Method of and system for computing effective atomic number images in multi-energy computed tomography

• US 20050259781A1
• Filed: 05/21/2004
• Published: 11/24/2005
• Est. Priority Date: 05/21/2004
• Status: Active Grant

• Current Assignee: Analogic Corporation
• Original Assignee: Analogic Corporation
• Inventors: Crawford, Carl R., Simanovsky, Sergey, Ying, Zhengrong, Naidu, Ram
• Granted Patent: US 7,190,757 B2
• Time in Patent Office: Days
• US Class Current: 378/5
• CPC Class Codes: G01N 2223/419 computed tomograph
• CPC Class Codes: G01N 23/046 using tomography, e.g. computed tomography [CT]

Abstract

A method of and a system for computing Z (effective atomic number) images from projection data are provided, wherein the projections are acquired using at least two x-ray spectra for a set of scanned objects, including a set of low energy projections and a set of high energy projections; the method comprises decomposing the low energy projections and high energy projections into photoelectric projections, reconstructing the photoelectric projections into photoelectric images, reconstructing one of the two sets of projections into CT images, and computing Z images from the CT images and the photoelectric images with parameters obtained from a calibration procedure.

Claims

1. A method of computing Z images from the CT projection data acquired by scanning a set of objects using at least two x-ray spectra, wherein said projection data includes a set of low energy projections and a set of high energy projections, comprising:

a. Reconstructing a CT image from one of the two sets of projections;

b. Obtaining the photoelectric projections from the high energy projections and low energy projections;

c. Reconstructing a photoelectric image from the photoelectric projections;

d. Computing the Z image from the photoelectric image and the CT image.

2. The method of claim 1, wherein said CT image can be reconstructed from the set of low energy projections.

3. The method of claim 1, wherein said CT image can be reconstructed from the set of high energy projections.

4. The method of claim 1, wherein reconstructing a CT image from one of the two sets of projections may include nonlinear beam hardening correction.

5. The method of claim 1, wherein computing the Z image from the photoelectric image and the CT image may involve at least two parameters K and n.

6. The method of claim 1, wherein said step of obtaining the photoelectric projections from the high energy projections and low energy projections may use a two-dimensional look-up table to generate the photoelectric projections.

7. The method of claim 5, wherein said parameters K and n are obtained through a calibration procedure comprising:

a. Scanning at least two different materials with known effective atomic numbers;

b. Reconstructing CT images;

c. Obtaining the photoelectric projections;

d. Reconstructing photoelectric images from the photoelectric projections;

e. Generating the Z images with K=1 and n=1;

f. Obtaining mean Z values for each of the two materials;

g. Calculating K and n based on the mean Z values and the known effective atomic numbers of the two materials.

8. A system for computing Z images from the projection data acquired by scanning a set of objects using at least two x-ray spectra, wherein said projection data includes a set of low energy projections and a set of high energy projections, comprising:

a. A reconstruction subsystem constructed and arranged so as to reconstruct CT images from one of the two sets of projections;

b. A dual energy decomposition subsystem constructed and arranged so as to obtain the photoelectric projections from low energy projections and high energy projections;

c. A reconstruction subsystem constructed and arranged so as to reconstruct photoelectric images from the photoelectric projections;

d. A Z image calculator constructed and arranged so as to compute the Z images from the CT images and the photoelectric images.

9. The system of claim 8, wherein the reconstruction subsystem is constructed and arranged so that said CT image can be reconstructed from the set of low energy projections.

10. The system of claim 8, wherein the reconstruction subsystem is constructed and arranged so that said CT image can be reconstructed from the set of high energy projections.

11. The system of claim 8, wherein said reconstruction subsystem for reconstructing CT images from one of the two sets of projections comprises a module for providing nonlinear beam hardening correction.

12. The system of claim 8, wherein said Z image calculator is constructed and arranged so as to compute the Z images from the photoelectric image and the CT image may include at least two parameters K and n.

13. The system of claim 8, wherein the dual energy decomposition subsystem may include a two-dimensional look-up table to generate the photoelectric projections.

14. The system of claim 12, wherein said system may include a calibration module constructed and arranged so as to obtain parameters K and n for the Z image calculator.