Alterations of Microstructure and Sodium Homeostasis in Fast Amyotrophic Lateral Sclerosis Progressors: A Brain DTI and Sodium MRI Study

BACKGROUND AND PURPOSE

While conventional MR imaging has limited value in amyotrophic lateral sclerosis, nonconventional MR imaging has shown alterations of microstructure using diffusion MR imaging and recently sodium homeostasis with sodium MR imaging. We aimed to investigate the topography of brain regions showing combined microstructural and sodium homeostasis alterations in amyotrophic lateral sclerosis subgroups according to their disease-progression rates.

MATERIALS AND METHODS

Twenty-nine patients with amyotrophic lateral sclerosis and 24 age-matched healthy controls were recruited. Clinical assessments included disease duration and the Revised Amyotrophic Lateral Sclerosis Functional Rating Scale. Patients were clinically differentiated into fast (n = 13) and slow (n = 16) progressors according to the Revised Amyotrophic Lateral Sclerosis Functional Rating Scale progression rate. 3T MR imaging brain protocol included ¹H T1-weighted and diffusion sequences and a ²³Na density-adapted radial sequence. Quantitative maps of diffusion with fractional anisotropy, mean diffusivity, and total sodium concentration were measured. The topography of diffusion and sodium abnormalities was assessed by voxelwise analyses.

RESULTS

Patients with amyotrophic lateral sclerosis showed significantly higher sodium concentrations and lower fractional anisotropy, along with higher sodium concentrations and higher mean diffusivity compared with healthy controls, primarily within the corticospinal tracts, corona radiata, and body and genu of the corpus callosum. Fast progressors showed wider-spread abnormalities mainly in the frontal areas. In slow progressors, only fractional anisotropy measures showed abnormalities compared with healthy controls, localized in focal regions of the corticospinal tracts, the body of corpus callosum, corona radiata, and thalamic radiation.

CONCLUSIONS

The present study evidenced widespread combined microstructural and sodium homeostasis brain alterations in fast amyotrophic lateral sclerosis progressors.

Functional connectivity and cognitive changes after donepezil treatment in healthy participants

RATIONALE

Donepezil is a potent, noncompetitive, reversible, clinically effective acetylcholinesterase inhibitor. The effects of this drug on healthy brains have seldom been investigated.

OBJECTIVES

The primary objective of the present study was to identify possible functional connectivity markers of the effect of donepezil in healthy young adult volunteers.

METHODS

The study had a double-blind, randomized, crossover design. 30 healthy adult volunteers underwent resting-state MRI scans during 15 days of donepezil or placebo treatment, in accordance with the design.

RESULTS

Results showed significant differences in intrinsic functional connectivity between donepezil and placebo, mainly in the right executive control network (RECN). More specifically, we found a decrease in the connectivity of the right inferior parietal node with other RECN nodes. Analysis using the cingulate cortex and parahippocampal regions as seeds also revealed complex modulation of functional connectivity in the donepezil condition.

CONCLUSIONS

In conclusion, donepezil treatment for 15 days may result in reorganization of resting-state networks, compared with placebo.

Sensitivity of the Inhomogeneous Magnetization Transfer Imaging Technique to Spinal Cord Damage in Multiple Sclerosis

BACKGROUND AND PURPOSE

The inhomogeneous magnetization transfer technique has demonstrated high specificity for myelin, and has shown sensitivity to multiple sclerosis-related impairment in brain tissue. Our aim was to investigate its sensitivity to spinal cord impairment in MS relative to more established MR imaging techniques (volumetry, magnetization transfer, DTI).

MATERIALS AND METHODS

Anatomic images covering the cervical spinal cord from the C1 to C6 levels and DTI, magnetization transfer/inhomogeneous magnetization transfer images at the C2/C5 levels were acquired in 19 patients with MS and 19 paired healthy controls. Anatomic images were segmented in spinal cord GM and WM, both manually and using the AMU₄₀ atlases. MS lesions were manually delineated. MR metrics were analyzed within normal-appearing and lesion regions in anterolateral and posterolateral WM and compared using Wilcoxon rank tests and z scores. Correlations between MR metrics and clinical scores in patients with MS were evaluated using the Spearman rank correlation.

RESULTS

AMU₄₀-based C1-to-C6 GM/WM automatic segmentations in patients with MS were evaluated relative to manual delineation. Mean Dice coefficients were 0.75/0.89, respectively. All MR metrics (WM/GM cross-sectional areas, normal-appearing and lesion diffusivities, and magnetization transfer/inhomogeneous magnetization transfer ratios) were observed altered in patients compared with controls (P < .05). Additionally, the absolute inhomogeneous magnetization transfer ratio z scores were significantly higher than those of the other MR metrics (P < .0001), suggesting a higher inhomogeneous magnetization transfer sensitivity toward spinal cord impairment in MS. Significant correlations with the Expanded Disability Status Scale (ρ = -0.73/P = .02, ρ = -0.81/P = .004) and the total Medical Research Council scale (ρ = 0.80/P = .009, ρ = -0.74/P = .02) were observed for inhomogeneous magnetization transfer and magnetization transfer ratio z scores, respectively, in normal-appearing WM regions, while weaker and nonsignificant correlations were obtained for DTI metrics.

CONCLUSIONS

With inhomogeneous magnetization transfer being highly sensitive to spinal cord damage in MS compared with conventional magnetization transfer and DTI, it could generate great clinical interest for longitudinal follow-up and potential remyelinating clinical trials. In line with other advanced myelin techniques with which it could be compared, it opens perspectives for multicentric investigations.

Evaluation of the Sensitivity of Inhomogeneous Magnetization Transfer (ihMT) MRI for Multiple Sclerosis

BACKGROUND AND PURPOSE

Inhomogeneous magnetization transfer is a new endogenous MR imaging contrast mechanism that has demonstrated high specificity for myelin. Here, we tested the hypothesis that inhomogeneous magnetization transfer is sensitive to pathology in a population of patients with relapsing-remitting MS in a way that both differs from and complements conventional magnetization transfer.

MATERIALS AND METHODS

Twenty-five patients with relapsing-remitting MS and 20 healthy volunteers were enrolled in a prospective MR imaging research study, whose protocol included anatomic imaging, standard magnetization transfer, and inhomogeneous magnetization transfer imaging. Magnetization transfer and inhomogeneous magnetization transfer ratios measured in normal-appearing brain tissue and in MS lesions of patients were compared with values measured in control subjects. The potential association of inhomogeneous magnetization transfer ratio variations with the clinical scores (Expanded Disability Status Scale) of patients was further evaluated.

