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Results for “functional MRI”

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At least 955 records · Page 53Linked to original sources
PubMed2000

Single breath-hold 3D contrast-enhanced method for assessment of cardiac function.

Cardiac MRI function measurements are typically performed using 2D sequences and require multiple breath-holds to image the entire heart. A single 3D acquisition using a T(1)-shortening agent has many potential advantages over techniques that acquire multiple 2D images, including more consistent contrast and precise slice coverage. However, 3D techniques currently require much longer than a single breath-hold to complete. It has been shown that for MR angiography undersampled projection reconstruction can acquire much higher resolution per unit time than Fourier imaging with acceptable artifacts. By employing a gated, undersampled projection technique, high-resolution 3D multiphase volumes of the heart can be acquired in a single breath-hold. Short repetition times result in good myocardial suppression and a temporal aperture of 60 ms.

Contrast Media↗
PubMed2003

Visualization of the eloquent motor system by integration of MEG, functional, and anisotropic diffusion-weighted MRI in functional neuronavigation.

BACKGROUND: In this study, we visualized the eloquent motor system including the somatosensory-motor cortex and corticospinal tract on a neuronavigation system, integrating magnetoencephalography (MEG), functional magnetic resonance imaging (fMRI), and anisotropic diffusion-weighted MRI (ADWI). METHODS: Four patients with brain lesions adjacent to the eloquent motor system were studied. Motor-evoked responses (MER) by finger-tapping paradigm were acquired with a 1.5-Tesla MR scanner, and somatosensory-evoked magnetic fields (SEF) by median nerve stimulation were measured with a 204-channel MEG system. In the same fMRI examination, ADWI and anatomic three-dimensional T1-weighted imaging (3-D MRI) were obtained. Activated areas of MER, estimated SEF dipoles, and the corticospinal tract on ADWI were coregistered to 3-D MRI, and the combined MR data were transferred to a neuronavigation system (functional neuronavigation). Intraoperative recording of cortical somatosensory-evoked potentials was performed for confirmation of the central sulcus. RESULTS: Combination of fMRI and MEG enabled firm identification of the central sulcus. Functional neuronavigation facilitated extensive tumor resection, having the advantage of sparing the motor cortex and corticospinal tract in all cases. CONCLUSIONS: The proposed functional neuronavigation allows neurosurgeons to perform effective and maximal resection of brain lesions, identifying and sparing eloquent cortical components and their subcortical connections. Potential clinical application of this technique is discussed.

Adolescent↗
PubMed2001

Relationship between muscle output and functional MRI-measured brain activation.

The relationship between functional MRI (fMRI)-measured brain signal and muscle force and or electromyogram (EMG) is critical in interpreting fMRI data and understanding the control mechanisms of voluntary motor actions. We designed a system that could record joint force and surface EMG online with fMRI data. High-quality force and EMG data were obtained while maintaining the quality of the fMRI brain images. Using this system, we determined the relationship between fMRI-measured brain activation and handgrip force and between fMRI-measured brain signal and EMG of extrinsic finger muscles. Ten volunteers participated in the experiments (only seven subjects' data were analyzed due to excessive noise in the fMRI data of three subjects). The participants exerted 20%, 35%, 50%, 65%, and 80% of the maximal force. During each contraction period, handgrip force, surface EMG of the finger flexor and extensor muscles, and fMRI brain images were acquired. The degree of muscle activation (force and EMG) was directly proportional to the amplitude of the brain signal determined by fMRI in the entire brain and in a number of motor function-related cortical fields, including primary motor, sensory regions, supplementary motor area, premotor, prefrontal, parietal and cingulate cortices, and cerebellum. All the examined brain areas demonstrated a similar relationship between the fMRI signal and force. A stronger fMRI signal during higher force indicates that more cortical output neurons and/or interneurons may participate in generating descending commands and/or processing additional sensory information. The similarity in the relationship between muscle output and fMRI signal in the cortical regions suggests that correlated or networked activation among a number of cortical fields may be necessary for controlling precise static force of finger muscles.

