Metabolic and cognitive response to human traumatic brain injury: a quantitative proton magnetic resonance study

Imaging neuroinflammation? A perspective from MR spectroscopy

Neuroinflammatory mechanisms contribute to the brain pathology resulting from human immunodeficiency virus (HIV) infection. Magnetic resonance spectroscopy (MRS) has been touted as a suitable method for discriminating in vivo markers of neuroinflammation. The present MRS study was conducted in four groups: alcohol dependent (A, n = 37), HIV-infected (H, n = 33), alcohol dependent + HIV infected (HA, n = 38) and healthy control (C, n = 62) individuals to determine whether metabolites would change in a pattern reflecting neuroinflammation. Significant four-group comparisons were evident only for striatal choline-containing compounds (Cho) and myo-inositol (mI), which follow-up analysis demonstrated were due to higher levels in HA compared with C individuals. To explore the potential relevance of elevated Cho and mI, correlations between blood markers, medication status and alcohol consumption were evaluated in H + HA subjects. Having an acquired immune deficiency syndrome (AIDS)-defining event or hepatitis C was associated with higher Cho; lower Cho levels, however, were associated with low thiamine levels and with highly active antiretroviral HIV treatment (HAART). Higher levels of mI were related to greater lifetime alcohol consumed, whereas HAART was associated with lower mI levels. The current results suggest that competing mechanisms can influence in vivo Cho and mI levels, and that elevations in these metabolites cannot necessarily be interpreted as reflecting a single underlying mechanism, including neuroinflammation.

Neurochemical analysis of primary motor cortex in chronic low back pain

The involvement of the primary motor cortex (M1) in chronic low back pain (LBP) is a relatively new concept. Decreased M1 excitability and an analgesic effect after M1 stimulation have been recently reported. However, the neurochemical changes underlying these functional M1 changes are unknown. The current study investigated whether neurochemicals specific to neurons and glial cells in both right and left M1 are altered. N-Acetylaspartate (NAA) and myo-inositol (mI) were measured with proton magnetic resonance spectroscopy in 19 subjects with chronic LBP and 14 healthy controls. We also examined correlations among neurochemicals within and between M1 and relationships between neurochemical concentrations and clinical features of pain. Right M1 NAA was lower in subjects with LBP compared to controls (p = 0.008). Left M1 NAA and mI were not significantly different between LBP and control groups. Correlations between neurochemical concentrations across M1s were different between groups (p = 0.008). There were no significant correlations between M1 neurochemicals and pain characteristics. These findings provide preliminary evidence of neuronal depression and altered neuronal-glial interactions across M1 in chronic LBP.

Temporal course of changes in gene expression suggests a cytokine-related mechanism for long-term hippocampal alteration after controlled cortical impact

Mild traumatic brain injury (mTBI) often has long-term effects on cognitive function and social behavior. Altered gene expression may be predictive of long-term psychological effects of mTBI, even when acute clinical effects are minimal or transient. Controlled cortical impact (CCI), which causes concussive, but nonpenetrant, trauma to underlying (non-cortical) brain, resulting in persistent changes in hippocampal synaptic function, was used as a model of mTBI. The hippocampal transcriptomes of sham-operated or injured male rats at 1, 7, and 30 days postinjury were examined using microarrays comprising a comprehensive set of expressed genes, subsequently confirmed by quantitative reverse-transcriptase polymerase chain reaction. Transcripts encoding the chemokines, chemokine (C-C motif) ligand (Ccl)2 and Ccl7, inflammatory mediators lipocalin-2 (Lcn2) and tissue inhibitor of metalloproteinase 1 (Timp1), immunocyte activators C-C chemokine receptor type 5 (Ccr5) and Fc fragment of IgG, low affinity IIb, receptor (CD32) (Fcgr2b), the major histocompatibility complex II immune response-related genes, Cd74 and RT1 class II, locus Da (RT1-Da), the complement component, C3, and the transcription factor, Kruppel-like factor 4 (Klf4), were identified as early (Ccl2, Ccl7, Lcn2, and Timp1), intermediate (Ccr5, Fcgr2b, Cd74, RT1-Da, and C3), and late (Klf4) markers for bilateral hippocampal response to CCI. Ccl2 and Ccl7 transcripts were up-regulated within 24 h after CCI, and their elevation subsided within 1 week of injury. Other transcriptional changes occurred later and were more stable, some persisting for at least 1 month, suggesting that short-term inflammatory responses trigger longer-term alteration in the expression of genes previously associated with injury, aging, and neuronal function in the brain. These transcriptional responses to mTBI may underlie long-term changes in excitatory and inhibitory neuronal imbalance in hippocampus, leading to long-term behavioral consequences of mTBI.

Biomarkers for the diagnosis and prognosis of mild traumatic brain injury/concussion

Mild traumatic brain injury (mTBI) results from a transfer of mechanical energy into the brain from traumatic events such as rapid acceleration/deceleration, a direct impact to the head, or an explosive blast. Transfer of energy into the brain can cause structural, physiological, and/or functional changes in the brain that may yield neurological, cognitive, and behavioral symptoms that can be long-lasting. Because mTBI can cause these symptoms in the absence of positive neuroimaging findings, its diagnosis can be subjective and often is based on self-reported neurological symptoms. Further, proper diagnosis can be influenced by the motivation to conceal or embellish signs and/or an inability of the patient to notice subtle dysfunctions or alterations of consciousness. Therefore, appropriate diagnosis of mTBI would benefit from objective indicators of injury. Concussion and mTBI are often used interchangeably, with concussion being primarily used in sport medicine, whereas mTBI is used in reference to traumatic injury. This review provides a critical assessment of the status of current biomarkers for the diagnosis of human mTBI. We review the status of biomarkers that have been tested in TBI patients with injuries classified as mild, and introduce a new concept for the discovery of biomarkers (termed symptophenotypes) to predict common and unique symptoms of concussion. Finally, we discuss the need for biomarker/biomarker signatures that can detect mTBI in the context of polytrauma, and to assess the consequences of repeated injury on the development of secondary injury syndrome, prolongation of post-concussion symptoms, and chronic traumatic encephalopathy.

Biomarkers of mild traumatic brain injury in cerebrospinal fluid and blood

Mild traumatic brain injury (TBI), which is defined as a head trauma resulting in a brief loss of consciousness and/or alteration of mental state, is usually benign, but occasionally causes persistent and sometimes progressive symptoms. Whether a threshold for the amount of brain injury and/or individual vulnerability might contribute to the development of these long-term consequences is unknown. Furthermore, reliable diagnostic methods that can establish whether a blow to the head has affected the brain (and in what way) are lacking. In this Review, we discuss potential biomarkers of injury to different structures and cell types in the CNS that can be detected in body fluids. We present arguments in support of the need for further development and validation of such biomarkers, and for their use in assessing patients with head trauma in whom the brain might have been affected. Specifically, we focus on the need for such biomarkers in the management of sports-related concussion, the most common cause of mild TBI in young individuals, to prevent long-term neurological sequelae due to concussive or subconcussive blows to the head.

Magnetic resonance spectroscopy in Alzheimer's disease

Aging is the primary risk factor for dementia. With increasing life expectancy and aging populations worldwide, dementia is becoming one of the significant public health problems of the century. The most common pathology underlying dementia in older adults is Alzheimer's disease. Proton magnetic resonance spectroscopy (MRS) may provide a window into the biochemical changes associated with the loss of neuronal integrity and other neurodegenerative pathology that involve the brain before the manifestations of cognitive impairment in patients who are at risk for Alzheimer's disease. This review focuses on proton MRS studies in normal aging, mild cognitive impairment, and dementia, and how proton MRS metabolite levels may be potential biomarkers for early diagnosis of dementia-related pathologic changes in the brain.

