385 research outputs found

    Coupling and robustness of intra-cortical vascular territories

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    Vascular domains have been described as being coupled to neuronal functional units enabling dynamic blood supply to the cerebral cyto-architecture. Recent experiments have shown that penetrating arterioles of the grey matter are the building blocks for such units. Nevertheless, vascular territories are still poorly known, as the collection and analysis of large three-dimensional micro-vascular networks are difficult. By using an exhaustive reconstruction of the micro-vascular network in an 18 mm 3 volume of marmoset cerebral cortex, we numerically computed the blood flow in each blood vessel. We thus defined arterial and venular territories and examined their overlap. A large part of the intracortical vascular network was found to be supplied by several arteries and drained by several venules. We quantified this multiple potential to compensate for deficiencies by introducing a new robustness parameter. Robustness proved to be positively correlated with cortical depth and a systematic investigation of coupling maps indicated local patterns of overlap between neighbouring arteries and neighbouring venules. However, arterio-venular coupling did not have a spatial pattern of overlap but showed locally preferential functional coupling, especially of one artery with two venules, supporting the notion of vascular units. We concluded that intra-cortical perfusion in the primate was characterised by both very narrow functional beds and a large capacity for compensatory redistribution, far beyond the nearest neighbour collaterals

    Arterial Spin Labeling Perfusion of the Brain: Emerging Clinical Applications

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    Arterial spin labeling (ASL) is a magnetic resonance (MR) imaging technique used to assess cerebral blood flow noninvasively by magnetically labeling inflowing blood. In this article, the main labeling techniques, notably pulsed and pseudocontinuous ASL, as well as emerging clinical applications will be reviewed. In dementia, the pattern of hypoperfusion on ASL images closely matches the established patterns of hypometabolism on fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) images due to the close coupling of perfusion and metabolism in the brain. This suggests that ASL might be considered as an alternative for FDG, reserving PET to be used for the molecular disease-specific amyloid and tau tracers. In stroke, ASL can be used to assess perfusion alterations both in the acute and the chronic phase. In arteriovenous malformations and dural arteriovenous fistulas, ASL is very sensitive to detect even small degrees of shunting. In epilepsy, ASL can be used to assess the epileptogenic focus, both in peri- and interictal period. In neoplasms, ASL is of particular interest in cases in which gadolinium-based perfusion is contraindicated (eg, allergy, renal impairment) and holds promise in differentiating tumor progression from benign causes of enhancement. Finally, various neurologic and psychiatric diseases including mild traumatic brain injury or posttraumatic stress disorder display alterations on ASL images in the absence of visualized structural changes. In the final part, current limitations and future developments of ASL techniques to improve clinical applicability, such as multiple inversion time ASL sequences to assess alterations of transit time, reproducibility and quantification of cerebral blood flow, and to measure cerebrovascular reserve, will be reviewed

    The Venular Side of Cerebral Amyloid Angiopathy: Proof of Concept of a Neglected Issue.

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    Small vessel diseases (SVD) is an umbrella term including several entities affecting small arteries, arterioles, capillaries, and venules in the brain. One of the most relevant and prevalent SVDs is cerebral amyloid angiopathy (CAA), whose pathological hallmark is the deposition of amyloid fragments in the walls of small cortical and leptomeningeal vessels. CAA frequently coexists with Alzheimer's Disease (AD), and both are associated with cerebrovascular events, cognitive impairment, and dementia. CAA and AD share pathophysiological, histopathological and neuroimaging issues. The venular involvement in both diseases has been neglected, although both animal models and human histopathological studies found a deposition of amyloid beta in cortical venules. This review aimed to summarize the available information about venular involvement in CAA, starting from the biological level with the putative pathomechanisms of cerebral damage, passing through the definition of the peculiar angioarchitecture of the human cortex with the functional organization and consequences of cortical arteriolar and venular occlusion, and ending to the hypothesized links between cortical venular involvement and the main neuroimaging markers of the disease

    Functional MR Imaging in intracranial and extracranial artery stenosis: evaluation of cerebral vasoreactivity with a breath-hold paradigm

