) and can competitively inhibit α-KG-dependent enzymes. This inhibition modulates numerous cellular processes, including histone and DNA methylation, and can ultimately impact oncogenesis. D-2-HG can be detected in vivo in glioma patients and animal models using advanced imaging modalities. Finally, pharmacologic inhibitors of mutant IDH 1/2 attenuate the production of D-2-HG and show great promise as therapeutic agents.

Non-invasive metabolic imaging of brain tumours in the era of precision medicine

The revolution in cancer genomics has uncovered a variety of clinically relevant mutations in primary brain tumours, creating an urgent need to develop non-invasive imaging biomarkers to assess and integrate this genetic information into the clinical management of patients. Metabolic reprogramming is a central hallmark of cancer, including brain tumours; indeed, many of the molecular pathways implicated in the pathogenesis of brain tumours result in reprogramming of metabolism. This relationship provides the opportunity to devise in vivo metabolic imaging modalities to improve diagnosis, patient stratification, and monitoring of treatment response. Metabolic phenomena, such as the Warburg effect and altered mitochondrial metabolism, can be leveraged to image brain tumours using techniques including PET and MRI. Moreover, genetic alterations, such as mutations affecting isocitrate dehydrogenase, are associated with unique metabolic signatures that can be detected using magnetic resonance spectroscopy. The need to translate our understanding of the molecular features of brain tumours into imaging modalities with clinical utility is growing; metabolic imaging provides a unique platform to achieve this objective. In this Review, we examine the molecular basis for metabolic reprogramming in brain tumours, and examine current non-invasive metabolic imaging strategies that can be used to interrogate these molecular characteristics with the ultimate goal of guiding and improving patient care.

Diagnostic value of glutamate with 2-hydroxyglutarate in magnetic resonance spectroscopy for IDH1 mutant glioma

BACKGROUND

Mutations in the isocitrate dehydrogenase 1 (IDH1) gene that are frequently observed in low-grade glioma are strongly associated with the accumulation of 2-hydroxyglutarate (2HG), which is a valuable diagnostic and prognostic biomarker of IDH1 mutant glioma. However, conventional MR spectroscopy (MRS)-based noninvasive detection of 2HG is challenging. In this study, we aimed to determine the additional value of other metabolites in predicting IDH1 mutations with conventional MRS.

METHODS

Forty-seven patients with glioma underwent conventional single voxel short echo time MRS prior to surgery. A stereotactic navigation-guided operation was performed to resect tumor tissues in the center of the MRS voxel. MRS-based measurements of metabolites were validated with gas chromatography-mass spectrometry. We also conducted integrated analyses of glioma cell lines and clinical samples to examine the other metabolite levels and molecular findings in IDH1 mutant gliomas.

RESULTS

A metabolomic analysis demonstrated higher levels of 2HG in IDH1 mutant glioma cells and surgical tissues. Interestingly, glutamate levels were significantly decreased in IDH1 mutant gliomas. Through an analysis of metabolic enzyme genes in glutamine pathways, it was shown that the expressions of branched-chain amino acid transaminase 1 were reduced and glutamate dehydrogenase levels were elevated in IDH1 mutant gliomas. Conventional MRS detection of glutamate and 2HG resulted in a high diagnostic accuracy (sensitivity 72%, specificity 96%) for IDH1 mutant glioma.

CONCLUSIONS

IDH1 mutations alter glutamate metabolism. Combining glutamate levels optimizes the 2HG-based monitoring of IDH1 mutations via MRS and represents a reliable clinical application for diagnosing IDH1 mutant gliomas.

Clinical impact of molecular biomarkers in gliomas

The World Health Organization (WHO) classification system for glial tumors provides guidance as to the predicted course of the disease and choice of treatment. However, histologically identical tumors may have a very different outcome and response to treatment. Molecular markers that carry both diagnostic and prognostic information add valuable tools by redefining tumor subtypes within each WHO category. Therefore, molecular biomarkers have become an integral part of tumor assessment in modern neuro-oncology and biomarker status now guides clinical decisions in some subtypes of gliomas, including anaplastic oligodendroglioma and glioblastoma in the elderly. This review discusses the prognostic and predictive impact of molecular markers that have undergone extensive study in recent years. The clinical relevance of contemporary molecular classification of gliomas using the routine assessment of IDH mutations, promoter methylation of MGMT, chromosomal deletion of 1p/19q, mutations of EGFR and ATRX genes, and BRAF fusion or point mutation is highlighted. The potential of molecular biomarker-based classification to guide future therapeutic approach is discussed and accentuated.