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 793 records · Page 44Linked to original sources
PubMed2003

Functional MRI using intravascular contrast agents: detrending of the relative cerebrovascular (rCBV) time course.

In pharmacological fMRI experiments in animal models, blood pool contrast agents may be used to map cerebral blood volume change as a surrogate for neural activation. When the background signal drift due to contrast agent washout is non-negligible over the duration of the signal changes of interest, time-course detrending is essential for accurate interpretation of the experiment. Detrending approaches based on estimation of the background signal from a baseline period of the time course prior to pharmacological (or functional) challenge were evaluated with the aim of identifying a robust method of estimating the contrast agent washout contribution to the background signal drift. For fMRI studies in the rat, it was found that a constrained fit of a mono-exponential washout model was more accurate than a constant background approximation and unconstrained fits for experiments investigating the functional response to rapid pharmacological challenges such as cocaine and amphetamine. Moreover, the constrained fitting approach allows shorter baseline periods than unconstrained extrapolation, reducing the required duration of the experiment.

Amphetamine↗
PubMed2004

Evidence of early neurobiological alternations in adolescents with posttraumatic stress disorder: a functional MRI study.

Neuroimaging studies of patients with posttraumatic stress disorder (PTSD) have largely been performed in adult populations. The purpose of the current study was to investigate neural correlates of PTSD in adolescents. Specifically, this study investigates whether a differential brain response was present during the visual perception and imaginary recollection of traumatic reminders in adolescents who developed PTSD versus those who did not after experiencing earthquake. Eleven Taiwanese adolescents (age range: 12-14 years) with traumatic experience of earthquake were enrolled. Five subjects fulfilled PTSD criteria, while the other six served as non-PTSD controls. Brain activation was measured by functional magnetic resonance image (fMRI) during visual perception and imagery recall of earthquake and neutral pictures at 14 months after earthquake. During earthquake imagery (as compared with neutral imagery), PTSD group demonstrated activation in the bilateral visual cortex, bilateral cerebellum and left parahippocampal gyrus, while control group did not. During earthquake perception (as compared with neutral perception), the control group showed activation over anterior cingulate, but the PTSD group did not. Intergroup comparison confirmed above discrepancies was significant. We concluded that neurobiological alternation of PTSD in adolescent was similar to those in adult and might have developed within 14 months after trauma exposure.

Adolescent↗
PubMed1999

Real-time adaptive functional MRI.

Adaptively limiting image acquisition to areas of interest will allow more efficient data acquisition time for in-depth characterization of areas of brain activation. We designed and implemented an adaptive image acquisition scheme that uses a multiresolution-based strategy to zoom into the regions of cortical activity. Real-time pulse prescription and data processing capabilities were combined with spatially selective radiofrequency encoding. The method was successfully demonstrated in volunteers performing simple sensorimotor paradigms for simultaneous activation of primary motor and cerebellar areas. We believe that real-time adaptation of spatial and temporal sampling to task-related changes will increase the efficiency and flexibility of functional mapping experiments. Contrast-to-noise analysis in selected regions-of-interest was performed to quantitatively assess the multiresolution adaptive approach.

Adult↗
PubMed2002

[Functional MRI procedures in the diagnosis of brain tumors: Perfusion- and diffusion-weighted imaging].

Despite the increased diagnostic accuracy of contrast material enhanced MR imaging, specification and grading of brain tumors are still only approximate at best: neither morphology, nor relaxation times or contrast material enhancement reliably predict tumor histology or tumor grade. As histology and tumor grade strongly influence which therapy concept is chosen, a more precise diagnosis is mandatory. With diffusion- and perfusion-weighted MR imaging (DWI, PWI) it is now possible to obtain important information regarding the cellular matrix and the relative regional cerebral blood volume (rrCBV) of brain tumors, which cannot be obtained with standard MR techniques. These dynamic-functional imaging techniques are very useful in the preoperative diagnosis of gliomas, lymphomas, and metastases, as well as in the differentiation of these neoplastic lesions from abscesses, atypical ischemic infarctions, and tumor-like manifestations of demyelinating disease. Additionally, they appear suitable for determining glioma grade and regions of active tumor growth which should be the target of stereotactic biopsy and therapy. After therapy these techniques are helpful to better assess the tumor response to therapy, possible therapy failure and therapy complications such as radiation necrosis.

