Regional metabolite concentrations in human brain as determined by quantitative localized proton MRS

Utility of magnetic resonance spectroscopic imaging for human epilepsy

This review discusses the potential utility of broad based use of magnetic resonance (MR) spectroscopic imaging for human epilepsy and seizure localization. The clinical challenges are well known to the epilepsy community, intrinsic in the variability of location, volumetric size and network extent of epileptogenic tissue in individual patients. The technical challenges are also evident, with high performance requirements in multiple steps, including magnet homogeneity, detector performance, sequence design, speed of acquisition in addition to large territory spectral processing. We consider how MR spectroscopy and spectroscopic imaging has been informative for epilepsy thus far, with specific attention to what is measured, the interpretation of such measurements and technical performance challenges. Examples are shown from medial temporal lobe and neocortical epilepsies are considered from 4T, 7T and most recently 3T.

Investigating the microstructural and neurochemical environment within the basal ganglia of current methamphetamine abusers

BACKGROUND

Methamphetamine is a highly addictive psychostimulant and the medical, social, and economic consequences associated with its use have become a major international problem. Current evidence has shown methamphetamine to be particularly neurotoxic to dopamine neurons and striatal structures within the basal ganglia. A previous study from our laboratory demonstrated larger putamen volumes in actively using methamphetamine-dependent participants. The purpose of this current study was to determine whether striatal structures in the same sample of participants also exhibit pathology on the microstructural and molecular level.

METHODS

Diffusion tensor imaging (DTI) and magnetic resonance spectroscopy (MRS) were carried out in current methamphetamine users (n = 18) and healthy controls (n = 22) to investigate diffusion indices and neurometabolite levels in the basal ganglia.

RESULTS

Contrary to findings from previous DTI and MRS studies, no significant differences in diffusion indices or metabolite levels were observed in the basal ganglia regions of current methamphetamine users.

CONCLUSIONS

These findings differ from those reported in abstinent users and the absence of diffusion and neurochemical abnormalities may suggest that striatal enlargement in current methamphetamine use may be due to mechanisms other than edema and glial proliferation.

Enhanced axonal metabolism during early natalizumab treatment in relapsing-remitting multiple sclerosis

BACKGROUND AND PURPOSE

The considerable clinical effect of natalizumab in patients with relapsing-remitting multiple sclerosis might be explained by its possible beneficial effect on axonal functioning. In this longitudinal study, the effect of natalizumab on absolute concentrations of total N-acetylaspartate, a marker for neuronal integrity, and other brain metabolites is investigated in patients with relapsing-remitting multiple sclerosis by using MR spectroscopic imaging.

MATERIALS AND METHODS

In this explorative observational study, 25 patients with relapsing-remitting multiple sclerosis initiating natalizumab treatment were included and scanned every 6 months for 18 months. Additionally 18 matched patients with relapsing-remitting multiple sclerosis continuing treatment with interferon-β or glatiramer acetate were included along with 12 healthy controls. Imaging included short TE 2D-MR spectroscopic imaging with absolute metabolite quantification of total N-acetylaspartate, creatine and phosphocreatine, choline-containing compounds, myo-inositol, and glutamate. Concentrations were determined for lesional white matter, normal-appearing white matter, and gray matter.

RESULTS

At baseline in both patient groups, lower concentrations of total N-acetylaspartate and creatine and phosphocreatine were found in lesional white matter compared with normal-appearing white matter and additionally lower glutamate in lesional white matter of patients receiving natalizumab. In those patients, a significant yearly metabolite increase was found for lesional white matter total N-acetylaspartate (7%, P < .001), creatine and phosphocreatine (6%, P = .042), and glutamate (10%, P = .028), while lesion volumes did not change. In patients receiving interferon-β/glatiramer acetate, no significant change was measured in lesional white matter for any metabolite, while whole-brain normalized lesion volumes increased.

CONCLUSIONS

Patients treated with natalizumab showed an increase in total N-acetylaspartate, creatine and phosphocreatine, and glutamate in lesional white matter. These increasing metabolite concentrations might be a sign of enhanced axonal metabolism.

Noninvasive evaluation of the regional variations of GABA using magnetic resonance spectroscopy at 3 Tesla

PURPOSE

Rapid regional fluctuations in GABA may result in inhomogeneous concentrations throughout the brain parenchyma. The goal of this study is to provide further insight into the natural distribution of GABA throughout the brain and thus determine if a surrogate site may be used for spectroscopy when evaluating motor diseases, neurological disorders, or psychiatric dysfunction.

MATERIALS AND METHODS

In this prospective study, eight healthy volunteers underwent spectroscopic evaluation of the frontal lobe, occipital lobe, lateral temporal lobe, basal ganglia, and both hippocampi using a spin echo variant of a J-difference editing method. Knowledge of the relative peak intensities of the macromolecule peaks at 3ppm and 0.9ppm was used to correct the contribution of co-edited macromolecules to the GABA peak at 3ppm. The GABA values were internally referenced to NAA. Linear regression was used to normalize the effect of regional tissue-fraction variation on the GABA/NAA values. A one-way ANOVA was performed with Tukey's multiple comparison test to compare the normalized GABA/NAA values in each pair of locations.

RESULTS

After accounting for the macromolecule contribution to the GABA signal and correction for tissue fraction variation, the normalized GABA/NAA ratios differ significantly between the six brain locations (p<0.001). Pairwise comparisons of the corrected normalized GABA/NAA ratios show statistically significant variation between the frontal lobe and the basal ganglia, frontal and lateral temporal lobes, and frontal lobe and right hippocampus. Variations in the normalized GABA/NAA ratios trend toward significance between the frontal lobe and left hippocampus, occipital lobe and the frontal lobe, occipital lobe and basal ganglia, and occipital lobe and right hippocampus.

CONCLUSION

Our study suggests that GABA concentration is inhomogeneous throughout the parenchyma. Studies evaluating the role of GABA must carefully consider voxel placement when incorporating spectroscopy.