Altered neurochemical profile after traumatic brain injury: (1)H-MRS biomarkers of pathological mechanisms

Specific neurochemicals measured with proton magnetic resonance spectroscopy ((1)H-MRS) may serve as biomarkers of pathological mechanism in the brain. We used high field in vivo (1)H-MRS to measure a detailed neurochemical profile after experimental traumatic brain injury (TBI) in rats. We characterized neurochemical changes in the contused cortex and the normal-appearing perilesional hippocampus over a time course from 1 hour to 2 weeks after injury. We found significant changes in 19 out of 20 neurochemicals in the cortex, and 9 out of 20 neurochemicals in the hippocampus. These changes provide evidence of altered cellular metabolic status after TBI, with specific compounds proposed to reflect edema, excitotoxicity, neuronal and glial integrity, mitochondrial status and bioenergetics, oxidative stress, inflammation, and cell membrane disruption. Our results support the utility of (1)H-MRS for monitoring cellular mechanisms of TBI pathology in animal models, and the potential of this approach for preclinical evaluation of novel therapies.

A new method for modulating traumatic brain injury with mechanical tissue resuscitation

BACKGROUND

Traumatic brain injuries remain a treatment enigma with devastating late results. As terminally differentiated tissue, the brain retains little capacity to regenerate, making early attempts to preserve brain cells after brain injury essential.

OBJECTIVE

To resuscitate damaged tissue by modulating edema, soluble cytokines, and metabolic products in the "halo" of damaged tissue around the area of central injury that progressively becomes compromised. By re-equilibrating the zone of injury milieu, it is postulated neurons in this area will survive and function.

METHODS

Mechanical tissue resuscitation used localized, controlled, subatmospheric pressure directly to the area of controlled cortical impact injury and was compared with untreated injured controls and with sham surgery in a rat model. Functional outcome, T2 magnetic resonance imaging hyperintense volume, magnetic resonance imaging spectroscopy metabolite measurement, tissue water content, injury cavity area, and cortical volume were compared.

RESULTS

There were significant differences between mechanical tissue resuscitation treated and untreated groups in levels of myoinositol, N-acetylaspartate, and creatine. Treated animals had significantly less tissue swelling and density than the untreated animals. Nonviable brain tissue areas were smaller in treated animals than in untreated animals. Treated animals performed better than untreated animals in functional tests. Histological analysis showed the remaining viable ipsilateral cerebral area was 58% greater for treated animals than for untreated animals, and the cavity for treated animals was 95% smaller than for untreated animals 1 month after injury.

CONCLUSION

Mechanical tissue resuscitation with controlled subatmospheric pressure can significantly modulate levels of excitatory amino acids and lactate in traumatic brain injury, decrease the water content and volume of injured brain, improve neuronal survival, and speed functional recovery.

The use of magnetic resonance spectroscopy in the subacute evaluation of athletes recovering from single and multiple mild traumatic brain injury

Advanced neuroimaging techniques have shown promise in highlighting the subtle changes and nuances in mild traumatic brain injury (MTBI) even though clinical assessment has shown a return to pre-injury levels. Here we use ¹H-magnetic resonance spectroscopy (¹H-MRS) to evaluate the brain metabolites N-acetyl aspartate (NAA), choline (Cho), and creatine (Cr) in the corpus callosum in MTBI. Specifically, we looked at the NAA/Cho, NAA/Cr, and Cho/Cr ratios in the genu and splenium. We recruited 20 normal volunteers (NV) and 28 student athletes recovering from the subacute phase of MTBI. The MTBI group was categorized based upon the number of MTBIs and time from injury to ¹H-MRS evaluation. Significant reductions in NAA/Cho and NAA/Cr ratios were seen in the genu of the corpus callosum, but not in the splenium, for MTBI subjects, regardless of the number of MTBIs. MTBI subjects recovering from their first MTBI showed the greatest alteration in NAA/Cho and NAA/Cr ratios. Time since injury to ¹H-MRS acquisition was based upon symptom resolution and did not turn out to be a significant factor. We observed that as the number of MTBIs increased, so did the length of time for symptom resolution. Unexpected findings from this study are that MTBI subjects showed a trend of increasing NAA/Cho and NAA/Cr ratios that coincided with increasing number of MTBIs.

Trauma and impaired consciousness

This article discusses brain trauma and impaired consciousness. It reviews the various states of impaired consciousness related to trauma, with an historical and current literature viewpoint. The causes and pathophysiology of impaired consciousness in concussion, diffuse axonal injury, and focal brain lesions are discussed and management options evaluated.

Concurrent hippocampal induction of MHC II pathway components and glial activation with advanced aging is not correlated with cognitive impairment

BACKGROUND

Age-related cognitive dysfunction, including impairment of hippocampus-dependent spatial learning and memory, affects approximately half of the aged population. Induction of a variety of neuroinflammatory measures has been reported with brain aging but the relationship between neuroinflammation and cognitive decline with non-neurodegenerative, normative aging remains largely unexplored. This study sought to comprehensively investigate expression of the MHC II immune response pathway and glial activation in the hippocampus in the context of both aging and age-related cognitive decline.

METHODS

Three independent cohorts of adult (12-13 months) and aged (26-28 months) F344xBN rats were behaviorally characterized by Morris water maze testing. Expression of MHC II pathway-associated genes identified by transcriptomic analysis as upregulated with advanced aging was quantified by qPCR in synaptosomal fractions derived from whole hippocampus and in hippocampal subregion dissections (CA1, CA3, and DG). Activation of astrocytes and microglia was assessed by GFAP and Iba1 protein expression, and by immunohistochemical visualization of GFAP and both CD74 (Ox6) and Iba1.

RESULTS

We report a marked age-related induction of neuroinflammatory signaling transcripts (i.e., MHC II components, toll-like receptors, complement, and downstream signaling factors) throughout the hippocampus in all aged rats regardless of cognitive status. Astrocyte and microglial activation was evident in CA1, CA3 and DG of intact and impaired aged rat groups, in the absence of differences in total numbers of GFAP+ astrocytes or Iba1+ microglia. Both mild and moderate microglial activation was significantly increased in all three hippocampal subregions in aged cognitively intact and cognitively impaired rats compared to adults. Neither induction of MHCII pathway gene expression nor glial activation correlated to cognitive performance.

CONCLUSIONS

These data demonstrate a novel, coordinated age-related induction of the MHC II immune response pathway and glial activation in the hippocampus, indicating an allostatic shift toward a para-inflammatory phenotype with advancing age. Our findings demonstrate that age-related induction of these aspects of hippocampal neuroinflammation, while a potential contributing factor, is not sufficient by itself to elicit impairment of spatial learning and memory in models of normative aging. Future efforts are needed to understand how neuroinflammation may act synergistically with cognitive-decline specific alterations to cause cognitive impairment.

Early microstructural and metabolic changes following controlled cortical impact injury in rat: a magnetic resonance imaging and spectroscopy study

Understanding tissue alterations at an early stage following traumatic brain injury (TBI) is critical for injury management and limiting severe consequences from secondary injury. We investigated the early microstructural and metabolic profiles using in vivo diffusion tensor imaging (DTI) and proton magnetic resonance spectroscopy ((1)H MRS) at 2 and 4 h following a controlled cortical impact injury in the rat brain using a 7.0 Tesla animal MRI system and compared profiles to baseline. Significant decrease in mean diffusivity (MD) and increased fractional anisotropy (FA) was found near the impact site (hippocampus and bilateral thalamus; p<0.05) immediately following TBI, suggesting cytotoxic edema. Although the DTI parameters largely normalized on the contralateral side by 4 h, a large inter-individual variation was observed with a trend towards recovery of MD and FA in the ipsilateral hippocampus and a sustained elevation of FA in the ipsilateral thalamus (p<0.05). Significant reduction in metabolite to total creatine ratios of N-acetylaspartate (NAA, p=0.0002), glutamate (p=0.0006), myo-inositol (Ins, p=0.04), phosphocholine and glycerophosphocholine (PCh+GPC, p=0.03), and taurine (Tau, p=0.009) were observed ipsilateral to the injury as early as 2 h, while glutamine concentration increased marginally (p=0.07). These metabolic alterations remained sustained over 4 h after TBI. Significant reductions of Ins (p=0.024) and Tau (p=0.013) and marginal reduction of NAA (p=0.06) were also observed on the contralateral side at 4 h after TBI. Overall our findings suggest significant microstructural and metabolic alterations as early as 2 h following injury. The tendency towards normalization at 4 h from the DTI data and no further metabolic changes at 4 h from MRS suggest an optimal temporal window of about 3 h for interventions that might limit secondary damage to the brain. Results indicate that early assessment of TBI patients using DTI and MRS may provide valuable information on the available treatment window to limit secondary brain damage.

