Age-related glutamate and glutamine concentration changes in normal human brain: 1H MR spectroscopy study at 4 T

[MR spectroscopy in dementia]

With an increasingly aging population we are faced with the problem of an increasing number of dementia patients. In addition to clinical, neuropsychological and laboratory procedures, MRI plays an important role in the early diagnosis of dementia. In addition to various morphological changes functional changes can also help in the diagnosis and differential diagnosis of dementia. Overall the diagnosis of dementia can be improved by using parameters from MR spectroscopy. This article focuses on MR spectroscopic changes in the physiological aging process as well as on changes in mild cognitive impairment a precursor of Alzheimer's dementia, in Alzheimer's dementia, frontotemporal dementia, vascular dementia and Lewy body dementia.

Neurones express glutamine synthetase when deprived of glutamine or interaction with astrocytes

Glutamine synthetase (GS) forms glutamine by catalyzing the ATP-dependent amidation of glutamate. In healthy brains, GS is restricted to astrocytes but in Alzheimer's disease and cell culture, GS has been detected in neurones. The present study demonstrates the expression of functional GS in cultured cerebellar granule cells and investigates conditions required to reduce this expression. Cerebellar granule cells from neonatal rats were grown in the absence of glutamine. Immunostaining revealed that the majority of neurones contained GS in their somata and dendrites. Treatment of neuronal cultures with glutamine greatly reduced the enzymatic activity of GS and also reduced the intensity of GS immunolabelling in dendrites. GS activity was reduced by 32% in neurones that had been transiently co-cultured with astrocytes, whereas GS immunoreactivity was largely abolished from neurones that had been directly seeded onto astrocytic monolayers. These results imply that GS expression in neurones occurs in response to a reduced availability of glutamine from astrocytes, and that neuronal GS expression represents a default phenotype which is normally suppressed via direct contacts with astrocytes. The aberrant expression of GS in sporadic neurones in Alzheimer's disease may indicate an impairment of such interactions.

In-vivo assessment of tissue metabolite levels using 1H MRS and the Electric REference To access In vivo Concentrations (ERETIC) method

Quantitative values of metabolite concentrations in (1)H magnetic resonance spectroscopy have been obtained using the Electric REference To access In vivo Concentrations (ERETIC) method, whereby a synthetic reference signal is injected during the acquisition of spectra. The method has been improved to enable quantification of metabolite concentrations in vivo. Optical signal transmission was used to eliminate random fluctuations in ERETIC signal coupling to the receiver coil due to changes in position of cables and highly dielectric human tissue. Stability and reliability of the signal were tested in vitro, achieving stability with a mean error of 2.83%. Scaling of the signal in variable loading conditions was demonstrated and in-vivo measurements of brain were acquired on a 3T Philips system using a transmit/receive coil. The quantitative brain water and metabolite concentration values are in good agreement with those in the literature.

BMI and neuronal integrity in healthy, cognitively normal elderly: a proton magnetic resonance spectroscopy study

Recent studies associated excess body weight with brain structural alterations, poorer cognitive function, and lower prefrontal glucose metabolism. We found that higher BMI was related to lower concentrations of N-acetyl-aspartate (NAA, a marker of neuronal integrity) in a healthy middle-aged cohort, especially in frontal lobe. Here, we evaluated whether NAA was also associated with BMI in a healthy elderly cohort. We used 4 Tesla proton magnetic resonance spectroscopy ((1)H MRS) data from 23 healthy, cognitively normal elderly participants (69.4 +/- 6.9 years; 12 females) and measured concentrations of NAA, glutamate (Glu, involved in cellular metabolism), choline-containing compounds (Cho, involved in membrane metabolism), and creatine (Cr, involved in high-energy metabolism) in anterior (ACC) and posterior cingulate cortices (PCC). After adjustment for age, greater BMI was related to lower NAA/Cr and NAA/Cho ratios (beta < -0.56, P < 0.008) and lower Glu/Cr and Glu/Cho ratios (beta < -0.46, P < 0.02) in ACC. These associations were not significant in PCC (beta > -0.36, P > 0.09). The existence of an association between NAA and BMI in ACC but not in PCC is consistent with our previous study in healthy middle-aged individuals and with reports of lower frontal glucose metabolism in young healthy individuals with elevated BMI. Taken together, these results provide evidence that elevated BMI is associated with neuronal abnormalities mostly in frontal brain regions that subserve higher cognitive functions and impulse control. Future studies need to evaluate whether these metabolite abnormalities are involved in the development and maintenance of weight problems.

