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Results for “functional MRI”

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At least 505 records · Page 28Linked to original sources
PubMed2006

Repeatability of functional MRI for conformal avoidance radiotherapy planning.

PURPOSE: To establish the repeatability of functional magnetic resonance imaging (fMRI) examinations in order to develop an appropriate margin for functional organs at risk (fOAR) in the radiotherapy planning process. MATERIALS AND METHODS: This work investigates the variability of motor cortex activation in the left and right hemispheres of 15 normal subjects. The uncertainty of the absolute position and volume of the activation was determined for each volunteer by repeating the fMRI examination three times in a single scan session. RESULTS: Our study proposes the use of 2.9 mm and 2.2 mm margins for the left and right motor cortices, respectively. CONCLUSION: From the sample of 15 volunteers we established an appropriate planning margin that is considered to represent the uncertainty in spatially measuring the fOAR for a single fMRI examination. The work will be of interest to anyone investigating the clinical robustness of fMRI.

Adult↗
PubMed2006

Variable precision registration via wavelets: optimal spatial scales for inter-subject registration of functional MRI.

The detection of significantly activated brain regions in multi-subject functional magnetic resonance imaging (fMRI) studies almost invariably entails the coregistration of individual subjects' data in a standard space. Here, we investigate how sensitivity to detect loci of generic activation in such studies may be conditioned by the precision of anatomical registration. We describe a novel algorithm, implemented in the wavelet domain, for inhomogeneous deformation of individual images to match a template. The algorithm matches anatomical features in a coarse-to-fine fashion, first minimising a cost function in terms of relatively coarse spatial features and then proceeding iteratively to match the images in terms of progressively more detailed anatomical features. Applying the method to data acquired from two groups of 12 healthy volunteers (with mean age 27 and 70 years, respectively), during performance of a paired associate learning task, we show that geometrical overlap between template and individual images is monotonically improved, compared to an affine transform, by additional inhomogeneous deformations informed by more detailed features. Likewise, sensitivity to detect activated voxels can be substantially improved, by a factor of 4 or more, if wavelet-mediated deformations informed by medium-sized anatomical features are applied in addition to a preliminary affine transform. However, sensitivity to detect activated voxels was reduced by "over-registering" data or matching anatomical features at the finest scales of the wavelet transform. The benefits of variable precision registration are particularly salient for data acquired in older subjects, which showed evidence of greater inter-subject anatomic variability and generally required more extensive local deformation to achieve a satisfactory match to the template image. We conclude that major benefits in sensitivity to detect functional activation in multi-subject fMRI studies can be attained with an inhomogeneous deformation applied over appropriate spatial scales.

Adult↗
PubMed2000

Functional MRI of apomorphine activation of the basal ganglia in awake rhesus monkeys.

Functional magnetic resonance imaging (fMRI) was used to analyze blood oxygen level-dependent (BOLD) responses in the nigrostriatal system (caudate nucleus, putamen and substantia nigra) of awake rhesus monkeys to systemic apomorphine administration. The study (1) measured BOLD responses as an index of neuronal activity in the three structures following injections of the mixed D1/D2 agonist, and (2) assessed the effects of isoflurane anesthesia on the fMRI responses. Compared to control saline injections, 0.1 mg/kg apomorphine significantly activated the caudate nucleus (P < or = 0.005), putamen (P < or = 0.001) and substantia nigra (P < or = 0.005). The responses were consistent with activation of GABAergic neurons in these three structures seen in other animal models. Isoflurane gas measurably blunted the response to apomorphine, so that a significant apomorphine activation was only seen in the substantia nigra of anesthetized animals. Even there, the mean MR signal change was reduced from 9.8% in awake monkeys to 2.3% in anesthetized animals. The data support the hypothesis that fMRI can be used to study the effects of drugs that alter basal ganglia activity in awake rhesus monkeys.

Animals↗
PubMed2001

Characterization of contrast changes in functional MRI of the human spinal cord at 1.5 T.