Biopsy↗
PubMed2005

A functional MRI study of the effects of bromocriptine, a dopamine receptor agonist, on component processes of working memory.

RATIONALE: Dopamine is abundant in the prefrontal cortex and striatum, regions implicated in working memory processes. Monkey studies suggest that subpopulations of prefrontal neurons are sensitive to component processes of working memory, and that dopaminergic actions at D1 and D2 receptors differentially affect these neurons. However, it is not known to what extent the effects of dopaminergic stimulation may differ in human subjects across the processing stages of working memory, and whether these effects are found throughout the network of task-related brain regions. OBJECTIVE: In this study we tested the effects of the D2 dopamine agonist bromocriptine during the performance of a delayed recognition task using functional magnetic resonance imaging (fMRI). METHODS: We measured blood oxygenation level dependent (BOLD) signals as subjects performed a spatial and object delayed recognition task. Subjects were scanned twice, once following 1.25 mg of bromocriptine and once following lactose placebo in a randomized double-blind design. Using an event-related design allowed for separate investigation of encoding, delay, and response period effects of dopaminergic stimulation. RESULTS: A group analysis revealed that bromocriptine treatment decreased activity in the task network at encoding and increased activity at response. There was no clear pattern of change in the delay period network. Across subjects, these BOLD signal changes were accompanied by reductions in accuracy and increases in response time during delayed recognition for spatial and object information. CONCLUSIONS: Decreased activity during encoding suggests that hyperdopaminergic stimulation may have reduced stimulus encoding processes, contributing to impaired performance.

Adult↗
PubMed1997

[Functional MRI in search of basal ganglia].

We investigated activation of the globus pallidus using conventional gradient echo sequence with a 1.5 tesla equipment. In accordance with complex finger tapping in the left hand, an increase in signal intensity from bilateral globus pallidus was attained, being grossly predominated on right side. On the other hand, activations in primary motor cortex were elicited mainly on right side, thereby being correctly accorded in attitude of on-off changes in signal intensity. fMRI in basal ganglia faces severer condition in detecting real activation, owing to influences to signal recording by ventricular pulsation, accumulation of iron by age, and differences in activation by the tasks applied. This study, however, suggests that fMRI of basal ganglia is a promising technique for mapping brain function in regard to correlations between cerebral cortex and deep structures.

Adolescent↗
PubMed1999

Functional MRI in ischemic heart disease based on detection of contraction abnormalities.

Even though several non-invasive techniques are available for the assessment of coronary artery disease and the detection of myocardial ischemia, many coronary angiograms yield negative results, thus, warranting higher accuracy for non-invasive tests. The detection of obstructive coronary artery disease is only possible during physical or pharmacological stress. Currently, the assessment of wall motion abnormalities by echocardiography is clinically the most widely used method. However, a significant number of patients yield suboptimal or non-diagnostic images despite improvements with harmonic imaging. Cardiovascular magnetic resonance (CMR) imaging allows a non-invasive visualization of the heart with high spatial and temporal resolution. Gradient echo CMR images permit an exact and reproducible determination of global and regional left ventricular function, wall thickness and wall thickening and identical pharmacological stress protocols, as currently used for dobutamine stress echocardiography, can be implemented for CMR imaging. A review of the literature on dobutamine stress CMR for the detection of stress induced wall motion abnormalities is presented and the safety of CMR stress examinations is discussed. The results show, that especially in those patients with suboptimal echocardiographic image quality dobutamine stress CMR is superior in comparison with dobutamine stress echocardiography and may replace echocardiography in these patients. Further possibilities by the use of myocardial tagging or intravascular contrast agents are outlined.

Cardiotonic Agents↗
PubMed1996

Commutator filter: a novel technique for the identification of structures producing significant susceptibility inhomogeneities and its application to functional MRI.

A robust postprocessing method to detect regions of magnetic field change is presented. High resolution gradient echo data is acquired to create a complex baseline image. From this image, two low resolution images are obtained by applying a low pass filter on the magnitude image and the complex image, respectively. Subtraction of the magnitude of the filtered complex image from the filtered magnitude image gives a new image called a commutator image in which regions of susceptibility-induced field variation are greatly enhanced. Results on phantoms and applications to visualize paramagnetic venous blood vessels in the human brain are presented. The use of this technique on a 3D gradient echo data set represents a new approach to obtain an MR venogram. The application of this method to blood oxygenation level dependent (BOLD) functional brain MR imaging is demonstrated and the important role susceptibility plays in this model is verified.

