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Results for “functional MRI”

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At least 199 records · Page 11Linked to original sources
PubMed2001

Functional MRI as a tool to assess vision in dogs: the optimal anesthetic.

Functional magnetic resonance imaging (fMRI) is a recent advance in neuroimaging that provides a picture of brain activity with excellent spatial resolution. Current methods used to evaluate canine vision are poorly standardized and vulnerable to bias. Functional MRI may represent a valuable method of testing vision in dogs if the impacts of anesthesia on fMRI are understood. Six dogs were scanned during visual stimulation, each under three different anesthetic protocols (isoflurane, propofol, fentanyl/midazolam) to address the questions: (1) Can visually evoked fMR signals be reliably recorded in anesthetized dogs? and (2) Which anesthetic agent permits the least suppression of visually induced fMR signal in dogs? This study confirms that visual stimuli reliably elicit neural activity and fMR signal change in anesthetized dogs. No significant differences in images acquired under the three anesthetics were found, and there was no significant relationship between anesthetic dose and brain activity, within the range of doses used in this study. Images obtained during isoflurane anesthesia were more consistent between dogs than those obtained with the other two agents. This reduced variation may reflect the fact that inhalant anesthesia is more easily controlled than intravenous anesthesia under conditions associated with high field fMRI.

Anesthesia↗
PubMed1995

Non-invasive measurement of brain activity using functional MRI: toward the study of brain response to acupuncture stimulation.

We studied functional MRI in 15 male and 13 female normal volunteers on a clinical MRI system using gradient echo sequence. During the experiments, brain activation was induced by grasping the unilateral hand once or twice a second for motor tasks. A localized increase of MRI signal in the contralateral motor cortex was observed in 17 out of 21 cases (81%) under right hand motor task and 11 out of 21 cases (52%) under left hand motor task. The application of this method may be useful to evaluate brain response to acupuncture.

Acupuncture Therapy↗
PubMed2004

A high-field functional MRI study of quadri-lingual subjects.

We assessed six multilingual subjects by functional MRI using a Noun Verb Generation task in four different languages. We hypothesised that the degree of proficiency in each language would be related to the extent of functional activity measured in a region of interest analysis. Proficiency in each language was quantified using two neuropsychological tests. All four languages activated overlapping brain areas, corresponding to the major language regions. The number of activated voxels correlated with proficiency, so that the activated volume increased for languages in which a subject had poorer proficiency. Activation did not appear to be dependent on the age at which the language was learnt.

Adult↗
PubMed1999

Real-time 3D image registration for functional MRI.

Subject head movements are one of the main practical difficulties with brain functional MRI. A fast, accurate method for rotating and shifting a three-dimensional (3D) image using a shear factorization of the rotation matrix is described. Combined with gradient descent (repeated linearization) on a least squares objective function, 3D image realignment for small movements can be computed as rapidly as whole brain images can be acquired on current scanners. Magn Reson Med 42:1014-1018, 1999.

Brain↗
PubMed2000

Effects of methylphenidate on functional MRI blood-oxygen-level-dependent contrast.

OBJECTIVE: The authors' goal was to determine potential hemodynamic consequences of methylphenidate on functional magnetic resonance imaging (MRI) blood-oxygen-level-dependent (BOLD) contrast. METHOD: BOLD and perfusion changes were recorded from the motor cortex of six healthy subjects while they performed flexion-extension movements of the right index finger (finger tapping) at varying rates before and after oral methylphenidate administration. RESULTS: Functional MRI signals increased monotonically with faster movement rates. Subjects' heart rates increased modestly after methylphenidate administration, but no changes in finger tapping performance or functional MRI signals were observed. CONCLUSIONS: Methylphenidate does not alter BOLD neural-hemodynamic coupling. Consequently, functional MRI can be used to map neural systems that subserve cognitive operations (e.g., attention and executive processes) in subjects taking methylphenidate.

Adult↗
PubMed2006

Improved anatomic delineation of the antidepressant response to partial sleep deprivation in medial frontal cortex using perfusion-weighted functional MRI.