Increased glutamate in the hippocampus after galantamine treatment for Alzheimer disease

Galantamine is a cholinesterase inhibitor and allosteric potentiating ligand modulating presynaptic nicotinic acetylcholine receptors that is used in the treatment of Alzheimer disease (AD). The purpose of this study was to determine if galantamine treatment would result in detectable hippocampal metabolite changes that correlated with changes in cognition, as measured by the Mini-Mental State Examination (MMSE) and the Alzheimer Disease Assessment Scale-cognitive subscale (ADAS-cog). Short echo-time proton magnetic resonance (MR) spectra were acquired from within the right hippocampus of ten patients using a 4 Tesla magnetic resonance imaging (MRI) scanner. Spectra were used to quantify absolute metabolite levels for N-acetylaspartate (NAA), glutamate (Glu), choline (Cho), creatine (Cr), and myo-inositol (mI). Patient scans and cognitive tests were performed before and 4 months after beginning galantamine treatment, which consisted of an 8 mg daily dose for the first month and a 16 mg daily dose for the remaining three months. The levels of Glu, Glu/Cr, and Glu/NAA increased after four months of treatment, while there were no changes in MMSE or ADAS-cog scores. Additionally, changes (Delta) in Glu over the four months (DeltaGlu) correlated with DeltaNAA, and Delta(Glu/Cr) correlated with DeltaMMSE scores. Increased Glu and the ratio of Glu to Cr measured by MR spectroscopy after galantamine treatment were associated with increased cognitive performance. The increase in Glu may be related to the action of galantamine as an allosteric potentiating ligand for presynaptic nicotinic acetylcholine receptors, which increases glutamatergic neurotransmission.

Regional age-related effects in the monkey brain measured with 1H magnetic resonance spectroscopy

The rhesus monkey is a useful model for examining age-related effects on the brain, because of the extensive neuroanatomical homology between the monkey and the human brain, the tight control for neurological diseases as well as the possibility of obtaining relevant behavioral data and post-mortem tissue for histological analyses. Here, proton magnetic resonance spectroscopy ((1)H-MRS) was used together with high-resolution anatomical MRI images to carefully assess regional concentrations of brain metabolites in a group of 20 rhesus monkeys. In an anterior volume of interest (VOI) that covered frontal and prefrontal areas, significant positive correlations of myo-inositol and of total creatine concentrations with age were detected, whereas N-acetyl aspartate (NAA) and choline compounds (Cho) were not significantly correlated with age. In an occipito-parietal VOI, all metabolites showed no statistically significant age-dependent trend. Strong correlations were found between NAA concentration and gray matter fraction in the VOIs as well as between choline compounds and white matter fraction.

Reduced hippocampal glutamate in Alzheimer disease

Altered neurometabolic profiles have been detected in Alzheimer disease (AD) using (1)H magnetic resonance spectroscopy (MRS), but no definitive biomarker of mild cognitive impairment (MCI) or AD has been established. This study used MRS to compare hippocampal metabolite levels between normal elderly controls (NEC) and subjects with MCI and AD. Short echo-time (TE=46 ms) (1)H spectra were acquired at 4T from the right hippocampus of 23 subjects with AD, 12 subjects with MCI and 15 NEC. Absolute metabolite levels and metabolite ratios were compared between groups using a multivariate analysis of covariance (covariates: age, sex) followed by post hoc Tukey's test (p<0.05 significant). Subjects with AD had decreased glutamate (Glu) as well as decreased Glu/creatine (Cr), Glu/myo-inositol (mI), Glu/N-acetylaspartate (NAA), and NAA/Cr ratios compared to NEC. Subjects with AD also had decreased Glu/mI ratio compared to MCI. There were no differences between subjects with MCI and NEC. Therefore, in addition to NAA/Cr, decreased hippocampal Glu may be an indicator of AD.

Effects of age and sex on brain glutamate and other metabolites

We previously reported the effects of sex and age on brain glutamate, as well as other brain metabolite concentrations, measured with a new technique called TE-averaged PRESS on a 3-T Siemens scanner in four brain regions of 50 healthy subjects. While revising the original IDL processing script for a scanner upgrade, we noted a programming error in the original code that did not use the unsuppressed water signal corrected for T2 decay and percentage of cerebrospinal fluid to calculate the metabolite concentrations. We report here the reanalyzed metabolite concentrations of glutamate and other metabolites that differ from our original article, based on measurements performed on the original 50 as well as the 12 new subjects (total 62 healthy subjects: 39 males and 23 females). Our reanalyzed data no longer show sex differences in brain glutamate levels in four brain regions measured, but we continue to observe significant age-related declines in glutamate, especially in the parietal gray matter and basal ganglia, and to a lesser degree in the frontal white matter. Further analyses confirm that the basal ganglia and frontal white matter glutamate declines were predominantly due to a decline in men, but not women. These findings indicate that brain glutamate concentrations decline markedly with age, and may be especially useful as a marker for brain diseases that are affected by aging.

