Infrared light from the bulb travels down the optical fibres and illuminates the head of the baby. Some of the light travels through the skull, into the brain and comes back to the surface. The light that reaches the surface is picked up by another optical fibre and travels to the spectrometer. A spectrometer splits the light into its colours, with a prism or diffraction grating, and detects how much light per colour has travelled through the brain, with a camera. This is known as a spectrum.
As the concentrations of absorbing compounds in the brain (such as blood and cytochrome-c-oxidase in the mitochondria) change, the spectrum of light detected changes. From this detected spectrum of light, we can calculate the levels of blood and cytochrome-c-oxidase in the brain.
This is one of the instruments, called CYRIL, that we have built. Our team of doctors and engineers use CYRIL in the hospital to monitor babies’ brains