Method and apparatus for calibrating an x-ray laminography imaging system

• US 6,819,739 B2
• Filed: 11/27/2002
• Issued: 11/16/2004
• Est. Priority Date: 11/27/2002
• Status: Expired due to Fees

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Eppler, Barry
• Primary Examiner(s): Church, Craig E.
• Assistant Examiner(s): Yun, Jurie
• Application Number:
  US10/306,681
• Publication Number:
  US 20040101110A1
• Time in Patent Office: 720 Days
• Field of Search: 378/207, 378/21-27
• US Class Current: 378/21
• CPC Class Codes: G01N 23/044 using laminography or tomosynthesis
• CPC Class Codes: H01J 35/30 by deflection of the cathode ray
• CPC Class Codes: H05G 1/52 Target size or shape; Direction of electron beam, e.g. in tubes with one anode and more than one cathode

Abstract

An x-ray laminography imaging system and an apparatus and method for calibrating the system. The x-ray laminography imaging system utilizes a stationary x-ray source and generates a moving pattern of x-ray spots on a target anode synchronously with rotation of an x-ray detector to reduce or eliminate the need to move an object being imaged. The present invention provides an apparatus and a method for calibrating the system based in part on empirical data gathered during physical calibration and in part on data analytically derived from the empirical data. Because calibration of the system can be performed in great part analytically rather than relying entirely on empirically generated data, the calibration process can be performed very quickly.

Claims

1. An x-ray laminography imaging system comprising:

a stationary x-ray source;

a target anode;

an x-ray detector, the x-ray source generating a moving pattern of x-ray spots on the target anode synchronously with rotation of the x-ray detector to reduce or eliminate the need to move an object being imaged by the system;

first logic configured to gather empirical calibration data generated during physical calibration of the system during which the stationary x-ray source generates a moving pattern of x-ray spots on the target anode synchronously with rotation of the x-ray detector, the empirical data corresponding to offsets to locations at which the x-ray spots of an on-axis x-ray spot pattern are formed on the target anode;

second logic configured to analytically derive calibration data from the empirical data, the analytically-derived calibration data corresponding to offsets to locations at which x-ray spots of an off-axis x-ray spot pattern are formed on the target anode; and

third logic configured to calibrate the system using the empirical data and the analytically-derived calibration data.

2. The system of claim 1, wherein the first, second and third logic correspond to a processor executing a calibration program.

3. An x-ray laminography imaging system comprising:

a stationary x-ray source;

a target anode;

an x-ray detector, the x-ray source generating a moving pattern of x-ray spots on the target anode synchronously with rotation of the x-ray detector to reduce or eliminate the need to move an object being imaged by the system;

a processor, the processor generating control signals and causing said control signals to be delivered to a controllable deflection yoke, the controllable deflection yoke controlling particular locations on the target anode upon which x-rays projected by the x-ray source along a Z-axis impinge, the target anode oriented substantially parallel to a plane that is substantially orthogonal to the Z-axis, the x-rays projected along the Z-axis impinging at particular locations on said target anode, said locations being dependent on control signals received by the controllable deflection yoke that cause the deflection yoke to direct x-rays onto said particular locations on the target anode to form substantially circular x-ray spot patterns on the target anode, each x-ray spot pattern being produced by movement of an x-ray spot in a substantially circular pattern, each x-ray spot corresponding to a beam of x-rays impinging on one of said particular locations on the target anode, the control signals causing the deflection yoke to form at least one substantially circular on-axis x-ray spot pattern on said target anode about the Z-axis and to form at least one substantially circular off-axis x-ray spot pattern on the target anode about an axis that is substantially parallel to the Z-axis, and wherein the processor determines the control signals needed to be delivered to the deflection yoke to cause said at least one off-axis x-ray spot pattern to be formed based on data associated with said at least one on-axis x-ray spot pattern.

4. The system of claim 3, wherein the control signals delivered to the deflection yoke cause at least two substantially circular on-axis x-ray spot patterns to be formed on the target anode about the Z-axis, and wherein the processor determines said at least one substantially circular off-axis x-ray spot pattern from data used by the processor to form said at least two substantially circular on-axis spot patterns.

5. The system of claim 3, wherein the control signals are voltage values and wherein the deflection yoke comprises an X-deflection coil and a Y-deflection coil, said plane being an X, Y plane, each particular location on the target anode corresponding to an X, Y coordinate pair, and wherein voltage values delivered to the X-deflection coil cause the X-deflection coil to direct x-rays in an X-direction, and wherein voltage values delivered to the Y-deflection coil cause the Y-deflection coil to direct x-rays in a Y-direction.

