Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “functional MRI”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
PubMed1997

[Theory and clinical application of functional MRI: 3D-functional brain mapping].

Functional magnetic resonance imaging (fMRI) was performed using a clinical 1.5 T MR scanner. Normal volunteers and patients with several neurological disorders were studied with somatosensory stimulation using sponge at right hand and visual stimulation using checkerboard pattern. Both fMR images by gradient echo echo planar imaging and three dimensional gradient echo images were studied. Reconstructed 3 dimensional functional brain mapping was superimposed on 3D anatomical images. Apparent signal increase was observed at contra lateral sensorimotor cortex and secondary sensory cortex with sponge stimulation. In the case of left homonymous hemianopia due to cerebral infarction, increasing signal was only observed surrounding left calcarine fissure by using stimulation of all visual field. In conclusion, fMRI and 3-D functional brain mapping has extremely high potentiality to examine pathophysiology of various neurological disorders.

Brain↗
PubMed1999

[Functional MRI: brain plasticity, brain disease and functional recovery].

Brain plasticity may be defined as long-term alteration in behavior related activity of distributed neural systems. Functional imaging, and particularly functional MRI, allows to investigate the mechanisms underlying brain plasticity. Two aspects may be distinguished: one is learning in healthy subjects; the other is functional reorganization following or associated with acute or chronic brain injury. Because functional MRI is totally non invasive, it appears well suited to follow such reorganization over time. This theme will be developed in the following text.

Brain Diseases↗
PubMed1996

[Functional MRI: imaging of motor cortex function].

OBJECTIVE: To image the motor cortex with functional MRI (fMRI), and locate the activated area with the proportional grid of Talairach. DESIGN: Descriptive. SETTING: St. Radboud Academic Hospital Nijmegen. METHODS: In ten volunteers functional images of the motor cortex were made during execution of a motor task (finger movements). From the functional images the positions of activated areas were calculated using the 3D Talairach grid system. RESULTS: fMRI of the motor cortex was possible using a 1.5 T MRI scanner. Task activation of the motor cortex gave a signal increase in Brodmann's area 4, the precentral gyrus. CONCLUSION: Imaging of the active motor cortex with fMRI is feasible. The use of the 3D Talairach proportional grid system for the calculation of the position of an activated area in the motor cortex is possible with adequate accuracy.

Adult↗
PubMed1999

[Brain plasticity during development: physiological bases and functional MRI approach].

Brain functional MRI (fMRI) is a new tool for the study of the development of cognitive functions in healthy children ("natural plasticity"), as well as for the assessment of functional reorganization following brain lesions. However, methodological difficulties related to the pediatric population (movements, cooperation), along with unsolved issues about the influence of physiological parameters of the immature brain on fMRI results, explain the limited number of published studies. Normal brain maturation is characterized by a transient phase of synaptic redundancy followed by selective synaptic regression until adulthood, that forms the neurobiological correlates of both learning and individual variability of cortical anatomy and functional organization, and of the large potential for post-lesional plasticity in children. fMRI in school-age children demonstrated activation patterns comparable to adults during motor, language, and working memory tasks. In neonates and infants, fMRI showed significant differences of visual cortex activation. Post-lesional plasticity is more pronounced in younger children. In motor cortex, activation of ipsilateral hemisphere may be seen in cases of rolandic lesions. Interhemispheric shift of language networks occurs mostly in cases of destructive or large brain lesions, or in cases of early refractory epilepsy.

Adult↗
PubMed2003

[Lyrical and musical auditive mental imagery in functional MRI].

PURPOSE: to explore with functional MRI cerebral areas involved in musical and lyrical sounds signal processing with the mental imagery method. MATERIAL: and METHODS: nine volunteers (mean age: 27 years old) underwent functional MRI with BOLD contrast at 1.5 T. Box-car paradigms of partial recollections of musical or lyrical memories tasks were performed. Statistical correlations mappings were calculated and superimposed on previously realigned anatomical reference imaging to observe activated cerebral areas. RESULTS: all except one subjects had activation areas in primary and secondary auditive cortices in the temporal Heschl gyrus and the Planum Temporale, unilaterally (n=2) or bilaterally (n=6) during both mental tasks. Contralateral activation improvement was observed in 4 cases when the lyrical tasks were performed. Temporal and insular regions involved in language processing were observed in eight of nine subjects. CONCLUSION: auditive mental imagery can show in functional MRI cerebral areas involved in auditive functions and some of the areas involved in language processing.

