Functional MRI and its applications to the clinical neurosciences

Inferring Macroscale Brain Dynamics via Fusion of Simultaneous EEG-fMRI

Advances in the instrumentation and signal processing for simultaneously acquired electroencephalography and functional magnetic resonance imaging (EEG-fMRI) have enabled new ways to observe the spatiotemporal neural dynamics of the human brain. Central to the utility of EEG-fMRI neuroimaging systems are the methods for fusing the two data streams, with machine learning playing a key role. These methods can be dichotomized into those that are symmetric and asymmetric in terms of how the two modalities inform the fusion. Studies using these methods have shown that fusion yields new insights into brain function that are not possible when each modality is acquired separately. As technology improves and methods for fusion become more sophisticated, the future of EEG-fMRI for noninvasive measurement of brain dynamics includes mesoscale mapping at ultrahigh magnetic resonance fields, targeted perturbation-based neuroimaging, and using deep learning to uncover nonlinear representations that link the electrophysiological and hemodynamic measurements.

Educational fMRI: From the Lab to the Classroom

Functional MRI (fMRI) findings hold many potential applications for education, and yet, the translation of fMRI findings to education has not flowed. Here, we address the types of fMRI that could better support applications of neuroscience to the classroom. This 'educational fMRI' comprises eight main challenges: (1) collecting artifact-free fMRI data in school-aged participants and in vulnerable young populations, (2) investigating heterogenous cohorts with wide variability in learning abilities and disabilities, (3) studying the brain under natural and ecological conditions, given that many practical topics of interest for education can be addressed only in ecological contexts, (4) depicting complex age-dependent associations of brain and behaviour with multi-modal imaging, (5) assessing changes in brain function related to developmental trajectories and instructional intervention with longitudinal designs, (6) providing system-level mechanistic explanations of brain function, so that useful individualized predictions about learning can be generated, (7) reporting negative findings, so that resources are not wasted on developing ineffective interventions, and (8) sharing data and creating large-scale longitudinal data repositories to ensure transparency and reproducibility of fMRI findings for education. These issues are of paramount importance to the development of optimal fMRI practices for educational applications.

Perfusion Changes with Photic Stimulation During two Phases of the Menstrual Cycle: A Pilot Study Comparing Controls and True Menstrual Migraine Patients

This pilot study investigated the effect of menstrual cycle phase (late luteal and mid-follicular) on cerebral perfusion changes during photic stimulation in both controls ( n = 5) and true menstrual migraine patients ( n = 5). No significant differences in resting baseline perfusion were observed between the two groups during either phase of the menstrual cycle. During the late luteal phase, changes in perfusion within the occipital lobe due to photic stimulation were similar for both groups. However, during the mid-follicular phase, occipital perfusion during visual stimulation decreased for controls but significantly increased for true menstrual migraine patients ( P < 0.05). A two way repeated measures ANOVA also demonstrated a significant difference between menstrual migraine patients and controls for photic activation ( P < 0.05).

A structural and functional magnetic resonance imaging dataset of brain tumour patients

We collected high resolution structural (T1, T2, DWI) and several functional (BOLD T2*) MRI data in 22 patients with different types of brain tumours. Functional imaging protocols included a motor task, a verb generation task, a word repetition task and resting state. Imaging data are complemented by demographics (age, sex, handedness, and pathology), behavioural results to motor and cognitive tests and direct cortical electrical stimulation data (pictures of stimulation sites with outcomes) performed during surgery. Altogether, these data are suited to test functional imaging methods for single subject analyses, in particular methods that focus on locating eloquent cortical areas, critical functional and/or structural network hubs, and predict patient status based on imaging data (presurgical mapping).

[On the question of the organization of brain function: cortical associations, «disconnection» syndrome and higher brain functions]

The review considers the structural/functional brain organization, the disturbance of which is accompanied by the development of cognitive and behavioral disorders. The significance of the disruption of parallel circuits connecting frontal lobes with subcortical structures (the basal ganglia, thalamus, cerebellum) is highlighted. This disruption is clinically described as "disconnection" syndrome. The associations between the basal ganglia and the cortex of the large cerebral hemispheres responsible for motor, cognitive and emotional/behavioral functions do not restricted to these spheres and is characteristic not only of frontal brain areas. There are circuits connecting other brain compartments and the basal ganglia that provide perception, and are involved in decision making on the basis of input information of different modalities.The improvement of understanding of the pathophysiology and neurochemistry of these structures opens new possibilities for selective action on some or other circuit to achieve the best therapeutic result.

