Obesity is associated with the insulin resistance metabolic syndrome, postulated to be mediated by stress-induced alterations within the hypothalamic-pituitary-adrenal (HPA) axis. In adult bonnet macaques we examined relationships between components of the metabolic syndrome, hippocampal neurometabolic asymmetry, an indicator of negative affect, and juvenile cerebrospinal fluid (csf) corticotropin-releasing factor (CRF) levels obtained after stress exposure associated with maternal food insecurity and in controls.
Eleven adult male monkeys (seven with early life stress) who had undergone csf-CRF analyses as juveniles had magnetic resonance spectroscopic imaging (MRSI) of bilateral hippocampus, morphometry (body mass index, BMI; sagittal abdominal diameter, SAD) and determination of fasting plasma glucose and insulin as adults. Neurometabolite ratios included N-acetyl-aspartate as numerator (NAA; a marker of neuronal integrity) and choline (Cho; cell turnover) and creatine (Cr; reference analyte) as denominators.
Elevated juvenile csf-CRF levels positively predicted adult BMI and SAD and were associated with right > left shift of NAA ratio within the hippocampus. Adult visceral obesity and insulin level correlated with right > left shift in hippocampal NAA concentrations, controlling for age and denominator.
Juvenile csf-CRF levels, a neuropeptide associated with early life stress, predict adult visceral obesity and hippocampal asymmetry supporting the hypothesis that metabolic syndrome in adults may be related to early life stress. Furthermore, this study demonstrates asymmetrical hippocampal alterations related to obesity.
Corticotropin releasing factor; hippocampus; stress; metabolic syndrome; food insecurity; obesity
Although magnetic resonance spectroscopy has identified metabolic abnormalities in adult and childhood schizophrenia, no prior studies have investigated the relationship between neurometabolites and thought disorder. This study examined this association in language-related brain regions using proton magnetic resonance spectroscopic imaging (1H MRSI).
MRSI was acquired bilaterally from 28 youth with childhood-onset schizophrenia and 34 healthy control subjects in inferior frontal, middle frontal, and superior temporal gyri at 1.5 T and short echo time (TR/TE=1500/30 ms). CSF-corrected “total NAA” (tNAA; N-acetyl-aspartate+N-acetyl-aspartyl-glutamate), glutamate+glutamine (Glx), creatine+phosphocreatine (Cr+PCr), choline compounds (Cho), and myo-inositol (mI) were assayed in manually drawn regions-of-interest partitioned into gray matter, white matter, and CSF and then coregistered with MRSI. Speech samples of all subjects were coded for thought disorder.
In the schizophrenia group, the severity of formal thought disorder correlated significantly with tNAA in the left inferior frontal and superior temporal gyri and with Cr+PCr in left superior temporal gyrus.
Neurometabolite concentrations in language-related brain regions are associated with thought disorder in childhood-onset schizophrenia.
Childhood-onset schizophrenia; Thought Disorder; Magnetic Resonance Spectroscopy; N-acetyl aspartate; Choline compounds
To determine the relationship of cerebral degeneration with survival in amyotrophic lateral sclerosis (ALS).
Patients with probable or definite ALS underwent magnetic resonance spectroscopic imaging (MRSI) of the brain between July 1996 and May 2002, and were followed prospectively until March 2004. Creatine (Cr), choline (Cho) and the neuronal marker N‐acetylaspartate (NAA) were quantified as ratios in the motor cortex.
In 63 patients compared with 18 healthy people, NAA/Cho was reduced by 13% (p<0.001), NAA/Cr was reduced by 5% (p = 0.01) and Cho/Cr was increased by 8% (p = 0.01). NAA/Cho was used for survival analysis, given its larger effect size and superior test accuracy (a sensitivity of 67% and a specificity of 83%). Median survival after MRSI was 24 months. Multivariate analysis showed reduced survival for lower NAA/Cho (hazard ratio (HR) 0.24, 95% confidence interval (CI) 0.08 to 0.72, p = 0.01), older age (HR 1.03, 95% CI 1.00 to 1.06, p = 0.04) and shorter symptom duration (HR 0.96, 95% CI 0.93 to 0.99, p = 0.01). Patients with NAA/Cho <2.11 had a reduced survival of 19.4 v 31.9 months (HR 2.05, 95% CI 1.12 to 4.03, p = 0.02).