Adult↗
PubMed2007

Brain imaging correlates of depressive symptom severity and predictors of symptom improvement after antidepressant treatment.

BACKGROUND: It would be therapeutically useful to predict clinical response to antidepressant drugs. We evaluated structural magnetic resonance imaging (MRI) and functional MRI (fMRI) data as predictors of symptom change in people with depression. METHODS: Brain structure and function were measured with MRI in 17 patients with major depression immediately before 8 weeks treatment with fluoxetine 20 mg/day. For fMRI, patients were scanned during visual presentation of faces representing different intensities of sadness. Clinical response was measured by change in serial scores on the Hamilton Rating Scale for Depression. Symptom change scores (and baseline symptom severity) were regressed on structural and functional MRI data to map brain regions where grey matter volume, or activation by sad facial affect processing, was significantly associated with symptom change (or baseline severity). RESULTS: Faster rates of symptom improvement were strongly associated with greater grey matter volume in anterior cingulate cortex, insula, and right temporo-parietal cortex. Patients with greater than median grey matter volume in this system had faster rates of improvement and significantly lower residual symptom scores after 8 weeks' treatment. Faster improvement was also predicted by greater functional activation of anterior cingulate cortex. Baseline symptom severity was negatively correlated with greater grey matter volume in dorsal prefrontal and anterior midcingulate regions anatomically distinct from the pregenual and subgenual cingulate regions predicting treatment response. CONCLUSIONS: Structural MRI measurements of anterior cingulate cortex could provide a useful predictor of antidepressant treatment response.

Adult↗
PubMed2004

Polyamine dendrimer-based MRI contrast agents for functional kidney imaging to diagnose acute renal failure.

PURPOSE: To choose an efficacious renal functional MRI contrast agent to image early renal tubular damage. We synthesized and compared smaller polyamine dendrimer-based MRI contrast agents (<60 kD) that, unlike Gd-[DTPA], transiently accumulate in renal tubules and can be used to visualize renal structural and functional damage. MATERIALS AND METHODS: Six dendrimer-based MRI contrast agents smaller than 60 kD were studied by high resolution dynamic micro-MRI and compared to Gd-[DTPA]-dimeglumine and Gadomer-17. The best agent, DAB-G2, was further tested in a mouse ischemia/reperfusion model to validate its efficacy. RESULTS: Despite unequal renal clearance rates, all polyamine dendrimer agents visualized the renal functional anatomy of the mice better than Gd-[DTPA]-dimeglumine and Gadomer-17. DAB-G2 was excreted most rapidly, yet was able to visualize mild renal tubular injury very early after injury. CONCLUSION: DAB-G2 was found to be the best candidate for functional kidney imaging and enabled early diagnosis of acute renal injury.

Acute Kidney Injury↗
PubMed1997

[Functional brain mapping in motor task and somatosensory stimulation using echo planar MRI].

Functional brain mapping was performed with a 1.5T clinical MRI apparatus. Single shot gradient echo echo-planar imaging (EPI) sequence was employed. Normal volunteers were studied with the task of grasping hand or opposition of fingers at the frequency of 3 Hz, median nerve electro-stimulation, pure somatosensory stimulation by roller for acupuncture. Apparent signal increase was observed at contralateral sensorimotor cortex with motor task. Signal changes delayed about 5 seconds compared with the start and the cessation of the task, which may suggest that regional changes of CBF and blood oxygen level in capillary and/or in venule lag behind electrical excitation. It was hard to detect the activated area with median nerve electro-stimulation. On the other hand, roller stimulation provoked distinct activated areas at contralateral sensorimotor cortex. The activated areas caused by the roller stimulation and the motor task coincided entirely, which suggests the possibility of the intermixed localization of primary areas of motor and somatosensory. It was also clearly demonstrated that the activated area was broader with quick (3 Hz) and complicated motor task (finger opposition) than with slow (1Hz) and simple motor task (hand grasping).

Adult↗
PubMed2000

Simultaneous measurement of human joint force, surface electromyograms, and functional MRI-measured brain activation.

