1,721,002 research outputs found
Functional MRI
No full textFunctional MRI plays a dominant role amongst brain mapping techniques, in large part due to its non-invasiveness, relatively high spatiotemporal resolution, and the wide availability of clinical MRI scanners. It is important to note that fMRI measures a surrogate signal originating from the vascular response to neuronal mass activity and is therefore subjected to several constraints. Nevertheless, its capacity to map the entire network of brain areas engaged by a specific task is unrivalled among non-invasive techniques like MEG and EEG. The possibility to obtain both functional and anatomical images in the same study session is a further attraction of fMRI.The major impact of the fMRI techniques has been in the field of basic cognitive neuroscience, but they have gained a growing role in translational medicine and clinical practice. Several approaches have been developed for MR imaging of brain function, including contrast agent-enhanced imaging, arterial spin labelling (ASL) and blood oxygenation level dependent (BOLD) imaging, the latter being the most commonly used. Functional activation of the brain can be detected using these techniques through their ability to measure or depict changes in tissue perfusion, blood-volume, or the vascular concentration of deoxy-hemoglobin. While the BOLD technique can provide reliable information on the neuroanatomy underlying transient sensorimotor and to a lesser extent cognitive functions, perfusion techniques are more suitable for studying relatively long term effects on cerebral blood flow (CBF) both at rest or during brain activation. Behind the functional images obtained through BOLD or ASL contrasts, there are complex physical and biophysical principles as well as engineering procedures. The continuous technical improvement of fMRI techniques is most evident in the development of high-field scanner and the optimization of pulse sequences. As with data acquisition, many methods have been proposed for analysing fMRI data, and a variety of these are in general use. The overall aim of such analyses is to produce an image (map) identifying the regions which show significant signal change in response to a specific stimulus or task performed by the subject. In the following sections, after a brief introduction to the physiological correlates of neuronal activity, a description of the main principles and techniques of fMRI based on perfusion and BOLD contrasts will be provided. At the end of the chapter, the main processing steps necessary to obtain a brain activation map by statistical analysis of BOLD data are outlined. Since no gold standard exists among the various methods developed for statistically analysing fMRI data, the most commonly adopted approach, the General Linear Model (GLM) is used in this summary
Experimental errors in digital image processing for the determination of geometrical parameters of the human eye.
No full textMethod to evidence errors in acquiring information about shape and dimension of anterior segment of the human eye through processing of images obtaiuned from slit lamp
Multimodal MRI in the characterization of glial neoplasms: the combined role of single-voxel MR spectroscopy, diffusion imaging and echo-planar perfusion imaging
No full textINTRODUCTION: Diffusion-weighted imaging (DWI), perfusion-weighted imaging (PWI) and MR spectroscopy (MRS) provide useful data for tumor evaluation. To assess the contribution of these multimodal techniques in grading glial neoplasms, we compared the value of DWI, PWI and MRS in the evaluation of histologically proven high- and low-grade gliomas in a population of 105 patients. METHODS: Independently for each modality, the following variables were used to compare the tumors: minimum apparent diffusion coefficient (ADC) and maximum relative cerebral blood volume (rCBV) normalized values between tumor and healthy tissue, maximum Cho/Cr ratio and minimum NAA/Cr ratio in tumor, and scored lactate and lipid values in tumor. The Mann-Whitney and Wilcoxon tests were employed to compare DWI, PWI and MRS between tumor types. Logistic regression analysis was used to determine which parameters best increased the diagnostic accuracy in terms of sensitivity, specificity, and positive and negative predictive values. ROC curves were determined for parameters with high sensitivity and specificity to identify threshold values to separate high- from low-grade lesions. RESULTS: Statistically significant differences were found for rCBV tumor/normal tissue ratio, and NAA/Cr ratio in tumor and Cho/Cr ratio in tumor between low- and high-grade tumors. The best performing single parameter for group classification was the normalized rCBV value; including all parameters, statistical significance was reached by rCBV tumor/normal tissue ratio, NAA/Cr tumor ratio and lactate. From the ROC curves, a high probability for a neoplasm to be a high-grade lesion was associated with a rCBV tumor/normal tissue ratio of >1.16 and NAA/Cr tumor ratio of <0.44. CONCLUSION: Combining PWI and MRS with conventional MR imaging increases the accuracy of the attribution of malignancy to glial neoplasms. The best performing parameter was found to be the perfusion level
Visual function in term newborn infants and preterm neonates (at the same conceptional age)
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VISION IN THE NEONATE (FULL TERM AND PREMATURE): PRELIMINART RESULT OF THE APPLICATION OF SOME TESTING METHODS
No full textLittle information is avaible on the functionally of the visual system in neonates,. Comparison was made between neonates born at full term and prematures equated for conceptional age, using two methods of investigation: the visual evoked potential (VEP) and the "forced preferential lookun" (FPL). The results obtained by the FPL method indicate a grater visual acuity in premature subjects, whereas the results obtained by the VEP method point to non significant difference of implicit time between the two groups
Incremental binocular amplitude of the pattern visual evoked potential during the first five months of life: electrophysiological evidence of the development of binocularity.