Cerebral degeneration is predictive of reduced survival in ALS.
Multiple sclerosis (MS) is a highly prevalent cause of neurological disability and has different clinical subtypes with potentially different underlying pathologies. Differentiation of primary progressive multiple sclerosis (PPMS) from relapsing remitting multiple sclerosis (RRMS) could be difficult especially in its early phases.
We compared brain metabolite concentrations and ratios in patients with PPMS and RRMS by magnetic resonance spectroscopic imaging (MRSI).
Patients and Methods
Thirty patients with definite MS (15 with RRMS and 15 with PPMS) underwent MRSI and their non-enhancing lesion metabolites were measured. N-acetyl aspartate (NAA), Creatine (Cr), Choline (Cho), NAA/Cr and NAA/Cho were measured and compared between the two MS subtypes.
When the two MS groups were compared together, we found that Cr was significantly increased (P value=0.008) and NAA/Cr was significantly decreased (P value=0.03) in non-enhancing lesions in PPMS compared with RRMS. There was no significant difference in NAA, Cho or NAA/Cho between the two MS subtypes.
MRS is a potential way to differentiate PPMS and RRMS.
Multiple Sclerosis, Chronic Progressive; Multiple Sclerosis, Relapsing-Remitting; Magnetic Resonance Spectroscopy
This study was conducted to corroborate prior evidence of an effect of the BDNF Val66Met polymorphism on measures of N-acetyl aspartate containing compounds (NAA) in healthy subjects.
The NAA to creatine (Cre) ratio (NAA/Cre), NAA to choline (Cho) ratio (NAA/Cho), and Cho to Cre ratio (Cho/Cre) were measured in the left and right hippocampi, left and right dorsolateral prefrontal cortices, occipital lobe, anterior cingulate and white matter of the centrum semiovale of 69 carefully screened healthy volunteers utilizing proton magnetic resonance spectroscopic imaging (MRSI) at 3T.
Val/Met subjects exhibited significantly reduced levels of left hippocampal NAA/Cre and NAA/Cho compared to Val/Val subjects. This effect was independent of age, IQ, number of voxels, hippocampal volume or gray matter content in the voxels of interest. Analysis of other brain regions showed no effect of BDNF genotype on NAA measures.
We confirmed the association between the Met-BDNF variant and reduced levels of hippocampal NAA found with a similar technique at 1.5T. The consonance of our results with prior findings adds to the evidence that the BDNF Val/Met genotype affects hippocampal biology with implications for a variety of neuropsychiatric disorders.
To determine 1) the reproducibility of metabolite measurements by 1H MRS in the motor cortex; 2) the extent to which 1H MRS imaging (MRSI) detects abnormal concentrations of N-acetylaspartate (NAA)-, choline (Cho)-, and creatine (Cre)-containing compounds in early stages of ALS; and 3) the metabolite changes over time in ALS.
Sixteen patients with definite or probable ALS, 12 with possible or suspected ALS, and 12 healthy controls underwent structural MRI and multislice 1H MRSI. 1H MRSI data were coregistered with tissue-segmented MRI data to obtain concentrations of NAA, Cre, and Cho in the left and right motor cortex and in gray matter and white matter of nonmotor regions in the brain.
The interclass correlation coefficient of NAA was 0.53 in the motor cortex tissue and 0.83 in nonmotor cortex tissue. When cross-sectional data for patients were compared with those for controls, the NAA/(Cre + Cho) ratio in the motor cortex region was significantly reduced, primarily due to increases in Cre and Cho and a decrease in NAA concentrations. A similar, although not significant, trend of increased Cho and Cre and reduced NAA levels was also observed for patients with possible or suspected ALS. Furthermore, in longitudinal studies, decreases in NAA, Cre, and Cho concentrations were detected in motor cortex but not in nonmotor regions in ALS.
Metabolite changes measured by 1H MRSI may provide a surrogate marker of ALS that can aid detection of early disease and monitor progression and treatment response.
