Methods and apparatus for artifact reduction in computed tomography imaging systems

• US 20050100124A1
• Filed: 11/11/2003
• Published: 05/12/2005
• Est. Priority Date: 11/11/2003
• Status: Active Grant

• Current Assignee: GE Medical Systems Global Technology Company LLC (GE Healthcare Technologies, Inc.)
• Original Assignee: GE Medical Systems Global Technology Company LLC (GE Healthcare Technologies, Inc.)
• Inventors: Grekowicz, Brian James, Thibault, Jean-Baptiste, Hsieh, Jiang, Chao, Edward Henry
• Granted Patent: US 6,944,260 B2
• Time in Patent Office: Days
• US Class Current: 378/4
• 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 6/583 using calibration phantoms
• 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: G06T 11/006 Inverse problem, transformation from projection-space into object-space, e.g. transform methods, back-projection, algebraic methods
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

Some configurations of the present invention provide a method for reconstructing an image of an object of a computed tomographic imaging system having a detector array and a radiation source, wherein an arc of the detector array is not concentric to a focal spot of the radiation source. The method includes scanning the object with the computed tomographic imaging system to obtain a fan beam dataset, rebinning the fan beam dataset into a set of parallel datasets; and reconstructing an image utilizing the set of parallel datasets.

Claims

1. A method for reconstructing an image of an object of a computed tomographic imaging system having a detector array and a radiation source, wherein an arc of the detector array is not concentric to a focal spot of the radiation source, said method comprising:

scanning the object with the computed tomographic imaging system to obtain a projection dataset;

performing a geometric correction of the projection dataset according to a corrected fan angle; and

reconstructing an image utilizing the corrected projection dataset.

2. A method in accordance with claim 1 wherein said performing a geometric correction comprises interpolating the projection dataset into a uniformly spaced projection dataset.

3. A method in accordance with claim 1 wherein said performing a geometric correction comprises rebinning the projection dataset into a set of parallel datasets.

4. A method in accordance with claim 3 wherein rebinning the projection dataset into a set of parallel datasets comprises interpolating a sinogram along a line defined by a relationship written as:

$\mathrm{\beta <br><br>}={\mathrm{\beta <br><br>}}_0-{\mathrm{\gamma <br><br>}}^{\mathrm{\prime <br><br>}},<br><br>\mathrm{where}<br><br>\text{;<br><br>}$ ${\mathrm{\gamma <br><br>}}^{\mathrm{\prime <br><br>}}={\tan }^{-1}<br><br>\left[\frac{R<br><br>\text{\hspace{1em}<br><br>}<br><br>\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}}{R<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}+{\mathrm{\Delta <br><br>}}_s+{\mathrm{\Delta <br><br>}}_d}\right]$

and β

₀ is an angle of an isoray of a radiation beam from the radiation source, γ

is a detector fan angle, β

is a projection angle, R is a radiation source to detector element distance in an original geometry in which an arc of the detector array is concentric to a focal spot of the radiation source, and Δ

_s and Δ

_d are distances that the radiation source and the detector element are from their respective positions in the original geometry, respectively.

5. A method in accordance with claim 3 further comprising resampling the parallel datasets so that the datasets are uniformly spaced.

6. A method in accordance with claim 5 wherein resampling the parallel datasets so that the datasets are uniformly spaced further comprises determining a distance of radiation rays to an isocenter.

7. A method in accordance with claim 6 wherein said distance of radiation rays to an isocenter is determined in accordance with a relationship written as:

t=(r+Δ

_s)sin γ

′

where t is the distance of a ray to the isocenter, r is the distance of the radiation source to the isocenter distance in an original geometry in which an arc of the detector array is concentric to a focal spot of the radiation source.

8. A method in accordance with claim 7 further comprising determining a detector array index s utilizing said distance t in accordance with a relationship written as:

$s=\frac{1}{\mathrm{\Delta <br><br>\gamma <br><br>}}<br><br>\left\{{\sin }^{-1}<br><br>\left[\frac{t}{r+{\mathrm{\Delta <br><br>}}_s}\right]+{\sin }^{-1}<br><br>\left[\frac{\left({\mathrm{\Delta <br><br>}}_s+{\mathrm{\Delta <br><br>}}_d\right)<br><br>t}{R<br><br>\left(r+{\mathrm{\Delta <br><br>}}_s\right)}\right]\right\}$

where Δ

γ

is a fan angle between adjacent detector elements in the original geometry.

