Tomographic inspection system

• US 6,081,580 A
• Filed: 09/08/1998
• Issued: 06/27/2000
• Est. Priority Date: 09/09/1997
• Status: Expired due to Term

• Current Assignee: American Science and Engineering Incorporated (OSI Systems Incorporated)
• Original Assignee: American Science and Engineering Incorporated (OSI Systems Incorporated)
• Inventors: Grodzins, Lee, Adams, William L.
• Primary Examiner(s): Dunn, Drew A.
• Assistant Examiner(s): Schwartz, Michael J.
• Application Number:
  US09/149,204
• Time in Patent Office: 658 Days
• Field of Search: 378/87, 378/86, 378/70, 378/76, 378/88, 378/89, 378/57, 378/53, 378/54, 378/95
• US Class Current: 378/87
• CPC Class Codes: G01N 2223/419 computed tomograph
• CPC Class Codes: G01N 23/044 using laminography or tomosynthesis
• 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
• CPC Class Codes: G01V 5/228 using stereoscopic means

Abstract

A tomography system for analyzing an object concealed within an enveloping surface. The system has multiple beams of penetrating radiation, each beam disposed with a distinct orientation with respect to the enveloping surface. Detectors are provided for measuring radiation backscattered by the contents of the enveloping surface and for measuring radiation transmitted through the enveloping surface. The enveloping surface is moved with respect to the multiple beams, and a timer provides for measurement of a time difference between the appearance of features in signals of respective detectors, allowing geometrical characteristics of the features to be determined and displayed.

Claims

1. A tomography system for analyzing an object concealed within an enveloping surface, the system comprising:

a. at least one source of penetrating radiation for emitting a plurality of beams, each beam emitted along a beam axis disposed with an orientation with respect to the enveloping surface such that the orientations of respective beams are distinct;

b. a plurality of scatter detectors for detecting, at distinct times, penetrating radiation scattered by a feature of the object and for generating signals;

c. a scanning arrangement for moving the enveloping surface in a direction of motion with respect to the at least one source of penetrating radiation;

and

d. a timer for comparing the times at which penetrating radiation scattered by the feature of the object is detected by the plurality of scatter detectors.

2. The tomography system in accordance with claim 1, additionally comprising a controller for processing said signals and determining a position in three-dimensional space of the feature of the object.

3. The tomography system in accordance with claim 1, additionally comprising a transmission detector for detecting radiation traversing the enveloping surface in a direction perpendicular to the direction of motion of the enveloping surface.

4. The tomography system in accordance with claim 1, wherein the source of penetrating radiation is an x-ray source.

5. The tomography system in accordance with claim 1, wherein two beams of penetrating radiation are incident upon the enveloping surface at angles disposed on opposite sides measured from the normal to the direction of motion of the enveloping surface in a plane parallel to the plane of motion of the enveloping surface.

6. The tomography system in accordance with claim 1, additionally comprising a conveyor for transporting the enveloping surface.

7. A method for determining the depth of a feature from an edge of an enveloping surface undergoing motion at a constant velocity, the method comprising:

a. illuminating the enveloping surface with a pair of beams of penetrating radiation, each beam incident on the enveloping surface along a beam axis disposed with an orientation with respect to the motion of the enveloping surface such that the orientations of respective beams are distinct, the pair of beams having a vertex;

b. detecting penetrating radiation scattered by the feature with a plurality of scatter detectors;

c. comparing the time penetrating radiation scattered by the feature is detected by respective detectors to establish a time difference;

d. determining a distance from the vertex to the feature on the basis of the time difference penetrating radiation scattered by the feature is detected by respective detectors;

e. measuring a distance from the vertex to the edge of the enveloping surface; and

f. calculating the depth of the feature from the edge of the enveloping surface.

