On the design of a multi-channel NIR system to monitor functional brain activity

Multi-channel near-infrared spectroscopy (NIRS) offers the potential to substitute, or at least complement, electroencephalography (EEG) to detect functional activity e.g., in the motor area of the brain. Bedside NIR sensors have been used to investigate the haemodynamic shift caused by specific brain activity, such as epileptic seizures (Watanabe et al., 2000). Although it is clearly a promising data acquisition method, several open issues remain i.e. some NIR systems toggle sequentially through measurement channels, which leads to a slower acquisition time (Bunce et al., 2006). Another issue is caused by unaccounted signal contributions from superficial blood vessels within the scalp and skull. This may dilute the significance of NIR data obtained e.g. when measuring specific regional oxygenation levels during a mental or physical task. In order to investigate both effects, the following study presents the design of a multichannel NIR system that is able to perform both sequential and channel-interleaved signal acquisition. At the same time, we used two NIR detectors per measuring channel to separate the scalp and skull effects (Gersten et al., 2012; Schepens and Waanders, 2008). In order to thoroughly test this NIR system, we improved on an optical brain tissue phantom introduced by Kashyap (2007).