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Results for “functional MRI”

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At least 1,261 records · Page 70Linked to original sources
PubMed2002

[The role of MRI for the evaluation of atrial septal defects before and after percutaneous occlusion with the amplatzer septal occluder(R)].

PURPOSE: Evaluation of morphologic and functional MRI of atrial septal defects (ASD) before and after percutaneous occlusion with the Amplatzer Septal Occluder (AOC). Comparison of MRI with transesophageal echocardiography (TEE), balloon measurement (IVBM) and cardiac catheterization with shunt quantification (CCSQ). MATERIALS AND METHODS: Twenty patients with ASD were examined before and three months after AOC implantation. ECG-triggered, breath-hold T1-weighted Turbo Spin Echo Segmented FLASH 2D and dynamic turbo-FLASH-GRE sequences after application of 0.2 mmol gadolinium DTPA per kg body weight were obtained in a 1.5 T MRI system. Defect size, and distance to coronal sinus (CS) and right upper pulmonary vein (RUPV) were determined for pre-interventional planning, and the AOC size was measured quantitatively for post-interventional follow-up. The shunts were evaluated qualitatively (occurrence of jets), semiquantitatively (jet length, turbulence square product) and quantitatively (flow measurement in the thoracic aorta and in the left and right pulmonary arteries). RESULTS: The average size of the ASD measured by MRI was 17.6 mm (11 - 24.8 mm) in the axial view, 15.9 mm (10.8 - 28.9 mm) in the sagittal view and 16.4 mm (12.1 - 24.8 mm) in the short axis view. In comparison, the average defect size was 15 mm (8 - 24 mm) by TEE and 20 mm (13 - 27 mm) by IVBM. The average distance to the RUPV was 17 mm (9.6 - 21.9 mm) and to the CS 11.2 mm (5 - 17 mm). The AOC was visualized with only minimal artifacts. Qualitative analysis of the MRI findings revealed an occurrence of jets in 17/20 patients. Semiquantitative analysis documented a high correlation for jet length and square product of the turbulence to defect size r = 0.81 resp. r = 0.82. Mean QP/QS-ratio measured by MR-volumetry was 1.6 +/- 0.29 and by MR-flow 1.6 +/- 0.26. The corresponding measurements were 1.7 +/- 0.3 for TEE and 1.5 +/- 0.5 for CCSQ. In comparison to TEE, the correlation coefficient was r = 0.96 for MR-volumetry and r = 0.85 for MR-flow measurement. CONCLUSION: MRI is found to be a valuable diagnostic method for pre-interventional planning and post-interventional follow-up of atrial septal defects occluded by the Amplatzer septal occluder.

Adult↗
PubMed1992

[Evaluation of kidney graft function with dynamic MRI--preliminary report].

The value of dynamic magnetic resonance imaging (MRI) in the examination of the function of transplanted kidneys was examined. Dynamic MRI was performed on 14 renal transplant patients. After the injection of Gd-DTPA (dimeglumine gadopentetate), we used small tip angle gradient echo (STAGE) technique with a flip angle of 20 degrees. The cortex was higher in signal intensity of well functioning grafts than the medulla before the injection in Gd-DTPA. Signal intensity of the cortex decreased after 30 seconds. After 1 minute the signal intensity of the cortex recovered and low intensity band meaning passage of Gd-DTPA at corticomedullary differentiation was displayed. Signal intensity of the medulla decreased after 3 minutes. Signal intensity of the parenchyma of transplanted kidney after 5 minutes was much the same as that before injection. Image of poor functioning grafts displayed unclear figures. Time-intensity values of both cortex and medulla in well functioning grafts decreased rapidly after about 2 minutes, and rose thereafter. Time-intensity curves of both cortex and medulla were almost flat on and after 5 minutes. Time-intensity curves of both cortex and medulla in poor functioning grafts were almost flat through out the examination. We concluded that effective parameters of the graft function for the time-intensity curve were delta I1 and delta I2. Dynamic MRI was suggested to be useful in the evaluation of kidney graft function.

