Image reconstruction using multiple X-ray projections

• US 20020106051A1
• Filed: 12/20/2000
• Published: 08/08/2002
• Est. Priority Date: 12/20/2000
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: Cedara Software, Corp (International Business Machines Corporation)
• Inventors: Menhardt, Wido
• Granted Patent: US 6,470,070 B2
• Time in Patent Office: Days
• US Class Current: 378/4
• CPC Class Codes: G01N 23/04 and forming images of the material

Abstract

A method for reconstructing two and three dimensional images of objects using X-ray image projections and iterative reconstruction techniques is provided. More specifically, the method provides an image of the object to be corrected. Two or more X-ray absorbance profiles of the image are obtained along two or more different projection directions. These profiles are compared with the corresponding absorbance profiles of the object substantially filled with an X-ray contrast agent and, based on this comparison, the image is corrected using the iterative reconstruction techniques. Before each iteration the pixels of the image are updated so that if the absorbance value of the pixel is below a preselected value then the pixel is set to 0, otherwise the pixel is set to the absorbance value corresponding to the concentration of the X-ray contrast agent within the object. The iteration stops when the difference between the absorbance profiles of the image and the object falls below a preselected value.

Claims

1. A method for reconstructing the image of an object using at least 2 single plane X-ray projections, the method comprising the steps of;

a) substantially uniformly filling the object with an X-ray contrast agent;

b) irradiating said contrast agent-filled object with X-rays from at least two directions;

c) detecting said X-rays transmitted through said contrast agent-filled object to define at least two live X-ray projection absorbance profiles;

d) providing a first image to be corrected;

e) updating the image provided in step d) by setting the absorbance value to 0 for all picture elements having an absorbance below a preselected threshold value and by setting all other picture elements to the absorbance value corresponding to the concentration of the X-ray contrast agent within the object;

f) forward projecting the image obtained in step e) into said at least 2 planes of projection along said at least two directions to obtain X-ray absorbance profiles of said image to be corrected;

g) calculating the difference between the absorbance profiles of the object and of the image to be corrected;

h) correcting the image obtained in step e) using iterative reconstruction techniques;

i) repeating steps e) to h) until the difference between the current absorbance profiles and the object absorbance profiles is less than a selected value;

j) displaying the image.

2. The method of claim 1 further comprising the steps of;

Prior to step a) of claim 1;

i) irradiating said object with X-rays from at least two directions;

ii) detecting said X-rays transmitted through said object to define at least two projection mask X-ray absorbance profiles;

after step c) and before step d) of claim 1;

iii) subtracting said mask profiles from said live profiles to define a final absorbance profile for each projection.

3. The method of claim 1 or 2 wherein the picture elements having an absorbance value equals to or greater than the preselected threshold value are set to the treshold value.

4. The method of claim 1 or 2 the value of the preselected threshold is between 0 and the absorbance value corresponding to the concentration of the X-ray contrast agent within the object.

5. The method of claim 1 or 2 wherein the preselected threshold value is substantially identical to the concentration of the X-ray contrast agent within the object.

6. The method of the claim 5 wherein the preselected threshold value is within 1% of the concentration of the X-ray contrast agent.

7. The method of claim 5 wherein said threshold substantially identical to the concentration of the X-ray contrast agent within the object is determined by modifying the threshold of said image to be corrected until its total absorbance is substantially identical to the total absorbance of the object.

8. The method of claim 5 wherein said threshold substantially identical to the concentration of the X-ray contrast agent within the object is determined by modifying the threshold of said image to be corrected until its area is substantially identical to the area of the object.

9. The method of claim 1 or 2 wherein the threshold value is modified before each iteration.

10. The method of claim 1 or 2 wherein said difference in absorbance between the current projections and the object projections is the mean square difference.

11. The method of claim 1 or 2 wherein the X-ray contrast agent is an iodine-containing compound.

12. The method of claim 1 or 2 wherein the object has at least one axis of symmetry and wherein the object is free of gaps along any line perpendicular to the axis of symmetry.

13. The method of claim 12 wherein the image is reconstructed using 2 projections.

14. The method of claim 13 wherein the 2 projections are separated by an angle of 90°

.

15. The method of claim 14 wherein the X-ray beam of at least one of the projections is substantially parallel to said at least one axis of symmetry.

16. The method of claim 15 wherein the X-ray beam of at least one of the projection is within 10°

of the axis of symmetry.

17. The method according to claims 15 wherein the object is the left ventricle.

18. The method according to claim 17 wherein the axis of symmetry is the parasternal axis of the left ventricle.

19. A device for reconstructing an image according to th e method of claim 1 or 2.