Assessing recovery from neurodegeneration in spinocerebellar ataxia 1: Comparison of in vivo magnetic resonance spectroscopy with motor testing, gene expression and histology

Suppression of transgene expression in a conditional transgenic mouse model of spinocerebellar ataxia 1 (SCA1) reverses the Purkinje cell pathology and motor dysfunction that are hallmarks of SCA1. We previously showed that cerebellar neurochemical levels measured by magnetic resonance spectroscopy (MRS) correlate with progression of pathology and clinical status of patients and that abnormal neurochemical levels normalize upon suppression of transgene expression, indicating their potential as robust surrogate markers of treatment effects. Here we investigated the relative sensitivities of MRS, histology, transgene expression and motor behavioral testing to disease reversal in conditional SCA1 mice. Transgene expression was suppressed by doxycycline administration and treated and untreated mice were assessed by MRS at 9.4tesla before and after treatment and with an accelerating Rotarod, histology and quantitative polymerase chain reaction (qPCR) for ataxin-1 transgene expression following doxycycline treatment. The MRS-measured N-acetylaspartate-to-myo-inositol ratio (NAA/Ins) correlated significantly with the molecular layer (ML) thickness and transgene expression. NAA/Ins, ML thickness and transgene expression were highly significantly different between the treated vs. untreated groups (p<0.0001), while the Rotarod assessment showed a trend for treatment effect. MRS, qPCR and histology had high sensitivity/specificity to distinguish treated from untreated mice, all with areas under the curve (AUC)=0.97-0.98 in receiver operating characteristic (ROC) analyses, while Rotarod had significantly lower sensitivity and specificity (AUC=0.72). Therefore, MRS accurately reflects the extent of recovery from neurodegeneration with sensitivity similar to invasive measures, further validating its potential as a surrogate marker in pre-clinical and clinical treatment trials.

N-acetylaspartate decrease in acute stage of ischemic stroke: a perspective from experimental and clinical studies

N-acetylaspartate (NAA) appears in a prominent peak in proton magnetic resonance spectroscopy ((1)H-MRS) of the brain. Exhibition by NAA of time-dependent attenuation that reflects energy metabolism during the acute stage of cerebral ischemia makes this metabolite a unique biomarker for assessing ischemic stroke. Although magnetic resonance (MR) imaging is a powerful technique for inspecting the pathological changes that occur during ischemic stroke, biomarkers that directly reflect the drastic metabolic changes associated with acute-stage ischemia are strongly warranted for appropriate therapeutic decision-making in daily clinical settings. In this review, we provide a brief overview of NAA metabolism and focus on the use of attenuation in NAA as a means for assessing the pathophysiological changes that occur during the acute stage of ischemic stroke.

Brain region mapping using global metabolomics

Historically, studies of brain metabolism have been based on targeted analyses of a limited number of metabolites. Here we present an untargeted mass spectrometry-based metabolomic strategy that has successfully uncovered differences in a broad array of metabolites across anatomical regions of the mouse brain. The NSG immunodeficient mouse model was chosen because of its ability to undergo humanization leading to numerous applications in oncology and infectious disease research. Metabolic phenotyping by hydrophilic interaction liquid chromatography and nanostructure imaging mass spectrometry revealed both water-soluble and lipid metabolite patterns across brain regions. Neurochemical differences in metabolic phenotypes were mainly defined by various phospholipids and several intriguing metabolites including carnosine, cholesterol sulfate, lipoamino acids, uric acid, and sialic acid, whose physiological roles in brain metabolism are poorly understood. This study helps define regional homeostasis for the normal mouse brain to give context to the reaction to pathological events.

Evaluation of normal changes in pons metabolites due to aging using turbo spectroscopic imaging

BACKGROUND AND PURPOSE

To date, MRS study of both normal and pathologic brains have focused mainly on the supratentorial regions; few studies have investigated the infratentorial regions. However, the pons, an important structure of the brain, is associated with many neurodegenerative diseases and is often damaged by brain trauma. For MRS study of pontine disease, one must obtain MRS reference data on normal metabolite levels in the pons, including data on how these levels vary with age. The aim of this study was to analyze normal, age-related, metabolic changes in the pons by using turbo spectroscopic imaging.

MATERIALS AND METHODS

Seventy-eight healthy subjects with ages ranging from 5 days to 78 years were included in this study. NAA/Cr, Cho/Cr, and Cho/NAA ratios were measured by using turbo spectroscopic imaging. The 78 cases were divided into 4 groups by age: 0-5, 6-20, 21-50, and older than 50 years. The metabolite levels were compared with observed age-related changes among the groups.

RESULTS

The normal mean pontine metabolite ratios obtained for the combined age groups were NAA/Cr, 2.44 ± 0.45 (mean); Cho/Cr, 1.93 ± 0.25; and Cho/NAA, 0.83 ± 0.28. Statistically significant differences were found in the NAA/Cr between the 0- to 5- and 6- to 20-year-old groups, and among the 6- to 20-, 21- to 50-, and older than 50-year-old groups. A statistically significant difference was found in Cho/Cr between the 0- to 5- and 6- to 20-year-old subjects; however, no differences were found among the 6- to 20-, 21- to 50-, and older than 50-year-old groups. Statistically significant differences in Cho/NAA were also found among the 4 age groups. The NAA/Cr at birth was low, it rose rapidly at 0-5 years, reaching a peak at approximately 10-20 years, and then gradually decreased. The Cho/Cr decreased rapidly at 0-5 years, then continued to decline, and was stable after 20 years of age.

CONCLUSIONS

Turbo spectroscopic imaging is a good method for analyzing normal changes in the pons metabolites during growth, maturation, and aging.

Regional and tissue-specific differences in brain glutamate concentration measured by in vivo single voxel MRS

BACKGROUND

There is growing interest in characterizing spatial distribution of glutamate (Glu) in brain disorders. Comparing the differences in Glu concentration using magnetic resonance spectroscopy (MRS) is hampered by the confounding effects of different anatomical regions and tissue composition.

NEW METHOD

Effect of tissue composition on Glu concentrations was studied by selecting closely adjacent voxels within a designated cortical region. Glu regional differences were assessed using voxels comprising essentially the same tissue composition from different cortical regions.

RESULTS

Using point-resolved-spectroscopy (PRESS)-based averaged echo time method, Glu concentration in the anterior cingulate cortex (ACC) was found to correlate strongly with tissue gray matter (GM) fraction (r=0.87, p=10(-5)). No significant regional difference in Glu concentration was found between frontal and occipital lobes (p=0.23) when the two measured voxels had essentially the same tissue composition.

COMPARISON WITH EXISTING METHODS

The method of the current study is aimed to circumvent the difficulties in differentiating anatomical region from tissue composition, given that both can lead to Glu variations in brain. Glu concentration versus tissue composition was measured in the same anatomical region, while the comparison of regional differences was performed with the two regions that had essentially the same tissue composition.

CONCLUSIONS

In brain cortices, Glu level is significantly higher in GM than in WM. Glu level difference between frontal lobe and occipital lobe is insignificant.

