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At least 1,009 records · Page 56Linked to original sources
PubMed1999

MRI of functional deactivation: temporal and spatial characteristics of oxygenation-sensitive responses in human visual cortex.

Magnetic resonance imaging (MRI) of neuronal "activation" relies on the elevation of blood flow and oxygenation and a related increase of the blood oxygenation level-dependent (BOLD) MRI signal. Because most cognitive paradigms involve both switches from a low degree of activity to a high degree of activity and vice versa, we have undertaken a baseline study of the temporal and spatial characteristics of positive and negative BOLD MRI responses in human visual cortex. Experiments were performed at 2.0 T using a multislice gradient-echo EPI sequence (TR = 1 s, mean TE = 54 ms, flip angle 50 degrees) at 2x2-mm2 spatial resolution. Activation and "deactivation" processes were accomplished by reversing the order of stimulus presentations in paradigms using homogeneous gray light and an alternating checkerboard as distinct functional states. For sustained stimulation (> or = 60 s) the two conditions resulted in markedly different steady-state BOLD MRI signal strengths. The transient responses to brief stimulation (< or = 18 s) differed insofar as activation processes temporally separate positive BOLD and negative undershoot effects by about 10 s, whereas negative BOLD effects and undershoot contributions overlap for deactivation processes. Apart from differences in stimulus features (e.g., motion) the used activation and deactivation protocols revealed similar maps of neuronal activity changes.

Adult↗
PubMedDate not supplied

The Webb-Bannister percutaneous technique for acute Achilles' tendon ruptures: a functional and MRI assessment.

This was a study of 57 patients treated for Achilles' tendon rupture between 1994 and 2002: 35 with an open repair and 22 with the Webb-Bannister percutaneous technique. The aim of the study was to evaluate this percutaneous method as compared to other percutaneous and open techniques, with respect to functional result and complications. In addition, postoperative MRI was performed on 40 patients in order to determine whether there were any correlations between clinical results and MRI findings. No significant differences were found between the 2 surgical methods with respect to clinical and functional results, and no wound dehiscence or infections were found in the Webb-Bannister group. There was an 8.6% incidence of wound complications in the open repair group. Similarly, return to work times were not significantly different between the groups (4 months for open repair and 3.75 months for percutaneous repair). Two patients experienced re-rupture after open repair and there was 1 re-rupture following the Webb-Bannister technique. Early weight bearing and the use of the percutaneous repair did correlate to increased postoperative tendon lengthening, though this did not appear to have any clinical consequence. MRI did not appear to be of any value in the clinical or functional evaluation, but it demonstrated a relationship between increased tendon diameter and tendon elongation (P=.0038). In those patients with thicker tendon repair sites, the dorsiflexion tended to exceed the uninjured leg. The functional results of the Webb-Bannister technique were comparable to the open repair. This technique is an effective treatment for acute ruptures less wound complications.

Achilles Tendon↗
PubMed2005

Anterior temporal laterality in primary progressive aphasia shifts to the right.

In aphasia due to stroke, language-related activity shifts not only to undamaged cortex within the dominant hemisphere but also toward right-sided areas homotopical to the left-sided lesion. We examined whether a rightward shift takes place in primary progressive aphasia (PPA). Nineteen PPA patients participated, 19 healthy subjects and 14 patients with amnestic mild cognitive impairment who served as controls. Subjects underwent neuropsychological assessment, structural magnetic resonance imaging (MRI), and a functional MRI with a factorial design: words versus pictures and associative-semantic versus visuoperceptual task. Measures of neuropsychological performance were entered as regressors into a multiple linear regression analysis, with response amplitude during the associative-semantic versus control conditions as outcome variable. Language competence correlated negatively with responses in the right anterior temporal cortex and positively with volume and responses in the left-sided homotope. In normal subjects, anterior temporal activation was more extensive to the left than the right (laterality index [LI], +0.64; standard error [SE], 0.11). Laterality was inverted in PPA with word comprehension deficit (LI, - 0.34; SE, 0.19), with an intermediate pattern in PPA without comprehension deficit (LI, +0.23; SE, 0.14). The rightward laterality shift previously reported in aphasic stroke extends to PPA, in particular, when comprehension is deficient.

