EP2118683A2

EP2118683A2 - Computed tomography inspection

Info

Publication number: EP2118683A2
Application number: EP08709998A
Authority: EP
Inventors: Jens-Peter Schlomka
Original assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips Electronics NV
Current assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips NV
Priority date: 2007-02-16
Filing date: 2008-02-12
Publication date: 2009-11-18
Also published as: CN101617246A; WO2008099334A2; JP2010519519A; WO2008099334A3

Abstract

A method includes detecting transmission radiation, from an x-ray source, that traverses an inspection region and an object therein and emission radiation from a radioactive material in the object, generating a signal indicative of the detected radiation, energy resolving the detected radiation, and processing the energy resolved radiation to identify detected radiation that has energy corresponding to the radioactive material.

Description

Computed tomography inspection

The present application generally relates to imaging systems. While it finds particular application to security inspection, it also relates to other applications in which it is desirable to obtain information indicative of a material of interest within an object under examination.

X-ray computed tomography (CT) systems have been used in security inspection applications to inspect objects such as baggage to detect the presence of weapons, explosives, and other contraband which may pose a security risk within the baggage.

Conventionally, CT systems have generated volumetric image data indicative of the radiation attenuation of an object under inspection. Unfortunately, the radiation attenuation characteristics of some contraband materials can be similar to those of legitimate materials, thus complicating the security inspection task.

Coherent scatter CT (CSCT) systems have also been used in security screening applications. These systems, which measure the energy and spatial distribution of elastic x-ray scatter, can provide a relatively more definitive indication of an object's molecular structure, for example, to more positively detect the presence of a contraband material. More particularly, an x-ray diffraction pattern for an object under examination is compared with a stored diffraction pattern(s) for a contraband material(s) of interest and/or a legitimate material(s). This additional information can be used to better determine whether the object contains contraband.

An example of a baggage inspection system that includes a CT system and a CSCT system is disclosed in US Publication 2006/0083346 to Schlomka, et al.

Although radiation attenuation coefficient and x-ray diffraction pattern based inspection techniques have been used for detecting the presence of a contraband material in baggage, there nonetheless remain situations in which it is desirable to obtain still further additional information about an object under inspection. Aspects of the present application address the above-referenced matters and others. According to one aspect, a method includes detecting transmission radiation, from an x-ray source, that traverses an inspection region and an object therein and emission radiation from a radioactive material in the object, generating a signal indicative of the detected radiation, energy resolving the detected radiation, and processing the energy resolved radiation to identify detected radiation that has energy corresponding to the radioactive material.

According to another aspect, a system includes an x-ray source that produces transmission radiation that traverses the inspection region and an object disposed therein. An energy resolving detector detects coherently scattered transmission radiation and emission radiation emitted by a radioactive material in the object, and generates data indicative the detected radiation. A diffraction processor processes the data to generate a diffraction pattern indicative of the coherent scatter radiation. A processing component processes the energy resolved radiation to identify detected radiation having energy corresponding to the radioactive material.

According to another aspect, a computer readable storage medium contains instructions that, when executed by a computer, cause the steps of detecting transmission radiation, from an x-ray source, that traverses an inspection region and an object therein and emission radiation from a radioactive material in the object, generating a signal indicative of the detected radiation, energy resolving the detected radiation, and processing the energy resolved radiation to identify detected radiation that has energy corresponding to the radioactive material.

Still further aspects of the present invention will be appreciated to those of ordinary skill in the art upon reading and understand the following detailed description.

The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention.

FIGURE 1 illustrates an exemplary imaging system FIGURE 2 illustrates an exemplary method

With reference to FIGURE 1 , a computed tomography (CT) scanner 100 includes a rotating gantry portion 104 that surrounds a perimeter of an inspection region 108 and rotates around an axis of rotation. The rotating gantry portion 104 supports an x-ray detector 112 that detects radiation emanating from the inspection region 108, including transmission radiation (primary radiation and coherent scatter radiation) from an x-ray source 116 and emission radiation from decaying radioactive or nuclear material disposed within the inspection region 108, and generates data or signals indicative thereof. A collimator lamella is positioned next to the detector 112 within the inspection region 108 to block radiation originating in areas outside of the inspection region 108 from striking the detector 112.

The x-ray detector 112 includes a generally two-dimensional matrix of detector elements, including a plurality of rows 120 of detector elements that are generally orthogonal to the rotation axis and a plurality of columns 128 of detector elements that are generally parallel to the rotation axis.

