Metabolite changes with age measured by proton magnetic resonance spectroscopy in normal subjects

Global brain volume and N-acetyl-aspartate decline over seven decades of normal aging

We characterize the whole-brain N-acetyl-aspartate (WBNAA) and brain tissue fractions across the adult lifespan and test the hypothesis that, despite age-related atrophy, neuronal integrity (reflected by WBNAA) is preserved in normal aging. Two-hundred-and-seven participants: 133 cognitively intact older adults (73.6 ± 7.4 mean ± standard deviation, range: 60-90 year old) and 84 young (37.9 ± 11, range: 21-59 year old) were scanned with proton magnetic resonance spectroscopy and T₁-weighted MRI. Their WBNAA, fractional brain parenchyma, and gray and white matter volumes (fBPV, fGM, and fWM) were compared and modeled as functions of age and sex. Compared with young, older-adults' WBNAA was lower by ~35%, and fBPV, fGM and fWM were lower by ~10%. Linear regressions found 0.5%/year WBNAA and 0.2%/year fBPV and fGM declines, whereas fWM rose to age ~40 years, and declined thereafter. fBPV and fGM were 1.8% and 4% higher in women, with no sex decline rates difference. We conclude that contrary to our hypothesis, atrophy was accompanied by WBNAA decline. Across the entire age range, women's brains showed less atrophy than men's. Formulas to estimate WBNAA and brain tissue fractions in healthy adults are provided to help differentiate normal from abnormal aging.

From fetus to older age: A review of brain metabolic changes across the lifespan

INTRODUCTION

The knowledge of metabolic changes across the lifespan is poorly understood. Thus we systematically reviewed the available literature to determine the changes in brain biochemical composition from fetus to older age and tried to explain them in the context of neural, cognitive, and behavioural changes.

METHODS

The search identified 1262 articles regarding proton magnetic resonance spectroscopy (1H MRS) examinations through December 2017. The following data was extracted: age range of the subjects, number of subjects studied, brain regions studied, MRS sequence used, echo time, MR system, method of statistical analysis, metabolites analyzed, significant differences in metabolites concentrations with age as well as the way of presentation of the results.

RESULTS

82 studies that described brain metabolite changes with age were identified. Reports on metabolic changes related to healthy aging were analyzed and discussed among six basic age groups: fetuses, infants, children, adolescents, adults, and the elderly as well as between groups and during the whole lifetime.

DISCUSSION

The results presented in the reviewed papers provide evidence that normal aging is associated with a number of metabolic changes characteristic for every period of life. Therefore, it can be concluded that the age matching is essential for comparative studies of disease states using 1H MRS.

A quantitative analysis of (1)H-MR spectroscopy at 3.0 T of three brain regions from childhood to middle age

OBJECTIVE

To study age-related metabolic changes in different brain regions.

METHODS

Point-resolved spectroscopy (repetition time/echo time = 2000 ms/30 ms) was performed in the left and right hippocampus, the left thalamus and the left centrum semiovale of 80 healthy subjects (37 females and 43 males aged 7-64 years). Analysis of covariance and linear regression were used for statistical analysis. Both metabolite concentration ratios with respect to total creatine (tCr) and absolute metabolite concentrations were included for analysis.

RESULTS

Ins (myo-inositol)/tCr (p < 0.001) and absolute Ins concentration (p = 0.031) were significantly increased with age after adolescence. NAA (N-acetylaspartic acid)/tCr (p < 0.001) and absolute NAA concentration (p = 0.010) significantly declined with age after adolescence.

CONCLUSION

Age-related increase of Ins and decline of NAA are found in all three regions, especially at the hippocampus, indicating possible gliosis in the ageing brain.

ADVANCES IN KNOWLEDGE

We could use NAA/tCr and Ins/tCr as an indicator to estimate the neurons-to-glial cells ratio at the thalamus. This may be an index to distinguish normal tissues from gliosis.