Contrast changes observed in functional magnetic resonance imaging in the human spinal cord were investigated with both motor and sensory tasks over a range of echo times. Data were acquired using a single-shot fast spin-echo sequence at 1.5 Tesla. Data were analyzed with two different correlation thresholds and the effects of altering the order of repeated experiments was also investigated. Plots of the fractional signal change as a function of echo time yielded linear functions with slopes corresponding to relaxation rate changes of -0.30 sec(-1) with sensory stimulation and approximately -0.50 sec(-1) with a motor task. However, the fractional signal change extrapolated to an echo time of zero was significantly greater than zero in each case and was roughly 2.5%. This suggests that in addition to the BOLD effect there is a baseline signal change which occurs concomitant to neuronal activation in the spinal cord.

Adult↗
PubMed1999

Post-registration spatial filtering to reduce noise in functional MRI data sets.

Image registration is commonly performed in the analysis of functional magnetic resonance imaging data sets. However, the nature of artifacts introduced in the process of alignment has not been well described. In this manuscript, high-frequency losses inherent in image registration are discussed, together with a conceptual division into acquisition- and resampling-related artifacts. Simulated and experimental data are presented to illustrate these artifacts. In simulations comparing corrected and reference images, root mean square (RMS) difference errors of 0.74% and 2.62% were observed following the correction of one degree of rotation for images registered with frequency regridding and bilinear interpolation, respectively. In human experiments, regression of RMS difference error as a percentage of mean brain signal yielded slopes of 0.69 to 1.31% per degree corrected by regridding. A post-registration spatial filtering technique is presented to reduce noise introduced during registration by selectively attenuating high frequencies near the corners of k-space. Filtering following regridding resulted in reductions in RMS error of 49.6% for simulated data and of 17.4% to 32.5% in human experiments, demonstrating the effectiveness of the filtering technique.

Brain↗
PubMed2005

Neurophysiological correlates of increased verbal working memory in high-dissociative participants: a functional MRI study.

BACKGROUND: Dissociation, defined as a disruption in usually integrated mental functions, is found not only in DSM-IV dissociative disorders, but also in post-traumatic stress disorder and eating disorders. Dissociative phenomena are also common in the general population, and may reflect a constitutionally determined cognitive style rather than a pathological trait acquired through experiencing adverse life events. In pathological dissociation, evidence has been presented for episodic memory dysfunction. In contrast, in high-dissociative subjects increased performance has been found for episodic memory and dual task performance. These findings have been linked to changes in working memory capacity. METHOD: In the present study, the authors sought to extend these findings by using functional magnetic resonance imaging during performance of two parametric working memory tasks. We tested 21 healthy low- and high-dissociative participants. RESULTS: High-dissociative participants performed slightly better during both tasks. Imaging data showed that both groups activated similar networks for both tasks, i.e. (bilateral) dorsolateral (DL) and ventrolateral prefrontal cortex (PFC), parietal cortex, and supplementary motor area. Group x task interactions were found in the high-dissociative group in L DLPFC and L parietal cortex; in the low-dissociative group in R fusiform gyrus. The differences in the high-dissociative group were independent from performance differences, implying that high-dissociative subjects generally recruit this network to a greater extent. CONCLUSIONS: These results confirm earlier findings using a verbal WM task in high-dissociative participants, and are compatible with the conceptualization of non-pathological dissociation as an information-processing style, characterized by distinct attentional and mnemonic abilities.

Adult↗
PubMed2002

Evidence for widespread movement-associated functional MRI changes in patients with PPMS.