In the illustrated embodiment, the detector 112 is an energy- resolving detector that concurrently measures the intensity of radiation received in a plurality of energy ranges or bins. In one implementation, the energy range for one or more bins advantageously corresponds to the energy characteristic of decay radiation emitted by one or more radioactive materials of interest.

A suitable energy-resolving detector includes a direct conversion detector such as a Cadmium Zinc Telluride (CdZnTe, or CZT) detector or a Cadmium Telluride (CdTe) detector, or other detector having energy-resolving capabilities. The detector 112 may alternatively be implemented using multiple scintillation or direct conversion detectors, or other energy-resolving techniques, either alone or in combination.

The rotating gantry portion 104 also supports the x-ray source 116, which is located opposite the detector 112 with respect to the inspection region 108. The x-ray source 116 rotates in coordination with the detector 112, via the rotating gantry portion 104, and produces x-ray radiation that traverses the inspection region 108 when performing a transmission scan. In one embodiment, the tube acceleration voltage is advantageously set to about 150 keV.

A first collimator 132 collimates radiation emitted by the x-ray source 116 to form a generally cone-shaped radiation beam 136 that illuminates the two- dimensional matrix of detector elements. A second, adjustable collimator 140 is positionable within the path of the beam to collimate the beam to form a generally fan- shaped beam 144, when such beam is desired. When not employed, the second collimator 140 is positioned so as to provide the generally cone shaped beam. For a transmission scan, the x-ray detector 112 and the x-ray source 116 rotate so that x-ray projections are obtained over at least one hundred and eighty (180) degrees plus a fan angle. Decay radiation is substantially concurrently detected while performing the transmission scan. Additionally or alternatively, decay radiation is detected while the x-ray source 116 is turned off or the transmission radiation is blocked from reaching the detector 112, and, optionally, the rotating gantry portion 104 and, thus, the detector 112 is stopped at a generally static position.

A reconstructor 148 reconstructs the data indicative of the detected transmission (primary, coherent scatter, or both) radiation to generate volumetric image data, including attenuation coefficients of the inspection region 108. The image data can be further processed by an imager 150 to generate one or more images of the inspection region 108.

A diffraction processor 152 processes the data indicative of coherent scatter radiation to generate diffraction patterns of the inspection region 108 and objects therein. A suitable technique for generating x-ray diffraction patterns from coherent scatter radiation is discussed in US patent 6,470,067 to Harding, which is expressly incorporated herein by reference in its entirety. In general, diffraction patterns are caused by the coherence between scattered x-rays and are a function of the momentum transfer. The momentum transfer can be estimated as the product of the energy of the scatter x-rays and the sine of half the scatter angle. Such energy is obtained from the energy-resolving detector. The scatter angle generally is the angle enclosed by the trajectory of the scatter x-rays relative to the trajectory that would have been followed by the x-rays in the absence of scattering. This angle can be obtained from the location of the detector elements and the location in the primary fan beam at which the scatter has occurred.

A binner 156 bins the energy-resolved data across a plurality of energy bins having different energy ranges.

A processor 160 processes the attenuation coefficients, the diffraction patterns, and the binned data. As described in greater detail below, in one instance this includes processing this data to detect the presence of radioactive material and optionally materials found weapons, explosives, timing and detonation devices, and wires, and other objects of interest in objects disposed within the inspection region 108.

A storage component 164 stores the known attenuation coefficients, diffraction patterns, and energy ranges for the materials of interest

An object support 168 such as a conveyer belt supports and positions the object in the inspection region 108. A general purpose computer serves as an operator console 172.

The console 172 includes a human readable output device such as a monitor or display and an input device such as a keyboard and mouse. Software resident on the console allows the operator to control and interact with the scanner 100, for example, through a graphical user interface (GUI). As generally noted above, the detector 112 can substantially concurrently detect decay radiation and coherent scatter radiation. For detecting coherent scatter radiation, the second adjustable collimator 140 is moved within the path of the beam to collimate the beam to form the generally fan-shaped beam 144. As depicted in FIGURE 1 , the beam is collimated so that it strikes a generally middle or central row 176 of the detector elements. As a consequence, the detector elements in the row 176 detect primary radiation, which is used to energy-correct coherent scatter data. The detector elements in the other rows detect the coherent scatter radiation.