Regional apparent metabolite concentrations in young adult brain measured by (1)H MR spectroscopy at 3 Tesla

PURPOSE

To quantify and examine the distribution of brain metabolites in normal young adults using single voxel MR spectroscopy at 3 Tesla (T).

MATERIALS AND METHODS

Short-echo time single-voxel PRESS technique was used to measure the apparent concentration of five metabolites at nine locations in the brains of young adults. Concentrations were estimated by means of an automated fitting method (LCModel) with reference to an unsuppressed water signal and were corrected for T(1) relaxation, T(2) relaxation, and cerebrospinal fluid partial volume. Analysis of variance with Tukey post hoc test was used to evaluate regional variations.

RESULTS

Statistically significant differences in regional concentrations were detected for each of the metabolites. The number of significant differences was greatest for total choline, whereas myo-inositol and the sum of glutamine and glutamate had the fewest. Magnitude of variation was greatest for total choline and least for the sum of N-acetyl aspartate and N-acetylaspartylglutamate.

CONCLUSION

In agreement with previous studies at other field strengths, we found heterogeneous distribution of the major spectroscopically measurable brain metabolites. Although the most distinct differences are between tissue types, there is appreciable variation within a tissue type at different locations. The spectra and metabolite concentrations presented should provide a useful reference for both clinical and research MR spectroscopy studies performed at 3T.

High field (1)H MRS of the hippocampus after donepezil treatment in Alzheimer disease

The purpose of this study was to measure metabolite level changes in patients with newly diagnosed Alzheimer Disease (AD) following four months of donepezil treatment. A small number of cognitively normal elderly subjects were also scanned longitudinally (twice within one year) to assess the reproducibility. Short echo-time (1)H magnetic resonance spectra were acquired at 4.0 T in the right hippocampus. Subjects were scanned at the time of first diagnosis (prior to receiving donepezil) and then following four months of donepezil treatment (5 mg/day for the first month, 10 mg/day thereafter). Changes in absolute metabolite levels and metabolite ratios were quantified and compared. There was no change in measured cognitive function following four months of donepezil treatment in the AD patients. Decreased levels of N-acetylaspartate, choline, N-acetylaspartate/creatine, choline/creatine, and myo-inositol/creatine were observed in AD patients after four months of treatment. Cognitively normal elderly subjects showed an increase in myo-inositol/choline ratio following one year. The reduced levels of N-acetylaspartate in AD patients indicates continued decline in neuronal function and/or integrity. However decreased levels of choline and myo-inositol/creatine ratio may indicate a positive treatment effect.

In vivo proton magnetic resonance spectroscopy in patients with mood disorders: a technically oriented review

Proton MR spectroscopy (1HMRS) has been extensively used among mood disorders patients. A review of the published literature in 1HMRS studies of mood disorders was carried out for the period 1991 to July 2006. Of 71 1HMRS studies, 77.5% were done at 1.5T and 66.2% used single voxel sequences (SVS), implying limitations of spectral resolution and anatomic coverage, respectively. In all, 47.9% of studies relied on creatine (Cr) as internal signal standard, although Cr changes were reported in major depression (MD). Most reported metabolic alterations related to mood state affected the left frontal lobe. Depressed adult and pediatric MD patients had reduced glutamate (Glu) in frontal lobe regions, which reversed with successful treatment. A consistent reduction of N-acetyl-aspartate (NAA) was reported in the hippocampal formation among bipolar disorder (BD) patients, along with an increment in frontal Glu. The differences in results of 1HMRS studies in mood disorders reflect heterogeneity of technical factors and subject selection. Future studies should benefit from higher spectral resolution and more extensive anatomic coverage as well as standardized data-processing protocols and subject selection criteria.