Magnetic resonance imaging (MRI) studies have produced controversial results concerning the correlation of hippocampal volume loss with increasing age. The goals in this study were: 1) to test whether levels of N-acetyl aspartate (NAA, a neuron marker) change in the hippocampus during normal aging and 2) to determine the relationship between hippocampal NAA and volume changes. Proton magnetic resonance spectroscopic imaging (1H MRSI) and MRI were used to measure hippocampal metabolites and volumes in 24 healthy adults from 36 to 85 years of age. NAA/Cho decreased by 24% (r = 0.53, p = 0.01) and NAA/Cr by 26% (r = 0.61, p < 0.005) over the age range studied, whereas Cho/Cr remained stable, implying diminished NAA levels. Hippocampal volume shrank by 20% (r = 0.64, p < 0.05). In summary, aging effects must be considered in 1H MRSI brain studies. Furthermore, because NAA is considered a marker of neurons, these results provide stronger support for neuron loss in the aging hippocampus than volume measurements by MRI alone.
Magnetic resonance spectroscopy; Magnetic resonance imaging; Aging; Hippocampus; Atrophy; Neuron loss; N-acetyl aspartate
Since mild traumatic brain injury (mTBI) often leads to neurological symptoms even without clinical MRI findings, our goal was to test whether diffuse axonal injury is quantifiable with multivoxel proton MR spectroscopic imaging (1H-MRSI). T1- and T2-weighted MRI and three dimensional 1H-MRSI (480 voxels over 360 cm3, ∼30% of the brain) were acquired at 3 Tesla from 26 mTBI patients (mean Glasgow Coma Scale score 14.7), 18–56 years old, 3–55 days post injury and 13 healthy matched contemporaries. The N-acetylaspartate (NAA), choline (Cho), creatine (Cr) and myo-inositol (mI) concentrations and gray-, white-matter (GM/WM) and cerebrospinal fluid fractions were obtained in each voxel. Global GM and WM absolute metabolic concentrations were estimated using linear regression, and patients were compared with controls using two-way analysis of variance. Patients' mean NAA, Cr, Cho and mI concentrations in GM (8.4±0.7, 6.9±0.6, 1.3±0.2, 5.5±0.6 mM) and Cr, Cho and mI in WM (4.8±0.5, 1.4±0.2, 4.6±0.7 mM) were not different from controls'. NAA, however, was significantly lower in patients' than controls' WM (7.2±0.8 versus 7.7±0.6 mM, p=0.0125). The Cho and Cr levels in patients' WM positively correlated with time from mTBI. This 1H-MRSI approach allowed us to ascertain that early mTBI sequelae are (i) diffuse (not merely local), (ii) neuronal (not glial) and (iii) in the global white (not gray) matter. These findings support the hypothesis that, similarly to more severe head trauma, mTBI also results in diffuse axonal injury, but that dysfunction, rather than cell death, dominates shortly after injury.
Brain Injury; Diffuse Axonal Injury; Magnetic Resonance Spectroscopy
The purpose of this study was to compare 2-[18F]fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET), hippocampal volumetry (HV), T2 relaxometry, and proton magnetic resonance spectroscopic imaging (1H-MRSI) in the presurgical neuroimaging lateralization of patients with nonlesional, electroencephalogram (EEG)-defined unilateral temporal lobe epilepsy (TLE). Twenty-five patients were prospectively studied, along with age-matched controls. T2 relaxometry examinations were performed in 13 patients. Comparison of FDG-PET, HV, and 1H-MRSI was possible in 23 patients. FDG-PET lateralized 87% of patients, HV 65%, N-acetyl aspartate (NAA)/(choline [Cho] + creatine [Cr]) 61%, and [NAA] 57%. Combined HV and NAA/(Cho + Cr) results lateralized 83% of the patients, a value similar to PET. Of 10 patients with normal magnetic resonance imaging (MRI) scans, 2 were lateralized with HV, 6 with FDG-PET, 4 with NAA/(Cho + Cr), and 3 with [NAA]. T2 relaxometry lateralized no patients without hippocampal atrophy. Bilateral abnormality was present in 29 to 33% of patients with 1H-MRSI measures and 17% with HV. Only hippocampal atrophy correlated with postoperative seizure-free outcome. FDG-PET remains the most sensitive imaging method to correlate with EEG-lateralized TLE. Both FDG-PET and 1H-MRSI can lateralize patients with normal MRI, but only the presence of relative unilateral hippocampal atrophy is predictive of seizure-free outcome. Bilaterally abnormal MRI and 1H-MRSI measures do not preclude good surgical outcome.
