Optical cerebral oximeter

Abstract

A spectrophotometric instrument for conducting in vivo patient examinations has a sensor which is applied to the patient target area, e.g. the forehead, which includes a source for emitting electromagnetic energy e.g. selected wavelengths in the near infrared range, such that the energy passes through the underlying tissue and is emitted at other locations spaced from the point of entry. The sensor also includes detectors for receiving the resulting light energy at two or more such other locations and sending corresponding signals to a processor for analysis, by which characteristics of the tissue transmissed by the examination wavelengths may be determined. Processing of such signals includes the contrasting of detected intensity levels corresponding to a reference wavelength received at one detection location with intensity signals representative of an investigative wavelength also received at such location to determine a first resultant signal, repeating the process for the same wavelengths at another detection location, to thus determine another resultant signal, and the contrasting of such two resultant signals. In a particular application, the instrument is used to determine regional cerebral blood oxygenation by processing the detection signals to obtain a first resultant having a value proportional to the ratio of deoxygenated hemoglobin with respect to oxygenated hemoglobin and then using the value of such resultant to compute a further resultant having a value proportional to the ratio of oxygenated hemoglobin with respect to the sum of oxygenated hemoglobin and deoxygenated hemoglobin.