Ketogenic diet prevents alterations in brain metabolism in young but not adult rats after traumatic brain injury

Previous studies have shown that the change of cerebral metabolic rate of glucose (CMRglc) in response to traumatic brain injury (TBI) is different in young (PND35) and adult rats (PND70), and that prolonged ketogenic diet treatment results in histological and behavioral neuroprotection only in younger rat brains. However, the mechanism(s) through which ketones act in the injured brain and the biochemical markers of their action remain unknown. Therefore, the current study was initiated to: 1) determine the effect of injury on the neurochemical profile in PND35 compared to PND70 rats; and 2) test the effect of early post-injury administration of ketogenic diet on brain metabolism in PND35 versus PND70 rats. The data show that alterations in energy metabolites, amino acid, and membrane metabolites were not evident in PND35 rats on standard diet until 24  h after injury, when the concentration of most metabolites was reduced from sham-injured values. In contrast, acute, but transient deficits in energy metabolism were measured at 6  h in PND70 rats, together with deficits in N-acetylaspartate that endured until 24  h. Administration of a ketogenic diet resulted in significant increases in plasma β-hydroxybutyrate (βOHB) levels. Similarly, brain βOHB levels were significantly elevated in all injured rats, but were elevated by 43% more in PND35 rats compared to PND70 rats. As a result, ATP, creatine, and phosphocreatine levels at 24  h after injury were significantly improved in the ketogenic PND35 rats, but not in the PND70 group. The improvement in energy metabolism in the PND35 brains was accompanied by the recovery of NAA and reduction of lactate levels, as well as amelioration of the deficits of other amino acids and membrane metabolites. These results indicate that the PND35 brains are more resistant to the injury, indicated by a delayed deficit in energy metabolism. Moreover, the younger brains revert to ketones metabolism more quickly than do the adult brains, resulting in better neurochemical and cerebral metabolic recovery after injury.

1H-MR spectroscopy in traumatic brain injury

Traumatic brain injury (TBI) is a common cause of neurological damage and disability. Conventional imaging (CT scan or MRI) is highly sensitive in detecting lesions and provides important clinical information regarding the need for acute intervention. However, abnormalities detected by CT scan or conventional MRI have limited importance in the classification of the degree of clinical severity and in predicting patients' outcome. This can be explained by the widespread microscopic tissue damage occurring after trauma, which is not observable with the conventional structural imaging methods. Advances in neuroimaging over the past two decades have greatly helped in the clinical care and management of patients with TBI. The advent of newer and more sensitive imaging techniques is now being used to better characterize the nature and evolution of injury and the underlying mechanisms that lead to progressive neurodegeneration, recovery or subsequent plasticity. This review will describe the role of proton magnetic resonance spectroscopic (MRS), an advanced MRI technique as related to its use in TBI. Proton MRS is a noninvasive approach that acquires metabolite information reflecting neuronal integrity and function from multiple brain regions and allows to assess clinical severity and to predict disease outcome.

A longitudinal proton magnetic resonance spectroscopy study of mild traumatic brain injury

Despite the prevalence and impact of mild traumatic brain injury (mTBI), common clinical assessment methods for mTBI have insufficient sensitivity and specificity. Moreover, few researchers have attempted to document underlying changes in physiology as a function of recovery from mTBI. Proton magnetic resonance spectroscopy (¹H-MRS) was used to assess neurometabolite concentrations in a supraventricular tissue slab in 30 individuals with semi-acute mTBI, and 30 sex-, age-, and education-matched controls. No significant group differences were evident on traditional measures of attention, memory, working memory, processing speed, and executive skills, though the mTBI group reported significantly more somatic, cognitive, and emotional symptoms. At a mean of 13 days post-injury, white matter concentrations of creatine (Cre) and phosphocreatine (PCre) and the combined glutamate-glutamine signal (Glx) were elevated in the mTBI group, while gray matter concentrations of Glx were reduced. Partial normalization of these three neurometabolites and N-acetyl aspartate occurred in the early days post-injury, during the semi-acute period of recovery. In addition, 17 mTBI patients (57%) returned for a follow-up evaluation (mean = 120 days post-injury). A significant group × time interaction indicated recovery in the mTBI group for gray matter Glx, and trends toward recovery in white matter Cre and Glx. An estimate of premorbid intelligence predicted the magnitude of neurometabolite normalization over the follow-up interval for the mTBI group, indicating that biological factors underlying intelligence may also be associated with more rapid recovery.

Anterior cingulate and frontal lobe white matter spectroscopy in early childhood of former very LBW premature infants

Neurometabolic sequelae of children born at very LBW (VLBW) are not well characterized in early childhood. Proton magnetic resonance spectroscopy (1H-MRS) and developmental assessments were acquired from children age 18-22 mo (16 VLBW/7 term) and 3-4 y (12 VLBW/8 term) from the anterior cingulate and left frontal periventricular white matter. Metabolites obtained included combined N-acetylaspartylglutamate and N-acetylaspartate (NAA), total choline-containing compounds (Cho), combined glutamate and glutamine (Glx), combined creatine and phosphocreatine (Cr), myoinositol (mI), and the following ratios: NAA/Cr, Cho/Cr, Glx/Cr, mI/Cr, and NAA/Cho. Significant differences were present only in white matter: at 18-22 mo, NAA was decreased in VLBW children (p < 0.04), and at 3-4 y, VLBW children showed lower Cr (p < 0.01), lower NAA/Cho (p < 0.005), higher Glx/Cr (p < 0.02), and higher Cho/Cr (p < 0.005). On developmental testing, VLBW children scored lower on language expression (p < 0.05) and on the A-not-B test of early executive function (p < 0.01) at 18-22 mo and had lower verbal intelligence quotient (IQ) (p < 0.005), performance IQ (p < 0.04), and several measures of early executive function including the bear-dragon test (p < 0.004), gift delay (p < 0.07), and summary categorization score (p < 0.03) at 3-4 y. VLBW children may have neurometabolic and developmental abnormalities that persist at least through early childhood.

Common data elements in radiologic imaging of traumatic brain injury

Traumatic brain injury (TBI) has a poorly understood pathology. Patients suffer from a variety of physical and cognitive effects that worsen as the type of trauma worsens. Some noninvasive insights into the pathophysiology of TBI are possible using magnetic resonance imaging (MRI), computed tomography (CT), and many other forms of imaging as well. A recent workshop was convened to evaluate the common data elements (CDEs) that cut across the imaging field and given the charge to review the contributions of the various imaging modalities to TBI and to prepare an overview of the various clinical manifestations of TBI and their interpretation. Technical details regarding state-of-the-art protocols for both MRI and CT are also presented with the hope of guiding current and future research efforts as to what is possible in the field. Stress was also placed on the potential to create a database of CDEs as a means to best record information from a given patient from the reading of the images.