Recent studies have indicated a gene by environment interaction between serotonin transporter gene (5-HTTLPR) polymorphism and childhood abuse on depressive symptoms. In addition, persistent elevation of cerebrospinal fluid (CSF) corticotropin-releasing factor (CRF) concentrations following early-life adversity has been posited to underlie the subsequent development of major depression. This pilot study tested the hypothesis that elevations of juvenile CSF CRF concentrations are, in part, determined by an interaction between polymorphisms of the 5-HTTLPR and early-life stress. Nine juvenile male bonnet macaques (Macaca radiata) had been raised under variable foraging demand (VFD) conditions, a nonhuman primate model of early-life stress, whereas nine subjects were normatively raised under LFD (low foraging demand) conditions. Genotyping revealed that four (44.4%) of the VFD-reared monkeys possessed at least one “s” allele whereas five VFD monkeys were of the l/l genotype. Of the nine LFD subjects, two (22%) had the s/l genotype and seven had the l/l genotype. A “juvenile” CSF sample was obtained at approximately three years of age. CSF CRF concentrations were elevated specifically in the VFD “s/s” and “s/l” allele group in comparison to each of the remaining three groups, indicating a gene by environment (GxE) interaction.
Nonhuman primates; corticotropin-releasing hormone; early-life stress; serotonin transporter gene; major depression; anxiety disorders; gene by environment interaction
Conventional MRI can provide critical information for care of patients with traumatic brain injury (TBI), but MRI abnormalities rarely correlate to clinical severity and outcome. Previous magnetic resonance spectroscopy studies have reported clinically relevant brain metabolic changes in patients with TBI. However, these changes were often assessed a few to several days after the trauma, with a consequent variation of the metabolic pattern due to temporal changes.
Proton magnetic resonance spectroscopic imaging (1H‐MRSI) examinations were performed in 10 patients with TBI 48–72 h after the trauma, to obtain early measurements of central brain levels of N‐acetylaspartate (NAA), choline (Cho), creatine (Cr) and lactate (La). Metabolite values were expressed as ratios to (1) a metabolic pattern, given by the sum of the resonance intensities of all metabolites detected in the same voxel and (2) intravoxel Cr.
NAA ratios were found to be significantly lower in patients with TBI than in normal controls. In contrast, Cho ratios were significantly higher in patients with TBI than in normal controls. Increased La levels were found in 5 of 10 patients with TBI. Both NAA and La values correlated closely with those of the Glasgow Coma Scale at presentation (r = 0.73 and −0.62, respectively; p<0.01 for both) and the Glasgow Outcome Scale at 3 months (r = −0.79 and 0.79, respectively; p<0.01 for both).
Spectroscopic measures of neuro‐axonal damage occurring soon after a brain trauma are clinically relevant. Significant increases in cerebral La level also may be detected when 1H‐MRSI is performed early after the trauma and, at this stage, can represent a reliable index of injury severity and disease outcome in patients with TBI.
N-acetylaspartate (NAA) is found exclusively in neurons and their processes in the adult brain. Since the regional distribution of NAA may be imaged using magnetic resonance spectroscopic imaging (1H-MRSI), a regional measure of neuronal density may be noninvasively obtained. The technique may be particularly useful in the diagnosis of diseases where neurons are selectively injured, since these diseases do not result in definitive changes on conventional imaging studies. The goal of this study was to determine whether 1H-MRSI measurement of NAA detects neuronal loss following global ischemia. 1H-MRSI was performed in rats 24 h after global ischemia was induced by bilateral carotid occlusion plus hypotension.1−H-MRSI showed that NAA was decreased by 29–74% in vulnerable regions, including the cortex, striatum, hippocampus, and, to a lesser extent, the thalamus. No change was observed in the brain stem or cerebellum. Regions where 1H-MRSI observed NAA was decreased also had histological evidence of selective neuronal necrosis and showed marked increase of lactate and alanine. These results show that 1H-MRSI detected loss of NAA in brain regions with selective neuronal loss, suggesting that 1H-MRSI measurements of NAA could detect neuronal loss in a variety of disease states where there is selective neuronal necrosis.
N-acetylasparte; magnetic resonance spectroscopy; global ischemia
The aim of this study was to evaluate volumetric proton magnetic resonance spectroscopic imaging (MRSI) for localization of epileptogenic foci in neocortical epilepsy.
