Imaging system calibration

Patent metadata

Field	Value
Publication number	US-9693749-B2
Application number	US-201514598877-A
Country	US
Kind code	B2
Filing date	Jan 16, 2015
Priority date	Jan 20, 2014
Publication date	Jul 4, 2017
Grant date	Jul 4, 2017

Abstract

A system includes determination of a first sub-matrix of a projection matrix which describes a geometrical relationship between points of a three-dimensional coordinate system of the imaging system and points of a two-dimensional coordinate system of an image detector, determination of a second sub-matrix of the projection matrix, where the first and second sub-matrixes comprise a decomposition of the projection matrix, conversion of a first point of the two-dimensional coordinate system to a first point of the three-dimensional coordinate system based on the first and second sub-matrixes, determination of an updated first sub-matrix of an updated projection matrix, where the updated projection matrix describes a second geometrical relationship between points of the three-dimensional coordinate system and points of the two-dimensional coordinate system, and conversion of a second point of the two-dimensional coordinate system to a second point of the three-dimensional coordinate system based on the updated first and second sub-matrixes.

First claim

What is claimed is:

1. A calibration method for an imaging system comprising an imaging source and an image detector, comprising:
determining a first sub-matrix of a projection matrix, the projection matrix describing a geometrical relationship between points of a three-dimensional coordinate system of the imaging system and points of a two-dimensional coordinate system of the image detector;
determining a second sub-matrix of the projection matrix, where the first sub-matrix and the second sub-matrix comprise a decomposition of the projection matrix;
converting a first point of the two-dimensional coordinate system to a first point of the three-dimensional coordinate system based on the first sub-matrix and the second sub-matrix;
determining an updated first sub-matrix of an updated projection matrix according to a first calibration schedule, where the updated projection matrix describes a second geometrical relationship between points of the three-dimensional coordinate system and points of the two-dimensional coordinate system, and where the updated first sub-matrix and the second sub-matrix comprise a decomposition of the updated projection matrix; and
converting a second point of the two-dimensional coordinate system to a second point of the three-dimensional coordinate system based on the updated first sub-matrix and the second sub-matrix.

2. The method according to claim 1 , further comprising:
determining an updated second sub-matrix of a second updated projection matrix according to a second calibration schedule, where the second calibration schedule is different from the first calibration schedule, where the second updated projection matrix describes a third geometrical relationship between points of the three-dimensional coordinate system and points of the two-dimensional coordinate system, and where the updated first sub-matrix and the updated second sub-matrix comprise a decomposition of the second updated projection matrix; and
converting a third point of the two-dimensional coordinate system to a third point of the three-dimensional coordinate system based on the updated first sub-matrix and the updated second sub-matrix.

3. A method according to claim 1 ,
wherein determining the first sub-matrix comprises determining in-plane rotation φ of the image detector and determining a point of the two-dimensional coordinate system which is intercepted by a beam axis of the imaging source.

4. The method according to claim 3 , wherein determining the first sub-matrix comprises:
acquiring a projection image of a predefined collimator leaf pattern;
determining one or more differences between the projection image of the predefined collimator leaf pattern and an expected projection image of the predefined collimator leaf pattern; and
determining in-plane rotation φ of the image detector and a point of the two-dimensional coordinate system which is intercepted by a beam axis of the imaging source based on the one or more differences.

5. The method according to claim 3 , wherein determining the first sub-matrix comprises:
acquiring a first projection image of a predefined collimator leaf pattern with the collimator at a 0 degree position;
acquiring a second projection image of the predefined collimator leaf pattern with the collimator at a 90 degree position;
combining the first projection image and the second projection image to generate a superimposed image; and
determining in-plane rotation φ of the image detector and a point of the two-dimensional coordinate system which is intercepted by a beam axis of the imaging source based on the superimposed image.

6. The method according to claim 3 , wherein determining the first sub-matrix comprises:
acquiring a projection image of a predefined collimator leaf pattern;
identifying an X r axis based on one or more locations of lateral edges of one or more leaves in the predefined collimator leaf pattern; and
identifying a Y r axis based on one or more locations of longitudinal edges of one or more leaves in the predefined collimator leaf pattern.

7. The method according to claim 3 , wherein determining the first sub-matrix comprises:
acquiring a projection image of a predefined collimator leaf pattern in which edges of one or more leaves are symmetrically located about the X r and Y r axes;
identifying a first one or more lines defined by lateral edges of one or more leaves in the projection image;
identifying a first one or more lines defined by longitudinal edges of one or more leaves in the projection image;
identifying an axis of symmetry of the first one or more lines as the X r axis; and
identifying an axis of symmetry of the second one or more lines as the Y r axis.

8. The method according to claim 3 , wherein determining the first sub-matrix comprises:
acquiring a projection image of a collimator comprising two opposing Y-jaws, in which each Y-jaw defines a notch at its lateral center;
identifying each notch in the projection image; and
identifying the Y r axis as a line joining the notches.

9. The method according to claim 3 , wherein determining the first sub-matrix comprises:
acquiring a projection image of a collimator in which a first pair of opposing leaves located at an upper Y boundary of the collimator define a first narrow gap, and a second pair of opposing leaves located at a lower Y boundary of the collimator define a second narrow gap;
identifying the first narrow gap and the second narrow gap in the projection image; and
identifying the Y r axis as a line joining the first narrow gap and the second narrow gap.

10. The method according to claim 1 , wherein the first sub-matrix is determined as

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Assignees

• Shanghai United Imaging Healthcare Co Ltd

Inventors

• Ni Cheng
• Stahl Johannes
• Bose Supratik
• Maltz Jonathan

Classifications

• G06T12/10

  Image preprocessing, e.g. calibration, positioning of sources or scatter correction · CPC title

• G01N2223/303

  calibrating, standardising · CPC title

• G01N23/046

  using tomography, e.g. computed tomography [CT] · CPC title

• A61B6/582 Primary

  Calibration · CPC title

• G06T11/005

  Physics · mapped topic