The role of advanced MR imaging findings as biomarkers of traumatic brain injury

Treatment of traumatic brain injury (TBI) requires proper classification of the pathophysiology. Clinical classifiers and conventional neuroimaging are limited in TBI detection, outcome prediction, and treatment guidance. Advanced magnetic resonance imaging (MRI) techniques such as susceptibility weighted imaging, diffusion tensor imaging, and magnetic resonance spectroscopic imaging are sensitive to microhemorrhages, white matter injury, and abnormal metabolic activities, respectively, in brain injury. In this article, we reviewed these 3 advanced MRI methods and their applications in TBI and report some new findings from our research. These MRI techniques have already demonstrated their potential to improve TBI detection and outcome prediction. As such, they have demonstrated the capacity of serving as a set of biomarkers to reveal the heterogeneous and complex nature of brain injury in a regional and temporal manner. Further longitudinal studies using advanced MRI in a synergistic approach are expected to provide insight in understanding TBI and imaging implications for treatment.

Immunosuppressant neurotoxicity in rat brain models: oxidative stress and cellular metabolism

Coadministration of the calcineurin inhibitor cyclosporine (CsA) and the mTOR inhibitors sirolimus (SRL) or everolimus (RAD) increases the efficacy of immunosuppression after organ transplantation. Neurotoxicity of CsA is a major clinical problem. Our goal was to assess the effects of CsA, SRL, and RAD on brain cell metabolism. The studies included the comparison of immunosuppressant-mediated effects on glucose metabolism, energy production, and reactive oxygen species (ROS) formation in perfused rat brain slices, primary rat astrocytes, and C6 glioma cells. In brain slices and astrocytes, CsA inhibited Krebs cycle metabolism, while activating anaerobic glycolysis, most likely to compensate for the inhibition of mitochondrial energy production. SRL and RAD inhibited cytosolic glycolysis but did not cause changes in mitochondrial energy production. CsA + SRL inhibited Krebs cycle and glycolysis, thus reducing the ability of the cell to compensate for the negative effects of CsA on mitochondrial nucleoside triphosphate synthesis. In contrast to SRL at the concentrations tested, RAD reduced the CsA-induced ROS formation and antagonized CsA-induced effects on glucose and energy metabolism. Surprisingly, in C6 cells, SRL and RAD exposure resulted in high ROS concentrations without significant impairment of cell metabolism. Our results suggested that SRL enhances CsA-induced ROS formation and negative metabolic effects in brain cells, while RAD seems to antagonize the CsA effects. However, the three models showed different metabolic responses when challenged with the study drugs. In contrast to SRL, RAD enhances ROS formation in C6 glioma cells but has only minor effects on normal rat brain tissue.

Whole-brain proton MR spectroscopic imaging of mild-to-moderate traumatic brain injury and correlation with neuropsychological deficits

Changes in the distribution of the magnetic resonance (MR)-observable brain metabolites N-acetyl aspartate (NAA), total choline (Cho), and total creatine (Cre), following mild-to-moderate closed-head traumatic brain injury (mTBI) were evaluated using volumetric proton MR spectroscopic imaging (MRSI). Studies were carried out during the subacute time period following injury, and associations of metabolite indices with neuropsychological test (NPT) results were evaluated. Twenty-nine subjects with mTBI and Glasgow Coma Scale (GCS) scores of 10-15 were included. Differences in individual metabolite and metabolite ratio distributions relative to those of age-matched control subjects were evaluated, as well as analyses by hemispheric lobes and tissue types. Primary findings included a widespread decrease of NAA and NAA/Cre, and increases of Cho and Cho/NAA, within all lobes of the TBI subject group, and with the largest differences seen in white matter. Examination of the association between all of the metabolite measures and the NPT scores found the strongest negative correlations to occur in the frontal lobe and for Cho/NAA. No significant correlations were found between any of the MRSI or NPT measures and the GCS. These results demonstrate that significant and widespread alterations of brain metabolites occur as a result of mild-to-moderate TBI, and that these measures correlate with measures of cognitive performance.

Magnetic resonance spectroscopy in pediatric neuroradiology: clinical and research applications

Magnetic resonance spectroscopy (MRS) offers a unique, noninvasive approach to assess pediatric neurological abnormalities at microscopic levels by quantifying cellular metabolites. The most widely available MRS method, proton ((1)H; hydrogen) spectroscopy, is FDA approved for general use and can be ordered by clinicians for pediatric neuroimaging studies if indicated. There are a multitude of both acquisition and post-processing methods that can be used in the implementation of MR spectroscopy. MRS in pediatric neuroimaging is challenging to interpret because of dramatic normal developmental changes that occur in metabolites, particularly in the first year of life. Still, MRS has been proven to provide additional clinically relevant information for several pediatric neurological disease processes such as brain tumors, infectious processes, white matter disorders, and neonatal injury. MRS can also be used as a powerful quantitative research tool. In this article, specific research applications using MRS will be demonstrated in relation to neonatal brain injury and pediatric brain tumor imaging.

Experience of diffusion tensor imaging and 1H spectroscopy for outcome prediction in severe traumatic brain injury: Preliminary results

OBJECTIVE

The objective of the study is to test whether multimodal magnetic resonance imaging can provide a reliable outcome prediction of the clinical status, focusing on consciousness at 1 year after severe traumatic brain injury (TBI).

DESIGN

Single center prospective cohort with consecutive inclusions.

SETTING

Critical Care Neurosurgical Unit of a university hospital.

PATIENTS

Forty-three TBI patients not responding to simple orders after sedation cessation and 15 healthy controls.

INTERVENTIONS

A multimodal magnetic resonance imaging combining morphologic sequences, diffusion tensor imaging (DTI), and H proton magnetic resonance spectroscopy (MRS) was performed 24 +/- 11 days after severe TBI. The ability of DTI and MRS to predict 1-year outcome was assessed by linear discriminant analysis (LDA). Robustness of the classification was tested using a bootstrap procedure.

MEASUREMENTS AND MAIN RESULTS

Fractional anisotropy (FA) was computed as the mean of values at discrete brain sites in the infratentorial and supratentorial regions. The N-acetyl aspartate/creatine (NAA/Cr) ratio was measured in the thalamus, lenticular nucleus, insular cortex, occipital periventricular white matter, and pons. After 1 year, 19 (44%) patients had unfavorable outcomes (death, persistent vegetative state, or minimally conscious state) and 24 (56%) favorable outcomes (normal consciousness with or without functional impairments). Analysis of variance was performed to compare FA and NAA/Cr in the two outcome groups and controls. FA and MRS findings showed highly significant differences between the outcome groups, with significant variables by LDA being supratentorial FA, NAA/Cr (pons), NAA/Cr (thalamus), NAA/Cr (insula), and infratentorial FA. LDA of combined FA and MRS data clearly separated the unfavorable outcome, favorable outcome, and control groups, with no overlap. Unfavorable outcome was predicted with up to 86% sensitivity and 97% specificity; these values were better than those obtained with DTI or MRS alone.

CONCLUSION

FA and NAA/Cr hold potential as quantitative outcome-prediction tools at the subacute phase of TBI.

Imaging intelligence with proton magnetic resonance spectroscopy

Proton magnetic resonance spectroscopy ((1)H-MRS) is a technique for the assay of brain neurochemistry in vivo. N-acetylaspartate (NAA), the most prominent metabolite visible within the (1)H-MRS spectrum, is found primarily within neurons. The current study was designed to further elucidate NAA-cognition relationships, particularly whether such relationships are moderated by sex, or tissue type (gray or white matter). We administered standard measures of intelligence to 63 young, healthy subjects and obtained spectroscopic imaging data within a slab of tissue superior to the lateral ventricles. We found that lower NAA within right anterior gray matter predicted better performance VIQ (F=6.83, p=.011, r(2)=.10), while higher NAA within the right posterior gray matter region predicted better PIQ (F=8.175, p=.006, r(2)=.12). These findings add to the small but growing body of literature linking brain biochemistry to intelligence in normal healthy subjects using (1)H-MRSI.

