The Value of Resting-State Functional Magnetic Resonance Imaging in Stroke

Abstract

In the acute phase of stroke, the use of imaging techniques aims to provide pathophysiological information concerning vascular patency, areas of hypoperfusion, and metabolic and structural damage. Based on such information, therapeutic decisions such as the administration of reperfusion medications are made. After the acute phase, brain plasticity and reorganization are the main mechanisms underlying functional recovery, and improvement is determined by functional adaptations of distributed brain networks mediated by connectivity.1 Accordingly, new therapeutic approaches, such as noninvasive brain stimulation, target the modulation of connectivity and network function. 2,3 At this stage, imaging-based biomarkers should reflect the status of cerebral networks. As the relevance of the network view of stroke becomes increasingly evident, 4 so does the usefulness of imaging techniques in the assessment of cerebral network function in clinical populations. Most notably is the use of resting-state functional MRI (rs-fMRI).rs-fMRI is a task-independent functional neuroimaging approach based on intrinsic low-frequency fluctuations (typically <0.1 Hz) in the blood oxygenation level-dependent (BOLD) signal. This signal can be used to compute the temporal correlations between spatially remote areas, termed: functional connectivity. In the healthy brain, functional connectivity is increased between areas that are part of the same functional network even in the absence of task. The resulting spatial patterns closely resemble the activation patterns identified during specific tasks, 5 and these networks are referred to as resting-state networks. 6 Thus, rs-fMRI provides an approach for detailed investigation of functional networks, as well as a more general method for assessing changes in intrinsic neuronal activity. Unlike task-based methods, measures of intrinsic functional connectivity allow for flexible post hoc analyses that probe multiple functional networks. Additionally, the minimal demands on the patient during the scanning session make the technique an optimal choice for clinical settings.rs-fMRI may offer the prospect of providing therapeutically useful information on both the focal vascular lesion and the connectivity-based reorganization and subsequent functional recovery. Here we provide an overview of recent applications of rs-fMRI to stroke diagnostics and prognostics and discuss future perspectives and considerations. We begin with methods used to characterize local alterations in acute stroke and proceed to describe studies of specific and general connectivity changes at various phases of the recovery process. For a detailed description of the studies reviewed here, see Table I in the online-only Data Supplement. Local Intrinsic BOLD Activity as a Measure of HypoperfusionCorrelation analyses based on the BOLD signal are thought to reflect neuronal synchronization. 7 However, the BOLD signal additionally contains information concerning local blood flow and oxygen consumption 8 and is, therefore, potentially...

Structural connectome disruption at baseline predicts 6-months post-stroke outcome

“…In stroke, the connectome plays an essential role in both continuing degeneration via diaschisis, i.e., the indirect disconnection/degeneration of remote areas due to spreading of the initial injury Von Monakow, 1914;Puig et al, 2010], and recovery via modification/rewiring of damaged connections [Carter et al, 2012;Urbin et al, 2014]. Studies investigating changes to the functional connectome have been most prevalent [Carter et al, 2009;Ovadia-Caro et al, 2014], and are especially important in the context of non-invasive stimulation therapies like transcranial magnetic stimulation [Nouri and Cramer, 2011;Plow et al, r The Connectome and Recovery From Stroke r r 2595 r 2014]. Other approaches focus on the structural white matter connectome measured via diffusion MRI.…”

Relating resting-state hemodynamic changes to the variable language profiles in post-stroke aphasia

“…Measuring changes in resting-state functional MRI (rs-fMRI) may provide insights into recovery mechanisms after brain damage (Carter et al, 2010; Carter et al, 2012; Grefkes and Fink, 2011, Grefkes and Fink, 2014; Ovadia-Caro et al, 2014). There are some advantages in collecting rs-fMRI data in patient populations as the technique can non-invasively measure hemodynamic responses of patients (Biswal et al, 1995) and the participant is simply asked to remain still in the scanner for around six minutes (Ovadia-Caro et al, 2014).…”

“…There are some advantages in collecting rs-fMRI data in patient populations as the technique can non-invasively measure hemodynamic responses of patients (Biswal et al, 1995) and the participant is simply asked to remain still in the scanner for around six minutes (Ovadia-Caro et al, 2014). These features suggest that the use of rs-fMRI might be one of the easiest and most feasible approaches to identifying functional networks in patient groups (Tie et al, 2014) and thus provide important information for possible recovery studies.…”

Acetazolamide-augmented dynamic BOLD (aczBOLD) imaging for assessing cerebrovascular reactivity in chronic steno-occlusive disease of the anterior circulation: An initial experience

“…Despite growing motivation for the use of ASL in the setting of cerebrovascular disease, its use in CVR studies may be challenged by inherent limitations of the technique, including quantitative errors due to the long tag arrival time in regions with hemodynamic compromise (Bokkers et al, 2012, Petersen et al, 2006). BOLD imaging was more recently reported as a viable alternative (Ovadia-Caro et al, 2014), offering relative immunity to such errors, and thus represents a promising imaging method for interrogation of CVR.…”