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Results for “functional MRI”

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At least 937 records · Page 52Linked to original sources
PubMed1997

[Brain functional MRI using 3D-SPGR pulse sequence].

We reported the effects of motor cortex stimulation of normal volunteers using conventional MR imaging techniques on standard 1.5 T clinical scanner. The imaging technique was an optimized conventional 2D and 3D spoiled GRASS. In the 3D-SPGR measurement, a slab of 96 mm with 32 partition was evaluated in sagital direction. The motor cortex stimulation was achieved by touching each finger to thumb in a sequential, self-paced, and repetitive manner. During stimulation, areas of increased signal intensity were identified in the sensorimotor cortex with both 2D and 3D SPGR method. The 3D-SPGR method in sagital direction is rather insensitive to inflow effects, thus signal increases with 3D-SPGR method is mainly due to the blood oxygenation level dependent effects.

Brain↗
PubMed1997

Proton NMR relaxation times of human blood samples at 1.5 T and implications for functional MRI.

To further investigate the dependency of fMRI signal changes on echo time TE, we measured T2 and T2* values, obtained from human blood samples at various oxygenation levels and used them in a simple model to calculated signal enhancement in fMRI. In addition, the longitudinal relaxation time T1 of human blood was determined for reference. All measurements were performed at 23 degrees C to reduce blood cell metabolism during the measurement procedure. At 23 degrees C T1 values of 1434 +/- 48 ms for arterial human blood were obtained after correcting for hematocrit content, as hematocrit values ranged fro 28% to 34% only. The T2 relaxation times obtained are 181 +/- 23 ms for venous and 254 +/- 26 ms for arterial human blood, T2* relaxation times corrected for inhomogeneities of the static magnetic field (B0) are 42 +/- 2.8 ms and 254 +/- 32 ms, respectively. Furthermore, absolute and relative signal changes in fMRI experiments are calculated. The results from these model calculations reveal that contrast in fMRI can be optimised by choosing an appropriate echo time.

Adult↗
PubMed2006

Long-term changes of functional MRI-based brain function, behavioral status, and histopathology after transient focal cerebral ischemia in rats.

BACKGROUND AND PURPOSE: The relation between recovery of brain function and neurological status after clinical and experimental cerebral ischemia is incompletely characterized. We assessed the evolution of ischemic injury, behavioral status, and brain activity at acute to chronic periods after transient middle cerebral artery occlusion (tMCAO) in rats. METHODS: Male Sprague-Dawley rats were subjected to 20-minute tMCAO (n=10) or sham operation (n=10). Sensorimotor behavioral testing and multimodal (diffusion, perfusion, T2, and functional) MRI, as well as postmortem hematoxylin-eosin staining, were performed before and up to 21 days after tMCAO. MRI and histological parameters were evaluated in 5 regions of interest within the sensorimotor network. Diffusion, perfusion, and T2 lesion volumes were calculated according to previously established viability thresholds. RESULTS: Diffusion and perfusion lesions were present during occlusion but disappeared completely and permanently within 30 minutes after reperfusion, with no T2 lesions seen. Functional MRI and behavioral deficits did not normalize until 1 and 21 days after tMCAO, respectively. Histology demonstrated selective neuronal cell death at 7 and 21 days after reperfusion. CONCLUSIONS: Twenty-minute tMCAO produced distinct changes on multimodal MRI, histology, and behavioral parameters acutely and chronically. Normal findings on MRI after transient ischemia may not indicate normal tissue status, as behavioral and histological anomalies remain. Behavioral dysfunction persisting long after the recovery of MRI parameters may relate to the subtle neuronal damage seen on histology. Together, these results may help explain unremitting neurological deficits in stroke or transient ischemic attack patients with normal MRI findings.

Animals↗
PubMed1995

[MR functional diagnosis of the cervical spine after strain injury].

