Three-dimensional reconstruction based on a limited number of X-ray projections

• US 5,442,672 A
• Filed: 03/31/1993
• Issued: 08/15/1995
• Est. Priority Date: 03/31/1993
• Status: Expired due to Fees

• Current Assignee: EG&G Astrophysics Research Corporation (Revvity, Inc.)
• Original Assignee: Keith E. Moler, Khai M. Le, Paul J. Bjorkholm
• Inventors: Bjorkholm, Paul J., Le, Khai M., Moler, Keith E.
• Primary Examiner(s): Dzierzynski, Paul M.
• Assistant Examiner(s): Bruce, David Vernon
• Application Number:
  US08/040,174
• Time in Patent Office: 867 Days
• Field of Search: 378/4, 378/5, 378/10, 378/98.9, 378/901, 364/413.15, 364/413.16
• US Class Current: 378/4
• CPC Class Codes: G01N 2223/419 computed tomograph
• CPC Class Codes: G01N 23/046 using tomography, e.g. computed tomography [CT]
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

A limited number of views or projections, e.g., two, are used to generated a reconstructed image of an object. In order to improve the quality of the image, terracing and smoothing functions are implemented. In addition, the reconstructed image may be divided into objects and background prior to terracing and smothing and the object and background can be reconstructed separately. Further, after the reconstructed image is generated threat and texture analyses of the reconstructed image may be performed.

Claims

1. A method for generating a tomographically reconstructed image of an object comprising the steps of:

creating a first projected image of the object by exposing the object to electromagnetic radiation and measuring, at a first plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a second projected image of the object by exposing the object to the electromagnetic radiation and measuring, at a second plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a reconstructed image of the object having a plurality of pixels including the steps of;

setting each of said pixels to an initialized value in accordance with a corresponding momentum factor; and

adjusting the initialized value of each of said pixels based on said first and second projected images;

performing a terracing function on said reconstructed image;

performing a smoothing function on said reconstructed image; and

displaying said tomographically reconstructed image on the basis of said reconstructed image.

2. The method of claim 1, wherein the intensity of said electromagnetic radiation is indicative of a density of organic material in said object.

3. The method of claim 2, wherein said electromagnetic radiation includes radiation of a first photon energy and radiation of a second photon energy.

4. The method of claim 1, wherein said step of performing the terracing function on said reconstructed image comprises the steps of:

determining a value of a density of a region of said object within a region corresponding to one of said plurality of pixels;

comparing the determined value of the density with a plurality of ranges of density values, each of said plurality of ranges having a corresponding terrace value, the value of the density falling within one of said plurality of ranges;

selecting said one of said plurality of ranges of density values; and

replacing the determined value of the density with a terrace value corresponding to the selected one of the plurality of ranges of density values.

5. The method of claim 1, wherein the step of creating the reconstructed image includes application of a multiplicative algebraic reconstruction technique to said first and second projected images.

6. The method of claim 1, wherein said step of performing a smoothing function on said reconstructed image includes performing a series of mean function convolutions.

7. The method of claim 1, wherein the step of creating the reconstructed image of the object further includes the step of obtaining pixel information of the reconstructed image from a ray mask array, and the adjustment of the initialized value of each of said pixels is also based on said pixel information.

8. A method for generating a tomographically reconstructed image of an object including first and second reconstructed slice images comprising the steps of:

generating said first reconstructed slice image including the steps of;

creating a first projected image of the object by exposing the object to electromagnetic radiation and measuring, at a first plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a second projected image of the object by exposing the object to the electromagnetic radiation and measuring, at a second plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a first reconstructed image, including a plurality of pixels, of the object from said first and second projected images and predetermined values of said plurality of pixels;

performing a terracing function on said first reconstructed image; and

performing a smoothing function on said first reconstructed image;

moving said object a fixed distance relative to said first and second plurality of locations; and

generating a second reconstructed slice image including the steps of;

creating a third projected image of the object by exposing the object to said electromagnetic radiation and measuring, at the first plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a fourth projected image of the object by exposing the object to the electromagnetic radiation and measuring, at the second plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a second reconstructed image, including a plurality of pixels, of the object from said third and fourth projected images and values of each said plurality of pixels corresponding to values of pixels of said first reconstructed slice image;

performing a terracing function on said second reconstructed image; and

performing a smoothing function on said second reconstructed image; and

displaying said first and second reconstructed slice images on the basis of said first and second reconstructed images, respectively.