Telling true from false: cannabis users show increased susceptibility to false memories

Previous studies on the neurocognitive impact of cannabis use have found working and declarative memory deficits that tend to normalize with abstinence. An unexplored aspect of cognitive function in chronic cannabis users is the ability to distinguish between veridical and illusory memories, a crucial aspect of reality monitoring that relies on adequate memory function and cognitive control. Using functional magnetic resonance imaging, we show that abstinent cannabis users have an increased susceptibility to false memories, failing to identify lure stimuli as events that never occurred. In addition to impaired performance, cannabis users display reduced activation in areas associated with memory processing within the lateral and medial temporal lobe (MTL), and in parietal and frontal brain regions involved in attention and performance monitoring. Furthermore, cannabis consumption was inversely correlated with MTL activity, suggesting that the drug is especially detrimental to the episodic aspects of memory. These findings indicate that cannabis users have an increased susceptibility to memory distortions even when abstinent and drug-free, suggesting a long-lasting compromise of memory and cognitive control mechanisms involved in reality monitoring.

Metabolomic approach to human brain spectroscopy identifies associations between clinical features and the frontal lobe metabolome in multiple sclerosis

Proton magnetic resonance spectroscopy ((1)H-MRS) is capable of noninvasively detecting metabolic changes that occur in the brain tissue in vivo. Its clinical utility has been limited so far, however, by analytic methods that focus on independently evaluated metabolites and require prior knowledge about which metabolites to examine. Here, we applied advanced computational methodologies from the field of metabolomics, specifically partial least squares discriminant analysis and orthogonal partial least squares, to in vivo (1)H-MRS from frontal lobe white matter of 27 patients with relapsing-remitting multiple sclerosis (RRMS) and 14 healthy controls. We chose RRMS, a chronic demyelinating disorder of the central nervous system, because its complex pathology and variable disease course make the need for reliable biomarkers of disease progression more pressing. We show that in vivo MRS data, when analyzed by multivariate statistical methods, can provide reliable, distinct profiles of MRS-detectable metabolites in different patient populations. Specifically, we find that brain tissue in RRMS patients deviates significantly in its metabolic profile from that of healthy controls, even though it appears normal by standard MRI techniques. We also identify, using statistical means, the metabolic signatures of certain clinical features common in RRMS, such as disability score, cognitive impairments, and response to stress. This approach to human in vivo MRS data should promote understanding of the specific metabolic changes accompanying disease pathogenesis, and could provide biomarkers of disease progression that would be useful in clinical trials.

Frontal white matter biochemical abnormalities in first-episode, treatment-naive patients with major depressive disorder: a proton magnetic resonance spectroscopy study

BACKGROUND

Previous neuroimaging studies found evidence of brain functional and structural abnormalities in patients with major depressive disorder (MDD), but they rarely excluded compounding effects of some important factors, such as medication and brain degeneration. This study sought to explore the brain biochemical changes of first-episode, treatment-naive, non-late-life adult patients with MDD in the frontal white matter and gray matter by using proton magnetic resonance spectroscopy (1H MRS).

METHODS

Twenty-four first-episode, treatment-naive, non-late-life adult depressed patients and 13 healthy controls were enrolled in this study. Subjects underwent two-dimensional multivoxel 1H MRS at 1.5 T to obtain bilateral metabolite levels from the dorsolateral prefrontal white matter and anterior cingulate gray matter.

RESULTS

Patients with MDD showed significantly lower N-acetylaspartate/creatine (NAA/Cr) and choline/creatine (Cho/Cr) ratios in the left dorsolateral prefrontal white matter, and lower NAA/Cr ratios in the right dorsolateral prefrontal white matter when compared with the control subjects. There were no significant differences in the metabolite ratios in the bilateral anterior cingulate gray matter.

CONCLUSIONS

These findings suggest that biochemical abnormalities in prefrontal white matter may occur early in the course of MDD and may be related to the neuropathology of depression.

