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PubMedDate not supplied

Magnetic resonance imaging in primary progressive multiple sclerosis.

Ten to fifteen percent of patients with multiple sclerosis (MS) have a condition that is progressive from onset without a preceding relapsing-remitting phase: this is known as primary progressive multiple sclerosis (PPMS). Patients with PPMS tend to be older, often present with motor symptoms and, in contrast to relapsing MS, are as likely to be male as female. The conventional magnetic resonance imaging (MRI) characteristics of PPMS include a tendency to lower lesion loads and lower rate of new lesion formation. In common with relapsing MS, the relation between conventional MRI abnormalities and clinical condition is poor. Studies using newer MRI techniques, such as magnetization transfer imaging (MTI), diffusion-weighted imaging (DWI), magnetic resonance spectroscopy (MRS), and functional MRI (fMRI), have also been carried out. These techniques are sensitive to a wider range of abnormalities within tissue, and their increased pathological specificity may be helpful in clarifying the underlying pathology of the condition.

Contrast Media↗
PubMed2004

Right hemispheric dysfunction in a case of pure progressive aphemia: fusion of multimodal neuroimaging.

This article describes the unusual case of a 60-year-old woman suffering from pure progressive aphemia. The fusion of multimodal neuroimaging (MRI, perfusion SPECT) implicated the right frontal lobe, especially the inferior frontal gyrus. This area also showed the greatest functional MRI activation during the performance of a covert phonemic fluency task. Results are discussed in terms of bihemispheric language representation. The fusion of three sets of neuroimages has aided in the interpretation of the patient's cognitive brain dysfunction.

Aphasia, Broca↗
PubMed2003

Spin-echo fMRI in humans using high spatial resolutions and high magnetic fields.

The Hahn spin-echo (HSE)-based BOLD effect at high magnetic fields is expected to provide functional images that originate exclusively from the microvasculature. The blood contribution that dominates HSE BOLD contrast at low magnetic fields (e.g., 1.5 T), and degrades specificity, is highly attenuated at high fields because the apparent T(2) of venous blood in an HSE experiment decreases quadratically with increasing magnetic field. In contrast, the HSE BOLD contrast is believed to arise from the microvasculature and increase supralinearly with the magnetic field strength. In this work we report the results of detailed and quantitative evaluations of HSE BOLD signal changes for functional imaging in the human visual cortex at 4 and 7 T. This study used high spatial resolution, afforded by the increased signal-to-noise ratio (SNR) of higher field strengths and surface coils, to avoid partial volume effects (PVEs), and demonstrated increased contrast-to-noise ratio (CNR) and spatial specificity at the higher field strengths. The HSE BOLD signal changes induced by visual stimulation were predominantly linearly dependent on the echo time (TE). They increased in magnitude almost quadratically in going from 4 to 7 T when the blood contribution was suppressed using Stejskal-Tanner gradients that suppress signals from the blood due to its inhomogeneous flow and higher diffusion constant relative to tissue. The HSE signal changes at 7 T were modeled accurately using a vascular volume of 1.5%, in agreement with the capillary volume of gray matter. Furthermore, high-resolution acquisitions indicate that CNR increased with voxel sizes < 1 mm(3) due to diminishing white matter or cerebrospinal fluid-space vs. gray matter PVEs. It was concluded that the high-field HSE functional MRI (fMRI) signals originated largely from the capillaries, and that the magnitude of the signal changes associated with brain function reached sufficiently high levels at 7 T to make it a useful approach for mapping on the millimeter to submillimeter spatial scale.

Adult↗
PubMed2004

Combination of event-related fMRI and diffusion tensor imaging in an infant with perinatal stroke.

Focal ischemic brain injury, or stroke, is an important cause of later handicap in children. Early assessment of structure-function relationships after such injury will provide insight into clinico-anatomic correlation and potentially guide early intervention strategies. We used combined functional MRI (fMRI) with diffusion tensor imaging (DTI) in a 3-month-old infant to explore the structure-function relationship after unilateral perinatal stroke that involved the visual pathways. With visual stimuli, fMRI showed a negative BOLD activation in the visual cortex of the intact right hemisphere, principally in the anterior part, and no activation in the injured hemisphere. The functional activation in the intact hemisphere correlated clearly with the fiber tract of the optic radiation visualized with DTI. DTI confirmed the absence of the optic radiation in the damaged left hemisphere. In addition, event-related fMRI (ER-fMRI) experiments were performed to define the characteristics of the BOLD response. The shape is that of an inverted gamma function (similar to a negative mirror image of the known positive adult BOLD response). The maximum decrease was reached at 5-7 s with signal changes of -1.7 +/- 0.4%.Thus, this report describes for the first time the combined use of DTI and event-related fMRI in an infant and provides insight into the localization of the fMRI visual response in the young infant and the characteristics of the BOLD response.