Striatal GABA-MRS predicts response inhibition performance and its cortical electrophysiological correlates

Response inhibition processes are important for performance monitoring and are mediated via a network constituted by different cortical areas and basal ganglia nuclei. At the basal ganglia level, striatal GABAergic medium spiny neurons are known to be important for response selection, but the importance of the striatal GABAergic system for response inhibition processes remains elusive. Using a novel combination of behavior al, EEG and magnetic resonance spectroscopy (MRS) data, we examine the relevance of the striatal GABAergic system for response inhibition processes. The study shows that striatal GABA levels modulate the efficacy of response inhibition processes. Higher striatal GABA levels were related to better response inhibition performance. We show that striatal GABA modulate specific subprocesses of response inhibition related to pre-motor inhibitory processes through the modulation of neuronal synchronization processes. To our knowledge, this is the first study providing direct evidence for the relevance of the striatal GABAergic system for response inhibition functions and their cortical electrophysiological correlates in humans.

Early metabolic development of posteromedial cortex and thalamus in humans analyzed via in vivo quantitative magnetic resonance spectroscopy

The posteromedial cortex (PMC) including the posterior cingulate, retrosplenial cortex, and medial parietal cortex/precuneus is an epicenter of cortical interactions in a wide spectrum of neural activity. Anatomic connections between PMC and thalamic components have been established in animal studies, but similar studies do not exist for the fetal and neonatal period. Magnetic resonance spectroscopy (MRS) allows for noninvasive measurement of metabolites in early development. Using single-voxel 3-T MRS, healthy term neonates (n = 31, mean postconception age 41.5 weeks ± 3.8 weeks) were compared with control children (n = 23, mean age 9.4 years ± 5.1 years) and young adults (n = 10, mean age 24.1 years ± 2.6 years). LCModel-based calculations compared metabolites within medial parietal gray matter (colocalizing to the PMC), posterior thalamus, and parietal white matter voxels. Common metabolic changes existed for neuronal-axonal maturation and structural markers in the PMC, thalamus, and parietal white matter with increasing NAA and glutamate and decreasing myoinositol and choline with age. Key differences in creatine and glucose metabolism were noted in the PMC, in contrast to the thalamic and parietal white matter locations, suggesting a unique role of energy metabolism. Significant parallel metabolite developmental changes of multiple other metabolites including aspartate, glutamine, and glutathione with age were present between PMC and parietal white matter but not between PMC and thalamus. These findings offer insight into the metabolic architecture of the interface between structural and functional topology of brain networks. Further investigation unifying metabolic changes with functional and anatomic pathways may further enhance the understanding of the PMC in posterior default mode network development.

Two-site reproducibility of cerebellar and brainstem neurochemical profiles with short-echo, single-voxel MRS at 3T

PURPOSE

To determine whether neurochemical concentrations obtained at two MRI sites using clinical 3T scanners can be pooled when a highly optimized, nonvendor short-echo, single-voxel proton MRS pulse sequence is used in conjunction with identical calibration and quantification procedures.

METHODS

A modified semi-LASER sequence (TE = 28 ms) was used to acquire spectra from two brain regions (cerebellar vermis and pons) on two Siemens 3T scanners using the same B0 and B1 calibration protocols from two different cohorts of healthy volunteers (N = 24-33 per site) matched for age and body mass index. Spectra were quantified with LCModel using water scaling.

RESULTS

The spectral quality was very consistent between the two sites and allowed reliable quantification of at least 13 metabolites in the vermis and pons compared with 3-5 metabolites in prior multisite magnetic resonance spectroscopy trials using vendor-provided sequences. The neurochemical profiles were nearly identical at the two sites and showed the feasibility to detect interindividual differences in the healthy brain.

CONCLUSION

Highly reproducible neurochemical profiles can be obtained on different clinical 3T scanners at different sites, provided that the same, optimized acquisition and analysis techniques are used. This will allow pooling of multisite data in clinical studies, which is particularly critical for rare neurological diseases.

Contributions of magnetic resonance spectroscopy to understanding development: potential applications in the study of adolescent alcohol use and abuse

A growing body of research has documented structural and functional brain development during adolescence, yet little is known about neurochemical changes that occur during this important developmental period. Magnetic resonance spectroscopy (MRS) is a well-developed technology that permits the in vivo quantification of multiple brain neurochemicals relevant to neuronal health and functioning. However, MRS technology has been underused in exploring normative developmental changes during adolescence and the onset of alcohol and drug use and abuse during this developmental period. This review begins with a brief overview of normative cognitive and neurobiological development during adolescence, followed by an introduction to MRS principles. The subsequent sections provide a comprehensive review of the existing MRS studies of development and cognitive functioning in healthy children and adolescents. The final sections of this article address the potential application of MRS in identifying neurochemical predictors and consequences of alcohol use and abuse in adolescence. MRS studies of adolescent populations hold promise for advancing our understanding of neurobiological risk factors for psychopathology by identifying the biochemical signatures associated with healthy brain development, as well as neurobiological and cognitive correlates of alcohol and substance use and abuse.

Longitudinal absolute metabolite quantification of white and gray matter regions in healthy controls using proton MR spectroscopic imaging

The purpose of this study was to evaluate quality parameters, metabolite concentrations and concentration ratios, and to investigate the reproducibility of quantitative proton magnetic resonance spectroscopic imaging ((1)H-MRSI) of selected white and gray matter regions of healthy adults. 2D-quantitative short-TE (1)H-MRSI spectra were obtained at 1.5T from the healthy human brain. Subjects (n = 12) were scanned twice with an interval of six months. Absolute metabolite concentrations were obtained based on coil loading, taking into account differences in sensitivity of the phased-array head coil. Spectral quality parameters, absolute metabolite concentrations, concentration ratios, and their reproducibility were determined and compared between time-points using a repeated measures general linear model. The quality of the spectra of selected brain areas was good, as determined by a mean spectral linewidth between 4.8 and 7.3 Hz (depending on the region). No significant differences between the two time-points were observed for spectral quality, concentrations, or concentration ratios. The mean intrasubject coefficient of variation (CoV) varied between 4.0 and 8.5% for total N-acetylaspartate, 7.2 and 10.8% for total creatine, 5.9 and 9.8% for myo-inositol, and 8.0 and 13.3% for choline, and remained below 20% for glutamate. CoV was generally lower when concentration ratios were considered. The study shows that longitudinal quantitative short-TE (1)H-MRSI generates reproducible absolute metabolite concentrations in healthy human white and gray matter. This may serve as a background for longitudinal clinical studies in adult patients.

