Primary progressive multiple sclerosis takes centre stage

Multimodal 3D Mouse Brain Atlas Framework with the Skull-Derived Coordinate System

Magnetic resonance imaging (MRI) and light-sheet fluorescence microscopy (LSFM) are technologies that enable non-disruptive 3-dimensional imaging of whole mouse brains. A combination of complementary information from both modalities is desirable for studying neuroscience in general, disease progression and drug efficacy. Although both technologies rely on atlas mapping for quantitative analyses, the translation of LSFM recorded data to MRI templates has been complicated by the morphological changes inflicted by tissue clearing and the enormous size of the raw data sets. Consequently, there is an unmet need for tools that will facilitate fast and accurate translation of LSFM recorded brains to in vivo, non-distorted templates. In this study, we have developed a bidirectional multimodal atlas framework that includes brain templates based on both imaging modalities, region delineations from the Allen's Common Coordinate Framework, and a skull-derived stereotaxic coordinate system. The framework also provides algorithms for bidirectional transformation of results obtained using either MR or LSFM (iDISCO cleared) mouse brain imaging while the coordinate system enables users to easily assign in vivo coordinates across the different brain templates.

rs-fMRI and machine learning for ASD diagnosis: a systematic review and meta-analysis

Autism Spectrum Disorder (ASD) diagnosis is still based on behavioral criteria through a lengthy and time-consuming process. Much effort is being made to identify brain imaging biomarkers and develop tools that could facilitate its diagnosis. In particular, using Machine Learning classifiers based on resting-state fMRI (rs-fMRI) data is promising, but there is an ongoing need for further research on their accuracy and reliability. Therefore, we conducted a systematic review and meta-analysis to summarize the available evidence in the literature so far. A bivariate random-effects meta-analytic model was implemented to investigate the sensitivity and specificity across the 55 studies that offered sufficient information for quantitative analysis. Our results indicated overall summary sensitivity and specificity estimates of 73.8% and 74.8%, respectively. SVM stood out as the most used classifier, presenting summary estimates above 76%. Studies with bigger samples tended to obtain worse accuracies, except in the subgroup analysis for ANN classifiers. The use of other brain imaging or phenotypic data to complement rs-fMRI information seems promising, achieving higher sensitivities when compared to rs-fMRI data alone (84.7% versus 72.8%). Finally, our analysis showed AUC values between acceptable and excellent. Still, given the many limitations indicated in our study, further well-designed studies are warranted to extend the potential use of those classification algorithms to clinical settings.

Impaired olfactory neural circuit in patients with SLE at early stages

OBJECTIVE

To investigate the changes of olfactory function and odor-induced brain activation in patients with systemic lupus erythematosus (SLE) at early stages compared with healthy controls.

MATERIALS AND METHODS

Olfactory function and odor-induced brain activation in 12 SLE patients at early stages and 12 age, gender and education matched healthy controls were evaluated using olfactory behavior test and odor-induced task-functional magnetic resonance imaging (task-fMRI).

RESULTS

No significant differences in olfactory behavior scores (including olfactory threshold, olfactory identification, and olfactory memory) were found in the patients with SLE at early stages compared with the healthy controls, while significantly decreased odor-induced activations in olfactory-related brain regions were observed in the patients. In the SLE group, the patients with better performance in the olfactory threshold test had significantly lower levels of anti-dsDNA antibody.

CONCLUSION

The current study demonstrated that significant alterations in odor-induced brain activations occurred prior to measurable olfactory decline in SLE at early stages, which provided a new method for early diagnosis of olfactory dysfunction in SLE.

Magnetic resonance of the brain in chronic and acute liver failure

Brain alterations such as hepatic encephalopathy or brain edema are usually associated with liver failure. The mechanisms that lead to the generation of edema seem to be different depending on the course of liver failure (acute, chronic or acute-on-chronic liver failure). Several neuroimaging methods allow a non-invasive assessment of brain alterations in liver failure. Magnetic resonance has gained more interest due to the ability of giving information about cerebral metabolism using spectroscopy, water distribution by diffusion methods or neuronal connectivity by means of resting state magnetic resonance. These techniques have been applied to experimental models and patients with liver failure to elucidate cerebral pathways involved in the pathogenesis of hepatic encephalopathy. In the future, the development of new magnetic resonance implementations will generate handy tools for the study of the brain and get better understanding of the mechanisms that take place in liver failure. This could be useful for the early diagnosis, as well as for the design of new treatments for cerebral complications of liver failure.

