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At least 1,135 records · Page 63Linked to original sources
PubMed2006

Uncoupled leftward asymmetries for planum morphology and functional language processing.

Explanations for left hemisphere language laterality have often focused on hemispheric structural asymmetry of the planum temporale. We examined the association between an index of language laterality and brain morphology in 99 normal adults whose degree of laterality was established using a functional MRI single-word comprehension task. The index of language laterality was derived from the difference in volume of activation between the left and right hemispheres. Planum temporale and brain volume measures were made using structural MRI scans, blind to the functional data. Although both planum temporale asymmetry (t(1,99) = 6.86, p < .001) and language laterality (t(1,99) = 15.26, p < .001) were significantly left hemisphere biased, there was not a significant association between these variables (r(99) = .01,ns). Brain volume, a control variable for the planum temporale analyses, was related to language laterality in a multiple regression (beta = -.30, t = -2.25, p < .05). Individuals with small brains were more likely to demonstrate strong left hemisphere language laterality. These results suggest that language laterality is a multidimensional construct with complex neurological origins.

Adolescent↗
PubMed2004

The role of microembolisation in cerebral injury as defined by functional magnetic resonance imaging.

OBJECTIVE: Cerebral injury, in both overt and subtle forms, is common following cardiac surgery. Current methods of assessment, most commonly neuropsychological testing, have several limitations and do not accurately define the anatomical and functional injury that occurs. We have assessed the degree of cerebral injury following on-pump and off-pump cardiac surgery using functional magnetic resonance imaging and correlated this with the severity of microembolism as measured by transcranial Doppler ultrasound. METHODS: Sixteen patients undergoing cardiac surgery (8 off-pump coronary artery bypass grafting (CABG), 4 on-pump CABG and 4 open-heart surgery) underwent functional magnetic resonance imaging of the brain pre-operatively and 4 weeks post-operatively. The functional magnetic resonance images demonstrated brain activation during performance of a verbal working memory paradigm. Each patient had continuous transcranial Doppler monitoring intraoperatively using a recently validated technique (multirange, multifrequency Doppler) that allows rejection of artefacts and separation of gas and solid microemboli. Covariate analysis of pre- and post-operative functional magnetic resonance images was performed to correlate local mean signal intensity change with the extent of gas and solid microembolism. RESULTS: The median number of microemboli was 34 (range 10-176) in the off-pump group, 229 (range 127-314) in the on-pump CABG group, and 1220 (range 874-1261) in the open-heart group (P<0.05). The proportion of solid microemboli was significantly lower in the off-pump group in comparison to the on-pump CABG and open-heart groups (9 vs. 25 vs. 20%, respectively, P<0.01). Comparison of pre- and post-operative functional magnetic resonance images demonstrated an overall reduction in task-associated activation in the post-operative period. However, and paradoxically, in certain specific regions of interest there was an increase in the signal intensity which correlated with the total number of microemboli (r=0.9, P<0.01). CONCLUSIONS: Patients undergoing on-pump surgery have a higher degree of gas and solid microembolism which correlates with post-operative cerebral functional MRI activation. As activation with functional magnetic resonance imaging of the brain is known to be sensitive to a wide range of insults, it may prove to be a useful marker of perioperative cerebral injury that could help in the evaluation of potential cerebroprotective strategies.

Adult↗
PubMed2006

Pediatric epilepsy models.

Pediatric epilepsy models are needed to help with development of drugs for specific childhood and infantile epilepsy syndromes. The major forms of pediatric epilepsy can be divided into those that occur in the neonatal period, infancy, early childhood and late childhood. Seizures in the immature brain are different from those in adult brain, often resulting in neuronal death. Rodent models are useful in mimicking seizures in the immature brain (neonatal seizures, infantile spasms, and febrile seizures). No specific models exist for syndromes (e.g., Lennox-Gastaut, Landau-Kleffner). The interaction between brain development and epilepsy in humans can be assisted by use of high resolution MRI, diffusion tensor imaging, and functional MRI.

Animals↗
PubMed2004

Changes in connectivity profiles define functionally distinct regions in human medial frontal cortex.

