Human brain functional imaging with reflectance CWS.

Continuous Wave Spectroscopy (CWS) has been used in human subjects to detect brain function by observation of brain oxygenation and blood volume changes. In this research, we have developed a device for imaging brain oxygenation and blood volume with multiple sources and detectors in an area of 10 x 12 cm. Twelve, 1 watt tungsten bulbs were used as a light source, together with 8 detectors consisting of silicon-photodiodes with band-pass filters at 760 and 850 nms. The detectors were placed on a model system of the human head, providing 16 source-detector combinations with 4 cm separation. Eight to 16 seconds were required to image a brain function. Models using resin and a black object which have similar optical characteristics to a brain were studied. The model study showed that we can detect changes in absorption as deep as 2 cm from the surface. Human subjects with relatively thin hair, who volunteered for this study, were asked to tap fingers and rest, or to observe light flashing and darkness alternatively for 10 to 20 minutes while the images were being taken. In the finger tapping, the blood volume increased in a small, 1-2 cm area, while in the light stimulation, a much larger area was affected with a greater increased blood volume. Oxygenation occurred also in the area where blood volume increased. We concluded that the CWS can be used to image the location of brain activity by means of blood volume increase and oxygenation. In addition, brain disfunction and diseases, such as learning disability and brain hematoma may be detected with this imaging device.