Contrast Media↗
PubMed2002

A parametric study of mental spatial transformations of bodies.

TWO CLASSES OF MENTAL SPATIAL TRANSFORMATION CAN BE DISTINGUISHED: Object-based spatial transformations are imagined movements of objects; and egocentric perspective transformations are imagined movements of one's point of view. The hypothesis that multiple neural systems contribute to these mental imagery operations was tested with functional MRI. Participants made spatial judgments about pictures of human bodies, and brain activity was analyzed as a function of the judgment required and the time taken to respond. Areas in right temporal, occipital and parietal cortex and the medial superior cerebellum appear to be differentially involved in object-based spatial transformations. Additionally, midline structures and lateral parietal cortex were found to decrease in activity during the spatial reasoning tasks, independently of the judgment required or of the latency of response. The results are discussed in terms of a model of spatial reasoning that postulates specialized subsystems for performing object-based and egocentric perspective image transformations.

Adult↗
PubMed2005

1.5 T: intraoperative imaging beyond standard anatomic imaging.

Intraoperative high-field MRI with integrated microscope-based neuronavigation is a safe and reliable technique providing immediate intraoperative quality control. Major indications are pituitary tumor, glioma, and epilepsy surgery. Intraoperative high-field MRI provides intraoperative anatomic images at high quality that are up to the standard of pre- and postoperative neuroradiologic imaging. Compared with previous low-field MRI systems used for intraoperative imaging, not only is the image quality is clearly superior but the imaging spectrum is much wider and the intraoperative work flow is improved. Furthermore, high-field MRI offers various modalities beyond standard anatomic imaging, such as magnetic resonance spectroscopy, diffusion tensor imaging, and functional MRI.

Brain Diseases↗
PubMed2001

Functional magnetic resonance imaging of reorganization in rat brain after stroke.

Functional recovery after stroke has been associated with brain plasticity; however, the exact relationship is unknown. We performed behavioral tests, functional MRI, and histology in a rat stroke model to assess the correlation between temporal changes in sensorimotor function, brain activation patterns, cerebral ischemic damage, and cerebrovascular reactivity. Unilateral stroke induced a large ipsilateral infarct and acute dysfunction of the contralateral forelimb, which significantly recovered at later stages. Forelimb impairment was accompanied by loss of stimulus-induced activation in the ipsilesional sensorimotor cortex; however, local tissue and perfusion were only moderately affected and cerebrovascular reactivity was preserved in this area. At 3 days after stroke, extensive activation-induced responses were detected in the contralesional hemisphere. After 14 days, we found reduced involvement of the contralesional hemisphere, and significant responses in the infarction periphery. Our data suggest that limb dysfunction is related to loss of brain activation in the ipsilesional sensorimotor cortex and that restoration of function is associated with biphasic recruitment of peri- and contralesional functional fields in the brain.

Animals↗
PubMed2006

Non-invasive mapping of corticofugal fibres from multiple motor areas--relevance to stroke recovery.

Recovery of motor function after subcortical stroke appears to be related to the integrity of descending connections from the ipsilesional cortical motor system, a view supported by the observation of greater than normal movement-related activation in ipsilesional motor regions in chronic subcortical stroke patients. This suggests that damage to the descending output fibres from one region of the cortical motor system may be compensated by activity in areas that retain corticofugal outputs. Though the trajectories of corticofugal fibres from each major component of the motor system through the corona radiata and internal capsule are well described in non-human primates, they have not been described fully in humans. Our study set out to map the trajectories of these connections in a group of healthy volunteers (8 male, 4 female; age range = 31-68 years, median = 48.5 years) and establish whether this knowledge can be used to assess stroke-induced disconnection of the cortical motor system and better interpret functional reorganization of the cortical motor system. We describe the trajectories of the connections from each major component of the motor system to the cerebral peduncle using diffusion-weighted imaging and probabilistic tractography in normal subjects. We observed good reproducibility of these connections over subjects. The comparative topography of these connections revealed many similarities between humans and other primates. We then inferred damage to corticofugal pathways in stroke patients (n = 3) by comparing the overlap between regions of subcortical white matter damage with the trajectories of the connections to each motor area. In a small series of case studies, we found that inferred disconnections could explain enhanced hand-grip-related responses, as assessed with functional MRI, in the ipsilesional motor system. These results confirm that selective disruption of motor corticofugal fibres influences functional reorganization and outcome in individual patients.

