Means and method for measuring absorption of radiation-scattering samples

• US 5,963,335 A
• Filed: 06/24/1998
• Issued: 10/05/1999
• Est. Priority Date: 06/25/1997
• Status: Expired due to Term

• Current Assignee: Waters Medical Systems, Inc. (Groupe Cair SA)
• Original Assignee: Waters Instruments, Inc. (Woodstream Corporation)
• Inventors: Boutelle, Steven J.
• Primary Examiner(s): Pham, Hoa Q.
• Application Number:
  US09/103,782
• Time in Patent Office: 468 Days
• Field of Search: 356/432, 356/433, 356/434, 356/435, 356/436, 356/440, 356/39, 356/437, 356/73, 356/236, 250/339.13, 250/565, 250/228
• US Class Current: 356/433
• CPC Class Codes: G01J 3/0224 using polarising or depolarising elements
• CPC Class Codes: G01J 3/0229 using masks, aperture plates, spatial light modulators or spatial filters, e.g. reflective filters
• CPC Class Codes: G01J 3/4412 Scattering spectrometry particle sizing by light scattering G01N15/0205; optical velocimetry of particles G01P5/20, G01P5/26
• CPC Class Codes: G01N 21/47 Scattering, i.e. diffuse reflection G01N21/25, G01N21/41 take precedence G01N21/55 takes precedence
• CPC Class Codes: G01N 21/59 Transmissivity G01N21/25 takes precedence

Abstract

The present invention provides methods and devices for measuring radiation absorption by a sample. The invention enables one to determine whether the sample scatters the radiation of interest and, if so, to factor out the effects of such scattering and ore accurately determine the true absorption of the sample. The invention may employ a selectively controllable occluder which is moved between three or more different positions to yield three or more different radiation measurements. These measurements can then be compared to one another to determine the nature of any radiation scattering and factor out its effects, enabling more accurate absorption determinations.

Claims

1. A method of measuring radiation absorption of a sample, comprising:

a) providing an analyzer including a radiation source, a sample holder, a radiation detector, and a selectively operable radiation occluder positioned between the source and the detector along a radiation path;

b) placing a sample in the sample holder;

c) positioning the occluder at a first position;

directing radiation from the source toward the sample; and

taking a first radiation measurement with the detector;

d) positioning the occluder at a second position, the percentage of radiation occluded by the occluder in the second position being different from the percentage of radiation occluded in the first position;

directing radiation from the source toward the sample; and

taking a second radiation measurement with the detector;

e) positioning the occluder at a third position, the percentage of radiation occluded by the occluder in the third position being different from the percentage of radiation occluded in either of the first or second positions;

directing radiation from the source toward the sample; and

taking a third radiation measurement with the detector;

f) comparing the first, second and third radiation measurements to determine radiation attenuation attributable to scattering by the sample; and

g) factoring out said radiation attenuation attributable to scattering to determine a radiation absorption value for the sample.

2. The method of claim 1 wherein the comparison of the first, second and third measurements comprises calculating a first ratio as a ratio of the second measurement to the first measurement;

calculating a second ratio as a ratio of the third measurement to the first measurement; and

comparing the first and second ratios to determine whether the sample scatters the radiation and, if so, whether the scattering is coherent or incoherent.

3. The method of claim 2 wherein said attenuation attributable to scattering is factored out if scattering is determined to be coherent by dividing out a fixed scattering coefficient.

4. The method of claim 2 wherein said attenuation attributable to scattering is factored out if scattering is determined to be incoherent by

a) subtracting the second ratio from the first ratio;

b) determining a variable scattering coefficient which is directly proportional to the difference between the first and second ratios; and

c) dividing out the variable scattering coefficient.

5. The method of claim 1 wherein the radiation source radiates visible light and the radiation detector is a photometer, the steps of taking said first, second and third radiation measurements comprising measuring photons at said photometer.

6. The method of claim 1 wherein the occluder is positioned to occlude more radiation in its third position than in either its first position or its second position.

7. The method of claim 6 wherein the first radiation measurement is taken prior to taking the second radiation measurement.

8. The method of claim 7 wherein the second radiation measurement is taken prior to taking the third radiation measurement.

9. The method of claim 1 wherein the occluder is positioned along the radiation path between the radiation source and the sample container in each of its first, second and third positions.

10. The method of claim 1 wherein the occluder comprises a moveable plate having an area which is highly transmissive of radiation in a predetermined band of wavelengths and at least one area which is less transmissive of radiation in said band of wavelengths, the occluder being moved between its first, second and third position by varying the position of the plate with respect to the radiation path.

11. The method of claim 10 wherein the plate comprises a sheet having a first transmission-reducing dot and a second transmission-reducing dot, the second dot having a larger surface area than the first dot, the occluder being positioned in its first position by positioning the sheet without any dot along the radiation path, in its second position by positioning the first dot along the radiation path, and in its third position by positioning the second dot along the radiation path.

12. The method of claim 10 wherein the plate comprises a sheet having a transmission-reducing dot, the occluder being positioned in its first position by positioning the sheet without any dot along the radiation path, in its second position by positioning a portion of the dot along the radiation path, and in its third position by positioning a different portion of the dot along the radiation path.

13. The method of claim 12 wherein the entire dot is positioned along the radiation path when the occluder is positioned in its third position, and less than the entire dot is positioned along the radiation path when the occluder is positioned in its second position.