BACKGROUND: Previous work has suggested that functional reorganization of cortical motor areas might have a role in limiting the motor deficits in patients with MS. OBJECTIVE: To test whether movement-associated cortical changes in MS might extend beyond the "classic" motor areas and involve sites for multimodal integration. METHODS: fMRI was used to assess patterns of brain activations associated with 3 different motor tasks in 30 right-handed patients with primary progressive MS (PPMS) and variable degrees of motor impairment, which were compared with those from 15 right-handed, sex- and age-matched control subjects. RESULTS: Compared with control subjects, patients with MS showed increased activation of brain regions within both traditional motor planning and execution regions (including the supplementary motor area and the cingulate motor area), the insula (a region implicated in sensory processing), and several multimodal cortical regions in the temporal, parietal, and occipital lobes. In patients, the extent of the fMRI activations was strongly correlated with MR lesion burden (r ranging from 0.70 to 0.86, p < 0.001). CONCLUSIONS: This study shows that movement-associated cortical activation in patients with PPMS is widely distributed and also involves multimodal "nonmotor" cortical networks. It also suggests that adaptive cortical reorganization might be one of the mechanisms limiting the clinical impact of MS in the progressive phases of the disease.

Adult↗
PubMed2000

[Practical role of functional MRI in neurosurgery].

INTRODUCTION: Since its description in the early 1990's, functional magnetic resonance imaging (fMRI) has been used first for research purposes, and after in clinical applications in the field of neurosurgery. The purpose of this article was to critically review the literature on fMRI to achieve a better understanding of the usefulness of fMRI in brain surgery for tumors, epilepsy surgery, and radiosurgery. MATERIAL AND METHODS: Medical literature databases containing peer-review articles dating from 1990 were queried for key words related to fMRI. RESULTS: On 3,065 references scanned for relevance, 256 articles with direct or indirect relationships between fMRI and neurosurgery were analyzed. DISCUSSION: fMRI can be useful in the selection of patients for whom a surgical resection is attempted and could aid in the decision-making whether to operate on a patient who has been previously considered inoperable. fMRI is a useful tool in the decisional scheme of treatment of low-grade astrocytomas or arteriovenous malformations in the rolandic area in intact or slightly impaired patients. fMRI can be repeated in selected patients with slow growing brain tumors or congenital lesions such as AVM to study cortical reorganization phenomena. In epilepsy surgery, the Wada-test could be substituted by fMRI to determine the hemispheric dominance of language. The choice of standardized tasks and a better understanding of analysis problems in the treatment of fMRI images must be achieved before drawing more accurate conclusions on fMRI and brain tumors.

Brain Diseases↗
PubMed2000

[Clinical application of functional MRI: a strategic tool for neurosurgery].

The purpose was to incorporate preoperative functional imaging data into anatomic data of operative microscope for neurosurgical procedures of patients suffering from lesions contiguous to eloquent brain areas. The day before surgery, patients bearing scalp markers underwent fMRI, just before anatomical contrast-enhanced MR images. FMRI data analysis were realised using a t test (p<0.0001). The resulting functional-anatomical images were downloaded onto a surgical neuronavigation computer in order to outline tumoral target and functional areas. At surgery, cortical stimulation has been used to confirm functional data. Functional image-guided surgery of lesions abutting functional cortex can be safely performed.

Adult↗
PubMed1998

[Motor association cortex activity in Parkinson's disease--a functional MRI study].

The purpose of this study was to examine the activation of motor association cortex using functional magnetic resonance imaging (fMRI) in patients with Parkinson's disease (PD) and control subjects during performed hand movements. There were 26 patients with PD (12 patients with Hoehn and Yahr stage I-II, 14 patients with stage III) and 8 control subjects. Functional imaging was performed using a 1.5 tesla MRI system equipped with a single-shot, echo-planar pulse sequence. The significant signal changes were observed within the primary sensorimotor area, the supplementary motor area (SMA), and the parietal association area in both PD and control subjects. In PD subjects, the SMA was less activated than in control subjects; there were significant differences in the number of pixels activated in SMA between control and Yahr III group (p < 0.01), and between Yahr I-II and Yahr III group (p < 0.01). Our results demonstrated that movement related cerebral activity in the SMA is reduced in PD subjects, consistent with previously published data using other methods. It is well known from anatomical studies that one of the major cortical outputs of the basal ganglia is the SMA. This may explain the hypoactivation of the SMA in PD. Studies using fMRI provide a promising method not only for localizing cortical activation related to voluntary movements but also for investigating pathophysiology of movement disorders.