9. A method for reconstructing an image of an object of a computed tomographic imaging system having a detector array and a radiation source, wherein an arc of the detector array is not concentric to a focal spot of the radiation source, said method comprising:

scanning the object with the computed tomographic imaging system to obtain a projection dataset;

rebinning the projection dataset into a set of parallel datasets including interpolating a sinogram along a line defined by a relationship written as;

$\mathrm{\beta <br><br>}={\mathrm{\beta <br><br>}}_0-{\mathrm{\gamma <br><br>}}^{\mathrm{\prime <br><br>}},<br><br>\mathrm{where}<br><br>\text{;<br><br>}$${\mathrm{\gamma <br><br>}}^{\mathrm{\prime <br><br>}}={\tan }^{-1}<br><br>\left[\frac{R<br><br>\text{\hspace{1em}<br><br>}<br><br>\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}}{R<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}+{\mathrm{\Delta <br><br>}}_s+{\mathrm{\Delta <br><br>}}_d}\right]$

and β

₀ is an angle of an isoray of a radiation beam from the radiation source, γ

is a detector fan angle, β

is a projection angle, R is a radiation source to detector element distance in an original geometry in which an arc of the detector array is concentric to a focal spot of the radiation source, and Δ

_s and Δ

_d are distances that the radiation source and the detector element are from their respective positions in the original geometry, respectively;

resampling the parallel datasets so that the datasets are uniformly spaced; and

reconstructing an image utilizing the set of resampled parallel datasets.

10. A method in accordance with claim 9 wherein resampling the parallel datasets so that the datasets are uniformly spaced further comprises determining a distance of radiation rays to an isocenter.

11. A method in accordance with claim 10 wherein said distance of radiation rays to an isocenter is determined in accordance with a relationship written as:

t=(r+Δ

_s)sin γ

′

where t is the distance of a ray to the isocenter, r is the distance of the radiation source to the isocenter distance in an original geometry in which an arc of the detector array is concentric to a focal spot of the radiation source.

12. A method in accordance with claim 11 further comprising determining a detector array index s utilizing said distance t in accordance with a relationship written as:

$s=\frac{1}{\mathrm{\Delta <br><br>\gamma <br><br>}}<br><br>\left\{{\sin }^{-1}<br><br>\left[\frac{t}{r+{\mathrm{\Delta <br><br>}}_s}\right]+{\sin }^{-1}<br><br>\left[\frac{\left({\mathrm{\Delta <br><br>}}_s+{\mathrm{\Delta <br><br>}}_d\right)<br><br>t}{R<br><br>\left(r+{\mathrm{\Delta <br><br>}}_s\right)}\right]\right\}$

where Δ

γ

is a fan angle between adjacent detector elements in the original geometry.

13. A method for reconstructing an image of an object of a computed tomographic imaging system having a detector array and a radiation source, wherein an arc of the detector array is not concentric to a focal spot of the radiation source, said method comprising:

scanning the object using step-and-shoot scanning with the computed tomographic imaging system, without applying a weighting function, to obtain a projection dataset;

rebinning the projection dataset into a set of parallel datasets; and

reconstructing an image utilizing the set of parallel datasets.

14. A method for reconstructing an image of an object of a computed tomographic imaging system having a detector array and a radiation source, wherein an arc of the detector array is not concentric to a focal spot of the radiation source, said method comprising:

scanning the object with the computed tomographic imaging system using helical or halfscan acquisition to obtain a projection dataset;

weighting the projection dataset in accordance with a weighting function w′

, derived from a weighting function w for an original geometry in which the arc of the detector array is concentric to the focal spot of the radiation source, wherein

