Localizing the focus of ischemic stroke with near infrared spectroscopy

Objective To evaluate the changes in near infrared spectroscopy (NIRS) absorptive properti es induced by cerebral ischemia. Methods A dual wavelength (760nm and 850nm) NIRS system measuring total hemoglobin c oncentration changes was constructed.Twenty Sprague-Dawley rats were used to set up middle cerebral artery occlusion (MCAO) model that had a stable ischemia focus on the cortex.We used NIRS to localize the ischemia focus that was confirmed with magnetic resonance imaging (MRI) and triphenyltetrazonlium chlori de brain staining.The cortical ischemia area and the geometric configuration o f the NIRS topograms were compared with those from MRI and the anatomical sample s for the same rat. Results The reconstructed NIRS topograms showed that there was an optical density decrea sed area on the left cortex of the rats with MCAO model.The mean ischemia area as shown in NIRS images was 19.50mm(2) (19.50±0.35mm(2), n=20).Ana tomi cal samples showed that the mean ischemic area located in the NIRS measurement a rea was 18.46mm(2) (18.46±0.38mm(2), n=20).For MRI, the mean isc hemia area located in the NIRS measurement area was 20.71mm(2) (20.71±0.27 mm(2), n=20).There were no significant differences among NIRS, MRI and anatomical samples (F(2,57)=2.47, P>0.05) for defining the ischemia area.The re sults showed that there was a significant correlation among NIRS, MRI (r=0 .782, P<0.05) and anatomical sample (r=0.851, P<0.05) for the same cortical ischemia area.Meanwhile, the location and geometric configuration of the ischemia focus shown by NIRS were identified by MRI and anatomical samples, though the NIRS images had worse spatial resolution.Conclusions NIRS showed a good agreement with MRI and anatomical samples in the ischemic are a and location determination of the infarction focus for the rat MCAO model.Th e study suggests that NIRS can non-invasively trace cortical hemodynamic change s induced by ischemia in real time.