Methods and systems for in situ calibration of imaging in biological analysis

• US 7,045,756 B2
• Filed: 08/05/2004
• Issued: 05/16/2006
• Est. Priority Date: 08/05/2004
• Status: Expired due to Fees

• Current Assignee: Applied Biosystems LLC (Thermo Fisher Scientific Incorporated)
• Original Assignee: Applera Corporation (Thermo Fisher Scientific Incorporated)
• Inventors: Kinney, Patrick D., Talbot, Ryan J.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): BUI PHO, PASCAL M
• Application Number:
  US10/911,887
• Publication Number:
  US 20060038109A1
• Time in Patent Office: 649 Days
• Field of Search: 250/559.4, 250/559.1, 250/252.1, 356/326
• US Class Current: 250/208.1
• CPC Class Codes: G01J 1/4228 arrangements with two or more detectors, e.g. for sensitivity compensation
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: H01L 27/148 Charge coupled imagers individual charge coupled devices H01L29/765
• CPC Class Codes: H04N 17/002 for television cameras
• CPC Class Codes: H04N 25/673 by using reference sources

Abstract

Software, methods, and systems for calibrating photometric devices are provided. These involve using a non-uniform test illumination field to approximate a photon transfer curve by calculating stable pixel values and statistical dispersions on a pixel-by-pixel basis.

Claims

1. A method for determining operating characteristics of a photometric detector comprising a plurality of photosensitive pixels, the method comprising:

illuminating an active surface of the photometric detector with electromagnetic radiation;

recording a plurality of varying brightness readings for the various pixels in the plurality of photosensitive pixels on the photometric detector;

calculating signal statistical dispersion values for the plurality of photosensitive pixels independently on a pixel-by-pixel basis over the plurality of varying brightness readings;

calculating stable intensity values for the plurality of photosensitive pixels independently on a pixel-by-pixel basis over the plurality of varying brightness readings; and

approximating a photon transfer curve based on the signal statistical dispersion values and the stable intensity values

wherein the photometric detector is adapted for biological analysis.

2. The method of claim 1, wherein the plurality of varying brightness readings numbers between approximately three and approximately one hundred.

3. The method of claim 1, wherein the plurality of varying brightness readings numbers approximately twenty.

4. The method of claim 1, wherein the step of calculating the signal statistical dispersion values further comprises calculating a signal standard deviation over the plurality of varying brightness readings.

5. The method of claim 1, wherein the step of calculating the stable intensity values further comprises calculating an average intensity value over the plurality of varying brightness readings.

6. The method of claim 1 further comprising:

determining whether the photometric detector is operating properly based on the photon transfer curve.

7. The method of claim 1 further comprising:

calibrating the photometric detector based on the photon transfer curve.

8. The method of claim 1, wherein determining operating characteristics comprises determining photometric detector gain.

9. The method of claim 1, wherein determining operating characteristics comprises determining photometric detector full well capacity.

10. The method of claim 1, wherein determining operating characteristics comprises determining photometric detector read noise.

11. The method of claim 1, wherein determining operating characteristics comprises determining photometric detector dynamic range.

12. The method of claim 1, wherein determining operating characteristics comprises determining a slope of a shot-noise region in the photon transfer curve to verify that the detector is shot-noise limited.

13. The method of claim 1, wherein the electromagnetic radiation is spatially non-uniform in intensity.

14. The method of claim 13, wherein the electromagnetic radiation is temporally constant.

15. The method of claim 13, wherein the electromagnetic radiation varies in spatial intensity over time to produce a time varying illumination field.

16. The method of claim 1, wherein the plurality of varying brightness readings ranges from substantially dark to an intensity that saturates at least one pixel in the plurality of photosensitive pixels.

17. A method for determining operating characteristics of a photometric detector, in situ, within an instrument, the photometric detector comprising a plurality of photosensitive pixels, the method comprising:

illuminating an active surface of the photometric detector with electromagnetic radiation, wherein the electromagnetic radiation is spatially non-uniform in intensity;

recording a plurality of varying brightness readings for the various pixels in the plurality of photosensitive pixels on the photometric detector;

calculating signal statistical dispersion values for the plurality of photosensitive pixels independently on a pixel-by-pixel basis over the plurality of varying brightness readings;

calculating stable intensity values for the plurality of photosensitive pixels independently on a pixel-by-pixel basis over the plurality of varying brightness readings;

approximating a photon transfer curve based on the signal statistical dispersion values and the stable intensity values; and

providing a proper operation indication regarding the photometric detector based on the photon transfer curve to indicate whether the photometric detector is operating properly,

wherein the instrument is adapted to imaging for biological analysis.

18. Apparatus for determining operating characteristics of a photometric sensing device contained within an instrument, the apparatus comprising:

a photometric sensor comprising a plurality of photosites capable of sensing intensity of electromagnetic energy at the plurality of photosites;

a test illumination field generator for generating a test illumination field optically coupled to the photometric sensor, the test illumination field comprising regions presenting a range of intensities to the photometric sensor;

a photometric sensor interface circuit coupled to the photometric sensor, the photometric sensor interface circuit operable to read out sets of photosite intensity values from the plurality of photosites, the sets of photosite intensity values corresponding to the intensity of electromagnetic energy sensed at the plurality of photosites; and

a memory coupled to the photometric sensor interface circuit, the memory comprising machine readable instructions comprising;

read instructions for reading a plurality of varying brightness readings of the sets of photosite intensity values while exposed to the test illumination field;

noise determination instructions for calculating statistical dispersions of the sets of photosite intensity values corresponding to the plurality of varying brightness readings;

stable intensity determination instructions for calculating stable intensity values corresponding to the sets of photosite intensity values at the plurality of photosites for the plurality of varying brightness readings; and

photon transfer curve approximation instructions for approximating a photon transfer curve corresponding to the photometric sensor based on the statistical dispersions and the stable intensity values,

wherein the instrument is adapted to imaging for biological analysis.

19. The apparatus of claim 18, wherein the photometric sensor comprises a charge coupled device (CCD).

20. The apparatus of claim 19, wherein the plurality of photosites comprises an array of pixels associated with the CCD.

21. The apparatus of claim 18, wherein the photometric sensor comprises a complimentary metal oxide semiconductor (CMOS) image sensor.

22. The apparatus of claim 18, wherein the photometric sensor comprises a spectrometer.

23. The apparatus of claim 18, wherein the photometric sensor comprises a line-scan camera.

24. The apparatus of claim 18, wherein the test illumination field generator further comprises an electromagnetic energy source.

25. The apparatus of claim 24, wherein the electromagnetic energy source comprises a point light source.

26. The apparatus of claim 24, wherein the electromagnetic energy source comprises a laser.

27. The apparatus of claim 24, wherein the electromagnetic energy source comprises a light emitting diode.

28. The apparatus of claim 24, wherein the electromagnetic energy source comprises a window to receive ambient light.

29. The apparatus of claim 28, wherein the window to receive ambient light comprises a filter.

30. The apparatus of claim 18, wherein the statistical dispersions are calculated as a standard deviation over the sets of photosite intensity values.

31. The apparatus of claim 18, wherein the stable intensity values are calculated by averaging the sets of photosite intensity values for particular photosites.

32. The apparatus of claim 18, wherein the sets of photosite intensity values number approximately twenty.