Patent ID: 8426819

Claim:
A method of the noninvasive optical determination of the temperature of a flowing stream of blood within a body, the method comprising the step of: marking a site within the body through which the blood stream passes with pulsed ultrasonic radiation, irradiating the flowing blood stream at and around the site with two discrete wavelengths of infrared and/or visible light that are near the absorption line of the blood on two different sides of the absorption maximum defined by the absorption line whose position depends on the temperature of the blood, whereby the light is absorbed or backscattered to a degree dependent on proximity of the wavelength of the light to the absorption line, determining from that portion of the absorbed or backscattered light that is temporally related to the ultrasonic radiation respective absorption values for the two wavelengths, deriving at least one measured value dependent on the temperature or a measuring function dependent on the temperature from a ratio or a functional relation of these two determined absorption values to one another, and determining the temperature from the measured value or the measuring function by comparison with previously recorded calibration data.