Whole brain N-acetylaspartate concentration is conserved throughout normal aging

We hypothesize that normal aging implies neuronal durability, reflected by age-independent concentrations of their marker--the amino acid derivative N-acetylaspartate (NAA). To test this, we obtained the whole-brain and whole-head N-acetylaspartate concentrations (WBNAA and WHNAA) with proton magnetic resonance (MR) spectroscopy; and the fractional brain parenchyma volume (fBPV)--a metric of atrophy, by segmenting the magnetic resonance image (MRI) from 42 (18 male) healthy young (31.9 ± 5.8 years old) and 100 (64 male, 72.6 ± 7.3 years old) cognitively normal elderly. The 12.8 ± 1.9 mM WBNAA of the young was not significantly different from the 13.1 ± 3.1 mM in the elderly (p > 0.05). In contrast, both fBPV (87.3 ± 4.7% vs. 74.8 ± 4.8%) and WHNAA (11.1 ± 1.7 mM vs. 9.8 ± 2.4 mM) were significantly higher in the young (approximately 14%; p < 0.0001 for both). The similarity in mean WBNAA between 2 cohorts 4 decades of normal aging apart suggests that neuronal integrity is maintained across the lifespan. Clinically, WBNAA could be used as a marker for normal (hence, also abnormal) brain aging. In contrast, WHNAA and fBPV seem age-related suggesting that brain atrophy may occur without compromising the remaining tissue.

Antidepressant effect detected on proton magnetic resonance spectroscopy in drug-naïve female patients with first-episode major depression

AIM

Recent neuroimaging studies support functional and structural alterations in the dorsolateral prefrontal cortex (DLPFC), particularly on the left side in patients with major depressive disorders (MDD). The aim of the present study was to examine the biochemical characteristics of left DLPFC as measured on proton ((1)H) magnetic resonance spectroscopy (MRS) in patients with drug-naïve first-episode MDD and a healthy control group. A second aim was to assess the effect of antidepressant treatment on the metabolites of DLPFC.

METHODS

Short-echo single-voxel (1)H-MRS was done for the left DLPFC in 17 female drug-free MDD patients (mean age +/- SD, 30.9 +/- 6.9 years) and 13 matched control subjects (mean age +/- SD, 29.1 +/- 6.2 years) and was repeated at 8 weeks following antidepressant treatment.

RESULTS

Comparison of baseline values indicated that there were no significant differences in any of the metabolite ratios (N-acetyl aspartate/creatine [NAA/Cr], myoinositol [Ino]/Cr, and choline [Cho]/Cr) between patients and controls. Significant differences were detected between pre- and post-treatment Ino/Cr ratios (0.67 +/- 0.13, 0.58 +/- 0.22, P = 0.032, respectively), although there was no difference in NAA/Cr and Cho/Cr ratios.

CONCLUSION

Although no significant metabolic alterations exist in female patients with drug-naïve first-episode MDD as evaluated on (1)H-MRS, an increase in Ino/Cr was observed following 8-week antidepressant treatment. These findings give rise to the possibility that non-neuronal cells, particularly glial cells that are probably damaged, play a role in the action of antidepressant treatment.

A systematic review of brain metabolite changes, measured with 1H magnetic resonance spectroscopy, in healthy aging

BACKGROUND

(1)H MR spectroscopy (MRS) can identify metabolite abnormalities in age-related, neurological diseases. However, there is little information on how metabolites change with healthy aging.

METHODS

We systematically reviewed the literature on MRS, from 1980 to 2006, for studies where healthy young subjects (<60 years) were compared to healthy older subjects (>60 years). We extracted metabolite data reported as "no change", "increase" or "decrease" for each metabolite by brain region and, where data were available, meta-analysed mean metabolite concentrations (mM) for young versus old subjects.

RESULTS

Eighteen studies met the inclusion criteria (total n=703 subjects, 284 >60 years old). Most data came from the frontal region, and reported "no change" in older subjects; however, a meta-analysis revealed a decrease in frontal NAA (p=0.05) and increases in parietal choline (p=0.003) and creatine (p<0.001).

DISCUSSION

These data suggest that NAA may decrease and choline and creatine increase with age. Therefore, more data are needed from older subjects to characterise age effects better and ratios in older subjects should be interpreted with caution.