$w^{\mathrm{\prime <br><br>}}=w<br><br>\left({\mathrm{\gamma <br><br>}}^{\mathrm{\prime <br><br>}},\mathrm{\beta <br><br>},n\right)$$\mathrm{and}$${\mathrm{\gamma <br><br>}}^{\mathrm{\prime <br><br>}}={\tan }^{-1}<br><br>\left[\frac{R<br><br>\text{\hspace{1em}<br><br>}<br><br>\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}}{R<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}+{\mathrm{\Delta <br><br>}}_s+{\mathrm{\Delta <br><br>}}_d}\right]$

wherein γ

is a detector fan angle, β

is a projection angle, R is a radiation source to detector element distance in the original geometry, and Δ

_s and Δ

_d are distances that the radiation source and the detector element are from their respective positions in the original geometry, respectively;

rebinning the projection dataset into a set of parallel datasets; and

reconstructing an image utilizing the set of parallel datasets.

15. A computed tomography imaging system having a detector array and an radiation source, wherein an arc of the detector array is not concentric to a focal spot of the radiation source, said imaging system configured to:

scan an object to obtain a projection dataset;

perform a geometric correction of the projection dataset according to a corrected fan angle; and

reconstruct an image utilizing the corrected projection dataset.

16. A system in accordance with claim 15 wherein to perform a geometric correction, said system is configured to interpolate the projection dataset into a uniformly spaced projection dataset.

17. A system in accordance with claim 15 wherein to perform a geometric correction, said system is configured to rebin the projection dataset into a set of parallel datasets.

18. A system in accordance with claim 17 wherein to rebin the projection dataset into a set of parallel datasets, said system is configured to interpolate a sinogram along a line defined by a relationship written as:

$\mathrm{\beta <br><br>}={\mathrm{\beta <br><br>}}_0-{\mathrm{\gamma <br><br>}}^{\mathrm{\prime <br><br>}},<br><br>\mathrm{where}<br><br>\text{;<br><br>}$ ${\mathrm{\gamma <br><br>}}^{\mathrm{\prime <br><br>}}={\tan }^{-1}<br><br>\left[\frac{R<br><br>\text{\hspace{1em}<br><br>}<br><br>\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}}{R<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}+{\mathrm{\Delta <br><br>}}_s+{\mathrm{\Delta <br><br>}}_d}\right]$

and β

₀ is an angle of an isoray of a radiation beam from the radiation source, γ

is a detector fan angle, β

is a projection angle, R is a radiation source to detector element distance in an original geometry in which an arc of the detector array is concentric to a focal spot of the radiation source, and Δ

_s and Δ

_d are distances that the radiation source and the detector element are from their respective positions in the original geometry, respectively.

19. A system in accordance with claim 17 further configured to resample the parallel datasets so that the datasets are uniformly spaced.

20. A system in accordance with claim 19 wherein to resample the parallel datasets so that the datasets are uniformly spaced, said system is further configured to determine a distance of radiation rays to an isocenter.

21. A system in accordance with claim 20 configured to determine said distance of radiation rays to an isocenter in accordance with a relationship written as:

t=(r+Δ

_s)sin γ

′

where t is the distance of a ray to the isocenter, r is the distance of the radiation source to the isocenter distance in an original geometry in which an arc of the detector array is concentric to a focal spot of the radiation source.

22. A system in accordance with claim 21 further configured to determine a detector array index s utilizing said distance t in accordance with a relationship written as:

$s=\frac{1}{\mathrm{\Delta <br><br>\gamma <br><br>}}<br><br>\left\{{\sin }^{-1}<br><br>\left[\frac{t}{r+{\mathrm{\Delta <br><br>}}_s}\right]+{\sin }^{-1}<br><br>\left[\frac{\left({\mathrm{\Delta <br><br>}}_s+{\mathrm{\Delta <br><br>}}_d\right)<br><br>t}{R<br><br>\left(r+{\mathrm{\Delta <br><br>}}_s\right)}\right]\right\}$

where Δ

γ

is a fan angle between adjacent detector elements in the original geometry.

