Method and apparatus for scanning with lowered dose
View Patent ↗A method and an apparatus for scanning with a lowered dose are provided. The method includes: determining a dynamic changing model of a prepatient collimator according to a rotation angle of a tube in a scanning mode; in a case that the scanning mode is a normal scan, controlling an opening angle of the prepatient collimator according to the dynamic changing model of the prepatient collimator at an initial stage and an end stage of the normal scan; and in a case that the scanning mode is a scan with phase control, controlling an opening angle of the prepatient collimator according to the dynamic changing model of the prepatient collimator at an initial stage and an end stage of a phase of the scan with phase control.
1. A method for scanning with a lowered dose, comprising:
determining a dynamic changing model of a prepatient collimator according to a rotation angle of a tube in a scanning mode;
in a case that the scanning mode is a normal scan, controlling an opening angle of the prepatient collimator according to the dynamic changing model of the prepatient collimator at an initial stage and an end stage of the normal scan; and
in a case that the scanning mode is a scan with phase control, controlling an opening angle of the prepatient collimator according to the dynamic changing model of the prepatient collimator at an initial stage and an end stage of a phase of the scan with phase control,
wherein the dynamic changing model of the prepatient collimator is a dynamic changing model of the prepatient collimator in a direction of an X-axis;
in a fanbeam scan, a sampling angle α is an angle between a positive direction of a Y-axis and a central channel of a fanbeam, wherein α is in a range of [0, α max ], α max ≧π+2β max ; the fanbeam comprises channels in a range of [−β max ,β max ] with the central channel as an axis; the dynamic changing model of the prepatient collimator is:
controlling each of the channels of the fanbeam to be opened in sequence in a direction from −β max to β max at a first velocity in a case that a is in a range of [0, α end ], wherein all of the channels of the fanbeam are open in a case of α=α end ; and/or
controlling each of the channels of the fanbeam to be closed in sequence in a direction from −β max to β max at a second velocity in a case that a is in a range of [α max −α end , α max ], wherein all of the channels of the fanbeam are close in a case of α=α max .
2. The method according to claim 1 , wherein
in a case of 0<α end ≦2β max , the first velocity
V
1
=
2
β
max
α
end
*
α
-
β
max
.
3. The method according to claim 2 , wherein, in a case of 0<α end ≦2β max , α max =π+2α max and a tomography scan, the method further comprises:
setting a weight ω(α,β) of sampling data corresponding to the sampling angle α and the channel β as follows:
ω
(
α
,
β
)
=
{
α
2
β
max
+
2
β
-
α
end
4
β
max
α
end
2
β
max
(
β
+
β
max
)
<
α
<
4
β
max
-
α
end
2
β
max
(
β
+
β
max
)
1
4
β
max
-
α
end
2
β
max
(
β
+
β
max
)
≤
α
<
4
β
max
-
α
end
2
β
max
(
β
-
β
max
)
+
π
+
2
β
max
2
β
max
+
π
-
α
2
β
max
-
2
β
+
α
end
4
β
max
4
β
max
-
α
end
2
β
max
(
β
-
β
max
)
+
π
+
2
β
max
≤
α
<
α
end
2
β
max
(
β
-
β
max
)
+
π
+
2
β
max
0
else
.
4. The method according to claim 1 , wherein
in a case of 0<α end ≦2β max , the second velocity
V
2
=
2
β
max
α
end
*
(
α
-
α
max
)
+
β
max
.
5. The method according to claim 4 , wherein, in a case of 0<α end ≦2β max , α max =π+2β max and a tomography scan, the method further comprises:
setting a weight ω(α,β) of sampling data corresponding to the sampling angle α and the channel β as follows:
ω
(
α
,
β
)
=
{
α
2
β
max
+
2
β
-
α
end
4
β
max
α
end
2
β
max
(
β
+
β
max
)
<
α
<
4
β
max
-
α
end
2
β
max
(
β
+
β
max
)
1
4
β
max
-
α
end
2
β
max
(
β
+
β
max
)
≤
α
<
4
β
max
-
α
end
2
β
max
(
β
-
β
max
)
+
π
+
2
β
max
2
β
max
+
π
-
α
2
β
max
-
2
β
+
α
end
4
β
max
4
β
max
-
α
end
2
β
max
(
β
-
β
max
)
+
π
+
2
β
max
≤
α
<
α
end
2
β
max
(
β
-
β
max
)
+
π
+
2
β
max
0
else
.