Simple fMRI postprocessing suffices for normal clinical practice

BACKGROUND AND PURPOSE

Whereas fMRI postprocessing tools used in research are accurate but unwieldy, those used for clinical practice are user-friendly but are less accurate. We aimed to determine whether commercial software for fMRI postprocessing is accurate enough for clinical practice.

METHODS

Ten volunteers underwent fMRI while performing motor and language tasks (hand, foot, and orolingual movements; verbal fluency; semantic judgment; and oral comprehension). We compared visual concordance, image quality (noise), voxel size, and radiologist preference for the activation maps obtained by using Neuro3D software (provided with our MR imaging scanner) and by using the SPM program commonly used in research.

RESULTS

Maps obtained with the 2 methods were classified as "partially overlapping" for 70% for motor and 72% for language paradigm experiments and as "overlapping" in 30% of motor and in 15% of language paradigm experiments.

CONCLUSIONS

fMRI is a helpful and robust tool in clinical practice for planning neurosurgery. Widely available commercial fMRI software can provide reliable information for therapeutic management, so sophisticated, less widely available software is unnecessary in most cases.

Functional magnetic resonance imagery (fMRI) in fibromyalgia and the response to milnacipran

Functional imaging has been used to study response to pain in fibromyalgia patients. Functional magnetic resonance imagery (fMRI) which tracks local changes in blood flow has a higher spatial and temporal resolution than other techniques such as positron emission tomography (PET) or single-photon emission tomography (SPECT). fMRI studies in fibromyalgia patients suggest that similar levels of subjective pain result in similar central nervous system (CNS) activation in both fibromyalgia patients and controls. For a similar stimulus, however, fibromyalgia patients have a greater subjective sensation of pain. This increased sensitivity is accompanied with a decreased activity in brain regions implicated in the descending pain inhibitory pathways. The hypothesis that increased sensitivity to pain is due to decreased activity of the descending inhibitory pathways is supported by results with milnacipran. Fibromyalgia patients treated with the serotonin and noradrenaline reuptake inhibitor, milnacipran, exhibited a reduction in pain sensitivity and a parallel increase in activity in brain regions implicated in the descending pain inhibitory pathways compared to placebo-treated patients.

Measures of emotion: A review

A consensual, componential model of emotions conceptualises them as experiential, physiological, and behavioural responses to personally meaningful stimuli. The present review examines this model in terms of whether different types of emotion-evocative stimuli are associated with discrete and invariant patterns of responding in each response system, how such responses are structured, and if such responses converge across different response systems. Across response systems, the bulk of the available evidence favours the idea that measures of emotional responding reflect dimensions rather than discrete states. In addition, experiential, physiological, and behavioural response systems are associated with unique sources of variance, which in turn limits the magnitude of convergence across measures. Accordingly, the authors suggest that there is no "gold standard" measure of emotional responding. Rather, experiential, physiological, and behavioural measures are all relevant to understanding emotion and cannot be assumed to be interchangeable.

[Functional magnetic resonance imaging in brain tumour neurosurgical resection risk assessment]

To establish the possibilities of functional magnetic resonance (fMRI) in the assesment of preservation of the motor and speech brain functions in the primary brain tumour patients planed for neurosurgery.

METHODS AND MATERIAL

fMRI of motor and/or speech areas was performed on 3T MRI unit in 17 patients with primary brain tumours and dominant focal epileptic symptomatology.

RESULTS

None of the patients demonstrated motor neurologic deficit before the operation, while in one patient a moderate speech disorder was noted. Operative treatment has been performed in 11/17 patients, and in 6/11 patients total tumour resection has been performed. Motor deficit has not been noted in any of the patients. Transitory speech deficit was noted in 3/11 patients, while 1/11 patients demonstrated a permanent but mild speech deficit.

CONCLUSION

fMRI may be of significant help in the assessment of potential postoperative neurological deficit risks, enabling the optimization of neurosurgical resection procedure in the brain tumour patients.