23. A computed tomography imaging system having a detector array and a radiation source, wherein an arc of the detector array is not concentric to a focal spot of the radiation source, said imaging system configured to:

scan the object to obtain a projection dataset;

rebin the projection dataset into a set of parallel datasets including interpolating a sinogram along a line defined by a relationship written as;

$\mathrm{\beta <br><br>}={\mathrm{\beta <br><br>}}_0-{\mathrm{\gamma <br><br>}}^{\mathrm{\prime <br><br>}},<br><br>\mathrm{where}<br><br>\text{;<br><br>}$${\mathrm{\gamma <br><br>}}^{\mathrm{\prime <br><br>}}={\tan }^{-1}<br><br>\left[\frac{R<br><br>\text{\hspace{1em}<br><br>}<br><br>\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}}{R<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}+{\mathrm{\Delta <br><br>}}_s+{\mathrm{\Delta <br><br>}}_d}\right]$

and β

₀ is an angle of an isoray of a radiation beam from the radiation source, γ

is a detector fan angle, β

is a projection angle, R is a radiation source to detector element distance in an original geometry in which an arc of the detector array is concentric to a focal spot of the radiation source, and Δ

_s and Δ

_d are distances that the radiation source and the detector element are from their respective positions in the original geometry, respectively;

resample the parallel datasets so that the datasets are uniformly spaced; and

reconstruct an image utilizing the set of resampled parallel datasets.

24. A system in accordance with claim 23 wherein to resample the parallel datasets so that the datasets are uniformly spaced, said system is further configured to determine a distance of radiation rays to an isocenter.

25. A system in accordance with claim 24 configured to determine said distance of radiation rays to an isocenter in accordance with a relationship written as:

t=(r+Δ

_s)sin γ

′

where t is the distance of a ray to the isocenter, r is the distance of the radiation source to the isocenter distance in an original geometry in which an arc of the detector array is concentric to a focal spot of the radiation source.

26. A system in accordance with claim 25 further configured to determine a detector array index s utilizing said distance t in accordance with a relationship written as:

$s=\frac{1}{\mathrm{\Delta <br><br>\gamma <br><br>}}<br><br>\left\{{\sin }^{-1}<br><br>\left[\frac{t}{r+{\mathrm{\Delta <br><br>}}_s}\right]+{\sin }^{-1}<br><br>\left[\frac{\left({\mathrm{\Delta <br><br>}}_s+{\mathrm{\Delta <br><br>}}_d\right)<br><br>t}{R<br><br>\left(r+{\mathrm{\Delta <br><br>}}_s\right)}\right]\right\}$

where Δ

γ

is a fan angle between adjacent detector elements in the original geometry.

27. A computed tomography imaging system having a detector array and a radiation source, wherein an arc of the detector array is not concentric to a focal spot of the radiation source, said imaging system configured to:

scan the object using step-and-shoot scanning without applying a weighting function to obtain a projection dataset;

rebin the projection dataset into a set of parallel datasets; and

reconstruct an image utilizing the set of parallel datasets.

28. A computed tomography imaging system having a detector array and a radiation source, wherein an arc of the detector array is not concentric to a focal spot of the radiation source, said imaging system configured to:

scan the object using helical or halfscan acquisition to obtain a projection dataset;

weight the projection dataset in accordance with a weighting function w¹, derived from a weighting function w for an original geometry in which the arc of the detector array is concentric to the focal spot of the radiation source, wherein

$w^{\mathrm{\prime <br><br>}}=w<br><br>\left({\mathrm{\gamma <br><br>}}^{\mathrm{\prime <br><br>}},\mathrm{\beta <br><br>},n\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}$${\mathrm{\gamma <br><br>}}^{\mathrm{\prime <br><br>}}={\tan }^{-1}<br><br>\left[\frac{R<br><br>\text{\hspace{1em}<br><br>}<br><br>\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}}{R<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}+{\mathrm{\Delta <br><br>}}_s+{\mathrm{\Delta <br><br>}}_d}\right]$

wherein γ

is a detector fan angle, β

is a projection angle, R is a radiation source to detector element distance in the original geometry, and Δ

_s and Δ

_d are distances that the radiation source and the detector element are from their respective positions in the original geometry, respectively;

rebin the projection dataset into a set of parallel datasets; and

reconstruct an image utilizing the set of parallel datasets.