Operation will now be described in connection with FIGURE 2. At reference numeral 204, an object such as baggage is placed in the inspection region 108 and the energy-resolving detector 112 detects radiation emanating from the inspection region 108, including emission radiation from radioactive materials disposed within the inspection region 108 and transmission radiation from the x-ray source 116 that traverses the inspection region 108. The output of the detector 112, which is indicative of the detected radiation and the baggage in the inspection region 108, is used to detect the presence of radioactive materials and contraband materials in the inspection region 108 as described below.

At 208, the signal indicative of the detected radiation is energy binned across a plurality of energy bins.

At 212, the binned data is processed to determine whether radiation having energy greater than the acceleration voltage of the x-ray source 116 is detected. Such radiation is indicative of radiation emitted by a source other than the x- ray source 116. By way of example, as noted above the tube acceleration voltage for the illustrated system is about 150 keV. Detection of radiation with energy greater than the threshold energy of approximately 150 keV indicates that radiation from a source other than the x-ray source 116 is emitting radiation that is being detected by the detector 112.

If radiation having such energy is detected, then at 216 the baggage is identified as including a radioactive material that emits radiation having energy greater than the acceleration voltage of the x-ray source 116. Optionally, the baggage may be further inspected for radioactive materials emitting radiation having energy less than the acceleration voltage of the x-ray source 116 as described below.

If radiation having such energy is not detected (or if further inspection for radiation having energy less than the acceleration voltage of the x-ray source 116 if desired) then at 220 the intensity for an energy bin having an energy range that includes the energy characteristic of a radioactive material of interest is compared with the intensity for a neighboring energy bin(s). Some radioactive isotopes and mixtures of isotopes emit radiation at more than one energy level. In such a case, the intensity for a plurality of energy bins is compared with the intensity for the other energy bins. Alternatively, the binned data can be processed to identify an energy bin having an intensity peak indicative of the radioactive material of interest.

If the intensity corresponding to the subject bin is larger than the intensity for the neighboring energy bin(s) or if an intensity peak is identified, then the baggage is further inspected as described next at 228. Otherwise, the baggage is deemed not to include a radioactive material at 226.

At 228, the x-ray source 116 is turned off or shielded so that the detector 112 is not illuminated by radiation produced by the x-ray source 116. As noted above, the rotating gantry portion 104 is optionally stopped so that the detector 112 is stopped at a generally static position.

At 232, the energy-resolving detector 112 detects radiation emanating from the inspection region 108, and at 236 the signals indicative of the energy resolved detected radiation are binned across a plurality of energy bins, each corresponding to a different energy range.

At 240, the binned data is processed to determine whether radiation having energy characteristic of radioactive materials of interest is detected.

This includes determining whether detected radiation having such energy corresponds to stored known energy ranges for radioactive materials of interest. Since the binned data is used to determine the presence of decay radiation and spatial information is not needed, the signals for a given energy bin can be summed together to increase sensitivity.

If radiation having an energy corresponding to a stored energy range is detected, then at 244 the object is identified as including radioactive material.

Otherwise, the object is cleared. Examples of radioactive isotopes or radionuclides that have been of interest in illicit trafficking include Uranium-233, Uranium-235, Plutonium-239,

Thorium-232, Americium-241, Cadmium- 109, Caesium- 137, Californium-252, Cobalt-

60, Iridium- 192, Krypton-85, Lead-210, Strontium-90, Radium-226, and Technetium-

99, as well as other isotopes of interest. At 248, the signals indicative of the detected coherent scatter radiation are processed to generate an x-ray diffraction pattern. At 252, the computed diffraction pattern is compared with stored known diffraction patterns of known materials of interest. If the computed diffraction pattern matches a diffraction pattern of a diffraction pattern of a known legitimate material, then the baggage is deemed not to include a contraband material at 256. Otherwise, at 260 the baggage is flagged and, if desired, further inspected.

If desired, the second collimator 140 can be suitably positioned so that the cone-shaped beam 136 is formed instead of the fan- shape beam 144. With this configuration, primary radiation is detected along with decay radiation, and the signal indicative of the detected primary radiation can be reconstructed to generate image data indicative of the radiation attenuation of the baggage. The generated attenuation data can then be compared against stored attenuation data of contraband material of interest to determine if such contraband material is present in the object.

Variations are also contemplated.

It is to be appreciated that the signal indicative of the detected coherent scatter radiation can be reconstructed to generate volumetric image data indicative of the radiation attenuation of the baggage and compared against stored attenuation data of contraband material of interest to determine if such contraband material is present in the inspection region 108. A suitable technique for reconstructing a signal indicative of coherent scatter radiation via a back projection technique is discussed in US publication 2006/0153328 to Schlomka et al.