RESULTS

The magnetization transfer ratio and inhomogeneous magnetization transfer ratio measured in the thalami and frontal, occipital, and temporal WM of patients with MS were lower compared with those of controls (P < .05). The mean inhomogeneous magnetization transfer ratio measured in lesions was lower than that in normal-appearing WM (P < .05). Significant (P < .05) negative correlations were found between the clinical scores and inhomogeneous magnetization transfer ratio measured in normal-appearing WM structures. Weaker nonsignificant correlation trends were found for the magnetization transfer ratio.

CONCLUSIONS

The sensitivity of the inhomogeneous magnetization transfer technique for MS was highlighted by the reduction in the inhomogeneous magnetization transfer ratio in MS lesions and in normal-appearing WM of patients compared with controls. Stronger correlations with the Expanded Disability Status Scale score were obtained with the inhomogeneous magnetization transfer ratio compared with the standard magnetization transfer ratio, which may be explained by the higher specificity of inhomogeneous magnetization transfer for myelin.

MRI/MRS of corpus callosum in patients with clinically isolated syndrome suggestive of multiple sclerosis

A trophy of corpus callosum (C C) related to axonal loss has previously been observed in patients at the early stage of clinically definite multiple sclerosis (CDMS). Atrophy increases with the progression of the disease. Nevertheless, no data concerning the onset of atrophy of C C are currently available. The purpose of this study is to determine if damage in callosal tissue was present at the earliest stage of MS, in a subgroup of patients presenting with a clinically isolated syndrome suggestive of MS (C ISSMS), fulfilling the dissemination in space criteria according to McDonald. Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) techniques were applied to measure C C volume, magnetization transfer ratio (MTR), mean diffusivity (MD), N-acetyl aspartate/choline-containing compounds (NAA/C ho) ratio, N-acetyl aspartate/total creatine (NA A/C r) ratio and C ho/C r ratio inside the C C of 46 C ISSMS patients and 24 sexand age-matched controls. No atrophy of C C was observed in the C ISSMS group. C C of patients was character ized by decreased MTR and increased MD. No change in the NA A/C r ratio was observed while the NA A/C ho ratio decreased and C ho/C r ratio increased in the splenium and the central anterio r part of C C. These abnormalities were present in patients with, but also without, macroscopic lesions inside the C C. O ur results indicate that diffuse structural and metabolic changes, which may be interpreted as representing predominantly myelin patho logy, occur in the C C at the earliest stage of MS before any atrophy is detected.

Onset and underpinnings of white matter atrophy at the very early stage of multiple sclerosis - a two-year longitudinal MRI/MRSI study of corpus callosum

Backgrounds Atrophy of corpus callosum (CC), a white matter structure linking the two hemispheres, is commonly observed in multiple sclerosis (MS). However, the occurrence and processes leading to this alteration are not yet determined.

Goal and methods To better characterize the onset and progression of CC atrophy from the early stage of MS, we performed a two-year follow-up magnetic resonance imaging/magnetic resonance spectroscopic imaging (MRI/MRSI) exploration of CC in 24 patients with clinically isolated syndrome. These patients were explored using the same protocol at month (M)6, M12 and M24. MRI/MRSI techniques were applied to measure CC volume, and relative concentrations of N-acetylaspartate (NAA), creatine/phosphocreatine (Cr) and choline-containing compounds (Cho). A group of matched controls was also explored.

Results Atrophy of CC, not present at baseline, was observed at M12 and progressed over the second year (M24). At baseline, a decrease in relative NAA level was observed in the anterior and posterior body of CC, with normalization during the follow-up period. In the anterior body, an increase in relative Cho level was observed, with normalization at M6. Normal relative Cr levels were observed at all time points in all sub-regions. The rate of CC atrophy was correlated with the change in the Expanded Disability Status Scale (EDSS) during the follow-up period.

Conclusion These results suggest that CC atrophy appears over a period of one year after the first acute inflammatory episode, and that this atrophy is accompanied, especially in the anterior body of CC, by a normalization of the relative Cho levels, marker of acute inflammation, and NAA levels, marker of neuronal dysfunction and/or loss.

Clinical and biomarker profiling of prodromal Alzheimer's disease in workpackage 5 of the Innovative Medicines Initiative PharmaCog project: a 'European ADNI study'

BACKGROUND

In the field of Alzheimer's disease (AD), the validation of biomarkers for early AD diagnosis and for use as a surrogate outcome in AD clinical trials is of considerable research interest.

OBJECTIVE

To characterize the clinical profile and genetic, neuroimaging and neurophysiological biomarkers of prodromal AD in amnestic mild cognitive impairment (aMCI) patients enrolled in the IMI WP5 PharmaCog (also referred to as the European ADNI study).

METHODS

A total of 147 aMCI patients were enrolled in 13 European memory clinics. Patients underwent clinical and neuropsychological evaluation, magnetic resonance imaging (MRI), electroencephalography (EEG) and lumbar puncture to assess the levels of amyloid β peptide 1-42 (Aβ42), tau and p-tau, and blood samples were collected. Genetic (APOE), neuroimaging (3T morphometry and diffusion MRI) and EEG (with resting-state and auditory oddball event-related potential (AO-ERP) paradigm) biomarkers were evaluated.

RESULTS

Prodromal AD was found in 55 aMCI patients defined by low Aβ42 in the cerebrospinal fluid (Aβ positive). Compared to the aMCI group with high Aβ42 levels (Aβ negative), Aβ positive patients showed poorer visual (P = 0.001), spatial recognition (P < 0.0005) and working (P = 0.024) memory, as well as a higher frequency of APOE4 (P < 0.0005), lower hippocampal volume (P = 0.04), reduced thickness of the parietal cortex (P < 0.009) and structural connectivity of the corpus callosum (P < 0.05), higher amplitude of delta rhythms at rest (P = 0.03) and lower amplitude of posterior cingulate sources of AO-ERP (P = 0.03).

