Imaging system

Details Imaging system Imaging system

1995-12-15

1997-10-28

Wong, Don

X-ray or gamma ray systems or devices

Electronic circuit

With display or signaling

378 988, H05G 164

Patent

active

056824114

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention concerns X-ray imaging systems, particularly systems for imaging large objects. By "large" is meant objects having an area which is much greater than the area of the radiation detector employed so that only a very small part of the overall article can be seen by the detector at any instant.
An imaging system is described in EP 0286393 devised by some of the present inventors in which an X-ray source irradiates an object and an elongate detecting means is located on the other side of the object operable to emit light in response to incident radiation after passing through the object, and an array of optical fibres is arranged so that for each fibre an input end thereof is positioned at the detecting means for receiving light therefrom and the output end thereof is positioned at a camera, such as an intensified charge coupled device (CCD), wherein the optical fibres are regrouped so that the aspect ratios of the input and output ends of the bundle of optical fibres match those of the detecting means and of the image intensifier or camera respectively.
An imaging system as described will be referred to as a system of the type described.
In a system as aforesaid high speed X-ray imaging with high sensitivity and good dynamic range is virtually impossible to achieve using conventional CCD read-out technology.
It is therefore an object of the present invention to provide a modified imaging system of the type described by which higher speed read-out is possible.


SUMMARY OF THE INVENTION

According to the present invention an X-ray scanning system for high speed imaging of an object comprises:
an X-ray source for generating a fan shaped X-ray beam for traversing a linear section or slice of the object,
a linear array of detectors on the opposite side of the object from the source which generate light depending on the X-ray image incident thereon,
at least one optical fibre linking each detector to the input of a camera such as an image intensified CCD camera, the fibre ends forming a planar array having an aspect ratio which is different from that of the linear array of detectors and which matches the aspect ratio of the camera, wherein the detector array has an addressable array of N.times.M pixels which during read out are addressed in groups (superpixels) to enable a higher read out speed to be obtained than if the pixels were read out individually, and wherein each said superpixel has an aspect ratio of A to B (where A/B is greater than 1), and the orientation of the superpixels is selected so as to produce a higher scanning resolution between regions of the camera ready which correspond to signals from detectors which are widely spaced in the original line detector and a lower scanning resolution in a direction generally perpendicular thereto.
Hereinafter it is assumed that the camera is a CCD camera preceded by an image intensifier.
Typically A may be equal to 8 and B have a value of 1.
The change of aspect ratio of detector to image intensifier input may for example be linear to square, linear to rectangular, linear to circular, or linear to oval.
High speed may also be achieved by building groups of pixels (superpixels) of appropriate dimensions and number into the CCD design at the initial manufacture stage, though such design and fabrication entails high cost. Such redesign may entail parallel read-out in which the imaging area is divided into a number (say 6) of contiguous subregions, which are fabricated on the chip to have their own independent read-out structures, with equivalent factor of increase in read-out rate. The image must then be electronically reassembled after read-out.
The higher resolution in the one direction enables buffer regions to be created between areas of interest in the CCD array.
If larger rectangular areas of silicon are used to define superpixels in a specially fabricated CCD array (instead of uniformly sized areas) the spacing perpendicular to the longer dimension of each pixel is important to prevent crosstalk and allow the advantage

REFERENCES:
patent: 4891844 (1990-01-01), Kiri
patent: 5138642 (1992-08-01), McCroskey et al.
patent: 5465284 (1995-11-01), Karellas

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