Survey of encoding and decoding of visual stimulus via FMRI: an image analysis perspective

A variety of exciting scientific achievements have been made in the last few decades in brain encoding and decoding via functional magnetic resonance imaging (fMRI). This trend continues to rise in recent years, as evidenced by the increasing number of published papers in this topic and several published survey papers addressing different aspects of research issues. Essentially, these survey articles were mainly from cognitive neuroscience and neuroimaging perspectives, although computational challenges were briefly discussed. To complement existing survey articles, this paper focuses on the survey of the variety of image analysis methodologies, such as neuroimage registration, fMRI signal analysis, ROI (regions of interest) selection, machine learning algorithms, reproducibility analysis, structural and functional connectivity, and natural image analysis, which were employed in previous brain encoding/decoding research works. This paper also provides discussions of potential limitations of those image analysis methodologies and possible future improvements. It is hoped that extensive discussions of image analysis issues could contribute to the advancements of the increasingly important brain encoding/decoding field.

Anesthetic effects of propofol in the healthy human brain: functional imaging evidence

Functional imaging methods, including positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), have become important tools for studying how anesthetic drugs act in the human brain to induce the state of general anesthesia. Recent imaging studies using fMRI and PET techniques have demonstrated the regional effects of propofol on the brain. However, the pharmacological mechanism of the action of propofol in the intact human central nervous system is unclear. To explore the possible action targets of propofol in the human brain, a systematic review of the literature was performed. The literature search was performed with limiting factors of "propofol," "functional imaging," "positron emission tomography", and "functional magnetic resonance imaging" from 1966 to July 2013 (using Medline, EMBASE, CINAHL and hand searches of references). Studies meeting the inclusion criteria were reviewed and critiqued for the purpose of this literature research. Eighteen researches meeting the inclusion criteria were reviewed in terms of the appropriateness of valuation technique. In the unconscious state, propofol sharply reduces the regional glucose metabolism rate (rGMR) and regional cerebral blood flow (rCBF) in all brain regions, particularly in the thalamus. However, GMR, such as in the occipital, temporal, and frontal lobes, was obviously decreased at a sedative dosage of propofol, whereas, changes in the thalamus were not obvious. Using fMRI, several studies observed a decrease of connectivity of the thalamus versus an increase of connectivity within the pons of the brainstem during propofol-induced mild sedation. During deep sedation, propofol preserves cortical sensory reactivity, the specific thalamocortical network is moderately affected, whereas the nonspecific thalamocortical network is severely suppressed. In contrast, several recent fMRI studies are consistent on the systemic decreased effects of propofol in the frontoparietal network. Accumulating evidence suggest that propofol-induced unconsciousness is associated with a global metabolic and vascular depression in the human brain and especially with a significant reduction in the thalamocortical network and the frontoparietal network.

Persistent differences in patterns of brain activation after sports-related concussion: a longitudinal functional magnetic resonance imaging study

Avoiding recurrent injury in sports-related concussion (SRC) requires understanding the neural mechanisms involved during the time of recovery after injury. The decision for return-to-play is one of the most difficult responsibilities facing the physician, and so far this decision has been based primarily on neurological examination, symptom checklists, and neuropsychological (NP) testing. Functional magnetic resonance imaging (fMRI) may be an additional, more objective tool to assess the severity and recovery of function after concussion. The purpose of this study was to define neural correlates of SRC during the 2 months after injury in varsity contact sport athletes who suffered a SRC. All athletes were scanned as they performed an n-back task, for n=1, 2, 3. Subjects were scanned within 72 hours (session one), at 2 weeks (session two), and 2 months (session three) post-injury. Compared with age and sex matched normal controls, concussed subjects demonstrated persistent, significantly increased activation for the 2 minus 1 n-back contrast in bilateral dorsolateral prefrontal cortex (DLPFC) in all three sessions and in the inferior parietal lobe in session one and two (α≤0.01 corrected). Measures of task performance revealed no significant differences between concussed versus control groups at any of the three time points with respect to any of the three n-back tasks. These findings suggest that functional brain activation differences persist at 2 months after injury in concussed athletes, despite the fact that their performance on a standard working memory task is comparable to normal controls and normalization of clinical and NP test results. These results might indicate a delay between neural and behaviorally assessed recovery after SRC.