Evaluation of delayed neuronal and axonal damage secondary to moderate and severe traumatic brain injury using quantitative MR imaging techniques

BACKGROUND AND PURPOSE

Traumatic brain injury (TBI) is a classic model of monophasic neuronal and axonal injury, in which tissue damage mainly occurs at the moment of trauma. There is some evidence of delayed progression of the neuronal and axonal loss. Our purpose was to test the hypothesis that quantitative MR imaging techniques can estimate the biologic changes secondary to delayed neuronal and axonal loss after TBI.

MATERIALS AND METHODS

Nine patients (age, 11-28 years; 5 male) who sustained a moderate or severe TBI were evaluated at a mean of 3.1 years after trauma. We applied the following techniques: bicaudate (BCR) and bifrontal (BFR) ventricle-to-brain ratios; T2 relaxometry; magnetization transfer ratio (MTR); apparent diffusion coefficient (ADC); and proton spectroscopy, by using an N-acetylaspartate/creatine (NAA/Cr) ratio measured in normal-appearing white matter (NAWM) and the corpus callosum (CC). The results were compared with those of a control group.

RESULTS

BCR and BFR mean values were significantly increased (P < or = .05) in patients due to secondary subcortical atrophy; increased T2 relaxation time was observed in the NAWM and CC, reflecting an increase in water concentration secondary to axonal loss. Increased ADC mean values and reduced MTR mean values were found in the NAWM and CC, showing damage in the myelinated axonal fibers; and decreased NAA/Cr ratio mean values were found in the CC, indicating axonal loss.

CONCLUSIONS

These quantitative MR imaging techniques could noninvasively demonstrate the neuronal and axonal damage in the NAWM and CC of human brains, secondary to moderate or severe TBI.

Post-acute pathological changes in the thalamus and internal capsule in aged mice following controlled cortical impact injury: a magnetic resonance imaging, iron histochemical, and glial immunohistochemical study

Traumatic brain injury (TBI) is a major cause of neurological disability across all ages, but the elderly are particularly vulnerable and have a worse prognosis than younger individuals. To advance the understanding of long-term pathogenesis induced by TBI in the elderly, aged mice (21 -- 24 months) were given a controlled cortical impact (CCI) injury to the sensorimotor cortex, and their brains were analyzed by MRI and histopathology at 1 and 2 months after CCI injury, a post-acute period. A T2 hypointensity was observed in the ipsilateral thalamus but not in the contralateral thalamus or in the thalamus of sham operated, control mice. The hypointensity was co-localized with increased histochemical staining of iron, a paramagnetic substance that causes a shortening of the T2 relaxation time. Since iron catalyzes reactions that lead to toxic free radicals, the deposition of iron in the thalamus raises the possibility that it promotes pathogenesis following TBI. Astrocyte gliosis and microgliosis were also observed in the ipsilateral thalamus in the post-acute period. The ipsilateral internal capsule displayed a trend for a T2 hypointensity, however, unlike the thalamus it did not have an increase of iron or GFAP staining, but it did have evidence of microgliosis. In summary, areas of T2 hypointensity were revealed in both the thalamus and internal capsule during the post-acute period following CCI injury, but the underlying pathology appeared to be distinct between these regions.

Short-term DTI predictors of cognitive dysfunction in mild traumatic brain injury

PRIMARY OBJECTIVE

To explore whether baseline diffusion tensor imaging (DTI) metrics are predictive of cognitive functioning 6 months post-injury in patients with mild traumatic brain injury (MTBI).

RESEARCH DESIGN

Seventeen patients with MTBI and 29 sex- and age-matched healthy controls were studied.

METHODS AND PROCEDURES

Participants underwent an MRI protocol including DTI, at an average of 4.0 (range: 1-10) days post-injury. Mean diffusivity (MD) and fractional anisotropy (FA) were measured in the following white matter (WM) regions: centra semiovale, the genu and the splenium of the corpus callosum and the posterior limb of the internal capsule. Participants underwent neuropsychological (NP) testing at baseline and at 6-month follow-up. Least squares regression analysis was used to evaluate the association of MD and FA with each NP test score at baseline and follow-up.

MAIN OUTCOMES AND RESULTS

Compared to controls, average MD was significantly higher (p = 0.02) and average FA significantly lower (p = 0.0001) in MTBI patients. At the follow-up, there was a trend toward a significant association between baseline MD and response speed (r = -0.53, p = 0.087) and a positive correlation between baseline FA and Prioritization form B (r = 0.72, p = 0.003).

CONCLUSIONS

DTI may provide short-term non-invasive predictive markers of cognitive functioning in patients with MTBI.

Early and sustained alterations in cerebral metabolism after traumatic brain injury in immature rats

Although studies have shown alterations in cerebral metabolism after traumatic brain injury (TBI), clinical data in the developing brain is limited. We hypothesized that post-traumatic metabolic changes occur early (<24 h) and persist for up to 1 week. Immature rats underwent TBI to the left parietal cortex. Brains were removed at 4 h, 24 h, and 7 days after injury, and separated into ipsilateral (injured) and contralateral (control) hemispheres. Proton nuclear magnetic resonance (NMR) spectra were obtained, and spectra were analyzed for N-acetyl-aspartate (NAA), lactate (Lac), creatine (Cr), choline, and alanine, with metabolite ratios determined (NAA/Cr, Lac/Cr). There were no metabolic differences at any time in sham controls between cerebral hemispheres. At 4 and 24 h, there was an increase in Lac/Cr, reflecting increased glycolysis and/or decreased oxidative metabolism. At 24 h and 7 days, there was a decrease in NAA/Cr, indicating loss of neuronal integrity. The NAA/Lac ratio was decreased ( approximately 15-20%) at all times (4 h, 24 h, 7 days) in the injured hemisphere of TBI rats. In conclusion, metabolic derangements begin early (<24 h) after TBI in the immature rat and are sustained for up to 7 days. Evaluation of early metabolic alterations after TBI could identify novel targets for neuroprotection in the developing brain.

Alzheimer disease: postmortem neuropathologic correlates of antemortem 1H MR spectroscopy metabolite measurements

PURPOSE

To determine the neuropathologic correlates of antemortem hydrogen 1 ((1)H) magnetic resonance (MR) spectroscopy metabolite measurements in subjects with Alzheimer disease (AD)-type pathology.

MATERIALS AND METHODS

This study was approved by the institutional review board and was compliant with HIPAA regulations. Informed consent was obtained from each subject. The authors identified 54 subjects who underwent antemortem (1)H MR spectroscopy and were clinically healthy or had AD-type pathology with low to high likelihood of AD according to National Institute on Aging-Reagan neuropathologic criteria at autopsy. They investigated the associations between (1)H MR spectroscopy metabolite measurements and Braak neurofibrillary tangle stage (Braak stage), neuritic plaque score, and AD likelihood, with adjustments for subject age, subject sex, and time between (1)H MR spectroscopy and death.

RESULTS

Decreases in N-acetylaspartate-to-creatine ratio, an index of neuronal integrity, and increases in myo-inositol-to-creatine ratio were associated with higher Braak stage, higher neuritic plaque score, and greater likelihood of AD. The N-acetylaspartate-to-myo-inositol ratio proved to be the strongest predictor of the pathologic likelihood of AD. The strongest association observed was that between N-acetylaspartate-to-myo-inositol ratio and Braak stage (R(N)(2) = 0.47, P < .001).

CONCLUSION

Antemortem (1)H MR spectroscopy metabolite changes correlated with AD-type pathology seen at autopsy. The study findings validated (1)H MR spectroscopy metabolite measurements against the neuropathologic criteria for AD, and when combined with prior longitudinal (1)H MR spectroscopy findings, indicate that these measurements could be used as biomarkers for disease progression in clinical trials.