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    PURPOSE In the clinical practice cerebral vasoreactivity (CVR) can be evaluated by Trans-Cranial Doppler (TCD) examination or by Nuclear Medicine. In this study we test the feasibility of Functional Magnetic Resonance Imaging (f-MRI) to measure the CVR in patient with stenosis of internal carotid artery (ICA) or middle cerebral artery (MCA). The results were compared to those obtained by TCD. MATERIAL AND METHODS We enrolled 21 patients affected by stenosis of the internal carotid artery (ICA) or the middle cerebral artery (MCA). All patients underwent a 3 Tesla MR examination. Cerebral vasoreactivity was evaluated by a breath-hold f-MRI protocol. F-MRI data analysis was performed using FEAT tool of FSL package. Activation Maps in Regions of Interest (ROIs) of the MCA were obtained for each patient, with calculation of the percentage of activated voxels (% Act Vox) and the maximum (Z-max) and mean (Z-mean) values of the magnitude of the response. BOLD indexes (maximum peak, slope half-maximum, full-width half-maximum) were also obtained by placing ROIs in the cortex of temporal lobe, the occipital lobe, the temporal-occipital junction and in the central fissure. The MR protocol also included MR-angiography and MR perfusion sequences. A breath-hold TCD examination for the evaluation of cerebral vasoreactivity was performed in 12 of 21 patients. A ROC curve analysis was performed to compare the accuracy of breath-hold FMR with respect to breath-hold TCD in detecting a reduced CVR. RESULTS CVR evaluated by breath-hold f-MRI was significantly reduced in the cerebral tissue irrorated by the stenotic vessels. The group of patients with occlusion/subocclusion had a BOLD-CVR significantly reduced with respect to the group with moderate stenoses. Perfusional data showed a moderate positive correlation between the CBF and the BOLD-CVR. The ROC curve analysis demonstrated that breath-hold FMRI has an accuracy of 80% in detecting compromised CVR as identified by TCD. CONCLUSIONS fMRI with breath-hold paradigm is an alternative tool in the evaluation of cerebral vasoreactivity. Its advantages are the non-invasiveness, the operator-indipendence and the possibility to perform in the same examination also morphologic and angiographic sequences for a complete evaluation of brain parenchima and circulation. The measurement of BOLD response could also be helpful in the assessment of cerebral vasoreactivity in the subjects in which the trans-cranial Doppler examination is doubt, not diagnostic or not practicable

    The Measurement of Language Lateralization with Functional Transcranial Doppler and Functional MRI: A Critical Evaluation

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    Cerebral language lateralization can be assessed in several ways. In healthy subjects, functional MRI (fMRI) during performance of a language task has evolved to be the most frequently applied method. Functional transcranial Doppler (fTCD) may provide a valid alternative, but has been used rarely. Both techniques have their own strengths and weaknesses and as a result may be applied in different fields of research. Until now, only one relatively small study (n = 13) investigated the correlation between lateralization indices (LIs) measured by fTCD and fMRI and showed a remarkably high correlation. To further evaluate the correlation between LIs measured with fTCD and fMRI, we compared LIs of 22 healthy subjects (12 left- and 10 right-handed) using the same word generation paradigm for the fTCD as for the fMRI experiment. LIs measured with fTCD were highly but imperfectly correlated with LIs measured with fMRI (Spearman's rho = 0.75, p < 0.001). The imperfectness of the correlation can partially be explained by methodological restrictions of fMRI as well as fTCD. Our results suggest that fTCD can be a valid alternative for fMRI to measure lateralization, particularly when costs or mobility are important factors in the study design

    A visual quality control scale for clinical arterial spin labeling images

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    Background: Image-quality assessment is a fundamental step before c linical evaluation of mag netic resonance images. The aim of this study was to introduce a vi sual scoring system that provides a qual ity control standard for arterial spin labeling (ASL) and that can be applied to cerebral blood flow (CBF) maps, as well as to ancillary ASL images. Methods: The proposed image quality control (QC) system had two components: (1) contrast-based QC (cQC), describing the visual contrast between anatomical structures; a nd (2) artifact-based QC (aQC), evaluating image quality of theCBFmapforthepresenceofcommontypesofartifacts. Three raters evaluated cQC an d aQC for 158 quantitative signal targeting with alternating radiofrequency labelling o f arterial regions (QUASAR) ASL scans (CBF, T1 relaxation rate, arterial blood volume, and arterial transie nt time). Spearman correlation coefficient ( r ), intraclass correlation coefficients (ICC), and receiver operating characteristic analysis were used. Results: Intra/inter-rater agreement ranged from moderate to excellent; inter-rater ICC was 0.72 for cQC, 0.60 for aQC, and 0.74 for the combined QC (cQC + aQC). Intra-rater ICC was 0.90 for cQC; 0.80 for aQC, and 0.90 for the combined QC. Strong correlations were found between aQC and CBF maps quality ( r = 0.75), and between aQC and cQC ( r = 0.70). A QC score of 18 was optimal to discriminate between high and low quality clinical scans. Conclusions: The proposed QC system provided high reproducibility and a reliable threshold for discarding low quality scans. Future research should compare this v isualQCsystemwithanautomaticQCsystem