This study used functional magnetic resonance imaging (fMRI) to clarify the sites of brain activity associated with the antidepressant effects of sleep deprivation (SD). We hypothesized: 1) depressed responders' baseline ventral anterior cingulate (AC) perfusion will be greater than that of nonresponders and controls; 2) following partial sleep deprivation (PSD), ventral AC perfusion will significantly decrease in responders only. Seventeen unmedicated outpatients with current major depression and eight controls received perfusion-weighted fMRI and structural MRI at baseline and following 1 night of late-night PSD. Talairach-transformed gray matter masks were merged with Talairach Daemon-based region of interest (ROI) templates. Baseline left ventral AC (LVAC) perfusion was greater in responders than nonresponders. There was no difference involving the medial frontal cortex. Responders' LVAC perfusion dropped from baseline to PSD scans compared with nonresponders and controls, as did perfusion in the right dorsal AC. In the patient group as a whole, decrease in LVAC perfusion from baseline to PSD scans correlated directly with the decrease in the modified 17-item Hamilton Depression Rating Scale (HDRS17) between baseline and PSD conditions. These data--the first using fMRI--show greater anatomic specificity than previous findings of SD and depression in linking decreased brain activity in this area with clinical improvement.

Adolescent↗
PubMed1999

EEG-triggered functional MRI of interictal epileptiform activity in patients with partial seizures.

EEG-triggered functional MRI (fMRI) offers the potential to localize the generators of scalp EEG events, such as interictal epileptiform discharges, using a biological measurement as opposed to relying solely on modelling techniques. Although recent studies have demonstrated these possibilities in a small number of patients, wider application has been limited by concerns about patient safety, severe problems due to pulse-related artefact obscuring the EEG trace, and lack of reproducibility data. We have systematically studied and resolved the issues of patient safety and pulse artefact and now report the application of the technique in 24 experiments in 10 consecutive patients with localization-related epilepsy and frequent interictal epileptiform discharges (spikes or spike wave). At least two experiments were performed for each patient. In each experiment, 10- or 20-slice snapshot gradient-echo planar images were acquired approximately 3.5 s after a single typical epileptiform discharge (activation image) and in the absence of discharges (control image). Between 21 and 50 epileptiform discharges were sampled in each experiment. The significance of functional activation was tested using the t test at 95% confidence on a pixel-by-pixel basis. Six of the 10 patients showed reproducible focal changes of the blood oxygen level-dependent (BOLD) signal, which occurred in close spatial relationship to the maximum of the epileptiform discharges in the concurrent EEG. No reproducible focal BOLD signal changes were observed in the remaining four patients. In conclusion, EEG-triggered fMRI is now a sufficiently developed technique to be more widely used in clinical studies, demonstrating that it can reproducibly localize the brain areas involved in the generation of spikes and spike wave in epilepsy patients with frequent interictal discharges.

Adult↗
PubMed2000

Pharmacological magnetic resonance imaging: a new application for functional MRI.

Various methods, including functional magnetic resonance imaging (fMRI), have recently been developed to allow investigators to study functional activity in the living brain. Such techniques are now being used to investigate regionally specific brain activity associated with the administration of CNS-active drugs. fMRI in particular is increasingly recognized as being a relatively non-invasive way to perform pharmacological investigations in experimental animals, healthy human volunteers, and individuals with CNS disease. This use of fMRI, dubbed 'pharmacological MRI' or 'phMRI', holds the promise of providing relatively straightforward pharmacodynamic assays and can be used to establish brain-penetrability parameters, or dose-ranging information for novel therapeutic compounds.

Anesthetics↗
PubMed2000

A milestone for normal development of the infantile brain detected by functional MRI.

OBJECTIVE: To investigate the relationship between cerebral cortical function and white matter myelination in the visual pathway in the evaluation of normal brain development. METHODS: The authors performed quantitative analysis of white matter myelination detected with conventional T1-weighted spin echo (SE) MRI and brain functional MRI (fMRI) using echoplanar imaging with photic stimulation in 27 neurologically normal infants (age range, 0 to 22 weeks). RESULTS: An age-dependent gradual increase in signal intensity was observed in optic radiation on the T1-weighted SE images, indicating progression of white matter myelination. A rapid age-dependent reverse in signal response was observed on fMRI. Infants older than 8 weeks showed a stimulus-induced signal decrease in the visual cortex, whereas infants younger than 7 weeks showed a signal increase. CONCLUSIONS: A rapid inversion of response revealed by fMRI with photic stimulation in infants suggests a change in oxygen consumption during neuronal activation, which is related to rapid synapse formation and accompanying increased metabolism. fMRI can detect dynamic metabolic changes during brain maturation, which is a different developmental process from white matter myelination. The metabolic changes detected by fMRI provide a milestone for the evaluation of normal brain development.

