Method in quality control of a spectrophotometer

• US 6,980,285 B1
• Filed: 06/10/1999
• Issued: 12/27/2005
• Est. Priority Date: 06/12/1998
• Status: Expired due to Fees

• Current Assignee: Radiometer Medical ApS (Danaher Corporation)
• Original Assignee: Radiometer Medical ApS (Danaher Corporation)
• Inventors: Hansen, Heine
• Primary Examiner(s): Smith, Zandra V.
• Assistant Examiner(s): Stock, Jr., Gordon J.
• Application Number:
  US09/719,415
• Time in Patent Office: 2,392 Days
• Field of Search: 356 39- 42, 356/319, 356/326, 356/300, 356440-442, 356432-436, 250/252.1, 702/85
• US Class Current: 356/41
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction

Abstract

The present invention relates to a method in quality control of a spectrophotometer, comprising the steps of determining with the spectrophotomer a spectrum A_m(λ) of a fluid QC sample containing a dye, and determining a wavelength shift Δλ from C_Δλ(λ), A_m(λ), in which C_Δλ(λ) is a predetermined coefficient vector previously stored in a memory of the spectrophotometer.

Claims

1. A quality control method for a spectrophotometer, comprising the steps of:

determining with the spectrophotometer an absorption spectrum A_m(λ

) of a fluid quality control sample containing a dye selected from such dyes which provide the quality control sample with an absorption spectrum with a significant absorbance peak showing a steep flank,

determining a wavelength shift Δ

λ

between the absorption A_m(λ

) of the actually measured quality control sample and a reference absorption spectrum A₀(λ

) of a reference quality control sample containing the dye stored in a memory of the spectrophotometer, and

comparing Δ

λ

with Δ

λ

_qc, wherein Δ

λ

_qc is a wavelength shift assigned to the quality control sample.

2. A method according to claim 1, wherein the wavelength shift Δ

λ

is determined from A_m(λ

) and a predetermined mathematical parameter stored in the memory of the spectrophotometer.

3. A method according to claim 2, wherein the mathematical parameter is a coefficient vector C_Δ

λ

(λ

) and wherein the wavelength shift Δ

λ

is determined from C<sub>Δ

λ</sub>

(λ

)·

A_m(λ

).

4. A method according to claim 3, wherein the vector C_Δ

λ

(λ

) fulfills the equation

Δ

λ

=C<sub>Δ

λ</sub>

(λ

)·

A_m(λ

).

5. A method according to claim 4, wherein C_Δ

λ

(λ

) has been determined from a Taylor series of the reference absorption spectrum A₀(λ

).

6. A method according to claim 5, wherein C_Δ

λ

(λ

) has been determined from a combination of the reference absorption spectrum A₀(λ

) and a first derivative A₀′

(λ

) of said reference absorption spectrum.

7. A method according to claim 1, wherein the wavelength shift Δ

λ

is determined after normalisation of the determined spectrum A_m(λ

) with an estimate of the concentration of the dye.

8. A method according to claim 1, wherein the quality control sample has a known dye concentration C_qc and the dye comprises a first and a second component, the method further comprising the steps of

calculating parameters s₁ and s₂ from

s₁=C₁(λ

)·

A_m(λ

)

s₂=C₂(λ

)·

A_m(λ

)

in which C₁(λ

) and C₂(λ

) are predetermined vectors previously stored in the memory of the spectrophotometer, and

calculating an estimated concentration C_est of the dye from

C_est=a s₁+b s₂

in which a and b are predetermined constants previously stored in the memory of the spectrophotometer.

9. A method according to claim 8, further comprising the step of comparing C_est and C_qc.

10. A method according to claim 8, further comprising the step of calculating a variable Q_est=s_2est/S_1est.

11. A method according to claim 10, wherein the quality control sample has an assigned value of Q_qc=s_2qc/s_1qc, which method further comprises the step of comparing Q_est with Q_qc.