Adult↗
PubMed2000

Functional MRI: background and clinical applications.

Functional MRI is gaining wider acceptance as a clinical tool that can be used for a variety of clinical indications. The goal of this article is to introduce the reader to functional MRI as a technique and present some clinical applications of functional MRI.

Brain↗
PubMed2000

Cortical motor reorganization in akinetic patients with Parkinson's disease: a functional MRI study.

Using functional MRI (fMRI), we have studied the changes induced by the performance of a complex sequential motor task in the cortical areas of six akinetic patients with Parkinson's disease and six normal subjects. Compared with the normal subjects, the patients with Parkinson's disease exhibited a relatively decreased fMRI signal in the rostral part of the supplementary motor area (SMA) and in the right dorsolateral prefrontal cortex, as previously shown in PET studies. Concomitantly, the same patients exhibited a significant bilateral relative increase in fMRI signal in the primary sensorimotor cortex, lateral premotor cortex, inferior parietal cortex, caudal part of the SMA and anterior cingulate cortex. These fMRI data confirm that the frontal hypoactivation observed in patients with Parkinson's disease is restricted to the rostral part of the SMA and to the dorsolateral prefrontal cortex. These results also show that, apart from the lateral premotor and parietal cortices, increased fMRI signals can be found in other cortical motor areas of these patients, including the posterior SMA, the anterior cingulate cortex and the primary sensorimotor cortices, which are then likely to participate in the same putative attempt by the dopamine-denervated brain to recruit parallel motor circuits in order to overcome the functional deficit of the striatocortical motor loops.

Aged↗
PubMed2001

Metabolic and electrophysiological validation of functional MRI.

OBJECTIVES: Although functional MRI is widely used for preoperative planning and intraoperative neuronavigation, its accuracy to depict the site of neuronal activity is not exactly known. Experience with methods that may validate fMRI data and the results obtained when coregistering fMRI with different preoperative and intraoperative mapping modalities including metabolically based (18)F-fluorodeoxyglucose PET, electrophysiologcally based transcranial magnetic stimulation (TMS), and direct electrical cortical stimulation (DECS) are described. METHODS: Fifty patients were included. PET was performed in 30, TMS in 10, and DECS in 41 patients. After coregistration using a frameless stereotactic system, results were grouped into overlapping (<1 cm distance), neighbouring (<2 cm), or contradictory (>2 cm). RESULTS: Comparing fMRI with PET, 18 overlapping, seven neighbouring, and one contradictory result were obtained. In four patients no comparison was possible (because of motion artefacts, low signal to noise ratio, and unusual high tumour metabolism in PET). The comparison of TMS and fMRI showed seven overlapping and three neighbouring results. In three patients no DECS results could be obtained. Of the remaining 38 patients, fMRI hand motor tasks were compared with DECS results of the upper limb muscles in 36 patients, and fMRI foot motor tasks were compared with DECS results of the lower limb on 13 occasions. Of those 49 studies, overlapping results were obtained in 31 patients, and neighbouring in 14. On four occasions fMRI did not show functional information (because of motion artefacts and low signal to noise). CONCLUSIONS: All validation techniques have intrinsic limitations that restrict their spatial resolution. However, of 50 investigated patients, there was only one in whom results contradictory to fMRI were obtained. Although it is not thought that fMRI can replace the intraoperatively updated functional information (DECS), it is concluded that fMRI is an important adjunct in the preoperative assessment of patients with tumours in the vicinity of the central region.

Adult↗
PubMed1997

Object shape processing in the visual system evaluated using functional MRI.

We used functional MRI (fMRI) to determine the cortical regions activated during processing of visual object shape in humans in six men and three women, using a paradigm with a baseline condition of simple shape detection and an activated condition of object/nonobject shape discrimination. Eight of the nine subjects studied showed significant signal changes. Seven of eight showed changes in the occipital lobes (five bilateral, two right only, one left only). All eight subjects with signal changes exhibited changes in the parietal lobes bilaterally. In the occipitotemporal gyri, there were signal changes bilaterally in seven subjects and unilaterally, on the right, in one. Activation-related fMRI signal increases were also present in the posterior superior and middle temporal gyri in seven of the subjects, with four showing bilateral signal changes, two showing signal changes on the left only, and one only on the right. The data strongly suggest that processing of object shape information in humans activates both the ventral and dorsal visual processing pathways ("what" and "where" pathways), described previously both in humans and in nonhuman primates.