Aged↗
PubMed2002

Cortical sources of the early components of the visual evoked potential.

This study aimed to characterize the neural generators of the early components of the visual evoked potential (VEP) to isoluminant checkerboard stimuli. Multichannel scalp recordings, retinotopic mapping and dipole modeling techniques were used to estimate the locations of the cortical sources giving rise to the early C1, P1, and N1 components. Dipole locations were matched to anatomical brain regions visualized in structural magnetic resonance imaging (MRI) and to functional MRI (fMRI) activations elicited by the same stimuli. These converging methods confirmed previous reports that the C1 component (onset latency 55 msec; peak latency 90-92 msec) was generated in the primary visual area (striate cortex; area 17). The early phase of the P1 component (onset latency 72-80 msec; peak latency 98-110 msec) was localized to sources in dorsal extrastriate cortex of the middle occipital gyrus, while the late phase of the P1 component (onset latency 110-120 msec; peak latency 136-146 msec) was localized to ventral extrastriate cortex of the fusiform gyrus. Among the N1 subcomponents, the posterior N150 could be accounted for by the same dipolar source as the early P1, while the anterior N155 was localized to a deep source in the parietal lobe. These findings clarify the anatomical origin of these VEP components, which have been studied extensively in relation to visual-perceptual processes.

Adolescent↗
PubMed1995

Development of an MRI-compatible needle insertion manipulator for stereotactic neurosurgery.

A variety of medical robots for stereotactic neurosurgery has been developed in recent years. Almost of all these robots use computed tomography (CT) to scan the brain of the patient before and during surgery. Currently, we are developing a needle insertion manipulator for magnetic resonance imaging (MRI)-guided neurosurgery. MRI techniques, including MRI angiography and functional MRI, are attractive for the development of interventional MRI therapies and operations. If a robot were available, these therapies would be minimally invasive, with more accurate guidance than is possible with current CT-guided systems. Actuation of a robot in an MRI environment is difficult because of the presence of strong magnetic fields. Therefore, the robot must be constructed of nonmagnetic materials. The system frame was manufactured using polyethylene terephthalate (PET) and was actuated using ultrasonic motors. Accuracy-evaluation procedures and phantom tests have been performed. The total accuracy of the system was approximately 3.0 mm. No artifacts caused by the manipulator were observed in the images.

Brain↗
PubMed2005

An optimized workflow for the integration of biological information into radiotherapy planning: experiences with T1w DCE-MRI.

Planning of radiotherapy is often difficult due to restrictions on morphological images. New imaging techniques enable the integration of biological information into treatment planning and help to improve the detection of vital and aggressive tumour areas. This might improve clinical outcome. However, nowadays morphological data sets are still the gold standard in the planning of radiotherapy. In this paper, we introduce an in-house software platform enabling us to combine images from different imaging modalities yielding biological and morphological information in a workflow driven approach. This is demonstrated for the combination of morphological CT, MRI, functional DCE-MRI and PET data. Data of patients with a tumour of the prostate and with a meningioma were examined with DCE-MRI by applying pharmacokinetic two-compartment models for post-processing. The results were compared with the clinical plans for radiation therapy. Generated parameter maps give additional information about tumour spread, which can be incorporated in the definition of safety margins.

Algorithms↗
PubMed2005

Neural processes associated with antisaccade task performance investigated with event-related FMRI.