Moderate relationships between NAA and cognitive ability in healthy adults: implications for cognitive spectroscopy

BACKGROUND

Proton Magnetic Resonance Spectroscopy ((1)H-MRS) is a non-invasive imaging technique that enables quantification of neurochemistry in vivo and thereby facilitates investigation of the biochemical underpinnings of human cognitive variability. Studies in the field of cognitive spectroscopy have commonly focused on relationships between measures of N-acetyl aspartate (NAA), a surrogate marker of neuronal health and function, and broad measures of cognitive performance, such as IQ.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we used (1)H-MRS to interrogate single-voxels in occipitoparietal and frontal cortex, in parallel with assessments of psychometric intelligence, in a sample of 40 healthy adult participants. We found correlations between NAA and IQ that were within the range reported in previous studies. However, the magnitude of these effects was significantly modulated by the stringency of data screening and the extent to which outlying values contributed to statistical analyses.

CONCLUSIONS/SIGNIFICANCE

(1)H-MRS offers a sensitive tool for assessing neurochemistry non-invasively, yet the relationships between brain metabolites and broad aspects of human behavior such as IQ are subtle. We highlight the need to develop an increasingly rigorous analytical and interpretive framework for collecting and reporting data obtained from cognitive spectroscopy studies of this kind.

Brain proton magnetic resonance spectroscopy of alcohol use disorders

This chapter critically reviews brain proton magnetic resonance spectroscopy ((1)H MRS) studies performed since 1994 in individuals with alcohol use disorders (AUD). We describe the neurochemicals that can be measured in vivo at the most common magnetic field strengths, summarize our knowledge about their general brain functions, and briefly explain some basic human (1)H MRS methods. Both cross-sectional and longitudinal research of individuals in treatment and of treatment-naïve individuals with AUD are discussed and interpreted on the basis of reported neuropathology. As AUDs are highly comorbid with chronic cigarette smoking and illicit substance abuse, we also summarize reports on their respective influences on regional proton metabolite levels. After reviewing research on neurobiologic correlates of relapse and genetic influences on brain metabolite levels, we finish with suggestions on future directions for (1)H MRS studies in AUDs. The review demonstrates that brain metabolic alterations associated with AUDs as well as their cognitive correlates are not simply a consequence of chronic alcohol consumption. Future MR research of AUDs in general has to be better prepared - and supported - to study clinically complex relationships between personality characteristics, comorbidities, neurogenetics, lifestyle, and living environment, as all these factors critically affect an individual's neurometabolic profile. (1)H MRS is uniquely positioned to tackle these complexities by contributing to a comprehensive biopsychosocial profile of individuals with AUD: it can provide non-invasive biochemical information on select regions of the brain at comparatively low overall cost for the ultimate purpose of informing more efficient treatments of AUDs.

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.

A Novel SLC6A8 Mutation in a Large Family with X-Linked Intellectual Disability: Clinical and Proton Magnetic Resonance Spectroscopy Data of Both Hemizygous Males and Heterozygous Females

X-linked creatine transport (CRTR) deficiency, caused by mutations in the SLC6A8 gene, leads to intellectual disability, speech delay, epilepsy, and autistic behavior in hemizygous males. Additional diagnostic features are depleted brain creatine levels and increased creatine/creatinine ratio (cr/crn) in urine. In heterozygous females the phenotype is highly variable and diagnostic hallmarks might be inconclusive. This survey aims to explore the intrafamilial variability of clinical and brain proton Magnetic Resonance Spectroscopy (MRS) findings in males and females with CRTR deficiency. X-chromosome exome sequencing identified a novel missense mutation in the SLC6A8 gene (p.G351R) in a large family with X-linked intellectual disability. Detailed clinical investigations including neuropsychological assessment, measurement of in vivo brain creatine concentrations using quantitative MRS, and analyses of creatine metabolites in urine were performed in five clinically affected family members including three heterozygous females and one hemizygous male confirming the diagnosis of CRTR deficiency. The severe phenotype of the hemizygous male was accompanied by most distinct aberrations of brain creatine concentrations (-83% in gray and -79% in white matter of age-matched normal controls) and urinary creatine/creatinine ratio. In contrast, the heterozygous females showed varying albeit generally milder phenotypes with less severe brain creatine (-50% to -33% in gray and -45% to none in white matter) and biochemical urine abnormalities. An intrafamilial correlation between female phenotype, brain creatine depletion, and urinary creatine abnormalities was observed. The combination of powerful new technologies like exome-next-generation sequencing with thorough systematic evaluation of patients will further expand the clinical spectrum of neurometabolic diseases.

Magnetic resonance spectroscopy in mild cognitive impairment: systematic review and meta-analysis

Research using proton magnetic resonance spectroscopy (MRS) can potentially elucidate metabolite changes representing early degeneration in Mild Cognitive Impairment (MCI), an early stage of dementia. We integrated the published literature using meta-analysis to identify patterns of metabolite changes in MCI. 29 MRS studies (with a total of 607 MCI patients and 862 healthy controls) were classified according to brain regions. Hedges' g was used as effect size in a random effects model. N-Acetyl Aspartate (NAA) measures were consistently reduced in posterior cingulate (PC), hippocampus, and the paratrigonal white matter (PWM). Creatine (Cr) concentration was reduced in the hippocampus and PWM. Choline (Cho) concentration was reduced in the hippocampus while Cho/Cr ratio was raised in the PC. Myo-inositol (mI) concentration was raised in the PC and mI/Cr ratio was raised in the hippocampus. NAA/mI ratio was reduced in the PC. NAA may be the most reliable marker of brain dysfunction in MCI though mI, Cho, and Cr may also contribute towards this.

