WO2010100274A2

WO2010100274A2 - Scanning imaging system, apparatus and method

Info

Publication number: WO2010100274A2
Application number: PCT/EP2010/052869
Authority: WO
Inventors: David Prendergast; Michael Anderson
Original assignee: Consiglia Services Ltd.
Priority date: 2009-03-05
Filing date: 2010-03-05
Publication date: 2010-09-10
Also published as: GB0903813D0; WO2010100274A3

Abstract

One or more embodiments of the present invention provide a scanning system for imaging one or more objects, comprising: an imaging element; a conveyor for providing relative movement between an object to be scanned and said imaging element; said imaging element comprising a high-energy radiation emitter and a high-energy radiation detector spaced from the high-energy radiation emitter to allow passage of the object to be scanned between the high-energy radiation emitter and radiation detector, and the high-energy radiation detector operative to receive radiation emitted from said high- energy radiation emitter and incident on said object; wherein said high-energy radiation detector comprises two or more detection elements disposed in a direction of relative motion of the object to be scanned and said imaging element, with each detection element operative to detect high-energy radiation received at the high-energy radiation detector in a particular energy range. One or more embodiments of the present invention also provide a scanning device and method.

Description

SCANNING IMAGING SYSTEM, APPARATUS AND METHOD

One or more embodiments of the present invention relate to scanning imaging systems, methods and apparatus, and particularly, but not exclusively, to a linear array of detection cells arranged to produce a pixelated sensor operable to form a scanned image of an object.

One or more embodiments of the present invention can also relate to the use of pixelated semiconductor and scintillation devices where the energy response sensitivity of detection cells may be adjusted on a row-wise or columnar basis.

The current state of the art in this field may be exemplified by multi-channel pixilated sensors. In such sensors a signal output from a pixel is separated automatically into one or more energy bins, using custom Application Specific Integrated Circuits (ASICs). These ASICs are usually designed to read information from a detection substrate via pads or directly coupled to the ASIC in the form of a detector hybrid. In the current state of the art, the number of energy bins is limited, typically eight or less, due to the complexity of using multiple comparator stages.

The information provided by conventional radiographic images is limited, even when augmented by tomographic analysis to provide 3-D representations. Such approaches essentially provide an image based on the integral of the transmission spectrum. By contrast the information inherent in hyperspectral approaches pertains to multiple different transmission energies, preserving spectral information. This has the potential to allow the calculation of both density and atomic number to aid material identification. Furthermore, the additional information facilitates numerous techniques for image and contrast enhancement. Consequently, it is reasonable to say that such images provide a more rigorous foundation on which to build both automated and operator based inspection systems when compared with conventional radiographic images.

The energy separation provided by current systems is usually performed at source level, e.g. dual energy systems, or provided by very limited non-contiguous energy binning (Nova-rad, Nexis).

Hyperspectral imaging is the analysis of images using a large number of channels (corresponding to spectrum intervals). The distinction between hyperspectral and multispectral is not defined by a set number of spectral bands. It is best defined by the manner in which the data is collected. Hyperspectral data is a set of contiguous bands (usually by one sensor). Multispectral data is a set of optimally chosen spectral bands that are typically not contiguous (usually by multiple sensors). Capturing the same object on many bands of the spectrum to generate a data cube can reveal objects and information that more limited scanners cannot pick up.

The use of scanning ladders which use the relative motion of an imaged object and a linear array of sensors is well known in industrial inspection, security inspection (e.g. baggage scanning), dental and medical imaging.

In typical photon counting ASICs, one photon counting pixel is normally configured to provide information about photon hits that lay within a certain energy range, i.e. between a high and low threshold, or alternatively information of hits on several energy bins. The number of energy bins is limited by the number of comparator stages that are stored per channel on the ASIC. Typically, this is less than eight bins per channel (pixel).

Conventional scanning imaging systems, methods and apparatus employ image analysis and pattern recognition algorithms which share a central tenet, principally that they cannot create information. If the imaging process discards this information, then this information is lost. This occurs in current radiographic approaches. In these approaches, each pixel contains information that relates to the integral of the transmission spectrum, thereby discarding the transmission spectral information. Even in more sophisticated systems, the information about the imaged object relates to either two overlapping transmission spectra, or alternatively a crude spectral binning. Alternatively, each pixel in the hyperspectral data block contains a transmission spectrum of corresponding volume image object.

