Patent ID: 7463343

Claim:
An optical sensing assembly for differentiating between the presence of platelets and red blood cells in a plasma flow comprising a first emitter of light at a first wavelength (λ 1 ) having a known optical attenuation for platelets at the first wavelength (ε platelets λ 1 ) and a known optical attenuation for hemoglobin at the first wavelength (ε Hb λ 1 ), a second emitter of light at a second wavelength (λ 2 ) having a known optical attenuation for platelets at the second wavelength (ε platelets λ 2 ) and a known optical attenuation for hemoglobin at the second wavelength (ε Hb λ 2 ), wherein: λ 1 ≠λ 2 ; ε platelets λ 1 ≈ε platelets λ 2 ε Hb λ 1 >ε Hb λ 2 , a path transparent to light at the first and second wavelengths to convey the plasma flow past the first and second emitters, a light detector to receive light emitted by the first and second emitters through the path and to generate signals proportional to intensities of received light, and a module coupled to the light detector to analyze the signals to derive intensities of the received light at the first and second wavelengths and generate an output representing presence of a blood cell concentration in the plasma flow, and to compare changes in the signals over time to derive changes in intensities of received light at the first and second wavelengths over time and generate an output that differentiates between changes in intensity attributable to changes in platelet concentration in the plasma flow and changes in intensity attributable to changes in red blood cell concentration in the plasma flow.