14. A method of measuring light absorption of a light-scattering sample, comprising:

a) providing an analyzer including a light source, a sample holder, a light detector, and a selectively operable occluder positioned between the source and the detector along a light path;

b) placing a sample in the sample holder;

c) positioning the occluder at a first position;

directing light from the source toward the sample; and

taking a first light measurement with the detector;

d) positioning the occluder at a second position, the percentage of light occluded by the occluder in the second position being different from the percentage of light occluded in the first position;

directing light from the source toward the sample; and

taking a second light measurement with the detector;

e) positioning the occluder at a third position, the percentage of light occluded by the occluder in the third position being different from the percentage of light occluded in either of the first or second positions;

directing light from the source toward the sample; and

taking a third light measurement with the detector;

f) comparing the first, second and third light measurements to determine light attenuation attributable to scattering caused by the sample; and

g) factoring out said attenuation attributable to scattering to determine a light absorption value for the sample.

15. The method of claim 14 wherein the comparison of the first, second and third measurements comprises calculating a first ratio as a ratio of the second measurement to the first measurement;

calculating a second ratio as a ratio of the third measurement to the first measurement; and

comparing the first and second ratios to determine whether the sample scatters the radiation and, if so, whether the scattering is coherent or incoherent.

16. The method of claim 15 wherein said attenuation attributable to scattering is factored out if scattering is determined to be coherent by dividing out a fixed scattering coefficient.

17. The method of claim 15 wherein said attenuation attributable to scattering is factored out if scattering is determined to be incoherent by

a) subtracting the second ratio from the first ratio;

b) determining a variable scattering coefficient which is directly proportional to the difference between the first and second ratios; and

c) dividing out the variable scattering coefficient.

18. The method of claim 14 wherein the occluder is positioned to occlude more light in its third position than in either its first position or its second position.

19. The method of claim 18 wherein the first light measurement is taken prior to taking the second light measurement.

20. The method of claim 19 wherein the second light measurement is take prior to taking the third light measurement.

21. The method of claim 14 wherein the occluder is positioned between the source and the sample container in each of its first, second and third positions.

22. The method of claim 14 wherein the occluder comprises a moveable plate having an area which is highly transmissive of light in a predetermined band of wavelengths and at least one area which is less transmissive of light in said band of wavelengths, the occluder being moved between its first, second and third position by varying the position of the plate with respect to the light source.

23. The method of claim 22 wherein the plate comprises a transparent sheet having a first transmission-reducing dot and a second transmission-reducing dot, the second dot being larger than the first dot, the occluder being positioned in its first position by positioning the transparent sheet between the source and the detector, in its second position by positioning the first dot between the source and the detector, and in its third position by positioning the second dot between the source and the detector.

24. The method of claim 22 wherein the plate comprises a sheet having a transmission-reducing dot, the occluder being positioned in its first position by positioning the sheet without any dot along the radiation path, in its second position by positioning a portion of the dot along the radiation path, and in its third position by positioning a different portion of the dot along the radiation path.

25. The method of claim 24 wherein the entire dot is positioned along the radiation path when the occluder is positioned in its third position, and less than the entire dot is positioned along the radiation path when the occluder is positioned in its second position.

26. The method of claim 25 wherein the sample comprises a blood sample, further comprising the step of determining hemoglobin concentration for the sample based on said light absorption value.

27. The method of claim 14 wherein the occluder comprises a first and second polarizing plates, the first polarizing plate being positioned between the light source and the sample holder and the second polarizing plate being positioned between the sample holder and the light detector, the occluder being moved between its first, second and third positions by varying the relative orientation of the first and second polarizing plates along the optical path.

28. The method of claim 27 wherein at least one of the first and second polarizing plates is rotatable about a rotational axis generally orthogonal to each of the first and second polarizing pates, the occluder being moved from its first position to its second position by rotating said at least one polarizing plate about the rotational axis to a position wherein the phase relationship of the first and second polarizing plates differs from the phase relationship of the first and second polarizing plates in the first position.

29. An analyzer for measuring light attenuation of a sample comprising:

a) a light source;

b) a sample holder;

c) a light detector;

d) a selectively controllable light occluder positioned between the light source and the light detector along a light path, the occluder comprising a plate having an area which is highly transmissive of light at a predetermined wavelength and at least one area which is less transmissive of light at said wavelength; and

e) a motor for moving the occluder between a first position wherein the plate of the occluder is positioned relative to the light path to occlude a first percentage of the light, a second position wherein the plate of the occluder is positioned relative to the light path to occlude a second percentage of the light, and a third position wherein the plate of the occluder is positioned relative to the light path to occlude a third percentage of the light.

30. The analyzer of claim 29 wherein the plate comprises a transparent sheet having a first transmission-reducing dot and a second transmission-reducing dot, the second dot being larger than the first dot, a location of the transparent sheet without a transmission-reducing dot being disposed along the light path when the occluder is in its first position, the first dot being disposed along the light path when the occluder is in its second position, and the second dot being disposed along the light path when the occluder is in its third position.

31. An analyzer for measuring light attenuation of a sample comprising:

a) a light source;

b) a sample holder;

c) a light detector;

d) an occluder comprising first and second polarizing plates, the first polarizing plate being positioned between the light source and the sample holder along a light path and the second polarizing plate being positioned between the sample holder and the light detector along the light path; and

e) at least one motor for moving the at least one of the first and second polarizing plates with respect to the other from a first relative orientation wherein the polarizing plates of the occluder occlude a first percentage of the light, a second relative orientation wherein the polarizing plates occlude a second percentage of the light, and a third relative orientation wherein the polarizing plates occlude a third percentage of the light.