One of the hallmarks of cognitive control is the suppression of prepotent but inappropriate responses. Here we used event-related functional MRI to measure functional brain activation during a stimulus-response incompatibility task. Subjects were instructed before a stimulus appeared either to look at the stimulus (prosaccade) or to look away from the stimulus (antisaccade). Eye movements were recorded so that functional brain activation could be grouped into prosaccades, correct antisaccades, and errors (saccades toward the stimulus on antisaccade trials). Correct antisaccade trials were associated with significantly more activation in frontal and parietal cortical areas compared with prosaccade trials during the late preparatory period before stimulus appearance. Correct antisaccades evoked more activation than errors in the right dorsolateral prefrontal cortex, anterior cingulate cortex (ACC), and presupplementary eye fields during this period. No significant differences were found for any comparisons early in the preparatory period. Our data suggest that the preparation of an antisaccade activates a large frontal and parietal network that may be involved in presetting the oculomotor system for the antisaccade task. These findings indicate that a large network of frontal and posterior areas is modulated during the latter component of the preparatory period on antisaccade compared with prosaccade trials. The results further suggest that the activation level of frontal cortical areas before stimulus presentation is associated with subjects' performance in the antisaccade task. In contrast, we found no areas that were more active for correct antisaccades than prosaccades or for correct antisaccades than error antisaccades during the stimulus-response period. In fact, a number of posterior cortical areas and a few areas in the superior frontal lobe were more active during the stimulus-response period on prosaccade trials than on antisaccade trials. Error antisaccades showed a larger activation in the ACC during the stimulus-response period compared with correct antisaccades.

Adult↗
PubMed2002

New techniques in cerebral imaging.

This article presents a review of the current techniques in Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) that enhance the usefulness of these tests for the diagnosis of cerebral disease. We were able to analyze concepts and definitions and give a comparative description for each test studied including Multidetector/Perfusion CT, Xenon CT, CT-Angiogram, MRI-Perfusion, MRI-Diffusion, MRI-Spectroscopy, MRI CSF Flow, Functional MRI studies and Cerebral Angiography.

Brain Diseases↗
PubMed2006

Application of magnetic resonance imaging to study pathophysiology in brain disease models.

Magnetic resonance imaging (MRI) provides a noninvasive and multimodal tool to study neurological disorders in experimental models. MRI experiments can be sensitized to various contrast parameters and, hence, enable comprehensive assessment of normal and abnormal brain physiology. Different conventional and novel MRI techniques have been developed that supply specific information on lesion location and size (e.g., T2- and diffusion-weighted MRI), alterations in tissue structure (e.g., magnetization transfer imaging and diffusion tensor imaging), perfusion deficits (perfusion MRI), brain activation (functional MRI), cell migration (cellular MRI), gene expression (molecular MRI), and more. The advantages of in vivo, longitudinal, and multiparametric studies with MRI provide unique opportunities for characterizing and delineating experimental models of neurological diseases and pathophysiological mechanisms, as well as spontaneous and treatment-induced recovery mechanisms.

Animals↗
PubMed2003

Further experience with extradural motor cortex stimulation for treatment of advanced Parkinson's disease. Report of 3 new cases.

AIM: To report the results obtained with the extradural motor cortex stimulation in Parkinson's disease. METHODS: Three patients were submitted to MRI images and functional MRI in order to identify the upper limb motor area. Then a quadripolar electrostimulator was introduced in the extradural space, through 2 burr holes. RESULTS: Unilateral, extradural motor cortex stimulation relieves, at least partially, but sometime dramatically, the whole spectrum of symptoms in advanced Parkinson disease: tremor and rigor bilaterally in all limbs; akinesia; standing, anteropulsion, gait; motor performance; dysphagia; speech and swallowing. Also the symptoms of long term dopa syndrome--dyskinesias, and other secondary effect of L-dopa administration, psychiatric symptoms--are improved. CONCLUSION: The results seems do not fade away with time. Drug dosage may be reduced by 50%. We suggest early employ of transdural motor cortex stimulation.

Aged↗
PubMedDate not supplied

[Neuroimaging in Alzheimer's disease: an overview].

INTRODUCTION: Clinically, computerized tomography scanning and magnetic resonance imaging (MRI) are the neuroimaging techniques most frequently used in the work up of progressive cognitive impairment, in order to rule out tumors or other treatable etiologies. However, as we move closer to having more effective treatments for Alzheimer's disease (AD), we experience a greater need to use markers of early brain injury. Among them is neuroimaging. In this review we give some examples of the role of MRI and of functional MRI (fMRI) as markers of early brain changes. DEVELOPMENT: Regional metabolism, studied with positron emission tomography (PET) can also be used advantageously to depict early cortical changes in mild cognitive impairment (MCI) and even presymptomatic AD. SPECT, less expensive than PET, has a lower sensitivity, but has been extensively studied and using quantification methods can help even in MCI. Newer PET markers allow for the evaluation of activated microglia in vivo, as well as for the study of amyloid deposition in the brain and the activity of enzymes such as acetyl-cholinesterase. CONCLUSION: Future refinements in the neuroimaging techniques seem likely to help in the early diagnosis, evaluation of potential treatments and clarification of pathogenetic mechanisms in AD.