6. The system of claim 3, wherein said at least one on-axis substantially circular x-ray spot pattern is determined by the processor at least partially based on empirical data and wherein said at least one substantially circular off-axis x-ray spot pattern is interpolated by the processor from said at least one on-axis substantially circular x-ray spot pattern.

7. The system of claim 3, wherein said at least one on-axis substantially circular x-ray spot pattern is produced by moving the x-ray spot in a circular pattern over the target anode about the Z-axis in an X, Y plane that is orthogonal to the Z-axis, the movement of the location of the x-ray spot being based on the control signals delivered to the deflection yoke, and wherein the control signals are sinusoidal, each of the sinusoidal signals having a magnitude that dictates the Z-coordinate of an X, Y plane within the object that is imaged by the system.

8. The system of claim 6, wherein said at least one on-axis substantially circular x-ray spot pattern comprises first and second sets of x-ray spots, the first set of x-ray spots being determined empirically by the processor through physical calibration of the system during which the detector and the on-axis substantially circular x-ray spot pattern are synchronously rotated and offsets are determined for each x-ray spot of the first set to form a first set of offset x-ray spots, and wherein once the offsets of said first set of x-ray spots have been empirically determined, the x-ray spots of the second set are interpolated by the processor from the offset first set of x-ray spots.

9. The system of claim 8, wherein once said at least one on-axis substantially circular x-ray spot pattern comprising the first and second sets of x-ray spots has been determined by the processor, said at least one off-axis substantially circular x-ray spot pattern is determined by the processor by interpolating the x-ray spots of the off-axis substantially circular x-ray spot pattern from the on-axis substantially circular x-ray spot pattern, the processor interpolating the off-axis x-ray spots by assigning each off-axis x-ray spot the offset associated with a respective on-axis x-ray spot.

10. The system of claim 9, wherein the processor interpolates the second set of x-ray spots from the first set of x-ray spots by performing a curve-fitting algorithm that uses the first set of x-ray spots to interpolate locations on the target anode of the second set of x-ray spots.

11. The system of claim 9, wherein the processor interpolates the off-axis x-ray spots by executing a curve fitting algorithm that assigns each off-axis x-ray spot the offset associated with a respective on-axis x-ray spot.

12. The system of claim 9, wherein the processor interpolates the off-axis x-ray spots by executing a nearest-neighbor algorithm that assigns each off-axis x-ray spot the offset associated with the on-axis x-ray spot that is nearest to the off-axis x-ray spot.

13. The system of claim 10, wherein the curve fitting algorithm that uses the first set of x-ray spots to interpolate locations on the target of the second set of x-ray spots is a cubic spline algorithm.

14. An apparatus for calibrating an x-ray laminography imaging system, the system utilizing a stationary x-ray source, a rotatably mounted detector, and generating a moving pattern of x-ray spots on a target anode to reduce or eliminate the need to move an object being imaged, the apparatus comprising:

a stationary x-ray source;

a target anode;

an x-ray detector, the x-ray source generating a moving pattern of x-ray spots on the target anode synchronously with rotation of the x-ray detector to reduce or eliminate the need to move an object being imaged by the system;

first logic, the first logic determining control signals needed to be delivered to a deflection yoke to cause at least one substantially circular on-axis x-ray spot pattern to be formed on the target anode about a Z-axis to simulate rotation of the x-ray source, the target anode lying in an X, Y plane that is substantially orthogonal to the Z-axis, each spot of the x-ray spot pattern formed on the target anode having an X-coordinate and a Y-coordinate;

second logic, the second logic processing data to determine offsets to the X, Y coordinates of the x-ray spots of the pattern on the target anode, wherein the data is gathered through calibration of the system as a rotating x-ray detector is synchronized to the motion of the x-ray spots about the Z-axis that form the on-axis x-ray spot pattern;

third logic, the third logic using the offsets to offset the X, Y coordinates of the x-ray spots of the on-axis x-ray spot pattern as they x-ray spot pattern is being formed on the target anode, thereby causing an offset on-axis x-ray spot pattern to be formed on the target anode about the Z-axis; and

fourth logic, the fourth logic using the x-ray spot offsets associated with the on-axis x-ray spot pattern to determine a substantially circular off-axis x-ray spot pattern to be formed on the target anode about an axis that is substantially parallel to the Z-axis.

15. The apparatus of claim 14, further comprising:

fifth logic, the fifth logic generating control signals to be delivered to a deflection yoke, the control signals corresponding to voltage values that have been offset in accordance with the x-ray spot offsets; and

sixth logic, the sixth logic causing the control signals to be delivered to the deflection yoke, wherein the delivery of the control signals to the deflection yoke causes the offset on-axis x-ray spot pattern to be formed on the target anode about the Z-axis and causes said at least one substantially circular off-axis x-ray spot pattern to be formed on the target anode about an axis that is parallel to the Z-axis.