Asphyxia Neonatorum↗
PubMed1998

Selective effects of methylphenidate in attention deficit hyperactivity disorder: a functional magnetic resonance study.

Functional MRI revealed differences between children with Attention Deficit Hyperactivity Disorder (ADHD) and healthy controls in their frontal-striatal function and its modulation by methylphenidate during response inhibition. Children performed two go/no-go tasks with and without drug. ADHD children had impaired inhibitory control on both tasks. Off-drug frontal-striatal activation during response inhibition differed between ADHD and healthy children: ADHD children had greater frontal activation on one task and reduced striatal activation on the other task. Drug effects differed between ADHD and healthy children: The drug improved response inhibition in both groups on one task and only in ADHD children on the other task. The drug modulated brain activation during response inhibition on only one task: It increased frontal activation to an equal extent in both groups. In contrast, it increased striatal activation in ADHD children but reduced it in healthy children. These results suggest that ADHD is characterized by atypical frontal-striatal function and that methylphenidate affects striatal activation differently in ADHD than in healthy children.

Adolescent↗
PubMed2003

The significance of ear plugging in localization-related epilepsy.

PURPOSE: The localizing value of ear plugging in the treatment of auditory onset partial seizures, to our knowledge, has not been previously described. We propose that ear plugging is a clinical response to a sensory seizure manifested as an auditory hallucination and a tool for identifying the seizure focus in the auditory cortex on the superior temporal gyrus. METHODS: We report on three children who had prior epilepsy surgery for recurrent symptomatic localization-related epilepsy and who, subsequent to their surgery, displayed stereotyped unilateral or bilateral ear plugging at the onset of partial seizures. We studied scalp video electroencephalography (VEEG), magnetoencephalography (MEG), and magnetic resonance imaging (MRI) in all three. Additionally, we used electrocorticography (ECoG) in two patients, intracranial VEEG monitoring in one patient, and functional MRI language mapping in two patients. RESULTS: All three patients plugged their ears with their hands during auditory auras that localized to the superior temporal gyrus and were followed by partial seizures that spread to a wider field, as shown on scalp and intracranial VEEG. All three patients had MEG interictal discharges in the superior temporal gyrus. One patient who was nonverbal and unable to describe an auditory phenomenon plugged the ear contralateral to where temporal lobe-onset seizures and MEG interictal discharges occurred. CONCLUSIONS; Ear-plugging seizures indicate an auditory aura and may also lateralize seizure onset to the contralateral temporal lobe auditory cortex. Stereotyped behaviors accompanied by epileptic seizures in children who have poor communication skills are important in the seizure semiology of localization-related epilepsy.

Adolescent↗
PubMed2006

Policy adjustment in a dynamic economic game.

Making sequential decisions to harvest rewards is a notoriously difficult problem. One difficulty is that the real world is not stationary and the reward expected from a contemplated action may depend in complex ways on the history of an animal's choices. Previous functional neuroimaging work combined with principled models has detected brain responses that correlate with computations thought to guide simple learning and action choice. Those works generally employed instrumental conditioning tasks with fixed action-reward contingencies. For real-world learning problems, the history of reward-harvesting choices can change the likelihood of rewards collected by the same choices in the near-term future. We used functional MRI to probe brain and behavioral responses in a continuous decision-making task where reward contingency is a function of both a subject's immediate choice and his choice history. In these more complex tasks, we demonstrated that a simple actor-critic model can account for both the subjects' behavioral and brain responses, and identified a reward prediction error signal in ventral striatal structures active during these non-stationary decision tasks. However, a sudden introduction of new reward structures engages more complex control circuitry in the prefrontal cortex (inferior frontal gyrus and anterior insula) and is not captured by a simple actor-critic model. Taken together, these results extend our knowledge of reward-learning signals into more complex, history-dependent choice tasks. They also highlight the important interplay between striatum and prefrontal cortex as decision-makers respond to the strategic demands imposed by non-stationary reward environments more reminiscent of real-world tasks.

Adult↗
PubMed2004

Plastic changes of motor network after constraint-induced movement therapy.

