Methods and apparatus for calibrating spectral data

• US 20040206914A1
• Filed: 04/18/2003
• Published: 10/21/2004
• Est. Priority Date: 04/18/2003
• Status: Active Grant

• Current Assignee: Luma Imaging Corp. (SpectraScience, Inc.)
• Original Assignee: MediSpectra, Inc. (SpectraScience, Inc.)
• Inventors: Meese, Thomas M., Saager, Rolf B., Schomacker, Kevin T., Flanagan, John A., Zelenchuk, Alex
• Granted Patent: US 7,459,696 B2
• Time in Patent Office: Days
• US Class Current: 250/458.1
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 5/7264 Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems neural networks per se G06N3/00; expert systems per se G06N5/00
• CPC Class Codes: A61B 5/7267 involving training the classification device
• CPC Class Codes: G01N 21/31 Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry G01N21/72 takes precedence
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems

Abstract

The invention provides methods for calibrating spectral data acquisition systems. These calibration methods produce spectral data sufficiently accurate for use in tissue classification algorithms. The invention improves the accuracy of spectral-based tissue classification schemes, in part, by properly accounting for spatial variations, instrument-to-instrument variations, and patient-to-patient variations in the acquisition of spectral data from tissue samples. Effects that are accounted for include, for example, stray light effects, electronic background effects, variation in light energy delivered to a tissue sample, spatial heterogeneities of the illumination source, chromatic aberrations of the scanning optics, variation in wavelength response of the collection optics, and efficiency of the collection optics.

Claims

1. A method of calibrating spectral data obtained from a tissue sample, the method comprising the steps of:

(a) obtaining calibration data from a plurality of spaced-apart locations on a calibration target;

(b) obtaining a set of spectral data from spaced-apart locations of a tissue sample, wherein at least some of said spaced-apart locations of said tissue sample correspond to said spaced-apart locations on said calibration target; and

(c) calibrating said spectral data obtained from said tissue sample using said calibration data, thereby to produce calibrated data.

2. The method of claim 1, wherein said calibration data comprises reflectance spectral data.

3. The method of claim 1, wherein said calibration data comprises fluorescence spectral data.

4. The method of claim 1, wherein said first obtaining step comprises using an optical instrument to obtain said calibration data as part of an initial calibration of said optical instrument.

5. The method of claim 1, wherein said first obtaining step comprises using an optical instrument to obtain said calibration data as part of a periodic calibration of said optical instrument.

6. The method of claim 1, wherein said calibration target comprises a fluorescent dye.

7. The method of claim 6, wherein said calibration target comprises coumarin-515 dye.

8. The method of claim 1, further comprising the step of:

obtaining measures of instrument response using a reference light source.

9. The method of claim 8, wherein said reference light source comprises a filament that approximates a blackbody emitter.

10. The method of claim 9, wherein said filament is a tungsten filament.

11. The method of claim 1, further comprising the steps of:

obtaining a mercury spectrum and an argon spectrum; and

converting a CCD pixel index to a wavelength using data from said mercury spectrum and said argon spectrum.

12. The method of claim 1, further comprising the step of:

processing said calibrated-data in a tissue classification algorithm.

13. A method of calibrating spectral data obtained from a tissue sample, the method comprising the steps of:

(a) obtaining a first set of calibration data from a plurality of spaced-apart locations on a first calibration target;

(b) obtaining a second set of calibration data from a plurality of spaced-apart locations on a second calibration target;

(c) obtaining a set of spectral data from spaced-apart locations of a tissue sample, wherein at least some of said spaced-apart locations of said tissue sample correspond to said spaced-apart locations on said first calibration target and said spaced-apart locations on said second calibration target; and

(c) calibrating said spectral data obtained from said tissue sample using said first set of calibration data and said second set of calibration data, thereby to produce calibrated data.

14. The method of claim 13, wherein said second calibration target is a single-use disposable target.

15. The method of claim 13, wherein said first calibration target has a reflectance of about 60% and said second calibration target has a reflectance of about 10%.

16. The method of claim 13, wherein said second set of calibration data is obtained within about 24 hours of obtaining said set of spectral data from said tissue sample.

17. The method of claim 13, wherein said second set of calibration data is obtained within about 1 hour of obtaining said set of spectral data from said tissue sample.

