Quantitation of brain oxygenation and blood volume using a new intensity modulated NIR instrument

During the past decade, instruments that can non-invasively monitor the oxygenation state of tissues have become increasingly common. This has primarily been accomplished by measuring the attenuation of the near infrared (NIR) light that has passed through the tissue. Instruments based on light attenuation alone can provide trend information but not quantitative information. A new intensity modulated near infrared spectrophotometry (IMNIRS) instrument has been developed, measuring the attenuation, phase shift and modulation depth of light that has passed through blood perfused tissue. This technique opens up the possibility of providing quantitative data for chromophore (Hb, HbO/sub 2/, and Cytaa/sub 3/) concentrations and hence the calculation of cerebral blood volume. The design of the instrument and preliminary results will be discussed.