X-ray or gamma ray systems or devices – Specific application – Absorption
Patent
1999-05-27
2000-12-19
Bruce, David V.
X-ray or gamma ray systems or devices
Specific application
Absorption
378 54, 378 89, G01N 2302
Patent
active
06163591&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a screening apparatus and method of the type that may, for example, be used to screen aircraft-hold luggage for concealed weapons or explosive devices.
It is known from International Published Patent Application WO-A-9309512 to provide an object-based 3D X-ray imaging technique that based upon the principal of imaging objects/regions within an item by detecting discontinuities in the opacity to the transmission of X-rays from different directions surrounding the item. This technique is based upon taking approximately ten views through the item with those views being uniformly distributed in solid angle.
Whilst the above mentioned imaging technique is capable of imaging weapons within aircraft-hold luggage, it suffers from the disadvantage that the uniform distribution in solid angle of the views requires an extremely bulky device to operate upon luggage sized items and would be ill-suited to anything other than piecewise operation.
European Published Patent Application EP-A-0,485,872 discloses a baggage security screening system including a portion that contains several X-ray sources and line detectors for detecting the opacity to radiation in a series of planes intersecting an object under test. The signals detected are processed to produce an opacity map of the object.
BRIEF SUMMARY OF THE INVENTION
Viewed from one aspect the present invention provides apparatus for screening an item to detect regions within said item having different opacity to radiation, said apparatus comprising: radiation detector disposed upon opposite sides of said path and serving to generate transmission signals indicative of opacity to radiation between said radiation source and said radiation detector in a plane intersecting said path, said sensors being disposed at a plurality of different locations along said path and being arranged to irradiate said item from a plurality of different angular orientations about said path; characterised by of sensors to detect contours of maximum local rate of change in opacity within a plane through said item to generate cross section signals indicative any boundaries in said plane between said regions having different opacity to radiation and responsive to said cross section signals for a plurality of planes through a region to detect if said region matches one or more predetermined screening criteria.
The invention recognizes that an imaging technique based upon the detection of contours or maximum local rate of change in opacity to the transmission of radiation need not provide the maximum 3D imaging resolution and yet still be able to spot potential security hazards and adopt a sensor arrangement more suited for continuous operation with a large number of items to be screened.
Whilst the invention could use shape recognition algorithms as the predetermined screening criteria (e.g. to detect handguns), it is preferred that said predetermined screening criteria is whether said regions is of material having an opacity to radiation with a predetermined characteristic, said signal processor using said cross section signals in combination with said transmission signals to determine said opacity to radiation of said region.
It has been found that the opacity to radiation is characteristic of the material through which the radiation is travelling and accordingly this technique makes it possible to screen for explosives largely irrespective of the shape into which they are formed.
This capacity is further enhanced in embodiments in which at least one of said radiation sources generates radiation at at least two frequencies and said predetermined characteristic is a relative opacity at at least two frequencies of said radiation falling within a predetermined range of relative opacities.
Whilst the absolute value of the opacity may be subject to error depending upon the precise location of the region being investigated within the item and the nature of the surrounding regions within the item, it has been found that the relative opacity at two
REFERENCES:
patent: 5182764 (1993-01-01), Peschmann et al.
patent: 5261931 (1993-11-01), Wright
patent: 5442672 (1995-08-01), Bjorkholm et al.
patent: 5642393 (1997-06-01), Krug et al.
Conference Paper "Automatic X-Ray Screening of Aircraft Hold Luggage", R. Benjamin et al, Apr. 1997.
Bruce David V.
Dunn Drew A.
The Imperial College of Science
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