Computed tomography scanning apparatus and method using adaptive reconstruction window

• US 6,256,404 B1
• Filed: 10/10/1997
• Issued: 07/03/2001
• Est. Priority Date: 10/10/1997
• Status: Expired due to Term

• Current Assignee: Analogic Corporation
• Original Assignee: Analogic Corporation
• Inventors: Bailey, Eric M., Gordon, Bernard M., Schafer, David A., Ruth, Christopher C., Crawford, Carl R.
• Primary Examiner(s): Patel, Jay
• Application Number:
  US08/949,127
• Time in Patent Office: 1,362 Days
• Field of Search: 382/100, 382/103, 382/128-133, 382/149, 382/152, 382/286, 382/291, 382/317-318, 382/199, 382/214, 382/266, 382/141, 382/203, 382/312, 250/370.08, 250/370.09, 378/4, 378/21-27, 378/63, 378/56, 378/57, 378/62, 378/88, 378/146, 378/8, 72/74, 72/83, 72/94, 72/111, 72/162, 72/173, 144/387, 144/392, 144/402, 209/589, 427/595, 427/160, 604/20, 702/40, 702/172
• US Class Current: 382/131
• CPC Class Codes: G01V 5/226 using tomography

Abstract

A method and apparatus for performing CT scans of baggage being carried or loaded onto commercial aircraft are described. The CT baggage scanner of the invention includes numerous features which provide the system with high baggage throughput on the order of seven hundred bags per hour as well as improved image quality and accurate target detection. In one aspect, the scanner includes an adaptive image reconstruction window which identifies data collected from the field of view that are not related to the baggage being scanned. These unrelated data are excluded from the image reconstruction process, resulting in greatly reduced reconstruction time and increased baggage throughput. The invention also includes the capability of performing calibration “air scans” with objects such as the system conveyor in the field of view. Data gathered during the calibration scan are applied to a threshold, and data exceeding the threshold are assumed to be from X-rays that are unobstructed by objects in the field of view and are therefore used to perform the air calibration. The baggage scanner can also analyze scan data to identify shapes of objects, particularly, objects formed in the shape of a sheet. This greatly improves the ability of the system to detect sheet explosives. The system also compensates for detector dark currents and provides dark current offsets which can be dependent upon detector temperature.

Claims

1. A method of scanning each of a plurality of different objects sequentially transported through a CT scanning machine such that each object is scanned within a field of view of the CT scanning machine, comprising:

scanning each object within the field of view so as to generate the scan data for the entire field of view at a predetermined resolution;

determining the size, shape and location of the object within the field of view including determining the number of pixels required to produce a computed tomographic image of the cross-sectional area of the object, and whether the number of pixels required to reproduce a computed tomographic image of the cross-sectional area of the object exceeds a predetermined limit;

choosing one of a plurality of predetermined sub-fields of view, each disposed within and smaller in cross-sectional area than the field of view, which best corresponds to said object size and object shape; and

reconstructing the pixels that comprise the chosen sub-field of view at said object location with the predetermined resolution using the relevant scan data and computed tomographic image reconstruction techniques so as to produce a pixelated image of the sub-field of view within a predefined pixel window corresponding to a reconstruction window area;

wherein (a) all of the pixels required to produce the pixelated computed tomographic image of the cross-sectional area of the object are reconstructed within a pixel window corresponding to the predefined reconstruction window area when the number of pixels required to reproduce the computed tomographic image is less than or equal to the predetermined limit; and

(b) the predetermined limited number of pixels required to produce the computed tomographic image of that portion of the cross-sectional area of the object within a predefined reconstruction area making a fit to the best possible pixel window when the number of pixels required to reproduce the computed tomographic image is greater than the predetermined limit.

2. The method according to claim 1, further comprising:

choosing the predetermined number of pixels as a function of the throughput of the machine.