A fundamental issue in neuroscience is the relation between structure and function. However, gross landmarks do not correspond well to microstructural borders and cytoarchitecture cannot be visualized in a living brain used for functional studies. Here, we used diffusion-weighted and functional MRI to test structure-function relations directly. Distinct neocortical regions were defined as volumes having similar connectivity profiles and borders identified where connectivity changed. Without using prior information, we found an abrupt profile change where the border between supplementary motor area (SMA) and pre-SMA is expected. Consistent with this anatomical assignment, putative SMA and pre-SMA connected to motor and prefrontal regions, respectively. Excellent spatial correlations were found between volumes defined by using connectivity alone and volumes activated during tasks designed to involve SMA or pre-SMA selectively. This finding demonstrates a strong relationship between structure and function in medial frontal cortex and offers a strategy for testing such correspondences elsewhere in the brain.

Adult↗
PubMed2002

Neural basis of protracted developmental changes in visuo-spatial working memory.

Developmental studies have shown that visuo-spatial working memory (VSWM) performance improves throughout childhood and adolescence into young adulthood. The neural basis of this protracted development is poorly understood. In this study, we used functional MRI (fMRI) to examine VSWM function in children, adolescents, and young adults, ages 7-22. Subjects performed a 2-back VSWM experiment that required dynamic storage and manipulation of spatial information. Accuracy and response latency on the VSWM task improved gradually, extending into young adulthood. Age-related increases in brain activation were observed in focal regions of the left and right dorsolateral prefrontal cortex, left ventrolateral prefrontal cortex (including Broca's area), left premotor cortex, and left and right posterior parietal cortex. Multiple regression analysis was used to examine the relative contributions of age, accuracy, and response latency on activation. Our analysis showed that age was the most significant predictor of activation in these brain regions. These findings provide strong evidence for a process of protracted functional maturation of bilateral fronto-parietal neural networks involved in VSWM development. At least two neural systems involved in VSWM mature together: (i) a right hemisphere visuo-spatial attentional system, and (ii) a left hemisphere phonological storage and rehearsal system. These observations suggest that visually and verbally mediated mnemonic processes, and their neural representations, develop concurrently during childhood and adolescence and into young adulthood.

Adolescent↗
PubMed2006

[Neuronal injury in multiple sclerosis].

The concept of multiple sclerosis (MS) as a demyelinating disease is deeply ingrained. Although the existence of a neurodegenerative component has always been apparent, it has only recently become emphasized. Thus, in recent years several studies have identified axonal degeneration as the major determinant of irreversible neurological disability in patients with MS. Axonal injury begins at disease onset and remains clinically silent for many years; irreversible neurological disability develops when a threshold of axonal loss is reached and CNS compensatory mechanisms are exhausted. The precise mechanisms of axonal loss are poorly understood, and three hypotheses have been proposed: 1) The damage is caused by an inflammatory process, 2) There is an excessive accumulation of intra-axonal Ca2+, 3) Demyelinated axons undergo degeneration due to lack of trophic support by myelin, or myelin forming cells. Although MS has traditionally been regarded as a disease of white matter, demyelination can also occur in the cerebral cortex. Cortical lesions exhibit neuronal injury represented by dendritic and axonal transection as well as neuronal apoptosis. Because conventional nuclear magnetic resonance (NMR) is limited in its ability to provide specific information about axonal pathology in MS, new techniques such as, diffusion-weighted MRI, proton magnetic resonance spectroscopy, functional MRI, as well as novel techniques designed to measure atrophy have been developed to monitor MS evolution. Recognition that MS is in part a neurodegenerative disease should trigger critical rethinking on the pathogenic mechanisms of this disease and provides new targets for a rational treatment.

Apoptosis↗
PubMed1995

[Results of magnetic resonance imaging in the acute phase of cerebral infarction].

Brain ischemia is now possible to trace through the multiple facets of MRI, morphological as well as functional. Experimental studies have been conducted for many years and clinical feasibility is reached. Although the initial decrease in blood flow does not influence morphological imaging, this early phase is shown with functional MRI, either with diffusion imaging or with cerebral blood volume imaging. The later is achieved either with the calculation of the integral of the first passage of a bolus of a diffusible paramagnetic agent or with the circulation of positive or negative blood pool contrast agents. This may serve to confirm an early diagnosis before inclusion in therapeutic trials. Immediate metabolic changes are reflected on phosphorus and proton spectroscopy achievable during the same session as imaging. This type of information may at this stage serve as a reference. It allows observation of the turnover of lactate over time in the lesion and the neuronal loss shown by decreased N-acetyl-aspartate. Edema, as a reaction to ischemia, builds up over time and has already been described for long as it modifies T1- and T2- weighted sequences. Similarly the breakdown of the blood-brain barrier is well known on conventional sequences because it produces contrast enhancement.

