Optimization of the source firing pattern for X-ray scanning systems
The present application discloses a computed tomography system having non-rotating X-ray sources that are programmed to optimize the source firing pattern. In one embodiment, the CT system is a fast cone-beam CT scanner which uses a fixed ring of multiple sources and fixed rings of detectors in an offset geometry. It should be appreciated that the source firing pattern is effectuated by a controller, which implements methods to determine a source firing pattern that are adapted to geometries where the X-ray sources and detector geometry are offset.
1. An X-ray imaging apparatus for obtaining a radiation image of an object having a length, comprising:
N number of X-ray sources; and
a controller in communication with each of said N number of X-ray sources, wherein the controller is programmed to cause each of said N number of X-ray sources to activate in a sequence, wherein said sequence is programmatically defined by a relationship:
φ( i )=( k ( i− 1)mod N s )+1
wherein the controller is programmed to model said X-ray sources as being distributed around a surface of a cylinder in a form of a uniform distribution of triangles, wherein k is equal to an increment between X-ray sources being activated and is selected to make said triangles as equilateral as possible, and wherein i is equal to a projection number.
2. The X-ray imaging apparatus of claim 1 wherein the sequence of X-ray source activation creates a trajectory and wherein the trajectory is helical.
3. The X-ray imaging apparatus of claim 1 wherein said sequence of X-ray source activation is dynamically modulated based upon image data obtained from a prior scan.
4. The X-ray imaging apparatus of claim 1 wherein the sequence of X-ray source activation creates a trajectory and wherein the trajectory is non-helical.
5. The X-ray imaging apparatus of claim 4 wherein k is not equal to 1.
6. The X-ray imaging apparatus of claim 1 wherein said sequence of X-ray source activation is selected to obtain an even distribution of X-ray angles intersecting each voxel of a reconstruction volume over a range of 360 degrees over a length of the object.
7. The X-ray imaging apparatus of claim 1 wherein k is defined at least in part by using a relation:
l
1
2
=
d
2
+
(
k
-
1
p
z
N
s
)
2
wherein d is a distance between adjacent sources, p z is a measure of pitch z, k −1 is an inverse of k modulo Ns and l 1 is a length of a side of a triangle.
8. The X-ray imaging apparatus of claim 1 wherein k is defined at least in part by using a relation:
l
2
2
=
(
2
d
)
2
+
p
z
2
(
2
k
-
1
N
s
-
1
)
2
wherein d is a distance between adjacent sources, p z is a measure of pitch z, k −1 is an inverse of k modulo Ns and l 2 is a length of a side of a triangle.
9. The X-ray imaging apparatus of claim 1 wherein k is defined at least in part by using a relation:
l
3
2
=
d
2
+
p
z
2
(
1
-
k
-
1
N
s
)
2
wherein d is a distance between adjacent sources, p z is a measure of pitch z, k −1 is an inverse of k modulo Ns and l 3 is a length of a side of a triangle.
10. The X-ray imaging apparatus of claim 1 wherein the X-ray sources are stationary.
11. The X-ray imaging apparatus of claim 10 wherein the X-ray sources have a rotationally invariant activation sequence.
12. The X-ray imaging apparatus of claim 1 wherein a configuration of the X-ray sources and a plurality of detectors has multi-fold symmetry.
13. The X-ray imaging apparatus of claim 12 wherein said configuration of the X-ray sources and the plurality of detectors exhibit 24 fold symmetry.
14. The X-ray imaging apparatus of claim 1 wherein said controller selects the sequence of X-ray source activation in order to create an evenly spaced sampling lattice over a surface of a virtual cylinder.
15. The X-ray imaging apparatus of claim 14 wherein a length of the virtual cylinder is equal to the length of the object plus a distance, wherein said distance is within a range of 0 mm to 100 mm.
16. The X-ray imaging apparatus of claim 1 further comprising a plurality of sensors arranged in a ring around the object for detecting X-rays emitted from the X-ray sources after passing through the object, wherein the sensors are offset from the X-ray sources along a predefined axis.