50 patients with a history of distortion injury of the cervical spine were examined with static and functional MRI. Functional MRI consisted of different patient's positions from maximal extension to maximal flexion (30 degrees, 0 degrees, 25 degrees, 40 degrees, 50 degrees). T2*-weighted gradient echo sequences were performed in a sagittal view for the different positions. Ligamentous instabilities and disc protrusions were seen only in functional MRI in 17 patients. These findings correlated with the neurological symptoms. Two patients were treated by operative fusion because of these findings.

Adult↗
PubMed1989

Human callosal function: MRI-verified neuropsychological functions.

A commissurotomy patient, with MRI-revealed sparing of some rostral and splenial fibers of the corpus callosum, judged whether pairs of words rhymed. We presented one word in each pair to her left visual field and the other to her right visual field. The 2 words in each pair either sounded and looked alike (R + L +), sounded alike but looked different (R + L -), sounded different but looked alike (R - L +), or both sounded and looked different (R - L -). Although in previous studies the patient has demonstrated little or no ability to transfer information between her brain hemispheres, she was able to perform the rhyming judgment significantly better than chance when the words both looked and sounded alike. However, her accuracy did not differ from chance in the other 3 conditions, or when she was asked to indicate if 2 letters presented to her opposing visual fields were the same or different. A second commissurotomy patient, with an MRI-verified full callosal section, performed at chance in all conditions, and normal control subjects were significantly better than chance in all conditions but R + L -. We discuss the results in terms of the specificity of the information carried by groups of callosal fibers.

Adult↗
PubMed1993

[Visualization of brain function using MRI-MR functional brain imaging].

The effects of photic stimulation on the visual cortex of human brain were studied by means of gradient-echo magnetic resonance imaging (MRI). Fast low-angle shot (FLASH) MRI was used to monitor changes in brain oxygenation in the human visual cortex during photic stimulation (PS). Whole-body 1.5 T clinical MR system was used. Elevation of image intensity up to 2% was observed in primary and associative visual cortex, corresponding to an increase of blood oxygenation in regions of increased neural activity. After the PS was switched off, the MR signal fell below the pre-PS baseline level, which may be understood as an displacement of the oxygen-hemoglobin dissociation curve (the Bohre effect).

Adult↗
PubMed2005

Combining functional and diffusion tensor MRI.

Functional magnetic resonance imaging (fMRI) of the perceptual, motor, and cognitive capacities in humans is of increasing importance for basic and clinical neurosciences. The explanatory power of current fMRI techniques could be greatly expanded, however, if the pattern of the neuronal connections between the active cortical areas could likewise be visualized. In this study, we acquired blood-oxygenation level dependent (BOLD) fMRI signals during the stimulation of subjects with a set of localizer stimuli for cortical visual areas. Subsequently, diffusion tensor imaging (DTI) data from the same subjects were obtained, and the activation areas identified through fMRI were utilized as seeding points for 3D DTI fiber reconstruction algorithms. The methods developed in this study have the potential to lay a foundation for in vivo neuroanatomy and the ability for noninvasive longitudinal studies of brain development.

Algorithms↗
PubMed2005

The contribution of novel brain imaging techniques to understanding the neurobiology of mental retardation and developmental disabilities.

Studying the biological mechanisms underlying mental retardation and developmental disabilities (MR/DD) is a very complex task. This is due to the wide heterogeneity of etiologies and pathways that lead to MR/DD. Breakthroughs in genetics and molecular biology and the development of sophisticated brain imaging techniques during the last decades have facilitated the emergence of a field called Behavioral Neurogenetics. Behavioral Neurogenetics focuses on studying genetic diseases with known etiologies that are manifested by unique cognitive and behavioral phenotypes. In this review, we describe the principles of magnetic resonance imaging (MRI) techniques, including structural MRI, functional MRI, and diffusion tensor imaging (DTI), and how they are implemented in the study of Williams (WS), velocardiofacial (VCFS), and fragile X (FXS) syndromes. From WS we learn that dorsal stream abnormalities can be associated with visuospatial deficits; VCFS is a model for exploring the molecular and brain pathways that lead to psychiatric disorders for which subjects with MR/DD are at increased risk; and finally, findings from multimodal imaging techniques show that aberrant frontal-striatal connections are implicated in the executive function and attentional deficits of subjects with FXS. By deciphering the molecular pathways and brain structure and function associated with cognitive deficits, we will gain a better understanding of the pathophysiology of MR/DD, which will eventually make possible more specific treatments for this population.

