Monte Carlo Simulation of Implanted Intracranial fNIRS

Functional Near Infrared Spectroscopy (fNIRS) is limited to the external layers of the brain, and is impeded by motion artifacts and hemodynamic "noise" from scalp. Often, prior to epilepsy surgery, depth-electrodes are implanted, yet this approach is limited by "tunnel vision" effect. To overcome these limitations, we developed an implanted fNIRS (ifNIRS) sensor using optical fibers. To simulate the use of this sensor we employed a Monte Carlo (MC) method. When compared to standard scalp positioning (3 cm distance between emitter and detector), the simulated intracranial fNIRS resulted in a >20-fold increase in measured signal at 3 cm distance and a >4-fold increase at 5cm. Simulations with different scatter coefficients of the white matter demonstrated substantial differences in measurable signal for intracranial fNIRS. MC simulations highlighted notable differences between scalp and ifNIRS, emphasizing the advantages of intracranial positioning. We propose that ifNIRS can be combined with stereo EEG or responsive neurostimulation (RNS) to improve seizure detection.