Background and Purpose-Functional MRI is a powerful tool to investigate recovery of brain function in patients withstroke. An inherent assumption in functional MRI data analysis is that the blood oxygenation level-dependent (BOLD) signal is stable over the course of the examination. In this study, we evaluated the validity of such assumption in patients with chronic stroke. Methods-Fifteen patients performed a simple motor task with repeated epochs using the paretic and the unaffected hand in separate runs. The corresponding BOLD signal time courses were extracted from the primary and supplementary motor areas of both hemispheres. Statistical maps were obtained by the conventional General Linear Model and by a parametric General Linear Model. Results-Stable BOLD amplitude was observed when the task was executed with the unaffected hand. Conversely, the BOLD signal amplitude in both primary and supplementary motor areas was progressively attenuated in every patient when the task was executed with the paretic hand. The conventional General Linear Model analysis failed to detect brain activation during movement of the paretic hand. However, the proposed parametric General Linear Model corrected the misdetection problem and showed robust activation in both primary and supplementary motor areas. Conclusions-The
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.
Our study suggests that a single MT intervention in stroke survivors is related to increased MEP of the affected limb, and a more constrained activity of the affected M1, as if activity had become more constrained and limited to the affected hemisphere.
Purpose To quantify the amplitude and temporal aspects of the 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 ± 3.7 years, 11 women) were subjected to a functional paradigm composed of five epochs of auditory stimulus (3 seconds) intercalated by six intervals of rest (21 seconds). 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-half-maximum (FWHM) and amplitude. Results BOLD onset time (p < 0.001) and 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 envisages future application of this protocol in clinical studies aimed at evaluating CVR of the MCA territory.
Background and Purpose: Previous transcranial Doppler studies have suggested that, in patients with severe carotid stenosis, the lack of cerebrovascular reactivity (CVR) is an independent predictor of ipsilateral stroke. The BOLD (Blood Oxygenation Level-Dependent) fMRI contrast can be used to assess the CVR during normal condition and during hemodynamic stress, like hypercapnia. The purpose of this study is to evaluate the BOLD signal parameters on the Middle Cerebral Artery (MCA) territory, induced by auditory stimulus, during different levels of hypercapnia in patients with severe unilateral carotid stenosis, comparing the ipsilateral hemisphere (IH) to the contralateral hemisphere (CH). Methods: The images were obtained from 16 patients with severe unilateral carotid stenosis. Patients were submitted to an auditory stimulus (3s) in three different conditions: normocapnia and at EtCO2 increase of 5 and 10mmHg. The images were acquired with a 3T Philips MR, preprocessed and analyzed using an autoregressive method. Results: The BOLD signal from the IH was different from the CH during the basal condition and at 5mmHg (p<0.0001), but not at the 10mmHg ETCO2 increase. For each BOLD parameter, the major differences between the hemispheres were seen on the onset time (p<0.0001) and amplitude of BOLD signal (p<0.0001). The width difference was significant between the basal and 10mmhHg increase (p<0.01). In these three parameters, the BOLD signal of the IH presented no significant variations with the CO2 increment. However, the BOLD signal for CH showed an increase on the time-to-onset and width and amplitude decrease. The time to peak parameters of the BOLD signal showed no differences between the hemispheres and at hypercapnic conditions. Conclusion: In our results the IH did not respond to the hypercapnic stress as the CH. Therefore, among patients with severe carotid stenosis, BOLD can reliably identify some that have an exhausted CVR, which cannot respond to a vasodilatory stress like hypercapnia. Future studies using this technique may help to select patients for recanalization procedures.
Background: Cerebrovascular reactivity (CVR) has been suggested as an independent predictor of stroke in patients with severe carotid stenosis. Functional-MRI (fMRI) can be used to assess CVR by comparing latency parameters of the neurovascular coupling, i.e. BOLD response at baseline and during hypercarbic challenge. We aim to compare BOLD amplitude and latency parameters in the ipsilateral (IH) and contralateral hemispheres (CH) induced by auditory stimulus, under different hypercapnia levels in diabetic and non-diabetic patients with symptomatic carotid stenosis, before and after carotid stenting. Methods: seven diabetic and eight non-diabetic patients with unilateral severe symptomatic carotid stenosis and similar clinical characteristics were evaluated. The protocol was undertaken one week before and three months after the endovascular intervention. Subjects were submitted to auditory stimulus (3s) under normocapnia and EtCO2 increase of 5 and 10mmHg. The images were acquired with a 3T MRI-scanner, preprocessed and BOLD response amplitude and latency parameters were analyzed. Results: We observed decreased BOLD amplitude in the IH compared to the CH (p<0.05) in non-diabetic patients in hypercapnic conditions, and was compromised bilaterally in diabetic patients before the stenting. In diabetic patients the mean change on BOLD latency parameters were not significant with CO2 increment. After carotid stenting, BOLD amplitude (p<0.05) under hypercapnic conditions and area under the curve (P<0.05) were increased for non-diabetic patients but not for diabetic patients. Conclusions: diabetic patients have diffuse baseline compromise of CVR and their cerebrovascular reactivity measured on BOLD fMRI does not respond to carotid stenting as non-diabetic patients.
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