Functional magnetic resonance imaging (fMRI) has been increasingly used in studying human brain function given its non-invasive feature and good spatial resolution. However, difficulties in acquiring data from peripheral (e.g. information from muscle) during fMRI studies of motor function hinder interpretation of fMRI data and designing more sophisticated investigations. Here we describe a system that was designed to concurrently measure handgrip force, surface electromyograms (EMG) of finger flexor and extensor muscles, and fMRI of human brain. The system included a pressure transducer built in a hydraulic environment, a heavily shielded EMG recording element, and a visual feedback structure for online monitoring of force and/or EMG signal, by the subject positioned in the scanner during an fMRI experiment. System evaluation and subsequent fMRI motor function studies have indicated that by using this system, high quality force and EMG signals can be recorded without sacrificing the quality of the fMRI data.

Brain Mapping↗
PubMedDate not supplied

Using a bidimensional t test to compare simultaneous activations in functional brain MRI.

The aim of functional brain magnetic resonance imaging studies is to determine which regions of the brain are related to a given specific task. Different methods can be used to extract the functional signal and there is currently no consensus for this operation. Measures based on correlation are only relevant for a single task. In this paper, we propose a method based on a multivariable Student's t test that permits the comparison of the results of successive activations. This technique allows a qualitative analysis of complex tasks, making possible to deal with both similar and different activated cortical areas.

Adult↗
PubMed2005

Functional organization of human occipital-callosal fiber tracts.

Diffusion tensor imaging (DTI) and fiber tracking (FT) were used to measure the occipital lobe fiber tracts connecting the two hemispheres in individual human subjects. These tracts are important for normal vision. Also, damage to portions of these tracts is associated with alexia. To assess the reliability of the DTI-FT measurements, occipital-callosal projections were estimated from each subject's left and right hemispheres independently. The left and right estimates converged onto the same positions within the splenium. We further characterized the properties of the estimated occipital-callosal fiber tracts by combining them with functional MRI. We used functional MRI to identify visual field maps in cortex and labeled fibers by the cortical functional response at the fiber endpoint. This labeling reveals a regular organization of the fibers within the splenium. The dorsal visual maps (dorsal V3, V3A, V3B, V7) send projections through a large band in the middle of the splenium, whereas ventral visual maps (ventral V3, V4) send projections through the inferior-anterior corner of the splenium. The agreement between the independent left/right estimates, further supported by previous descriptions of homologous tracts in macaque, validates the DTI-FT methods. However, a principal limitation of these methods is low sensitivity: a large number of fiber tracts that connect homotopic regions of ventral and lateral visual cortex were undetected. We conclude that most of the estimated tracts are real and can be localized with a precision of 1-2 mm, but many tracts are missed because of data and algorithm limitations.

Adult↗
PubMedDate not supplied

Evaluation of soft palate function with MRI: application to the cleft palate patient.

Magnetic resonance imaging was employed to evaluate soft palate function in four normal volunteers and four patients with surgically repaired cleft palate, using a GE Signa clinical scanner at 1.5 T and a custom designed receive coil with a sensitivity profile encompassing from the nasopharynx to the larynx. Midsagittal images were obtained using spoiled gradient recalled acquisition at steady state while the subject phonated the following sounds: (a) MMM, (b) SSS, (c) DAH, and (d) EEE. An image at rest with normal breathing was also obtained. The soft palate and its relationship to the airway and the posterior pharyngeal wall were clearly visualized in all cases. Phonation of the prescribed sounds demonstrated the normal range of soft palate motion. The images also depicted the ability of the soft palate to divert airflow to the nasopharynx. Interpretation of functional MRI may be of value in evaluation of surgical results, guidance of speech therapy, and surgical planning in the cleft palate patient. This noninvasive alternative to conventional methods of visualization provides advantages in resolution, repeatability, and patient comfort.

Adolescent↗
PubMed2000

[Aphasia research and speech localization in the brain].