Algorithms↗
PubMed1997

Suppression of physiological eye movement artifacts in functional MRI using slab presaturation.

Reduction of image-to-image signal fluctuations and imaging artifacts is important for fMRI studies. The imaging artifacts caused by respiration, cardiac pulsation, and gross head motion and the suppression of these artifacts have been studied for many years. However, the artifacts caused by eye movement and their effects on fMRI mapping are not well known. It is demonstrated in this report that involuntary eye movements during resting conditions can cause substantial signal fluctuations in the phase-encoding direction even for a fast echo-planar imaging sequence. An oblique slab presaturation technique is proposed for saturating the magnetization of eyes and suppressing the artifacts from eye movements with minimal signal loss of other brain tissues. The results show that the technique significantly reduces signal fluctuations and improves fMRI reliability for mapping functional activation in the human brain.

Artifacts↗
PubMed1998

Localizing the site of magnetic brain stimulation by functional MRI.

In order to locate the site of action of transcranial magnetic stimulation (TMS) within the human motor cortices, we investigated how the optimal positions for evoking motor responses over the scalp corresponded to the hand and leg primary-motor areas. TMS was delivered with a figure-8 shaped coil over each point of a grid system constructed on the skull surface, each separated by 1 cm, to find the optimal site for obtaining motor-evoked potentials (MEPs) in the contralateral first dorsal interosseous (FDI) and tibialis anterior (TA) muscles. Magnetic resonance imaging scans of the brain were taken for each subject with markers placed over these sites, the positions of which were projected onto the cortical region just beneath. On the other hand, cortical areas where blood flow increased during finger tapping or leg movements were identified on functional magnetic resonance images (fMRI), which should include the hand and leg primary-motor areas. The optimal location for eliciting MEPs in FDI, regardless of their latency, lay just above the bank of the precentral gyrus, which coincided with the activated region during finger tapping in fMRI studies. The direction of induced current preferentially eliciting MEPs with the shortest latency in each subject was nearly perpendicular to the course of the precentral gyrus at this position. The optimal site for evoking motor responses in TA was also located just above the activated area during leg movements identified within the anterior portion of the paracentral lobule. The results suggest that, for magnetic stimulation, activation occurs in the primary hand and leg motor area (Brodmann area 4), which is closest in distance to the optimal scalp position for evoking motor responses.

Brain Mapping↗
PubMed2003

Rehabilitation technique facilitates association cortices in hemiparetic patients: functional MRI study.

We used fMRI to study brain activation with facilitative rehabilitation techniques (passive hand movements and visual feedback) in two patients with subcortical lesions. Two tasks were given in a sequence. The first task (trial 1) was repetitive hand grasping by the paretic hand at a rate of 0.5 Hz with the eyes closed. The second task (trial 2), the facilitative rehabilitation technique, included task 1 plus support by a trainer to move the paretic hand with the eyes open to get visual feedback of the movement. The data were analyzed by a subtractive method. When task 1 was subtracted from task 2, it was found that the bilateral visual cortex, contralateral premotor cortex and posterior parietal cortex were involved with the passive hand movement and visual feedback. These facilitative rehabilitation techniques may integrate networks between sensory information and motor commands, and lead to functional reorganization.

Adult↗
PubMed2005

The moral affiliations of disgust: a functional MRI study.