The effects of short-term constraint-induced movement (CIM) therapy on the activation of the motor network were investigated with functional magnetic resonance imaging (fMRI). Movement of the less-affected arms of five patients was restricted and intensive training of the affected upper limb was performed. Functional MRI was acquired before and after two-weeks of CIM therapy. All patients showed significant improvement of motor function in their paretic limbs after CIM therapy. For three patients, new activation in the contralateral motor/premotor cortices was observed after CIM therapy. Increased activation of the ipsilateral motor cortex and SMA was observed in the other patient. Our results demonstrated that plastic changes of the motor network occurred as a neural basis of the improvement subsequent to CIM therapy following brain injury.

Adult↗
PubMed1996

[Is magnetic resonance the first indication in neurologic imaging?].

Various methods of neuroradiologie examination are described, with an emphasis on recent developments, in particular in CT scan (angioscan, spiral acquisition) and MRI. CT scan, which is the most accessible method, can answer most questions in intracerebral emergencies (trauma, vascular accidents, intracerebral hypertension ...). Outside the emergency setting, morphological study of the brain by MRI is much superior to that provided by CT scan and should be the first-line examination for investigation of suspected tumour, wite matter lesion.... This is even more evident in exploration of lesions of the posterior cranial fossa. In addition, introduction in the near future of functional MRI should lead to better knowledge of the relationship between cerebral lesions and functional zones. Ultrasonography remains a noninvasive and effective technique to seek lesions of the arteries supplying the brain. For spinal cord disorders, MRI is by far the examination of choice, except when contraindicated by the presence of cardiac pacemaker, metallic foreign bodies in the patient.

Brain Diseases↗
PubMed2006

Non-invasive monitoring of renal oxygenation using BOLD-MRI: a reproducibility study.

Blood oxygenation level-dependent (BOLD) MRI was shown to allow non-invasive observation of renal oxygenation in humans. However, clinical applications of this type of functional MRI of the kidney are still limited, most likely because of difficulties in obtaining reproducible and reliable information. The aim of this study was to evaluate the reproducibility and robustness of a BOLD method applied to the kidneys and to identify systematic physiological changes potentially influencing the renal oxygenation of healthy volunteers. To measure the BOLD effect, a modified multi-echo data image combination (MEDIC) sequence was used to acquire 12 T2*-weighted images within a single breath-hold. Three identical measurements were performed on three axial and three coronal slices of right and left kidneys in 18 volunteers. The mean R2* (1/T2*) values determined in medulla and cortex showed no significant differences over three repetitions and low intra-subject coefficients of variation (CV) (3 and 4% in medulla and cortex, respectively). The average R2* values were higher in the medulla (16.15 +/- 0.11) than in the cortex (11.69 +/- 0.18) (P < 0.001). Only a minor influence of slice orientation was observed. Mean R2* values were slightly higher (3%) in the left than in the right kidney (P < 0.001). Differences between volunteers were identified (P < 0.001). Part of these differences was attributable to age-dependent R2* values, since these values increased with age when medulla (P < 0.001, r = 0.67) or cortex (P < 0.020, r = 0.42) were considered. Thus, BOLD measurements in the kidney are highly reproducible and robust. The results allow one to identify the known cortico-medullary gradient of oxygenation evidenced by the gradient of R2* values and suggest that medulla is more hypoxic in older than younger individuals. BOLD-MRI is therefore a useful tool to study sequentially and non-invasively regional oxygenation of human kidneys.

Adult↗
PubMed2004

Active deep brain stimulation during MRI: a feasibility study.

The goal of this study was to evaluate the feasibility of active deep brain stimulation (DBS) during the application of standard clinical sequences for functional MRI (fMRI) in phantom measurements. During active DBS, we investigated induced voltage, temperature at the electrode tips and lead, forces on the electrode and lead, consequences of defective leads and loose connections, proper operation of the neurostimulator, and image quality. Sequences for diffusion- and perfusion-weighted imaging, fMRI, and morphologic MRI were used. The DBS electrode and lead were placed in a NaCl solution-filled phantom. The results indicate that there are severe potential hazards for patients. Strong heating, high induced voltage, and even sparking at defects in the connecting cable could be observed. However, it was demonstrated that under certain conditions, safe MR examinations during active DBS are feasible. Certain safety precautions are recommended in this report.

Body Temperature↗
PubMedDate not supplied

From signal to image: magnetic resonance imaging physics for cardiac magnetic resonance.