Group analysis and the subject factor in functional magnetic resonance imaging: analysis of fifty right-handed healthy subjects in a semantic language task

Before considering a given fMRI paradigm as a valid clinical tool, one should first assess the reliability of functional responses across subjects by establishing a normative database and defining a reference activation map that identifies major brain regions involved in the task at hand. However, the definition of such a reference map can be hindered by inter-individual functional variability. In this study, we analysed functional data obtained from 50 healthy subjects during a semantic language task to assess the influence of the number of subjects on the reference map and to characterise inter-individual functional variability. We first compared different group analysis approaches and showed that the extent of the activated network depends not only on the choice of the analysis approach but also on the statistical threshold used and the number of subjects included. This analysis suggested that, while the RFX analysis is suitable to detect confidently true positive activations, the other group approaches are useful for exploratory investigations in small samples. The application of quantitative measures at the voxel and regional levels suggested that while approximately 15-20 subjects were sufficient to reveal reliable and robust left hemisphere activations, >30 subjects were necessary for revealing more variable and weak right hemisphere ones. Finally, to visualise inter-individual variability, we combined two similarity indices that assess the percentages of true positive and false negative voxels in individual activation patterns relative to the group map. We suggest that these measures can be used for the estimation of the degree of 'normality' of functional responses in brain-damaged patients, where this question is often raised, and recommend the use of different quantifications to appreciate accurately the inter-individual functional variability that can be incorporated in group maps.

Brain mapping in cognitive disorders: a multidisciplinary approach to learning the tools and applications of functional neuroimaging

BACKGROUND

With rapid advances in functional imaging methods, human studies that feature functional neuroimaging techniques are increasing exponentially and have opened a vast arena of new possibilities for understanding brain function and improving the care of patients with cognitive disorders in the clinical setting. There is a growing need for medical centers to offer clinically relevant functional neuroimaging courses that emphasize the multifaceted and multidisciplinary nature of this field. In this paper, we describe the implementation of a functional neuroimaging course focusing on cognitive disorders that might serve as a model for other medical centers. We identify key components of an active learning course design that impact student learning gains in methods and issues pertaining to functional neuroimaging that deserve consideration when optimizing the medical neuroimaging curriculum.

METHODS

Learning gains associated with the course were assessed using polychoric correlation analysis of responses to the SALG (Student Assessment of Learning Gains) instrument.

RESULTS

Student gains in the functional neuroimaging of cognition as assessed by the SALG instrument were strongly associated with several aspects of the course design.

CONCLUSION

Our implementation of a multidisciplinary and active learning functional neuroimaging course produced positive learning outcomes. Inquiry-based learning activities and an online learning environment contributed positively to reported gains. This functional neuroimaging course design may serve as a useful model for other medical centers.

Continuous ASL perfusion fMRI investigation of higher cognition: quantification of tonic CBF changes during sustained attention and working memory tasks

Arterial spin labeling (ASL) perfusion fMRI is an emerging method in clinical neuroimaging. Its non-invasiveness, absence of low frequency noise, and ability to quantify the absolute level of cerebral blood flow (CBF) make the method ideal for longitudinal designs or low frequency paradigms. Despite the usefulness in the study of cognitive dysfunctions in clinical populations, perfusion activation studies to date have been conducted for simple sensorimotor paradigms or with single-slice acquisition, mainly due to technical challenges. Using our recently developed amplitude-modulated continuous ASL (CASL) perfusion fMRI protocol, we assessed the feasibility of a higher level cognitive activation study in twelve healthy subjects. Taking advantage of the ASL noise properties, we were able to study tonic CBF changes during uninterrupted 6-min continuous performance of working memory and sustained attention tasks. For the visual sustained attention task, regional CBF increases (6-12 ml/100 g/min) were detected in the right middle frontal gyrus, the bilateral occipital gyri, and the anterior cingulate/medial frontal gyri. During the 2-back working memory task, significantly increased activations (7-11 ml/100 g/min) were found in the left inferior frontal/precentral gyri, the left inferior parietal lobule, the anterior cingulate/medial frontal gyri, and the left occipital gyrus. Locations of activated and deactivated areas largely concur with previous PET and BOLD fMRI studies utilizing similar paradigms. These results demonstrate that CASL perfusion fMRI can be successfully utilized for the investigation of the tonic CBF changes associated with high level cognitive operations. Increased applications of the method to the investigation of cognitively impaired populations are expected to follow.

