PTB News 2/2005 (107 kB) PTB News 2/2005, English edition, Issue August 2005PTB has developed a new measurement procedure based on near-infrared reflectometry and spectroscopy. The new method can distinguish between variations in blood perfusion occurring in the cerebral cortex and in overlying tissue layers (skin, bone). This enables optical and thus non-invasive monitoring of the blood perfusion in the brain of stroke patients.
Near-infrared reflectometry exploits the fact that the penetration depth of light into biological tissue can reach several centimetres in the spectral range between 650 nm and 900 nm. It can be applied as a spectroscopic probe for medical-diagnostic purposes. For instance, near-infrared reflectometry can reach through skin and bones to the cerebral cortex. Changes in perfusion as well as oxygen saturation of the blood can be measured. Using short laser pulses and measuring the dwell time (time of flight) of the photons in the tissue the depth at which photons were absorbed can be concluded. The time resolution of the method is in the sub-nanosecond range.
A promising application of this method is monitoring of blood perfusion in the brain of stroke patients. In case of reduced perfusion in certain areas of the cerebral cortex as a result of a stroke this can be detected and monitored, since an intravenously applied optical contrast agent will arrive there with a time delay. This has been demonstrated by PTB in cooperation with the Department of Neurology of the Charité, Berlin, within the framework of the Berlin Neuroimaging Centre (BNIC), a joint project funded by the German Federal Ministry of Education and Research (BMBF).
In a project funded by the German Federal Ministry of Economics and Labour, BMWA, PTB is currently cooperating with the companies Pico Quant GmbH and Loptek GmbH to set up an imaging system based on the measurement procedure described before. The aim is to localize variations in blood perfusion of the cerebral cortex within a larger section on the surface of the head.