Process for reconstructing a three-dimensional image of an object

• US 6,510,241 B1
• Filed: 06/04/1999
• Issued: 01/21/2003
• Est. Priority Date: 06/11/1998
• Status: Expired due to Term

• Current Assignee: GE Medical Systems Norway AS (General Electric Company)
• Original Assignee: GE Medical Systems Norway AS (General Electric Company)
• Inventors: Romeas, Rene, Launay, Laurant, Vaillant, Regis, Trousset, Yves Lucien Marie
• Primary Examiner(s): Mehta, Bhavesh
• Assistant Examiner(s): DESIRE, GREGORY M
• Application Number:
  US09/326,013
• Time in Patent Office: 1,327 Days
• Field of Search: 382/154, 382/285, 382/274, 382/130, 382/133, 378/4, 700/98, 700/120, 700/182, 345/419, 345/420
• US Class Current: 382/154
• CPC Class Codes: A61B 6/583 using calibration phantoms
• CPC Class Codes: G06T 11/005 Specific pre-processing for tomographic reconstruction, e.g. calibration, source positioning, rebinning, scatter correction, retrospective gating
• CPC Class Codes: G06T 11/006 Inverse problem, transformation from projection-space into object-space, e.g. transform methods, back-projection, algebraic methods
• CPC Class Codes: G06T 2211/424 Iterative

Abstract

The process comprises a calibration of the apparatus, in which a virtual volume surrounding the object is generated and broken down into voxels, an acquisition of the set of numbered projected two-dimensional images, and a reconstruction of the three-dimensional image from the projected acquired two-dimensional images, and from an iterative algebraic image reconstruction algorithm. A first iteration of the algorithm is performed with a predetermined initial image resolution so as to obtain, at the end of this first iteration, first density values for the voxels of the volume, at least one part of the voxels of the virtual volume is subdivided into several sets, respectively, corresponding to different image resolutions that are multiples or sub-multiples of the initial resolution, and during each subsequent iteration of the algorithm, the algorithm is successively aplied to each of the sets of voxels.

Claims

1. A process for reconstructing a three-dimensional image of an object from a set of numbered projected two-dimensional images of the object obtained from various positions of an imaging around the object, comprising the steps of generating a calibrating a virtual volume surrounding the object and broken down into voxels acquiring the set of numbered projected two-dimensional images, and reconstructing the three-dimensional image from the projected acquired two-dimensional images and from an iterative algebraic image reconstruction algorithm, wherein a first iteration of the algorithm is performed with a predetermined initial image resolution so as to obtain, at the end of this first iteration, first density values for the voxels of the volume, at least one part of the voxels of the virtual volume is subdivided into several sets, respectively, corresponding to different image resolutions that are multiples or sub-multiples of the initial resolution, and during each subsequent iteration of the algorithm, the algorithm is successively applied to each of the sets of voxels.

2. The process according to claim 1, wherein during each sub-sequent iteration of the algorithm, a virtual image is determined for each projected acquired image, by successively combining the elementary virtual images respectively obtained from the projections of the corresponding sets of voxels into the acquisition plane of the projected acquired image.

3. The process according to claim 2, wherein the elementary virtual images are generated in the increasing order of the resolution values, beginning with the elementary virtual image corresponding to the lowest resolution value, and after an elementary virtual image is determined, a scaling is performed in order to obtain an enlarged virtual image whose resolution corresponds to that of the next elementary virtual image to be determined, and the enlarged virtual image is combined with the next elementary virtual image.

4. The process according to claim 3, wherein projected two-dimensional images having a predetermined base resolution are acquired, an initial resolution is chosen which is equal to a sub-multiple of the base resolution, and chosen from among the different image resolutions are the base resolution, the initial resolution, and at least one first additional resolution, which is a sub-multiple of the initial resolution.

5. The process according to claim 3, wherein a first density threshold is generated as a function of a predetermined selection criterion, each voxel having a density higher than or equal to the first threshold is subdivided into a first number of subdivided voxels, the first number being defined based on the relationship between the base resolution and the initial resolution, all of which subdivided voxels form a first set of voxels corresponding to the base resolution, at least some of the voxels whose density is lower than the first threshold and which meet a predetermined regrouping criterion are regrouped so as to form regrouped voxels which together form a second set of voxels corresponding to the first additional resolution, the number of regrouped voxels in each group being based on the relationship between the initial resolution and the first additional resolution, and in that the voxels whose density is lower than the first threshold and which do not meet the predetermined regrouping criterion form a third set of voxels corresponding to the initial resolution.

6. The process according to claim 5, wherein a first density threshold is generated as a function of a predetermined selection criterion, each voxel having a density higher than or equal to the first threshold is subdivided into a first number of subdivided voxels, the first number being defined based on the relationship between the base resolution and the initial resolution, all of which subdivided voxels form a first set of voxels corresponding to the base resolution, at least some of the voxels whose density is lower than the first threshold and which meet a predetermined regrouping criterion are regrouped so as to form regrouped voxels which together form a second set of voxels corresponding to the first additional resolution, the number of regrouped voxels in each group being based on the relationship between the initial resolution and the first additional resolution, and in that the voxels whose density is lower than the first threshold and which do not meet the predetermined regrouping criterion form a third set of voxels corresponding to the initial resolution.

7. The process according to claim 5, wherein the regrouped voxels which meet the regrouping criterion are regrouped in order to from a fourth set of voxels corresponding to a second additional resolution, which is a sub-multiple of the first additional resolution.