Adult↗
PubMed2002

Accessory hardware for neuromuscular measurements during functional MRI experiments.

Functional magnetic resonance imaging (fMRI) is increasingly being used for human sensorimotor function research. Few studies, however, have been able to acquire peripheral neuromuscular data (e.g. joint force and electromyograms [EMG]) online with fMRI measurements. The lack of muscle output information hinders interpretation of fMRI data and prevents investigators from designing more sophisticated experiments. We developed a data-acquisition system that can record force and EMG data simultaneously with fMRI signals. This system included three major components: a hydraulic, pressure transducer-based force measurement device, a well-shielded EMG-recording apparatus, and a visual feedback setup. The three components were integrated with a laptop computer equipped with data acquisition hardware and software. System evaluation experiments demonstrated that no significant mutual interference occurred between the MRI environment and the force-EMG data-acquisition system, i.e. the system can record relatively noise-free force and EMG signals while maintaining the quality of fMRI data. The system has enabled us to study human motor control function involving motor tasks such as handgrip and finger pinch that require precision control of force and EMG. This accessory equipment can facilitate fMRI investigations of human sensorimotor function.

Brain↗
PubMed1999

Sources of distortion in functional MRI data.

Functional magnetic resonance image (fMRI) experiments rely on the ability to detect subtle signal changes in magnetic resonance image time series. Any areas of signal change that correlate with the neurological stimulus can then be identified and compared with a corresponding high-resolution anatomical scan. This report reviews some of the several artefacts that are frequently present in fMRI data, degrading their quality and hence their interpretation. In particular, the effects of magnetic field inhomogeneities are described, both on echo planar imaging (EPI) data and on spiral imaging data. The modulation of these distortions as the subject moves in the magnet is described. The effects of gradient coil nonlinearities and EPI ghost correction schemes are also discussed.

Artifacts↗
PubMed2002

Test-retest reliability estimation of functional MRI data.

Functional magnetic resonance imaging (fMRI) data are commonly used to construct activation maps for the human brain. It is important to quantify the reliability of such maps. We have developed statistical models to provide precise estimates for reliability from several runs of the same paradigm over time. Specifically, our method extends the premise of maximum likelihood (ML) developed by Genovese et al. (Magn Reson Med 1997;38:497-507) by incorporating spatial context into the estimation process. Experiments indicate that our methodology provides more conservative estimates of true positives compared to those obtained by Genovese et al. The reliability estimates can be used to obtain voxel-specific reliability measures for activated as well as inactivated regions in future experiments. We derive statistical methodology to determine optimal thresholds for region- and context-specific activations. Empirical guidelines are also provided on the number of repeat scans to acquire in order to arrive at accurate reliability estimates. We report the results from experiments involving a motor paradigm performed on a single subject several times over a period of 2 months.

Brain↗
PubMed2004

Default-mode network activity distinguishes Alzheimer's disease from healthy aging: evidence from functional MRI.

Recent functional imaging studies have revealed coactivation in a distributed network of cortical regions that characterizes the resting state, or default mode, of the human brain. Among the brain regions implicated in this network, several, including the posterior cingulate cortex and inferior parietal lobes, have also shown decreased metabolism early in the course of Alzheimer's disease (AD). We reasoned that default-mode network activity might therefore be abnormal in AD. To test this hypothesis, we used independent component analysis to isolate the network in a group of 13 subjects with mild AD and in a group of 13 age-matched elderly controls as they performed a simple sensory-motor processing task. Three important findings are reported. Prominent coactivation of the hippocampus, detected in all groups, suggests that the default-mode network is closely involved with episodic memory processing. The AD group showed decreased resting-state activity in the posterior cingulate and hippocampus, suggesting that disrupted connectivity between these two regions accounts for the posterior cingulate hypometabolism commonly detected in positron emission tomography studies of early AD. Finally, a goodness-of-fit analysis applied at the individual subject level suggests that activity in the default-mode network may ultimately prove a sensitive and specific biomarker for incipient AD.

Adult↗
PubMed2005

Reduced basal activity and increased functional homogeneity in sensorimotor and striatum of a Parkinson's disease rat model: a functional MRI study.