CONCLUSION

These results suggest that, in aMCI patients, prodromal AD is characterized by a distinctive cognitive profile and genetic, neuroimaging and neurophysiological biomarkers. Longitudinal assessment will help to identify the role of these biomarkers in AD progression.

Structural and functional reorganization of working memory system during the first decade in schizophrenia. A cross-sectional study

INTRODUCTION

Progressive atrophy occurs in brain regions involved in the working memory network along the schizophrenia's course, but without parallel evolution of working memory impairment. We investigated the functional organization inside this network at different stages of the disease.

METHODS

Twenty-eight patients with schizophrenia (16 with long disease duration (>60 months) and 12 with short disease duration (<60 months)) and eleven healthy controls underwent structural and functional MRI during an n-back task to determine atrophy and activation patterns.

RESULTS

At similar n-back performances and relative to short disease duration patients, long disease duration patients activated more frontal temporal parietal and frontal network during 0-back and 1-back tasks respectively. n-back scores were correlated to atrophy in the frontal-temporal areas.

DISCUSSION

Functional reorganization in the working memory network may play a compensatory role during the first ten years of schizophrenia.

Sodium imaging as a marker of tissue injury in patients with multiple sclerosis

Recent studies have suggested that intra-axonal sodium accumulation contribute to axonal degeneration in patients with MS. Advances in MRI hardware and software allow acquisition of brain sodium signal in vivo. This review begins with a summary of the experimental evidence for impairment of sodium homeostasis in MS. Then, MRI methods for sodium acquisition are reviewed and the application of the techniques in patients with MS is discussed. Sodium imaging and ultra-high field MRI have the potential to provide tissue-specific markers of neurodegeneration in MS.

Combined diffusion imaging and MR spectroscopy in the diagnosis of human prion diseases

BACKGROUND AND PURPOSE

The physiopathologic bases underlying the signal intensity changes and reduced diffusibility observed in prion diseases (TSEs) are still poorly understood. We evaluated the interest of MRS combined with DWI both as a diagnostic tool and a way to understand the mechanism underlying signal intensity and ADC changes in this setting.

MATERIALS AND METHODS

We designed a prospective study of multimodal MR imaging in patients with suspected TSEs. Forty-five patients with a suspicion of TSE and 11 age-matched healthy volunteers were included. The MR imaging protocol included T1, FLAIR, and DWI sequences. MRS was performed on the cerebellum, pulvinar, right lenticular nucleus, and frontal cortex. MR images were assessed visually, and ADC values were calculated.

RESULTS

Among the 45 suspected cases, 31 fulfilled the criteria for probable or definite TSEs (19 sCJDs, 3 iCJDs, 2 vCJDs, and 7 genetic TSEs); and 14 were classified as AltDs. High signals in the cortex and/or basal ganglia were observed in 26/31 patients with TSEs on FLAIR and 29/31 patients on DWI. In the basal ganglia, high DWI signals corresponded to a decreased ADC. Metabolic alterations, increased mIns, and decreased NAA were observed in all patients with TSEs. ADC values and metabolic changes were not correlated; this finding suggests that neuronal stress (vacuolization), neuronal loss, and astrogliosis do not alone explain the decrease of ADC.

CONCLUSIONS

MRS combined with other MR imaging is of interest in the diagnosis of TSE and provides useful information for understanding physiopathologic processes underlying prion diseases.

[Cognitive impairment]

Cognitive impairment is common in multiple sclerosis (MS), occurring at all stages of the disease, even at the earliest, and can be a major source of disability, social impairment, and impoverished quality of life. Cognitive dysfunction is mainly focused on working memory, conceptual reasoning, verbal fluency, speed of information processing, attention and executive function. Measures of information-processing speed appear to be the most robust and sensitive markers of cognitive impairment in MS patients. Cognitive testing in MS patients is complex and cognitive screening tests are time- and cost-saving test instruments. A comprehensive and sensitive cognitive test procedure should be administered to detect cognitive dysfunction, and recent studies demonstrate that single, predominantly speed-related cognitive tests may be superior to extensive and time-consuming test batteries in screening cognitive decline. Additional clinical factors, including disease course, fatigue, and affective disturbance, can impact the degree of MS-related cognitive impairment. Despite weak correlation with disease duration and physical disability status, the degree of cognitive impairment in MS has been related to the extent of topographically specific neuronal tissue damage and loss. Numerous studies have applied conventional and quantitative magnetic resonance imaging (MRI) techniques to correlate the profile and degree of cognitive impairment with various MRI-detectable abnormalities. The burden of MRI-visible lesions does not fully account for the degree of MS-related cognitive impairment. Nonconventional MRI findings suggest the extent of subtle tissue damage in normal-appearing white and grey matter to correlate best with the severity of cognitive impairment in MS patients. Structural MRI approaches have recently been extended by functional MRI studies scrutinizing the brain's ability for adaptive functional reorganization in the presence of widespread tissue damage. Cognitive impairment in MS seems to be not simply the result of tissue destruction, but also a balance between tissue destruction, tissue repair, and adaptive functional reorganization. These findings highlight the need to screen for cognitive deficits in MS patients to conduct potential cognitive rehabilitation intervention.

Efficiency of cognitive control recruitment in the very early stage of multiple sclerosis: a one-year fMRI follow-up study

Functional magnetic resonance imaging (FMRI) studies have established that patients with multiple sclerosis show stronger activation in the lateral prefrontal cortices (LPFC) than healthy control subjects during effortful cognitive tasks. The aim of the present study was to assess the impact of these activation changes on cognitive performances. In addition to 19 controls, who were tested at a single time-point to define a standard pattern of fMRI activation during the performance of the Paced Auditory Serial Addition Task (PASAT), 13 patients with clinically isolated syndrome underwent a longitudinal fMRI examination while performing the PASAT at the beginning of the study (M0) and one year later (M12). Relative to the M0 scores, PASAT performances improved in eight patients (group A) and either decreased ( n = 4) or remained unchanged ( n = 1) (group B) in five patients at M12. Random effect analyses (SPM2; Wellcome Institute, London, England) were performed to compare intra-group time-related effects on brain activation (paired t-test between M0 and M12), and inter-group differences were also compared between the two groups of patients (analysis of covariance with PASAT performances as the covariate). Relative to group B, group A showed larger increase in activation between M0 and M12 in the right LPFC. In the whole group of patients, interaction analyses showed that the differences in the PASAT scores between M0 and M12 were correlated with the differences in activation observed in the right LPFC. This longitudinal study shows that in patients with early multiple sclerosis, the increased levels of activation in the right LPFC was associated with improved individual working memory and processing speed performances.