The exemplary system illustrated herein includes the first collimator 132 and the second collimator 140 for respectively forming a cone-shape beam and a fan-shaped beam for performing a CT scan and CSCT scan. In another embodiment, the first collimator 132 may be omitted, and the scanner performs CSCT scans along with detecting decay radiation. In yet another embodiment, the second collimator 140 may be omitted, and the scanner performs CT scans along with detecting decay radiation.

The reconstructed signal is also indicative of the radiation attenuation characteristics of shielding material within the inspection region. Thus, by comparing the attenuation coefficients indicative of the scanned baggage with stored known attenuation coefficients of shielding materials of interest, the presence of a shielding material within the inspection region 108 can be detected. The amount of time it takes to sample enough decay radiation of objects behind a shielding material is a function of the attenuation properties of the shielding material. Hence, the attenuation coefficient of matched shielding material can be used to determine a suitable amount of radiation sampling time for allowing enough decay radiation to pass through the shielding material and strike the detector 112.

Applications of the forgoing and variations thereof include, but are not limited to, non-destructive imaging of check-in and hand-held baggage and break bulk, air, and sea cargo. The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be constructed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

CLAIMS:

1. A method, comprising: detecting transmission radiation, from an x-ray source (116), that traverses an inspection region (108) and an object therein and emission radiation from a radioactive material in the object; generating a signal indicative of the detected radiation; energy resolving the detected radiation; and processing the energy resolved radiation to identify detected radiation that has energy corresponding to energy of the emission radiation.

2. The method of claim 1, wherein the step of processing the energy resolved radiation includes identifying radiation that has energy greater than an acceleration voltage of the x-ray source (116).

3. The method of claim 1, wherein the step of processing the energy resolved radiation includes identifying an energy bin having an intensity peak.

4. The method of claim 1 , wherein the step of processing the energy resolved radiation includes comparing intensity information for an energy bin having an energy range corresponding to the radioactive material with intensity information for at least one other energy bin.

5. The method of claim 1, wherein the step of processing the energy resolved radiation includes computing a difference in intensity between energy bins.

6. The method of claim 1 , wherein the detected transmission radiation includes coherent scatter radiation, and further including generating a diffraction pattern indicative of the object from the coherent scatter radiation, wherein the diffraction pattern is used to identify contraband in the object.

7. The method of claim 1 , further including one of turning off the x-ray source (116) and blocking the transmission radiation from illuminating a detector (112), while detecting the emission radiation.

8. The method of claim 1, further including using one of a direct conversion detector and multiple scintillation detectors to detect the radiation.

9. The method of claim 1, wherein the object includes baggage.

10. The method of claim 1 , wherein the detected transmission radiation includes coherent scatter radiation, and further including reconstructing the data indicative of the coherent scatter radiation to generate image data including an attenuation coefficient for the object.

11. The method of claim 1 , wherein the detected transmission radiation includes primary radiation, and further including reconstructing the data indicative of the primary radiation to generate image data including an attenuation coefficient for the object.

12. The method of claim 1 , wherein the transmission and emission radiation are detected by only one common detector.

13. The method of claim 1, wherein the x-ray source (116) and a detector (112) are disposed on a rotating gantry (104) that rotates about the inspection region.

14. A system, comprising: a x-ray source (116) that produces transmission radiation that traverses the inspection region (108) and an object disposed therein; an energy resolving detector (112) that detects coherently scattered transmission radiation and emission radiation emitted by a radioactive material in the object, and generates data indicative the detected radiation; a diffraction processor (152) that processes the data to generate a diffraction pattern indicative of the coherent scatter radiation ;and a processing component (160) that processes the energy resolved radiation to identify detected radiation having energy corresponding to energy of the emission radiation.

15. The system of claim 14, wherein the system is a baggage inspection system.

16. The system of claim 14, wherein the system includes a coherent scatter computed tomography scanner.

17. The system of claim 14, wherein the x-ray source (116) and the energy resolving detector (112) are disposed on a rotating gantry (104) that rotates about the inspection region.

18. A computer readable storage medium containing instructions that, when executed by a computer, cause the steps of: detecting transmission radiation, from an x-ray source (116), that traverses an inspection region (108) and an object therein and emission radiation from a radioactive material in the object; generating a signal indicative of the detected radiation; energy resolving the detected radiation; and processing the energy resolved radiation to identify detected radiation that has energy corresponding to the radioactive material.