Low striatal glutamate levels underlie cognitive decline in the elderly: evidence from in vivo molecular spectroscopy

Glutamate (Glu), the principal excitatory neurotransmitter of prefrontal cortical efferents, potentially mediates higher order cognitive processes, and its altered availability may underlie mechanisms of age-related decline in frontally based functions. Although animal studies support a role for Glu in age-related cognitive deterioration, human studies, which require magnetic resonance spectroscopy for in vivo measurement of this neurotransmitter, have been impeded because of the similarity of Glu's spectroscopic signature to those of neighboring spectral brain metabolites. Here, we used a spectroscopic protocol, optimized for Glu detection, to examine the effect of age in 3 brain regions targeted by cortical efferents--the striatum, cerebellum, and pons--and to test whether performance on frontally based cognitive tests would be predicted by regional Glu levels. Healthy elderly men and women had lower Glu in the striatum but not pons or cerebellum than young adults. In the combined age groups, levels of striatal Glu (but no other proton metabolite also measured) correlated selectively with performance on cognitive tests showing age-related decline. The selective relations between performance and striatal Glu provide initial and novel, human in vivo support for age-related modification of Glu levels as contributing to cognitive decline in normal aging.

Proton echo-planar spectroscopic imaging of J-coupled resonances in human brain at 3 and 4 Tesla

In this multicenter study, 2D spatial mapping of J-coupled resonances at 3T and 4T was performed using short-TE (15 ms) proton echo-planar spectroscopic imaging (PEPSI). Water-suppressed (WS) data were acquired in 8.5 min with 1-cm(3) spatial resolution from a supraventricular axial slice. Optimized outer volume suppression (OVS) enabled mapping in close proximity to peripheral scalp regions. Constrained spectral fitting in reference to a non-WS (NWS) scan was performed with LCModel using correction for relaxation attenuation and partial-volume effects. The concentrations of total choline (tCho), creatine + phosphocreatine (Cr+PCr), glutamate (Glu), glutamate + glutamine (Glu+Gln), myo-inositol (Ins), NAA, NAA+NAAG, and two macromolecular resonances at 0.9 and 2.0 ppm were mapped with mean Cramer-Rao lower bounds (CRLBs) between 6% and 18% and approximately 150-cm(3) sensitive volumes. Aspartate, GABA, glutamine (Gln), glutathione (GSH), phosphoethanolamine (PE), and macromolecules (MMs) at 1.2 ppm were also mapped, although with larger mean CRLBs between 30% and 44%. The CRLBs at 4T were 19% lower on average as compared to 3T, consistent with a higher signal-to-noise ratio (SNR) and increased spectral resolution. Metabolite concentrations were in the ranges reported in previous studies. Glu concentration was significantly higher in gray matter (GM) compared to white matter (WM), as anticipated. The short acquisition time makes this methodology suitable for clinical studies.

Amperometric measures of age-related changes in glutamate regulation in the cortex of rhesus monkeys

l-glutamate (glutamate) is the principal excitatory neurotransmitter of the central nervous system and is involved in altered neural function during aging and in neurodegenerative diseases. Relatively little is known about the mechanisms of glutamate signaling in the primate brain, in part, because there is an absence of a method capable of rapidly measuring glutamate in either a non-clinical or a clinical setting. We have addressed this paucity of information by measuring extracellular glutamate at 1 Hz in the pre-motor and motor cortices of young, middle-aged, and aged monkeys using a minimally invasive amperometric recording method. In the motor cortex, mean resting glutamate levels were five times higher in the aged group compared to the young group while the pre-motor cortex showed an increasing trend in resting glutamate levels that was not statistically significant. In addition, we measured rapid, phasic glutamate release after local pressure-ejection of nanoliter volumes of either isotonic 70 mM potassium (to stimulate glutamate release) or 1 mM glutamate (to study glutamate uptake) into the pre-motor and motor cortex. In the pre-motor cortex, we measured reproducible glutamate uptake signals that had a significantly decreased (47%) rate of glutamate uptake in aged animals compared to young animals. However, following a 70 mM potassium delivery, we did not observe any consistent changes in evoked release between young versus aged animals. Using these non-clinical microelectrodes to measure glutamate signaling in the brain, our results support the hypothesis that the glutamatergic system undergoes reorganization with aging of the central nervous system.