Adult↗
PubMed2000

Cerebellar activation during optokinetic stimulation and saccades.

OBJECTIVE: To investigate the activation pattern of cerebellar structures during small-field optokinetic stimulation (OKN) by functional MRI (fMRI) and compare it with that obtained during voluntary saccades and fixation suppression of OKN. METHODS: Functional images were acquired from oblique transverse slices of eight healthy, right-handed volunteers using a radio frequency-spoiled, single-slice, fast low-angle shot (FLASH) pulse sequence with high-spatial resolution. RESULTS: Horizontal OKN and saccades were associated with bilateral activity in the cerebellar hemispheres (superior semilunar lobule, simple lobule, quadrangular lobule, inferior semilunar lobule), the middle cerebellar peduncle, the dentate nucleus, and medially in the culmen and uvula of cerebellar nuclei. The pattern and extent of activation were independent of the stimulus direction for OKN and saccades. During fixation suppression, the extent of activation was significantly diminished (hemispheres) or even absent (uvula, culmen). CONCLUSION: The differential effects of fixation suppression on this complex pattern of cerebellar activation in part allow us to separate visual and attentional from ocular motor processing. Our data agree with behavioral and physiologic animal data about ocular motor processes and motor learning in the vestibulospinal and optokinetic reflex. This suggests that hemispheric cerebellar activity may be mainly associated with changes in attention, whereas vermal activity seems to be associated with ocular motor control, and activity of the dentate nuclei and the cerebellar peduncles seems to be associated with both.

Adult↗
PubMed2003

The use of quantitative magnetic-resonance-based techniques to monitor the evolution of multiple sclerosis.

Conventional MRI can improve accuracy in the diagnosis of multiple sclerosis (MS) and monitor the efficacy of experimental treatments. However, conventional MRI provides only gross estimates of the extent and nature of tissue damage associated with this disease. Other quantitative magnetic-resonance-based techniques have the potential to overcome the limitations of conventional MRI and, as a consequence, to improve our understanding of the natural history of MS. Magnetisation-transfer, diffusion-weighted, and functional MRI--as well as proton magnetic-resonance spectroscopy--are helping us to elucidate the mechanisms that underlie injury, repair, and functional adaptation in patients with MS. These techniques are substantially changing our understanding of how MS causes irreversible disability and should be used more extensively in clinical trials and in studies of disease progression.

Brain Mapping↗
PubMed2007

Effect of the number of response alternatives on brain activity in response selection.

It is well-known in motor control literature that a response time (RT) increases as a logarithmic function of the number of response alternatives (NA) (Hick's law). In this study, we identified neural correlates for this relationship using event-related functional MRI and a choice finger-movement task. Behaviorally, average RTs of all subjects increased as a logarithmic function of the NA in accordance with the law. From a voxel-wise search for brain areas where the activity was correlated with NA and thence the RT, a positive correlation was found at the posterior cingulate and left superior frontal gyri, whereas a negative correlation was observed at areas in bilateral inferior parietal lobules. This differential modulation by the task context, namely, the NA available for a choice response with identical stimulus and response, indicates that these regions are involved in various aspects of response selection, intentional retrieval of motor program, or spatial expectancy.

Adult↗
PubMed2006

Stimulation of the rat somatosensory cortex at different frequencies and pulse widths.

