REGISTRATION APPARATUS FOR REGISTERING IMAGES

• US 20180174314A1
• Filed: 06/17/2016
• Published: 06/21/2018
• Est. Priority Date: 06/30/2015
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips N.V.
• Inventors: BIPPUS, Rolf Dieter, KABUS, Sven, GRASS, Michael
• Granted Patent: US 10,685,452 B2
• Time in Patent Office: Days
• CPC Class Codes: G06T 11/006 Inverse problem, transformation from projection-space into object-space, e.g. transform methods, back-projection, algebraic methods
• CPC Class Codes: G06T 2207/10081 Computed x-ray tomography [CT]
• CPC Class Codes: G06T 2207/20076 Probabilistic image processing
• CPC Class Codes: G06T 2207/30048 Heart; Cardiac
• CPC Class Codes: G06T 2207/30104 Vascular flow; Blood flow; Perfusion
• CPC Class Codes: G06T 3/147 using affine transformations
• CPC Class Codes: G06T 7/33 using feature-based methods
• CPC Class Codes: G06T 7/35 using statistical methods

Abstract

The invention relates to a registration apparatus (14) for registering images comprising a unit (11) for providing a first and a second image of an object, such that an image element of the first image at a respective position has been reconstructed by multiplying projection data values of rays traversing the image element with weights and by backprojecting the weighted projection data values, a unit (12) for providing a confidence map comprising for different positions in the first image confidence values being indicative of a likelihood that an image feature is caused by a structure of the object, the confidence value being calculated as a sum of a function, which depends on the respective weight, over the rays traversing the respective image element, and a unit (13) for determining a transformation for registering the first and second image to each other under consideration of the confidence map.

Claims

1. A registration apparatus for registering images, the registration apparatus comprising:

an images providing unit for providing a first image and a second image of an object, wherein the images providing unit is adapted to provide the first image such that an image element of the first image at a respective position has been reconstructed by multiplying projection data values, which are assigned to rays traversing the image element, with weights and by backprojecting the weighted projection data values along the rays,

a confidence map providing unit for providing a confidence map comprising for different positions in the first image confidence values being indicative of a likelihood that an image feature is caused by a structure of the object, wherein the confidence map providing unit is adapted to determine for the image element a confidence value by calculating a sum of a function, which depends on the respective weight, over the rays traversing the image element,

a registration unit for determining a registration transformation for registering the first image and the second image to each other under consideration of the confidence map.

2. The registration apparatus as defined in claim 1, wherein the confidence map providing unit is adapted to provide a directional confidence map comprising for different positions in the first image confidence values being indicative of a directional likelihood that an image feature is caused by a structure of the object.

3. The registration apparatus as defined in claim 1, wherein the confidence map providing unit is adapted to provide an isotropic confidence map comprising for different positions in the first image confidence values being indicative of an isotropic likelihood that an image feature is caused by a structure of the object.

4. The registration apparatus as defined in claim 1, wherein the function further depends on the inverse variance of the respective projection data value.

5. The registration apparatus as defined in claim 1, wherein each ray has a ray angle relative to a reference line, wherein the function further depends on the respective ray angle.

6. The registration apparatus as defined in claim 5, wherein the confidence map providing unit is adapted to:

determine for the image element a first intermediate value by calculating a sum of a first function, which depends on the respective weight and which has a first dependence on the respective ray angle, over the rays traversing the image element,

determine for the image element a second intermediate value by calculating a sum of a second function, which depends on the respective weight and which has a second dependence on the respective ray angle, over the rays traversing the image element, and

determine the confidence value for the image element based on the determined first and second intermediate values.

7. The registration apparatus as defined in claim 6, wherein the confidence map providing unit is adapted such that the first function and the second function further depend on the inverse variance of the respective projection data value.

8. The registration apparatus as defined in claim 6, wherein the confidence map providing unit is adapted to:

determine for the image element a third intermediate value by calculating a sum of a third function, which depends on the weight of the respective projection data value, but which does not depend on the respective ray angle, over the rays traversing the image element,

determine the confidence value for the image element based on the determined first, second and third intermediate values.

9. The registration apparatus as defined in claim 8, wherein the confidence map providing unit is adapted such that the third function further depends on the inverse variance of the respective projection data value.

10. The registration apparatus as defined in claim 1, wherein the registration unit is adapted to:

determine a force vector field by applying a force vector field determination algorithm to the first image and to the second image, wherein the force vector field indicates for different positions within at least one of the first and second images virtual forces to be applied to the at least one of the first and second images at the respective positions for registering the first and second images to each other,

correct the force vector field by using the confidence map, and

determine the registration transformation based on the corrected force vector field.

11. The registration apparatus as defined in claim 1, wherein the confidence map providing unit is adapted to provide a further confidence map comprising for different positions in the second image confidence values being indicative of a likelihood that an image feature is caused by a structure of the object, wherein the registration unit is adapted to determine a registration transformation for registering the first and second images to each other under consideration of a) the confidence map comprising for different positions in the first image confidence values being indicative of a likelihood that an image feature is caused by a structure of the object, and b) the further confidence map.

12. An imaging system for generating an image of a moving object, the imaging system comprising:

a registration apparatus as defined in claim 1 for determining a registration transformation for registering a first image and a second image to each other, wherein the images providing unit is adapted to provide the first image and the second image such that they show the same object at different times, wherein the first and second images have been reconstructed based on projection data values acquired in different acquisition directions,

a motion field determination unit for determining a motion field describing a movement of the object based on the determined registration transformation,

wherein the images providing unit is adapted to reconstruct a motion-compensated image of the object based on the provided projection data values and the determined motion field.

13. A registration method for registering images, the registration method comprising:

providing a first image and a second image of an object by an images providing unit, wherein the first image is provided such that an image element of the first image at a respective position has been reconstructed by multiplying projection data values, which are assigned to rays traversing the image element, with weights and by backprojecting the weighted projection data values along the rays,

providing a confidence map comprising for different positions in the first image confidence values being indicative of a likelihood that an image feature is caused by a structure of the object by a confidence map providing unit, wherein a confidence value for the image element is determined by calculating a sum of a function, which depends on the respective weight, over the rays traversing the image element, and

determining a registration transformation for registering the first image and the second image to each other under consideration of the confidence map by a registration unit.

14. A computer program for controlling a registration apparatus, the computer program comprising program code means for causing the registration apparatus to carry out the registration method as defined in claim 13, when the computer program is run on the registration apparatus.