Frontiers of brain mapping using MRI

Over the past dozen years, the use of MRI techniques to map brain function (fMRI) has sparked a great deal of research. The ability of fMRI to image several different physiological processes concurrently (i.e., blood oxygenation, blood flow, metabolism) and noninvasively over large volumes make it the ideal choice for many different areas of neuroscience research in addition to countless applications in clinical settings. Furthermore, with the advent of high magnetic fields (and other hardware advancements, i.e., parallel imaging) for both human and animal research, spatial and temporal resolutions continue to be pushed to higher levels because of increases in the sensitivity as well as specificity of MR-detectable functional signals. fMRI methodology continues to grow and has the ability to cater to many different research applications. There seems to be no foreseeable end in sight to the advancement of fMRI techniques and its subsequent use in basic research as well as in clinical settings. In this work, fMRI techniques and the ongoing development of existing techniques are discussed with implications for the future of fMRI.

Neuroimaging of epilepsy: therapeutic implications

Neuroimaging has important applications in the diagnosis and treatment of patients with seizures and epilepsy. Having replaced computed tomography (CT) in many situations, MRI is the preferred imaging technique for patients with epilepsy. Advances in radionuclide-based techniques such as single-photon emission CT/positron emission tomography and electromagnetic source imaging with magnetoencephalography are providing new insights into the pathophysiology of epilepsy. In addition, techniques such as magnetic resonance spectroscopy are beginning to impact treatment. In this review, I discuss how these techniques are used in clinical practice but more importantly, how imaging findings play an increasing role in neurotherapeutics.

Imaging structure and function in refractory focal epilepsy

Over the past decade there have been many advances in data acquisition and analysis for structural and functional neuroimaging of people with epilepsy. New imaging sequences and analysis techniques have increased the resolution of images such that underlying structural pathology can be seen in many patients with "cryptogenic" epilepsy. When an epileptogenic lesion is present, antiepileptic drugs alone rarely prevent seizures. However, the success of surgical treatment is improved when a structural lesion has been identified. Lesions might not overlap with the area of the cortex generating seizures and may continue into areas sustaining normal functions. To prevent postsurgical morbidity, the spatial relation between functionally important areas and the epileptogenic lesion must be assessed before surgery. In this review we describe the potential of different neuroimaging techniques to show lesions, assess neuronal function, and assist with the prognosis of postsurgical outcome in patients with refractory focal epilepsy.

fMRI: Applications in Epilepsy

Functional MRI (fMRI) methods use currently standard MRI scanning hardware to detect changes in regional blood flow and metabolism that accompany regional brain activation. Major applications of fMRI in epilepsy include the localization of task-correlated language and memory function, and the localization of ictal and paroxysmal phenomena. Language lateralization by fMRI provides comparable results to intracarotid amobarbital testing, and memory lateralization by fMRI also shows promise. The recent development of methodologies to allow interpretable electroencephalographic data to be recorded during MRI scanning has opened up new opportunities for combining the spatial resolution of imaging with the temporal resolution of electrophysiology in seizure localization.

Monitoring photodynamic therapy of solid tumors online by BOLD-contrast MRI

Antivascular photodynamic therapy (PDT) of tumors with palladium-bacteriopheophorbide (TOOKAD) relies on in situ photosensitization of the circulating drug by local generation of cytotoxic reactive oxygen species, which leads to rapid vascular occlusion, stasis, necrosis and tumor eradication. Intravascular production of reactive oxygen species is associated with photoconsumption of O(2) and consequent evolution of paramagnetic deoxyhemoglobin. In this study we evaluate the use of blood oxygenation level-dependent (BOLD) contrast magnetic resonance imaging (MRI) for real-time monitoring of PDT efficacy. Using a solid tumor model, we show that TOOKAD-PDT generates appreciable attenuation (25-40%) of the magnetic resonance signal, solely at the illuminated tumor site. This phenomenon is independent of, though augmented by, ensuing changes in blood flow. These results were validated by immunohistochemistry and intravital microscopy. The concept of photosensitized BOLD-contrast MRI may have intraoperative applications in interactive guidance and monitoring of antivascular cancer therapy, PDT treatment of macular degeneration, interventional cardiology and possibly other biomedical disciplines.