Aphasia research has become an acknowledged branch of modern cognitive neuropsychology research whose aim is to explore more fully the structures of knowledge and of cerebral processes which might both be affected in patients with aphasia. Up to the second half of this century, a model based on a specific cerebral localisation of language processes had emerged based on brain localisation research by Broca and Wernicke (among others). New modern neuroimaging techniques, however, such as computed tomography and magnetic resonance imaging (MRI), but also functional imaging modalities such as positron emission tomography or functional MRI, have modified these concepts. It emerges that in comprehension as well as in production of language, not only a few well defined centres are responsible for the activity, but there is a synchronised activity in large neuronal networks connecting various regions located both in the cortex and in the deep subcortical structures; today, this activity can be demonstrated best in a non-invasive and reproducible way with functional MRI.

Aphasia↗
PubMed1995

Neuropsychological function and MRI abnormalities in neurofibromatosis type 1.

This study investigated the relationship between MRI abnormalities and cognitive function in neurofibromatosis type 1.40 children aged eight to 16 years underwent comprehensive neuropsychological, medical and neuroradiological assessments. MRI scans revealed a characteristic pattern of T2-weighted signals ('UBOs') located primarily in the basal ganglia, brainstem and cerebellum in 25 of the children. Reductions in global IQ, attention, and visuopatial and executive functions were shown to occur in association with the presence of UBOs. These findings establish a link between changes in neuropsychological functions and MRI abnormalities in NF-1, and further support neuropathological findings which suggest that UBOs may be a manifestation of delayed or disordered myelination.

Adolescent↗
PubMed2006

Measuring the hemodynamic response in chronic hypoperfusion.

Although structural brain scans help assess brain injury in stroke, they cannot identify regions that are functionally disabled due to disrupted perfusion. Perfusion and functional MRI have the potential for determining the functional consequences of stroke. Here we examine the effectiveness of functional MRI to measure brain function in a single patient (LB) with chronic hypoperfusion. When LB made sustained hand movements we observed a sustained decrease in the fMRI signal, while normal individuals exhibit a sustained increase in signal while conducting this task. This work has clear implications for understanding stroke using functional MRI.

Brain Injuries↗
PubMed1996

Functional magnetic resonance imaging in a stereotactic setup.

The localization of critical structures within the brain is important for the planning of therapeutic strategies. Functional MRI is capable to assess functional response of cortical structures to certain stimuli. The authors present two techniques for functional MRI (fMRI) in a stereotactic set-up. The skull of the patients has been immobilized for stereotactic treatment planning either with a self developed stereotactic ceramic frame and bony fixation or with an individual precision mask system made of light cast. It has been shown that this frame does not produce any image distortion. fMRI was performed using a modified FLASH sequence on a conventional 1.5 T MRI scanner with a specially developed linear polarized head coil. The imaging technique used was an optimized conventional 2D and 3D, first order flow rephased, gradient echo sequence (FLASH) with fat-suppression and reduce bandwidth (16-28 Hz/pixel) and TR = 80-120 ms, TE = 60 ms, flip angle = 40 degrees, matrix = 128 x 128, FOV = 150-250 mm, slice-thickness = 2-5 mm, NEX = 1, and a total single scan time for one image of about 7 sec. The motor cortex stimulation was achieved by touching each finger to thumb in a sequential, self-paced, and repetitive manner. Statistical parametric maps based on student's test were calculated. Pixels with a highly significant signal increase (p < 0.001) are overlaid on T1w SE images. The primary motor and sensory cortex could be visualized with this method in all 10 patients that were imaged in this study. Due to tight fixation of the patient's skull there have been no motion artifacts. These results show that functional MRI is feasible in an stereotactic set-up with an standard 1.5 T scanner. This is a prerequisite for the exact pre therapeutic assessment of the function of cortical centers.

Brain↗
PubMed2003

Magnetic resonance imaging in experimental models of brain disorders.

This review gives an overview of the application of magnetic resonance imaging (MRI) in experimental models of brain disorders. MRI is a noninvasive and versatile imaging modality that allows longitudinal and three-dimensional assessment of tissue morphology, metabolism, physiology, and function. MRI can be sensitized to proton density, T1, T2, susceptibility contrast, magnetization transfer, diffusion, perfusion, and flow. The combination of different MRI approaches (e.g., diffusion-weighted MRI, perfusion MRI, functional MRI, cell-specific MRI, and molecular MRI) allows in vivo multiparametric assessment of the pathophysiology, recovery mechanisms, and treatment strategies in experimental models of stroke, brain tumors, multiple sclerosis, neurodegenerative diseases, traumatic brain injury, epilepsy, and other brain disorders. This report reviews established MRI methods as well as promising developments in MRI research that have advanced and continue to improve our understanding of neurologic diseases and that are believed to contribute to the development of recovery improving strategies.