Functional neuro-imaging studies of Parkinson's disease (PD) patients and animal models show inconsistent cortical responses to sensory stimulation: some present increased sensorimotor cortex activation contradicting classical basal ganglia-cortex circuitry models, whereas others show decreased activation. As functional neuro-imaging activation is defined as the signal difference between stimulation ON and stimulation OFF, reduced 'activation' can point to either increased neuronal activity during stimulation ON or to decreased basal neuronal activity during stimulation OFF. A unique non-invasive method that uses the temporal and the spatial variances of functional magnetic resonance imaging signal is employed here to compare basal neuronal activity levels and 'functional homogeneity' between groups. Based on the assumption that the temporal variance reflects average neuronal activity, the variance of activity within a predefined region is defined as the region's 'functional homogeneity', which is assumed to estimate neuronal synchronization. Comparison of temporal and spatial variances of the sensorimotor cortex and the striatum in the 6-hydroxydopamine (6-OHDA) PD rat model and a control rat group show bilaterally decreased temporal and spatial variances in the 6-OHDA rat group, suggesting bilateral reduction of basal neuronal activity levels together with an increase in local neuronal synchronization in line with classical basal ganglia-cortex circuit models.

Adrenergic Agents↗
PubMed2000

Brain activation in the processing of Chinese characters and words: a functional MRI study.

Functional magnetic resonance imaging was used to identify the neural correlates of Chinese character and word reading. The Chinese stimuli were presented visually, one at a time. Subjects covertly generated a word that was semantically related to each stimulus. Three sorts of Chinese items were used: single characters having precise meanings, single characters having vague meanings, and two-character Chinese words. The results indicated that reading Chinese is characterized by extensive activity of the neural systems, with strong left lateralization of frontal (BAs 9 and 47) and temporal (BA 37) cortices and right lateralization of visual systems (BAs 17-19), parietal lobe (BA 3), and cerebellum. The location of peak activation in the left frontal regions coincided nearly completely both for vague- and precise-meaning characters as well as for two-character words, without dissociation in laterality patterns. In addition, left frontal activations were modulated by the ease of semantic retrieval. The present results constitute a challenge to the deeply ingrained belief that activations in reading single characters are right lateralized, whereas activations in reading two-character words are left lateralized.

Adult↗
PubMed1999

Perfusion-based event-related functional MRI.

Perfusion-based event-related functional MRI was performed by measuring flow-sensitive alternating inversion recovery (FAIR) signal changes during repeated single-trial, short visual stimulation (250 msec). In the visual cortex activation area, the blood flow increases immediately after the stimulus, reaches the maximum 4 sec later with a perfusion-sensitized signal change of 16. 1 +/- 2.6 %, and then decreases to baseline approximately 11 sec after the stimuli. As it is a more direct reflection of the hemodynamic response, perfusion-based event-related functional MRI techniques may be more useful for human cognitive function studies, compared with blood oxygenation level-dependent (BOLD)-based event-related functional MRI techniques. Magn Reson Med 42:1011-1013, 1999.

Cerebrovascular Circulation↗
PubMed1998

Pilot study of functional MRI to assess cerebral activation of motor function after poststroke hemiparesis.

BACKGROUND AND PURPOSE: Studies of cerebral activation of motor function after ischemic stroke may enhance our understanding of the underlying mechanisms of motor functional recovery, including the role of the noninfarcted hemisphere. METHODS: Eight right-handed recovering hemiparetic or hemiplegic patients were studied using functional MRI. Results were evaluated for each patient to consider individual variability in original functional organization, neuroanatomy, infarct size and extent, treatment, age, and sex. The results were also pooled as a group for comparison with a control group of eight right-handed normal subjects. RESULTS: In six of eight stroke patients, extended activation in ipsilateral sensorimotor cortex was observed during paretic hand movements. Bilateral activation of the primary sensorimotor cortex was recorded in three of these six patients; ipsilateral activation alone was recorded in the remaining three patients. Only two patients had mild synkinesia. Furthermore, in two male patients, the paretic hand movements activated extended areas of ipsilateral premotor and dorsolateral prefrontal cortex, when compared with normal subjects. In two patients with left frontal infarction, profound activation in the right supramarginal gyrus and in the right premotor cortex was observed during the ipsilateral paretic hand movements. CONCLUSIONS: Synkinesia alone cannot explain the extent of ipsilateral activation in primary sensorimotor cortex. The explanation offered for our findings is that preexisting uncrossed motor neural pathways may be accessed or recruited to compensate for damage to the crossed motor pathways after ischemic stroke.

Adult↗