Backscatter imaging system
An x-ray system, comprising: a backscatter detector, comprising: an x-ray conversion material; a plurality of sensors configured to generate electrical signals in combination with the x-ray conversion material in response to incident x-rays; and a collimator disposed on the x-ray conversion material and including a plurality of partitions extending away from the x-ray conversion material and the sensors and forming a plurality of openings, each opening corresponding to one of the sensors.
1. An x-ray system, comprising:
a backscatter detector, comprising:
an x-ray conversion material;
a plurality of sensors configured to generate electrical signals in combination with the x-ray conversion material in response to incident x-rays; and
a collimator disposed on the x-ray conversion material and including a plurality of partitions extending away from the x-ray conversion material and the sensors and forming a plurality of openings, each opening corresponding to one of the sensors;
wherein:
each of the openings is associated with a set of one or more sensors of the sensors that is different from sets of sensors associated with the other openings; and
a length (L) and a pitch (P) of the partitions are related to a target resolution (R) and an offset (H) from an object by an equation:
R
=
PH
L
-
1
2
.
2. The x-ray system of claim 1 , further comprising:
a scintillator including the x-ray conversion material;
wherein the collimator is disposed on a surface of the scintillator.
3. The x-ray system of claim 2 , further comprising:
a plurality of septa disposed in the scintillator;
wherein the collimator is separate from the septa.
4. The x-ray system of claim 2 , wherein:
the scintillator has a thickness such that a conversion rate for photon energies above 1 megaelectronvolt (MeV) is less than 50%.
5. The x-ray system of claim 2 , wherein:
the scintillator is selected from a group consisting essentially of:
a cesium iodide (CsI) scintillator having a thickness between 5 to 17 millimeters (mm);
a cadmium tungstate (CdWO 4 ) scintillator having a thickness between 1.5 to 7 mm; and
a polyvinyl toluene (PVT) scintillator having a thickness between 25 to 60 mm.
6. The x-ray system of claim 1 , further comprising:
a megavolt (MV) x-ray source configured to generate a MV x-ray beam;
wherein the backscatter detector is disposed to receive photons generated during scattering events from the MV x-ray beam.
7. The x-ray system of claim 6 , wherein:
the MV x-ray beam is a MV x-ray fan beam.
8. The x-ray system of claim 6 , wherein:
the backscatter detector further comprises a back shield disposed between the backscatter detector and the MV x-ray source.
9. The x-ray system of claim 8 , wherein:
the back shield is configured to reduce photons having energies above 1 megaelectronvolt (MeV) from the MV x-ray source to less than 1×10 −6 .
10. The x-ray system of claim 8 , wherein:
the backscatter detector further comprises a side shield; and
the side shield is thinner than the back shield.
11. The x-ray system of claim 6 , further comprising:
a transmission detector configured to receive at least part of the MV x-ray beam.
12. The x-ray system of claim 1 , wherein:
the backscatter detector is one of a plurality of backscatter detectors disposed in relation to each other to detect backscatter from different depths within an object.
13. The x-ray system of claim 1 , wherein:
the sensors are direct conversion sensors including the x-ray conversion material.
14. The x-ray system of claim 1 , wherein:
the collimator includes a frame; and
optionally at least one of:
the partitions are removably mounted in the frame;
the partitions are rotatable by the frame;
a pitch of the partitions is adjustable by the frame; and
a distance of the partitions from the sensors is adjustable by the frame.
15. A method of operating the x-ray system of claim 1 , comprising:
generating a megavolt (MV) x-ray beam;
backscattering the MV x-ray beam towards the backscatter detector;
collimating the backscattered MV x-ray beam at the backscatter detector;
filtering energies above 1 megaelectronvolts (MeV) at the backscatter detector; and
detecting the backscattered MV x-ray beam.
16. The method of claim 15 , wherein filtering energies above 1 MeV at the backscatter detector comprises:
detecting the backscattered MV x-ray beam to generate a signal; and
rejecting portions of the signal based on energy levels of the received photons.
17. The method of claim 15 , wherein filtering energies above 1 MeV at the backscatter detector comprises:
shielding the backscatter detector from leakage from a source of the MV x-ray beam.
18. The method of claim 15 , wherein filtering energies above 1 MeV at the backscatter detector comprises:
converting photons of the MV x-ray beam in a scintillator such that a conversion rate for photon energies above 1 MeV is less than 50%.
19. The x-ray system of claim 1 , wherein:
the backscatter detector further comprises a filter disposed on the scintillator between the backscatter detector and the object.
20. An x-ray system, comprising:
an x-ray source for generating a megavolt (MV) x-ray beam;
a backscatter detector for detecting backscatter from the MV x-ray beam; and
means for filtering photons from the MV x-ray beam having energies above 1 megaelectronvolts (MeV) before detection in the backscatter detector, the means for filtering photons comprising:
a collimator including a plurality of partitions forming a plurality of openings, a length (L) and a pitch (P) of the partitions being related to a target resolution (R) and an offset (H) from an object by an equation:
R
=
PH
L
-
1
2
.