Bedside functional imaging of the premature infant brain during passive motor activation

Changes in regional brain blood flow and hemoglobin oxygen saturation occur in the human cortex in response to neural activation. These changes create a signal that can be imaged and quantitated using various methods, most of which do not allow for continuous bedside measurements. Imaging methods using near-infrared light, however, have been described. These allow for non-invasive measurements, and take advantage of the fact that hemoglobin is a strong absorber at these wavelengths and thus acts as a "natural" contrast agent. We have generated brain functional images of ill, premature infants during passive movement of the forearm using the Boston Diffusion Optical Tomography System (DOTS), a system which allows for near real-time bedside assessments. For these initial feasibility studies in the neonatal intensive care unit (NICU), custom-made soft flexible probes were made, and passive motor tasks were performed during imaging. We found that specific passive movements of the arm resulted in focal, reproducible changes in cerebral absorption at 830 nm, indicating an increase in regional blood flow and oxygenation. Further bedside studies have since been undertaken using 780 nm and 830 nm lasers. These studies indicate that the Boston DOTS is a safe and feasible bedside near-infrared functional imaging device, and underline the importance of further studies in this critically ill patient group at high risk for brain injury.