Acetylcholinesterase↗
PubMed2006

Left ventricular remodeling or restoration for congestive heart failure.

Large numbers of people have anterior myocardial infarctions, many in mid-life, with progressive left ventricular dilatation and heart failure with diminished life expectancy. Myocardial revascularization alone helps ischemia, but does little in cases of large ventricular volume, which is the major determinant of post infarction mortality. Ventricular restoration results in immediate improvement in size and function and when added to revascularization, has markedly improved survival and freedom from congestive heart failure. When coronary bypass is being considered after anterior infarction or in patients with reduced ventricular function, MRI to determine function and viability is recommended. Then a valid, informed judgment can be made about patch reconstruction of the left ventricle.

Heart Failure↗
PubMed2004

New developments in magnetic resonance imaging of the brain.

Magnetic resonance imaging (MRI) continues to have a large impact on the diagnosis and management of a number of diseases, especially diseases associated with brain injury. The strengths of MRI are the unique contrast that can be obtained, and the fact that it is not harmful and that it can be readily applied to human and animal models. The past decade has seen development of functional MRI techniques that measure aspects of hemodynamics and water diffusion that are playing an important role. Indeed, these techniques are having a major impact on management of brain injury. The development of MRI continues at a rapid pace and a renewed push to increased spatial and temporal resolution will extend the applicability of anatomical and functional MRI. Increased interest in molecular imaging using MRI is increasing the number of processes that can be imaged in the brain. This work reviews some new developments that are being made in anatomical, functional, and molecular MRI of the brain, with comments about usefulness for work in the area of neuroprotection.

Animals↗
PubMed2005

Adaptive cortical changes and the functional correlates of visuo-motor integration in relapsing-remitting multiple sclerosis.

Cortical reorganization has been demonstrated during performance of a motor task in patients with multiple sclerosis. Converging evidence suggests that changes in gray matter volume represent an early hallmark of the disease. We used functional MRI to investigate the role of cortical adaptive mechanisms in maintaining visuo-motor function in the face of structural damage. Two cohorts of patients with clinically definite relapsing-remitting multiple sclerosis were compared with healthy controls matched for demographic, motor and cognitive characteristics during the performance of a visuo-motor integration task. Direct comparison between the two groups demonstrated a greater response of the contralateral dorsal premotor cortex and of the ipsilateral superior parietal cortex in relapsing-remitting multiple sclerosis patients. The functional MRI changes in these areas were strongly correlated with decreased gray matter volumes and increased lesion burden, respectively. Our study demonstrated a selective involvement of the parieto-premotor circuitry in a relatively early stage of the disease, which was not influenced by clinical, motor or cognitive variables. Moreover these results confirm the potential for functional recovery and the adaptive role of these areas in the motor reorganization of multiple sclerosis patients.

Adolescent↗
PubMed2006

Effects of illness duration on memory processing of patients with temporal lobe epilepsy.

PURPOSE: To examine the effects of illness duration on the neural processing of memory in patients with temporal lobe epilepsy (TLE) by using functional MRI. METHODS: Twenty-three TLE patients (16 left, seven right) performed a complex visual scene-encoding task during functional MRI. Region-of-interest (ROI) analyses were used to quantity functional activation in the mesial temporal and frontal lobes. The patients' verbal and visual memory performances were evaluated by standardized neuropsychological tests. Analyses included group comparison and correlations of duration of epilepsy with functional activation and memory performance. RESULTS: Compared with normal controls, TLE patients demonstrated reduced activation bilaterally in the mesial temporal lobe (p=0.003), and the reduction was more pronounced on the ipsilateral side of the seizure focus. Moreover, a longer duration of illness was associated with fewer voxels activated in both the left (p=0.038) and right (p=0.017) mesial temporal lobe. Furthermore, the duration of illness was found to be significantly and negatively correlated with both verbal (p=0.020) and visual (p=0.000) memory functioning. CONCLUSIONS: TLE seems to affect the memory processes in the mesial temporal lobes progressively (i.e., the longer the duration of illness, the lower the brain activation). In turn, the reduction of brain activation negatively affects memory functioning. Finally, the reduction is not limited to the side of seizure but also is observed in the contralateral hemisphere.

