Computed tomography scanning target detection using non-parallel slices

• US 5,909,477 A
• Filed: 10/10/1997
• Issued: 06/01/1999
• Est. Priority Date: 04/09/1997
• Status: Expired due to Term

• Current Assignee: Analogic Corporation
• Original Assignee: Analogic Corporation
• Inventors: Crawford, Carl R., Ruth, Christopher C.
• Primary Examiner(s): Porta, David P.
• Assistant Examiner(s): Bruce, David Vernon
• Application Number:
  US08/948,491
• Time in Patent Office: 599 Days
• Field of Search: 378/4, 378/15, 378/901
• US Class Current: 378/4
• CPC Class Codes: A61B 6/027 characterised by the use of a particular data acquisition trajectory, e.g. helical or spiral
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

A nutating slice CT image reconstruction apparatus and method generates a set of projection data using helical cone-beam scanning. The three-dimensional projection data is used to reconstruct a series of planar image slices. The slices are selected such that they define a tilt angle and a rotation angle with respect to the longitudinal axes of the object being scanned. Successive slices have equal tilt angles but changing rotation angles such that normal axes of successive slices define a nutation and precession about the longitudinal axis of the object. Projection data for the tilted slices are formed of selected one-dimensional fan-beam data. As such, the projection data can be applied to conventional two-dimensional reconstruction approaches to generate an image. The projection data can also be used to generate two-dimensional projection images at one or more stationary projection angles through an object being scanned. The nutation or tilt of image volume elements can be compensated for to provide a more accurate image and more accurate target assessment such as accurate total mass determination. A parallel processing architecture can be used to generate and process the nutated slices with improved efficiency.

Claims

1. A method of processing computed tomography scan data for a region having a longitudinal axis, said method comprising:

scanning the region with a radiation source and an array of detectors to generate the scan data for the region;

defining a plurality of image data slices corresponding to a plurality of positions along the longitudinal axis of the region, successive image data slices being non-parallel with each other and each image data slice defining a plurality of image volume elements tilted with respect to the longitudinal axis, each image volume element being associated with an image density value; and

applying a correction factor to the image density values of the tilted volume elements to compensate for the tilt of the image volume elements.

2. The method of claim 1 further comprising processing the image density values to determine a mass of an object in the region.

3. The method of claim 2 wherein processing the image density values to determine a mass of an object in the region comprises applying a density threshold to the image density values.

4. The method of claim 3 wherein:

density values which exceed the density threshold are used to determine the mass of the object; and

density values which do not exceed the density threshold are not used to determine the mass of the object.

5. The method of claim 3 wherein image density values that exceed the threshold are considered to be associated with an explosive material.

6. The method of claim 2 where the object comprises an explosive material.

7. The method of claim 1 wherein scanning the region further comprises translating the radiation source and the array of detectors along the longitudinal axis of the region while rotating the radiation source and the array of detectors about the longitudinal axis of the region.

8. The method of claim 1 wherein the radiation source is a cone-beam source.

9. The method of claim 1 wherein successive image data slices are nutated with respect to each other.

10. The method of claim 1 wherein the array of detectors is a two-dimensional array.

11. The method of claim 1 wherein the scan data is generated using a helical scan.

12. The method of claim 1 wherein the scan data is generated using a helical cone-beam scan.

13. An apparatus for processing computed tomography scan data for a region having a longitudinal axis, said apparatus comprising:

an array of detectors for scanning the region to generate the scan data for the region;

a processor for defining a plurality of image data slices corresponding to a plurality of positions along the longitudinal axis of the region such that successive image data slices are non-parallel with each other and each image data slice defines a plurality of image volume elements tilted with respect to the longitudinal axis and each image volume element is associated with an image density value; and

means for applying a correction factor to the image density values of the tilted volume elements to compensate for the tilt of the image volume element.

14. The apparatus of claim 13 further comprising means for processing the image density values to determine a mass of an object in the region.

15. The apparatus of claim 14 wherein the means for processing the image density values to determine a mass of an object in the region comprises means for applying a density threshold to the image density values.

16. The apparatus of claim 15 wherein:

density values which exceed the density threshold are used to determine the mass of the object; and

density values which do not exceed the density threshold are not used to determine the mass of the object.

17. The apparatus of claim 15 wherein image density values that exceed the threshold are considered to be associated with an explosive material.

18. The apparatus of claim 14 wherein the object comprises an explosive material.

19. The apparatus of claim 13 further comprising means for translating the radiation source and the array of detectors along the longitudinal axis of the region while the radiation source and the array of detectors are rotated about the longitudinal axis of the region.

20. The apparatus of claim 13 wherein the radiation source is a cone-beam source.

21. The apparatus of claim 13 wherein the array of detectors is a two-dimensional array.

22. The apparatus of claim 13 wherein the array of detectors is adapted to perform a helical scan of the region.

23. The apparatus of claim 13 wherein the array of detectors is adapted to perform a helical cone-beam scan of the region.