Magnetic resonance imaging biomarkers in patients with progressive ataxia: current status and future direction

A diagnostic challenge commonly encountered in neurology is that of an adult patient presenting with ataxia. The differential is vast and clinical assessment alone may not be sufficient due to considerable overlap between different causes of ataxia. Magnetic resonance (MR)-based biomarkers such as voxel-based morphometry, MR spectroscopy, diffusion-weighted and diffusion-tensor imaging and functional MR imaging are gaining great attention for their potential as indicators of disease. A number of studies have reported correlation with clinical severity and underlying pathophysiology, and in some cases, MR imaging has been shown to allow differentiation of conditions causing ataxia. However, despite recent advances, their sensitivity and specificity vary. In addition, questions remain over their validity and reproducibility, especially when applied in routine clinical practice. This article extensively reviews the current literature regarding MR-based biomarkers for the patient with predominantly adult-onset ataxia. Imaging features characteristic of a particular ataxia are provided and features differentiating ataxia groups and subgroups are discussed. Finally, discussion will turn to the feasibility of applying these biomarkers in routine clinical practice.

Partly reversible central auditory dysfunction induced by cerebral vasospasm after subarachnoid hemorrhage

The authors describe a rare case of central auditory dysfunction induced by cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH). A 55-year-old woman who was admitted after aneurysmal SAH developed cerebral vasospasm on Day 3 affecting mainly the right middle cerebral artery (MCA) and partly the left MCA. The vasospasm became refractory to conventional therapy and was ultimately improved by intraarterial infusion of nimodipine in the right MCA and angioplasty. Severe auditory dysfunction was apparent from Day 10 as the patient was not reactive to speech or environmental sounds. Brain MRI on Day 17 demonstrated infarcted areas mainly in the right hippocampus, medial occipital lobe, and thalamus. The patient underwent further examination using audiometry, speech testing, auditory evoked potentials, functional MRI, and cerebral PET. The initial diagnosis was extended nonverbal agnosia and total pure word deafness. The central auditory dysfunction improved over 6 months, with persisting hyperacusis, tinnitus, and amusia. Central auditory dysfunction is a rare complication after SAH. While cortical deafness may be associated with bilateral lesions of the temporal cortex, partly reversible central auditory dysfunction was observed in this patient after prominently unilateral right temporal lesions. The role of the interthalamic connections can be discussed, as well as the possibility that a less severe vasospasm on the left MCA could have transiently impaired the left thalamocortical auditory pathways.

Resting-state functional magnetic resonance imaging analysis with seed definition constrained by regional homogeneity

Researchers have recently focused their attention on the intrinsic functional connectivity (FC) in the brain using resting-state functional magnetic resonance imaging. Seed-based correlation analysis (SCAC), which correlates a predefined seed region with other voxels in the brain, is a common index for FC. However, definition of seed sizes and locations was ambiguous in previous studies and this may lead to spurious results for people with a unique functional anatomy. To address this issue, this study proposes a novel method (SCAReHo) that provides a data-driven seed selection (including sizes and locations) method by incorporating regional homogeneity (ReHo) in the SCAC method. The disparities between SCAC and SCAReHo methods among 12 healthy participants were evaluated in the FC of default mode network (DMN), task-positive network (TPN), and amygdala network. The SCAReHo method bypasses the seed-selection ambiguity and enhances the sensitivity in detecting FC of the DMN, TPN, and amygdala network. This study suggests that the SCAReHo method improves the sensitivity of FC analysis and reduces the uncertainty of seed selection. Thus, this method may be particularly useful for psychiatric and neurological investigations.

