Spectral analysis of near-infrared spectroscopy signals measured from prefrontal lobe in subjects at risk for stroke

Purpose: The objective of this study was to assess the spontaneous cerebral oscillations based on the wavelet transform of near-infrared spectroscopy (NIRS) signals in subjects at risk for atherosclerotic stroke. Methods: A total of 32 subjects were recruited from the university to participate in this study: 20 were normal subjects (age = 59.6 ± 10.2 year) and the other 12 were subjects at risk for ischemic stroke (age = 60.2 ± 10.1 year).The cerebral oxygenation signal was monitored for 10 min from the left prefrontal lobe using NIRS. Results: With spectral analysis based on wavelet transform, five frequency intervals were identified (I, 0.005-0.02 Hz; II, 0.02-0.06 Hz; III, 0.06-0.15 Hz; IV, 0.15-0.40 Hz; and V, 0.40-2.0 Hz). The amplitude of the Hb in the frequency intervals from I to V and of the HbO2in frequency intervals I and V in subjects at risk for stroke were found to be significantly lower compared to the amplitudes in normal subjects. Conclusions: The reduction of spontaneous oscillations in these subjects suggests an increased stiffness in the cerebral artery. This indicates the possibility of applying spontaneous oscillations, based on the wavelet transform of NIRS signals, to assess the risk in subjects with atherosclerosis.