Visualization of Altered Neurovascular Coupling in Chronic Stroke Patients using Multimodal Functional MRI
Blicher JU., Stagg CJ., O'Shea J., Østergaard L., MacIntosh BJ., Johansen-Berg H., Jezzard P., Donahue MJ.
Evaluation of cortical reorganization in chronic stroke patients requires methods to accurately localize regions of neuronal activity. Blood oxygenation level-dependent ( BOLD) functional magnetic resonance imaging (fMRI) is frequently employed; however, BOLD contrast depends on specific coupling relationships between the cerebral metabolic rate of oxygen ( CMRO2), cerebral blood flow ( CBF), and volume ( CBV), which may not exist following stroke. The aim of this study was to understand whether CSF-weighted ( CBFw) and CSV-weighted ( CBVw) fMRI could be used in sequence with BOLD to characterize neurovascular coupling mechanisms poststroke. Chronic stroke patients ( n = 11) with motor impairment and age-matched controls ( n = 11) performed four sets of unilateral motor tasks (60 seconds/30 seconds off/on) during CBFw, CBVw, and BOLD fMRI acquisition. While control participants elicited mean BOLD, CBFw, and CBVw responses in motor cortex ( P < 0.01), patients showed only mean changes in CBF ( P < 0.01) and CBV ( P < 0.01), but absent mean BOLD responses ( P = 0.20). BOLD intersubject variability was consistent with differing coupling indices between CBF, CBV, and CMRO2. Thus, CBFw and/or CBVw fMRI may provide crucial information not apparent from BOLD in these patients. A table is provided outlining distinct vascular and metabolic uncoupling possibilities that elicit different BOLD responses, and the strengths and limitations of the multimodal protocol are summarized.