System and method for correction of vignetting effect in multi-camera flat panel x-ray detectors

• US 9,360,571 B2
• Filed: 04/24/2012
• Issued: 06/07/2016
• Est. Priority Date: 04/25/2011
• Status: Active Grant

• Current Assignee: Cmosaix Limited
• Original Assignee: Generic Imaging, Ltd.
• Inventors: Batkilin, Eduard, Karelin, Irina, Feldman, Alex
• Primary Examiner(s): Porta, David
• Assistant Examiner(s): Riddick, Blake
• Application Number:
  US14/113,590
• Publication Number:
  US 20140042310A1
• Time in Patent Office: 1,505 Days
• Field of Search: 250/370.09, 250/370.11, 250/252.1, 382/254, 382/274, 382/275
• US Class Current: 1/1
• CPC Class Codes: G01T 7/005 calibration techniques stabilization of spectrometer G01T1/40

Abstract

A system and method for correcting vignetting distortion in an imaging sensor of a multi-camera flat panel X-Ray detector. A scintillator converts X-Ray radiation generated by an X-Ray source into detectable radiation. A displacement unit generates, during a calibration phase, relative displacement between the X-Ray detector and an X-Ray source at a plane parallel to the scintillator. The imaging sensor acquires, during the calibration phase, a first and a second partial images, the first partial image is acquired before the relative displacement is generated, and the second partial image is acquired after the relative displacement is generated. A relative displacement measurement unit measures the relative displacement. Coefficients of a preliminary inverse vignetting function are calculated based on differences between corresponding pixels of the two partial images.

Claims

1. A method for correcting vignetting distortion in an optical module comprising imaging sensor and at least one lens, of a multi-camera flat panel X-Ray detector, the method comprising:

taking a first partial X-Ray image by the imaging sensor;

creating relative displacement between the X-Ray detector and an X-Ray source at a plane parallel to a plane of a scintillator of the detector;

taking a second partial X-Ray image by the imaging sensor;

obtaining the relative displacement between the first partial X-Ray image and the second partial X-Ray image; and

calculating coefficients of a preliminary inverse vignetting function based on differences between corresponding pixels of the two partial images.

2. The method of claim 1, comprising:

calculating a gain for the optical module by equalizing values of pixels captured by the imaging sensor as well as by at least one other imaging sensor of the multi-camera flat panel X-Ray detector; and

adjusting the coefficients of the preliminary inverse vignetting function by the gain to obtain coefficients of a final inverse vignetting function.

3. The method of claim 2, comprising:

during routine operation of the detector;

acquiring routine partial X-Ray images; and

adjusting the routine partial X-Ray images, using the final inverse vignetting function to obtain adjusted partial X-Ray images.

4. The method of claim 3, comprising:

compensating for non-uniformity of noise contribution in the adjusted partial X-Ray images using simulated noise calculated based on measured noise parameters of the imaging sensor.

5. The method of claim 1, wherein the initial and final inverse vignetting functions are polynomial functions.

6. The method of claim 1, wherein the relative displacement between the first partial X-Ray image and the second partial X-Ray image is obtained based on the differences between coordinates of a marker visible on the first partial X-Ray image and the second partial X-Ray image, wherein the marker remains in a constant location relatively to X-Ray source when the relative displacement is generated.

7. The method of claim 1, wherein the relative displacement between the first partial X-Ray image and the second partial X-Ray image is obtained based on the differences between coordinates of a first marker and a second marker visible on the second partial X-Ray image, wherein the first marker and the second marker are aligned with respect to an axis perpendicular to the scintillator of the detector before the relative displacement is generated, and wherein the first marker remains in a constant location relatively to X-Ray source, and the second marker remains in a constant location relatively to the detector, when the relative displacement is generated.

8. A multi-camera flat panel X-Ray detector, the detector comprising:

a scintillator to convert X-Ray radiation generated by an X-Ray source into detectable radiation;

a displacement unit to generate, during a calibration phase, relative displacement between the X-Ray detector and an X-Ray source at a plane parallel to the scintillator;

at least one optical module, wherein the optical module comprises an imaging sensor and at least one lens, the imaging sensor to acquire, during the calibration phase, a first and a second partial images related to the detectable radiation, at a field of view of the at least one imaging sensor, wherein the first partial image is to be acquired before the relative displacement is generated, and the second partial image is to be acquired after the relative displacement is generated;

a relative displacement measurement unit to measure the relative displacement; and

a processing unit to;

obtain the relative displacement, the first and the second partial images; and

to

calculate coefficients of a preliminary inverse vignetting function based on differences between corresponding pixels of the two partial images.

9. The detector of claim 8, wherein the processing unit is further to:

calculate a gain for the optical module by equalizing values of pixels captured by the imaging sensor as well as by at least one other imaging sensor of the multi-camera flat panel X-Ray detector; and

adjusting the coefficients of the preliminary inverse vignetting function by the gain to obtain coefficients of a final inverse vignetting function.

10. The detector of claim 9, wherein during routine operation of the detector

the at least one imaging sensor is further to acquire routine partial X-Ray images;

and

the processing unit is further to adjust the routine partial X-Ray images, using the final inverse vignetting function to obtain adjusted partial X-Ray images.

11. The detector of claim 10, wherein during routine operation of the detector the processing unit is further to compensate for non-uniformity of noise contribution in the adjusted partial X-Ray images using simulated noise calculated based on measured noise parameters of the imaging sensor.

12. The detector of claim 8, wherein the initial and final inverse vignetting functions are polynomial functions.

13. The detector of claim 8,

wherein the relative displacement measurement unit comprises a marker visible on the first partial X-Ray image and the second partial X-Ray image,

wherein the marker remains in a constant location relatively to X-Ray source when the relative displacement is generated, and

wherein relative displacement between the first partial X-Ray image and the second partial X-Ray image is measured based on the differences between coordinates of the marker on the first partial X-Ray image and the second partial X-Ray image.

14. The detector of claim 8,

wherein the relative displacement measurement unit comprises a first marker and a second marker visible on the second partial X-Ray image,

wherein the first marker and the second marker are aligned with respect to an axis perpendicular to the scintillator before the relative displacement is generated, and

wherein the first marker remains in a constant location relatively to X-Ray source, and the second marker remains in a constant location relatively to the detector, when the relative displacement is generated, and wherein the relative displacement between the first partial X-Ray image and the second partial X-Ray image is obtained based on the differences between coordinates of the first marker and the second marker on the second partial X-Ray image.