Acute Disease↗
PubMed2000

Registration of functional and anatomical MRI: accuracy assessment and application in navigated neurosurgery.

OBJECTIVE: A procedure for acquisition, automated registration, and fusion of functional and anatomical magnetic resonance images is presented. Its accuracy is quantitatively assessed using a publicly available gold standard. A patient case is used to illustrate the technique's clinical usefulness in image-guided neurosurgery. MATERIALS AND METHODS: Before and after functional MRI (fMRI) acquisition, additional anatomical images were acquired at spatial locations identical to those of the functional images (5-10 slices) for the purpose of voxel-based image registration. Registration accuracy of the anatomical volumes and high-resolution 3D MRI volumes (MP-RAGE imaging) was quantified using adapted data (8 patients) originating from the Vanderbilt Retrospective Registration Evaluation Project (NIH project 1 R01 NS33926-02). Selecting three subsets of slices from that data (5 slices/6 mm slice distance, 10 slices/3 mm distance, and 10 slices/6 mm distance), the small number of images available from fMRI acquisition was taken into account. Accuracies in registering these sparse data sets were then compared to the accuracy achieved using complete data. For clinical patient data (16 patients), fMRI images were fused with MP-RAGE images, thereby integrating anatomical images with information about the locations of functional areas. The resulting images were used for planning and navigation during tumor resections using an operating microscope (MKM, Zeiss). RESULTS: Quantitative analysis showed no loss of registration accuracy due to a reduced number of slices, regardless of whether 5 or 10 slices were used. For small-volume coverage in the anatomical images (thickness 24 mm), registration of one patient failed, and this could easily be identified by visual inspection. No failures were experienced when 54 mm was covered. In the clinical environment, all 16 interventions using fused fMRI and MRI data were successful. CONCLUSIONS: Automatic registration of functional and high-resolution anatomical MRI was found to be sufficiently accurate and reliable for use in stereotactic neurosurgery.

Adolescent↗
PubMed2005

Visual recovery after perinatal stroke evidenced by functional and diffusion MRI: case report.

BACKGROUND: After perinatal brain injury, clinico-anatomic correlations of functional deficits and brain plasticity remain difficult to evaluate clinically in the young infant. Thus, new non-invasive methods capable of early functional diagnosis are needed in young infants. CASE PRESENTATION: The visual system recovery in an infant with perinatal stroke is assessed by combining diffusion tensor imaging (DTI) and event-related functional MRI (ER-fMRI). All experiments were done at 1.5T. A first DTI experiment was performed at 12 months of age. At 20 months of age, a second DTI experiment was performed and combined with an ER-fMRI experiment with visual stimuli (2 Hz visual flash). At 20 months of age, ER-fMRI showed significant negative activation in the visual cortex of the injured left hemisphere that was not previously observed in the same infant. DTI maps suggest recovery of the optic radiation in the vicinity of the lesion. Optic radiations in the injured hemisphere are more prominent in DTI at 20 months of age than in DTI at 12 months of age. CONCLUSION: Our data indicate that functional cortical recovery is supported by structural modifications that concern major pathways of the visual system. These neuroimaging findings might contribute to elaborate a pertinent strategy in terms of diagnosis and rehabilitation.

Asphyxia Neonatorum↗
PubMedDate not supplied

MRI assessment of ventricular function.

Cine-MRI is a robust non invasive technique able to assess regional and global systolic function of both ventricles. Conventinal cine-MRI was used for LV global function parameters both on horizontal long axis and vertical long axis, applying area-length methods, as in echocardiography. Recent developments of segmented k-space techniques allowed breath-held cine-MRI, making possible a rapid acquisition of the entire ventricles, both left and right. Using the Simpson's rule volumes are estimated with high accuracy, without any geometrical assumption; this method is considered gold standard for global function assessment. Regional function is studied by cine-MRI both qualitatively and quantitatively, as it represents the best technique in defining endo- and epi-cardial borders. The ability of quantify wall thickness and wall thickening makes cine-MRI highly suitable for stress-imaging, both in ischemia detection and viability assessment. Tagging is a novel technique, able to assess the complex mechanism of myocardial contraction and to quantify myocardial strain. Finally MRI is also able to assess diastolic function with phase velocity mapping.

