X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2003-06-27
2004-11-09
Bruce, David V (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S004000, C378S008000, C378S901000
Reexamination Certificate
active
06816565
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to computed tomography (CT) and more particularly to matched view weighting methods for computed tomography scanners using multiple tilted reconstruction planes.
A single tilted-plane-based reconstruction (sTPR) algorithm has been proposed to combat cone beam and helical artifacts in helical multi-detector-row CT. Each tilted reconstruction plane (RP) in sTPR uses two freedoms of rotation. A virtual x-ray source trajectory (VT) is defined as the intersection of a RP with the cylinder containing an actual helical x-ray source trajectory (AT) to reconstruct an image on each tilted RP. The error between VT and AT (namely trajectory error) is globally minimized and symmetric if the central intersection point between a RP and an AT is taken as the origin. However, noise characteristics of sTPR may be compromised because only short scan (180°+fan angle) projection data are used to reconstruct an image on a tilted RP. To improve the noise characteristics of sTPR, a multiple-tilted-plane-based reconstruction (mTPR) algorithm has been proposed, in which each tilted RP uses three freedoms of rotation. As a result, the trajectory error in mTPR is no longer globally minimized and symmetric.
BRIEF DESCRIPTION OF THE INVENTION
In one aspect, a method for Computed Tomography scanners using multiple tilted reconstruction planes is provided. The method includes view weighting data in accordance with
χ
(
β
,
γ
)
=
{
w
b
0
≤
β
≤
2
γ
m
-
2
γ
1
2
γ
m
-
2
γ
<
β
≤
π
-
2
γ
ω
(
β
,
γ
)
=
3
χ
2
(
β
,
γ
)
-
2
χ
3
(
β
,
γ
)
where
β
w
t
π
-
2
γ
<
β
≤
π
+
2
γ
m
is a central view angle, &ggr; is a fan angle, &ggr;
m
is a maximum half fan angle of an x-ray beam, and w
b
and w
t
are each weights no greater than 1.
In another aspect, a Computed Tomography (CT) system includes an x-ray source, a detector positioned to receive x-rays emitted from the source, and a computer operationally coupled to the source and the detector. The computer is configured to receive data from a scan of an object, and weight the received data in accordance with
χ
(
β
,
γ
)
=
{
w
b
0
≤
β
≤
2
γ
m
-
2
γ
1
2
γ
m
-
2
γ
<
β
≤
π
-
2
γ
ω
(
β
,
γ
)
=
3
χ
2
(
β
,
γ
)
-
2
χ
3
(
β
,
γ
)
where
β
w
t
π
-
2
γ
<
β
≤
π
+
2
γ
m
is a central view angle, &ggr; is a fan angle, &ggr;
m
is a maximum half fan angle of an x-ray beam, and w
b
and w
t
are each weights no greater than 1.
In another aspect, a method of obtaining and using weights is provided. The method includes setting
w
b
=
e
t
e
t
+
e
b
and
w
t
=
e
b
e
t
+
e
b
with
e
b
=
∫
0
π
2
+
γ
m
&LeftBracketingBar;
A
T
(
β
)
-
V
T
(
β
)
&RightBracketingBar;
ⅆ
β
and
e
t
=
∫
π
2
+
γ
m
π
+
2
γ
m
&LeftBracketingBar;
A
T
(
β
)
-
V
T
(
β
)
&RightBracketingBar;
ⅆ
β
wherein AT(&bgr;) is an actual helical x-ray source trajectory (AT) of &bgr; and VT(&bgr;) is a virtual x-ray source trajectory (VT) of &bgr;, and weighting image data with w
b
and w
t
prior to filtering and backprojecting the image data to reconstruct an image.
In still another aspect, a computer readable medium encoded with a program configured to instruct a computer is provided. The program is configured to instruct the computer to receive data from a scan of an object, and weight the received data in accordance with
χ
(
β
,
γ
)
=
{
w
b
0
≤
β
≤
2
γ
m
-
2
γ
1
2
γ
m
-
2
γ
<
β
≤
π
-
2
γ
ω
(
β
,
γ
)
=
3
χ
2
(
β
,
γ
)
-
2
χ
3
(
β
,
γ
)
where
β
w
t
π
-
2
γ
<
β
≤
π
+
2
γ
m
is a central view angle, &ggr; is a fan angle, &ggr;
m
is a maximum half fan angle of an x-ray beam, and w
b
and w
t
are each weights no greater than 1.
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