Brain↗
PubMed1999

Multiple region MRI.

Traditional Fourier MR imaging (FT MRI) utilizes the Whittaker-Kotel'nikov-Shannon (WKS) sampling theorem. This theorem specifies the spatial frequency components which need to be measured to reconstruct an image with a known field of view (FOV). In this paper, we generalize this result in order to find the optimal k-space sampling for images that vanish except in multiple, possibly non-adjacent regions within the FOV. This provides the basis for "multiple region MRI" (mrMRI), a method of producing such images from a traction of the k-space samples required by the WKS theorem. Image reconstruction does not suffer from noise amplification and can be performed rapidly with fast Fourier transforms, just as in conventional FT MRI. The mrMRI method can also be used to reconstruct images that have low spatial-frequency components throughout the entire FOV and high spatial frequencies (i.e. edges) confined to multiple small regions. The greater efficiency of mrMRI sampling can be parlayed into increased temporal or spatial resolution whenever the imaged objects have signal or "edge" intensity confined to multiple small portions of the FOV. Possible areas of application include MR angiography (MRA), interventional MRI, functional MRI, and spectroscopic MRI. The technique is demonstrated by using it to acquire Gd-enhanced first-pass 3D MRA images of the carotid arteries without the use of bolus-timing techniques.

Carotid Arteries↗
PubMed2004

Neuroimaging in human immunodeficiency virus infection.

Human immunodeficiency virus (HIV) is associated with central nervous system (CNS) changes that may affect cerebral blood flow (CBF), metabolism, structure, and diffusion. Each of the available neuroimaging techniques offers unique insight into the neural mechanisms underlying HIV, as well as a potential means of monitoring disease progression and treatment response. The purpose of the article is to provide a review of experimental studies evaluating changes related to HIV with imaging techniques, including single-photon emission computed tomography (SPECT), positron emission tomography (PET), volumetric magnetic resonance imaging (MRI), functional MRI (fMRI), magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), and perfusion MRI (pMRI).

AIDS Dementia Complex↗
PubMed2005

Assessment of rigid multi-modality image registration consistency using the multiple sub-volume registration (MSR) method.

Registration of different imaging modalities such as CT, MRI, functional MRI (fMRI), positron (PET) and single photon (SPECT) emission tomography is used in many clinical applications. Determining the quality of any automatic registration procedure has been a challenging part because no gold standard is available to evaluate the registration. In this note we present a method, called the 'multiple sub-volume registration' (MSR) method, for assessing the consistency of a rigid registration. This is done by registering sub-images of one data set on the other data set, performing a crude non-rigid registration. By analysing the deviations (local deformations) of the sub-volume registrations from the full registration we get a measure of the consistency of the rigid registration. Registration of 15 data sets which include CT, MR and PET images for brain, head and neck, cervix, prostate and lung was performed utilizing a rigid body registration with normalized mutual information as the similarity measure. The resulting registrations were classified as good or bad by visual inspection. The resulting registrations were also classified using our MSR method. The results of our MSR method agree with the classification obtained from visual inspection for all cases (p < 0.02 based on ANOVA of the good and bad groups). The proposed method is independent of the registration algorithm and similarity measure. It can be used for multi-modality image data sets and different anatomic sites of the patient.

Algorithms↗
PubMed2005

Foundations of advanced magnetic resonance imaging.

During the past decade, major breakthroughs in magnetic resonance imaging (MRI) quality were made by means of quantum leaps in scanner hardware and pulse sequences. Some advanced MRI techniques have truly revolutionized the detection of disease states and MRI can now-within a few minutes-acquire important quantitative information noninvasively from an individual in any plane or volume at comparatively high resolution. This article provides an overview of the most common advanced MRI methods including diffusion MRI, perfusion MRI, functional MRI, and the strengths and weaknesses of MRI at high magnetic field strengths.