16. The apparatus of claim 15, wherein the deflection yoke comprises an X-deflection coil and a Y-deflection coil, and wherein voltage values delivered to the X-deflection coil cause the X-deflection coil to deflect x-rays away from the Z-axis in an X-direction, and wherein voltage values delivered to the Y-deflection coil cause the Y-deflection coil to deflect x-rays away from the Z-axis in a Y-direction, and wherein the deflection of the x-rays in the X and Y-directions causes the x-ray spots to be formed at particular X, Y coordinate locations on the target anode.

17. The apparatus of claim 15, wherein the third logic determines the on-axis substantially circular x-ray spot pattern at least partially based on empirical data and wherein said at least one substantially circular off-axis x-ray spot pattern is interpolated by the fourth logic from the offset on-axis substantially circular x-ray spot pattern determined by the third logic.

18. The apparatus of claim 15, wherein the control signals are sinusoidal, each of the sinusoidal signals having a magnitude that dictates a location along the Z-axis of the X, Y plane.

19. The apparatus of claim 14, wherein the offset on-axis substantially circular x-ray spot pattern comprises first and second sets of x-ray spots, the first set of x-ray spots being determined empirically by the third logic from data gathered through physical calibration of the system during which the detector is rotated synchronously with the motion of x-ray spots of the on-axis substantially circular x-ray spot pattern and offsets to the X, Y coordinates of the x-ray spots of the on-axis x-ray spot pattern are determined for each x-ray spot of the first set, and wherein once the offsets to the X, Y coordinates of the first set of x-ray spots have been empirically determined, the third logic interpolates X, Y coordinates of x-ray spots of the second set from the offsets to the X, Y coordinates of the first set.

20. The apparatus of claim 19, wherein once the x-ray spot pattern comprising the first and second sets of x-ray spots has been determined by the third logic, the off-axis substantially circular x-ray spot pattern is determined by the fourth logic from the offset x-ray spots of the on-axis substantially circular x-ray spot pattern by offsetting the X, Y coordinates of each x-ray spot of the off-axis x-ray spot pattern by an amount equal to the offset of respective X, Y coordinates of a respective x-ray spot of the offset on-axis x-ray spot pattern.

21. The apparatus of claim 19, wherein the third logic interpolates the X, Y coordinates of the second set of x-ray spots from the X, Y coordinates of the first set of x-ray spots by performing a curve-fitting algorithm that uses the first set of x-ray spots to interpolate X, Y coordinate locations on the target anode of the second set of x-ray spots.

22. The apparatus of claim 19, wherein the fourth logic interpolates the X, Y coordinates of the off-axis x-ray spots by executing a curve fitting algorithm that utilizes the offset X, Y coordinates of the x-ray spots of the offset on-axis x-ray spot pattern.

23. The apparatus of claim 19, wherein the fourth logic interpolates the X, Y coordinates of the x-ray spots of the off-axis x-ray spot pattern by performing a nearest-neighbor algorithm that assigns the X, Y coordinates of each off-axis x-ray spot the offset associated with the X, Y coordinates of the on-axis x-ray spot that is nearest to the respective off-axis x-ray spot on the target anode.

24. A method for calibrating an x-ray laminography imaging system, the system utilizing a stationary x-ray source, a rotatably mounted detector, and generating a moving pattern of x-ray spots on a target anode to reduce or eliminate the need to move an object being imaged, the method comprising the steps of:

determining control signals needed to be delivered to a deflection yoke to cause at least one substantially circular on-axis x-ray spot pattern to be formed on a target anode about a Z-axis to simulate rotation of an x-ray source, the target anode lying in an X, Y plane that is substantially orthogonal to the Z-axis, each spot of the x-ray spot pattern formed on the target anode having an X-coordinate and a Y-coordinate;

processing data to determine offsets to the X, Y coordinates of the x-ray spots of the pattern on the target anode, wherein the data is gathered through calibration of the system as a rotating x-ray detector is synchronized to the motion of the x-ray spots about the Z-axis that form the on-axis x-ray spot pattern;

using the offsets to offset the X, Y coordinates of the x-ray spots of the on-axis x-ray spot pattern as they x-ray spot pattern is being formed on the target anode, thereby causing an offset on-axis x-ray spot pattern to be formed on the target anode about the Z-axis; and

using the x-ray spot offsets associated with the on-axis x-ray spot pattern to determine a substantially circular off-axis x-ray spot pattern to be formed on the target anode about an axis that is substantially parallel to the Z-axis.