Twenty-five subjects reporting seizures considered to be of neocortical origin were recruited to take part in a 3-Tesla MR study that included high-resolution structural MRI and a whole-brain MRSI acquisition. Using a fully-automated MRSI processing protocol, maps for signal-intensity normalized N-Acetylaspartate (NAA), creatine, and choline were created, together with the relative volume fraction of grey-matter, white-matter, and CSF within each MRSI voxel. Analyses were performed using visual observation of the metabolite and metabolite ratio maps; voxel-based calculation of differences in these metabolite maps relative to normal controls; comparison of average grey- and white-matter metabolite values over each lobar volume; and examination of relative left-right asymmetry factors by brain region.
Data from fourteen subjects were suitable for inclusion in the analysis. Eight subjects had MRI-visible pathologies that were associated with decreases in NAA/Creatine, which extended beyond the volume indicated by the MRI. Five subjects demonstrated no significant metabolic alterations using any of the analysis methods, and one subject had no findings on MRI or MRSI.
This proof of principle study supports previous evidence that alterations of MR-detected brain metabolites can be detected in tissue areas affected by neocortical seizure activity, while additionally demonstrating advantages of the volumetric MRSI approach.
Neocortical Epilepsy; MRI; MR Spectroscopy; MRSI
To characterize and follow the diffuse gray and white matter (GM/WM) metabolic abnormalities in early relapsing-remitting multiple sclerosis using proton magnetic resonance spectroscopic imaging (1H-MRSI).
Eighteen recently diagnosed, mildly disabled patients (mean baseline time from diagnosis 32 months, mean Expanded Disability Status Scale [EDSS] score 1.3), all on immunomodulatory medication, were scanned semiannually for 3 years with T1-weighted and T2-weighted MRI and 3D 1H-MRSI at 3 T. Ten sex- and age-matched controls were followed annually. Global absolute concentrations of N-acetylaspartate (NAA), choline (Cho), creatine (Cr), and myo-inositol (mI) were obtained for all GM and WM in the 360 cm3
1H-MRSI volume of interest.
Patients' average WM Cr, Cho, and mI concentrations (over all time points), 5.3 ± 0.4, 1.6 ± 0.1, and 5.1 ± 0.7 mM, were 8%, 12%, and 11% higher than controls' (p ≤ 0.01), while their WM NAA, 7.4 ± 0.7 mM, was 6% lower (p = 0.07). There were increases with time of patients' WM Cr: 0.1 mM/year, Cho: 0.02 mM/year, and NAA: 0.1 mM/year (all p < 0.05). None of the patients' metabolic concentrations correlated with their EDSS score, relapse rate, GM/WM/CSF fractions, or lesion volume.
Diffuse WM glial abnormalities were larger in magnitude than the axonal abnormalities and increased over time independently of conventional clinical or imaging metrics and despite immunomodulatory treatment. In contrast, the axonal abnormalities showed partial recovery, suggesting that patients' lower WM NAA levels represented a dysfunction, which may abate with treatment. Absence of detectable diffuse changes in GM suggests that injury there is minimal, focal, or heterogeneous between cortex and deep GM nuclei.
The aim of this study was to identify metabolically abnormal extrahippocampal brain regions in patients with temporal lobe epilepsy with (TLE-MTS) and without (TLE-no) magnetic resonance imaging (MRI) evidence for mesial-temporal sclerosis (MTS) and to assess their value for focus lateralization by using multislice 1H magnetic resonance spectroscopic imaging (MRSI).
MRSI in combination with tissue segmentation was performed on 14 TLE-MTS and seven TLE-no and 12 age-matched controls. In controls, N-acetylaspartate/(creatine + choline) [NAA/(Cr+Cho)] of all voxels of a given lobe was expressed as a function of white matter content to determine the 95% prediction interval for any additional voxel of a given tissue composition. Voxels with NAA/(Cr+Cho) below the lower limit of the 95% prediction interval were defined as “pathological” in patients and controls. Z-scores were used to identify regions with a higher percentage of pathological voxels than those in controls.
Reduced NAA/(Cr+Cho) was found in ipsilateral temporal and parietal lobes and bilaterally in insula and frontal lobes. Temporal abnormalities identified the epileptogenic focus in 70% in TLE-MTS and 83% of TLE-no. Extratemporal abnormalities identified the epileptogenic focus in 78% of TLE-MTS but in only 17% of TLE-no.
