Functional brain imaging with a supercontinuum time-domain NIRS system

Abstract

We have developed the second generation of our time-domain near-infrared spectroscopy (TD-NIRS) system for baseline and functional brain imaging. The instrument uses a pulsed broadband supercontinuum laser emitting a large spectrum between 650 and 1700 nm, and a gated detection based on an intensified CCD camera. The source laser beam is split into two arms, below and above 776 nm. In each arm, a fast motorized filter wheel enables selection of a bandpass filter at the required wavelength. Each filtered laser beam is then launched into one array of source fibers. The multiplexing through the array of fibers is implemented through a very compact home-made design consisting of two galvanometer mirrors followed by an achromatic doublet. Source fibers are then recombined one-by-one from both arms into the source optodes to be positioned on the head. The detection fibers are all imaged in parallel through a relay lens on an intensified CCD camera. By using detection fibers of different lengths, we introduce optical delays that enable simultaneous recording in different delay windows of the temporal point spread functions. We present the instrumentation and show its preliminary functional imaging capabilities. We also introduce a new probe where we use different fiber lengths on the source and the detector sides in order to record simultaneously both wavelengths from one location through different sets of fibers.