Navegando por Autor "Leoni, Renata F."

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Arterial Spin Labeling Measurements of Cerebral Perfusion Territories in Experimental Ischemic Stroke
(2011) Leoni, Renata F.; Paiva, Fernando F.; Kang, Byeong-Teck; Henning, Erica C.; Nascimento, George Carlos; Tannús, Alberto; Araújo, Dráulio Barros de; Silva, Afonso C.
Collateral circulation, defined as the supplementary vascular network that maintains cerebral blood flow (CBF) when the main vessels fail, constitutes one important defense mechanism of the brain against ischemic stroke. In the present study, continuous arterial spin labeling (CASL) was used to quantify CBF and obtain perfusion territory maps of the major cerebral arteries in spontaneously hypertensive rats (SHRs) and their normotensive Wistar-Kyoto (WKY) controls. Results show that both WKY and SHR have complementary, yet significantly asymmetric perfusion territories. Right or left dominances were observed in territories of the anterior (ACA), middle and posterior cerebral arteries, and the thalamic artery. Magnetic resonance angiography showed that some of the asymmetries were correlated with variations of the ACA. The leptomeningeal circulation perfusing the outer layers of the cortex was observed as well. Significant and permanent changes in perfusion territories were obtained after temporary occlusion of the right middle cerebral artery in both SHR and WKY, regardless of their particular dominance. However, animals with right dominance presented a larger volume change of the left perfusion territory (23±9%) than animals with left dominance (7±5%, P<0.002). The data suggest that animals with contralesional dominance primarily safeguard local CBF values with small changes in contralesional perfusion territory, while animals with ipsilesional dominance show a reversal of dominance and a substantial increase in contralesional perfusion territory. These findings show the usefulness of CASL to probe the collateral circulation.
Assessing Cerebrovascular Reactivity in Carotid Steno-Occlusive Disease UsingMRI BOLD and ASL Techniques
(2012-04-17) Leoni, Renata F.; Mazzetto-Betti, Kelley C.; Silva, Afonso C.; Santos, Antonio C. dos; Araújo, Dráulio Barros de; Leite, João P.; Pontes-Neto, Octavio M.
Impaired cerebrovascular reactivity (CVR), a predictive factor of imminent stroke, has been shown to be associated with carotid steno-occlusive disease. Magnetic resonance imaging (MRI) techniques, such as blood oxygenation level-dependent (BOLD) and arterial spin labeling (ASL), have emerged as promising noninvasive tools to evaluate altered CVR with whole-brain coverage, when combined with a vasoactive stimulus, such as respiratory task or injection of acetazolamide. Under normal cerebrovascular conditions, CVR has been shown to be globally and homogenously distributed between hemispheres, but with differences among cerebral regions. Such differences can be explained by anatomical specificities and different biochemical mechanisms responsible for vascular regulation. In patients with carotid steno-occlusive disease, studies have shown that MRI techniques can detect impaired CVR in brain tissue supplied by the affected artery. Moreover, resulting CVR estimations have been well correlated to those obtained with more established techniques, indicating that BOLD and ASL are robust and reliable methods to assess CVR in patients with cerebrovascular diseases. Therefore, the present paper aims to review recent studies which use BOLD and ASL to evaluate CVR, in healthy individuals and in patients with carotid steno-occlusive disease, providing a source of information regarding the obtained results and the methodological difficulties.
Magnetic resonance imaging quantification of regional cerebral blood flow and cerebrovascular reactivity to carbon dioxide in normotensive and hypertensive rats
(2011-06-25) Leoni, Renata F.; Paiva, Fernando F.; Henning, Erica C.; Nascimento, George Carlos do; Tannús, Alberto; Araújo, Dráulio Barros de; Silva, Afonso C.
Hypertension afflicts 25% of the general population and over 50% of the elderly. In the presentwork, arterial spin labeling MRI was used to non-invasively quantify regional cerebral blood flow (CBF), cerebrovascular resistance and CO2 reactivity in spontaneously hypertensive rats (SHR) and in normotensive Wistar Kyoto rats (WKY), at two different ages (3 months and 10months) and under the effects of two anesthetics, α-chloralose and 2% isoflurane (1.5 MAC). Repeated CBF measurements were highly consistent, differing by less than 10% and 18% within and across animals, respectively. Under α-chloralose, whole brain CBF at normocapnia did not differ between groups (young WKY: 61±3 ml/100 g/min; adult WKY: 62±4 ml/100 g/min; young SHR: 70± 9 ml/100 g/min; adult SHR: 69±8 ml/100 g/min), indicating normal cerebral autoregulation in SHR. At hypercapnia, CBF values increased significantly, and a linear relationship between CBF and PaCO2 levels was observed. In contrast, 2% isoflurane impaired cerebral autoregulation. Whole brain CBF in SHR was significantly higher than inWKYrats at normocapnia (young SHR: 139±25 ml/100 g/min; adult SHR: 104±23 ml/100 g/min; young WKY: 55±9ml/100 g/min; adult WKY: 71±19 ml/100 g/min). CBF values increased significantly with increasing CO2; however, there was a clear saturation of CBF at PaCO2 levels greater than 70 mm Hg in both young and adult rats, regardless of absolute CBF values, suggesting that isoflurane interferes with the vasodilatory mechanisms of CO2. This behavior was observed for both cortical and subcortical structures. Under either anesthetic, CO2 reactivity values in adult SHRwere decreased, confirming that hypertension, when combined with age, increases cerebrovascular resistance and reduces cerebrovascular compliance.
Quantification of BOLD fMRI Parameters to Infer Cerebrovascular Reactivity of the Middle Cerebral Artery
(2013) Mazzetto-Betti, Kelley C.; Leoni, Renata F.; Pontes-Neto, Octavio M.; Sturzbecher, Marcio J.; Santos, Antonio C.; Leite, Joao P.; Silva, Afonso C.; Araújo, Dráulio Barros de
Purpose: To quantify the amplitude and temporal aspects of the blood oxygenation level-dependent (BOLD) response to an auditory stimulus during normocapnia and hypercapnia in healthy subjects in order to establish which BOLD parameters are best suited to infer the cerebrovascular reactivity (CVR) in the middle cerebral artery (MCA) territory. Materials and Methods: Twenty healthy volunteers (mean age: 23.6 6 3.7 years, 11 women) were subjected to a functional paradigm composed of five epochs of auditory stimulus (3 sec) intercalated by six intervals of rest (21 sec). Two levels of hypercapnia were achieved by a combination of air and CO2 while the end-tidal CO2 (ETCO2) was continually measured. An autoregressive method was applied to analyze four parameters of the BOLD signal: onset-time, time-to-peak, full-width-at-halfmaximum (FWHM), and amplitude. Results: BOLD onset time (P < 0.001) and full-width at half-maximum (FWHM) (P < 0.05) increased linearly, while BOLD amplitude decreased (P < 0.001) linearly with increasing levels of hypercapnia. Test–retest for reproducibility in five subjects revealed excellent concordance for onset time and amplitude. Conclusion: The robust linear dependence of BOLD onset time, FWHM, and amplitude to hypercapnia suggest future application of this protocol in clinical studies aimed at evaluating CVR of the MCA territory.

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Navegando por Autor "Leoni, Renata F."