Role of emerging neuroimaging modalities in patients with cognitive impairment: a review from the Canadian Consensus Conference on the Diagnosis and Treatment of Dementia 2012

The Fourth Canadian Consensus Conference on the Diagnosis and Treatment of Dementia (CCCDTD4) was held 3 to 4 May 2012 in Montreal, Quebec, Canada. A group of neuroimaging experts were assigned the task of reviewing and summarizing the literature on clinical and research applications of different neuroimaging modalities in cognitive disorders. This paper summarizes the literature and recommendations made to the conference regarding the role of several emerging neuroimaging modalities in cognitive disorders. Functional magnetic resonance imaging (MRI), magnetic resonance spectroscopy, and diffusion tensor imaging are discussed in detail within this paper. Other emergent neuroimaging modalities such as positron emission tomography with novel ligands, high-field MRI, arterial spin labeling MRI and noncerebral blood flow single-photon emission computerized tomography are only discussed briefly. Neuroimaging modalities that were recommended at the CCCDTD4 for both clinical and research applications such as amyloid and flurodeoxyglucose positron emission tomography, computerized tomography and structural MRI are discussed in a separate paper by the same authors. A literature search was conducted using the PubMed database including articles in English that involved human subjects and covered the period from the last CCCDTD publication (CCCDTD3; January 2006) until April 2012. Search terms included the name of the specific modality, dementia, Alzheimer's disease, and mild cognitive impairment. A separate search used the same parameters but was restricted to review articles to identify recent evidence-based reviews. Case studies and small case series were not included. Papers representing current evidence were selected, reviewed, and summarized, and the results were presented at the CCCDTD4 meeting with recommendations regarding the utility of various neuroimaging modalities in cognitive disorders. The evidence was graded according to the Oxford Centre for Evidence Based Medicine guidelines. Due to the limitations of current evidence, the neuroimaging modalities discussed in this paper were not recommended for clinical investigation of patients presenting with cognitive impairment. However, in the research setting, each modality provides a unique contribution to the understanding of basic mechanisms and neuropathological markers of cognitive disorders, to the identification of markers for early detection and for the risk of conversion to dementia in the at-risk populations, to the differentiation between different types of cognitive disorders, and to the identification of treatment targets and indicators of treatment response. In conclusion, for all of the neuroimaging modalities discussed in this paper, further studies are needed to establish diagnostic utility such as validity, reliability, and predictive and prognostic value. More multicenter studies are therefore needed with standardized image acquisition, experimental protocols, definition of the clinical population studied, larger numbers of participants, and longer duration of follow-up to allow generalizability of the results to the individual patient.

Computerized MRS voxel registration and partial volume effects in single voxel 1H-MRS

Partial volume effects in proton magnetic resonance spectroscopy in the brain have been studied previously in terms of proper water concentration calculations, but there is a lack of disclosure in terms of voxel placement techniques that would affect the calculations. The purpose of this study is to facilitate a fully automated MRS voxel registration method which is time efficient, accurate, and can be extended to all imaging modalities. A total of thirteen healthy adults underwent single voxel 1H-MRS scans in 3.0T MRI scanners. Transposition of a MRS voxel onto an anatomical scan is derived along with a full calculation of water concentration with a correction term to account for the partial volume effects. Five metabolites (tNAA, Glx, tCr, mI, and tCho) known to yield high reliability are studied. Pearson's correlation analyses between tissue volume fractions and metabolite concentrations were statistically significant in parietal (tCr, Glx, and tNAA) lobe and occipital lobe (tNAA). MRS voxel overlaps quantified by dice metric over repeated visits yielded 60%~70% and coefficients of variance in metabolites concentration were 4%~10%. These findings reiterate an importance of considering the partial volume effects when tissue water is used as an internal concentration reference so as to avoid misinterpreting a morphometric difference as a metabolic difference.

In vivo glutamate measured with magnetic resonance spectroscopy: behavioral correlates in aging

Altered availability of the brain biochemical glutamate might contribute to the neural mechanisms underlying age-related changes in cognitive and motor functions. To investigate the contribution of regional glutamate levels to behavior in the aging brain, we used an in vivo magnetic resonance spectroscopy protocol optimized for glutamate detection in 3 brain regions targeted by cortical glutamatergic efferents-striatum, cerebellum, and pons. Data from 61 healthy men and women ranging in age from 20 to 86 years were used. Older age was associated with lower glutamate levels in the striatum, but not cerebellum or pons. Older age was also predictive of poorer performance on tests of visuomotor skills and balance. Low striatal glutamate levels were associated with high systolic blood pressure and worse performance on a complex visuomotor task, the Grooved Pegboard. These findings suggest that low brain glutamate levels are related to high blood pressure and that changes in brain glutamate levels might mediate the behavioral changes noted in normal aging.

Altered reward circuitry in the norepinephrine transporter knockout mouse

Synaptic levels of the monoamine neurotransmitters dopamine, serotonin, and norepinephrine are modulated by their respective plasma membrane transporters, albeit with a few exceptions. Monoamine transporters remove monoamines from the synaptic cleft and thus influence the degree and duration of signaling. Abnormal concentrations of these neuronal transmitters are implicated in a number of neurological and psychiatric disorders, including addiction, depression, and attention deficit/hyperactivity disorder. This work concentrates on the norepinephrine transporter (NET), using a battery of in vivo magnetic resonance imaging techniques and histological correlates to probe the effects of genetic deletion of the norepinephrine transporter on brain metabolism, anatomy and functional connectivity. MRS recorded in the striatum of NET knockout mice indicated a lower concentration of NAA that correlates with histological observations of subtle dysmorphisms in the striatum and internal capsule. As with DAT and SERT knockout mice, we detected minimal structural alterations in NET knockout mice by tensor-based morphometric analysis. In contrast, longitudinal imaging after stereotaxic prefrontal cortical injection of manganese, an established neuronal circuitry tracer, revealed that the reward circuit in the NET knockout mouse is biased toward anterior portions of the brain. This is similar to previous results observed for the dopamine transporter (DAT) knockout mouse, but dissimilar from work with serotonin transporter (SERT) knockout mice where Mn²⁺ tracings extended to more posterior structures than in wildtype animals. These observations correlate with behavioral studies indicating that SERT knockout mice display anxiety-like phenotypes, while NET knockouts and to a lesser extent DAT knockout mice display antidepressant-like phenotypic features. Thus, the mainly anterior activity detected with manganese-enhanced MRI in the DAT and NET knockout mice is likely indicative of more robust connectivity in the frontal portion of the reward circuit of the DAT and NET knockout mice compared to the SERT knockout mice.

Regional difference in GABA levels between medial prefrontal and occipital cortices

PURPOSE

To avoid the confounding effects of variations in tissue composition this study measured regional GABA differences using two voxels with the same tissue composition.

MATERIALS AND METHODS

Eighteen healthy adult volunteers were scanned using a 3 Tesla GE clinical scanner with a J-coupling based editing sequence. Spectroscopy voxels were placed in the medial prefrontal (MPFC) and occipital cortex (OCC) with essentially the same gray and white matter fractions.

RESULTS

A 16% (P = 0.0001) significantly higher GABA to creatine ratio was found in the OCC (0.1103 ± 0.0050) compared with the MPFC (0.0953 ± 0.0041). When normalized to tissue water, GABA concentrations in the OCC were 14% higher than in the MPFC.

