Abstract
PurposeQuantitative imaging of neuromagnetic fields based on automated region of interest (ROI) setting was analyzed to determine the characteristics of cerebral neural activity in ischemic areas.MethodsMagnetoencephalography (MEG) was used to evaluate spontaneous neuromagnetic fields in the ischemic areas of 37 patients with unilateral internal carotid artery (ICA) occlusive disease. Voxel-based time-averaged intensity of slow waves was obtained in two frequency bands (0.3–4 Hz and 4–8 Hz) using standardized low-resolution brain electromagnetic tomography (sLORETA) modified for a quantifiable method (sLORETA-qm). ROIs were automatically applied to the anterior cerebral artery (ACA), anterior middle cerebral artery (MCAa), posterior middle cerebral artery (MCAp), and posterior cerebral artery (PCA) using statistical parametric mapping (SPM). Positron emission tomography with 15O-gas inhalation (15O-PET) was also performed to evaluate cerebral blood flow (CBF) and oxygen extraction fraction (OEF). Statistical analyses were performed using laterality index of MEG and 15O-PET in each ROI with respect to distribution and intensity.ResultsMEG revealed statistically significant laterality in affected MCA regions, including 4–8 Hz waves in MCAa, and 0.3–4 Hz and 4–8 Hz waves in MCAp (95% confidence interval: 0.020–0.190, 0.030–0.207, and 0.034–0.213), respectively. We found that 0.3–4 Hz waves in MCAp were highly correlated with CBF in MCAa and MCAp (r = 0.74, r = 0.68, respectively), whereas 4–8 Hz waves were moderately correlated with CBF in both the MCAa and MCAp (r = 0.60, r = 0.63, respectively). We also found that 4–8 Hz waves in MCAp were statistically significant for misery perfusion identified on 15O-PET (p<0.05).ConclusionsQuantitatively imaged spontaneous neuromagnetic fields using the automated ROI setting enabled clear depiction of cerebral ischemic areas. Frequency analysis may reveal unique neural activity that is distributed in the impaired vascular metabolic territory, in which the cerebral infarction has not yet been completed.
Highlights
Imaging of the ischemic penumbra [1, 2], in which cerebral blood flow is reduced but neurons have not yet become necrotic, is currently a key area of interest in the investigation of cerebrovascular disease [3, 4] because ischemic penumbra, which is evident in the brain of patients suffering from ischemic cerebrovascular disease, commonly progresses to cerebral infarction [5]
We found that 0.3–4 Hz waves in MCAp were highly correlated with cerebral blood flow (CBF) in middle cerebral artery (MCAa) and MCAp (r = 0.74, r = 0.68, respectively), whereas 4–8 Hz waves were moderately correlated with CBF in both the MCAa and PLOS ONE | DOI:10.1371/journal.pone
We subsequently developed standardized low-resolution brain electromagnetic tomography modified for a quantifiable method, which is a spatial filtering technique that enables quantitative assessment of the current intensity of intracerebral neural activity [23], and reported that sLORETA-qm enables both quantitative imaging of cerebral slow-wave distribution in patients with ischemic cerebrovascular disease, and visualization of the changes in slow-wave distribution that are associated with the cerebrovascular condition [24]
Summary
Imaging of the ischemic penumbra [1, 2], in which cerebral blood flow is reduced but neurons have not yet become necrotic, is currently a key area of interest in the investigation of cerebrovascular disease [3, 4] because ischemic penumbra, which is evident in the brain of patients suffering from ischemic cerebrovascular disease, commonly progresses to cerebral infarction [5]. Ischemic penumbra can be assessed on the basis of the clinical symptoms (e.g., transient ischemic attack, TIA), anatomical findings (computed tomography, CT; and magnetic resonance imaging, MRI), and by measuring cerebral blood flow and metabolism (single photon emission computed tomography (SPECT) and positron emission tomography (PET)). Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) of MRI have been utilized to evaluate ischemic cerebrovascular disorders, and the area of DWI-PWI mismatch is thought to represent the area of reversible ischemia [8, 9]. CT perfusion imaging has been utilized to evaluate the ischemic area in the acute stage of stroke [10, 11]. CT and MRI cannot always determine the area of reversible ischemia because these methods image the secondary change of tissues caused by a decrease in cerebral blood flow. PET and SPECT are the gold standards for evaluating cerebral ischemia, they cannot be casually performed due to risks such as radiation exposure or arterial blood sampling
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