18. The method of claim 13, wherein said calibrating step comprises processing said spectral data according to the equation:

R(i,λ

,t′

)=[I_m(i,λ

,t′

)/(I_cp(i,λ

,t′

))_i]·

[<

I_fc(i,λ

,t_o)>

_i/I_fc(i,λ

,t_o)]·

R_cp,

wherein R(i,λ

,t′

) is an array comprising calibrated reflectance spectral data from said tissue sample at regions i, wavelengths λ

, and at time t′

, I_m(i,λ

,t′

) is an array comprising reflectance spectral data from said tissue sample, I_fc(i,λ

,t_o) is an array comprising said first set of calibration data obtained at time t_o different from t′

, <

I_fc(i,λ

,t_o)>

_i is an array comprising said first set of calibration data averaged over said i regions, <

I_cp(i,λ

,t′

)>

_i is an array comprising said second set of calibration data averaged over said i regions, and R_cp is the reflectance of said second calibration target.

19. The method of claim 18, wherein data in array I_m(i,λ

,t′

) are background subtracted.

20. The method of claim 18, wherein data in at least one of arrays I_cp(i,λ

,t′

) and I_fc(i,λ

,t_o) are background subtracted.

21. The method of claim 13, further comprising the step of:

obtaining a third set of calibration data using said second calibration target, wherein said calibration step comprises calibrating said spectral data obtained from said tissue sample using said first set of calibration data, said second set of calibration data, and said third set of calibration data.

22. The method of claim 21, wherein said calibrating step comprises processing said spectral data according to the equation:

R(i,λ

,t′

)=[I_m(i,λ

,t′

)/(I_cp(i,λ

,t′

))_i]·

[<

I_fc(i,λ

,t_o)>

_i/I_fc(i,λ

,t_o)]·

R_cp,fitted,

wherein R(i,λ

,t′

) is an array comprising calibrated reflectance spectral data from said tissue sample at regions i, wavelengths λ

, and at time t′

, I_m(i,λ

,t′

) is an array comprising reflectance spectral data from said tissue sample, I_fc(i,λ

,t_o) is an array comprising said first set of calibration data obtained at time to different from t′

, <

I_fc(i,λ

,t_o)>

_i is an array comprising said first set of calibration data averaged over said i regions, <

I_cp(i,λ

,t′

)>

_i is an array comprising said second set of calibration data averaged over said i regions, R_cp,fitted is an array of values of a curve fit of R_cp(λ

), where R_cp(λ

)=[<

I_cp(i,λ

,t_o)>

i/<

I_fc(i,λ

,t_o)>

_i]·

R_fc, and where <

I_cp(i,λ

,t_o)>

_i is an array comprising said third set of calibration data obtained at time to and averaged over said i regions, and R_fc is the reflectance of said first calibration target.

23. A method of calibrating spectral data obtained from a tissue sample, the method comprising the steps of:

(a) obtaining calibration data from a plurality of spaced-apart locations on a calibration target using an optical instrument with a first attached disposable component;

(b) obtaining a set of spectral data from spaced-apart locations of a tissue sample, wherein at least some of said spaced-apart locations of said tissue sample correspond to said spaced-apart locations on said calibration target; and

(c) calibrating said spectral data obtained from said tissue sample using said calibration data, thereby to produce .calibrated data.;

24. The method of claim 23, wherein said disposable component is a protective sheath.

25. The method of claim 23, wherein said set of spectral data from said tissue sample is obtained using said optical instrument with a second attached disposable component in place, of said first disposable component.

26. The method of claim 23, further comprising the step of:

obtaining an additional set of calibration data from a plurality of spaced-apart locations on an additional calibration target using said optical instrument with a second attached disposable component in place of said first disposable component, wherein said calibrating step comprises calibrating said spectral data obtained from said tissue sample using said calibration data and said additional calibration data.

27. The method of claim 26, wherein said set of spectral data from said tissue sample is obtained using said optical instrument with said second attached disposable component.

28. A method of correcting spectral data from a tissue sample for stray light internal to an optical instrument, the method comprising the steps of:

(a) obtaining a first set of spectral data using a target and using a light source internal to an optical instrument, wherein said instrument yields a residual optical signal;

(b) obtaining a second set of spectral data using a light source internal to said optical instrument, with no external light source;

(c) obtaining a third set of spectral data from a tissue sample; and

(d) adjusting said third set of data using a subset of said first set of data and a subset of said second set of data.

29. The method of claim 28, wherein said second obtaining step comprises obtaining said second set of spectral data without a target.

30. The method of claim 28, wherein said target has substantially no diffuse reflectance.

31. The method of claim 28, further comprising the step of:

obtaining a fourth set of spectral data from a target yielding substantially no optical signal, wherein said adjusting step comprises adjusting said third set of data using a subset of said first set of data, a subset of said second set of data, and a subset of said fourth set of data.

32. The method of claim 31, wherein the step of obtaining the fourth set of spectral data is performed within about one hour of obtaining said third set of spectral data.