Image processing method, image processing apparatus and radiation tomographic imaging apparatus, and program

• US 20170055930A1
• Filed: 08/24/2016
• Published: 03/02/2017
• Est. Priority Date: 08/27/2015
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Hagiwara, Akira
• Granted Patent: US 10,194,879 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/5258 involving detection or reduction of artifacts or noise
• CPC Class Codes: G06T 11/008 Specific post-processing after tomographic reconstruction, e.g. voxelisation, metal artifact correction
• CPC Class Codes: G06T 2207/10081 Computed x-ray tomography [CT]
• CPC Class Codes: G06T 2207/20012 Locally adaptive
• CPC Class Codes: G06T 2207/30008 Bone
• CPC Class Codes: G06T 2207/30016 Brain
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/70 Denoising; Smoothing

Abstract

To reduce variability in a result of correction by beam-hardening correction in a radiation tomographic image: There is provided an image processing apparatus comprising: a first-index obtaining component configured to obtain, for each individual subregion in a beam-hardening correction-processed image representing a body region including a bone part and a soft part, a first index indicating how much beam hardening due to the bone part affects the subregion based on pixel values at a plurality of positions surrounding the subregion and a distance from the subregion; a determining component configured to determine an amount of correction on a pixel value for the subregion using the first index for the subregion; and a pixel-value correcting component configured to correct the pixel value of the subregion according to the amount of correction on the subregion.

Claims

1. An image processing method causing a computer to execute:

a first-index obtaining step of obtaining, for each individual subregion in a beam-hardening correction-processed image representing a body region including a bone part and a soft part, a first index indicating how much beam hardening due to the bone part affects the subregion based on pixel values at a plurality of positions surrounding the subregion and a distance from the subregion;

a determining step of determining an amount of correction on a pixel value for the subregion using the first index for the subregion; and

a pixel-value correcting step of correcting the pixel value of the subregion according to the amount of correction on the subregion.

2. An image processing apparatus comprising:

a first-index calculating component configured to obtain, for each individual subregion in a beam-hardening correction-processed image representing a body region including a bone part and a soft part, a first index indicating how much beam hardening due to the bone part affects the subregion based on pixel values at a plurality of positions surrounding the subregion and a distance from the subregion;

a correction determining component configured to determine an amount of correction on a pixel value for the subregion using the first index for the subregion; and

a pixel-value correcting component configured to correct the pixel value of the subregion according to the amount of correction on the subregion.

3. The image processing apparatus as recited in claim 2, wherein the first-index calculating component obtains as the first index a value containing as components, for each of a plurality of positions surrounding the subregion, a first value growing according to a pixel value at the position, and a second value growing according to a distance from the subregion to the position.

4. The image processing apparatus as recited in claim 3, wherein the first-index calculating component obtains, for each of a plurality of positions surrounding the subregion, a multiplied value of the first value with the second value, and obtains as the first index a value containing as a component an added value of the multiplied value obtained for each of the plurality of positions.

5. The image processing apparatus as recited in claim 4, wherein the first-index calculating component obtains, for each of a plurality of positions surrounding the subregion, a product of the first value with the second value, and obtains as the first index a value containing as a component a sum of the product obtained for each of the plurality of positions.

6. The image processing apparatus as recited in claim 2, further comprising:

a differential pixel value calculating component configured to obtain, for each the individual subregion, a difference between a pixel value of the subregion and a reference value for pixel values representing the soft part; and

a second-index calculating component configured to obtain, for each the individual subregion, a second index indicating a degree of a correlation between a change of the first index in a direction passing through the subregion and a change of the difference in the direction,

wherein the differential pixel value calculating component determines an amount of correction on a pixel value for the subregion based on the second index for the subregion.

7. The image processing apparatus as recited in claim 6, wherein the correction determining component determines as the amount of correction a product of a value according to the second index for the subregion and the difference for the subregion.

8. The image processing apparatus as recited in claim 7, wherein the reference value for pixel values representing the soft part is an average of pixel values in a region representing the soft part in the image.

9. The image processing apparatus as recited in claim 7, wherein the reference value for pixel values representing the soft part is a representative value of pixel values considered to correspond to the soft part.

10. The image processing apparatus as recited in claim 6, further comprising:

a first smoothing processing component configured to apply smoothing processing to a distribution of the first index in the image and a distribution of the difference in the image,

wherein the second-index calculating component obtains the second index based on a correlation between a change of the first index to which the smoothing processing has been applied in the direction and a change of the difference to which the smoothing processing has been applied in the direction.

11. The image processing apparatus as recited in claim 10, wherein the second-index calculating component obtains the second index so that it has a greater value for higher the correlation.

12. The image processing apparatus as recited in claim 2, further comprising:

a correction upper-limit value determining component configured to determine an upper-limit value of the amount of correction for the subregion according to a magnitude of the first index for the subregion,

wherein the pixel-value correcting component corrects a pixel value of the subregion so that the amount of correction does not exceed an upper-limit value determined for the subregion.

13. The image processing apparatus as recited in claim 2, further comprising:

a second smoothing processing component configured to apply smoothing processing to a distribution of the amount of correction in the image,

wherein the pixel-value correcting component makes a correction using an amount of correction to which the smoothing processing has been applied.

14. The image processing apparatus as recited in claim 2, wherein the image is an image reconstructed based on projection data for the body region to which beam-hardening correction processing has been applied.

15. The image processing apparatus as recited in claim 2, wherein the beam-hardening correction processing uses an algorithm designed to correct beam hardening due to the bone part.

16. The image processing apparatus as recited in claim 2, wherein the body region is a head.

17. The image processing apparatus as recited in claim 2, wherein the subregion is a region corresponding to a single pixel.

18. A radiation tomographic imaging apparatus comprising:

an X-ray source configured to emit X-rays;

an X-ray detector facing the X-ray source and configured to generate signals in response to X-rays incident on the X-ray detector; and

an operation console, comprising;

a first-index calculating component for obtaining, for each individual subregion in a beam-hardening correction-processed image representing a body region including a bone part and a soft part, a first index indicating how much beam hardening due to the bone part affects the subregion based on pixel values at a plurality of positions surrounding the subregion and a distance from the subregion;

a correction determining component for determining an amount of correction on a pixel value for the subregion using the first index for the subregion; and

a pixel-value correcting component for correcting the pixel value of the subregion according to the amount of correction on the subregion.

19. The radiation tomographic imaging apparatus of claim 18, wherein the operation console further comprises:

a differential pixel value calculating component for obtaining, for each the individual subregion, a difference between a pixel value of the subregion and a reference value for pixel values representing the soft part; and

a second-index calculating component for obtaining, for each the individual subregion, a second index indicating a degree of a correlation between a change of the first index in a direction passing through the subregion and a change of the difference in the direction,

wherein the differential pixel value calculating component determines an amount of correction on a pixel value for the subregion based on the second index for the subregion.

20. The radiation tomographic imaging apparatus of claim 19, wherein the operation console further comprises:

a first smoothing processing component for applying smoothing processing to a distribution of the first index in the image and a distribution of the difference in the image,

wherein the second-index calculating component obtains the second index based on a correlation between a change of the first index to which the smoothing processing has been applied in the direction and a change of the difference to which the smoothing processing has been applied in the direction.