Exercise Test↗
PubMed1999

[Kinematic versus static MRI study of the cervical spine in patients with rheumatoid arthritis].

PURPOSE: The objective of this study was to compare the diagnostic value of cinematic magnetic resonance imaging with static MRI examinations in patients with rheumatoid arthritis and concomitant attack of the cervical spine. METHODS: Dynamic functional MRI examinations of the cervical spine were performed one five subjects without complaints and 20 patients with rheumatoid arthritis. For the functional studies, a positioning frame was used that allowed infinitely variable forward and backward inclinations of the head. RESULTS: Functional magnetic resonance imaging made possible a sufficiently good differentiation of the extension of pannus tissue cranial, ventral, and dorsal of the dens with possible displacing and impinging effects on the spinal cord during flexing and stretching movements. In addition, it is suitable for demonstration of the degree of instability in the atlanto-occipital and atlanto-axial planes. In contrast to conventional X-rays, CT, and static MRI, basilary impression as well as compressions and angulations of the cervical bone marrow are better visualized by cinematic magnetic resonance tomography. CONCLUSIONS: Functional magnetic resonance tomography is an important diagnostic method for the induction of the cervical spine in patients with rheumatoid arthritis. In particular, fusion and instabilities as well as compressions of the bone marrow often can only be detected with the help of functional MRI.

Cervical Vertebrae↗
PubMed1998

[Functional MRT of the LS in an open magnet system--the initial results].

PURPOSE: Description of the procedure and first results with functional MRI of the lumbar spine for the investigation of discoligamentous instability. MATERIAL AND METHOD: 21 patients--11 female and 10 male--were studied with rapid True-FISP- and FLASH sequences. With the intention to document movements in maximal ante- and retroflexion a special kidney belt was used containing an inserted multi-purpose flexible coil. With this approach reproducible functional studies can be obtained. RESULTS: Movements in ante- and retroflexion could be performed manually and gradually without technical limitation of restrictions due to the equipment. The location of a patient's pain was determined by indication from the patient and correlated with the finding on the functional MR images. In 71% of patients a gain of information was obtained with regard to discoligamentous instability of the lumbar spine when compared to earlier studies (CT, MRI in neutral position). CONCLUSIONS: Functional MRI of the lumbar spine can contribute additional segmental information and contribute to further therapy planning. With this method discoligamentous instability can be documented, which is less likely with static MRI in a closed MR system.

Adolescent↗
PubMed2002

Dynamic activity-induced manganese-dependent contrast magnetic resonance imaging (DAIM MRI).

Activity-induced manganese-dependent contrast (AIM) MRI is a hemodynamic-independent functional MRI method that used manganese ion as an MR-detectable contrast agent. In AIM, MnCl(2) is infused intra-arterially after the blood-brain barrier (BBB) is opened with a hyperosmolar agent. Upon functional stimulation of the brain, Mn(2+) accumulates in the active region(s) by entering active cells through voltage-gated Ca(2+) channels, causing local signal increases in T(1)-weighted images. The contrast of AIM MRI depends strongly on the depth of anesthesia, and the low levels used in somatosensory stimulation studies can lead to significant nonspecific accumulation of manganese ion throughout the brain. The purpose of this study was to produce an AIM functional map of somatosensory stimulation, which separates the stimulation-specific signal increase from the nonspecific activation due to light anesthesia. A dynamic AIM (DAIM) paradigm was developed, which used sequential MR scans during MnCl(2) infusion, prior to and following functional stimulation of the brain. Stimulation-specific functional maps were produced using time-course analysis. The new method was tested during glutamate administration and electric stimulation of the rat forepaw. It was shown that DAIM maps are better confined to the specific region of brain activated by somatosensory stimulation as compared to AIM MRI.

Analysis of Variance↗
PubMed1998

Magnetic resonance imaging and temporal lobe epilepsy.

Surgical treatment is a well established option for patients with medically refractory temporal lobe epilepsy. Magnetic resonance imaging (MRI) has revolutionized the evaluation of these patients. New techniques can identify structural, metabolic and functional abnormalities associated with the epileptogenic zone. Mesial temporal sclerosis is the most common pathological finding and presents as hippocampal atrophy, which can be detected by visual inspection in most cases. Volumetric analysis of medial temporal structures offers the advantage of detecting bilateral abnormalities. Magnetic resonance spectroscopy can detect metabolic abnormalities associated with the epileptogenic focus. Functional MRI allows for the non-invasive evaluation of cognitive function, allowing for the localization of the neuroanatomic substrate of motor, sensory and cognitive functions. Intraoperative MRI-based image guided systems are a useful adjunct in the surgical treatment of this epileptic syndrome.

