Abstract 1063
Neonatology: Clinical Investigation Platform, Monday, 5/3
Functional brain activity in newborn infants was studied by a dual wavelength, frequency encoded, phased array imaging system which allows detection of blood volume and oxygenation changes resulting from neurovascular coupling during brain activation. This system uses two frequencies (50 and 52 MHz) to encode two wavelengths (750 and 830nm) for localization of changes in absorption. The subtraction and sum of these wavelength data indicate oxygenation and blood volume, respectively and is highly sensitive to perturbations of the size of 70 microns volume and 20 picomole of an absorber. We studied 7 infants (26 ± 4 wks gestational age) at an average postnatal age of 30 ± 18 days. Two infants suffered a Grade III intracranial hemorrhage, one had hypoxic-ischemic encephalopathy while the other 4 were considered normal. Longitudinal, sequential imaging studies were performed using a probe with 9 pairs of laser diodes and 4 detector fiber bundles mounted on a rubber pad with a source-detector separation of 2.0 cm resulting in an image with spatial resolution of ≈ 1.0 cm and a signal to noise ratio of 500. The probe was placed on the head and centered to cover the sensorimotor cortex. Infants were stimulated by separately touching the four extremities while signals were concurrently recorded over a 30 sec time period. Images were made using a back projection algorithm by subtracting the signals obtained from a "resting" state to those obtained during activation of the somatosensory cortex following tactile stimulation. The difference between the rest state and activated state, which forms the images, reflects functional changes in the brain. The results of our study indicate that in the preterm brain, the sensory pathway is intact and capable of responding to tactile stimuli. Further, in the normal babies a reproducible response occurs with intense signal changes detectable in the region of the somatosensory cortex contralateral to the tactile stimulus. On the contrary, in infants with brain injury, the signal was much lower in intensity and non-localized. In summary we have used a sensitive, non-invasive bed-side optical tomography system capable of linking changes in brain function with specific areas in the cortex. These preliminary studies suggest that this technique may be useful to detect metabolic alterations, as a result of changes in brain tissue oxygenation, in infants at risk for hypoxic-ischemic brain injury. We speculate that application of this technique to infants sustaining acute brain injury and studied longitudinally might provide prognostic information regarding recovery of function.