Aged↗
PubMed2005

Neuromuscular activation of triceps surae using muscle functional MRI and EMG.

PURPOSE: The aim of the present study was to clarify the neuromuscular activation patterns among individual triceps surae (TS) muscles during a repetitive plantarflexion using muscle functional magnetic resonance imaging (MRI) (mfMRI) and electromyography (EMG). METHODS: Six healthy men participated in this study, performing 5 sets of 10 repetitions of a calf-raise exercise bilaterally, unilaterally, and unilaterally with an additional 15% of body-weight load. The transverse relaxation times (T2) in the medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL) muscles were measured from mfMR images obtained with the subject at rest and immediately after exercise; integrated EMG (iEMG) activity was recorded from the same muscles during exercise using surface electrodes. RESULTS: There was remarkable correspondence between the changes in T2 values and iEMG activity under the three different workloads for individual TS muscles. In addition, changes in T2 value that occurred as a function of increasing exercise loads were linearly correlated with iEMG activity in the MG (r=0.58, P<0.05) and SOL (r=0.63, P<0.01), but not in the LG. CONCLUSIONS: These results suggest that 1) mfMRI signals and iEMG activity correlate with workload in individual TS muscles, 2) mfMRI signals are associated with neuromuscular activity reflected in iEMG in the MG and SOL but not in the LG, and 3) these relationships are associated with neuromuscular and metabolic factors during exercise.

Adult↗
PubMedDate not supplied

Methods for assessing accuracy and reliability in functional MRI.

In this paper, methods for assessing the accuracy and the reliability of functional magnetic resonance imaging techniques are presented. First, a modified receiver operating characteristic analysis is described for evaluating the accuracy of fMRI studies. With this modified approach, the true positives or the activated pixels are estimated based on highly averaged experimental data acquired with the same stimulation/task. Unlike ROC analysis based on simulated activation data, the present approach can be applied to experimentally acquired data without simplifying the activation related changes. To assess the reliability of fMRI studies, the kappa statistic was adopted for evaluating the overall agreement of functional activation maps from repeated experiments in individual subjects. To demonstrate the utility of these techniques, both the ROC analysis and the reliability assessment were applied to quantitatively evaluate the improvement in accuracy and reliability of a retrospective technique for physiological noise reduction in fMRI.

Magnetic Resonance Imaging↗
PubMed2001

Detection of neural activity in functional MRI using canonical correlation analysis.

A novel method for detecting neural activity in functional magnetic resonance imaging (fMRI) data is introduced. It is based on canonical correlation analysis (CCA), which is a multivariate extension of the univariate correlation analysis widely used in fMRI. To detect homogeneous regions of activity, the method combines a subspace modeling of the hemodynamic response and the use of spatial relationships. The spatial correlation that undoubtedly exists in fMR images is completely ignored when univariate methods such as as t-tests, F-tests, and ordinary correlation analysis are used. Such methods are for this reason very sensitive to noise, leading to difficulties in detecting activation and significant contributions of false activations. In addition, the proposed CCA method also makes it possible to detect activated brain regions based not only on thresholding a correlation coefficient, but also on physiological parameters such as temporal shape and delay of the hemodynamic response. Excellent performance on real fMRI data is demonstrated. Magn Reson Med 45:323-330, 2001.

Brain↗
PubMed2002

In vivo animal functional MRI: improved image quality with a body-adapted mold.

PURPOSE: To reduce functional magnetic resonance imaging (fMRI) susceptibility distortion at the air/tissue interphase in animal experiments. MATERIALS AND METHODS: We investigated the applicability of a body-adaptable flexible mold consisting of a fast-setting alginate. This technique was implemented for subcutaneous growing tumors in rats and for the brains of monkeys. RESULTS: The T(2)*-weighted gradient-echo, echo-planar imaging (GE-EPI) data obtained with the body-adapted mold showed a reduction of susceptibility artifacts and improved image quality. With both rat tumor and monkey brain, an optimized match with the anatomical T(1) images was possible. CONCLUSION: The present mold methodology is a rapid, easy, and inexpensive way to reduce magnetic susceptibility during animal GE-EPI.