Metabolic alterations in medication-free patients with bipolar disorder: a 3T CSF-corrected magnetic resonance spectroscopic imaging study

The objective of this study was to determine whether cerebrospinal fluid(CSF)-corrected concentrations of N-acetylaspartate are lower in several brain regions of drug- and medication-free subjects with bipolar disorder as compared with matched healthy controls. Bipolar subjects (n=21) and age- and sex-matched healthy control (n=21) were studied using proton magnetic resonance spectroscopic imaging on a 3T magnetic resonance (MR) scanner. Spectra were quantified using the LCModel, and metabolite values were CSF-corrected to yield metabolite concentrations. Fourteen regions of interest and five metabolite concentrations in each subject were selected for statistical analysis. We found that bipolar subjects had significantly decreased N-acetylaspartate concentrations in both caudate heads and the left lentiform nucleus. Choline and creatine in the head of the right caudate were also significantly decreased in bipolar subjects. Significantly increased myo-inositol was found in the left caudate head in bipolar subjects. Bipolar subjects showed significantly decreased glutamate/glutamine concentrations in the frontal white matter bilaterally and in the right lentiform nucleus. No differences were found for other metabolites examined. These preliminary findings suggest decreased neuronal density or viability in the basal ganglia and neurometabolic abnormalities in the frontal lobes of subjects with bipolar disorder.

Proton magnetic resonance spectroscopy (1H-MRS) of hippocampus, basal ganglia, and vermis of cerebellum in schizophrenia associated with idiopathic unconjugated hyperbilirubinemia (Gilbert's syndrome)

OBJECTIVE

Whether patients with schizophrenia-associated idiopathic unconjugated hyperbilirubinemia (Gilbert's syndrome, GS) have specific changes in brain metabolism was examined in this study.

METHOD

This study applied proton magnetic resonance spectroscopy (1H-MRS) to the hippocampus, basal ganglia, and vermis of the cerebellum of schizophrenic patients with GS (n=15) or without GS (n=15), all diagnosed according to DSM-IV criteria, and healthy subjects (n=15).

RESULTS

In the hippocampus, schizophrenic patients with GS showed a significant decrease of N-acetyl aspartate/creatine-phosphocreatinine (NAA/Cr) and myoinositol/creatine-phosphocreatinine (mI/Cr) ratios compared to healthy subjects and schizophrenic patients without GS, while schizophrenic patients without GS showed only a significant decrease of NAA/Cr compared to healthy subjects. In the basal ganglia, schizophrenic patients with GS showed a significant decrease of ml/Cr compared to schizophrenic patients without GS and healthy subjects, and schizophrenic patients with GS showed a significant decrease of NAA/Cr compared to healthy subjects. In the vermis of the cerebellum, schizophrenic patients with GS showed only a significant decrease of ml/Cr compared to healthy subjects, although schizophrenic patients without GS did not show a significant decrease of ml/Cr compared to healthy subjects.

CONCLUSION

The findings suggest that schizophrenia with GS is a more severe sub-type with regard to brain metabolism.

In vivo proton magnetic resonance spectroscopy of the temporal lobe in Alzheimer's disease

PURPOSE

Prior proton magnetic resonance spectroscopy (MRS) studies have consistently reported decreased brain n-acetyl aspartate (NAA) levels and increased myo-inositol (mI) levels in subjects with Alzheimer's disease (AD) relative to healthy comparison subjects. These studies have usually been conducted in small and homogeneous populations of patients with established Alzheimer's disease. Few studies have tested the usefulness of this finding in a general population seeking evaluation for memory loss and other cognitive declines. We designed a study to evaluate the significance of single-voxel proton MRS findings in these patients with memory loss and other cognitive declines. GENERAL METHOD: Thirty-five subjects with a primary complaint of memory loss and other cognitive declines were consecutively referred over a period of 13 months to a specialty clinic. Patients with a diagnosis of mild to moderate probable Alzheimer's disease (N = 22), non-Alzheimer's dementia (depression, multiinfarct dementia, Parkinson's Disease, Korsakoff's Psychosis, and bipolar disorder; N = 13), and healthy comparison subjects (N = 18) were examined with respect to possible differences in metabolites using proton MRS in a 3.4-ml anterior temporal lobe voxel.

FINDINGS

The Alzheimer's disease group had 10.7% lower NAA/creatine (Cr) ratios relative to the healthy comparison group and 9.4% lower NAA/creatine relative to the non-Alzheimer's dementia group (15.0% lower NAA/creatine relative to the depression subgroup of the non-Alzheimer's dementia group). There were no significant differences in choline (Cho) or myo-inositol ratios among the groups. There were significant correlations between NAA/creatine ratios and mini-mental status exam (MMSE) scores in subjects with Alzheimer's disease (t = 2.41, p = 0.032) but not in subjects with non-Alzheimer's dementia or in its depression subgroup.

