Optical performance of minimally invasive brain implants: a simulation and phantom study

Despite significant progress in non-invasive techniques to sense brain activity through highly scattering biological tissue, these modalities are inherently limited by the physical process of diffusion. We explore minimally invasive transdermal and transcranial optical implants that directly reduce light diffusion by bypassing highly scattering superficial tissues, and quantitatively evaluate their impact on detected photon energy and sensitivity profiles to provide engineering insights for the optimisation of optical interface design and placement. Simulations using an anatomical head model show increased energy detection by 1-4 orders of magnitude, with improved cerebral cortex sensitivity by up to 3 orders of magnitude for longer SDS. Optical implants for SDS of a few millimetres also enable the probing of cerebral cortex with high ∼1 mm localisation. Experiments with an anatomically correct (based on an MRI scan) but simplified resin-based phantom validate the numerical modelling and show good agreement with the simulated detected energies. Further development of these optical implants could be an option for longitudinal brain sensing and imaging measurements.