Welcome to the optical topography world! We would like to briefly introduce you to this fantastic system.
When we hold our hand up to the sun, as you well know, we can see the red fringes of the hand and the fingers, where flesh is thinner.
This shows that the red light in the sunlight can penetrate the human body more easily than the other light waves.
Additionally, it is well known to scientists that the transmission and absorption of light in human body tissues is sensitive to its hemoglobin concentration.
The fundamentals of the optical topography system utilize the phenomenon, using the better penetrating near infrared light, rather than visible light, to measure changes in blood hemoglobin concentrations in the brain.
Infrared light is a type of radio wave that has a longer wavelength than that of visible light. The system uses near infrared light to measure the changes of oxy- and deoxy-hemoglobin as well as total blood volume changes in various regions of the brain's upper levels ( cerebral cortex ), showing the data as images.
When a specific area of the brain is activated, the localized blood volume in that area changes quickly. It can thus be determined by the system, where and how active the specific regions of the brain are, by continuously monitoring the blood hemoglobin levels, while having the examinee do some specific action or task paradigm.
It takes only 0.1 second to perform one cycle of measurement, calculation and display, so this system provides a "real-time" measurement of the brain's activity.
The system has several unique advantages over current measurement methods. It is non-invasive, and can be used under a variety of conditions with minimal restriction on the examinee. Measurements can be made under more natural conditions, giving more freedom in task design. It also enables simultaneous measurements with other testing modalities such as EEG, fMRI and MEG. The system's design facilitates longitudinal studies and monitoring over extended time periods.
The system has been developed by the Advanced Research Laboratory of Hitachi, Ltd. Thanks to their assistance, Hitachi-medical Co. began to produce the system on commercial bases.
Principle of optical topography