CONCLUSIONS

This study found a reduction in the neuronal marker NAA in the anterior temporal lobe of patients diagnosed with probable Alzheimer's disease, using a short add-on proton MRS exam. This change was not observed in patients whose memory loss and other cognitive declines were not attributed to Alzheimer's disease, suggesting that it may aid in the diagnosis or detection of Alzheimer's disease.

Qualitative MRI: evidence of usual aging in the brain

The understanding of aging in our society with steadily increasing life expectancy is an important challenge in medical science since socioeconomic pressure increases in parallel. Magnetic resonance imaging is a most useful tool to explore age related changes in the central nervous system especially in the brain. This article will focus on current knowledge and importance of such changes. Special attention will paid to white matter hyperintensities in terms of occurrence and progression and cerebral microbleeds in terms of their association to various diseases and their possible influence on thrombolytic therapy. Furthermore the meaning of darkening of the basal ganglia will be discussed and, in more general terms, the occurrence of virchow robin spaces and changes in cerebral metabolites assessable by proton magnetic resonance spectroscopy.

Quantitative MR analyses of the hippocampus: Unspecific metabolic changes in aging

The age-related structural changes of the human hippocampus are not entirely understood. The goal of the present investigation was to understand better the nature of age-related hippocampal changes by a comparative MR-analysis of four complementary aspects of hippocampal integrity: total volume, metabolite concentration, neuron to glial cell ratio and amount of extracellular diffusion space for water. To that end, we applied MR-based methods of manual and computerized (voxel-based morphometry) volumetry, diffusion-weighted imaging and 1H MR spectroscopy to characterize specific age-related hippocampal effects in a group of 22 healthy old adults in comparison with a group of 13 healthy younger adults. Age-related reductions of the hippocampal N-acetyl aspartate to creatine/choline ratio together with only marginal age-related reductions in hippocampal volumes and increases in diffusion parameters suggest that the process of aging affects mainly the metabolic status of the hippocampus with little equivalent age-related changes in hippocampal cell density. The metabolic changes are unspecific as they are not restricted to the hippocampus but equally occur in measures obtained from extrahippocampal temporal lobe regions.

Magnetic resonance spectroscopy in cognitive research

The neurophysiological basis of cognition is relatively unexplained, with most studies reporting weak relationships between cognition and measures of brain function, such as event-related potentials, brain size and cerebral blood flow. Magnetic resonance spectroscopy (MRS) is an in vivo method used to detect neurochemicals within the brain that are relevant to certain brain processes. The most widely used methods are 1H-MRS and 31P-MRS, which detect compounds that contain hydrogen and phosphorus, respectively. Recent studies have shown that the absolute concentrations or ratios of these neurochemicals, in particular N-acetyl aspartate (NAA), which is associated with neuronal viability, correlate with performance on neuropsychological tests or other measures of cognitive function in normal subjects. Many studies in adults and children have shown a relationship between neurometabolite values and cognitive status or extent of cognitive dysfunction in various neurological and neuropsychiatric disorders. We review these studies and conclude that MRS has potential applications for the study of cognitive processes in health and disease and may be used clinically for differential diagnosis, the early detection of pathology and the examination of longitudinal change.

1H magnetic resonance spectroscopy in human hydrocephalus

PURPOSE

To evaluate cerebral metabolism in clinical hydrocephalus with (1)H magnetic resonance spectroscopy (MRS).

MATERIALS AND METHODS

In 24 children and adults with progressive, arrested, or normal pressure hydrocephalus, long-echo time (1)H MR spectra were acquired from periventricular white matter and intraventricular cerebrospinal fluid (CSF). Metabolite ratios, and the presence of lactate, were compared with 38 age-matched controls.

RESULTS

Metabolite ratios of patients were within the 95% confidence interval (CI) of controls. A small lactate resonance was detected in 20% of control and hydrocephalic subjects. Lactate was consistently visible in CSF spectra, though lactate concentrations were normal. The CSF lactate T(2) was long in comparison with the known intracellular metabolite T(2) relaxation times. In three neonates with hydrocephalus and spina bifida, 3-hydroxybutyrate was detected in CSF in vivo.