Functional MRI (fMRI) during electrical somatosensory stimulation of the rat forepaw is a widely used model to investigate the functional organization of the somatosensory cortex or to study the underlying mechanisms of the blood oxygen level-dependent (BOLD) response. In reality, somatosensory stimuli have complex timing relationships and are of long duration. However, by default electrical sensory stimulation seems to be performed at an extremely short pulse width (0.3 ms). As the pulse duration may alter the neuronal response, our aim was to investigate the influence of a much longer stimulus pulse width (10 ms) using BOLD fMRI during electrical forepaw stimulation. The optimal neuronal response was investigated by varying the stimulus frequency at a fixed pulse duration (10 ms) and amplitude (1 mA). In a parallel experiment we measured the neuronal response directly by recording the somatosensory evoked potentials (SEPs). Quantification of the BOLD data revealed a shift in the optimal response frequencies to 8-10 Hz compared with 1 Hz at 0.3 ms. The amplitude of the recorded SEPs decreased with increasing stimulation frequency and did not display any correlation with the BOLD data. Nevertheless, the summated SEPs, which are a measure of the integrated neuronal activity as a function of time, displayed a similar response profile, with a similar maximum as observed by relative BOLD changes. This shift in optimal excitation frequencies might be related to the fact that an increased pulse width of an electrical stimulus alters the nature of the stimulation, generating also sensorimotor instead of merely somatosensory input. This may influence or alter the activated pathways, resulting in a shift in the optimal response profile.

Animals↗
PubMed2003

An expanded role for functional neuroimaging in schizophrenia.

Functional magnetic resonance imaging is a surprisingly versatile tool in the quest for disentangling the complexities of mental illnesses such as schizophrenia. Yet, the identification of pathognomonic physiological features of the illness or even a consensus regarding the interpretation of reported findings remain unfulfilled goals, in spite of the increasing sophistication of this technology. Nonetheless, by providing quantification of brain function during various cognitive challenges, functional MRI has been used to leap ahead of these quandaries to identify relationships between genetic variation and brain function. By examining recent findings and efforts to link these findings to genes, this article will review these exciting developments in schizophrenia research.

Brain Mapping↗
PubMed2004

Functional neuroimaging of headaches.

Functional neuroimaging, mainly PET and functional MRI, is the main tool that allows the capturing of neurovascular events during a headache attack. In migraine, functional imaging has clarified the underlying pathophysiology of the visual aura, whereas in migraine without aura, brainstem findings suggest a dysfunctional pain system. In cluster headache, the activation and morphological changes seen in a region posterior and inferior to the hypothalamus has provided a useful therapeutic target using deep-brain stimulation. We will discuss the main neuroimaging findings pertaining to the pathophysiology of these two common headache disorders, migraine and cluster headache.

Headache Disorders↗
PubMed2005

[Gender differences in cognitive functions].

Gender differences in neuropsychological functioning of patients with psychiatric disorders have been studied extensively in the last years. The available studies provide conflicting results, which can be attributed to the complexity of variables influencing cognitive sex differences. In this article we review the literature about gender differences in cognitive functions in healthy men and women and discuss the relevance of hormones, socio-cultural factors, educational factors and training on the occurrence of these sex differences. Furthermore we summarize the results from functional MRI experiments, which is a useful tool for noninvasively localizing areas in the brain involved in specific cognitive functions.

Brain↗
PubMed2005

Neural activity in speech-sensitive auditory cortex during silence.

That auditory hallucinations are voices heard in the absence of external stimuli implies the existence of endogenous neural activity within the auditory cortex responsible for their perception. Further, auditory hallucinations occur across a range of healthy and disease states that include reduced arousal, hypnosis, drug intoxication, delirium, and psychosis. This suggests that, even in health, the auditory cortex has a propensity to spontaneously "activate" during silence. Here we report the findings of a functional MRI study, designed to examine baseline activity in speech-sensitive auditory regions. During silence, we show that functionally defined speech-sensitive auditory cortex is characterized by intermittent episodes of significantly increased activity in a large proportion (in some cases >30%) of its volume. Bilateral increases in activity are associated with foci of spontaneous activation in the left primary and association auditory cortices and anterior cingulate cortex. We suggest that, within auditory regions, endogenous activity is modulated by anterior cingulate cortex, resulting in spontaneous activation during silence. Hence, an aspect of the brain's "default mode" resembles a (preprepared) substrate for the development of auditory hallucinations. These observations may help explain why such hallucinations are ubiquitous.