Morphometric MRI findings in the thalamus and brainstem in children after moderate to severe traumatic brain injury

Generalized whole brain volume loss is well documented in moderate to severe traumatic brain injury. Whether this atrophy occurs in the thalamus and brainstem has not been systematically studied in children. Magnetic resonance imaging (MRI) quantitative analysis was used to investigate brain volume loss in the thalamus and brainstem in 16 traumatic brain injury subjects (age range 9-16 years) compared with 16 age and demo-graphically matched controls. Based on multiple analysis of covariance, controlling for age and head size, reduced volume in the thalamus and the midbrain region of the brainstem were found. General linear model analyses revealed a relation between processing speed on a working memory task and midbrain and brain stem volumes. Reduced volume in thalamic and brainstem structures were associated with traumatic brain injury. Reduction in midbrain and thalamic volume is probably a reflection of the secondary effects of diffuse axonal injury and reduction in cortical volume from brain injury.

Clinical review: Prognostic value of magnetic resonance imaging in acute brain injury and coma

Progress in management of critically ill neurological patients has led to improved survival rates. However, severe residual neurological impairment, such as persistent coma, occurs in some survivors. This raises concerns about whether it is ethically appropriate to apply aggressive care routinely, which is also associated with burdensome long-term management costs. Adapting the management approach based on long-term neurological prognosis represents a major challenge to intensive care. Magnetic resonance imaging (MRI) can show brain lesions that are not visible by computed tomography, including early cytotoxic oedema after ischaemic stroke, diffuse axonal injury after traumatic brain injury and cortical laminar necrosis after cardiac arrest. Thus, MRI increases the accuracy of neurological diagnosis in critically ill patients. In addition, there is some evidence that MRI may have potential in terms of predicting outcome. Following a brief description of the sequences used, this review focuses on the prognostic value of MRI in patients with traumatic brain injury, anoxic/hypoxic encephalopathy and stroke. Finally, the roles played by the main anatomical structures involved in arousal and awareness are discussed and avenues for future research suggested.

1H magnetic resonance spectroscopy in dementia

Present data support the concept that (1)H magnetic resonance spectroscopy ((1)H MRS) may become an adjunct to clinical evaluation for differential diagnosis of dementia in the future. The value of (1)H MRS in monitoring the disease progression in dementia is expected to be in areas where group effects are sought such as monitoring effectiveness of therapies in drug trials. Elevation of myoinositol to creatine (mI/Cr) and choline to creatine (Cho/Cr) and reduction in the neuronal integrity marker N-acetylaspartate to creatine (NAA/Cr) levels in individuals with mild cognitive impairment and pre-symptomatic Alzheimer's disease suggests that (1)H MRS may also be valuable in predicting future development of dementia and monitoring early disease progression for preventive therapies. Investigations of in vivo (1)H MRS as a marker for differential diagnosis and progression of dementia, however, has been limited to clinically confirmed cohorts and remains to be validated by histopathology at autopsy. Overall, MRS is a promising investigational technique in ageing and dementia at this time. The potential clinical application of MRS in ageing and dementia, however, is growing with technical advances in the field.

Assessment of mitochondrial impairment in traumatic brain injury using high-resolution proton magnetic resonance spectroscopy

Object

The goal of this study was to demonstrate the posttraumatic neurochemical damage in normal-appearing brain and to assess mitochondrial dysfunction by measuring N-acetylaspartate (NAA) levels in patients with severe head injuries, using proton (1H) magnetic resonance (MR) spectroscopy.

Methods

Semiquantitative analysis of NAA relative to creatine-containing compounds (Cr) and choline (Cho) was carried out from proton spectra obtained by means of chemical shift (CS) imaging and single-voxel (SV) methods in 25 patients with severe traumatic brain injuries (TBIs) (Glasgow Coma Scale scores ≤ 8) using a 1.5-tesla MR unit. Proton MR spectroscopy was also performed in 5 healthy volunteers (controls).

Results

The SV studies in patients with diffuse TBI showed partial reduction of NAA/Cho and NAA/Cr ratios within the first 10 days after injury (means ± standard deviations 1.59 ± 0.46 and 1.44 ± 0.21, respectively, in the patients compared with 2.08 ± 0.26 and 2.04 ± 0.31, respectively, in the controls; nonsignificant difference). The ratios gradually declined in all patients as time from injury increased (mean minimum values NAA/Cho 1.05 ± 0.44 and NAA/Cr 1.05 ± 0.30, p < 0.03 and p < 0.02, respectively). This reduction was greater in patients with less favorable outcomes. In patients with focal injuries, the periphery of the lesions revealed identical trends of NAA/Cho and NAA/Cr decrease. These reductions correlated with outcome at 6 months (p < 0.01). Assessment with multivoxel methods (CS imaging) demonstrated that, in diffuse injury, NAA levels declined uniformly throughout the brain. At 40 days postinjury, initially low NAA/Cho levels had recovered to near baseline in patients who had good outcomes, whereas no recovery was evident in patients with poor outcomes (p < 0.01).

Conclusions

Using 1H-MR spectroscopy, it is possible to detect the posttraumatic neurochemical damage of the injured brain when conventional neuroimaging techniques reveal no abnormality. Reduction of NAA levels is a dynamic process, evolving over time, decreasing and remaining low throughout the involved tissue in patients with poor outcomes. Recovery of NAA levels in patients with favorable outcomes suggests marginal mitochondrial impairment and possible resynthesis from vital neurons.

Structural and functional neuroimaging in mild-to-moderate head injury

Head injury is a major cause of disability and death in adults. Significant developments in imaging techniques have contributed to the knowledge of the pathophysiology of head injury. Although extensive research is available on severe head injury, less is known about mild-to-moderate head injury despite the fact that most patients sustain this type of injury. In this review, we focus on structural and functional imaging techniques in patients with mild-to-moderate head injury. We discuss CT and MRI, including different MRI sequences, single photon emission computed tomography, perfusion-weighted MRI, perfusion CT, PET, magnetic resonance spectroscopy, functional MRI and magnetic encephalography. We outline the advantages and limitations of these various techniques in the contexts of the initial assessment and identification of brain abnormalities and the prediction of outcome.

Neural injury and recovery near cortical contusions: a clinical magnetic resonance spectroscopy study

Object

Proton magnetic resonance (MR) spectroscopy can detect neural metabolic alterations noninvasively after traumatic brain injury (TBI) even in areas that appear normal. Unlike metabolic depression in diffuse TBI, focal metabolic alterations near cortical contusions in humans have not been previously investigated in a longitudinal study. The object of this study was to identify these alterations and examine their course.

Methods

At 1 week and 1 month after mild to moderate TBI involving cortical contusion, 30 patients underwent 1H MR spectroscopy examination that focused bilaterally on normal-appearing frontal and temporal white matter. Levels of N-acetylaspartate (NAA), choline (Cho) compounds, and creatine (Cr) were measured to obtain two metabolite ratios, NAA/Cr and Cho/Cr. The ratios were compared with those of 11 healthy individuals.

At 1 week after TBI, the NAA/Cr ratio was significantly lower near cortical contusions than it was in white matter remote from the injury or in controls, while the Cho/Cr ratios did not differ significantly. At 1 month, the decreased NAA/Cr ratios near contusions had increased significantly from 1 week, as had the Cho/Cr ratio.

Conclusions

Metabolic depression reflecting neural injury was apparent in subjacent normal-appearing white matter at 1 week after cortical contusion; this had normalized substantially at 1 month.

Magnetic resonance spectroscopy detects brain injury and predicts cognitive functioning in children with brain injuries

Proton magnetic resonance spectroscopy (1H-MRS) and neuropsychological assessment were utilized in a longitudinal investigation of traumatic brain injury (TBI) in children. A spectroscopic imaging protocol was implemented, and neurometabolite ratios of NAA/Cre and Cho/Cre were calculated for anterior and posterior halves of a supraventricular slab of brain tissue. NAA/Cre was reduced and Cho/Cre increased in TBI patients as compared to controls, for both brain regions. Each ratio predicted aspects of neuropsychological performance, though the specific relationships varied somewhat by region and function. Anterior NAA/Cre increased and anterior Cho/Cre decreased from 3 to 21 weeks post-injury, suggesting neurometabolic recovery.