6. The method according to claim 1 , wherein, in a case of 0<α end ≦2β max , α max =π+2β max and a tomography scan, the method further comprises:
setting a weight ω(α,β) of sampling data corresponding to the sampling angle α and the channel β as follows:
ω
(
α
,
β
)
=
{
α
2
β
max
+
2
β
-
α
end
4
β
max
α
end
2
β
max
(
β
+
β
max
)
<
α
<
4
β
max
-
α
end
2
β
max
(
β
+
β
max
)
1
4
β
max
-
α
end
2
β
max
(
β
+
β
max
)
≤
α
<
4
β
max
-
α
end
2
β
max
(
β
-
β
max
)
+
π
+
2
β
max
2
β
max
+
π
-
α
2
β
max
-
2
β
+
α
end
4
β
max
4
β
max
-
α
end
2
β
max
(
β
-
β
max
)
+
π
+
2
β
max
≤
α
<
α
end
2
β
max
(
β
-
β
max
)
+
π
+
2
β
max
0
else
.
7. The method according to claim 1 , wherein, in a case that channels [−β max , β end ] are open, channels (β end , β max ] are close, and α end =β max −β end ,
controlling each of the channels of the fanbeam to be opened in sequence in a direction from −β max to β max at the first velocity comprises:
controlling channels [β end ,β max ] of the fanbeam to be opened in sequence in a direction from β end to β max at the first velocity V 1 =α−β max .
8. The method according to claim 7 , wherein, in a case of α end =β max −β end , α max =π+2β max and a tomography scan, the method further comprises:
setting a weight ω(α,β) of sampling data corresponding to the sampling angle α and the channel β as follows:
ω
(
α
,
β
)
=
{
α
-
h
α
2
-
h
1
h
1
<
α
<
α
2
1
α
2
≤
α
<
α
3
α
-
h
2
α
3
-
h
2
α
3
≤
α
<
h
2
0
else
,
wherein
h
1
=
max
(
0
,
α
1
)
,
α
1
=
β
-
β
max
+
α
end
,
h
2
=
min
(
α
4
,
π
+
2
β
max
)
,
α
4
=
β
+
β
max
+
π
+
2
β
max
-
α
end
,
α
2
=
4
β
max
-
α
end
2
β
max
(
β
+
β
max
)
,
and
α
3
=
4
β
max
-
α
end
2
β
max
(
β
+
β
max
)
+
π
-
2
β
max
+
α
end
.
9. The method according to claim 1 , wherein, in a case that channels [−β max ,β end ] are open (β end ,β max ] are close, and α end =β max −β end ,
controlling each of the channels of the fanbeam to be closed in sequence in a direction from −β max to β max at the second velocity comprises:
controlling preset channels [−β max , β end ] of the fanbeam to be closed in sequence in a direction from −β max to β end at the second velocity V 2 =α−β max −π.
10. The method according to claim 9 , wherein, in a case of α end =β max −β end , α max =π+2β max and a tomography scan, the method further comprises:
setting a weight ω(α,β) of sampling data corresponding to the sampling angle α and the channel β as follows:
ω
(
α
,
β
)
=
{
α
-
h
α
2
-
h
1
h
1
<
α
<
α
2
1
α
2
≤
α
<
α
3
α
-
h
2
α
3
-
h
2
α
3
≤
α
<
h
2
0
else
,
wherein
h
1
=
max
(
0
,
α
1
)
,
α
1
=
β
-
β
max
+
α
end
,
h
2
=
min
(
α
4
,
π
+
2
β
max
)
,
α
4
=
β
+
β
max
+
π
+
2
β
max
-
α
end
,
α
2
=
4
β
max
-
α
end
2
β
max
(
β
+
β
max
)
,
and
α
3
=
4
β
max
-
α
end
2
β
max
(
β
+
β
max
)
+
π
-
2
β
max
+
α
end
.
