Monte Carlo scatter correction method for computed tomography of general object geometries

• US 6,256,367 B1
• Filed: 01/04/2000
• Issued: 07/03/2001
• Est. Priority Date: 06/14/1997
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Vartanian, Michael H.
• Primary Examiner(s): BRUCE, DAVID VERNON
• Application Number:
  US09/477,152
• Time in Patent Office: 546 Days
• Field of Search: 378/4, 378/7, 378/8, 378/15, 378/901, 382/131
• US Class Current: 378/7
• 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 method of correcting aberrations caused by target x-ray scatter in three-dimensional images generated by a volumetric computed tomographic system is disclosed. The method uses a Monte Carlo simulation to determine the distribution of scattered radiation reaching the detector plane. The geometry for the scatter calculation is determined using the uncorrected three-dimensional tomographic image. The calculated scatter is used to correct the primary projection data which is then processed routinely to provide the corrected image.

Claims

1. A method of eliminating artifacts that corrupt a reconstructed image of an object using computed tomography wherein the artifacts are caused by the scattering of the photons interacting with the object, comprising:

configuring a Monte Carlo simulation that corresponds to a specific orientation of a computer tomography system having a source of photons and a projection plane for receiving the photons and the object placed between the source of photons and the projection plane;

receiving a reconstructed image array of values corresponding to the object including artifacts caused by one or more of the photons scattering wherein the reconstructed image array is transformed to a coordinate geometry of the Monte Carlo simulation;

identifying a threshold value within the range of values in the reconstructed image array of the object to assist in identifying the surface of the object wherein values above the threshold correspond to the interior of the object and below the threshold to empty space;

importing a digital projection view into the Monte Carlo simulation having one or more pixels corrupted by the scattered photons and measured by the computed tomography system wherein the projection view is data collected at a specific orientation of the source and the projection plane relative to the object;

orienting the reconstructed image array to correspond to the specific orientation of the computed tomography system that generated the particular projection view;

determining a probability, using the Monte Carlo simulation, that a photon emitted from the source at a given orientation will travel along a given direction within the object, interact with the object, and escape the surface of the object, becoming scattered photons detected at the projection plane;

counting the scattered photons using the Monte Carlo simulation causing radiation absorption by the projection plane at a particular orientation of the source and projection plane relative to the object; and

subtracting values from one or more pixels in the digital projection view that corresponds to a photon energy deposited by the scattered photons thereby removing the effects of the scattered photons from the digital projection view.

2. The system of claim 1, wherein the source is an optical source.

3. The method of claim 1, wherein the Monte Carlo simulation is performed using an ESG4 code system.

4. The method of claim 1, wherein configuring the Monte Carlo simulation includes adjusting the position and characteristics of the x-ray source and those of the projection plane used in generating the digital projection view.

5. The method of claim 1, wherein the effects of the scattered photons are removed from the projection view obtained at each orientation of the projection plane and the source relative to the object.

6. The method of claim 5, wherein the set of projection views that have been processed to remove the scatter radiation are used to in the reconstructed image of the object.

7. The method of claim 1, wherein identifying the threshold value includes finding the maximum value in the image array and subtracting one-half of this maximum value from all other values in the image array and then setting the threshold value to zero.

8. The method of claim 1, wherein determining a probability, using the Monte Carlo simulation, includes using a HOWFAR subroutine in a EGS4 Monte Carlo Code system modified to compute the distance from a given point along a given direction to the point where the reconstructed image array values below the threshold, define the surface of the object.

9. The method of claim 1, wherein the object is an industrial part.

10. The method of claim 1, wherein the object includes some portion of a human body.

11. The method of claim 1, wherein the source is an x-ray source.

12. A computed tomographic system that eliminates artifacts corrupting a reconstructed image of an object wherein the artifacts are caused by the scattering of the photons interacting with the object, comprising:

a Monte Carlo simulation system configured to correspond to a specific orientation of a source photons and a projection plane for receiving the photons and the object placed between the source of photons and the projection plane in the computed tomographic system;

a storage area having a reconstructed image array of values corresponding to the object including artifacts caused by the one or more photons scattering wherein the image array of values are transformed to a coordinate geometry of the Monte Carlo simulation system;

a processor configured to execute instructions that,

identify a threshold value within the range of values in the reconstructed image array of the object and assist in identifying the surface of the object wherein values above the threshold value correspond to the interior of the object and below the threshold to empty space,

import a digital projection view into the Monte Carlo simulation having one or more pixels corrupted by the scattered photons and measured by the computed tomography system wherein the projection view is data collected at a specific orientation of the source and the projection plane relative to the object,

orient the reconstructed image array to correspond to the specific orientation of the computed tomography system that generated the particular projection view,

determine a probability, using the Monte Carlo simulation, that a photon emitted from the source at a given orientation will travel along a given direction within the object, interact with the object, and escape the surface of the object, becoming scattered photons detected at the projection plane,

count the scattered photons using the Monte Carlo simulation that cause radiation absorbed by the projection plane at a particular orientation of the source and projection plane relative to the object, and

subtract the values from one or more pixels in the digital projection view that corresponds to a photon energy deposited by the scatter radiation thereby removing the effects of the scattered photons from the digital projection view.

13. The system of claim 12, wherein the source is an optical source.

14. The system of claim 12, wherein the Monte Carlo simulation system is compatible with an ESG4 code system.

15. The system of claim 12, wherein the Monte Carlo simulation system is configured by adjusting the position and characteristics of the source and those of the projection plane used in generating the digital projection view.

16. The system of claim 12, wherein the scatter radiation is removed from the projection view obtained at each orientation of the projection plane and the source relative to the object.

17. The method of claim 16, wherein the set of projection views that have been processed to remove the scatter radiation are used to generate a reconstruction of the object.

18. The system of claim 12, wherein identifying the threshold value includes finding the maximum value in the image array and subtracting one-half of this maximum value from all other values in the image array and then setting the threshold value to zero.

19. The system of claim 12, wherein determining a probability, using the Monte Carlo simulation, includes using a HOWFAR subroutine in a EGS4 Monte Carlo Code system modified to compute the distance from a given point along a given direction to the point where the reconstructed image array values below the threshold define the surface of the object.

20. The system of claim 12, wherein the object is an industrial part.

21. The system of claim 12, wherein the object includes some portion of a human body.

22. The system of claim 12, wherein the source is an x-ray source.