9. A method for generating a three dimensional tomographically reconstructed image of an object comprising the steps of:

creating a first projected image of the object by exposing the object to electromagnetic radiation and measuring, at a first plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a second projected image of the object by exposing the object to the electromagnetic radiation and measuring, at a second plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a first reconstructed slice, including a plurality of voxels having a specified physical characteristic, of the object from said first and second projected images;

creating a third projected image of the object by exposing the object to electromagnetic radiation and measuring, at a third plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a fourth projected image of the object by exposing the object to the electromagnetic radiation and measuring, at a fourth plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a second reconstructed slice, including a plurality of voxels having a specified physical characteristic, of the object from said third and fourth projected images;

comparing each of said plurality of voxels of said first reconstructed slice to a predetermined physical characteristics to select a first voxel whose specified physical characteristic matches the predetermined physical characteristic;

comparing the specified physical characteristics, of said plurality of voxels of said first reconstructed slice and said second reconstructed slice which are contiguous with said selected first voxel to select at least a second voxel whose specified physical characteristic matches the predetermined physical characteristic; and

displaying said first and second selected voxels.

10. The method of claim 9, wherein said specified physical characteristic and said predetermined physical characteristic include one or more of the following:

mass, shape and texture.

11. The method of claim 9 further comprising the step of:

creating at least a fifth projected image of the object by exposing the object to the electromagnetic radiation and measuring, at a fifth plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object; and

creating at least a sixth projected image of the object by exposing the object to the electromagnetic radiation and measuring, at a sixth plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

wherein

said first reconstructed slice of the object is created from said first, second and fifth projected images and said second reconstructed slice of the object is created from the third, fourth and sixth projected images.

12. The method of claim 9 wherein said predetermined physical characteristics can be varied or changed to deselect a voxel of said first reconstructed slice of the object.

13. An apparatus for generating a tomographically reconstructed image of an object comprising:

first projection means for creating a first projected image of the object by exposing the object to electromagnetic radiation and measuring, at a first plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

second projection means for creating a second projected image of the object by exposing the object to the electromagnetic radiation and measuring, at a second plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

reconstruction means for creating a reconstructed image of the object from said first and second projected images;

terracing means for performing a terracing function on said reconstructed image; and

smoothing means for performing a smoothing function on said reconstructed image; and

display means for displaying said tomographically reconstructed image on the basis of said reconstructed image.

14. The apparatus of claim 13 wherein said electromagnetic radiation includes dual energy X-ray radiation.

15. A method for generating a tomographically reconstructed image of an object comprising the steps of:

creating a first projected image of the object by exposing the object to electromagnetic radiation and measuring, at a first plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a second projected image of the object by exposing the object to the electromagnetic radiation and measuring, at a second plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a reconstructed image of the object from said first and second projected images;

separating the projected images into object portions and background portions;

generating a first reconstructed image on the basis of said object portions;

generating a second reconstructed image on the basis of said background portions; and

displaying said tomographically reconstructed image on the basis of said first and second reconstructed images.

16. A method for generating a tomographically reconstructed image of an object including current and next reconstructed slice images comprising the steps of:

generating said current reconstructed slice image including the steps of;

creating a first projected image of the object by exposing the object to electromagnetic radiation and measuring, at a first plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a second projected image of the object by exposing the object to the electromagnetic radiation and measuring, at a second plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a current reconstructed image, including a plurality of pixels, of the object from said first and second projected images and predetermined values of said plurality of pixels;

performing a terracing function on said current reconstructed image; and

performing a smoothing function on said current reconstructed image;

moving said object a fixed distance relative to said first and second plurality of locations; and

generating a next reconstructed slice image including the steps of;

creating a third projected image of the object by exposing the object to said electromagnetic radiation and measuring, at the first plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a fourth projected image of the object by exposing the object to the electromagnetic radiation and measuring, at the second plurality of locations spaced from said object, the intensity of said electromagnetic radiation transmitted through said object;

creating a next reconstructed image, including a plurality of pixels, of the object from said third and fourth projected images and values of each said plurality of pixels corresponding to values of pixels of said current reconstructed slice image;

performing a terracing function on said next reconstructed image;

performing a smoothing function on said next reconstructed image; and

displaying said current and next reconstructed slice images on the basis of said current and next reconstructed images, respectively.