Adolescent↗
PubMed1997

Analysis of cardiac function by MRI and stereology.

Design-based stereology and phase contrast magnetic resonance imaging (MRI) were combined to monitor changes in the volume of the four chambers of the human heart during the cardiac cycle. The data set consisted of 18 adjacent slices (or 'scanning levels') of 0.5 cm thickness, perpendicular to the long axis of the body, and encompassing the whole heart of a healthy volunteer. At each scanning level, a cardiac gated MR image was obtained at each of 16 equally spaced time frames within the cardiac cycle. Given stationarity with respect to time, absence of image artefacts and appropriate definition of chamber boundaries, for each time frame unbiased estimates of total blood volume in the relevant heart chambers were efficiently obtained using the Cavalieri method and point counting. Combined with a proper MRI acquisition, modern stereological methods constitute an efficient and reliable tool to quantify cardiac function noninvasively.

Blood Volume↗
PubMed2006

Functional organization of perisylvian activation during presentation of sentences in preverbal infants.

We examined the functional organization of cerebral activity in 3-month-old infants when they were listening to their mother language. Short sentences were presented in a slow event-related functional MRI paradigm. We then parsed the infant's network of perisylvian responsive regions into functionally distinct regions based on their speed of activation and sensitivity to sentence repetition. An adult-like structure of functional MRI response delays was observed along the superior temporal regions, suggesting a hierarchical processing scheme. The fastest responses were recorded in the vicinity of Heschl's gyrus, whereas responses became increasingly slower toward the posterior part of the superior temporal gyrus and toward the temporal poles and inferior frontal regions (Broca's area). Activation in the latter region increased when the sentence was repeated after a 14-s delay, suggesting the early involvement of Broca's area in verbal memory. The fact that Broca's area is active in infants before the babbling stage implies that activity in this region is not the consequence of sophisticated motor learning but, on the contrary, that this region may drive, through interactions with the perceptual system, the learning of the complex motor sequences required for future speech production. Our results point to a complex, hierarchical organization of the human brain in the first months of life, which may play a crucial role in language acquisition in our species.

Adult↗
PubMed1999

High-resolution EEG in poststroke hemiparesis can identify ipsilateral generators during motor tasks.

BACKGROUND AND PURPOSE: Multimodal neuroimaging with positron emission tomography (PET) scanning or functional MRI can detect and display functional reorganization of the brain's motor control in poststroke hemiplegia. We undertook a study to determine whether the new modality of 128-electrode high-resolution EEG, coregistered with MRI, could detect changes in cortical motor control in patients after hemiplegic stroke. METHODS: We recorded movement-related cortical potentials with left and right finger movements in 10 patients with varying degrees of recovery after hemiplegic stroke. All patients were male, and time since stroke varied from 6 to 144 months. All patients were right-handed. There was also a comparison group of 20 normal control subjects. RESULTS: Five of 8 patients with left hemiparesis had evidence of ipsilateral motor control of finger movements. There were only 2 cases of right hemiparesis; in addition, 1 patient had a posteriorly displaced motor potential originating behind a large left frontal infarct (rim). CONCLUSIONS: Reorganization of motor control takes place after stroke and may involve the ipsilateral or contralateral cortex, depending on the site and size of the brain lesion and theoretically, the somatotopic organization of the residual pyramidal tracts. Our results are in good agreement with PET and functional MRI studies in the current literature. High-resolution EEG coregistered with MRI is a noninvasive imaging technique capable of displaying cortical motor reorganization.

Aged↗