8. A method for calculating a mean atomic number characterizing a feature interior to an enveloping surface undergoing motion at a constant velocity, the method comprising:

a. illuminating the enveloping surface with a pair of beams of penetrating radiation, each beam incident on the enveloping surface along a beam axis disposed with an orientation with respect to the motion of the enveloping surface such that the orientations of respective beams are distinct, the pair of beams having a vertex;

b. detecting penetrating radiation scattered by the feature with a plurality of scatter detectors;

c. comparing the time penetrating radiation scattered by the feature is detected by respective detectors to establish a time difference;

d. determining a distance from the vertex to the feature and a distance from the feature to each detector on the basis of the time difference;

e. calculating a geometrical efficiency of detection based on the distance of the feature from the vertex and the distances of the feature from the respective detectors; and

f. calculating a mean atomic number characterizing the feature based on the intensity of the backscattered signal from the feature and the geometrical efficiency of detection.

9. A method for determining the relative depth of first and second features in an enveloping surface undergoing motion at a constant velocity, the method comprising:

a. illuminating the enveloping surface with a pair of beams of penetrating radiation, each beam incident on the enveloping surface along a beam axis disposed with an orientation with respect to the motion of the enveloping surface such that the orientations of respective beams are distinct, the pair of beams having a vertex;

b. detecting penetrating radiation scattered by the first and second features with a plurality of scatter detectors;

c. comparing the time penetrating radiation scattered by the first and second features is detected by respective detectors for determining a time difference;

d. determining a first distance from the vertex to the first feature and a second distance from the vertex to the second feature on the basis of the time difference; and

e. calculating the relative depth of the first and second features.

10. A method for producing a three-dimensional image of an object having edges, the object contained within an enveloping surface having contents, the enveloping surface undergoing motion at a constant velocity, the method comprising:

a. illuminating the enveloping surface with a pair of beams of penetrating radiation, each beam incident on the enveloping surface along a beam axis disposed with an orientation with respect to the motion of the enveloping surface such that the orientations of respective beams are distinct, the pair of beams having a vertex;

b. detecting penetrating radiation scattered by the edges of the object with a plurality of scatter detectors;

c. comparing the time penetrating radiation scattered by the edges of the object is detected by respective detectors for determining a time difference;

d. determining distances from the vertex to the edges of the object on the basis of the time difference; and

e. reconstructing the shape of the object based on the determined distances.

11. A method according to claim 10, further comprising displaying a stereographic display of the contents of the enveloping surface.

12. A method for producing a three-dimensional image of objects having edges contained within an enveloping surface having contents, the enveloping surface undergoing motion at a constant velocity, the method comprising:

a. illuminating the enveloping surface with a pair of beams of penetrating radiation, each beam incident on the enveloping surface along a beam axis disposed with an orientation with respect to the motion of the enveloping surface such that the orientations of respective beams are distinct, the pair of beams having a vertex;

b. detecting penetrating radiation scattered by the edges of the objects with a plurality of scatter detectors;

c. creating backscatter images corresponding to each incident beam;

d. correlating the backscatter images for creating correlated set of points, lines, and objects;

e. determining the depth of each point, line and object on the basis of the correlated set of points, lines, and objects; and

f. composing a three-dimensional image of the contents of the enveloping surface based on the depth of each point, line, and object.

13. A method for determining the density of an object having edges, the object contained within an enveloping surface having contents, the enveloping surface undergoing motion at a constant velocity, the method comprising:

a. illuminating the enveloping surface with a pair of beams of penetrating radiation, each beam incident on the enveloping surface along a beam axis disposed with an orientation with respect to the motion of the enveloping surface such that the orientations of respective beams are distinct, the pair of beams having a vertex;

b. detecting penetrating radiation scattered by the edges of the object with a plurality of scatter detectors;

c. detecting penetrating radiation transmitted in each beam through the enveloping surface for creating a measure of absorption of each beam;

d. comparing the time penetrating radiation scattered by the edges of the object is detected by respective detectors for determining a time difference;

e. determining distances from the vertex to the edges of the object on the basis of the time difference;

f. reconstructing the shape of the object based on the determined distances; and

g. calculating the density of the object based on the shape of the object and the measure of absorption of each beam.