Animals↗
PubMed1994

Recent advances in neuro-imaging and the impact on neuro-ophthalmology.

Neuro-imaging is an essential part of the evaluation in patients with neuro-ophthalmologic disorders. Over the last two decades enormous advances in this area have been made allowing noninvasive evaluation of the orbit and brain. The idea of using nuclear magnetic resonance technology to produce images rather than the ionizing radiation of computed tomography (CT) began to emerge clinically in the late 1970s and early 1980s. Although the quality of early magnetic resonance imaging (MRI) scans was not much better than CT images, by the early 1990s, it became obvious that MRI had particular strength in identifying lesions in the posterior fossa, and demyelinating plaques. With advances in magnetic strength, computer software, surface coils, contrast medium, and more attention to the basic physics of magnet technology, the clarity of MR images improved dramatically. Recent advances in CT scanning (spiral and three-dimensional CT) and MRI (functional MRI and cine MRI) continue to affect significant changes in the discipline of neuro-ophthalmology. Furthermore, advances in MR angiography promise to allow excellent and noninvasive analysis of the cerebral vasculature. This review highlights the recent advances in neuro-imaging.

Diagnostic Imaging↗
PubMedDate not supplied

Imaging tumor angiogenesis: functional assessment using MDCT or MRI?

Functional imaging using multidetector row computed tomography and dynamic contrast-enhanced magnetic resonance imaging are increasingly advocated for assessment of tumor vascularity because these techniques provide excellent anatomic imaging and reliable quantitative perfusion data and are easily incorporated into routine examinations. However, differences in acquisition techniques, mathematical analysis, measurement parameters, and propensity to artifacts influence the choice of imaging modality, which is explored in this review.

Contrast Media↗
PubMed2001

[Neuroimaging and electrophysiological study in epilepsy].

There exist various morphological and biochemical changes closely associated with electrophysiological phenomena which cause epileptic seizures in the brains of epilepsy patients. Recent developments in investigation methods, not only electrophysiological(EEG and MEG), but also neuroimaging involving morphological imaging(CT and conventional MRI) and functional imaging(SPECT, PET, functional MRI and MRS) is able to demonstrate these changes. SPECT and PET can particularly clarify the changes of cerebral blood flow and glucose metabolism between interictal and ictal periods. In our experience of 423 patients who underwent epilepsy surgery for intractable seizures, these interventions provide important information to identify the epileptogenic foci. However, in practice, discordance in the results of these presurgical evaluations is recognized, and invasive intracranial recordings are needed in such cases. These problems in diagnosis were shown especially in patients with mesial temporal sclerosis and focal cortical dysplasia. To detect an epileptogenic focus more clearly, a combination of morphological and functional findings, new functional imaging such as neurotransmitter receptor imaging, EEG-triggered or neuropharmacological functional MRI, as well as, statistical parametric analysis may be needed.

Electroencephalography↗
PubMed2000

Assessment of auditory cortex activation with functional magnetic resonance imaging.

OBJECTIVE: The goal was to assess auditory cortex activation evoked by pure-tone stimulus with functional MRI. METHODS: Five healthy children, aged 7 to 10 years, were studied. Hearing evaluation was performed by pure-tone audiometry in a sound-treated room and in the MRI scanner with the scanner noise in the background. Subjects were asked to listen to pure tones (500, 1000, 2000, and 4000 Hz) at thresholds determined in the MRI scanner. Functional image processing was performed with a cross-correlation technique with a correlation coefficient of 0.5 (P < 0.0001). Auditory cortex activation was assessed by observing activated pixels in functional images. RESULTS: Functional images of auditory cortex activation were obtained in 3 children. All children showed activation in Heschl's gyrus, middle temporal gyrus, superior temporal gyrus, and planum temporale. The number of activated pixels in auditory cortexes ranged from 4 to 33. CONCLUSIONS: Functional images of auditory cortex activation evoked by pure-tone stimuli are obtained in healthy children with the functional MRI technique.

Acoustic Stimulation↗