Patent ID: 7613489

Claim:
A method for reducing measurement error caused by water when determining the level of hemoglobin oxygenation in tissue, comprising the steps of: illuminating the tissue under study using light emitted from a light source having at least the wavelengths of substantially 692 nm, 720 nm, 732 nm, 748 nm, 760 nm and 788 nm; sensing light that has passed through a portion of the tissue, with a detector, at a predetermined distance from the source of the illumination, determining a value of attenuation of light at each of the wavelengths of illumination of the tissue; and with a processor: determining a second derivative value of the light attenuation at 720 nm through the equation (Second Derivative Attenuation) 720 =Attenuation 748 −2(Attenuation 720 )+Attenuation 692 ; determining a second derivative value of the light attenuation at 760 nm through the equation (Second Derivative Attenuation) 760 =Attenuation 788 −2(Attenuation 760 )+Attenuation 732 ; determining a scaled (Second Derivative Attenuation) 720 as a function of the (Second Derivative Attenuation) 720 divided by the (Second Derivative Attenuation) 760 ; and comparing the scaled (Second Derivative Attenuation) 720 to stored data relating hemoglobin oxygenation to the scaled (Second Derivative Attenuation) 720 to determine the level of hemoglobin oxygenation.