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

Background: Changes in regional brain blood flow and hemoglobin oxygen satu ration occur in the human cortex in response to neural activation. Traditio nal functional radiologic methods cannot provide continuous, portable measu rements. Imaging methods, which use near-infrared light allow for non-invas ive measurements by taking advantage of the fact that hemoglobin is a stron g absorber at these wavelengths. Aims: To test the feasibility of a new optical functional imaging system in premature infants, and to obtain preliminary brain imaging of passive moto r activation in this population. Methods: A new optical imaging system, the Diffuse Optical Tomography Syste m (DOTS), was used to provide real-time, bedside assessments. Custom-made s oft flexible fiberoptic probes were placed on two extremely ill, mechanical ly ventilated 24 week premature infants, and three healthier 32 week premat ure infants. Passive motor stimulation protocols were used during imaging. Results: Specific movement of the arm resulted in reproducible focal, contr alateral changes in cerebral absorption. The data suggest an overall increa se in blood volume to the imaged area, as well as an increase in deoxyhemog lobin concentration. These findings in premature infants differ from those expected in adults. Conclusions: In the intensive care setting, continuous non-invasive optical functional imaging could be critically important and, with further study, may provide a bedside monitoring tool for prospectively identifying patient s at high risk for brain injury.