TLE is associated with extrahippocampal reductions of NAA/(Cr+Cho) in several lobes consistent with those brain areas involved in seizure spread. Temporal and extratemporal NAA/(Cr+Cho) reductions might be helpful for focus lateralization.
TLE; Extratemporal; Normal MRI; Mesial-temporal sclerosis
Deep brain stimulation (DBS) of the anterior limb of the internal capsule (ALIC) may be effective in treating depression. Parental verbal abuse has been linked to decreased fractional anisotropy (FA) of white matter and reduced FA correlated with depression and anxiety scores. Utilizing a nonhuman primate model of mood and anxiety disorders following disrupted mother-infant attachment, we examined whether adverse rearing conditions lead to white matter impairment of the ALIC.
We examined white matter integrity using Diffusion Tensor Imaging (DTI) on a 3T-MRI. Twenty-one adult male Bonnet macaques participated in this study: 12 were reared under adverse [variable foraging demand (VFD)] conditions whereas 9 were reared under normative conditions. We examined ALIC, posterior limb of the internal capsule (PLIC) and occipital white matter.
VFD rearing was associated with significant reductions in FA in the ALIC with no changes evident in the PLIC or occipital cortex white matter.
Adverse rearing in monkeys persistently impaired frontal white matter tract integrity, a novel substrate for understanding affective susceptibility.
Diffusion tensor imaging; fractional anisotropy; white matter integrity; variable foraging demand
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.
brain; magnetic resonance spectroscopic imaging; magnetic resonance spectroscopy; neuropsychological test; traumatic brain injury
Chronic abuse of cocaine or alcohol is associated with structural, neuropathological and cognitive impairments that have been documented extensively. Little is known, however, about neurobiochemical changes in chronic substance abusers. We performed MRI and multi-slice brain proton magnetic resonance spectroscopic imaging (MRSI) to assess neuronal viability (via N-acetylaspartate (NAA)) and white matter metabolite status in 22 4-months-abstinent individuals dependent on crack cocaine only and on both crack cocaine and alcohol. Compared to 11 non-dependent controls we found (1) significantly lower NAA measures in the dorsolateral prefrontal cortex of the combined cocaine-dependent groups; (2) comparable spatial distribution and magnitude of these NAA effects for both cocaine-dependent groups; (3) higher choline-containing metabolites in frontal white matter of individuals dependent on both cocaine and alcohol; (4) absence of brain atrophy in both abstinent cocaine-dependent samples; and (5) partial recovery from prefrontal cortical NAA loss, primarily with abstinence from alcohol. The MRSI findings suggest preferential neuronal damage to the frontal cortex of both cocaine-dependent samples and gliosis in frontal white matter of individuals dependent on both alcohol and cocaine, conditions that persist for more than 4 months of abstinence.
The goal of these experiments was to test the hypothesis that in an animal model of temporal lobe epilepsy (TLE), magnetic resonance spectroscopic measurement of N-acetylaspartate (NAA) and other metabolites, together with magnetic resonance imaging, provides a sensitive in vivo method to localize and monitor the progression of neuronal cell death and gliosis. Seizures were induced in rats by unilateral hippocampal injection of kainate. Magnetic resonance measurements were made from 1 to 84 days using proton spectroscopic imaging (1H-MRSI), T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI). The results were compared with findings on histological sections. Decreased NAA and creatine levels and increased apparent diffusion coefficient of water were found in the ipsilateral hippocampus after 14 days where neuronal loss and gliosis were observed. In the contralateral hippocampus a significant increase of choline level was observed. These results suggest that 1H-MRSI is a useful in vivo method for localizing neuronal loss and may also indicate additional pathological and metabolic alterations. In addition, DWI may be a useful method for in vivo detection of tissue alterations due to TLE.