Diffusion tensor imaging in the corpus callosum in children after moderate to severe traumatic brain injury

Diffusion tensor imaging (DTI) is a recent imaging technique that assesses the microstructure of the cerebral white matter (WM) based on anisotropic diffusion (i.e., water molecules move faster in parallel to nerve fibers than perpendicular to them). Fractional anisotropy (FA), which ranges from 0 to 1.0, increases with myelination of WM tracts and is sensitive to diffuse axonal injury (DAI) in adults with traumatic brain injury (TBI). However, previous DTI studies of pediatric TBI were case reports without detailed outcome measures. Using mean FA derived from DTI fiber tractography, we compared DTI findings of the corpus callosum for 16 children who were at least 1 year (mean 3.1 years) post-severe TBI and individually matched, uninjured children. Interexaminer and intraexaminer reliability in measuring FA was satisfactory. FA was significantly lower in the patients for the genu, body, and splenium of the corpus callosum. Higher FA was related to increased cognitive processing speed and faster interference resolution on an inhibition task. In the TBI patients, higher FA was related to better functional outcome as measured by the dichotomized Glasgow Outcome Scale (GOS). FA also increased as a function of the area of specific regions of the corpus callosum such as the genu and splenium, and FA in the splenium was reduced with greater volume of lesions in this region. DTI may be useful in identifying biomarkers related to DAI and outcome of TBI in children.

Susceptibility-Weighted Imaging and Proton Magnetic Resonance Spectroscopy in Assessment of Outcome After Pediatric Traumatic Brain Injury

OBJECTIVE

To assess the role of magnetic resonance imaging, specifically magnetic resonance spectroscopy (MRS) and susceptibility-weighted imaging (SWI), in the evaluation of children with traumatic brain injury (TBI).

DATA SOURCES

Literature review and data from our recently published clinical studies.

STUDY SELECTION

Children with pediatric TBI who underwent SWI. SWI is a 3-dimensional high-resolution magnetic resonance imaging technique that is more sensitive in detecting hemorrhagic lesions seen with diffuse axonal injury (DAI) than conventional imaging. MRS acquires metabolite information that reflects neuronal integrity and function from multiple brain regions and offers early prognostic information regarding outcome.

DATA EXTRACTION

Literature review.

DATA SYNTHESIS

Literature review and review of recently published data from our institution.

CONCLUSIONS

The data suggest that more sensitive imaging techniques that provide early evidence of injury and that are better predictors of outcome are needed to identify children at risk for such deficits. Specifically, the number and volume of hemorrhagic DAI lesions as well as changes in spectral metabolites such as reduced N-acetylaspartate or elevations in choline-related compounds correlate with neurologic disability and impairments of global intelligence, memory, and attention.

In vivo measurement of tissue damage, oxygen saturation changes and blood flow changes after experimental traumatic brain injury in rats using susceptibility weighted imaging

Traumatic brain injury (TBI) is a prevalent disease, and many TBI patients experience disturbed cerebral blood flow (CBF) after injury. Moreover, TBI is difficult to quantify with conventional imaging modalities. In this paper, we utilized susceptibility weighted imaging (SWI) as a means to monitor functional blood oxygenation changes and to quantify CBF changes in animals after trauma. In this study using six rats, brain trauma was induced by a weight drop model and the brain was scanned over four time points: pre trauma, and 4 h, 24 h and 48 h post trauma. Five rats survived and one died after trauma. A blood phase analysis using filtered SWI phase images suggested that three rats recovered after 48 h and two rats deteriorated. SWI also suggested that CBF decreased by up to 26%. The CBF change is in agreement with the results of arterial spin labeling methods conducted in this study and with previously published results. Furthermore, SWI revealed an enlargement of the major venous vasculature in deep brain structures, in accordance with the location of diffuse axonal injury. Compared with the traditional, invasive, clinical monitoring of cerebral vascular damage and reduction in blood flow, this method offers a novel, safe and noninvasive approach to quantify changes in oxygen saturation and CBF and to visualize structural changes in blood vasculature after TBI.

Brain ischaemia after traumatic brain injury: lessons from 15O2 positron emission tomography

PURPOSE OF REVIEW

To describe the role of O2 positron emission tomography in studies aimed at understanding ischaemia in head injury. It has been difficult to use cerebral blood flow levels to provide a secure definition of cerebral ischaemia in head injury, since primary changes in cerebral metabolism may be responsible for coupled reductions in cerebral blood flow. Further, regional heterogeneity of pathophysiology can confound global measures of adequacy of cerebral oxygen delivery. There is a need for a technique that can provide a comprehensive and quantitative description of cerebral physiology in this setting.

RECENT FINDINGS

O2 positron emission tomography can image cerebral blood flow, cerebral blood volume, cerebral metabolic rate for oxygen and oxygen extraction fraction, and thus allows a robust and specific definition of true ischaemia. When used in combination with other monitoring tools and imaging modalities, positron emission tomography has also been used to validate and refine bedside monitors of cerebrovascular physiology, study the impact of therapeutic interventions and provide clues to novel pathophysiology.

SUMMARY

There is a clear role for O2 positron emission tomography in elucidating pathophysiology in head injury. The technique may provide most information when combined with other imaging and monitoring tools.

MR spectroscopy: Predicting long-term neuropsychological outcome following pediatric TBI

PURPOSE

To identify useful acute indicators of long-term neurocognitive outcome beyond clinical variables for children and adolescents treated for a traumatic brain injury (TBI).

MATERIALS AND METHODS

The efficacy of magnetic resonance spectroscopy (MRS) acquired 6+/-4 days after TBI in 20 children/adolescents in predicting intellectual and neuropsychological functioning one to four years post injury was assessed. Short echo-time single voxel MRS (SVS) from normal-appearing brain was compared to intermediate echo-time multivoxel MR spectroscopic imaging (MRSI) from normal-appearing and visibly-injured brain acquired through the level of the corpus callosum (CC).

RESULTS

N-acetyl aspartate (NAA) was moderate to strongly correlated with cognitive scores. Mean NAA/creatine (Cre) from MRSI alone explained over 40% of the variance in cognitive scores and 18% of the variance above and beyond demographic and clinical variables alone. Mild to moderate associations were noted between SVS metabolites (glutamate/glutamine [Glx] and myoinositol [mI]) and cognitive scores, with no such associations apparent for choline (Cho) or Cre. Exploratory analyses revealed trends for regional neuroimaging data and specific cognitive abilities.

CONCLUSION

Acute MR spectroscopy of the pediatric brain injury patient improves prognostic ability and may provide valuable information for early treatment and intervention planning.

Prognostic role of proton magnetic resonance spectroscopy in acute traumatic brain injury

Proton magnetic resonance spectroscopy (MRS) is being used to evaluate individuals after acute traumatic brain injury. These studies have shown that changes in certain brain metabolites are associated with poor neurologic outcomes. The majority of MRS studies have been obtained relatively late after injury, but there have been a few reports of use early after injury to assist with outcome prediction. Altered brain metabolites may be sensitive indicators of injury and thus provide additional prognostic information when spectroscopy is done early after injury. This technology may provide a noninvasive means to evaluate early excitotoxic injury, and show changes associated with both neuronal injury and membrane disruption secondary to diffuse axonal injury. This article will review the technology of MRS, discuss its role in patient assessment after traumatic brain injury, and present a summary of our published and ongoing research.

Systemic lupus erythematosus and the brain: what mice are telling us

Neuropsychiatric symptoms occur in systemic lupus erythematosus (SLE), a complex, autoimmune disease of unknown origin. Although several pathogenic mechanisms have been suggested to play a significant role in the etiology of the disease, the exact underlying mechanisms still remain elusive. Several inbred strains of mice are used as models to study SLE, which exhibit a diversity of central nervous system (CNS) manifestations similar to that observed in patients. This review will attempt to give a brief overview of the CNS alterations observed in these models, including biochemical, structural and behavioral changes.

