X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2001-06-28
2002-09-10
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S015000, C378S901000
Reexamination Certificate
active
06449330
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates generally to computed tomographic (CT) imaging methods and apparatus, and more particularly to methods and apparatus for reducing artifacts in computed tomographic imaging systems such as those used for medical imaging.
In recent computed tomographic (CT) imaging systems, scan speeds have been increased to sub-second gantry rotations to reduce patient motion, enable new applications, and to increase patient throughput. However, because of x-ray tube power limitations, x-ray currents cannot be kept as constant as at slower scan speeds, often causing image artifacts to be created. These artifacts appear in the images as noise and streaking, which are related to the generally lower signals levels available at higher gantry speeds. Corrections have been applied based upon a single signal threshold level to reduce image noise and streaking artifacts to some extent. However, there remain areas in which signals are slightly higher than the single threshold but for which corrections are still required. In addition, there remain areas in which a greater correction is needed than can be provided with such corrections. As a result, residual streaking artifacts often exist in images processed using this artifact reduction method.
SUMMARY OF INVENTION
Therefore, in one aspect of the present invention, a method for reducing artifacts in computed tomographic (CT) images is provided that is particularly useful for CT applications requiring higher gantry rotation rates. The method includes selecting a set of thresholds for projection view data; utilizing a smoothing kernel in accordance with the selected set of thresholds to produce a set of smoothed projections from a set of original projections obtained from a scan of an object, wherein an amount of smoothing applied varies depending upon a relationship of the original projections to the thresholds; producing a set of final projections utilizing the set of original projections and the set of smoothed projections; and reconstructing images of the object utilizing the final projections.
In another aspect of the present invention, there is provided a method for reducing artifacts in CT images that includes utilizing clinical image studies to select a set of thresholds, including thresholds T
1
, T
2
, and T
3
, for projection data, in accordance with a desired image resolution and noise, utilizing a smoothing kernel in accordance with the selected set of thresholds to produce a set of smooth projections from a set of original projections obtained from a scan of an object, wherein an amount of smoothing applied varies depending upon a relationship of the original projections to the thresholds; producing a set of final projections utilizing the set of original projections and the set of smoothed projections; and reconstructing at least one image of the object utilizing the final projections.
In yet another aspect of the present invention, there is provided a CT imaging system configured to acquire a set of original projections of an object; utilize a smoothing kernel to produce a set of smoothed projections from the set of original projections, wherein an amount of smoothing applied varies depending upon a relation of the original projections to the thresholds; produce a set of final projections utilizing the set of original projections and the set of smoothed projections; and reconstruct at least one image of the object utilizing the set of final projections.
In still another aspect of the present invention, there is provided a CT imaging system configured to: acquire a set of original projections; utilize a smoothing kernel in accordance with a selected set of thresholds T
1
, T
2
, and T
3
to produce a set of smoothed projections from the set of original projections, wherein an amount of smoothing applied varies depending upon a relationship of the original projections to the thresholds; produce a set of final projections utilizing the set of original projections and the set of smoothed projections; and reconstruct images of the object utilizing the set of final projections, wherein the smoothing kernel is a three-point kernel for views that are below T
1
but greater than T
2
, a five-point smoothing kernel for views that are below T
2
but greater than T
3
, and a nine-point kernel for views that are below T
3
.
In yet another aspect of the present invention, there is provided a processor for reducing artifacts in scanned images. The processor is configured to: utilize a smoothing kernel in accordance with a selected set of thresholds to produce a set of smoothed projections from a set of original projections obtained from a scan of an object, wherein an amount of smoothing applied varies depending upon a relationship of the original projections to the thresholds; produce a set of final projections utilizing the set of original projections and the set of smoothed projections; and reconstruct an image of the object utilizing the final projections.
In still another aspect of the present invention, there is provided a processor for reducing artifacts in scanned images. The processor is configured to: utilize a smoothing kernel in accordance with a selected set of thresholds T
1
, T
2
, and T
3
, to produce a set of smoothed projections from a set of original projections obtained from a scan of an object, wherein an amount of smoothing applied varies depending upon a relationship of the original projections to the thresholds; producing a set of final projections utilizing the set of original projections and the set of smoothed projections; and reconstructing images of the object utilizing the final projections, wherein the smoothing kernel is a 3-point kernel for views that are below T
1
but greater than T
2
, a 5-point kernel for views that are below T
2
but greater than T
3
, and a 9-point kernel for views that are below T
3
.
In another aspect of the present invention, there is provided a computer-readable medium having recorded thereon instructions configured to instruct a processor to: utilize a smoothing kernel in accordance with a selected set of thresholds to produce a set of smoothed projections from a set of original projections obtained from a scan of an object, wherein an amount of smoothing applied varies depending upon a relationship of the original projections to the thresholds; produce a set of final projections utilizing the set of original projections and the set of smoothed projections; and reconstruct an image of the object utilizing the final projections.
And in yet another aspect of the present invention, there is provided A computer-readable medium having recorded thereon instructions configured to instruct a processor to: utilize a smoothing kernel in accordance with a selected set of thresholds T
1
, T
2
, and T
3
, to produce a set of smoothed projections from a set of original projections obtained from a scan of an object, wherein an amount of smoothing applied varies depending upon a relationship of the original projections to the thresholds; produce a set of final projections utilizing the set of original projections and the set of smoothed projections; and reconstruct images of the object utilizing the final projections, wherein the smoothing kernel is a 3-point kernel for views that are below T
1
but greater than T
2
, a 5-point kernel for views that are below T
2
but greater than T
3
, and a 9-point kernel for views that are below T
3
.
The above-described embodiments of the present invention are useful in reducing image noise and streaking compared to previously known artifact reduction methods, while retaining image resolution and sharpness. Thus, embodiments of the invention can be advantageously used in situations in which faster scans and/or lower dose scans are required.
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patent: 5165100 (1992-11-01), Hsieh et al.
patent: 5237524 (1993-08-01), Heinemann
patent: 5396528 (1995-03-01), Hu et al.
patent: 5416815 (1995-05-01), Hsieh
patent: 5533091 (1996-07-01), Hsieh
patent: 5727041 (1998-03-01), Hsieh
patent: 5812628 (1998-09-01), Hsieh
patent:
Li Jianying
Shaughnessy Charles
Armstrong Teasdale LLP
Bruce David V.
GE Medical Systems Global Technology Company LLC
Horton Esq. Carl B.
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