CONCLUSION

Within the limits of the present methods, (1)H MRS could not detect cerebral metabolic abnormalities in human hydrocephalus and provided no additional diagnostic information. The long T(2) of lactate in CSF explains its high visibility. Hence, the detection of lactate in spectra acquired from voxels that contain CSF does not necessarily imply cerebral ischemia.

Brain metabolic differences as a function of hemisphere, writing hand preference, and gender

A total of 35 university-educated normal men (24 right handwriters and 11 left handwriters) and 36 age- and education-matched women (25 right handwriters and 11 left handwriters) underwent a proton magnetic resonance spectroscopy examination in seven 8 cm(3) voxels including the right and left frontal lobe tips, the right and left mid-temporal lobes, the right and left thalami, and the hypothalamus. Dependent measures were N-acetylaspartate (NAA), choline-containing compounds (Cho) and creatine/phosphocreatine (Cr) metabolite peak area ratios relative to total H(2)O. As expected, thalamic grey matter contained higher NAA ratios than telencephalic voxels (containing white and grey matter) (p < .001). The thalamic Cr/ H(2)O ratio was higher on the right, but the opposite asymmetry was observed for the temporal lobe (p < .05). Women had a higher left frontal NAA/ H(2)O ratio than men, but men had a higher hypothalamic NAA/ H(2)O ratio than women. Right-handers had a higher temporal lobe NAA/H(2)O ratio than left-handers, particularly in the left hemisphere. In addition, several significant 2- and 3-way interactions between writing hand preference, gender, and hemisphere were observed, but only in the frontal lobe.

A proton magnetic resonance spectroscopy study of age-related changes in frontal lobe metabolite concentrations

Ageing is associated with reduction of grey matter volume and it is reported that the frontal lobes are preferentially affected. We have applied quantitative magnetic resonance spectroscopy (MRS), incorporating measurement of brain tissue water content and metabolite T(2) relaxation times, to determine absolute concentrations of the putative neuronal marker N-acetylaspartate (NAA), creatine (Cr) and choline (Cho) compounds in the frontal lobe of 50 male subjects aged between 20 and 70 years (10 per decade). The fractional brain water content (beta(MR)) did not change significantly as a function of age (r = 0.07, P = 0.65) and had a mean value of 81% (CV = 2%). The concentration (in millimoles per litre brain tissue) of NAA decreased significantly with age (r = -0.42, P = 0.003), with an overall decrease of 12% between the third and seventh decades. The concentrations of Cr and Cho did not change significantly with age. The interpretation of the age-dependent decrease in NAA concentration as reflecting either a reduction in neuronal volume, number or function is discussed.

Chemical network of the living human brain. Evidence of reorganization with aging

We recently described the chemical network properties of the human brain using in vivo proton magnetic resonance spectroscopy ((1)H MRS). In a separate study of aging we found increased concentration of chemicals in the prefrontal and sensorimotor cortices up to the third decade of life, and subsequent decrease of chemical concentrations in the same brain regions after the third decade between young and middle age. We anticipated that these age-dependent differences in chemical concentrations might be a reflection of the chemical network reorganization of the brain during aging. The pattern of chemical connectivity within and across brain regions for all regional chemicals, and specific patterns of chemical connectivity for each chemical type were examined for young and middle age groups using (1)H MRS and correlation analysis. For all studied ages, the dominant positive correlations occurred within brain regions and negative correlations were seen across brain regions. However, the pattern of negative chemical connectivity across brain regions was weaker in middle-aged group (F = 40.4, P < 10(-7) comparing r-values between the two age groups, ANOVA). Within brain regions, the age effects on chemical correlations were seen in the cingulate cortex (46% decrease in the middle-aged group, F = 7.2, P < 0.007) and sensorimotor cortex (SMC) (27% decrease, F = 8.9, P<0.003). Between brain regions, the age effects on chemical correlations were seen in the chemical interactions between the thalamus (433.3% increase in the middle-aged group, F = 11.7, P < 0.003), SMC (280% increase, F=20.1, P < 10(-5)), cingulate cortex (100.7% increase, F = 21.3, P < 10(-7)), and other brain regions. We found also age-differential patterns of chemical connectivity across the studied brain regions for most chemical types. The results provide evidence that normal aging is associated with reorganization of chemical network of the human brain.