CONCLUSION

A difference in GABA concentration was found between the OCC and MPFC voxels in healthy subjects which is attributable to differences other than tissue composition.

Proton magnetic resonance spectroscopy: technique for the neuroradiologist

Magnetic resonance spectroscopy (MRS) provides information on neuronal and axonal viability, energetics of cellular structures, and status of cellular membranes. Proton MRS appeals to clinicians and scientists because its application in the clinical setting can increase the specificity of MR imaging. The objective of this article is to provide descriptive concepts of the technique and its application in vivo for a variety of patient populations. When appropriately incorporating MRS into the neuroradiologic evaluation, this technique produces relevant information to radiologists and clinicians for their understanding of adult and pediatric neurologically based disease processes.

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.

Brain dynamic neurochemical changes in dystonic patients: a magnetic resonance spectroscopy study

Measurements of the concentrations of γ-aminobutyric acid (GABA) and glutamate in the motor cortices and lentiform nuclei of dystonic patients using single-voxel (1)H magnetic resonance spectroscopy (MRS) have yielded conflicting results so far. This study aimed to investigate dynamic changes in metabolite concentrations after stimulation of the motor cortices in patients with upper limb dystonia. Using single-voxel MRS at 3 T, the concentrations of GABA, glutamate plus glutamine, and N-acetylaspartate were measured bilaterally in the primary sensorimotor cortex, lentiform nucleus, and occipital region before and after 5-Hz transcranial magnetic stimulation (TMS) over the dominant motor cortex. Data obtained from 15 patients with upper limb primary dystonia were compared with data obtained from 14 healthy volunteers. At baseline, there was no group difference in concentration of metabolites in any region. rTMS induced a local (in the stimulated motor cortex) decrease of N-acetylaspartate (P < .006) to the same extent in healthy volunteers and patients. GABA concentrations were modulated differently, however, decreasing mildly in patients and increasing mildly in healthy volunteers (P = .05). There were no remote effects in the lentiform nucleus in either group. The stimulation-induced changes in metabolite concentrations have been interpreted in view of the increased energy demand induced by rTMS. The dynamics of the GABA concentration were specifically impaired in dystonic patients. Whether these changes reflect changes in the extrasynaptic or synaptic GABA component is discussed.

Potential of MR spectroscopy for assessment of glioma grading

BACKGROUND

Magnetic resonance spectroscopy (MRS) is an imaging diagnostic method based that allows non-invasive measurement of metabolites in tissues. There are a number of metabolites that can be identified by standard brain proton MRS but only a few of them has a clinical significance in diagnosis of gliomas including N-acetylaspartate, choline, creatine, myo-inositol, lactate, and lipids.

METHODS

In this review, we describe potential of MRS for grading of gliomas.

RESULTS

Low-grade gliomas are generally characterized by a relatively high concentration of N-acetylaspartate, low level of choline and absence of lactate and lipids. The increase in creatine concentration indicates low-grade gliomas with earlier progression and malignant transformation. Progression in grade of a glioma is reflected in the progressive decrease in the N-acetylaspartate and myo-inositol levels on the one hand and elevation in choline level up to grade III on the other. Malignant transformation of the glial tumors is also accompanied by the presence of lactate and lipids in MR spectra of grade III but mainly grade IV gliomas. It follows that MRS is a helpful method for detection of glioma regions with aggressive growth or upgrading due to favorable correlation of the choline and N-acetylaspartate levels with histopathological proliferation index Ki-67. Thus, magnetic resonance spectroscopy is also a suitable method for the targeting of brain biopsies.

CONCLUSIONS

Gliomas of each grade have some specific MRS features that can be used for improvement of the diagnostic value of conventional magnetic resonance imaging in non-invasive assessment of glioma grade.

The role of gray and white matter segmentation in quantitative proton MR spectroscopic imaging

Since the brain's gray matter (GM) and white matter (WM) metabolite concentrations differ, their partial volumes can vary the voxel's ¹H MR spectroscopy (¹H-MRS) signal, reducing sensitivity to changes. While single-voxel ¹H-MRS cannot differentiate between WM and GM signals, partial volume correction is feasible by MR spectroscopic imaging (MRSI) using segmentation of the MRI acquired for VOI placement. To determine the magnitude of this effect on metabolic quantification, we segmented a 1-mm³ resolution MRI into GM, WM and CSF masks that were co-registered with the MRSI grid to yield their partial volumes in approximately every 1 cm³ spectroscopic voxel. Each voxel then provided one equation with two unknowns: its i- metabolite's GM and WM concentrations C(i) (GM) , C(i) (WM) . With the voxels' GM and WM volumes as independent coefficients, the over-determined system of equations was solved for the global averaged C(i) (GM) and C(i) (WM) . Trading off local concentration differences offers three advantages: (i) higher sensitivity due to combined data from many voxels; (ii) improved specificity to WM versus GM changes; and (iii) reduced susceptibility to partial volume effects. These improvements made no additional demands on the protocol, measurement time or hardware. Applying this approach to 18 volunteered 3D MRSI sets of 480 voxels each yielded N-acetylaspartate, creatine, choline and myo-inositol C(i) (GM) concentrations of 8.5 ± 0.7, 6.9 ± 0.6, 1.2 ± 0.2, 5.3 ± 0.6 mM, respectively, and C(i) (WM) concentrations of 7.7 ± 0.6, 4.9 ± 0.5, 1.4 ± 0.1 and 4.4 ± 0.6mM, respectively. We showed that unaccounted voxel WM or GM partial volume can vary absolute quantification by 5-10% (more for ratios), which can often double the sample size required to establish statistical significance.

Regional decoupling of N-acetyl-aspartate and glutamate in schizophrenia

Proton magnetic resonance spectroscopy (¹H-MRS) allows the non-invasive measurement of several metabolites, including N-acetyl-aspartate (NAA), an amino acid exclusively synthesized in the mitochondria of neurons, and glutamate, an amino acid involved in excitatory neurotransmission and metabolism. In view of recent postmortem studies in schizophrenia (SZ) revealing mitochondrial abnormalities as well as perturbed expression of the enzymes regulating the glutamate-glutamine cycle, we hypothesized that a disruption in the homeostasis of NAA and glutamate in SZ is present. Fifty subjects with SZ and 48 matched healthy controls (HC) were enrolled in this ¹H-MRS study. Voxels were placed in the anterior cingulate cortex (ACC) and hippocampus; NAA/Cr and glutamate + glutamine (Glx)/Cr ratios were obtained. We did not find any significant differences between the groups in metabolite levels in both the ACC and hippocampus. In the hippocampus we found that NAA/Cr and Glx/Cr ratios were significantly correlated in HC (r=0.40, p<0.01 (corrected p=0.048)) but not in SZ (r=-0.06; p=0.71), a difference that was statistically significant (z=2.22, p=0.02). Although no differences in neurometabolites between SZ and HC were apparent, correlations between NAA/Cr and Glx/Cr in healthy subjects in the hippocampus were found, and this correlation was lost in subjects with SZ. To our knowledge, this is the first study to suggest decoupling of these metabolites, a pathophysiological change that may be unique to SZ. However, these results warrant replication and further exploration before definite conclusions can be drawn.