[Future of non conventional MR techniques in MS]

Although conventional magnetic resonance imaging (MRI) is used for diagnosing multiple sclerosis (MS) and monitoring disease activity and course, the correlation between conventional MRI data and clinical findings remains weak. This "clinical-MRI paradox" could be partly due to the lack of MRI specificity related to the heterogeneous pathological substrates of MS and to its inability to quantify the extent of damage in the normal-appearing tissue. Recently, non-conventional MRI techniques, including magnetization transfer MRI, diffusion tensor MRI, and proton MR spectroscopy have been applied to improve our understanding of the pathophysiology of MS. These techniques may provide information about structural and biochemical changes occurring within and outside macroscopic MS lesions (inflammation, demyelination, axonal loss), in particular in the normal-appearing white and grey matter. These techniques could also significantly improve our ability to monitor inflammatory demyelination and axonal injury. In the same way, functional MRI gives us the potential substrate to assess the mechanisms of adaptive cortical reorganization, which may limit the irreversible consequences of MS tissue injury.

[Indications for cerebral MR proton spectroscopy in 2007]

Magnetic resonance spectroscopy (MRS) is being increasingly performed alongside the more conventional MRI sequences in the exploration of neurological disorders. It is however important to clearly differentiate its clinical applications aiming at improving the differential diagnosis or the prognostic evaluation of the patient, from the research protocols, when MRS can contribute to a better understanding of the pathophysiology of the disease or to the evaluation of new treatments. The most important applications in clinical practice are intracranial space occupying lesions (especially the positive diagnosis of intracranial abscesses and gliomatosis cerebri and the differential diagnosis between edema and tumor infiltration), alcoholic, hepatic, and HIV-related encephalopathies and the exploration of metabolic diseases. Among the research applications, MRS is widely used in multiple sclerosis, ischemia and brain injury, epilepsy and neuro degenerative diseases.

1H-MRS imaging in intractable frontal lobe epilepsies characterized by depth electrode recording

Presurgical evaluation of frontal lobe epilepsy (FLE) remains a challenging issue and frequently requires invasive depth electrode recording. In this study, we aimed at evaluating the potential usefulness of a non-invasive technique such as proton magnetic resonance spectroscopic imaging ((1)H-MRSI) in the presurgical evaluation of FLE and at investigating the potential electrophysiological correlates of the metabolic disturbances as defined by (1)H-MRSI. We compared the distribution of (1)H-MRSI abnormalities with the electrophysiological abnormalities defined by stereo-electroencephalography (SEEG) recording in 12 patients presenting with several subtypes of FLE. We also used 12 control subjects in order to obtain normative (1)H-MRSI data. We used a multilevel (1)H-MRSI protocol to better sample the principal regions of the frontal lobe. We also applied a metabolic mapping technique allowing a visual display of metabolic data. A significant decrease of both N-acetyl-aspartate/phosphocreatine-creatine and N-acetyl-aspartate/(choline-compounds + phosphocreatine-creatine) ratios was observed in regions involved in the epileptogenic zone (EZ) and/or the irritative zone (IZ) compared to regions without electrical abnormalities in the same patients (P = 0.044 and P = 0.018, respectively), and also compared to controls (P = 0.004 and P = 0.0001, respectively). No significant differences in metabolic ratios were observed between those regions involved in the EZ and those involved in the IZ only. Our results suggest a link between the relative decrease of N-acetyl-aspartate and the EZ as well as the IZ in FLE. Thus, multilevel (1)H-MRSI protocol may add pertinent information during the non-invasive presurgical evaluation of FLE.

A standardised method for measuring magnetisation transfer ratio on MR imagers from different manufacturers--the EuroMT sequence

Magnetisation transfer ratio (MTR) is increasingly used to evaluate neurological disorders, especially those involving demyelination. It shows promise as a surrogate marker of disease progression in treatment trials in multiple sclerosis (MS) but the value measured is highly dependent on pulse sequence parameters, making it hard to include the technique in large multi-centre clinical trials. The variations can be reduced by a normalisation procedure based on the flip angle and timing of the presaturation pulse, but correction for parameters such as saturation pulse shape, amplitude, duration and offset frequency remains problematic. We have defined a standard pulse sequence, to include a standard presaturation pulse and set of parameters, which can be implemented on scanners from both General Electric and Siemens, and has also been used on Phillips scanners. To validate the sequence and parameters, six European centres measured MTR in the frontal white matter of normal volunteers. It was possible to measure MTR values in controls which were consistent to within approximately +/-2.5 percentage units across sites. This degree of precision may be adequate in many situations. The remaining differences between sites and manufacturers are probably caused by B1 errors.

Functional MRI study of PASAT in normal subjects

The paced auditory serial addition test (PASAT) is routinely used to evaluate the cognitive part of the multiple sclerosis functional composite (MSFC) score, the new reference index of patient disability. PASAT is sensitive to subtle cognitive impairment related to MS, although the cognitive components of this test still remain unclear. In order to better characterize brain systems involved during this complex task, functional magnetic resonance imaging (fMRI) experiments were conducted during PASAT in a population of ten normal subjects. The paradigm consisted of a series of 61 single-digit numbers delivered every 3 s. After each number, subjects were asked to overt vocalize the result of the addition of the two last numbers heard. A control task consisting of the repetition of the same series of single-digit numbers was used. Statistical group analysis was performed using the random effect procedure (SPM 99). Cortical activation was observed in the left prefrontal cortex, the supplementary motor area, the lateral premotor cortex, the cingulate gyrus, the left parietal lobe, the left superior temporal gyrus, the left temporal pole, and visual associative areas. fMRI activations underlying PASAT were consistent with an involvement of verbal working memory and the semantic memory retrieval network which could be related to arithmetic fact retrieval. This study on normal subjects could provide a base for the understanding of the potential abnormal cortical activation in MS patients performing this test for a cognitive evaluation.