11. The method according to claim 1 , wherein, in a case of α end =β max −β end , α max =π+2β max and a tomography scan, the method further comprises:
setting a weight ω(α,β) of sampling data corresponding to the sampling angle α and the channel β as follows:
ω
(
α
,
β
)
=
{
α
-
h
α
2
-
h
1
h
1
<
α
<
α
2
1
α
2
≤
α
<
α
3
α
-
h
2
α
3
-
h
2
α
3
≤
α
<
h
2
0
else
,
wherein
h
1
=
max
(
0
,
α
1
)
,
α
1
=
β
-
β
max
+
α
end
,
h
2
=
min
(
α
4
,
π
+
2
β
max
)
,
α
4
=
β
+
β
max
+
π
+
2
β
max
-
α
end
,
α
2
=
4
β
max
-
α
end
2
β
max
(
β
+
β
max
)
,
and
α
3
=
4
β
max
-
α
end
2
β
max
(
β
+
β
max
)
+
π
-
2
β
max
+
α
end
.
12. An apparatus for scanning with a lowered dose, comprising:
a determining unit, configured to determine a dynamic changing model of a prepatient collimator according to a rotation angle of a tube in a scanning mode; and
a control unit, configured to, in a case that the scanning mode is a normal scan, control an opening angle of the prepatient collimator according to the dynamic changing model of the prepatient collimator at an initial stage and an end stage of the normal scan; and
the control unit is further configured to, in a case that the scanning mode is a scan with phase control, control an opening angle of the prepatient collimator according to the dynamic changing model of the prepatient collimator at an initial stage and an end stage of a phase of the scan with phase control,
wherein the dynamic changing model of the prepatient collimator determined by the determining unit is a dynamic changing model of the prepatient collimator in a direction of an X-axis;
in a fanbeam scanning, a sampling angle α is an angle between a positive direction of a Y-axis and a central channel of a fanbeam, wherein α is in a range of [0,α max ], α max ≧π+2β max ; the fanbeam comprises channels in a range of [−β max ,β max ] with the central channel as an axis; the control unit comprises:
a first control sub-unit, configured to control each of the channels of the fanbeam to be opened in sequence in a direction from −β max to β max at a first velocity in a case that a is in a range of [0, α end ], wherein all of the channels of the fanbeam are open in a case of α=α end ; and/or
a second control sub-unit, configured to control each of the channels of the fanbeam to be closed in sequence in a direction from −β max to β max at a second velocity in a case that a is in a range of [α max −α end , α max ], wherein all of the channels of the fanbeam are close in a case of α=α max .
13. The apparatus according to claim 12 , wherein
the first control sub-unit is configured to control each of the channels of the fanbeam to be opened in sequence in a direction from −β max to β max at the first velocity
V
1
=
2
β
max
α
end
*
α
-
β
max
in a case of 0<α end ≦2β max .
14. The apparatus according to claim 12 , wherein
the second control sub-unit is configured to control each of the channels of the fanbeam to be closed in sequence in a direction from −β max to β max at the second velocity
V
2
=
2
β
max
α
end
*
(
α
-
α
max
)
+
β
max
in a case of 0<α end ≦2β max .
15. The apparatus according to claim 12 , wherein, in a case that channels [−β max ,β end ] are open, channels (β ends ,β max ] are close, and α end =β max −β end ,
the first control sub-unit is configured to control channels [β end ,β max of the fanbeam to be opened in sequence in a direction from β end to β max at the first velocity V 1 =α−β max .
16. The apparatus according to claim 12 , wherein, in a case that channels [−β max ,β end ] are open, channels (β end ,β max ] are close, and α end =β max −β end ,
the second control sub-unit is configured to control preset channels [−β max ,β end ] max fiend of the fanbeam to be closed in sequence in a direction from −β max to β end at the second velocity V 2 =α−β max −π.