Acoustic Stimulation↗
PubMed1999

Semantic integration in reading: engagement of the right hemisphere during discourse processing.

We examined the brain areas involved in discourse processing by using functional MRI in 10 individuals as they read paragraphs, with or without a title, word by word for comprehension. Functional data were collected from 20 adjacent 5 mm axial slices. Discourse processing was associated with activation in inferior frontal and temporal regions of both cerebral hemispheres in the titled and untitled conditions. Moreover, there was substantially more right hemisphere activation for untitled than for the titled paragraphs. More specifically we found: (i) greater activation in the inferior temporal sulcus of both hemispheres for untitled than titled paragraphs; (ii) greater average volume of activation in response to untitled than titled paragraphs in the middle temporal sulcus of the right hemisphere and the reverse pattern in the left middle temporal sulcus. Consistent with previous studies of individuals with right hemisphere damage, we suggest that the right middle temporal regions may be especially important for integrative processes needed to achieve global coherence during discourse processing.

Adult↗
PubMed2002

Motor recovery after stroke: lessons from functional brain imaging.

Several theories have been proposed to explain recovery from stroke. Functional brain imaging offers an opportunity to evaluate these theories and visualize recovery after stroke. Functional brain imaging has proven to be an effective tool to map brain areas activated during a specific task. This paradigm can extend our understanding of the mechanisms of motor recovery after stroke. Functional brain imaging tools such as functional MRI, PET, transcranial Doppler ultrasonography, and transcranial magnetic stimulation can be used to evaluate motor activation after stroke. Functional imaging is proving useful in identifying areas, pathways and mechanisms involved in motor recovery after stroke. Studies have shown changes in motor organization with rehabilitation. Functional brain imaging may assist in the selection of rehabilitation methods that best foster recovery.

Cerebral Infarction↗
PubMed2005

Magnetic resonance imaging, microscopy, and spectroscopy of the central nervous system in experimental animals.

Over the last two decades, microscopic resolution in vivo magnetic resonance imaging (MRI) techniques have been developed and extensively used in the study of animal models of human diseases. Standard MRI methods are frequently used in clinical studies and in the general clinical practice of human neurological diseases. This generates a need for similar studies in experimental animal research. Because small rodents are the most commonly used species as animal models of neurological diseases, the MRI techniques need to be able to provide microscopic resolution and high signal-to-noise ratio images in relatively short time. Small animal MRI systems use very high field-strength magnets, which results in higher signal to noise ratio; however, the contrast characteristics of live tissue are different at these field strengths. In addition to standard MRI techniques, several new applications have been implemented in experimental animals, including diffusion and perfusion studies, MR angiography, functional MRI studies, MRI tractography, proton and phosphorous spectroscopy, cellular and molecular imaging using novel contrast methods. Here we give an overview of how to establish a small animal imaging facility with the goal of CNS imaging. We describe the basic physical processes leading to MR signal generation, highlighting the differences between standard clinical MRI and small animal MRI. Finally, typical findings in the most common neurological disease categories and novel MRI/magnetic resonance spectroscopy methods used in their study are also described.

Animals↗
PubMed2001

Magnetic resonance imaging of the pelvic floor--possibilities and present status.

MRI has had both an increasing availability and fuctionality during the last 5-10 years. In diagnosing problems of the pelvic floor, it has been shown to have a potential, but is at present not to be considered a routine examination. Today's use of MRI of the pelvis includes anatomical/topographical images of high quality, but to make it a valuable diagnostic tool, functional imaging is mandatory. Functional MRI with a potential of simultaneously examining defecation, micturition, bladder motion and pelvic floor muscles, seems promising, but with having practical problems. The use of open MRI systems reduce the practical problems, but does not give the optimum image quality. In the future it is likely that MRI will have an increasing importance concerning diagnoses of the pelvic floor. However, clinical research is needed to evaluate the possible diagnostic gains, and maybe even open for more use of MRI.

Humans↗