Magnetic resonance spectroscopic imaging; Diffusion-weighted imaging; N-Acetylaspartate; Creatine; Choline; Rat brain; Kainate; Epilepsy
Proton magnetic resonance spectroscopic imaging (1H MRSI) is a useful technique for measuring metabolite levels in vivo, with Choline (Cho), Creatine (Cr) and N-Acetyl-Aspartate (NAA) being the most prominent MRS-detectable brain biochemicals. 1H MRSI at very high fields, such as 7T, offers the advantages of higher SNR and improved spectral resolution. However, major technical challenges associated with high-field systems, such as increased B1 and B0 inhomogeneity as well as chemical shift localization (CSL) error, degrade the performance of conventional 1H MRSI sequences. To address these problems, we have developed a Position Resolved Spectroscopy (PRESS) sequence with adiabatic spatial-spectral (SPSP) refocusing pulses, to acquire multiple narrow spectral bands in an interleaved fashion. The adiabatic SPSP pulses provide magnetization profiles that are largely invariant over the 40% B1 variation measured across the brain at 7T. Additionally, there is negligible CSL error since the transmit frequency is separately adjusted for each spectral band. In vivo1H MRSI data was obtained from the brain of a normal volunteer using a standard PRESS sequence and the interleaved narrow-band PRESS sequence with adiabatic refocusing pulses. In comparison with conventional PRESS, this new approach generated high quality spectra from an appreciably larger region of interest and achieved higher overall SNR.
adiabatic; high-field; MRSI; B1 inhomogeneity; 7T; spectral interleaf
To test the hypothesis that diffuse abnormalities precede axonal damage and atrophy in the MRI normal-appearing tissue of relapsing-remitting (RR) multiple sclerosis (MS) patients, and that these processes continue during clinical remission.
Twenty-one recently diagnosed mildly disabled (mean disease duration 2.3 years, mean Expanded Disability Status Scale score of 1.4) RR MS patients and 15 healthy matched controls were scanned with MRI and proton MR spectroscopic imaging (1H-MRSI) at 3 T. Metabolite concentrations: N-acetylaspartate (NAA) for neuronal integrity; choline (Cho) for membrane turnover rate; creatine (Cr) and myo-inositol (mI) for glial status were obtained in a 360 cm3 volume-of-interest (VOI) with 3D multivoxel 1H-MRSI. They were converted into absolute amounts using phantom replacement and normalized into absolute concentrations by dividing by the VOI tissue volume fraction obtained from MRI segmentation.
The patients’ mean VOI tissue volume fraction, 0.92 and NAA concentration, 9.6 mM, were not different from controls’ 0.94 and 9.6 mM. In contrast, the patients’ mean Cr, Cho and mI levels 7.7, 1.9, 4.1 mM were 9%, 14% and 20%, higher than the controls’ 7.1, 1.6 and 3.4 mM (p=0.0097, 0.003 and 0.0023).
The absence of early tissue atrophy and apparent axonal dysfunction (NAA loss) in these RR MS patients suggests that both are preceded by diffuse glial proliferation (astrogliosis), as well as possible inflammation, de- and re-myelination reflected by elevated mI, Cho and Cr, even during clinical remission and despite immunomodulatory treatment.
Multiple Sclerosis; normal-appearing tissue; MR Spectroscopy
After replication of previous findings we aimed to: 1) determine if previously reported 1H MRSI differences between ALS patients and control subjects are limited to the motor cortex; and 2) determine the longitudinal metabolic changes corresponding to varying levels of diagnostic certainty.
Twenty-one patients with possible/suspected ALS, 24 patients with probable/definite ALS and 17 control subjects underwent multislice 1H MRSI co-registered with tissue-segmented MRI to obtain concentrations of the brain metabolites N-acetylaspartate (NAA), creatine, and choline in the left and right motor cortex and in gray matter and white matter of non-motor regions in the brain.
In the more affected hemisphere, reductions in the ratios, NAA/Cho and NAA/Cre+Cho were observed both within (12.6% and 9.5% respectively) and outside (9.2% and 7.3% respectively) the motor cortex in probable/definite ALS. However, these reductions were significantly greater within the motor cortex (P<0.05 for NAA/Cho and P<0.005 for NAA/Cre+Cho). Longitudinal changes in NAA were observed at three months within the motor cortex of both possible/suspected ALS patients (P<0.005) and at nine months outside the motor cortex of probable/definite patients (P<0.005). However, there was no clear pattern of progressive change over time.
