We combine continuous-wave (CW) and time-resolved (TR) near-infrared spectroscopy (NIRS) to effectively quantify tissue optical properties (OPs) of both shallow and deep regions in human heads. Utilizing iterative curve fitting in which artificial neural networks trained with Monte-Carlo simulated data serve as the forward model, we derive the OPs of interest such as the gray matter through TR NIRS with the assumption of known OPs of shallower tissue regions estimated from broadband CW-NIRS measurements. Preliminary results indicate improved accuracy in quantifying deep tissue absorption coefficients, while presenting more challenges in estimating scattering coefficients. Further research and refinements are essential to address this challenge to facilitate a more thorough understanding of photon propagation in the head composed of complex biological tissues.
KEYWORDS: 3D modeling, Photon transport, Infrared radiation, Head, Simulations, Monte Carlo methods, Near infrared spectroscopy, Magnetic resonance imaging, Data modeling, Optical properties
We study effects of long-term transcranial infrared light stimulation on cognitive functions of the elders. The fraction of photon energy penetrating to the brain is estimated noninvasively to enable the optimization of light source parameters.
Transcranial infrared light stimulation (TILS) has been shown to improve the performance of cognitive tests in adults with subjective memory complaints. Here we study whether long-term TILS benefits the cognitive functions of the elders. Through cognitive tests including card sorting test and delayed match-to-sample test, and functional near-infrared spectroscopy, we compared the cognitive tests performance and hemodynamics at the prefrontal cortex of healthy elders before and after two-to-four weeks of daily 10-mins TILS sessions. Results showed decreased hemodynamic responses after TILS, and greater cognitive enhancements in subjects receiving longer TILS. This may be explained by elevated efficiency of oxygen metabolism after TILS.
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