Brain water interhemispheric balance assessed by fNIRS from frontal lobe provides separation between stroke patients and controls

Using functional near-infrared spectroscopy (fNIRS) to get stroke biomarkers so far only focuses on the hemodynamic response, which may be limited, while other modalities, e.g., MRI, have started to observe brain water. To the best of our knowledge, this is the first study of using fNIRS that utilised water fluctuation in the brain. In this present study, we investigated the interhemispheric balance of the brain water (including water in blood, brain tissue, and CSF) measured using a novel fNIRS device capable of sensing both water and blood volume dynamics. Measurement was performed from the prefrontal cortex area for 5 minutes while subjects were resting in a sitting position. The analysis relied on correlation between signals from left and right hemispheres in two bands of interest, i.e., respiratory (0.1-0·6 Hz) and cardiac (0.6-5 Hz) bands. This study involved 58 stroke patients (27 females, 67.7 ± 11.9 years old) and 33 controls (22 females, 69.4 ± 8.0 years old). Here, we show that the brain water provides good separation (p-value<0·001) between patients and controls, which may be related to the swelling caused by stroke; it is even better than relying on the hemodynamic response.