Objectification and quantification of the cognitive impairment from an existing HIV infection or HIV encephalopathy using magnetic resonance spectroscopy

Some patients with HIV develop dementia. Using in vivo proton nuclear magnetic resonance ((1)H-NMR) spectroscopy, it is possible to measure the metabolic changes noninvasively. In this study, it is of interest to answer the clinically relevant question of whether magnetic resonance spectroscopy is suitable for the diagnosis of HIV encephalopathy. In total, 14 HIV-positive patients were investigated by means of localized (1)H-NMR spectroscopy in the following locations: (1) the mid-parietal gray matter, (2) the parietal white matter (PWM), and (3) the frontal white matter. All patients had no other brain diseases, apart from the HIV encephalopathy. The clinical extent of HIV encephalopathy of each patient was investigated using the following tests: (1) an electroencephalogram, (2) a neurological examination and psychiatric assessment, and (3) a psychometrical test. The spectroscopic changes in the PWM were more pronounced than those in the cortex, and the myo-inositol/creatine (mI/Cr) signal showed a clear increase in the cortex. Overall, the mI/Cr ratio emerged as the most reliable and earliest parameter to indicate an HIV encephalopathy.

In vivo spatially localized high resolution 1H MRS via intermolecular single-quantum coherence of rat brain at 7 T

PURPOSE

To compare the conventional localized point-resolved spectroscopy (PRESS) with localized 2D intermolecular single-quantum coherence (iSQC) magnetic resonance spectroscopy (MRS) and obtain in vivo MRS spectrum of rat brain using the latter technique.

MATERIALS AND METHODS

A brain phantom, an intact pig brain tissue, and mature Sprague-Dawley rat were studied by PRESS, Nano magic-angle spinning spectroscopy, and iSQC MRS.

RESULTS

Using PRESS, high-resolution MRS can be obtained from the brain phantom and pig brain tissue with a small voxel in a relatively homogeneous field. When a large voxel is selected, the field homogeneity is distinctly reduced. No useful information is obtained from the PRESS spectra. However, using the iSQC MRS, high-resolution spectra can be obtained from the two samples with a relatively large voxel. In the same way, an iSQC MRS spectrum can be obtained from a relatively large voxel of in vivo rat brain with a comparable resolution to the PRESS spectrum with a small voxel.

CONCLUSION

Compared to PRESS, the iSQC MRS may be more feasible and promising for detection of strongly structured tissues with relatively large voxels.

Anterior cingulate glutamate levels related to clinical status following treatment in first-episode schizophrenia

Many patients with schizophrenia show a limited symptomatic response to treatment with dopaminergic antipsychotics. This may reflect the additional involvement of non-dopaminergic neurochemical dysfunction in the pathophysiology of the disorder. We tested the hypothesis that brain glutamate levels would differ between patients with first-episode psychosis who were symptomatic compared with those with minimal symptoms following antipsychotic treatment. Proton magnetic resonance spectroscopy (1H-MRS) spectra were acquired at 3 Tesla in the anterior cingulate cortex and left thalamus in 15 patients with first-episode psychosis in symptomatic remission, and 17 patients with first-episode psychosis who were still symptomatic following at least one course of antipsychotic treatment. Metabolite levels were estimated in ratio to creatine (Cr) using LCModel. Levels of glutamate/Cr in the anterior cingulate cortex were significantly higher in patients who were still symptomatic than in those in remission (T(30)=3.02; P=0.005). Across the entire sample, higher levels of glutamate/Cr in the anterior cingulate cortex were associated with a greater severity of negative symptoms (r=0.42; P=0.017) and a lower level of global functioning (r=-0.47; P=0.007). These findings suggest that clinical status following antipsychotic treatment in schizophrenia is linked to glutamate dysfunction. Treatment with compounds acting on the glutamatergic system might therefore be beneficial in patients who respond poorly to dopaminergic antipsychotics.

Optimized quantitative magnetic resonance spectroscopy for clinical routine

Several practical obstacles in data handling and evaluation complicate the use of quantitative localized magnetic resonance spectroscopy (qMRS) in clinical routine MR examinations. To overcome these obstacles, a clinically feasible MR pulse sequence protocol based on standard available MR pulse sequences for qMRS has been implemented along with newly added functionalities to the free software package jMRUI-v5.0 to make qMRS attractive for clinical routine. This enables (a) easy and fast DICOM data transfer from the MR console and the qMRS-computer, (b) visualization of combined MR spectroscopy and imaging, (c) creation and network transfer of spectroscopy reports in DICOM format, (d) integration of advanced water reference models for absolute quantification, and (e) setup of databases containing normal metabolite concentrations of healthy subjects. To demonstrate the work-flow of qMRS using these implementations, databases for normal metabolite concentration in different regions of brain tissue were created using spectroscopic data acquired in 55 normal subjects (age range 6-61 years) using 1.5T and 3T MR systems, and illustrated in one clinical case of typical brain tumor (primitive neuroectodermal tumor). The MR pulse sequence protocol and newly implemented software functionalities facilitate the incorporation of qMRS and reference to normal value metabolite concentration data in daily clinical routine.