Axonal damage in multiple sclerosis plaques: a combined magnetic resonance imaging and 1H-magnetic resonance spectroscopy study

The purpose of this study was to compare magnetic resonance imaging (MRI) features and proton MR spectroscopy (1H-MRS) patterns of multiple sclerosis (MS) plaques in order to define the metabolic substrate in different lesion subtypes. Combined MRI and single-voxel 1H-MRS investigation was performed in 54 MS patients (47 relapsing remitting (RR) and seven secondary progressive (SP)). Sixty-seven MS lesions were selected. Thirty-seven lesions were Gadolinium (Gd) enhancing (nine isointense and 28 hypointense on pre-contrast T(1)-weighted scans) and 30 Gd unenhancing (six isointense and 24 hypointense on pre- and post-contrast T(1)-weighted scans). Choline (Cho), creatine (Cr), N-acetyl aspartate (NAA) and lactate were evaluated in 1H spectra acquired from MS plaques and from normal white matter (NWM) of 22 neurological controls. MS lesions of RR patients were characterized by a significant increase of Cho/Cr and decrease of NAA/Cr and NAA/Cho ratios. No significant metabolite changes were found in lesions of SP patients. Gd enhancing plaques showed lactate signal with higher frequency (37.8%) than Gd unenhancing plaques (16.7%) (p=0.04). A significant increase of Cho/Cr was found in Gd enhancing lesions when compared to controls (p<0.01), and to Gd unenhancing lesions (p<0.05). In particular, there was evidence of a significant increase of Cho/Cr in pre-contrast T(1) hypointense Gd enhancing lesions (p<0.01 vs. controls). The Gd unenhancing lesions (p<0.01), in particular the T(1) hypointense group (p<0.05), showed a significant decrease of NAA/Cr only when compared to controls. These data confirm that in vivo MRS indicates key pathological features of MS plaques. The increased Cho/Cr ratio found in Gd-enhancing plaques, in particular in the T(1) hypointense lesions, may reflect increased membrane cell turnover. The T(1) hypointense Gd unenhancing plaques better reflect axonal damage, as suggested by the decrease of NAA/Cr. Nevertheless, the lack of statistical differences in NAA/Cr between plaque subgroups suggests that axonal impairment might occur even in the early stages.

Aging alters regional multichemical profile of the human brain: an in vivo 1H-MRS study of young versus middle-aged subjects

Age-related differences in the multichemical proton magnetic resonance spectroscopy (1H-MRS) profile of the human brain have been reported for several age groups, and most consistently for ages from neonates to 16-year-olds. Our recent 1H-MRS study demonstrated a significant age-related increase of total chemical concentration (relative to creatine) in the prefrontal and sensorimotor cortices within young adulthood (19-31-year-olds). In the present study we test the hypothesis that the level of brain chemicals in the same cortices, which show increased chemical levels during normal development, are reduced with normal aging after young adulthood. The multichemical 1H-MRS profile of the brain was compared between 19 young and 16 middle-aged normal subjects across multiple brain regions for all chemicals of 1H-MRS spectra. Chemical concentrations were measured relative to creatine. Over all age groups the total relative chemical concentration was highest in the prefrontal cortex. Middle-aged subjects demonstrated a significant decrease of total relative chemical concentration in the dorsolateral prefrontal (F = 54.8, p < 10(-7), ANOVA), orbital frontal (F = 3.7, p < 0.05) and sensorimotor (F = 15.1, p < 0.0001) cortices, as compared with younger age. Other brain regions showed no age-dependent differences. The results indicate that normal aging alters multichemical 1H-MRS profile of the human brain and that these changes are region-specific, with the largest changes occuring in the dorsolateral prefrontal cortex. These findings provide evidence that the processes of neuronal maturation of the human brain, and neurotransmitters and other chemical changes as the marker of these neuronal changes are almost finished by young adulthood and then reduced during normal aging toward middle age period of life. The present data also support the notion of heterochronic regressive changes of the aging human brain, where the multichemical brain regional profile seems to inversely recapitulate cortical chemical maturation within normal development.

Proton magnetic resonance spectroscopy (1H-MRS) of the thalamus in schizophrenia

This study applied (1)H-MRS in the thalamus of schizophrenic patients and healthy subjects. There were no differences in the metabolite ratios (NAA/Cr, Cho/Cr or mI/Cr) between the two groups. Relationships were noted between NAA/Cr and age in patients with a trend toward this correlation in controls, suggesting an effect of age on the metabolism of the thalamus.

