Method of and system for X-ray spectral correction in multi-energy computed tomography

• US 7,224,763 B2
• Filed: 07/27/2004
• Issued: 05/29/2007
• Est. Priority Date: 07/27/2004
• Status: Active Grant

• Current Assignee: Analogic Corporation
• Original Assignee: Analogic Corporation
• Inventors: Subramanian, Chitra, Crawford, Carl R., Simanovsky, Sergey, Ying, Zhengrong, Naidu, Ram
• Primary Examiner(s): Thomas; Courtney
• Assistant Examiner(s): TANINGCO, ALEXANDER H
• Application Number:
  US10/899,775
• Publication Number:
  US 20060023844A1
• Time in Patent Office: 1,036 Days
• Field of Search: 378/210, 378156-159, 378/207, 378/901, 378/5, 378/57
• 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]
• CPC Class Codes: G01T 1/185 with ionisation chamber arrangements

Abstract

A method of and a system for spectral correction in multi-energy computed tomography are provided to correct reconstructed images, including high-energy CT images and Z (effective atomic number) images, for spectral variations, which include time variations on a scanner due to HVPS drift and scanner to scanner variations due to the beamline component differences. The method uses a copper filter mounted on the detector array for tracking the spectral changes. The method comprises: generating copper ratios; computing working air tables; calculating scales and offsets; and correcting high-energy CT images and Z images using calculated scales and offsets. The method further includes an off-line calibration procedure to generate necessary parameters for the online correction.

Claims

1. A method of correcting reconstructed images, reconstructed from projection data acquired while scanning objects with a scanner including a scanner detector array, for the spectral variation in multi-energy X-ray computed tomography using at least a portion of the same acquired projection data, wherein the projection data include at least a set of low-energy projections and a set high-energy projections obtained using at least two x-ray spectra, and wherein a filter is mounted relative to at least a portion but not the whole of the detector array, comprising:

A. Generating low-energy and high-energy working filter ratios respectively for each of the low-energy and high-energy projections, derived from data acquired by at least a portion of the detector array, and calculating spectral variation using low-energy and high-energy base filter ratios and the low-energy and high-energy working filter ratios;

B. Calculating working high-energy CT numbers and working effective atomic numbers as a function of the low-energy and high-energy working filter ratios, the low-energy and high-energy base filter ratios, and base high-energy CT numbers and base-effective atomic numbers for a set of three reference materials; and

C. Calculating scales and offsets using the working high-energy CT numbers and the working effective atomic numbers and correcting the reconstructed images using the scales and offsets.

2. The method of claim 1, further including, a calibration procedure comprising:

performing scans of each of the three reference materials at each of the three different pairs of low-energy and high-energy X-ray spectra, and measuring low-energy and high-energy base filter ratios, base high-energy CT numbers and base effective atomic numbers to generate parameters for step B.

3. The method of claim 2, wherein the three reference materials have different density and different atomic number.

4. The method of claim 1, wherein the reconstructed images include high-energy CT images, and step C includes correcting at least some of the high-energy CT images.

5. The method of claim 1, wherein reconstructed images derived from data acquired while scanning objects with a scanner include effective atomic number images, and step C includes correcting at least some of the effective atomic number images.

6. The method of claim 1, further including generating at least a low-energy working air table and a high-energy working air table, both corrected using the high and low energy working filter ratios.

7. A system for correcting reconstructed images, reconstructed from projection data acquired by a scanner including a detector array, while scanning objects for the spectral variation in multi-energy X-ray computed tomography using at least a portion of the same acquired projection data, wherein the projection data include at least a set of low-energy projections and a set of high-energy projections obtained using at least two x-ray spectra, and wherein a filter is mounted relative to at least a portion but not the whole of the detector array, comprising:

A. A subsystem configured and arranged so as to generate low-energy and high-energy working filter ratios for the respective low and high energy projections, all derived from data acquired by at least a portion of the detector array, and calculating spectral variation using low-energy and high-energy base filter ratios and the low-energy and high-energy working filter ratios;

B. A subsystem configured and arranged so as to calculate working high-energy CT numbers and working effective atomic numbers as a function of the low-energy and high-energy working filter ratios, the low-energy and high-energy base filter ratios and base high-energy CT numbers and base-effective atomic numbers for a set of three reference materials; and

C. A subsystem configured and arranged so as to calculate scales and offsets from the working high-energy CT numbers and the working effective atomic numbers and correct the reconstructed images using the scales and offsets.

8. The system of claim 7, further including, a calibration subsystem constructed and arranged so as to perform scans of the three reference materials at three different pairs of low-energy and high-energy X-ray spectra, and measure low-energy and high-energy base filter ratios, base high-energy CT numbers and base effective atomic numbers to generate parameters for subsystem B.

9. The system of claim 7, wherein the reconstructed images include high-energy CT images and subsystem C is further configured and arranged so as to correct at least some of the high-energy CT images.

10. The system of claim 7, wherein the reconstructed images include effective atomic number images, and subsystem C is further configured and arranged so as to correct at least some of the effective atomic number images.

11. The systcm of claim 7, further including a subsystem configured and arranged so as to generate at least a low-energy working air table and a high-energy working air tables, both corrected using the generated high and low energy filter ratios.