Cerebral hypoxia detection by diffuse reflectance spectroscopy through a transparent cranial implant: feasibility evaluation using Monte Carlo method

According to the World Health Organization, 31% of worldwide deaths are due to cardiovascular diseases (CVDs). The principal cause of death in 85% of the CVD cases are heart attack and stroke. About 795,000 people have a new or recurrent stroke annually in the U.S.A. alone. A study pointed out that 63% of stroke patients have at least one episode of cerebral hypoxia being able to cause coma, seizures, and even brain death. In previous work, we introduced a biocompatible, mechanically stable, and transparent nanocrystalline yttria-stabilized-zirconia (nc-YSZ) cranial implant to provide optical access to the brain. The nc-YSZ implant may facilitate the diagnosis and treatments of neurological disorders by imaging and laser-based techniques. In this study, we evaluate the scope of diffuse reflectance spectroscopy through the nc-YSZ cranial implant in the diagnosis of oxygen consumption in normal and hypoxic conditions (greater and less than 95%, respectively). We use the Monte Carlo method to assess the optical access provided by the implant to detect normal and decreased oxygen consumption. To emulate the brain tissue, we used a four-layer structure: skull, gray matter with an embedded blood vessel, white matter, and air at the top, structured in a numerical model with anisotropy as well as Rayleigh and Mie scattering. We analyze two scenarios, constant blood volume at variable oxyhemoglobin saturation, and constant oxyhemoglobin saturation at variable blood volume. We use light irradiation sources at 756 and 810 nm to compute light propagation in a semi-infinite medium and diffuse reflectance backward. The penetration depth and diffusely backscattered energy showed the feasibility of monitoring hypoxia episodes while blood flux in vessels decreases during a stroke with more accuracy when the volume of the blood vessel is reduced in a stroke.