Future aspects of the presurgical evaluation in epilepsy

Epilepsy surgery is a successful therapeutic approach in patients with medically intractable epilepsy. The presurgical evaluation aims to detect the epileptogenic brain area by use of different diagnostic techniques. In this review article the current diagnostic procedures applied for this purpose are described. The diagnostic armamentarium can be divided conceptually into three different groups: assessment of function/dysfunction, structural/morphologic imaging methods and functional neuroimaging techniques. Properties, diagnostic power and limits of all diagnostic tools used in the diagnostic evaluation are discussed. In addition, future perspectives and the diagnostic value of new technologies are mentioned. Some are increasingly gaining acceptance in the routine preoperative diagnostic procedure like MR volumetry or MR spectroscopy of the hippocampus in patients with temporal lobe epilepsy. Some, on the other hand, like MEG and 11C-flumazenil PET, still remain experimental diagnostic tools as they are technically demanding and cost intensive. Besides the refinement of established techniques, co-registration of different modalities like spike-triggered functional MRI will play an important role in the non-invasive detection of the epileptic seizure focus and may change the regimen of the preoperative diagnostic work up of epilepsy patients in the future.

Advanced brain imaging procedures and human memory disorder

The impact of advanced brain imaging procedures in the field of human memory disorder is reviewed, with particular emphasis on current and potential applications that may impact upon the diagnosis and management of memory-disordered patients. While both advanced structural, resting physiological and functional physiological brain imaging procedures have been applied to conditions where memory disorder is a major feature, the specific implications of research findings for diagnosis and treatment in routine clinical practice remain tentative and promising, but not yet substantive enough to inform clinical decisions to a significant degree. In terms of diagnostic applications, several promising areas include dementia, epilepsy, and transient amnesic states. In the case of applications in treatment settings, advanced brain imaging procedures may help to monitor neural correlates of spontaneous recovery or progression of memory function, and may also help in the planning and monitoring of therapeutic intervention.

Now you see it, now you don't: statistical and methodological considerations in fMRI

We illustrate the effects of statistical threshold, spatial clustering, voxel size, and two approaches to multiple comparison correction on fMRI results. We first analyzed fMRI images obtained from a single subject during a noun-verb matching task. Data were analyzed with Statistical Parametric Mapping (SPM) using two different voxel sizes, and results were displayed at three different levels of statistical significance. At each statistical threshold, results were first uncorrected for multiple comparisons and spatial extent and then presented using a spatial extent cluster of 20 voxels. We then statistically controlled the Type I error rate associated with multiple comparisons by using the false discovery rate and by the random field adjustment for false-positive rate used by SPM. We also examined group results from language and graphesthesia paradigms at three levels of statistical significance. In all circumstances, apparent random activations decreased as more conservative statistical approaches were employed, but activation in areas considered to be functionally significant was also reduced. These issues are important in the choice of analytic approach and interpretation of fMRI results, with clear implications for the surgical management of individual patients when fMRI results are used to delineate specific areas of eloquent cortex.

Ethical considerations for neuropsychologists as functional magnetic imagers

This discussion highlights ethical and practical issues potential neuropsychologist-imagers should consider in conducting functional magnetic resonance imaging (fMRI). While fMRI is not currently approved for clinical use, research is ongoing which has implications for clinical practice, from refining brain-behavior relationships, to assisting with diagnosis and treatment decisions. To protect the welfare of cognitively impaired populations requires special care with respect to MR risks and informed consent. Competent functional imaging requires an understanding of the strengths, limitations, and appropriate domain of applications of the measure.

Functional neuroimaging in neurology and psychiatry

How can functional neuroimaging be applied to clinical neurology and psychiatry? This article reviews selected contributions of functional neuroimaging to the clinical neurosciences. We review selected technical aspects of positron emission tomography, single photon emission tomography, and functional magnetic resonance imaging with a focus on the relative strengths and weaknesses of these techniques. Consumers of functional neuroimaging research are encouraged to consider the limitations of imaging techniques and theoretical pitfalls of cognitive task design when interpreting results of functional imaging studies. Then, we selectively review the contributions of functional neuroimaging to neurology and psychiatry, including the areas of epilepsy, stroke, chronic pain, schizophrenia, depression, and obsessive-compulsive disorder. Future directions of functional neuroimaging research are offered, with the emphasis that the best conclusions are informed by a convergence of research from functional neuroimaging, neurophysiological, and lesion studies.