Auditory hemodynamic studies of newborn infants using near-infrared spectroscopic imaging

The noninvasive study of tissue blood volume and oxygenation using near-infrared light is a new and actively developing technology. We have used near-infrared spectroscopic imaging (NIRSI) to study hemodynamic responses on the auditory cortices evoked by auditory stimulation. Ten healthy newborn infants were studied. The otoacoustic emission hearing test was performed for each infant. Pulse oximetry was used to monitor the heart rate during the measurement, video recording was used to monitor motion artifacts, and the eye movements were noted in order to determine sleep stage. A 16-channel frequency-domain optical imaging system developed in our laboratory was used for NIRSI measurements. The stimuli were presented in trains of seven 1 kHz beeps with 700-ms inter-stimulus intervals. The stimulus trains were separated by 25-s silent periods in order to allow for the hemodynamic delay. In 3/8 cases, we obtained a clear bilateral increase in [HbO₂], and in two additional cases, a clear response on one hemisphere. The mean change in [HbO₂] was +0.9±0.9μM and the mean change in [Hb] was -0.3±0.4μM for those channels producing the largest response for each subject. No statistically significant response was found in 3/8 cases.