Brain↗
PubMed2000

Frequency dependence of the functional MRI response after electrical median nerve stimulation.

Localizing sensorimotor areas with high resolution functional MRI is of considerable interest for a wide range of medical applications from the preoperative planning of neurosurgical interventions to determining the course of neuroplastic reorganisation after brain lesions. We examined the effect of the stimulation frequency on the blood oxygen level dependent (BOLD) fMRI response and on perfusion weighted fMRI using electrical median nerve stimulation at 5, 15, 40, and 100 Hz. BOLD fMRI was performed using a single shot gradient echo EPI sequence to acquire 15 contiguous slices. For the qualitative flow sensitive studies, a single slice inversion recovery prepared spin echo echoplanar sequence (IR-SE EPI) was used. In the primary sensorimotor cortex, a linear increase of the fMRI-BOLD response, affecting both the number of activated pixels and the amplitude of the signal changes, was seen with increasing stimulation frequencies. The qualitative in-flow sensitive studies, using the IR-SE EPI sequence, indicate that the tissue perfusion also increases over the same range of frequencies. This implicates that larger fMRI responses can be obtained if electrical median nerve stimulation is performed at higher frequencies. The results are compared with electrophysiological data, which show a decrease of the early somatosensory evoked potentials at higher frequencies.

Adult↗
PubMed2006

Discrimination of errors from neuronal activity in functional MRI of the human spinal cord by means of general linear model analysis.

Functional MRI (fMRI) of the spinal cord has been demonstrated to provide reliable and sensitive maps of neuronal activity, particularly when combined across several experiments. Individual experiments reveal neuronal activity as well as errors. The dominant source of errors is hypothesized to be physiological motion, including cardiac and respiratory motion, flow of blood and cerebrospinal fluid (CSF), and motion of the spinal cord within the spinal canal. All of the hypothesized sources of error are therefore related to cardiac and respiratory motion, which can be recorded during an fMRI experiment. Analyses were carried out with a general linear model (GLM) with peripheral pulse and respiration recordings used as models of errors. The results demonstrate that the sensitivity of spinal fMRI is improved and errors are reduced when peripheral pulse traces are used in the GLM, but no improvement was detected with the inclusion of respiratory traces.

Humans↗
PubMed2006

Somatomotor functional MRI in a hypertensive arachnoid cyst.

In this article the authors report the study by functional MRI, before and after surgery, of the motor cerebral cortex surrounding a large hypertensive arachnoid cyst. They stress that the functional modifications due to surgery are more relevant than suggested by the simple morphological data.

Arachnoid Cysts↗
PubMed1994

Reduction of signal fluctuation in functional MRI using navigator echoes.

Functional magnetic resonance imaging is sensitive to signal fluctuations due to physiological motion and system instability. In this paper, motion-related signal fluctuations are studied, and a method that uses navigator echoes to monitor and compensate for signal fluctuations in a gradient-echo sequence is described. The technique acquires a "navigator" signal before the application of the phase-encoding and readout gradients and corrects the phase of the subsequently acquired imaging data. This technique was implemented on a 4 Tesla whole body system and validated on normal volunteers. With this technique, temporal fluctuations in image intensity were substantially reduced and improved functional activation maps were obtained.

Artifacts↗
PubMed1997

Improved activation maps via the elimination of motion effects through time-domain mixing of data in conventional gradient echo functional MRI.

To date, most functional imaging centers have relied on ultrafast imaging approaches such as echo-planar imaging (EPI) techniques for acquiring functional brain activation data. These methods require specialized hardware and are not yet installed widely on clinical MR imagers, thus limiting the application of functional MR imaging at many sites. EPI is used to limit motion artifacts and to collect multiple images under different task paradigms in order to distinguish reliably true signal changes from noise. However, it suffers from poor signal to noise ratio because of the high sampling bandwidth employed. This work presents an approach for increasing the efficiency of functional studies that use conventional gradient echo imaging. In this approach, small numbers of image data sets are acquired and recombined to generate composite datasets with minimized motion artifacts. The technique is introduced, and several algorithms for combining the data are explored. A receiver operator characteristic analysis and in vivo studies are performed to examine the efficacy of this approach for improving functional MR imaging studies.