12. A method according to claim 1, wherein the spectrophotometer is an oximeter.

13. A method according to claim 12, wherein spectra are measured in the wavelength range from 400 to 800 nm.

14. A method according to claim 12, further comprising the step of determining estimated errors in blood parameter values reported by the oximeter caused by the wavelength shift Δ

λ

.

15. A method according to claim 8, wherein the spectrophotometer is an oximeter, further comprising the step of determining estimated errors in blood parameter values reported by the oximeter caused by a difference between C_est and C_qc.

16. A method according to claim 11, wherein the spectrophotometer is an oximeter, further comprising the step of determining estimated errors in blood parameter values reported by the oximeter caused by a difference between Q_est and Q_qc.

17. A method according to claim 1 further comprising the steps of:

determining a first reference absorption spectrum A₀₁(λ

) of a reference sample containing a dye in a first concentration with a reference spectrophotometer,

determining a first derivative A₀₁′

(λ

) of the first reference spectrum, and

determining from at least the first reference spectrum A₀₁(λ

) and the first derivative A₀₁′

(λ

) a mathematical parameter from which a wavelength shift Δ

λ

of the spectrophotometer can be determined, and

storing the mathematical parameter in a memory of the spectrophotometer.

18. A method according to claim 17, wherein the step of determining the mathematical parameter comprises the steps of

calculating a set of calibration vectors B_i(λ

) according to

B_i(λ

)=s_iA₁(λ

)+s_i3A₀₁′

(λ

)

in which i=1, 2, . . . , N (N>

1) and s_i and s_i3 are constants of selected values,

determining a coefficient vector C<sub>Δ

λ</sub>

(λ

) constituting the mathematical parameter so that each set of corresponding values s_i3, B_i(λ

) satisfies;

s_i3=C<sub>Δ

λ</sub>

(λ

)·

B_i(λ

), i=1,2, . . . , N.

19. A method according to claim 17, wherein the dye comprises a first component and a second component, and further comprising the step of determining a second reference A₀₂(λ

) of a second reference sample containing the dye in a second concentration with the reference spectrophotometer, and wherein the step of determining a mathematical parameter comprises the steps of

calculating a set of vectors B_i(λ

) from

B_i(λ

)=s_i1 A₁(λ

)+s_i2 A₂(λ

)+S_i3A₀′

(λ

)

in which A₁(λ

) and A₂(λ

) are derived from the first and second reference spectra A₀₁(λ

), A₀₂(λ

) and represent spectral information about the first and second components, respectively, and i=1, 2, . . . , N (N>

1), and S_i1, S_i2 and S_i3 are constants of selected values,

determining a vector C<sub>Δ

λ</sub>

(λ

) constituting the mathematical parameter so that

s_i3C<sub>Δ

λ</sub>

(λ

)·

B_i(λ

).

20. A spectrophotometer comprising a processor that is adapted to determine the wavelength shift Δ

λ

between an absorption spectrum A_m(λ

) determined with the spectrophotometer on a fluid quality control sample containing a dye selected from such dyes which provide the quality control sample with an absorption spectrum with a significant absorbance peak showing a steep flank and a reference absorption spectrum A₀(λ

) of a reference quality control sample containing the dye, stored in a memory of the spectrophotometer wherein the quality control sample has an assigned wavelength shift Δ

λ

_qc, and wherein the processor is adapted to compare Δ

λ

with Δ

λ

_qc.

21. A spectrophotometer according to claim 20, wherein the wavelength shift Δ

λ

is determined from A_m(λ

) and a predetermined mathematical parameter stored in the memory of the spectrophotometer.

22. A spectrophotometer according to claim 21, wherein the mathematical parameter is a coefficient vector c_Δ

2(λ

) and wherein the wavelength shift Δ

is determined from C<sub>Δ

λ</sub>

(λ

)·

A_m(λ

).