8. The process according to claim 2, wherein projected two-dimensional images having a predetermined base resolution are acquired, an initial resolution is chosen which is equal to a sub-multiple of the base resolution and chosen from among the different image resolutions are the base resolution, the initial resolution, and at least one first additional resolution, which is a sub-multiple of the initial resolution.

9. The process according to claim 2, wherein a first density threshold is generated as a function of a predetermined selection criterion, each voxel having a density higher than or equal to the first threshold is subdivided into a first number of subdivided voxels, the first number being defined based on the relationship between the base resolution and the initial resolution, all of which subdivided voxels form a first set of voxels corresponding to the base resolution, at least some of the voxels whose density is lower than the first threshold and which meet a predetermined regrouping criterion are regrouped so as to form regrouped voxels which together form a second set of voxels corresponding to the first additional resolution, the number of regrouped voxels in each group being based on the relationship between the initial resolution and the first additional resolution, and in that the voxels whose density is lower than the first threshold and which do not meet the predetermined regrouping criterion form a third set of voxels corresponding to the initial resolution.

10. The process according to claim 9, wherein a first density threshold is generated as a function of a predetermined selection criterion, each voxel having a density higher than or equal to the first threshold is subdivided into a first number of subdivided voxels, the first number being defined based on the relationship between the base resolution and the initial resolution, all of which subdivided voxels form a first set of voxels corresponding to the base resolution, at least some of the voxels whose density is lower than the first threshold and which meet a predetermined regrouping criterion are regrouped so as to form regrouped voxels which together form a second set of voxels corresponding to the first additional resolution, the number of regrouped voxels in each group being based on the relationship between the initial resolution and the first additional resolution, and in that the voxels whose density is lower than the first threshold and which do not meet the predetermined regrouping criterion form a third set of voxels corresponding to the initial resolution.

11. The process according to claim 9, wherein the regrouped voxels which meet the regrouping criterion are regrouped in order to from a fourth set of voxels corresponding to a second additional resolution, which is a sub-multiple of the first additional resolution.

12. The process according to claim 1, wherein projected two-dimensional images having a predetermined base resolution are required, an initial resolution is chosen which is equal to a sub-multiple of the base resolution, and chosen from among the different image resolutions are the base resolution, the initial resolution, and at least one first additional resolution, which is a sub-multiple of the initial resolution.

13. The process according to claim 12, wherein a first density threshold is generated as a function of a predetermined selection criterion, each voxel having a density higher than or equal to the first threshold is subdivided into a first number of subdivided voxels, the first number being defined based on the relationship between the base resolution and the initial resolution, all of which subdivided voxels form a first set of voxels corresponding to the base resolution, at least some of the voxels whose density is lower than the first threshold and which meet a predetermined regrouping criterion are regrouped so as to form regrouped voxels which together form a second set of voxels corresponding to the first additional resolution, the number of regrouped voxels in each group being based on the relationship between the initial resolution and the first additional resolution, and in that the voxels whose density is lower than the first threshold and which do not meet the predetermined regrouping criterion form a third set of voxels corresponding to the initial resolution.

14. The process according to claim 13, wherein a first density threshold is generated as a function of a predetermined selection criterion, each voxel having a density higher than or equal to the first threshold is subdivided into a first number of subdivided voxels, the first number being defined based on the relationship between the base resolution and the initial resolution, all of which subdivided voxels form a first set of voxels corresponding to the base resolution, at least some of the voxels whose density is lower than the first threshold and which meet a predetermined regrouping criterion are regrouped so as to form regrouped voxels which together form a second set of voxels corresponding to the first additional resolution, the number of regrouped voxels in each group being based on the relationship between the initial resolution and the first additional resolution, and in that the voxels whose density is lower than the first threshold and which do not meet the predetermined regrouping criterion form a third set of voxels corresponding to the initial resolution.

15. The process according to claim 13, wherein the regrouped voxels which meet the regrouping criterion are regrouped in order to from a fourth set of voxels corresponding to a second additional resolution, which is a sub-multiple of the first additional resolution.

16. The process according to claim 1, wherein a first density threshold is generated as a function of a predetermined selection criterion, each voxel having a density higher than or equal to the first threshold is subdivided into a first number of subdivided voxels, the first number being defined based on the relationship between the base resolution and the initial resolution, all of which subdivided voxels form a first set of voxels corresponding to the base resolution, at least some of the voxels whose density is lower than the first threshold and which meet a predetermined regrouping criterion are regrouped so as to form regrouped voxels which together form a second set of voxels corresponding to the first additional resolution, the number of regrouped voxels in each group being based on the relationship between the initial resolution and the first additional resolution, and in that the voxels whose density is lower than the first threshold and which do not meet the predetermined regrouping criterion form a third set of voxels corresponding to the initial resolution.

17. The process according to claim 16, wherein a voxel meets the regrouping criterion if each of the coordinates of the center of the voxel is a multiple of 2 and if the density of each voxel adjacent to said voxel is lower than the first threshold.

18. The process according to claim 16, wherein the regrouped voxels which meet the regrouping criterion are regrouped in order to from a fourth set of voxels corresponding to a second additional resolution, which is a sub-multiple of the first additional resolution.

19. The process according to claim 1, wherein the part of the voxels of the virtual volume that is subdivided is obtained by eliminating the voxels located in a layer of predetermined thickness of the surface of the volume.

20. The process according to claim 1, wherein the part of the voxels of the virtual volume that is subdivided is obtained by eliminating the isolated voxels whose density is higher than a second pre-determined threshold.

21. Process according to claim 1, wherein after the first iteration of the algorithm, each voxel whose density value is higher than a third predetermined threshold is assigned a density value equal to the maximum density value obtained among the density values of said voxel and the adjacent voxels.