Modulation of effective connectivity inside the working memory network in patients at the earliest stage of multiple sclerosis

fMRI and structural equation modeling (SEM) were used to study effective connectivity inside the working memory network in patients at the earliest stage of multiple sclerosis (MS), while performing paced auditory serial addition test (PASAT), a sensitive task to reveal subtle cognitive impairments related to working memory and information speed processing. The path model used for SEM included bilateral connections between left and right BA 46, left and right BA 40, left and right anterior cingulate cortex (ACC), left BA 44 and left BA 40, right BA 44 and right BA 40, and unidirectional ipsilateral connections from BA 46 to BA 44, from ACC to BA 46, and from ACC to BA 44. Experimental data from the two groups fit accurately the working memory model, in patients [chi20(2) = 13, P = 0.877] as well as in controls [chi20(2) = 13.54, P = 0.853]. The omnibus test indicated a significant difference of model fits in patients and in controls [chi40(2) = 160.07, P < 0.0001]. Connectivity strengths from right BA 46 to left BA 46, from left ACC to left BA 46 were lower in patients than in controls, and higher from right ACC to right BA 46, from left to right and from right to left ACC (stacked model). Effective connectivity inside the working memory network appears altered in patients at the earliest stage of MS. Modulation of effective connectivity is present in patients inside the executive subsystems of working memory, and could be related to adaptive cognitive control processes that may limit the clinical manifestation of MS.

High cerebral scyllo-inositol: a new marker of brain metabolism disturbances induced by chronic alcoholism

Cerebral metabolic changes that concur to motor and/or cognitive disorders in actively drinking alcoholics are not well established. We tested the hypothesis that chronic alcoholics exhibit profound alterations in the cerebral metabolism of scyllo-inositol. Brain metabolism was explored in nine actively drinking and 11 recently detoxified chronic alcoholics by in vivo brain (1)H-MRS and in vitro(1)H-MRS of blood serum and cerebrospinal fluid. The cohort was composed of individuals with acute, subacute or chronic encephalopathy or without any clinical encephalopathy. Chronic alcoholism is associated with a hitherto unrecognized accumulation of brain scyllo-inositol. Our results suggest that scyllo-inositol is produced within the central nervous system and shows a diffuse but heterogenous distribution in brain where it can persist several weeks after detoxification. Its highest levels were observed in subjects with a clinically symptomatic alcohol-related encephalopathy. When detected, brain scyllo-inositol takes part in a metabolic encephalopathy since it is associated with reduced N-acetylaspartate and increased creatine. High levels of cerebral scyllo-inositol are correlated with altered glial and neuronal metabolism. Our findings suggest that the accumulation of scyllo-inositol may precede and take part in the development of symptomatic alcoholic metabolic encephalopathy.

Multimodal magnetic resonance imaging of the central nervous system

The physiological and biochemical properties of the diseased brain that can be explored with magnetic resonance imaging (MRI) are increasing. Progress in MR-based technology affords a large panel of MRI sequences that explore different phenomena and, thus, provide complementary informations. The diagnostic accuracy of MRI is improved by the combination of all MR modalities. However, this abundance of data requires an efficient multiparametric analysis to fully achieve the goal of the multimodal strategy. We will discuss the potential impact of this advanced MRI analysis in the clinical management and the therapeutical strategies of the most common brain pathologies (intracranial tumors, multiple sclerosis, stroke, epilepsy and dementia). This non-invasive approach is of utmost importance since it already improves the diagnosis and the therapeutic choice in the management of several central nervous system diseases.

Metabolic counterpart of decreased apparent diffusion coefficient during hyperacute ischemic stroke: a brain proton magnetic resonance spectroscopic imaging study

BACKGROUND AND PURPOSE

Recent studies have shown that the brain ischemic area defined by the map of decreased apparent diffusion coefficient (ADC) obtained by diffusion-weighted imaging (DWI) during the first hours of ischemic stroke includes a significant part of ischemic penumbra. We hypothesize that the misjudgment of the final infarct size by ADC mapping may be related to a restricted ability of DWI to capture variations in the intensity of cellular suffering. In an attempt to characterize metabolically the hypoperfused brain parenchyma, we studied the relationship between ADC values and brain metabolic parameters measured by proton MR spectroscopic imaging (SI).

METHODS

Six patients with hyperacute ischemic stroke were explored within the first 7 hours after onset with the use of a MR protocol including T2*-weighted MRI, DWI, SI, perfusion-weighted imaging, and MR angiography.

RESULTS

This study demonstrates, for the first time, a wide gradient of ischemia-related metabolic anomalies within the abnormal area delineated by DWI during hyperacute ischemic stroke. In the narrow range of decreased mean ADC values (0.60 to 0.40 x 10(-9) m2 x s(-1)), a 33% decrease in mean ADC is associated with a 122% increase in lactate/N-acetyl aspartate ratio. Mean ADC values never fall below 0.40 x 10(-9) m2 x s(-1) within the severely affected ischemic tissue, while SI still detects a large metabolic heterogeneity inside areas showing similar decreased mean ADC values close to this threshold.

CONCLUSIONS

Our results indicate that the region of very low mean ADC values observed during hyperacute ischemic stroke contains areas of various tissue damage intensity characterized by SI in relation to different stages of cellular metabolic injury. This observation may explain why ADC mapping does not reliably predict final infarct size.

[Applications of magnetic resonance spectrometry (MRS) in the study of metabolic disturbances affecting the brain in alcoholism]

The purpose of this article is to provide an overview of the current applications of magnetic resonance spectroscopy (MRS) to the investigation of cerebral metabolism in alcoholic patients. The specific metabolic changes associated with the intoxication process (tolerance, dependance), abstinence and alcohol-related diseases (alcoholic encephalopathy, cirrhosis, Gayet-Wernicke's encephalopathy, Marchiafava-Bignami syndrome) are described.

Regional metabolite levels of the normal posterior fossa studied by proton chemical shift imaging

MR spectroscopy of the posterior fossa is pitted with numerous technical difficulties. It is, however, of great clinical interest in the study of the degenerative diseases and tumors of this area. We have developed a method to perform 2D CSI of this area, by using a sagittal slice and a careful positioning of outer volume saturation. We performed this acquisition in 30 healthy volunteers to determine the normal metabolic ratios in five voxels of this area (mesencephalon, pons, medulla oblongata, vermis, cerebellar white matter). The main technical difficulty was magnetic field inhomogeneity in the lower brainstem generated by dental alloys. However, 88% of the voxels were of sufficient quality to be analyzed. The statistically significant regional variations were a higher NAA/Cr ratio in the pons than in the medulla oblongata, higher Cho/Cr in the pons than in the mesencephalon and higher Cho/Cr in the cerebellar white matter than in the vermis. We conclude that 2D CSI of the brainstem, although technically delicate can be performed in most patients.