Animals↗
PubMed2006

Dynamic magnetic resonance inverse imaging of human brain function.

MRI is widely used for noninvasive hemodynamic-based functional brain imaging. In traditional spatial encoding, however, gradient switching limits the temporal resolution, which makes it difficult to unambiguously identify possible fast nonhemodynamic changes. In this paper we propose a novel reconstruction approach, called dynamic inverse imaging (InI), that is capable of providing millisecond temporal resolution when highly parallel detection is used. To achieve an order-of-magnitude speedup in generating time-resolved contrast estimates and dynamic statistical parametric maps (dSPMs), the spatial information is derived from an array of detectors rather than by time-consuming gradient-encoding methods. The InI approach was inspired by electroencephalography (EEG) and magnetoencephalography (MEG) source localization techniques. Dynamic MR InI was evaluated by means of numerical simulations. InI was also applied to measure BOLD hemodynamic time curves at 20-ms temporal resolution in a visual stimulation experiment using a 90-channel head array. InI is expected to improve the time resolution of MRI and provide increased flexibility in the trade-off between spatial and temporal resolution for studies of dynamic activation patterns in the human brain.

Brain Mapping↗
PubMed2005

Fatigue induced by intermittent maximal voluntary contractions is associated with significant losses in muscle output but limited reductions in functional MRI-measured brain activation level.

The main purpose of this study was to characterize brain activation patterns during a fatigue task involving repetitive maximal voluntary contractions (MVC) of finger flexor muscles. Fourteen young, healthy human participants performed approximately 100 handgrip MVCs (each 2-s contraction was followed by a 1-s rest) while their brain was imaged by functional MRI (fMRI). The handgrip force and electromyograms (EMG) of the finger flexors declined progressively to about 40% of the initial values at the end of the fatigue task, suggesting that significant muscle fatigue had occurred. In contrast, the level of the fMRI signal in the primary (sensorimotor), secondary (supplementary motor), and association (prefrontal and cingulate) motor-function cortices did not change significantly throughout the fatigue task (although the signal of the primary sensorimotor cortex showed a clear trend of decline). The fMRI data from the task of intermittent handgrip MVCs differed dramatically from those obtained in a 2-min sustained handgrip MVC published in a recent report, in which the overall fMRI-measured brain activation level was substantially lower and followed an increase-then-decrease pattern compared to the linear decreases in force and EMG. These results support the notion that the motor cortical centers control the tasks of repetitive and continuous muscle contractions differently and that there is a decoupling in the signal changes of the brain and muscles during muscle fatigue processes induced by maximal voluntary contractions.

Electromyography↗
PubMed2004

Radial correlation contrast--a functional connectivity MRI contrast to map changes in local neuronal communication.

A functional connectivity MRI method that groups neighboring voxels in relation to their degree of temporal cross-correlation between their time courses is presented. This grouping generates a vector field, which is assumed to provide insights into the local organization of neuronal activity. Application with high spatial resolution fMRI rat data subjected to electric forepaw sensory stimulation (156 . 156 . 1000 micron1) shows a significant localized increase of the vector field amplitude in cortical layers 4 and 2/3 of the primary sensory cortex and in layer 2/3 of the primary motor cortex, suggesting a strong correlation with local neuronal communication. Vector field phases exhibit a transition with neuronal activation from random-like orientations during rest to clusters of common orientations. Cluster size is shown to be weakly dependent on the radii of the vector field calculation, and shuffling voxel position within clusters generates a random-like vector orientation instead. This suggests that changes in vector orientations upon activation represent changes in the internal correlation between voxels that is interpreted as a change in the internal neuronal communication.

Animals↗