Magnetic resonance imaging (MRI) is a powerful tool which enables the visualization of anatomy and the assessment of many physiological aspects of organ function. MRI and magnetic resonance angiography and magnetic resonance spectroscopy will play critical roles in cardiac applications during the next millennium. Thus, it is important to have a basic understanding of the most important physical processes in MR--the generation of nuclear magnetic resonance signals and their transformation into images. A conceptual description of these processes is the primary focus of this article. Also discussed are some additional signal manipulations specific to the needs of cardiac MRI, a field readily identified as the most significant in modern MRI technology development.

Heart Diseases↗
PubMed2004

Hunting for neuronal currents: absence of rapid MRI signal changes during visual-evoked response.

While recent reports have advocated the use of magnetic resonance imaging (MRI) to detect the effects of neuronal currents associated with human brain activity, only preliminary experimental data have been presented so far to demonstrate the feasibility of the method. Furthermore, it has not been adequately demonstrated that (1) MRI can separate neuronal current (NC) effects from other effects such as blood oxygen level-dependent (BOLD) contrast; (2) MRI has adequate sensitivity to detect NCs in vivo. In this work, we introduce a method that can separate slow (e.g., BOLD) processes from potential rapid (e.g., NC) processes and apply this method to investigate whether MRI allows detection of an NC response to a visual stimulus. MRI studies (n = 8) at 3.0 T using a sensitive multichannel detector showed insignificant effects related to NCs (averaged t < 0.05), in the presence of a highly significant BOLD signal (t = 6.15 +/- 0.90). In contrast, magnetoencephalography (MEG) experiments performed under similar conditions on the same subjects showed highly significant electrical activity (t = 7.90 +/- 2.28). It is concluded that, under the conditions used in this study, the sensitivity of MRI to detect evoked responses through NCs is at least an order of magnitude below that of BOLD-based functional MRI (fMRI) or MEG and too low to be practically useful.

Data Interpretation, Statistical↗
PubMed1997

Vascular imprints of neuronal activity: relationships between the dynamics of cortical blood flow, oxygenation, and volume changes following sensory stimulation.

Modern functional neuroimaging methods, such as positron-emission tomography (PET), optical imaging of intrinsic signals, and functional MRI (fMRI) utilize activity-dependent hemodynamic changes to obtain indirect maps of the evoked electrical activity in the brain. Whereas PET and flow-sensitive MRI map cerebral blood flow (CBF) changes, optical imaging and blood oxygenation level-dependent MRI map areas with changes in the concentration of deoxygenated hemoglobin (HbR). However, the relationship between CBF and HbR during functional activation has never been tested experimentally. Therefore, we investigated this relationship by using imaging spectroscopy and laser-Doppler flowmetry techniques, simultaneously, in the visual cortex of anesthetized cats during sensory stimulation. We found that the earliest microcirculatory change was indeed an increase in HbR, whereas the CBF increase lagged by more than a second after the increase in HbR. The increased HbR was accompanied by a simultaneous increase in total hemoglobin concentration (Hbt), presumably reflecting an early blood volume increase. We found that the CBF changes lagged after Hbt changes by 1 to 2 sec throughout the response. These results support the notion of active neurovascular regulation of blood volume in the capillary bed and the existence of a delayed, passive process of capillary filling.

Animals↗
PubMed2002

Correlation between motor improvements and altered fMRI activity after rehabilitative therapy.

Motor rehabilitation therapy is commonly employed after strokes, but outcomes are variable and there is little specific information about the changes in brain activity that are associated with improved function. We performed serial functional MRI (fMRI) on a group of seven patients receiving a form of rehabilitation therapy after stroke in order to characterize functional changes in the brain that correlate with behavioural improvements. Patients were scanned while performing a hand flexion-extension movement twice before and twice after a two-week home-based therapy programme combining restraint of the unaffected limb with progressive exercises for the affected limb. As expected, the extent of improvement in hand function after therapy varied between patients. Therapy-related improvements in hand function correlated with increases in fMRI activity in the premotor cortex and secondary somatosensory cortex contralateral to the affected hand, and in superior posterior regions of the cerebellar hemispheres bilaterally (Crus I and lobule VI). fMRI offers a promising, objective approach for specifically identifying changes in brain activity potentially responsible for rehabilitation-mediated recovery of function after stroke. Our results suggest that activity changes in sensorimotor regions are associated with successful motor rehabilitation.

Adult↗
PubMed1998

Solvent relaxation by uniformly magnetized solute spheres. The classical-quantal connection.