Adaptive immune responses in CNS autoimmune disease: mechanisms and therapeutic opportunities

The processes underlying autoimmune CNS inflammation are complex, but key roles for autoimmune lymphocytes seem inevitable, based on clinical investigations in multiple sclerosis (MS) and related diseases such as neuromyelitis optica, together with the known pathogenic activity of T cells in experimental autoimmune encephalomyelitis (EAE) models. Despite intense investigation, the details of etiopathology in these diseases have been elusive. Here we describe recent advances in the rodent models that begin to allow a map of pathogenic and protective immunity to be drawn. This map might illuminate previous successful and unsuccessful therapeutic strategies targeting particular pathways, whilst also providing better opportunities for the future, leading to tailored intervention based on understanding the quality of each individual's autoimmune response.

The BOLD effect

The purpose of this chapter is to introduce the novice NMR imager to blood oxygen level dependent (BOLD) contrast as well as remind the seasoned veteran of its beauty. Introduction to many of the factors that influence the BOLD signal is given higher priority than pursuing any subset in exquisite detail. Instead, references are given for readers seeking intense investigations into a given aspect. The hope is that this overview inspires the reader with the elegant simplicity of BOLD contrast while not, at first, intimidating too much with the underlying complexity. As one's knowledge of NMR matures so too will one's understanding, appreciation, and application of BOLD MRI. BOLD contrast derives from variations in the magnetic susceptibility of blood due to variations in the concentration of deoxyhemoglobin. These magnetic susceptibility effects produce local magnetic fields around blood vessels that can result in phase dispersion of nearby spins and, therefore, changes in signal intensity in NMR images. After providing brief historical context for BOLD, this chapter will follow the trail of magnetic susceptibility through definition, its source and location in vivo, and how the source and location in vivo interact with anatomical (e.g., blood vessel size) and imaging considerations (e.g., pulse sequence) to influence the BOLD signal. We will conclude by briefly highlighting clinical and preclinical applications using BOLD contrast.

Mapping causal interregional influences with concurrent TMS-fMRI

Transcranial magnetic stimulation (TMS) produces a direct causal effect on brain activity that can now be studied by new approaches that simultaneously combine TMS with neuroimaging methods, such as functional magnetic resonance imaging (fMRI). In this review we highlight recent concurrent TMS-fMRI studies that illustrate how this novel combined technique may provide unique insights into causal interactions among brain regions in humans. We show how fMRI can detect the spatial topography of local and remote TMS effects and how these may vary with psychological factors such as task-state. Concurrent TMS-fMRI may furthermore reveal how the brain adapts to so-called virtual lesions induced by TMS, and the distributed activity changes that may underlie the behavioural consequences often observed during cortical stimulation with TMS. We argue that combining TMS with neuroimaging techniques allows a further step in understanding the physiological underpinnings of TMS, as well as the neural correlated of TMS-evoked consequences on perception and behaviour. This can provide powerful new insights about causal interactions among brain regions in both health and disease that may ultimately lead to developing more efficient protocols for basic research and therapeutic TMS applications.

Measuring oxygenation in vivo with MRS/MRI--from gas exchange to the cell

Oxygen plays a major role as a substrate in metabolic processes in numerous signaling pathways, in redox metabolism, and in free radical metabolism. To study the role of oxygen in normal and pathophysiological states, methods that can be used noninvasively are required. This review examines the potential of nuclear magnetic resonance techniques to study tissue oxygenation. It is written from a systems perspective, looking at detection methods with respect to the path that oxygen takes in the mammalian system-from the lungs, through the vascular system, into the interstitial space, and finally into the cell. Methods discussed range from those that are quantifiable, such as the assessment of spin lattice relaxation time in fluorocarbon solutions, to those that are more correlative, such as assessment of lactate and high energy phosphates. Since the methods vary in their site of application, sensitivity, and specificity to the quantification of oxygen, this review provides examples of how each method has been applied. This may facilitate the reader's understanding of how to optimally apply different methods to study specific biomedical problems.

