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Results for “functional MRI”

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At least 919 records · Page 51Linked to original sources
PubMed2001

Functional MRI assessment of the hemispheric predominance for language in epileptic patients using a simple rhyme detection task.

This study assesses the interest of a simple fMRI rhyme detection paradigm to determine hemispheric predominance for language in epileptic patients. Nineteen patients were examined. The findings derived from the fMRI examinations were compared with those obtained on the same patients using the Wada test, stereotactic intracerebral EEG stimulations and recordings, and/or video-EEG recordings. For the seventeen patients for whom language dominance could be assessed by means of at least one of the latter procedures, the fMRI examination provided concordant results in sixteen. In two patients, the hemispheric predominance for language could only be determined by fMRI. Nine patients underwent surgery subsequent to the fMRI examination. None of them exhibited any aphasic problems following surgery. The rhyme detection task used in the fMRI examination generates robust responses in the language areas, permits easy monitoring of the patient's task performance and can be easily undertaken by the epileptic patients. Thus, this study demonstrates that the fMRI rhyme detection paradigm is particularly well-suited for determining hemispheric language predominance in epileptic candidates for surgery.

Adult↗
PubMed2002

Simulation of the effects of global normalization procedures in functional MRI.

We report on differences in sensitivity and false-positive rate across five methods of global normalization using resting-state fMRI data embedded with simulated activation. These methods were grand mean session scaling, proportional scaling, ANCOVA, a masking method, and an orthogonalization method. We found that global normalization by proportional scaling and ANCOVA decreased the sensitivity of the statistical analysis and induced artifactual deactivation even when the correlation between the global signal and the experimental paradigm was relatively low. The masking method and the orthogonalization method performed better from this perspective but are both restricted to certain experimental conditions. Based on the results of these simulations, we offer practical guidelines for the choice of global normalization method least likely to bias the experimental results.

Algorithms↗
PubMed2002

Functional MRI of auditory cortex activated by multisite electrical stimulation of the cochlea.

Electrical stimulation of the ear of deaf patients via cochlear implants offers a unique occasion to study activity of central auditory pathways with fMRI, without bias due to scanner noise. Such measurements, however, require one to control the possible interference between fMRI acquisition and the implanted electrodes. A series of measurements on a customized phantom designed to characterize the level of induced currents during MRI acquisition is presented. These experiments demonstrate that the major artifactual contribution is due to radiofrequency interaction and that safe experimental conditions can be obtained with proper shielding of the stimulation cables. The induced currents could be reduced to low levels (<50 microA for a duration <2 ms), below the acoustic perceptual threshold of cochlear implant subjects. Subsequent fMRI experiments on a patient using an Ineraid cochlear implant were conducted. Results revealed bilateral localized activation of the primary auditory cortex. Stimulation of two different intracochlear electrodes elicited activity in two neighboring, but different, regions, in agreement with the known tonotopical organization of the auditory cortex. This work paves the way for fMRI studies of a broad selection of auditory paradigms without interference from unwanted noise.

Artifacts↗
PubMed2002

[Physiological basis of functional MRI].

Afferent neurotransmission of a given neuronal group and its subsequent dendritic activity are followed by a transient hemodynamic response such as an increase of the local blood flow and of the intravascular level of oxygen. This neurovascular regulation involves neurons, astrocytes, interneurons and various transmitter substances. The resulting changes in the magnetic susceptibility is then detected by the MRI machine which can specifically localize regional brain activity. Blood oxygenation level dependent contrast reflects afferent inputs and their post-synaptic (dendritic) processing, rather than the output from the concerned cerebral zone (spiking). In other words, this contrast depends on local informational treatment of an active zone without implying any effective influence upon its targets.

Afferent Pathways↗
PubMedDate not supplied

Functional MRI of the spinal cord: will it solve the puzzle of pain?

PURPOSE: Whether stimulation of the median nerve could evoke an fMR imaging response at 1.5 T in the cervical spinal cord was investigated and the response pattern was compared with that obtained by fist clenching. METHODS: Eleven subjects performed the fist-clenching task and in seven of them electrical stimulation was also applied. fMRI was performed using a T2* sensitive echo-planar imaging sequence gated by the heartbeat signal. A dynamic cardiac-gated T2*-weighted imaging sequence was used to quantify cervical spinal cord activation. Cord activation was measured in the sagittal and transverse imaging planes. RESULTS: With the fist-clenching task, activation of the spinal cord in the cervical intumescence could be seen in seven of eleven subjects in the sagittal plane and in six of nine subjects in whom axial images were acquired. When median nerve stimulation was applied, cord activation was seen in the sagittal images in five out of seven, and in the axial plane in two out of six subjects. A consistent cross-sectional localization of the activity measured in the spinal cord was not detected, either in terms of the right and left sides or in terms of the posterior and anterior directions. CONCLUSION: In the sagittal plane, median nerve stimulation at the elbow can evoke an fMR imaging response in the lower cervical spinal cord. The activation pattern was comparable with that obtained by fist clenching.

Cervical Vertebrae↗
PubMed1995

[The motor hand area. Noninvasive detection with functional MRI and surgical validation with cortical stimulation].

In this study, activation of cortical sites by specific motor tasks (opening and closing of the hand) was examined by fMRI utilizing the blood-oxygen-level-dependent (BOLD) technique. fMRI was employed in five volunteers and in six patients with tumors in the vicinity of the central region. In the patients, the fMRI data and intraoperative cortical mapping were compared. Our results indicate good correlation of these two methods and that there are no significant differences in the localization of the motor hand area.

Adult↗