Early morphologic and spectroscopic magnetic resonance in severe traumatic brain injuries can detect "invisible brain stem damage" and predict "vegetative states"

A precise evaluation of the brain damage in the first days of severe traumatic brain injured (TBI) patients is still uncertain despite numerous available cerebral evaluation methods and imaging. In 5-10% of severe TBI patients, clinicians remain concerned with prolonged coma and long-term marked cognitive impairment unexplained by normal morphological T2 star, flair, and diffusion magnetic resonance imaging (MRI). For this reason, we prospectively assessed the potential value of magnetic resonance spectroscopy (MRS) of the brain stem to evaluate the functionality of the consciousness areas. Forty consecutive patients with severe TBI were included. Single voxel proton MRS of the brain stem and morphological MRI of the whole brain were performed at day 17.5 +/- 6.4. Disability Rating Scale and Glasgow Outcome Scale (GOS) were evaluated at 18 months posttrauma. MRS appeared to be a reliable tool in the exploration of brainstem metabolism in TBI. Three different spectra were observed (normal, cholinergic reaction, or neuronal damage) allowing an evaluation of functional damage. MRS disturbances were not correlated with anatomical MRI lesions suggesting that the two techniques are strongly complementarity. In two GOS 2 vegetative patients with normal morphological MRI, MRS detected severe functional damage of the brainstem (NAA/Cr < 1.50) that was described as "invisible brain stem damage." MRI and MRS taken separately could not distinguish patients GOS 3 (n = 7) from GOS 1-2 (n = 11) and GOS 4-5 (n = 20). However, a principal component analysis of combined MRI and MRS data enabled a clear-cut separation between GOS 1-2, GOS 3, and GOS 4-5 patients with no overlap between groups. This study showed that combined MRI and MRS provide a reliable evaluation of patients presenting in deep coma, specially when there are insufficient MRI lesions of the consciousness pathways to explain their status. In the first few days post-trauma metabolic (brainstem spectroscopy) and morphological (T2 star and Flair) MRI studies can predict the long-term neurological outcome, especially the persistent vegetative states and minimally conscious state.

Longitudinal 1H MRS changes in mild cognitive impairment and Alzheimer's disease

Magnetic resonance (MR)-based volume measurements of atrophy are potential markers of disease progression in patients with amnestic mild cognitive impairment (MCI) and Alzheimer's disease (AD). Longitudinal changes in (1)H MR spectroscopy ((1)H MRS) metabolite markers have not been characterized in MCI subjects. Our objective was to determine the longitudinal (1)H MRS metabolite changes in patients with MCI, and AD, and to compare (1)H MRS metabolite ratios and ventricular volumes in tracking clinical disease progression in AD. The neuronal integrity marker N-acetylaspartate/creatine ratio declined in MCI and AD patients compared to cognitively normal elderly. The change in (1)H MRS metabolite ratios correlated with clinical progression about as strongly as the rate of ventricular expansion, suggesting that (1)H MRS metabolite ratios may be useful markers for the progression of AD. Choline/creatine ratio declined in stable MCI, compared to converter MCI patients and cognitively normal elderly, which may be related to a compensatory mechanism in MCI patients who did not to progress to AD.

[Brain perfusion and metabolism imaging techniques]

Due to recent efforts in improving spatial and temporal resolution in imaging techniques, it is now possible to get relevant information about brain perfusion and metabolism in humans. This information can significantly impact on brain pathophysiology, diagnosis assessment and therapy options, particularly in patients having brain ischemia. Among these imaging and metabolism techniques are dynamic perfusion computed tomography, perfusion MRI, positron emission tomography and NMR spectroscopic imaging. The goal of this article is an overview of these four techniques, with their own technical description, advantages and drawbacks. Details are provided about brain parameters given by each technique and their clinical relevance, the accessibility of the technique in the emergency setting and the optimal window to use it during the patient's evolution.

Glutamate and GABA metabolism in transient and permanent middle cerebral artery occlusion in rat: Importance of astrocytes for neuronal survival

The aim of the present study was to identify the distinguishing metabolic characteristics of brain tissue salvaged by reperfusion following focal cerebral ischemia. Rats were subjected to 120 min of middle cerebral artery occlusion followed by 120 min of reperfusion. The rats received an intravenous bolus injection of [1-(13)C]glucose plus [1,2-(13)C]acetate. Subsequently two brain regions considered to represent penumbra and ischemic core, i.e. the frontoparietal cortex and the lateral caudoputamen plus lower parietal cortex, respectively, were analyzed with (13)C NMRS and HPLC. The results demonstrated four metabolic events that distinguished the reperfused penumbra from the ischemic core. (1) Improved astrocytic metabolism demonstrated by increased amounts of [4,5-(13)C]glutamine and improved acetate oxidation. (2) Neuronal mitochondrial activity was better preserved although the flux of glucose via pyruvate dehydrogenase into the tricarboxylic acid (TCA) cycle in glutamatergic and GABAergic neurons was halved. However, NAA content was at control level. (3) Glutamatergic and GABAergic neurons used relatively more astrocytic metabolites derived from the pyruvate carboxylase pathway. (4) Lactate synthesis was not increased despite decreased glucose metabolism in the TCA cycle via pyruvate dehydrogenase. In the ischemic core both neuronal and astrocytic TCA cycle activity declined significantly despite reperfusion. The utilization of astrocytic precursors originating from the pyruvate carboxylase pathway was markedly reduced compared the pyruvate dehydrogenase pathway in glutamate, and completely stopped in GABA. The NAA level fell significantly and lactate accumulated. The results demonstrate that preservation of astrocytic metabolism is essential for neuronal survival and a predictor for recovery.

Hypothesis of the postconcussive vulnerable brain: experimental evidence of its metabolic occurrence

OBJECTIVE

We evaluated the effects of two consecutive concussive injuries on brain energy metabolism and N-acetylaspartate (NAA) to investigate how the temporal interval between traumatic events influences overall injury severity.

METHODS

Rats were injured to induce diffuse traumatic brain injury (TBI) (mild, 450 g/1 m; severe, 450 g/2 m). In two groups, two mild TBIs were delivered in 3- or 5-day intervals. Three additional animal groups were used: single mild TBI, single severe TBI, and sham. All animals were killed 48 hours postinjury. Adenosine 5'-triphosphate (ATP), adenosine diphosphate, and NAA concentrations were analyzed with high-performance liquid chromatography on deproteinized whole brain extracts.

RESULTS

In control animals, the NAA concentration was 9.17 +/- 0.38 micromol/g wet weight, the ATP concentration was 2.25 +/- 0.21 micromol/g wet weight, and the ATP-to-adenosine diphosphate ratio was 9.38 +/- 1.23. These concentrations decreased to 6.68 +/- 1.12 micromol/g wet weight, 1.68 +/- 0.24 micromol/g wet weight, and 6.10 +/- 1.21 micromol/g wet weight, respectively, in rats that received two mild TBIs at a 5-day interval (P < 0.01; not different from results in rats with single mild TBI). When a second TBI was delivered after 3 days, the NAA concentration was 3.86 +/- 0.53 micromol/g wet weight, the ATP concentration was 1.11 +/- 0.18 micromol/g wet weight, and the ATP-to-adenosine diphosphate ratio was 2.64 +/- 0.43 (P < 0.001 versus both controls and 3-day interval; not different from rats receiving a single severe TBI).

CONCLUSION

The biochemical modification severity in double TBI is dependent on the interval between traumatic events, which demonstrates the metabolic state of the vulnerable brain after mild TBI. These data support the hypothesis of the application of proton magnetic resonance spectroscopy to measure NAA as a possible tool to monitor the full recovery of brain metabolic functions in the clinical setting, particularly in sports medicine.