X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2002-04-01
2003-07-29
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S015000, C378S062000, C378S901000
Reexamination Certificate
active
06600802
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to computed tomographic (CT) imaging, and more particularly to methods and apparatus for reducing imaging artifacts in an image generated using a multi-slice CT imaging system.
In order to achieve a reasonable level of artifact suppression, a nearly 30% degradation in slice thickness is encountered using at least one known method for artifact reduction. However, it is advantageous to maintain the same slice thickness for some clinical applications.
BRIEF DESCRIPTION OF THE INVENTION
In one aspect, a method for facilitating a reduction of artifacts is provided. The method includes generating a first image of an object with a scanning system in native mode, generating a second image of the object with the scanning system with z-smoothing greater than any z-smoothing performed in native mode, and generating an artifact-candidate image by taking the difference between the first image and the second image.
In another aspect, a method for facilitating a reduction of artifacts includes generating a first image I
o
of an object with a scanning system in native mode, generating a second image I
s
of the object with the scanning system with z-smoothing greater than any z-smoothing performed in native mode, and generating an artifact-candidate image I
a
by taking the difference between the first image and the second image. The method also includes removing high-frequency content from the generated artifact-candidate image to generate an artifact image I
n
by removing all objects smaller than a pre-defined threshold size, and generating a mask image m(x,y) using at least one of a m
o
(x,y) and a m
s
(x,y) according to:
m
o
(
x
,
y
)
=
{
0
,
I
o
(
x
,
y
)
≤
t
low
I
o
(
x
,
y
)
-
t
low
t
high
-
t
low
,
t
low
<
I
o
(
x
,
y
)
≤
t
high
1
,
I
o
(
x
,
y
)
>
t
high
m
s
(
x
,
y
)
=
{
0
,
I
s
(
x
,
y
)
≤
t
low
I
s
(
x
,
y
)
-
t
low
t
high
-
t
low
,
t
low
<
I
s
(
x
,
y
)
≤
t
high
1
,
I
s
(
x
,
y
)
>
t
high
where the mask m(x,y)=m
o
(x,y)m
s
(x,y), where m
o
(x,y) represents a mask for the first image, m
s
(x,y) represents a mask for the second image, t
low
and t
high
are pre-determined thresholds. The method also includes generating a corrected image I
c
according to:
I
c
(x,y)=I
o
(x,y)−s×m(x,y)×I
n
(x,y), where s is a scaling factor.
In yet another aspect, a computer is programmed to generate a first image of an object with a scanning system in native mode, generate a second image of the object with the scanning system with z-smoothing greater than any z-smoothing performed in native mode, and generate an artifact-candidate image by taking the difference between the first image and the second image.
In a further aspect, a computer is programmed to generate a first image I
o
of an object with a scanning system in native mode, generate a second image I
s
of the object with the scanning system with z-smoothing greater than any z-smoothing performed in native mode, and generate an artifact-candidate image I
a
by taking the difference between the first image and the second image. The computer is also programmed to remove high-frequency content from the generated artifact-candidate image to generate an artifact image I
n
by removing all objects smaller than a pre-defined threshold size and generate a mask image m(x,y) using at least one of a m
o
(x,y) and a m
s
(x,y) according to:
m
o
(
x
,
y
)
=
{
0
,
I
o
(
x
,
y
)
≤
t
low
I
o
(
x
,
y
)
-
t
low
t
high
-
t
low
,
t
low
<
I
o
(
x
,
y
)
≤
t
high
1
,
I
o
(
x
,
y
)
>
t
high
m
s
(
x
,
y
)
=
{
0
,
I
s
(
x
,
y
)
≤
t
low
I
s
(
x
,
y
)
-
t
low
t
high
-
t
low
,
t
low
<
I
s
(
x
,
y
)
≤
t
high
1
,
I
s
(
x
,
y
)
>
t
high
where the mask m(x,y)=m
o
(x,y)m
s
(x,y), where m
o
(x,y) represents a mask for the first image, m
s
(x,y) represents a mask for the second image, t
low
and t
high
are pre-determined thresholds. The computer is further programmed to generate a corrected image I
c
according to:
I
c
(x,y)=I
o
(x,y)−s×m(x,y)×I
n
(x,y), where s is a scaling factor.
In another aspect, a computed tomographic (CT) imaging system for reconstructing an image of an object is provided. The imaging system includes a detector array, at least one radiation source, and a computer coupled to the detector array and the radiation source. The computer is configured to generate a first image of an object with a scanning system in native mode, generate a second image of the object with the scanning system with z-smoothing greater than any z-smoothing performed in native mode, and generate an artifact-candidate image by taking the difference between the first image and the second image.
In a still further aspect, a computed tomographic (CT) imaging system for reconstructing an image of an object is provided. The imaging system includes a detector array, at least one radiation source, and a computer coupled to the detector array and the radiation source. The computer is configured to generate a first image I
o
of an object with a scanning system in native mode, generate a second image I
s
of the object with the scanning system with z-smoothing greater than any z-smoothing performed in native mode, and generate an artifact-candidate image I
a
by taking the difference between the first image and the second image. The computer is also configured to remove high-frequency content from the generated artifact-candidate image to generate an artifact image I
n
by removing all objects smaller than a pre-defined threshold size, and to generate a mask image m(x,y) using at least one of a m
o
(x,y) and a m
s
(x,y) according to:
m
o
(
x
,
y
)
=
{
0
,
I
o
(
x
,
y
)
≤
t
low
I
o
(
x
,
y
)
-
t
low
t
high
-
t
low
,
t
low
<
I
o
(
x
,
y
)
≤
t
high
1
,
I
o
(
x
,
y
)
>
t
high
m
s
(
x
,
y
)
=
{
0
,
I
s
(
x
,
y
)
≤
t
low
I
s
(
x
,
y
)
-
t
low
t
high
-
t
low
,
t
low
<
I
s
(
x
,
y
)
≤
t
high
1
,
I
s
(
x
,
y
)
>
t
high
where the mask m(x,y)=m
o
(x,y)m
s
(x,y), where m
o
(x,y) represents a mask for the first image, m
s
(x,y) represents a mask for the second image, t
low
and t
high
are pre-determined thresholds. The computer is also configured to generate a corrected image I
c
according to:
I
c
(x,y)=I
o
(x,y)−s×m(x,y)×I
n
(x,y), where s is a scaling factor.
REFERENCES:
patent: 6061420 (2000-05-01), Strong et al.
patent: 6339632 (2002-01-01), Besson
patent: 6418184 (2002-07-01), Wang et al.
patent: 6421411 (2002-07-01), Hsieh
Armstrong Teasdale LLP
Bruce David V.
GE Medical Systems Global Technology Company LLC
Horton Esq. Carl B.
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