23. A spectrophotometer according to claim 22, wherein the vector C_Δ

λ

(λ

) fulfills the equation

Δ

λ

=C<sub>Δ

λ</sub>

(λ

)·

A_m(λ

).

24. A spectrophotometer according to claim 23, wherein C_Δ

λ

(λ

) has been determined from a Taylor series of the reference absorption spectrum A₀(λ

).

25. A spectrophotometer according to claim 24, wherein C_Δ

λ

(λ

) has been determined from a combination of the reference absorption spectrum A₀(λ

) and a first derivative A₀′

(λ

) of said reference absorption spectrum.

26. A spectrophotometer according to claim 20, wherein the wavelength shift Δ

λ

is determined after normalisation of the determined spectrum A_m(λ

) with an estimate of the concentration of the dye.

27. A spectrophotometer according to claim 20, wherein the quality control sample has a known dye concentration C_qc and the dye comprises a first and a second component, and wherein the processor is adapted to

calculate parameters s₁ and s₂ from

s₁=C₁(λ

)·

A_m(λ

)

s₂=C₂(λ

)·

A_m(λ

)

in which C₁(λ

) and C₂(λ

) are predetermined vectors previously stored in the memory of the spectrophotometer, and

calculate an estimated concentration C_est of the dye from

C_est=a s₁+b s₂

in which a and b are predetermined constants previously stored in the memory of the spectrophotometer.

28. A spectrophotometer according to claim 27, wherein the processor is further adapted to compare C_est with C_qc.

29. A spectrophotometer according to claim 27, wherein the processor is further adapted to calculate a variable Q_est=s_2est/s_1est.

30. A spectrophotometer according to claim 29, wherein the quality control sample has an assigned value of Q_qc=s_2qc/s_1qc and wherein the processor is further adapted to compare Q_est and Q_qc.

31. A spectrophotometer according to claim 20 which is an oximeter.

32. A spectrophotometer according to claim 31, wherein spectra are measured in the wavelength range from 400 to 800 nm.

33. A spectrophotometer according to claim 31, wherein the processor is adapted to determine estimated errors in blood parameter values reported by the spectrophotometer caused by the wavelength shift Δ

λ

.

34. A spectrophotometer according to claim 27, wherein the spectrophotometer is an oximeter and the processor is further adapted to determine estimated errors in blood parameter values reported by the spectrophotometer caused by a difference between C_est and C_qc.

35. A spectrophotometer according to claim 30, wherein the spectrophotometer is an oximeter and the processor is further adapted to determine estimated errors in blood parameter values reported by the spectrophotometer caused by a difference between Q_est and Q_qc.

36. A spectrophotometer according to claim 20 for the determination of a concentration c_y of a component y of a sample and wherein the memory further comprises

at least one vector A_int(λ

) representing spectral information of an interfering component in the sample at a concentration C_ref, and

at least one predetermined vector K_int(λ

) and wherein

the processor is further adapted to

calculate the concentration C_int of the interfering component according to

C_int=K_int(λ

)·

A_m(λ

), and

if C_int is greater than a predetermined threshold value, C_ref, calculate a modified absorbance spectrum A_mod(λ

) according to $A_{\mathrm{mod}}<br><br>\left(\mathrm{\lambda <br><br>}\right)=A_m<br><br>\left(\mathrm{\lambda <br><br>}\right)-\frac{C_{\mathrm{int}}}{C_{\mathrm{ref}}}<br><br>A_{\mathrm{int}}<br><br>\left(\mathrm{\lambda <br><br>}\right),\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}$

determine c_y from the modified spectrum A_mod(λ

) according to

C_y=K_y(λ

)·

A_mod(λ

)

where K_y(λ

) is a predetermined vector and whereby the effect of interfering components on determined concentrations C_y is minimised.

37. A spectrophotometer according to claim 36, wherein the interfering component is fetal hemoglobin.