Animals↗
PubMed1995

Postprocessing of functional MRI data of motor cortex stimulation measured with a standard 1.5 T imager.

Functional magnetic resonance imaging (fMRI) is usually based on acquisition of alternating series of images under rest and an activation task (stimulus). Brain activation maps can be generated from fMRI data sets by applying several mathematical methods. Two methods of image postprocessing have been compared: (i) simple difference of mean values between rest and stimulation, and (ii) Student's t-test. The comparison shows that the difference method is very sensitive to arbitrary signal fluctuations as seen mainly in large vessels (e.g., in the sagittal sinus), leading to insignificantly activated spots in brain activation maps. In contrary, Student's t-test maps show strongly reduced sensitivity for fluctuations and have the advantage of giving activation thresholds by setting significance levels. This allows the comparison of activation strength between patient collectives by using a grid overlay technique leading to an observer independent quantification of the stimulation effects. The method was able to reproduce previous findings of activation differences between healthy volunteers and schizophrenic patients. Moreover, a simple algorithm for the correction of slight head movements during the functional imaging task is presented. The algorithm is based on shifting the fMRI data set relative to a reference image by maximizing the linear correlation coefficients. This leads to a further reduction of insignificant brain activation and to an improvement in brain activation map quality.

Adult↗
PubMed2005

A signal processing model for arterial spin labeling functional MRI.

A model of the signal path in arterial spin labeling (ASL)-based functional magnetic resonance imaging (fMRI) is presented. Three subtraction-based methods for forming a perfusion estimate are considered and shown to be specific cases of a generalized estimate consisting of a modulator followed by a low pass filter. The performance of the methods is evaluated using the signal model. Contamination of the perfusion estimate by blood oxygenation level dependent contrast (BOLD) is minimized by using either sinc subtraction or surround subtraction for block design experiments and by using pair-wise subtraction for randomized event-related experiments. The subtraction methods all tend to decorrelate the 1/f type low frequency noise often observed in fMRI experiments. Sinc subtraction provides the flattest noise power spectrum at low frequencies, while pair-wise subtraction yields the narrowest autocorrelation function. The formation of BOLD estimates from the ASL data is also considered and perfusion weighting of the estimates is examined using the signal model.

Artifacts↗
PubMed2005

The brain basis for episodic memory: insights from functional MRI, intracranial EEG, and patients with epilepsy.

This article reviews the contributions that functional magnetic resonance imaging (fMRI), intracranial electroencephalography (iEEG), and patient studies have made to our current understanding of how memory functions arise from the brain. First, we briefly discuss the current classification of different memory systems and their neuroanatomical correlates, focusing on episodic memory and evidence from lesion studies. We then survey both fMRI and iEEG studies of memory function. For each modality, we discuss its physiological basis, as well as point out key studies that have led to new insights regarding memory. Advantages and disadvantages of each brain mapping modality are addressed. Wherever appropriate, we point out implications these studies have for the treatment of patients with epilepsy. We conclude this review with further discussion regarding the potential for combining fMRI and iEEG techniques in future investigations of memory function.

Electrodes, Implanted↗
PubMed2006

Functional MRI reveals declined prefrontal cortex activation in patients with epilepsy on topiramate therapy.

Functional magnetic resonance imaging of covert word generation was used to examine brain activation abnormalities associated with topiramate-induced cognitive language impairment in patients with epilepsy. Compared with a control epilepsy group, in the topiramate-treated group, there was significantly less activation in the language-mediating regions of the prefrontal cortex; the topiramate group also had significantly lower neuropsychological language scores. These findings suggest that topiramate has a critical effect on the cerebral neural systems that mediate expressive language.

Adult↗