Tomographic scanning X-ray inspection system using transmitted and compton scattered radiation

• US 20030076924A1
• Filed: 10/19/2001
• Published: 04/24/2003
• Est. Priority Date: 10/19/2001
• Status: Active Grant

• Current Assignee: Technology Asset Trust
• Original Assignee: Control Screening LLC
• Inventors: Mario, Arthur W., Kravis, Scott D.
• Granted Patent: US 6,661,867 B2
• Time in Patent Office: Days
• US Class Current: 378/57
• CPC Class Codes: G01N 2223/419 computed tomograph
• CPC Class Codes: G01N 23/046 using tomography, e.g. computed tomography [CT]
• CPC Class Codes: G01V 5/22 Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays
• CPC Class Codes: G01V 5/222 measuring scattered radiation
• CPC Class Codes: G01V 5/226 using tomography

Abstract

X-ray radiation is transmitted through and scattered from an object under inspection to detect weapons, narcotics, explosives or other contraband. Relatively fast scintillators are employed for faster X-ray detection efficiency and significantly improved image resolution. Detector design is improved by the use of optically adiabatic scintillators. Switching between photon-counting and photon integration modes reduces noise and significantly increases overall image quality.

Claims

2. A system as recited by claim 1, whereby said fast scattering detector comprises a scintillator having a short persistence phosphor and at least one photon detector.

1. A scanning X-ray inspection system, comprising:

a) a conveyor for moving an object to be scanned though said system;

b) an X-ray generation device for generating a pencil beam of X-rays repeatedly sweeping along a straight line across said conveyor, thereby scanning said object as it moves through said system;

c) a fast backscatter detector for generating a backscatter signal when detecting said X-rays backscattered by said object moving on said conveyor, said backscatter detector being disposed on the same side of said moving object as said X-ray generation device 20 and proximate to said straight line;

d) a transmission detector for generating a transmission signal when detecting said X-rays traversing said object moving on said conveyor, said transmission detector being positioned on the opposite side of said object as said backscatter detector, whereby said object moves between said transmission detector and said backscatter detector;

e) a processor for processing said backscatter and transmission signals for a display; and

f) a display means for displaying a backscatter image and/or a transmission image.

3. A system as recited by claim 2, wherein said short persistence phosphor is either Gd₂SiO₅ or Y₂O₂Si.

4. A system as recited by claim 1, said system being a tomographic system and further comprising a second fast backscatter detector positioned along said straight line and opposite from said fast backscatter detector.

5. A system as recited by claim 1, wherein said fast scattering detector comprises two elongated scintillator sections optically linked to at least one photon detector, each of said sections being oppositely disposed along said straight line.

6. A system as recited by claim 1, said system being a tomographic system and further comprising a plurality of distal fast backscatter detectors for detecting X-rays scattered from the distal portion of said object, said distal fast backscatter detectors being disposed alongside said fast backscatter detector whereby said fast backscatter detector is positioned between said straight line and said distal fast backscatter detectors.

7. A system as recited by claim 1, wherein said processor is switchable between photon counting and photon integration modes.

8. A system as recited by claim 7, wherein said processor is automatically switchable between photon counting and photon integration modes.

9. A system as recited by claim 1, whereby said transmission detector comprises a scintillator having a short persistence phosphor and at least one photon detector.

10. A system as by claim 9, wherein said short persistence phosphor is either Gd₂SiO₅ or Y₂O₂Si.

11. A system as recited by claim 9, wherein said fast scattering detector comprises an organic plastic scintillator and at least one photon detector.

12. A system as recited by claim 1, whereby said transmission detector comprises three elongated sections optically linked to at least one photon detector, said sections being linked to form three sides of an open rectangle.

19. A method as recited by claim 17, wherein said photon counting and photon integrating modes are combined and photon counting and photon integration are carried out simultaneously.

a. A system as recited by claim 1, wherein said conveyor has a belt and said system automatically adjusts the belt speed (i) to allow rapid entrance into an inspection zone wherein said object is contacted by said pencil beam of X-rays, (ii) to slow traverse through the inspection zone to prolong residence therein of said object, and (iii) to allow rapid exit from the inspection zone.

21. A system as recited by claim 1, further comprising at least one additional transmission detector overlaying said transmission detector for detecting high energy X-rays and transmitting them to said processor, said high energy X-rays being combined with the signal from said transmission detector to produce an information stream containing radiographic density and atomic number data.

23. A system as recited by claim 1, wherein said display means is operative to display each of said backscatter and transmission images, and said images displayed as adjacent windows on a single monitor.

24. A system as recited by claim 1, wherein said signal from said transmission detector is used to correct for attenuation effects in said backscatter image, thereby avoiding artifacts in the low Z images produced by attenuation due to high Z objects.

25. A system as recited by claim 1, wherein said signal from said backscatter detector is used to correct for scatter effects in said transmission image, thereby avoiding artifacts in the high Z image produced by scattering attenuation due to low Z objects.

3-1. A system as recited by claim 2, wherein said fast scattering detector comprises an organic plastic scintillator and at least one photon detector.

13. A backscatter detector for use in a tomographic scanning X-ray inspection system, comprising:

a) an organic plastic scintillator having one end formed as a semni-paraboloid; and

b) a photomultiplier tube mounted at the focus of said semi-paraboloid.

14. A backscatter detector as recited by claim 13, wherein a 45 degree angle cut is used in place of said semi-paraboloid.

15. A transmission detector for use in a tomographic scanning X-ray inspection system, comprising:

a) an organic plastic scintillator having the shape of a U, one end of which is formed as a semi-paraboloid; and

b) a photomultiplier tube mounted at the focus of said semi-paraboloid.

16. A transmission detector as recited by claim 15, wherein a 45 degree angle cut is used in place of said semi-paraboloid.

17. A method for X-ray inspection of an object using transmitted and Compton backscattered radiation, comprising the steps of:

a) generating a pencil beam of X-rays;

b) scanning said object with said pencil beam of X-rays;

c) detecting X-ray transmission through said object using a fast transmission detector;

d) selecting a detection mode for detecting said transmission X-rays, said mode being either photon integration or photon counting;

e) detecting X-rays backscattered from said object using a fast backscatter detector;

f) selecting a detection mode for detecting said backscattered X-rays, said mode being either photon integration or photon counting;

g) processing a transmission image from said detected transmission X-rays

h) displaying said transmission image;

i) processing a backscattered image from said detected backscattered X-rays; and

j) displaying said backscattered image.

18. A method as recited by claim 17, further comprising the steps of;

a) combining said backscattered image and said transmission image into a composite image; and

22. displaying said composite image.

22-2. A system as recited by claim 20, further comprising a filtering material disposed between said transmission detector and said additional transmission detector for increasing discrimination between X-rays having different energies.