Algorithms↗
PubMedDate not supplied

Functional MRI of the kidney.

Functional MR imaging of the kidney has a great potential of development because the functional parameters, which can be approached noninvasively, are multiple: glomerular filtration, tubular concentration and transit, blood volume and perfusion, diffusion, and oxygenation. Until now, its limitations in clinical applications are due to the difficulties in obtaining reproducible and reliable information in this mobile organ and, sometimes, in understanding the physiologic substrate of the signal changes observed. These approaches require either endogeneous contrast agents, such as water protons (for perfusion and diffusion) or deoxyhemogobin (for oxgenation), or exogeneous contrast agents such as gadolinium chelates (for filtration and perfusion) or iron oxide particles (for perfusion). Clinical validation of these methods and evaluation of their clinical impact are now worthwhile before diffusing them in clinical practice.

Contrast Media↗
PubMed2001

Neuroanatomical discrimination between manipulating and maintaining processes involved in verbal working memory; a functional MRI study.

We used functional magnetic resonance imaging (fMRI) to investigate neural correlates of processes concerning store and manipulation in verbal working memory. We prepared a revised lag 1 digit span, digit span and a simple number detection task. Specific activities in association with manipulating process were identified in the right middle (BA 9/46) and left precentral gyrus (BA 6). Activated areas specific to maintaining process were detected in the right middle (right BA 11/10) and medial (BA 6) frontal gyri, the right inferior parietal lobule (BA 40), and the left middle (BA 9) and inferior frontal gyri (BA 44). The process-nonspecific activated areas common to two processes were identified in the right inferior frontal gyrus (BA 47) and the left superior parietal lobule (BA 7). Using the signal percent change of each subject, we calculated the correlation coefficients among each activated area. The results of this analysis showed that two processes of verbal working memory were clearly discriminated. The two essential processes of manipulation and maintenance in working memory seem to activate process-specific and overlapping (process-nonspecific) areas, but the patterns of combination were definitely different.

Adult↗
PubMed2002

Insights into new techniques for high resolution functional MRI.

Non-invasive functional magnetic resonance imaging (fMRI) has opened a unique window into human and animal brain function, with a spatial resolution of a few millimeters and a temporal resolution of a few seconds. To further improve the current technical limitations of fMRI, various post-processing and data acquisition schemes were developed. Improved fMRI methods include variations of a conventional fMRI technique, mapping a single physiological parameter such as cerebral blood flow or cerebral blood volume, and direct mapping of neural activity. Advances in fMRI techniques allow scientists to map submillimeter columnar and laminar functional structures and to detect tens of millisecond neural activity in certain specific tasks.

Animals↗
PubMed2006

Neural correlates of enhanced working-memory performance in dissociative disorder: a functional MRI study.

BACKGROUND: Memory functioning has been highlighted as a central issue in pathological dissociation. In non-pathological dissociation, evidence for enhanced working memory has been found, together with greater task-load related activity. So far, no imaging studies have investigated working memory in dissociative patients. METHOD: To assess working memory in dissociative patients functional magnetic resonance imaging was used during performance of a parametric, verbal working-memory task in patients with a dissociative disorder (n=16) and healthy controls (n=16). RESULTS: Imaging data showed that both groups activated brain regions typically involved in working memory, i.e. anterior, dorsolateral and ventrolateral prefrontal cortex (PFC), and parietal cortex. Dissociative patients showed more activation in these areas, particularly in the left anterior PFC, dorsolateral PFC and parietal cortex. In line with these findings, patients made fewer errors with increasing task load compared to controls, despite the fact that they felt more anxious and less concentrated during task performance. CONCLUSIONS: These results extend findings in non-pathological high dissociative individuals, suggesting that trait dissociation is associated with enhanced working-memory capacities. This may distinguish dissociative patients from patients with post-traumatic stress disorder, who are generally characterized by impaired working memory.

Adult↗