Method and apparatus for cone beam CT dynamic imaging
A cone-beam scanning system scans along a half circle. The reconstruction uses a weighting function which decreases for rows farther from the scan plane to take the redundancy of the projection data into account. Another embodiment uses a circle plus sparse helical scan geometry. Image data can be taken in real time.
1. A method for forming an image of an object, the method comprising:
(a) performing a cone-beam scan of the object in a scanning plane by using a cone-beam emitter and a detector to perform a half-circle scanning geometry so as to obtain projection data for a plurality of rows;
(b) weighting the projection data with a weighting factor to produce weighted projection data, wherein the weighting factor decreases as the rows become farther from the scanning plane, wherein the weighting factor is a function of a weighting angle which is a function of the row and a scan angle, wherein the weighting angle is
β
′
=
β
1
1
+
m
2
ξ
2
/
so
2
where β is the scan angle, m is a number of the row, ξ is a virtual detector sampling interval of the detector, and so is a distance from the emitter to an origin of the scanning geometry; and
(c) forming the image from the weighted projection data.
2. The method of claim 1 , wherein step (c) comprises filtering the weighted projection data.
3. The method of claim 1 , wherein the weighting factor is
ω
(
β
′
,
np
)
=
{
sin
2
(
π
4
β
′
Δ
′
-
tan
-
1
(
np
so
′
)
)
,
0
≤
β
′
≤
2
Δ
′
-
2
tan
-
1
(
np
so
′
)
1
,
2
Δ
′
-
2
tan
-
1
(
np
so
′
)
≤
β
′
≤
π
-
2
tan
-
1
(
np
so
′
)
sin
2
(
π
4
π
+
2
Δ
′
-
β
′
Δ
′
+
tan
-
1
(
np
so
′
)
)
,
π
-
2
tan
-
1
(
np
so
′
)
≤
β
′
≤
π
+
2
Δ
′
where n is a column number, p is a virtual detector sampling interval along a t axis,
so
′
=
so
2
+
m
2
ξ
2
;
Δ
′
=
tan
-
1
(
MO
so
′
)
;
and
MO is a half-width of the detector.
4. The method of claim 1 , further comprising, between steps (b) and (c), adding to the weighted projection data a correction term representing information in Radon space which cannot be acquired through a circular scan.
5. The method of claim 1 , wherein steps (a), (b) and (c) are performed in real time.
6. A system for forming an image of an object, the system comprising:
a cone-beam emitter;
a detector;
a gantry for causing relative movement of the emitter and the detector for performing a cone-beam scan of the object in a scanning plane by using a cone-beam emitter and a detector to perform a half-circle scanning geometry so as to obtain projection data for a plurality of rows; and
a processor, receiving the projection data, for weighting the projection data with a weighting factor to produce weighted projection data, wherein the weighting factor decreases as the rows become farther from the scanning plane and forming the image from the weighted projection data, wherein the weighting factor is a function of a weighting angle which is a function of the row and a scan angle, wherein the weighting angle is
β
′
=
β
1
1
+
m
2
ξ
2
/
so
2
where β is the scan angle, m is a number of the row, ξ is a virtual detector sampling interval of the detector, and so is a distance from the emitter to an origin of the scanning geometry.
7. The system of claim 6 , wherein the processor filters the weighted projection data.
8. The system of claim 6 , wherein the weighting factor is
ω
(
β
′
,
np
)
=
{
sin
2
(
π
4
β
′
Δ
′
-
tan
-
1
(
np
so
′
)
)
,
0
≤
β
′
≤
2
Δ
′
-
2
tan
-
1
(
np
so
′
)
1
,
2
Δ
′
-
2
tan
-
1
(
np
so
′
)
≤
β
′
≤
π
-
2
tan
-
1
(
np
so
′
)
sin
2
(
π
4
π
+
2
Δ
′
-
β
′
Δ
′
+
tan
-
1
(
np
so
′
)
)
,
π
-
2
tan
-
1
(
np
so
′
)
≤
β
′
≤
π
+
2
Δ
′
where n is a column number, p is a virtual detector sampling interval along a t axis,
so
′
=
so
2
+
m
2
ξ
2
;
Δ
′
=
tan
-
1
(
MO
so
′
)
;
and
MO is a half-width of the detector.
9. The system of claim 6 , wherein the processor adds to the weighted projection data a correction term representing information in Radon space which cannot be acquired through a circular scan.
10. The system of claim 6 , wherein the emitter, detector, gantry and processor operate in real time.