Central Nervous System↗
PubMed2004

Event-related fMRI technique for auditory processing with hemodynamics unrelated to acoustic gradient noise.

Acoustic noise from the imaging gradients presents a major difficulty in functional MRI (fMRI) studies of auditory cortical function. For studies involving hearing-impaired pediatric subjects, the auditory stimuli should be presented during completely silent gradient intervals. In addition, the scan time is limited by constraints involving subject motion and subject compliance. A novel event-related method for conducting fMRI studies of auditory function is proposed. Auditory stimuli are presented during completely silent gradient intervals, but using a variable TR. A general nonlinear model (GNLM) is proposed as a postprocessing methodology for the data. The technique increases the flexibility of the experimental design, with minimal loss of sensitivity compared to standard fMRI acquisition techniques, and may therefore be useful for fMRI studies of auditory function in hearing-impaired pediatric subjects.

Adult↗
PubMed2003

Functional brain imaging using a blood oxygenation sensitive steady state.

Blood oxygenation level dependent (BOLD) functional MRI (fMRI) is an important method for functional neuroimaging that is sensitive to changes in blood oxygenation related to brain activation. While BOLD imaging has good spatial coverage and resolution relative to other neuroimaging methods (such as positron emission tomography (PET)), it has significant limitations relative to other MRI techniques, including poor spatial resolution, low signal levels, limited contrast, and image artifacts. These limitations derive from the coupling of BOLD functional contrast to sources of image degradation. This work presents an alternative method for fMRI that may over-come these limitations by establishing a blood oxygenation sensitive steady-state (BOSS) that inverts the signal from deoxygenated blood relative to the water signal. BOSS fMRI allows the imaging parameters to be optimized independently of the functional contrast, resulting in fewer image artifacts and higher signal-to-noise ratio (SNR). In addition, BOSS fMRI has greater functional contrast than BOLD. BOSS fMRI requires careful shimming and multiple acquisitions to obtain a precise alignment of the magnetization to the SSFP frequency response.

Artifacts↗
PubMed1999

Tracking neuronal fiber pathways in the living human brain.

Functional imaging with positron emission tomography and functional MRI has revolutionized studies of the human brain. Understanding the organization of brain systems, especially those used for cognition, remains limited, however, because no methods currently exist for noninvasive tracking of neuronal connections between functional regions [Crick, F. & Jones, E. (1993) Nature (London) 361, 109-110]. Detailed connectivities have been studied in animals through invasive tracer techniques, but these invasive studies cannot be done in humans, and animal results cannot always be extrapolated to human systems. We have developed noninvasive neuronal fiber tracking for use in living humans, utilizing the unique ability of MRI to characterize water diffusion. We reconstructed fiber trajectories throughout the brain by tracking the direction of fastest diffusion (the fiber direction) from a grid of seed points, and then selected tracks that join anatomically or functionally (functional MRI) defined regions. We demonstrate diffusion tracking of fiber bundles in a variety of white matter classes with examples in the corpus callosum, geniculo-calcarine, and subcortical association pathways. Tracks covered long distances, navigated through divergences and tight curves, and manifested topological separations in the geniculo-calcarine tract consistent with tracer studies in animals and retinotopy studies in humans. Additionally, previously undescribed topologies were revealed in the other pathways. This approach enhances the power of modern imaging by enabling study of fiber connections among anatomically and functionally defined brain regions in individual human subjects.

Brain↗
PubMed1994

Greater hemodynamic response to photic stimulation in schizophrenic patients: an echo planar MRI study.

Functional echo planar magnetic resonance imaging (MRI) probably will be of importance in assessing brain abnormalities in psychiatric disorders. The authors used functional MRI to measure the relative magnitude of the change in image signal intensity, reflecting changes in regional neuronal activity caused by photic stimulation, in eight patients with schizophrenia and nine normal comparison subjects. The mean signal intensity change in the primary visual cortex was significantly greater in patients with schizophrenia (mean = 4.6%, SD = 1.5%) than in normal comparison subjects (mean = 3.1%, SD = 1.3%). These results may reflect a variety of factors, including diffuse structural brain changes as well as primary or iatrogenic impairment of mitochondrial function or energy metabolism.

Adult↗