3. The method according to claim 1, wherein:

each object within the field of view has a cross-sectional area smaller than the field of view, the cross-sectional area being bounded by at least one of a plurality of predetermined sets of boundaries correspondingly denoting one of the plurality of predetermined sub-fields of view.

4. The method according claim 1, wherein determining the size, shape and location of the object within the field of view comprises detecting boundaries of the object from the scan data for the field of view so as to determine the size of the object.

5. The method according to claim 1, wherein determining the size, shape and location of the object within the field of view comprises detecting boundaries of the object from the scan data for the field of view so as to determine the shape of the object.

6. The method according to claim 1, wherein determining the size, shape and location of the object within the field of view includes providing a sensor to detect boundaries of the object.

7. The method according to claim 6, wherein the sensor comprises an optical device.

8. The method according to claim 7, wherein the optical device is a laser.

9. The method according to claim 7, wherein the optical device is a light emitting diode.

10. The method according to claim 7, wherein the optical device is an infrared detector.

11. The method according to claim 6, wherein the sensor comprises an ultrasound transducer.

12. The method according to claim 1, further comprising sequentially transporting the objects through the machine.

13. A CT scanning machine constructed and arranged so as to scan each of a plurality of different objects sequentially transported through the CT scanning machine such that each object is scanned within a field of view of the CT scanning machine, comprising:

a scanner constructed and arranged so as to scan each object within the field of view so as to generate the scan data for the entire field of view at a predetermined resolution;

a determination subsystem constructed and arranged so as to determine the size, shape and location of the object within the field of view, the number of pixels required to produce a computed tomographic image of the cross-sectional area of the object, and whether the number of pixels required to reproduce a computed tomographic image of the cross-sectional area of the object exceeds a predetermined limit;

a selection subsystem constructed and arranged so as to choose one of a plurality of predetermined sub-fields of view, each disposed within and smaller in cross-sectional area than the field of view, which best corresponds to said object size and object shape; and

a reconstruction subsystem constructed and arranged so as to reconstruct the pixels that comprise the chosen sub-field of view at said object location with the predetermined resolution using the relevant scan data and computed tomographic image reconstruction techniques so as to produce a pixelated image of the sub-field of view within a predefined pixel window corresponding to a reconstruction window area;

wherein (a) all of the pixels required to produce the pixelated computed tomographic image of the cross-sectional area of the object are reconstructed within a pixel window corresponding to the predefined reconstruction window area when the number of pixels required to reproduce the computed tomographic image is less than or equal to the predetermined limit; and

(b) the predetermined limited number of pixels required to produce the computed tomographic image of that portion of the cross-sectional area of the object within a predefined reconstruction area making a fit to the best possible pixel window when the number of pixels required to reproduce the computed tomographic image is greater than the predetermined limit.

14. The machine according to claim 13, wherein the predetermined number of pixels is chosen as a function of the throughput of the machine.

15. The machine according to claim 13, wherein each object within the field of view has a cross-sectional area smaller than the field of view, the cross-sectional area being bounded by at least one of a plurality of predetermined sets of boundaries correspondingly denoting one of the plurality of predetermined sub-fields of view.

16. The machine according to claim 13, wherein determining the size, shape and location of the object within the field of view comprises detecting boundaries of the object from the scan data for the field of view so as to determine the size of the object.

17. The machine according to claim 13, wherein determining the size, shape and location of the object within the field of view comprises detecting boundaries of the object from the scan data for the field of view so as to determine the shape of the object.

18. The machine according to claim 13, wherein determining the size, shape and location of the object within the field of view includes providing a sensor to detect boundaries of the object.

19. The machine according to claim 18, wherein the sensor comprises an optical device.

20. The machine according to claim 19, wherein the optical device is a laser.

21. The machine according to claim 19, wherein the optical device is a light emitting diode.

22. The machine according to claim 19, wherein the optical device is an infrared detector.

23. The machine according to claim 18, wherein the sensor comprises an ultrasound transducer.

24. The machine according to claim 13, further including a conveyor for transporting each of said objects through the scanner.