RATIONALE AND OBJECTIVES: Large magnetic entities, with diameters in the range of 4 nm to 4 microns, are becoming of increasing interest for magnetic resonance imaging (MRI). The smaller are iron oxide nanoparticles, used for the RE system, and the larger are deoxygenated blood cells, for functional MRI. It can be useful to model such systems as magnetized solute spheres in water. Classical computations of 1/T2 have been reported for the larger particles, in the micron range, where the computational complexities are simplified by Monte Carlo methods. For smaller particles, the quantum mechanical (quantal) expressions for outer sphere relaxation, for both 1/T1 and 1/T2, have been available for some time, and are particularly simple to apply at MRI fields. The questions that arise, and which the author addresses, are how to interrelate the classical and quantal approaches and when to use which. METHODS: The author compares published results of Monte Carlo calculations of 1/T2 for diamagnetic polystyrene solute spheres of various sizes in water, made paramagnetic by addition of dysprosium-(DTPA)2-, with quantum mechanical outer sphere theory applied to the same system. The latter includes the usual assumption of motional narrowing and yields both 1/T1 and 1/T2. RESULTS: For particles with diameters less than about 1 micron, both approaches give identical results for 1/T2. For larger particles, the conditions for motional narrowing breakdown, and quantal theory overestimates 1/T2. In addition, in the particular system studied, relaxation becomes so effective near solute that there is insufficient time for all water molecules to experience their maximal effect. Classical theory handles this well whereas quantal theory does not. CONCLUSIONS: In comparing the classical and quantal approaches, one balances computational complexity but broader applicability with more limited but far simpler mathematics. In addition, because the quantal approach shows that 1/T1 and 1/T2 are intimately related, the author suggests, by analogy, how to extend classical methods to computation of 1/T1.

Contrast Media↗
PubMed1996

What have we learned from functional imaging studies in schizophrenia? The role of frontal, striatal and temporal areas.

OBJECTIVES: Functional imaging technologies allow assessment of cerebral blood flow, cerebral metabolism, cellular metabolic processes, cerebral receptor density and occupancy. This review examines the contribution of such studies to our understanding of schizophrenia. The role of the frontal lobes, the basal ganglia, the temporal lobes and the neuronal circuits which connect them is examined with respect to this literature. METHOD: All studies in schizophrenia using positron emission tomography, single photon emission computerised tomography, xenon studies, functional and spectroscopic magnetic resonance imaging formed the basis of this review. Only those studies published in English were reviewed. RESULTS: The most consistent finding in schizophrenia has been that of hypofrontality, while the results of studies examining subcortical structures provide preliminary support for the concept of fronto-striatal dysfunction. Functional imaging has not yet provided consistent results in the study of temporal lobe function. Although receptor studies have shed light on the actions of antipsychotic medications, the findings for dopamine receptor numbers remain controversial. Spectroscopic and functional MRI remain in their infancy as research tools in schizophrenia. CONCLUSIONS: Although there are significant methodological issues to be addressed, functional imaging technology is providing increasing insights into schizophrenia and its treatment. Future research will be truly multidisciplinary as it will require the collaboration of psychiatrists, imaging physicians, neuropsychologists and neuroscientists.

Brain Mapping↗
PubMed1998

Early diagnostic indices for the prevention of Alzheimer's disease.

Recent progress in our understanding of the pathophysiology of Alzheimer's disease (AD) has made it clear that it is a heterogeneous disorder to which both genetic and environmental factors contribute. Therefore, it is unlikely that a single test for the diagnosis of this disease will be developed. Possible candidates for early diagnostic indices have been identified, in addition to biological markers, in the fields of neuropsychology, genetics and neuroimaging. Many studies have indicated that low scores in tests assessing delayed recall predict dementia already years before the actual criteria of dementia are fulfilled. Molecular genetic studies have confirmed that the epsilon4 allele of the apolipoprotein E (APOE) is also a definite risk factor for AD, and other susceptibility genes will probably be identified and confirmed in the near future. Evaluation of the hippocampal atrophy by magnetic resonance imaging (MRI) scans has been reported to be a sensitive and possible specific indicator of mild AD, while possibilities of using functional MRI are currently being explored. A combination of low scores in tests assessing delayed recall, small size of the hippocampus on MRI and APOE epsilon4 might point to a high risk of developing AD. We need extensive follow-up studies to identify which combination of molecular genetic factors and memory test scores supplemented with neuroimaging will prove to be most efficient in diagnosing AD in its preclinical phase, as this is the phase which offers the most promising therapeutic options.

Alzheimer Disease↗