25. The method of claim 24, further comprising:

generating the offset control signals to be delivered to a deflection yoke, the offset control signals corresponding to voltage values that have been offset in accordance with the x-ray spot offsets; and

causing the offset control signals to be delivered to the deflection yoke, wherein the delivery of the offset control signals to the deflection yoke causes the offset on-axis x-ray spot pattern to be formed on the target anode about the Z-axis and causes said at least one substantially circular off-axis x-ray spot pattern to be formed on the target anode about an axis that is parallel to the Z-axis.

26. The method of claim 25, wherein the deflection yoke comprises an X-deflection coil and a Y-deflection coil, and wherein voltage values delivered to the X-deflection coil cause the X-deflection coil to deflect x-rays away from the Z-axis in an X-direction, and wherein voltage values delivered to the Y-deflection coil cause the Y-deflection coil to deflect x-rays away from the Z-axis in a Y-direction, and wherein the deflection of the x-rays in the X and Y-directions causes the x-ray spots to be formed at particular X, Y coordinate locations on the target anode.

27. The method of claim 25, wherein the determination of the on-axis substantially circular x-ray spot pattern is based at least partially on empirical data and wherein said at least one substantially circular off-axis x-ray spot pattern is interpolated from the offset on-axis substantially circular x-ray spot pattern.

28. The method of claim 26, wherein the control signals are sinusoidal, each of the sinusoidal signals having a magnitude that dictates a location along the Z-axis of the X, Y plane.

29. The method of claim 24, wherein the offset on-axis substantially circular x-ray spot pattern comprises first and second sets of x-ray spots, the first set of x-ray spots being determined empirically from data gathered through physical calibration of the system during which the detector is rotated synchronously with the motion of x-ray spots of the on-axis substantially circular x-ray spot pattern, and wherein offsets to the X, Y coordinates of the x-ray spots of the on-axis x-ray spot pattern are determined for each x-ray spot of the first set, and wherein once the offsets to the X, Y coordinates of the first set of x-ray spots have been empirically determined, the X, Y coordinates of x-ray spots of the second set are interpolated from the offsets to the X, Y coordinates of the first set.

30. The method of claim 29, wherein once the x-ray spot pattern comprising the first and second sets of x-ray spots has been determined, the off-axis substantially circular x-ray spot pattern is determined from the offset x-ray spots of the on-axis substantially circular x-ray spot pattern by offsetting the X, Y coordinates of each x-ray spot of the off-axis x-ray spot pattern by an amount equal to the offset of respective X, Y coordinates of a respective x-ray spot of the offset on-axis x-ray spot pattern.

31. The method of claim 29, wherein the X, Y coordinates of the second set of x-ray spots are interpolated from the X, Y coordinates of the first set of x-ray spots by performing a curve-fitting algorithm that uses the first set of x-ray spots to interpolate X, Y coordinate locations on the target anode of the second set of x-ray spots.

32. The method of claim 29, wherein the X, Y coordinates of the off-axis x-ray spots are interpolated by executing a curve fitting algorithm that utilizes the offset X, Y coordinates of the x-ray spots of the offset on-axis x-ray spot pattern.

33. The method of claim 29, wherein the X, Y coordinates of the x-ray spots of the off-axis x-ray spot pattern are interpolated by performing a nearest-neighbor algorithm that assigns the X, Y coordinates of each off-axis x-ray spot the offset associated with the X, Y coordinates of the on-axis x-ray spot that is nearest to the respective off-axis x-ray spot on the target anode.

34. A computer-readable medium having a computer program embodied thereon for calibrating an x-ray laminography imaging system, the system utilizing a stationary x-ray source, a rotatably mounted detector, and generating a moving pattern of x-ray spots on a target anode to reduce or eliminate the need to move an object being imaged, the computer-readable medium comprising:

a first code segment for determining control signals needed to be delivered to a deflection yoke to cause at least one substantially circular on-axis x-ray spot pattern to be formed on a target anode about a Z-axis to simulate rotation of an x-ray source, the target anode lying in an X, Y plane that is substantially orthogonal to the Z-axis, each spot of the x-ray spot pattern formed on the target anode having an X-coordinate and a Y-coordinate;

a second code segment for processing data to determine offsets to the X, Y coordinates of the x-ray spots of the pattern on the target anode, wherein the data is gathered through calibration of the system as a rotating x-ray detector is synchronized to the motion of the x-ray spots about the Z-axis that form the on-axis x-ray spot pattern;

a third code segment that uses the offsets to offset the X, Y coordinates of the x-ray spots of the on-axis x-ray spot pattern as they x-ray spot pattern is being formed on the target anode, thereby causing an offset on-axis x-ray spot pattern to be formed on the target anode about the Z-axis; and

a fourth code segment that uses the x-ray spot offsets associated with the on-axis x-ray spot pattern to determine a substantially circular off-axis x-ray spot pattern to be formed on the target anode about an axis that is substantially parallel to the Z-axis.