X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
1999-05-04
2001-05-22
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S009000, C378S025000, C378S056000
Reexamination Certificate
active
06236709
ABSTRACT:
BRIEF DESCRIPTION OF THE INVENTION
The present invention relates generally to the X-ray computed tomographic imaging of articles, and more particularly to a continuous high speed tomographic imaging system with a three plane source detector assembly and method for reconstruction imaging.
BACKGROUND OF THE INVENTION
X-ray Computed Tomography (CT) is in wide use at the present time in the medical field for medical imaging. The use of CT produces a cross sectional image from a plurality of attenuation measurements taken at a plurality of angles around the object. However, none of the medical derived CT systems have been designed to meet the real-time inspection requirements for industrial applications. Such systems require an extensive time frame to accomplish scanning, acquire data and provide an image therefrom.
Attempts have been made to provide improved CT systems for nonmedical use. One such system employs an X-ray unit to pre-scan an object, and the pre-scan data is used to select locations for subsequent CT scanning. This system, which is illustrated by U.S. Pat. No. 5,367,552 to Peschmann, uses a rotating CT scanning unit which requires an object to remain stationary during scanning.
In an attempt to improve tomographic reconstruction imaging, algebraic reconstruction techniques (ART) have been employed, but known ART systems have many shortcomings in providing high quality reconstructed imagery. U.S. Pat. No. 5,442,672 to Bjorkholm et al. discloses a three-dimensioned reconstruction based upon a limited number of X-ray projections where algebraic reconstruction techniques are used to reconstruct an image from projected images.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a novel and improved continuous, high speed, tomographic imaging system and method to provide real time inspection of objects to identify an object concealed in a container.
Another object of the present invention is to provide a novel and improved continuous, high speed, tomographic imaging system and method utilizing a three plane source-detector geometry to provide an enhanced tomographic imaging reconstruction.
Yet another object of the present invention is to provide a novel and improved continuous, high speed, tomographic imaging system and method using a multiple plane scanning geometry and a basis function algebraic reconstruction technique whereby attenuation in an image area is modeled as the sum of smooth functions with diameters of at least two pixel intervals. The value appropriate for a pixel is determined by the sum of the basis functions times their amplitudes at the pixel position.
A further object of the present invention is to provide a novel and improved continuous, high speed, tomographic imaging system employing a three plane source-detector geometry which includes a vertical ray path in one plane and two horizontal ray paths in two other planes. The horizontal ray paths are displaced along the line of travel of an object begin scanned.
A still further object of the present invention is to provide a novel and improved continuous, high speed, tomographic imaging system using three stationary X-ray source arrays and three stationary detector arrays to scan objects continuously moving past the arrays.
These and other objects of the present invention are achieved by providing a continuous, high speed, tomographic imaging system wherein a closed package containing concealed objects is moved continuously along a conveyor belt past three spaced sensing stations. At each sensing station a plurality of X-ray sources each emit a fan beam in the same scan plane which passes through the package to a plurality of detectors opposite to the X-ray sources. One scan plane is a vertical perpendicular scan plane relative to the direction of travel of the package along the conveyor belt and the remaining two scan planes are horizontal scan planes at right angles and transverse to the direction of travel. One horizontal scan plane is a left to right scan plane while the remaining scan plane is a right to left scan plane. Each detector provides multiple energy outputs (5) for the same data point in a scan slice, and the detector outputs are stored until all three sensing stations have scanned the same cross sectional view of the package in three directions. Scans are sequentially taken as the package moves continuously through the sensing stations and scanned data corresponding to cross sectional views of the package is accumulated. The stored data is calibrated and normalized and then used in a CT algebraic reconstruction technique. This is a multispectral CT reconstruction, and the reconstructed data images are then detected, segmented and classified. This is accomplished by the fact that the density of a reconstructed object is determined by the attenuation which it causes in the scanning X-rays while the atomic number of the object is determined from the multiple energy scan output. In a classifier, the density and atomic number are compared to a stored look up table containing density and atomic number identification values for specific objects to be located.
After segmentation and classification, the data is sent to a computer coupled to a monitor where three dimensional CT scan data is displayed.
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Gamble Thomas D.
Perry John L.
Bruce David V.
Ensco Inc.
Hobden Pamela R.
Nixon & Peabody LLP
Sixbey Daniel W.
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