No full textThe amplitude of the pattern visual evoked potential (VEP) of a binocular stimulus has been shown to be generally larger than the VEP obtained monocularly. There is evidence that this effect can be considered an electrophysiological index of fusion. To study how binocular vision develops in infancy we evaluated the incremental binocular amplitude (IBA) in three infants in a longitudinal investigation during the first five months of life. The stimuli were phase-alternating square-wave gratings with spatial and temporal parameters chosen to be appropriate for neonates. IBA was defined as the percentage increment of the largest binocular response compared with the monocular response. In the first two months of life IBA values were near zero, that is, no summation occurred. Between the second and third month IBA values rose markedly and after the third month its value was greater than 100%, demonstrating binocular facilitation. Thus in the first two months of life the eyes do not seem to cooperate as in adults. By the second and third month the binocular pattern VEP reflects an increasing binocular interaction. Other studies of the development of stereopsis have also found evidence of binocularity at similar ages
Functional activity mapping of the mesial hemispheric wall during anticipation of pain
No full textThe relative contributions of autonomic arousal and of cognitive processing to cortical activity during anticipation of pain, and the role of changes in thalamic outflow, are still largely unknown. To address these issues, we investigated with functional magnetic resonance imaging (fMRI) the activity of the contralateral mesial hemispheric wall in 56 healthy volunteers while they expected the stimulation of one foot, which could be either painful or innocuous. The waiting period was characterized by emotional arousal, a moderate rise in heart rate, and by increases in mean fMRI signals in the medial thalamus, mid- and posterior cingulate cortex, and in the putative foot area of the primary somatosensory and motor cortex. The same brain regions, excepting posterior cingulate, were also activated by somatosensory stimulation. We identified by cross-correlation analysis a cluster population whose fMRI signal time course was related to the mean heart rate (HR) profile, showing selective changes of activity during the waiting period. Positively correlated clusters were found mainly in sensorimotor areas, mid- and posterior cingulate, and dorsomedial prefrontal cortex. Negatively correlated clusters predominated in the perigenual anterior cingulate and ventromedial prefrontal cortex. HR clusters had different characteristics from, and showed limited spatial overlap with, clusters whose fMRI signals were related to the psychophysical pain intensity profile; however, both cluster populations were affected by anticipation. These findings unravel a complex pattern of brain activity during uncertain anticipation of noxious input, likely related both to changes in the level of arousal and to cognitive modulation of the pain system. (C) 2003 Elsevier Science (USA). All rights reserved
Temporal and intensity coding of pain in human cortex
No full textWe used a high-resolution functional magnetic resonance imaging (fMRI) technique in healthy right-handed volunteers to demonstrate cortical areas displaying changes of activity significantly related to the time profile of the perceived intensity of experimental somatic pain over the course of several minutes. Twenty-four subjects (ascorbic acid group) received a subcutaneous injection of a dilute ascorbic acid solution into the dorsum of one foot, inducing prolonged burning pain (peak pain intensity on a 0-100 scale: 48 +/- 3, mean +/- SE; duration: 11.9 +/- 0.8 min). fMRI data sets were continuously acquired for similar to 20 min, beginning 5 min before and lasting 15 min after the onset of stimulation, from two sagittal planes on the medial hemispheric wall contralateral to the stimulated site, including the cingulate cortex and the putative foot representation area of the primary somatosensory cortex (SI). Neural clusters whose fMRI signal time courses were positively or negatively correlated (P < 0.0005) with the individual pain intensity curve were identified by cross-correlation statistics in all 24 volunteers. The spatial extent of the identified clusters was linearly related (P < 0.0001) to peak pain intensity. Regional analyses showed that positively correlated clusters were present in the majority of subjects in ST, cingulate, motor, and premotor cortex. Negative correlations were found predominantly in medial parietal, perigenual cingulate, and medial prefrontal regions. To test whether these neural changes were due to aspecific arousal or emotional reactions, related either to anticipation or presence of pain, fMRI experiments were performed with the same protocol in two additional groups of volunteers, subjected either to subcutaneous saline injection (saline: n = 16), inducing mild short-lasting pain (peak pain intensity 23 +/- 4; duration 2.8 +/- 0.6 min) or to nonnoxious mechanical stimulation of the skin (controls: n = 16) at the same body site. Subjects did not know in advance which stimulus would occur. The spatial extent of neural clusters whose signal time courses were positively or negatively correlated with the mean pain intensity curve of subjects injected with ascorbic acid was significantly larger (P < 0.001) in the ascorbic acid group than both saline and controls, suggesting that the observed responses were specifically related to pain intensity and duration. These findings reveal distributed cortical systems, including parietal areas as well as cingulate and frontal regions, involved in dynamic encoding of pain intensity over time, a process of great biological and clinical relevance
LA FONCTION VISUELLE CHEZ LE NOUVEAU-NES SAINS A TERME ET CHEZ LES PREMATURES PARVENUS AU MEME AGE CONCEPTIONEL
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Single-Trial Characterization of BOLD fMRI Responses by Self-Organizing Neural Networks
No full textFunctional magnetic resonance imaging (fMRI) plays a dominant role in human brain mapping studies. As of today, no standards exist for processing fMRI data and analysis techniques are often associated to the different stimulation paradigms used to acquire functional data. Being able to estimate the hemodynamic response following a single execution of a task permits to characterize its relationship to different aspects of the stimulus, and of the subject’s performance. This works is aimed to test a strategy for the characterization of single trial-related BOLD fMRI responses based on the self-organizing maps method of Kohonen (SOMs). Analysis have been carried out on synthetic fMRI images modeling activation and on data from a single-event fMRI experiment on one human subject performing a basic motor task. Results were able to define the potentiality range for this data-driven methodology in monitoring the evolution of the BOLD response deriving from a single stimulation
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