Method and apparatus for performing optical measurements of a material
A method of determining an optical parameter or function thereof for a liquid, the method comprising: flowing the liquid through a flow cell; transmitting a pulse of light into the liquid in the flow cell; generating a signal responsive to energy that the material emits responsive to a portion of the light from the light pulse that is absorbed by the liquid; and using the signal to determine the optical parameter or function thereof.
1. A method of determining an optical parameter or function thereof for blood ex-vivo, the method comprising:
withdrawing blood from a patient's vascular system;
flowing the blood through a flow cell ex-vivo;
transmitting a pulse of light into the blood in the flow cell as the blood flows through said flow cell, wherein transmitting the light in a direction along which the internal cross-section of the flow cell has a dimension that is greater than an absorption length of the light in the blood;
generating a signal responsive to energy that the material emits responsive to a portion of the light from the light pulse that is absorbed by the blood using the signal to determine the optical parameter or function thereof; and
recirculating the blood into the patient's vascular system.
2. A method according to claim 1 wherein the dimension is greater than two absorption lengths of the light in the blood.
3. A method according to claim 1 wherein the dimension is greater than five times the absorption length.
4. A method according to claim 1 wherein the dimension is greater than ten times the absorption length.
5. A method according to claim 1 wherein the energy that the blood emits is acoustic energy generated by a photoacoustic effect.
6. A method according to claim 1 wherein the energy that the blood emits is thermal energy.
7. A method according to claim 1 and comprising generating a signal responsive to light from the light pulse that is scattered by the blood and using the signal to determine the optical parameter or function thereof.
8. A method according to claim 1 and comprising:
receiving light scattered by the blood from the light pulse;
generating a signal responsive to the received scattered light;
providing a model that relates the received scattered light to a distance that the light travels in the blood;
assuming a value for the distance; and
determining the optical parameter or function thereof responsive to the signal, the model and the assumed value.
9. A method according to claim 8 wherein the assumed distance is infinite.
10. A method according to claim 8 wherein the assumed distance is substantially greater than an absorption length of the light in the material.
11. A method according to claim 8 wherein the optical parameter comprises an absorption coefficient for the light.