Metabolic changes in neuronal migration disorders: evaluation by combined MRI and proton MR spectroscopy

PURPOSE

To assess the role of 1H-magnetic resonance spectroscopy (MRS) in detecting biochemical abnormalities in neuronal migration disorders (NMDs).

METHODS

We performed 1H-MRS studies on 17 brain NMD areas [five polymicrogyria, eight subcortical heterotopia, and four cortical dysplasia on magnetic resonance imaging (MRI)]. The study group consisted of 15 patients, all but one affected by partial epileptic seizures. Spectra were acquired from volumes of interest localized on NMDs and contralateral sides and compared with those obtained on gray and white matter of 18 neurologic controls.

RESULTS

NMD lesions were characterized by lower N-acetylaspartate to creatine (NAA/Cr) and choline to Cr (Cho/Cr) ratios than those of the white (p = 0.002 and p = 0.004) and gray matter (p = 0.03 and p = 0.06) of neurologic controls. In addition, the normal-appearing contralateral sides to the NMD lesions showed a significant decrease of Cho/Cr ratio when compared with those of white (p = 0.003) and gray matter (p = 0.05) of neurologic controls. No relation was found between NAA/Cr decrease, EEG abnormalities, and NMD sides, or between NAA/Cr ratios, duration of epilepsy, and frequency of seizures. Lactate signal was detected in the spectra of four patients who had an epileptic seizure a short time before MR examination.

CONCLUSIONS

NAA/Cr decrease may be related more to structural and functional alteration of the NMD sides than to epileptic activity in these lesions. Low Cho/Cr may be related to a more extensive diffuse hypomyelination than suggested by the MRI findings. An activation of anerobic glycolysis during and after seizures could account for the presence of lactate. These data confirm that H-MRS is an advanced technique that may provide useful biochemical information in vivo on neurobiologic processes underlying NMDs.

In vivo spectroscopic quantification of the N-acetyl moiety, creatine, and choline from large volumes of brain gray and white matter: effects of normal aging

Volumetric proton magnetic resonance spectroscopic imaging (MRSI) was used to generate brain metabolite maps in 15 young and 19 elderly adult volunteers. All subjects also had structural MR scans, and a model, which took into account the underlying structural composition of the brain contributing to each metabolite voxel, was developed and used to estimate the concentration of the N-acetyl-moiety (NAc), creatine (Cr), and choline (Cho) in gray matter and white matter. NAc concentration (signal intensity per unit volume of brain) was higher in gray than white matter and did not differ between young and old subjects despite significant gray matter volume deficits in the older subjects. To the extent that NAc is an index of neuronal integrity, the available gray matter appears to be intact in these older healthy adults. Cr concentrations were much higher in gray than white matter and significantly higher in the old than young subjects. Cho concentration in gray matter was also significantly higher in old than young subjects. Independent determination of metabolite values rather than use of ratios is essential for characterizing age-related changes in brain MRS metabolites.

Age-related metabolite changes and volume loss in the hippocampus by magnetic resonance spectroscopy and imaging

Magnetic resonance imaging (MRI) studies have produced controversial results concerning the correlation of hippocampal volume loss with increasing age. The goals in this study were: 1) to test whether levels of N-acetyl aspartate (NAA, a neuron marker) change in the hippocampus during normal aging and 2) to determine the relationship between hippocampal NAA and volume changes. Proton magnetic resonance spectroscopic imaging (1H MRSI) and MRI were used to measure hippocampal metabolites and volumes in 24 healthy adults from 36 to 85 years of age. NAA/Cho decreased by 24% (r = 0.53, p = 0.01) and NAA/Cr by 26% (r = 0.61, p < 0.005) over the age range studied, whereas Cho/Cr remained stable, implying diminished NAA levels. Hippocampal volume shrank by 20% (r = 0.64, p < 0.05). In summary, aging effects must be considered in 1H MRSI brain studies. Furthermore, because NAA is considered a marker of neurons, these results provide stronger support for neuron loss in the aging hippocampus than volume measurements by MRI alone.