Measurement system for noninvasive dynamic optical topography

We have developed a 24-channel simultaneous measurement system for optical topography that noninvasively obtains dynamic images of brain activity using near-infrared light. To evaluate the system performance, we utilized a dynamic phantom containing a rotating absorber in a cylindrical scattering medium. In this system, eight incident and eight detecting optical fibers are arranged alternately at square lattice points on the phantom. The phantom is illuminated with light of two wavelengths (780 and 830 nm) from each incident fiber. Reflected light is received by the detecting fibers, each of which is connected to an avalanche photodiode. Multiple light intensity modulation and lock-in detection are used to enable highly sensitive measurement with negligible cross talk for multichannel measurement. In the phantom measurement, we obtained topographic dynamic images of the absorber rotating in the medium with a temporal resolution of 0.5 s over a measurement area of 90 mm×90 mm. © 1999 Society of Photo-Optical Instrumentation Engineers.