Regional variations and the effects of age and gender on glutamate concentrations in the human brain

Proton magnetic resonance spectroscopy was performed at 3 T using the echo time-averaged point-resolved spectroscopy method to determine the effects of age, gender and brain region on glutamate (Glu) concentrations in the healthy human brain. Thirty healthy men and 20 healthy women aged between 21 and 71 years were studied. Significant regional variations of Glu concentrations were observed. Glu concentration in the gray matter (GM) was approximately 25% higher than that in the white matter. Significant age-dependent decreases in Glu concentrations were observed in the basal ganglia (r=-0.75, P<.001) and parietal GM (r=-0.66, P<.001) of men but not those of women. Our findings demonstrate regional variations of Glu concentrations and suggest that the male brain may be more vulnerable to aging than the female brain. Our results also highlight the importance of brain region, age and gender matching in clinical studies.

MR spectroscopy, functional MRI, and diffusion-tensor imaging in the aging brain: a conceptual review

In vivo magnetic resonance spectroscopy (MRS), functional magnetic resonance imaging (fMRI), and diffusion-tensor imaging (DTI) have recently opened new possibilities for noninvasively assessing the metabolic, functional, and connectivity correlates of aging in research and clinical settings. The purpose of this article is to provide a conceptual review intended for a multidisciplinary audience, covering physical principles and main findings related to normal aging and senile cognitive impairment. This article is divided into 3 sections, dedicated to MRS, to fMRI, and to DTI. The spectroscopy section surveys physiological function of the observable metabolites, concentration changes in normal aging and their interpretation, and correlation with cognitive performance. The functional MRI section surveys the hemispheric asymmetry reduction model from compensation and de-differentiation viewpoints, memory encoding, retrieval and consolidation, inhibitory control, perception and action, resting-state networks, and functional deactivations. The DTI section surveys age-related changes, correlation with behavioral scores, and transition to cognitive impairment.

Does healthy aging affect the hemispheric activation balance during paced index-to-thumb opposition task? An fMRI study

Normal aging is generally associated with declining performance in cognitive and fine motor tasks. Previous functional imaging studies have been inconsistent regarding the effect of aging on primary motor cortex (M1) activation during finger movement, showing increased, unchanged or decreased activation contralaterally, and more consistently increased activation ipsilaterally. Furthermore, no study has addressed the effect of age on M1 hemispheric activation balance. We studied 18 optimally healthy right-handed subjects, age range 18-79 years (mean +/- SD: 47 +/- 17) using 3 T fMRI and right index finger-thumb tapping auditory-paced at 1.25 Hz. The weighted Laterality Index (wLI) for M1 was obtained according to Fernandez et al. (2001) [Fernandez, G., de Greiff, A., von Oertzen, J., Reuber, M., Lun, S., Klaver, P., et al. 2001. Language mapping in less than 15 min: real-time functional MRI during routine clinical investigation. Neuroimage 14 585-594], with some modifications. The wLI, as well as the total activation on each side, were assessed against age using non-parametric correlation. There was a highly significant negative correlation between age and wLI such that the older the subjects, the lower the wLI. Furthermore, there was a highly significant positive correlation between total activation for ipsilateral M1 and age, and a nearly significant trend for contralateral M1. This study documents that during execution of a simple paced motor task, the older the subject the less lateralized the M1 activation balance as a result of increasing amount of activation on both sides, more significantly so ipsilaterally. Thus, in aging, enhanced M1 recruitment bilaterally is required to produce the same motor performance, suggesting a compensatory process. These findings are in line with cognitive studies indicating a tendency for the aging brain to reduce its functional lateralization, perhaps from less efficient transcallosal connections.

A longitudinal study of oculomotor function in normal older people

Cross-sectional studies have found declines in most measures of oculomotor function in older subjects compared to young controls, but no prior study has followed the same subjects over time. We measured saccade peak velocity, saccade delay time, smooth pursuit, optokinetic nystagmus (OKN), visual-vestibular-ocular-reflex (VVOR), fixation suppression of the vestibulo-ocular reflex (VOR-fix), and the vestibulo-ocular reflex in 53 subjects (older than 75 years) able to complete at least 9 yearly evaluations. In addition at each visit all patients underwent a complete history and examination, a gait and balance assessment, mini-mental status evaluation, and visual acuity testing. A subset of subjects completed 12 yearly evaluations (14 patients). Despite significant declines of most variables over time, smooth pursuit gain and saccade peak velocity remained stable during the duration of the study both in the 9-year group and the patients completing 12 years. Decline in OKN, VVOR, and VOR were significantly correlated (P<0.001) with decline in the Tinetti gait and balance score, even after controlling for age. In normal healthy older subjects, smooth pursuit and saccade peak velocity are relatively maintained while OKN, VVOR, and VOR function decline. The significant correlation between decline in oculomotor measures and gait and balance measures (even after controlling for age) suggests a common mechanism for the decline in both measures.

