Abstract

Multi-source operation in time-domain optical brain imaging often relies on the use of piezomechanical fiber switches which limit the speed when recording dynamic processes. The concept presented in this work overcomes this limitation by multiplexing on the nanosecond and microsecond time scales. In particular, the source positions were encoded by different delays on the nanosecond time scale. Multiplexing of wavelengths on the microsecond time scale (e.g. within 100 µs) was achieved by burst-mode operation of picosecond diode lasers in combination with addressing of different memory blocks in time-correlated single photon counting by means of routing inputs. This concept was implemented for 4 detectors and 5 source optodes yielding 12 measurement channels per hemisphere. In order to largely equalize the count rates for all source-detector pairs with minimal overall losses, a setup was developed that enabled the freely adjustable distribution of laser power to the various source optodes. It was based on polarization splitters and motorized broadband polarization rotators. The method was successfully demonstrated in an in vivo experiment employing two different types of motor activation of the brain.

© 2013 SPIE