Recent investigations in cognitive neuroscience have shown that ordinary human behavior is guided by emotions that are uniquely human in their experiential and interpersonal aspects. These "moral emotions" contribute importantly to human social behavior and derive from the neurobehavioral reorganization of the basic plan of emotions that pervade mammalian life. Disgust is one prototypic emotion with multiple domains that include viscerosomatic reaction patterns and subjective experiences linked to (a) the sensory properties of a class of natural stimuli, (b) a set of aversive experiences and (c) a unique mode of experiencing morality. In the current investigation, we tested the hypotheses that (a) the experience of disgust devoid of moral connotations ("pure disgust") can be subjectively and behaviorally differentiated from the experience of disgust disguised in the moral emotion of "indignation" and that (b) pure disgust and indignation may have partially overlapping neural substrates. Thirteen normal adult volunteers were investigated with functional magnetic resonance imaging as they read a series of statements depicting scenarios of pure disgust, indignation, and neutral emotion. After the scanning procedure, they assigned one basic and one moral emotion to each stimulus from an array of six basic and seven moral emotions. Results indicated that (a) emotional stimuli may evoke pure disgust with or without indignation, (b) these different aspects of the experience of disgust could be elicited by a set of written statements, and (c) pure disgust and indignation recruited both overlapping and distinct brain regions, mainly in the frontal and temporal lobes. This work underscores the importance of the prefrontal and orbitofrontal cortices in moral judgment and in the automatic attribution of morality to social events. Human disgust encompasses a variety of emotional experiences that are ingrained in frontal, temporal, and limbic networks.

Adult↗
PubMed2005

Evaluating functional MRI procedures for assessing hemispheric language dominance in neurosurgical patients.

Two methods of quantifying hemispheric language dominance (HLD) in neurosurgical patients are compared: (1) an average magnitudes (AM) method, which is a calculation of the average signal intensity variation in regions of interest for each patient that were predefined in a group analysis for each task, and (2) a lateralization indices (LI) method, which is based on the number of activated pixels in regions of interest predefined in each individual patient. Four language tasks [a living/nonliving (LNL) judgment, word stem completion (WSC), semantic associate (SA) and a phonological associate (PA) task] were compared with "gold standard" measures such as the Wada test or electrocortical stimulation. Results showed that the LI method was more accurate (73% agreement with gold standard methods) than the AM method (only 40% agreement) across tasks and subjects. Furthermore, by varying the threshold used for determining laterality, the ability of functional magnetic resonance imaging (fMRI) to predict HLD was influenced for the AM method, whereas the LI method was relatively unaffected by changing the threshold. Using the LI method, the SA task was the most accurate for quantifying HLD (100% agreement with gold standard methods) with respect to the other three language tasks (80% accuracy for WSC, 65% for the LNL and 63% for phonological task). Depending on the method and the task, fMRI may be a promising tool for assessing HLD in neurosurgical patients.

Adult↗
PubMed2004

Functional MRI of the immediate impact of transcranial magnetic stimulation on cortical and subcortical motor circuits.

Recent studies indicate that the cortical effects of transcranial magnetic stimulation (TMS) may not be localized to the site of stimulation, but spread to other distant areas. Using echo-planar imaging with blood-oxygenation-level-dependent (BOLD) contrast at 3 Tesla, we measured MRI signal changes in cortical and subcortical motor regions during high-frequency (3.125 Hz) repetitive TMS (rTMS) of the left sensorimotor cortex (M1/S1) at intensities above and below the active motor threshold in healthy humans. The supra- and subthreshold nature of the TMS pulses was confirmed by simultaneous electromyographic monitoring of a hand muscle. Suprathreshold rTMS activated a network of primary and secondary cortical motor regions including M1/S1, supplementary motor area, dorsal premotor cortex, cingulate motor area, the putamen and thalamus. Subthreshold rTMS elicited no MRI-detectable activity in the stimulated M1/S1, but otherwise led to a similar activation pattern as obtained for suprathreshold stimulation though at reduced intensity. In addition, we observed activations within the auditory system, including the transverse and superior temporal gyrus, inferior colliculus and medial geniculate nucleus. The present findings support the notion that re-afferent feedback from evoked movements represents the dominant input to the motor system via M1 during suprathreshold stimulation. The BOLD MRI changes in motor areas distant from the site of subthreshold stimulation are likely to originate from altered synaptic transmissions due to induced excitability changes in M1/S1. They reflect the capability of rTMS to target both local and remote brain regions as tightly connected constituents of a cortical and subcortical network.

Adult↗
PubMed1997

Decoupled automated rotational and translational registration for functional MRI time series data: the DART registration algorithm.