    A visual quality control scale for clinical arterial spin labeling images

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    BACKGROUND: Image-quality assessment is a fundamental step before clinical evaluation of magnetic resonance images. The aim of this study was to introduce a visual scoring system that provides a quality control standard for arterial spin labeling (ASL) and that can be applied to cerebral blood flow (CBF) maps, as well as to ancillary ASL images. METHODS: The proposed image quality control (QC) system had two components: (1) contrast-based QC (cQC), describing the visual contrast between anatomical structures; and (2) artifact-based QC (aQC), evaluating image quality of the CBF map for the presence of common types of artifacts. Three raters evaluated cQC and aQC for 158 quantitative signal targeting with alternating radiofrequency labelling of arterial regions (QUASAR) ASL scans (CBF, T1 relaxation rate, arterial blood volume, and arterial transient time). Spearman correlation coefficient (r), intraclass correlation coefficients (ICC), and receiver operating characteristic analysis were used. RESULTS: Intra/inter-rater agreement ranged from moderate to excellent; inter-rater ICC was 0.72 for cQC, 0.60 for aQC, and 0.74 for the combined QC (cQC + aQC). Intra-rater ICC was 0.90 for cQC; 0.80 for aQC, and 0.90 for the combined QC. Strong correlations were found between aQC and CBF maps quality (r = 0.75), and between aQC and cQC (r = 0.70). A QC score of 18 was optimal to discriminate between high and low quality clinical scans. CONCLUSIONS: The proposed QC system provided high reproducibility and a reliable threshold for discarding low quality scans. Future research should compare this visual QC system with an automatic QC system

    Development of a novel diffuse correlation spectroscopy platform for monitoring cerebral blood flow and oxygen metabolism: from novel concepts and devices to preclinical live animal studies

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    New optical technologies were developed to continuously measure cerebral blood flow (CBF) and oxygen metabolism (CMRO2) non-invasively through the skull. Methods and devices were created to improve the performance of near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS) for use in experimental animals and humans. These were employed to investigate cerebral metabolism and cerebrovascular reactivity under different states of anesthesia and during models of pathological states. Burst suppression is a brain state arising naturally in pathological conditions or under deep general anesthesia, but its mechanism and consequences are not well understood. Electroencephalography (EEG) and cortical hemodynamics were simultaneously measured in rats to evaluate the coupling between cerebral oxygen metabolism and neuronal activity in the burst suppressed state. EEG bursts were used to deconvolve NIRS and DCS signals into the hemodynamic and metabolic response function for an individual burst. This response was found to be similar to the stereotypical functional hyperemia evoked by normal brain activation. Thus, spontaneous burst activity does not cause metabolic or hemodynamic dysfunction in the cortex. Furthermore, cortical metabolic activity was not associated with the initiation or termination of a burst. A novel technique, time-domain DCS (TD-DCS), was introduced to significantly increase the sensitivity of transcranial CBF measurements to the brain. A new time-correlated single photon counting (TCSPC) instrument with a custom high coherence pulsed laser source was engineered for the first-ever simultaneous measurement of photon time of flight and DCS autocorrelation decays. In this new approach, photon time tags are exploited to determine path-length-dependent autocorrelation functions. By correlating photons according to time of flight, CBF is distinguished from superficial blood flow. Experiments in phantoms and animals demonstrate TD-DCS has significantly greater sensitivity to the brain than existing transcranial techniques. Intracranial pressure (ICP) modulates both steady-state and pulsatile CBF, making CBF a potential marker for ICP. In particular, the critical closing pressure (CrCP) has been proposed as a surrogate measure of ICP. A new DCS device was developed to measure pulsatile CBF non-invasively. A novel method for estimating CrCP and ICP from DCS measurement of pulsatile microvascular blood flow in the cerebral cortex was demonstrated in rats.2018-03-08T00:00:00
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