Reconstruction method for tilted-gantry computed tomography

• US 6,751,283 B2
• Filed: 08/06/2002
• Issued: 06/15/2004
• Est. Priority Date: 08/06/2002
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: van de Haar, Peter G.
• Primary Examiner(s): BRUCE, DAVID VERNON
• Application Number:
  US10/213,467
• Publication Number:
  US 20040028173A1
• Time in Patent Office: 679 Days
• Field of Search: 378/4, 378/15, 378/17, 378/901
• US Class Current: 378/17
• CPC Class Codes: A61B 6/027 characterised by the use of a particular data acquisition trajectory, e.g. helical or spiral
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4447 Tiltable gantries
• CPC Class Codes: G06T 11/005 Specific pre-processing for tomographic reconstruction, e.g. calibration, source positioning, rebinning, scatter correction, retrospective gating
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

A computed tomography apparatus (10) for performing volumetric helical imaging acquires helical computed tomography imaging data (72) using a tilted gantry geometry. In the tilted gantry geometry, a rotational plane of a rotating radiation source (16) is tilted at an angle (χ) with respect to a direction (Z) of linear motion of a subject. A transform processor (40) transforms (74) the imaging data (72) to a zero tilt geometry. A rebinning processor (50) rebins (110) the transformed imaging data (76) to a non-sheared detector window. A reconstruction processor (54) reconstructs (130) the transformed and rebinned imaging data (112) to generate a three-dimensional image representation (132). Optionally, an image transform processor (56) transforms (134) the reconstructed image representation (132) with an inverse of the zero tilt geometry transformation (74).

Claims

1. An apparatus for generating an image representation of an imaged subject from volumetric helical computed tomography imaging data acquired using a tilted gantry geometry, the apparatus comprising:

a means for transforming the imaging data to a zero tilt geometry;

a means for rebinning the transformed imaging data to a non-sheared detector window; and

a means for reconstructing the transformed and rebinned imaging data to generate a three-dimensional image representation.

2. A method for generating an image representation of an imaged subject from volumetric helical computed tomography imaging data acquired using a tilted gantry geometry, the method comprising:

transforming the imaging data to a zero tilt geometry;

rebinning the transformed imaging data to a non-sheared detector window; and

reconstructing the transformed and rebinned imaging data to generate a three-dimensional image representation.

3. The method as-set forth in claim 2, wherein the transforming step includes:

linearly transforming a sheared coordinate.

4. The method as set forth in claim 3, wherein the sheared coordinate is perpendicular to a linear motion of the imaged subject.

5. The method as set forth in claim 3, wherein the linear transform of the sheared coordinate includes:

6. The method as set forth in claim 3, further including:

linearly transforming the sheared coordinate of the three-dimensional image representation to recover the tilted gantry geometry.

7. The method as set forth in claim 2, wherein the transforming step includes applying a three-dimensional transform:

$\left(\begin{array}{c}{x}^{\mathrm{\prime <br><br>}}\\ y^{\mathrm{\prime <br><br>}}\\ z^{\mathrm{\prime <br><br>}}\end{array}\right)=\left(\begin{array}{c}x+z<br><br>\text{\hspace{1em}<br><br>}<br><br>\tan <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\chi <br><br>}\\ y\\ z\end{array}\right)$

where x, y, and z are coordinates in a zero tilt geometry, x′

, y′

, and z′

are the corresponding coordinates in the tilted gantry geometry, and χ

is a shear angle of the tilted gantry geometry.

8. The method as set forth in claim 2, wherein the reconstructing step includes:

performing an n-PI reconstruction of the transformed and rebinned imaging data, where n is a positive odd integer greater than or equal to one.

9. The method as set forth in claim 8, wherein n is selected from a group of integers consisting of one and three.

10. The method as set forth in claim 8, wherein the n-PI reconstruction is selected from a group consisting of:

an exact n-PI reconstruction, and

an approximate n-PI filtered backprojection reconstruction.

11. The method as set forth in claim 2, wherein a helical pitch of the volumetric helical computed tomography imaging is selected such that a point within the imaged subject is imaged on a physical detector over a contiguous 180°

rotation of a radiation source.

12. The method as set forth in claim 11, wherein the physical detector is a focus-centered detector.

13. The method as set forth in claim 2, wherein the rebinning step includes:

receiving coordinates of a physical detector used in the imaging;

transforming the coordinates of the physical detector to the zero-tilt geometry wherein the transformed coordinates of the physical detector correspond to sheared detector coordinates; and

rebinning the transformed imaging data to non-sheared detector coordinates based on the sheared detector coordinates.

14. The method as set forth in claim 13, wherein the transforming and rebinning steps are performed using a lookup table containing transform coefficients.

15. The method as set forth in claim 14, wherein the transform coefficients include functional parameters that depend upon a radiation source angular coordinate.

16. The method as set forth in claim 2, wherein the rebinning step reduces a fan angle of the imaging data.

17. The method as set forth in claim 2, further including:

transforming the three-dimensional image representation to the tilted gantry geometry.

18. The method as set forth in claim 17, wherein the transform used in transforming the three-dimensional image representation to the tilted gantry geometry is an inverse transform of the transform used in transforming the imaging data to a zero tilt geometry.

19. An apparatus for performing volumetric helical computed tomography imaging of a subject, the apparatus comprising:

a computed tomography scanner that acquires helical computed tomography imaging data using a tilted gantry geometry wherein a rotational plane of a rotating radiation source is tilted with respect to a direction of linear motion of the subject;

a transform processor that transforms the imaging data to a zero tilt geometry;

a rebinning processor that rebins the transformed imaging data to a non-sheared detector window; and

a reconstruction processor that reconstructs the transformed and rebinned imaging data to generate a three-dimensional image representation.

20. The apparatus as set forth in claim 19, wherein the transform processor linearly transforms a sheared coordinate of the tilted gantry geometry to remove the shearing.

21. The apparatus as set forth in claim 20, wherein the linear transform of the sheared coordinate includes:

22. The apparatus as set forth in claim 19, wherein the transform processor applies a three-dimensional transform:

$\left(\begin{array}{c}{x}^{\mathrm{\prime <br><br>}}\\ y^{\mathrm{\prime <br><br>}}\\ z^{\mathrm{\prime <br><br>}}\end{array}\right)=\left(\begin{array}{c}x+p<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\tan <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\chi <br><br>}\\ y\\ z\end{array}\right)$

where x, y, and z are coordinates in a zero tilt geometry, x′

, y′

, and z′

are the corresponding coordinates in the tilted gantry geometry, p is a constant associated with the linear motion of the subject, α

is an angular position of the radiation source, and χ

is a shear angle of the tilted gantry geometry.

23. The apparatus as set forth in claim 19, wherein the reconstruction processor performs an n-PI reconstruction of the transformed and rebinned imaging data, where n is a positive odd integer greater than or equal to one.

24. The apparatus as set forth in claim 19, further including:

a rebinning lookup table in communication with the rebinning processor, the rebinning processor obtaining transform parameters from the rebinning lookup table.

25. The apparatus as set forth in claim 24, wherein the transform parameters include rebinning coefficients that depend upon a rotational angle of the radiation source.

26. The apparatus as set forth in claim 19, further including:

an image transform processor that transforms the three-dimensional image representation back to the tilted gantry geometry.