N-acetylcysteine normalizes glutamate levels in cocaine-dependent patients: a randomized crossover magnetic resonance spectroscopy study

Treatment with N-acetylcysteine (NAC) normalizes glutamate (Glu) homeostasis and prevents relapse in drug-dependent animals. However, the effect of NAC on brain Glu levels in substance-dependent humans has not yet been investigated. Proton magnetic resonance spectroscopy ((1)H MRS) was used to investigate Glu changes in the dorsal anterior cingulate cortex (dACC) after a single dose of NAC in cocaine-dependent patients and normal controls. In an open-label, randomized, crossover study, 8 cocaine-dependent patients and 14 healthy controls underwent two scan sessions: one group receiving no compound and the other following a single administration of 2400 mg NAC. The Barratt Impulsiveness Scale was administered to examine the relation between dACC Glu levels and impulsivity. In the medication-free condition, Glu levels in the dACC were significantly higher in cocaine-dependent patients compared with healthy controls. After administration of NAC, Glu levels were reduced in the cocaine-dependent group, whereas NAC had no effect in healthy controls. Higher baseline Glu levels were associated with higher impulsivity, and both were predictive of greater NAC-induced Glu reduction. The current findings indicate that NAC can normalize elevated Glu levels in cocaine-dependent patients. These findings may have important implications for treatment, because abnormal Glu levels are related to relapse, and treatment with NAC prevented relapse in animal studies. Furthermore, clinical studies have indicated beneficial effects of NAC in cocaine-dependent patients, and the current study suggests that these beneficial effects might in part be mediated by the ability of NAC to normalize glutamatergic abnormalities.

Quantitative short echo time 1H MRSI of the peripheral edematous region of human brain tumors in the differentiation between glioblastoma, metastasis, and meningioma

PURPOSE

To assess metabolite levels in peritumoral edematous (PO) and surrounding apparently normal (SAN) brain regions of glioblastoma, metastasis, and meningioma in humans with (1)H-MRSI to find biomarkers that can discriminate between tumors and characterize infiltrative tumor growth.

MATERIALS AND METHODS

Magnetic resonance (MR) spectra (semi-LASER MRSI, 30 msec echo time, 3T) were selected from regions of interest (ROIs) under MRI guidance, and after quality control of MR spectra. Statistical testing between patient groups was performed for mean metabolite ratios of an entire ROI and for the highest value within that ROI.

RESULTS

The highest ratios of the level of choline compounds and the sum of myo-inositol and glycine over N-acetylaspartate and creatine compounds were significantly increased in PO regions of glioblastoma versus that of metastasis and meningioma. In the SAN region of glioblastoma some of these ratios were increased. Differences were less prominent for metabolite levels averaged over entire ROIs.

CONCLUSION

Specific metabolite ratios in PO and SAN regions can be used to discriminate glioblastoma from metastasis and meningioma. An analysis of these ratios averaged over entire ROIs and those with most abnormal values indicates that infiltrative tumor growth in glioblastoma is inhomogeneous and extends into the SAN region.

Soft constraints in nonlinear spectral fitting with regularized lineshape deconvolution

This article presents a novel method for incorporating a priori knowledge into regularized nonlinear spectral fitting as soft constraints. Regularization was recently introduced to lineshape deconvolution as a method for correcting spectral distortions. Here, the deconvoluted lineshape was described by a new type of lineshape model and applied to spectral fitting. The nonlinear spectral fitting was carried out in two steps that were subject to hard constraints and soft constraints, respectively. The hard constraints step provided a starting point and, therefore, only the changes of the relevant variables were constrained in the soft constraints step and incorporated into the linear substeps of the Levenberg-Marquardt algorithm. The method was demonstrated using localized averaged echo time point resolved spectroscopy proton spectroscopy of human brains.

The heritability of brain metabolites on proton magnetic resonance spectroscopy in older individuals

Twin studies have shown that many aspects of brain structure are heritable, suggesting a strong genetic contribution to brain structure. Less is known about functional aspects of the brain, in particular biologically relevant metabolites in the brain such as those measured by proton magnetic resonance spectroscopy (((1))H MRS), N-acetyl-aspartate (NAA), creatine (Cr), choline (Cho) and myoinositol (ml), which have been suggested as possible markers of brain aging and early dementia. We examined 296 (56 male/108 female monozygotic and 43 male/89 female dizygotic) older twins (mean age 72.2 ± 5.5 years, range 65-88), for the levels of these metabolites relative to the H(2)O signal in the posterior cingulate cortex using ((1))H MRS. All metabolites showed substantial heritability, which was greatest for the neuronal integrity marker NAA (72%), and less so for the others - Cr (51%), Cho (33%) and ml (55%). The heritability of these markers did not change significantly with age or sex. The genetic determination of NAA, along with the evidence that NAA levels change in aging and neurodegenerative diseases suggest that it is a potential endophenotype of brain aging and dementia.

Hippocampal neurometabolite changes in depression treatment: a (1)H magnetic resonance spectroscopy study

Previous studies using magnetic resonance spectroscopy have related abnormalities in hippocampal metabolism to depression. Current evidence is consistent with the conclusion that the hippocampal formation plays an important role in the presentation of depressive symptoms. Eighteen adult patients with major depressive disorder, aged 20 to 60 years, underwent magnetic resonance spectroscopy of the hippocampus during a period of depressive symptomatology and after 7-11 weeks of antidepressant medication with at least 50% reduction in the Montgomery-Åsberg Depression Rating Scale ()MADRS score. During therapy, we found a significantly decreased Lac/Cr ratio in the left hippocampus. The Ins/Cr ratio showed a significant negative correlation with the severity of depression as assessed by the MADRS at baseline. Moreover, we found a negative association of NAA/Cho with age and a positive association of Cho/Cr with age, both on the left and right sides at baseline. In light of our findings and previous studies results we hypothesize that mitochondrial dysfunction leading to predominantly anaerobic glycolysis in connection with the intracellular signaling pathways disturbances and decreased astrocytic function/number might subsequently lead to decreased brain neuroplasticity in depression. These mechanisms could be positively influenced by antidepressant treatment with selective serotonin or norepineprine reuptake inhibitors, with potential effects on untimely neuronal aging in depression.

Localized 1H NMR spectroscopy in different regions of human brain in vivo at 7 T: T2 relaxation times and concentrations of cerebral metabolites

At the high field strength of 7 T, in vivo spectra of the human brain with exceptional spectral quality sufficient to quantify 16 metabolites have been obtained previously only in the occipital lobe. However, neurochemical abnormalities associated with many brain disorders are expected to occur in brain structures other than the occipital lobe. The purpose of the present study was to obtain high-quality spectra from various brain regions at 7 T and to quantify the concentrations of different metabolites. To obtain concentrations of metabolites within four different regions of the brain, such as the occipital lobe, motor cortex, basal ganglia and cerebellum, the T(2) relaxation times of the singlets and J-coupled metabolites in these regions were measured for the first time at 7 T. Our results demonstrate that high-quality, quantifiable spectra can be obtained in regions other than the occipital lobe at 7 T utilizing a 16-channel transceiver coil and B(1)(+) shimming.