Brain areas involved in rapid categorization of natural images: an event-related fMRI study

Event-related fMRI was used to investigate brain activation during a visual go/no-go categorization task based on colored photographs of natural scenes, similar to a previous ERP study by Thorpe et al. (1996, Nature 381: 520-522). Subjects had to press a key when an animal was present in the display. Stimuli were flashed for 33 ms using an intertrial interval of 5 s and a design that carefully balanced targets and distractors in a pseudo-random sequence. Activation produced by targets and distractors was compared with two different techniques, one based on correlations with the stimulation pattern, the other using simple t score statistics to compare selected scans. The contralateral primary motor cortex and the ipsilateral cerebellum were both more active following target trials than following distractors, thus confirming the sensitivity of the method. Differential activity was also seen in the posterior cingulate cortex, the fusiform, and the parahippocampic gyri. Activity in such structures could underlie the differential evoked-potentials reported previously in the same task. Surprisingly, in these visual structures, the signal was stronger following distractor trials than target ones. This result could be due to more prolonged processing on distractor trials. Alternatively, it could be that target detection induces strong activation of a small proportion of neurons, which, because of competitive inhibitory mechanisms, could result in a decrease in activity for the population as a whole. We suggest that this kind of mechanism could also account for the decreases in signal observed in perceptual priming experiments.

Magnetic resonance spectroscopy of brain in epilepsy

The current applications of magnetic resonance spectroscopy (MRS) in the clinical management of epileptic patients are reviewed. A major contribution of MRS to epilepsy is its ability to determine lateralisation before surgical resection of the diseased brain region. Phosphorus-31 and proton single-voxel MRS identify abnormalities in high-energy metabolism, neuronal function and neurotransmitter levels, but information can only be obtained from restricted regions of the brain. Spectroscopic imaging techniques (also known as chemical shift imaging) provide a metabolic mapping of the whole brain. They expand the range of applications of MRS to other types of epilepsy (neocortical, frontal) than temporal lobe epilepsy, which is the most often studied. Also, spectral editing techniques in proton MRS make it possible to detect and monitor drug-induced variations of GABA in the human brain, opening new insights into patient response to drug therapy of epilepsy. MRS is playing an increasing role in the noninvasive characterisation and management of epileptic patients.

Cerebral functional magnetic resonance imaging activation modulated by a single dose of the monoamine neurotransmission enhancers fluoxetine and fenozolone during hand sensorimotor tasks

Fluoxetine inhibits the reuptake of serotonin, and dextroamphetamine enhances presynaptic release of monoamines. Although the excitatory effect of both noradrenaline and dopamine on motor behavior generally is accepted, the role of serotonin on motor output is under debate. In the current investigation, the authors evidenced a putative role of monoamines and, more specifically, of serotonin in the regulation of cerebral motor activity in healthy subjects. The effects on cerebral motor activity of a single dose of fluoxetine (20 mg), an inhibitor of serotonin reuptake, and fenozolone (20 mg/50 kg), an amphetamine-like drug, were assessed by functional magnetic resonance imaging. Subjects performed sensorimotor tasks with the right hand. Functional magnetic resonance imaging studies were performed in two sessions on two different days. The first session, with two scan experiments separated by 5 hours without any drug administration, served as time-effect control. A second, similar session but with drug administration after the first scan assessed drug effects. A large increase in evoked signal intensity occurred in the ipsilateral cerebellum, and a parallel, large reduction occurred in primary and secondary motor cortices (P < 10(-3)). These results are consistent with the known effects of habituation. Both drugs elicited comparable effects, that is, a more focused activation in the contralateral sensorimotor area, a greater involvement of posterior supplementary motor area, and a widespread decrease of bilateral cerebellar activation (P < 10(-3)). The authors demonstrated for the first time that cerebral motor activity can be modulated by a single dose of fluoxetine or fenozolone in healthy subjects. Drug effects demonstrated a direct or indirect involvement of monoamines and serotonin in the facilitation of cerebral motor activity.

Temporal sorting of neural components underlying phonological processing

Event-related haemodynamic responses (EHRs) were recorded in subjects performing phonological tasks to test whether distinguishable temporal involvement of corresponding neural components would show through. A sequence of activation leading from primary auditory cortices to premotor regions emerged in the fast repetition and the phoneme monitoring tasks used. EHRs peaked significantly earlier in Wernicke's area (phonological decoding) than in Broca's area, the left supramarginal gyrus and the precentral gyrus (phonological rehearsal). Moreover, the sensitivity of within cluster temporal gradients to the nature of the tasks indicated either sensory to association cortex synchronization for fast repetition or delayed analysis for phoneme monitoring. These results are consistent with previous findings on working memory and show that fMRI permits temporal tracking of cognitive activations.

Usefulness of motor functional MRI correlated to cortical mapping in Rolandic low-grade astrocytomas

The indications for surgery of slow growing tumours like low grade astrocytomas in eloquent areas are difficult. The timing and the benefit/risk ratio of the surgery must be evaluated, taking into account the potential post operative deficit. The purpose of this study was: a) to validate the data obtained with functional MRI (FMRI) by direct cortical stimulation in patients who are candidate for surgery; b) to demonstrate the usefulness of FMRI coupled with cortical brain mapping and 3D reconstructions of the surfaces of the brain in low grade astrocytoma. FMRI of the hand-motor cortex was performed in 8 patients with low grade astrocytomas. They subsequently underwent direct cortical mapping to correlate the results of FMRI and resective surgery sparing the functional area. In the 8 cases, the results of direct cortical mapping in the precentral region matched accurately those obtained from FMRI. When surgical resection of low grade astrocytoma in the motor areas is considered, FMRI used with intra-operative cortical mapping can help the surgeon to spare functional areas during tumour removal.

Characterization of choline compounds with in vitro 1H magnetic resonance spectroscopy for the discrimination of primary brain tumors

RATIONALE AND OBJECTIVES

The authors sought to compare 1H magnetic resonance spectroscopy (MRS) spectra from extracts of low-grade and high-grade gliomas, especially with respect to the signals of choline-containing compounds.