Applications of fMRI in translational medicine and clinical practice

Functional MRI (fMRI) has had a major impact in cognitive neuroscience. fMRI now has a small but growing role in clinical neuroimaging, with initial applications to neurosurgical planning. Current clinical research has emphasized novel concepts for clinicians, such as the role of plasticity in recovery and the maintenance of brain functions in a broad range of diseases. There is a wider potential for clinical fMRI in applications ranging from presymptomatic diagnosis, through drug development and individualization of therapies, to understanding functional brain disorders. Realization of this potential will require changes in the way clinical neuroimaging services are planned and delivered.

Cognitive impairment and decline in different MS subtypes

This paper presents results of two studies conducted to investigate cognition in different MS subtypes. First, the results of a study that has previously been published will be discussed. This was a cross-sectional study with 108 relapsing-remitting (RR), 71 secondary progressive (SP), 55 primary progressive (PP) MS patients, and 67 healthy controls [S.C.J. Huijbregts, N.F. Kalkers, L.M.J. de Sonneville, V. de Groot, I.E.W. Reuling, C.H. Polman, Differences in cognitive impairment of relapsing-remitting, secondary and primary progressive MS. Neurology 63 (2004) 335-339]. The second study involved a follow-up assessment after 2 years and included 30 SPMS patients, 25 PPMS patients, and 33 controls. The Brief Repeatable Battery of Neuropsychological Tests (BRB-N) was used for all cognitive assessments. All patient groups demonstrated cognitive deficits compared to healthy controls. RRMS patients were less affected compared to patients with progressive MS subtypes on the Paced Auditory Serial Addition Task (PASAT) and the Symbol Digit Modalities Test (SDMT). These differences were attenuated after control for physical disability level as measured by the Expanded Disability Status Scale. RRMS and SPMS patients were more severely impaired than PPMS patients on the 10/36 Spatial Recall Task and Word List Generation. Results of the follow-up study indicated that both progressive MS subtypes showed a lack of improvement compared to controls on the PASAT and the SDMT, but not on the other tasks of the BRB-N, indicating that performance on tasks requiring multiple abilities concurrently, i.e. visuo-spatial ability and processing speed (SDMT) or working memory and processing speed (PASAT), is most likely to decline across time.

Evaluation of Intra-Renal Oxygenation by BOLD MRI

This is a review of blood oxygenation level-dependent (BOLD) MRI as applied to the kidney. It has been shown that BOLD MRI measurements reflect changes in renal oxygenation, especially in the medulla. Renal medulla functions in a hypoxic milieu and is extremely sensitive to further decrease in blood flow or increase in oxygen consumption. Availability of a non-invasive technique such as BOLD MRI should allow for better understanding of the factors involved in the maintenance of renal oxygenation status, not only in animal models, but also in humans.

Functional magnetic resonance imaging and multiple sclerosis

There is increasing evidence that the severity of the clinical manifestations of multiple sclerosis (MS) does not result simply from the extent of tissue destruction, rather it represents a complex balance between tissue damage, tissue repair and cortical reorganization. Functional magnetic resonance imaging provides information regarding the extent and nature of brain plasticity following MS-related structural injury, with the potential to limit the clinical manifestations of the disease. An altered recruitment of regions devoted normally to the performance of a given task and/or the recruitment of additional areas that are not typically activated by healthy people for performing that given task have been described in patients with MS, independent of their clinical phenotype, when investigating visual, cognitive and motor systems. These functional changes have been related not only to the extent and severity of brain damage within and outside T2-visible lesions and to the involvement of specific brain structures, but also to the degree of spinal cord and optic nerve involvement. It has also been suggested that an altered recruitment of specific brain regions might be associated with the appearance of clinical symptoms in MS, such as fatigue. Brain functional changes have been shown to be dynamic over time, not only after an acute relapse, but also in clinically stable patients. More recently, in patients at the earliest clinical stage of the disease, it has been shown that such changes might contribute to predicting the evolution to definite MS, and it has been postulated that dynamic changes of brain cortical activations might occur with the progression of the disease. An increased recruitment of the cerebral networks might represent the first step of cortical reorganization with the potential to maintain a normal level of function in the course of MS. The progressive failure of these mechanisms might, on the one hand, result in the activation of previously silent second-order compensatory areas, and on the other, contribute to the accumulation of irreversible disability.