NAA ratios are reduced in the motor cortex and outside the motor cortex in ALS, suggesting widespread neuronal injury. Longitudinal changes of NAA are not reliable, suggesting that NAA may not be a useful surrogate marker for treatment trials. (ALS 2004; 5: 141–149)
amyotrophic lateral sclerosis; magnetic resonance spectroscopic imaging; magnetic resonance imaging
Magnetic resonance spectroscopic imaging (MRSI) studies suggest hippocampal abnormalities in posttraumatic stress disorder (PTSD), whereas findings of volume deficits in the hippocampus, as revealed with magnetic resonance imaging (MRI), have been inconsistent. Co-morbidities of PTSD, notably alcohol abuse, may have contributed to the inconsistency. The objective was to determine whether volumetric and metabolic abnormalities in the hippocampus and other brain regions are present in PTSD, independent of alcohol abuse. Four groups of subjects, PTSD patients with (n=28) and without (n=27) alcohol abuse and subjects negative for PTSD with (n=23) and without (n=26) alcohol abuse, were enrolled in this observational MRI and MRSI study of structural and metabolic brain abnormalities in PTSD. PTSD was associated with reduced N-acetylaspartate (NAA) in both the left and right hippocampus, though only when normalized to creatine levels in the absence of significant hippocampal volume reduction. Furthermore, PTSD was associated with reduced NAA in the right anterior cingulate cortex regardless of creatine. NAA appears to be a more sensitive marker for neuronal abnormality in PTSD than brain volume. The alteration in the anterior cingulate cortex in PTSD has implications for fear conditioning and extinction.
Magnetic resonance imaging; Magnetic resonance spectroscopy; Brain metabolites; Brain atrophy; Alcoholism
To determine the feasibility of two magnetic resonance spectroscopy techniques in pediatric patients with diffuse intrinsic pontine gliomas (DIPGs) and evaluate the relationship of metabolic profiles determined by each technique. Utility of each technique for improving patient management is also discussed.
Methods and Materials
Children with DIPG (n=36) were evaluated using single voxel spectroscopy (SVS) and magnetic resonance spectroscopic imaging (MRSI) during the same imaging session. Patients were followed longitudinally (n=150 total studies). Technical feasibility was defined by sufficient water and lipid suppression for detection of metabolites. Correlation of metabolic data obtained by SVS and MRSI was determined using the Spearman rank method. Metabolite ratios, including Choline:N-acetyl-aspartate (Cho:NAA) and Cho:Creatine (Cho:Cr), were obtained from SVS and MRSI.
SVS and MRSI acquisition were feasible in >90% of studies. Maximum Cho:NAA and Cho:Cr from MRSI analysis were strongly associated with Cho:NAA and Cho:Cr obtained by SVS (r=0.67 and 0.76, respectively). MRSI Cho:NAA values were more heterogeneous compared to Cho:Cr values within the same lesion, and a strong linear relationship between the range and maximum Cho:NAA values was observed.
SVS and MRSI acquisition was feasible, with a strong correlation in metabolic data. Both techniques may improve diagnostic evaluation and management of DIPG. SVS is recommended for global assessment of tumor metabolism before and after therapy. MRSI showed heterogeneous patterns of metabolic activity within these tumors and is recommended for planning and monitoring targeted therapies and evaluating nearby tissue for tumor invasion.
Brainstem; glioma; pontine; children; tumor
Both AD and normal aging cause brain atrophy, limiting the ability of MRI to distinguish between AD and age-related brain tissue loss. MRS imaging (MRSI) measures the neuronal marker N-acetylaspartate (NAA), which could help assess brain change in AD and aging.
To determine the effects of AD on concentrations of NAA, and choline- and creatine-containing compounds in different brain regions and to assess the extent NAA in combination with volume measurements by MRI improves discrimination between AD patients and cognitively normal subjects.
Fifty-six patients with AD (mean age: 75.6 ± 8.0 years) and 54 cognitively normal subjects (mean age: 74.3 ± 8.1 years) were studied using MRSI and MRI.
NAA concentration was less in patients with AD compared with healthy subjects by 21% (p < 0.0001) in the medial temporal lobe and by 13% to 18% (p < 0.003) in parietal lobe gray matter (GM), but was not changed significantly in white matter and frontal lobe GM. In addition to lower NAA, AD patients had 29% smaller hippocampi and 11% less cortical GM than healthy subjects. Classification of AD and healthy subjects increased significantly from 89% accuracy using hippocampal volume alone to 95% accuracy using hippocampal volume and NAA together.
In addition to brain atrophy, NAA reductions occur in regions that are predominantly impacted by AD pathology.