METHODS

Perchloric acid extracts of six high-grade and six low-grade gliomas were analyzed by 1H MRS at 9.4 Tesla.

RESULTS

The signals of glycerophosphocholine (GPC) at 3.23 ppm, phosphocholine (PC) at 3.22 ppm, and choline (Cho) at 3.21 ppm were identified in both types of tumors. The absolute concentrations of all Cho-containing compounds (GPC + PC + Cho) in high-grade and low-grade gliomas were significantly different. The relative contributions of each of the Cho-containing compounds to the total choline signal were also statistically different. For high-grade gliomas, the choline signal is composed of GPC, PC, and Cho in a well-balanced contribution, whereas in low-grade gliomas, the signal is largely due to GPC with a small involvement of PC and Cho.

CONCLUSIONS

The differences in the concentration and the repartition of Cho-containing compounds seem to be a marker of high-grade gliomas. They could also help to discriminate between high- and low-grade gliomas in some difficult cases, especially if there is histologic uncertainty between anaplastic astrocytomas and low-grade oligodendrogliomas.

Cortical intraoperative stimulation in brain tumors as a tool to evaluate spatial data from motor functional MRI

RATIONALE AND OBJECTIVE

The purpose of this prospective, double-blind study was to correlate motor functional MRI (fMRI) with cortical brain mapping by intraoperative stimulation using 3D reconstructed images of the surface of the brain, and to validate the spatial data of fMRI in patients with brain tumors.

METHODS

Fourteen patients with tumors of the rolandic region underwent functional MR mapping of the hand region and subsequently cortical mapping before tumor resection. Data obtained with fMRI and brain mapping were not known previously by the neurosurgeon and by the neuroradiologist, respectively (double-blind study).

RESULTS

In each case, the results of direct cortical mapping matched those obtained with fMRI, both positively and negatively, although the extent of the functional activations was larger than the area required to elicit the corresponding movement during intraoperative brain mapping.

CONCLUSION

fMRI can be used before surgery to assess motor functional area in patients with rolandic tumors. More studies are needed to validate during surgery the real extent of fMRI activations.

Differential fMRI responses in the left posterior superior temporal gyrus and left supramarginal gyrus to habituation and change detection in syllables and tones

Using a habituation-recovery paradigm adapted to functional magnetic resonance imaging, we investigated the brain responses to syllables and tones in six right-handed male subjects. We opposed a standard condition (STD) in which the subjects were listening to homogeneous sequences of four identical stimuli, to a deviant condition (DEV) in which the fourth stimulus of the sequence differed in pitch or spectral content for tones and in the initial stop consonant for syllables. The corresponding runs alternated four rest periods with two STD and two DEV conditions. In addition to a marked rightward asymmetry in the primary and secondary auditory cortex for tones and a right inferior frontal activation for the tone condition where the deviant had increased spectral content, the experiment revealed differential activations in the left posterior superior temporal gyrus and in the left supramarginal gyrus. Activations within the left posterior superior temporal gyrus were observed for the DEV condition with tones and for the STD and DEV conditions with syllables. Activation within the inferior part of the left supramarginal gyrus was only observed for the DEV condition with syllables. The analysis of the decreases and increases in the BOLD signal across the STD, DEV, and rest conditions suggests that the left posterior superior temporal gyrus is implicated in the preattentive change detection of acoustic changes in speech as well as nonspeech stimuli, whereas the left supramarginal gyrus is more specifically engaged in the detection of changes in phonological units.

Event-related potentials elicited by passive movements in humans: characterization, source analysis, and comparison to fMRI

Cortical areas responsive to proprioceptive stimulation were assessed by ERP technique in normals and in selected patients with stroke and were compared to fMRI data. Repetitive extension of right and left forefinger elicited a P1/N1/P2 complex wave pattern. This pattern was absent in patient with complete sensory loss and present but spatially modified in patient with recovered sensory deficit. Source localization with a simple model showed three sources starting in the contralateral rolandic area (SI), then involving the inferior parietal lobe unilaterally and the supplementary motor area (10 to 134 ms). It was followed by a bilaterally distributed pattern of two sources located in the ipsilateral parietal region and in the contralateral insula. Right and left stimulation led to very symmetrical patterns. Comparison to fMRI obtained from passive extension of the wrist in normals showed very compatible data. We described in this paper, a sequential processing of proprioceptive inputs after passive movements involving primary and secondary sensory motor areas.

[MRI visualization of multiple sclerosis lesions]

Magnetic resonance imaging represents voxels (volume elements) of the body placed in a magnet, by their magnetization determined under various acquisition conditions weighting the contrast of the image by the density of free water protons and their relaxation times T1 and T2. Thus, the sensitivity in depicting lesions is high but pathological specificity is poor. Efforts are made to increase the diagnosis powerfulness of M.R.I. in multiple sclerosis: a careful correlation with the clinical presentation and the use of better M.R.I. criteria increase the specificity of the conventional T2 sequences. New sequences such as fast spin echo (F.S.E.), turbo spin echo (T.S.E.) or derived from inversion recovery (F.L.A.I.R.: fluid attenuated inversion recovery) improve the detection of lesions. Under specific conditions M.R.I. can be used to monitor the evolution of M.S. Acute phase monitoring focuses on changes in disease activity, new, recurring, enlarging, gadolinium (Gd) enhancing lesions, and chronic phase monitoring appreciate the burden of the disease. However M.R.I. is always considered as a secondary outcome in the phase III trials because insufficient correlations with the clinical disability. In the neurological daily practice conventional M.R.I. is of poor interest in the follow up of individual M.S. patients considering the weakness of prognosis value and the problems in the measurement of the lesions load which is emphasized in the methodology of the clinical trials. Nevertheless, there is a continuing search for techniques which correlate better with clinical measures of the disease such as the quantification of "black holes" on T1 w images or the cerebral and spinal atrophy. New techniques allow to weight the signal by the movement (diffusion imaging), by the complexity of the molecular architecture (magnetization transfer imaging), by the chemical shift (chemical shift imaging) or by the local status of oxygenation (functional M.R.I.). The basic aspects of the pathological lesions in M.S., edema, membrane disruption, demyelination, gliosis, cellular infiltration and axonal loss can be studied more precisely by these new M.R. techniques which should better describe the actual clinical impact of the destructive process. In the last year the importance of axonal loss has simultaneously been confirmed by M. R. spectroscopy and pathological findings. However, magnetization transfer imaging, M.R. diffusion imaging and functional M.R.I. are intensively under investigation for a better analysis of these different factors conditioning the reversibility of the patient disability.

