Patent ID: 8538499

Claim:
A method of obtaining a hematocrit from a sample of in vivo tissue comprising: (a) irradiating the sample with a single incident wavelength on a sample of tissue; (b) simultaneously measuring wavelength shifted (IE) and unshifted (EE) light emitted from the tissue; and (c) determining a relative volume of light emitted from two phases, wherein the two phases comprise a first Rayleigh and Mie scattering and fluorescent phase associated with red blood cells, and a second, non-scattering phase associated with plasma, wherein the hematocrit is calculated from the volume of light emitted by the first phase (φ r ) relative to the total volume of light emitted from the first and second phases (φ r +φ p ), wherein the determining comprises calculating: ϕ r / ( ϕ r + ϕ p ) [ 5 ] wherein ⁢ ⁢ ϕ r = a + ( b ⁢ EE EE 0 ) + ( c ⁢ IE IE 0 ) [ 8 ] ϕ p = d + ( e ⁢ EE EE 0 ) + ( f ⁢ IE IE 0 ) [ 9 ] EE = ℵ 1 + ℵ 2 ⁢ ϕ p + ℵ 3 ⁢ ϕ r [ 6 ] IE = ℵ 4 + ℵ 5 ⁢ ϕ p + ℵ 6 ⁢ ϕ r [ 7 ] wherein EE is total elastically (unshifted) emitted light, IE is total inelastically (shifted) emitted light, and are the fractions of EE and IE, respectively, from static tissue; and are the fractions of EE and IE, respectively, from plasma; , and are the fractions of EE and IE, respectively, from red blood cells; and are calculated numerically using the radiative transport equation (RTE) to determine EE and IE as a function of φ r and φ p ; wherein EE 0 and IE 0 are average values of EE and IE over a calibration time period; and wherein a-f are obtained by inverting equations [6] and [7] to express φ r and φ p in terms of EE and IE.