A rapid, in-plane image registration algorithm that accurately estimates and corrects for rotational and translational motion is described. This automated, one-pass method achieves its computational efficiency by decoupling the estimation of rotation and translation, allowing the application of rapid cross-correlation and cross-spectrum techniques for the determination of displacement parameters. k-space regridding and modulation techniques are used for image correction as alternatives to linear interpolation. The performance of this method was analyzed with simulations and echo-planar image data from both phantoms and human subjects. The processing time for image registration on a Hewlett-Packard 735/125 is 7.5 s for a 128 x 128 pixel image and 1.7 s for a 64 x 64 pixel image. Imaging phantom data demonstrate the accuracy of the method (mean rotational error, -0.09 degrees; standard deviation = 0.17 degrees; range, -0.44 degrees to +0.31 degrees; mean translational error = -0.035 pixels; standard deviation = 0.054 pixels; range, -0.16 to +0.06 pixels). Registered human functional imaging data demonstrate a significant reduction in motion artifacts such as linear trends in pixel time series and activation artifacts due to stimulus-correlated motion. The advantages of this technique are its noniterative one-pass nature, the reduction in image degradation as compared to previous methods, and the speed of computation.

Adult↗
PubMed2003

A virtual reality system for neurobehavioral and functional MRI studies.

We are developing a VR system of integrated software and hardware for scientific research and clinical application. The system is sufficiently flexible and broad-based in appeal that neurobehavioral researchers from a variety of disciplines might be interested in using it for basic research and clinical studies. The system runs on a standard Windows-based personal computer with a high-performance graphics card. Options allow a head-mounted display, dataglove, simultaneous physiological monitoring or use within neuroimaging machines such as magnetic resonance imaging (MRI) scanners. Currently, the software consists of a virtual world of nearly a dozen interconnected environments that the subject can freely navigate. Additional environments can be built and easily added to the application. A startup interface provides menus for selecting characters and objects that a researcher might want to put at specific locations within the simulation. Interactivity is provided for many typical objects such as doors, chairs and money. There are more than 50 characters in the world, most of them animated or interactive. All movements and actions of the subject within the world are tracked and recorded to an Excel spreadsheet for data analysis. Overlay maps are available as navigational aids. Concurrent physiological data can be acquired on up to 16 channels. The system provides synchronization of the VR simulation with physiological recordings and functional MR images. A spatial navigation memory task was performed with the integrated VR/fMRI system, and some pilot data is presented that shows robust activation in multiple cortical areas appropriate to the task.

Brain↗
PubMed2003

Sex differences in semantic language processing: a functional MRI study.

Predictions based on two models of sex differences in cerebral organization of language were compared by examining fMRI patterns of 10 females and 9 males during a semantic processing task. Both groups displayed activation of left inferior frontal gyrus (IFG), left superior temporal gyrus (STG), and cingulate. Females, but not males, showed bilateral IFG and STG activation. Further analyses revealed females had less diffuse left activation and greater right posterior temporal and insula region activation than males. Results support both an interhemispheric and an intrahemispheric model of sex differences in language, suggesting that the models may not be mutually exclusive.

Brain↗
PubMed2006

Hypocapnia related changes in pain-induced brain activation as measured by functional MRI.

Stress, acute pain and chronic pain may often result in hyperventilation (HV) which produces hypocapnia. The aim of this fMRI-study was to investigate the influence of hypocapnia on cortical activation during noxious stimulation in 14 healthy volunteers. The intensity of voluntary HV was controlled by capnometry Three tasks were performed in the fMRI sessions: (I) three 3-min HV periods with 7-min periods of recovery in between; (II) mechanically induced phasic pain stimulation--pain task (PT); (III) tapping--motor task (MT). The last two of these protocols were performed under normocapnic and hypocapnic conditions. HV decreased the fMRI signal by 3-7% in all regions of the cortex and subcortical nuclei. This decrease was most prominent in the opercular, frontal and temporal areas. When the PT was performed during hypocapnia a strong reduction in cluster sizes and lower t-values in S1 and insular cortex were found. In contrast MT was accompanied by an increase in cluster sizes and higher t-values. From this we conclude that hypocapnia significantly influences the BOLD signal in nociceptive and motor systems, indicating that either the coupling between the BOLD effect and neuronal processing changed or that the activity in the cortical network which represents the pain processing is decreased. These effects should be considered for functional brain imaging studies on the nociceptive system.

Adult↗