Motor functional MRI for presurgical evaluation of cerebral tumors

OBJECTIVE

To evaluate the capabilities and the limitations of motor functional magnetic resonance imaging (fMRI) in the presurgical evaluation of the cerebral tumors located in or near the motor homunculus. To correlate each type of activation with the histologic characteristics of each tumor.

MATERIALS AND METHODS

fMRI was performed in 17 patients (14 adults and 3 children), without any motor deficit, presenting with various intracerebral tumors. Three fMRI activation paradigms were used: contralateral to the lesion: ballistic opposition of the fingers, flexion-extension of the foot and click of the tongue. Four patients, without motor deficit, with cerebral tumors far from the motor homunculus were used as control group to look for nonspecific activations. In all cases, the histopathology of the tumor was known accurately.

RESULTS

In 11 patients with infiltrating tumors, the activated areas were clearly displaced. They were often intratumoral and scattered in correlation with the degree of infiltration. Two patients with noninfiltrating tumors (meningioma) showed extratumoral shift of the activated areas. Four patients presenting cerebral tumors far from the homunculus motor did not show intratumoral activation. The supplementary motor area and the ipsilateral primary motor cortex were also reproducibly activated during the motor tasks. The task of the tongue was often artifacted, probably because of the head motion.

CONCLUSIONS

These preliminary results suggest that the histopathologic characteristics of a tumor, and especially its microscopic structure, play a role in the organization of the motor functional area. In a small number of cases, fMRI could be used intraoperatively with a neuronavigation system.

[Presurgical evaluation of cerebral tumors with functional MRI]

PURPOSE

To evaluate the capabilities and the limitations of motor functional magnetic resonance imaging (FMRI) in the presurgical planning of the cerebral tumors located in or near the motor homunculus and to correlate each type of activation with the histologic characteristics of each tumor.

MATERIALS AND METHODS

FMRI was performed in 17 patients (14 adults and 3 children), without motor deficit, presenting with various intra cerebral tumors. Three FMRI activation paradigms were used, controlateral to the lesion: ballistic opposition of the fingers, flexion-extension of the foot and click of the tongue. Four patients, without motor deficit, with cerebral tumors far from the motor homunculus were used as control group to look for non specific activations. In all cases, the histopathology of the tumor was known accurately.

RESULTS

In 11 patients with infiltrating tumors, the activated areas were clearly displaced. They were often intratumoral and scattered in correlation with the degree of infiltration. Two patients with non infiltrating tumors (meningioma) showed extratumoral shift of the activated areas. Four patients presenting cerebral tumors far from the homunculus motor did not show intratumoral activation. The supplementary motor area and the ipsilateral primary motor cortex were also sometimes activated during the motor tasks. The task of the tongue was often artifacted, probably because of the head motion.

CONCLUSIONS

These preliminary results suggest that the histopathologic characteristics of a tumor and especially its microscopic structure plays a role, with others factors, on the motor functional area organization. In a small number of cases, the data obtained from the FMRI could be used intraoperatively, with a neuronavigation system.

Diffusion- and magnetisation transfer-weighted MRI in childhood moya-moya

MRI in two children with moya-moya demonstrated low signal on T2-weighted images in the acute and subacute phases of ischaemia. Gradient-echo sequences, more sensitive to magnetic susceptibility, demonstrated these abnormalities better. Signal loss, due to temporary accumulation of iron, decreases progressively and disappears in the chronic stage of the disease. Diffusion-weighted MRI allows early detection of ischaemic lesions and can be used to monitor progressive spreading of the lesions. Magnetisation transfer maps provide sharp contrast, useful for demonstrating cortical atrophy.

Diffusion and perfusion MRI, measurements of acute stroke events and outcome: present practice and future hope

The morphological, metabolic and functional changes of brain ischaemia can be studied using various MRI methods. These are readily available should the early visualisation of affected territories be needed. Morphological changes include the depiction of oedema on T1- and T2-weighted images, and metabolic changes are reflected on magnetic resonance spectroscopy. Functional changes reflect haemodynamic failure seen on diffusion- and perfusion-weighted imaging. Modelling of behaviour of T2 and diffusion changes could predict the histological outcome of affected tissue regarding cell recovery on necrosis. In addition, the combination of diffusion and perfusion MRI offers a potential prognostic value.

Magnetization transfer with echo planar imaging

The aim of magnetization transfer is to saturate the protons of the macromolecule pool with a radiofrequency (RF) pulse leading to differences in free water pool signal. Magnetization transfer (MT) contrast is difficult to achieve with the echo planar imaging (EPI) technique, although its short acquisition time would be most beneficial. Indeed, the RF saturation pulses can only be applied once before sampling the whole k-space in a single-short sequence. A possible solution to improve the sensitivity of EPI to magnetization transfer consists in applying a train of several saturation RF pulses before image acquisition. The different parameters of a RF pulse train and their influence on the MT rate have been tested to optimize an EPI clinical sequence. Our experimental procedure makes it possible to obtain a MT map in about 1 second. The technique is evaluated by multiple sclerosis lesion characterization.

Contribution of Sinerem used as blood-pool contrast agent: detection of cerebral blood volume changes during apnea in the rabbit

The authors suggest that ultra-small paramagnetic iron oxide (USPIO) particles used as blood pool contrast agents may increase the sensitivity of midfield MRI (i.e., less than 1.5 Tesla) to physiological variations in cerebral blood volume. This hypothesis was tested on a rabbit model of apnea which increases pCO2 and cerebral blood volume. Using Sinerern as the USPIO at a blood concentration of 60 mumol Iron/kg body weight, an 8% T2*-weighted signal decrease could be observed at 1.0 T with 25-33% increase in pCO2. Comparatively, in the absence of USPIO, T2*-weighted signal dropped only 4% during apnea and after mild hyperoxygenation beforehand, due to increased deoxyhemoglobin content. These preliminary data suggest that USPIOs could play an important role in functional MRI at midfield strength, by sensitizing the signal to cerebral blood volume changes.