Physiologic aspects of aging: impact on cancer management and decision making, part II

In this second article of our two-part review, we focus on age-associated physiologic changes involving the nervous, endocrine, hematologic, immune, and musculoskeletal systems, with close attention to the interconnected nature of these systems. There is a well-known connection between the neuroendocrine and immune systems via the hypothalamic-pituitary-adrenal axis and via interaction by means of cytokines, hormones, and neurotransmitters. These changes may lead to a loss of integration and resiliency with age, thus decreasing the ability of the elderly patient with cancer to adapt to stressful circumstances. Prominent changes include decline in memory and cognition, and increased susceptibility to peripheral neuropathy. Hematologic and immune changes like reduced bone marrow reserve and increased susceptibility to infections have far reaching implications for cancer care in the elderly. Gradual decline in hormone levels, and changes in muscle and body composition, can lead to functional decline and frailty. Use of the clinical interventions suggested in this article, along with an appreciation of the interplay of these age-related physiologic changes and their consequences, allows oncology professionals to customize therapy and minimize side effects in the geriatric oncology patient.

Measurement of brain glutamate and glutamine by spectrally-selective refocusing at 3 tesla

A new single-voxel proton NMR spectrally-selective refocusing method for measuring glutamate (Glu) and glutamine (Gln) in the human brain in vivo at 3T is reported. Triple-resonance selective 180 degrees RF pulses with a bandwidth of 12 Hz were implemented within point-resolved spectroscopy (PRESS) for selective detection of Glu or Gln, and simultaneous acquisition of creatine singlets for use as a reference in phase correction. The carriers of the spectrally-selective 180 degrees pulses and the echo times (TEs) were optimized with both numerical and experimental analyses of the filtering performance, which enabled measurements of the target metabolites with negligible contamination from N-acetylaspartate and glutathione. The concentrations of Glu and Gln in the prefrontal cortex were estimated to be 9.7+/-0.5 and 3.0+/-0.7 mM (mean+/-SD, N=7), with reference to Cr at 8 mM.

The role of glutamate in anxiety and related disorders

Anxiety, stress, and trauma-related disorders are a major public health concern in the United States. Drugs that target the gamma-aminobutyric acid or serotonergic system, such as benzodiazepines and selective serotonin reuptake inhibitors, respectively, are the most widely prescribed treatments for these disorders. However, the role of glutamate in anxiety disorders is becoming more recognized with the belief that drugs that modulate glutamatergic function through either ionotropic or metabotropic glutamate receptors have the potential to improve the current treatment of these severe and disabling illnesses. Animal models of fear and anxiety have provided a method to study the role of glutamate in anxiety. This research has demonstrated that drugs that alter glutamate transmission have potential anxiolytic action for many different paradigms including fear-potentiated startle, punished responding, and the elevated plus maze. Human clinical drug trials have demonstrated the efficacy of glutamatergic drugs for the treatment of obsessive-compulsive disorder, posttraumatic stress disorder, generalized anxiety disorder, and social phobia. Recent data from magnetic resonance imaging studies provide an additional link between the glutamate system and anxiety. Collectively, the data suggest that future studies on the mechanism of and clinical efficacy of glutamatergic agents in anxiety disorders are appropriately warranted.

Die Entwicklung der Neuroradiologie

Since the discovery of X-rays, rapid and significant progress has been and continues to be made in imaging techniques, particularly neuroradiology. Milestones along the way included use of contrast agents, digital subtraction angiography, computed tomography, and magnetic resonance imaging. The most recent achievements are visualization of cerebral activation and fiber systems in the brain parenchyma. Application of new contrast agents seems to make imaging at the "molecular" level also possible.

Scyllo-inositol in normal aging human brain: 1H magnetic resonance spectroscopy study at 4 Tesla

The scyllo-inositol and myo-inositol concentrations of 24 normal human subjects were measured in vivo using 1H magnetic resonance spectroscopy at 4 T. Single-voxel short-echo (TE = 15 ms) metabolite spectra were collected from the white matter region of the corona radiata. Test-retest studies performed on 10 normal subjects demonstrated coefficient of variation for scyllo-inositol measurement of 37%, compared with 6% for N-acetyl aspartate. Comparisons between old and young subjects showed higher concentration of scyllo-inositol and myo-inositol in older subjects and a trend for a correlation between scyllo-inositol and myo-inositol levels across subjects.