Whilst these known scanning imaging systems, methods and apparatus offer various advantages, it is desirable to provide a scanning imaging system, method and apparatus which offers improved properties and which differ frcm known such scanning imaging systems, methods and apparatus. Viewed from a first aspect, there is provided a scanning system for imaging one or more objects, comprising: an imaging element; a conveyor for providing relative movement between an object to be scanned and the imaging element; the imaging element comprising a high-energy radiation emitter and a high-energy radiation detector spaced from the high- energy radiation emitter to allow passage of the object to be scanned between the high-energy radiation emitter and radiation detector, and the high-energy radiation detector operative to receive radiation emitted from the high-energy radiation emitter and incident on the object; wherein the high-energy radiation detector comprises two or more detection elements disposed in a direction of relative motion of the object to be scanned and the imaging element, with each detection element operative to detect high-energy radiation received at the high- energy radiation detector in a particular energy range.

Each of the two or more detection elements may comprise an array of detection pixels, of which the detection pixels may optionally comprise: a detector substrate for generating charge responsive to high-energy incident radiation, the detector substrate configured to form a high- energy radiation sense volume; and a circuit substrate supporting a read-out circuit corresponding to the sense volume and operative to count photons incident upon a corresponding sense volume, the read-out circuit including count incrementing circuitry for incrementing a photon count of photons incident upon a corresponding sense volume responsive to a radiation photon interaction event in a the corresponding sense volume; wherein the read-out circuit is operative to output a detection value corresponding to a number of photons incident upon a corresponding sense volume.

Each of the two or more detection elements may comprise an array of detection pixels, of which the detection pixels may optionally comprise: a detector substrate for generating charge responsive to high-energy incident radiation, the detector substrate configured to form a high- energy radiation sense volume; and a circuit substrate supporting a read-out circuit corresponding to the sense volume and operative to collect charge from a corresponding sense volume, the read-out circuit including charge integration circuitry for integrating charge of a corresponding sense volume responsive to a radiation photon interaction event in a the corresponding sense volume; wherein the read-out circuit is operative to output a detection value corresponding to a charge of a corresponding sense volume. A first of the two or more detection elements may be operative to detect radiation in a first energy range between a first energy level and a second energy level, and a second of the two or more detection elements is operative to detect radiation in a second energy range between the second energy level and a third energy level. Further, an nth of the two or more detection elements may be operative to detect radiation in an nth energy range between an nth energy level and an n+lth energy level. These n-lth and nth energy ranges may be adjacent and may also be contiguous.

Two or more detection elements may be configured in a columnar arrangement transverse to a direction of relative motion of the object to be scanned and the imaging element.

The detection pixels forming the array may be configured in a linear arrangement. Also, the array may be located in a plane substantially parallel to a plane in which the object to be scanned is arranged to move relative to the imaging element.

A speed at which the object to be scanned is advanced relative to the imaging element may be substantially equal to one half of a width of a pixel.

A number of detection pixels in the array may comprise 256.

Radiation emitted by the high-energy radiation emitter may comprise one or more of the following: high-energy electro-magnetic (EM) radiation; or neutron radiation. The high- energy EM radiation may be, for example, in an X-ray region and/or a gamma-ray region of an EM spectrum.

The particular energy range over which each one of the two or more detection elements is operative to detect radiation may be adjustable.

The high-energy radiation detector may be coupled to an image compiler, and where the image compiler is operative to receive output data from the high-energy radiation detector to prepare an image of an object scanned in the scanning system.

Output data from each one of the two or more detection elements at a particular time may represent a particular energy range image of a particular part of the object to be scanned which is adjacent to the one of the two or more detection elements at the particular time.

The image compiler may be operative to perform time delay integration on the output data for preparation of a hyperspectral image comprising a combination of particular energy range images of each particular part of the object to be scanned from each of the two or more detection elements.

A number of spectral image components of the hyperspectral image may correspond to a number of detection elements.

Viewed from a second aspect, there is provided a high-energy radiation detector for a scanning system for imaging one or more objects, the high-energy radiation detector operative to receive radiation emitted from a high-energy radiation emitter and incident on the object; wherein the high-energy radiation detector comprises two or more detection elements disposed in a direction of relative motion of the object to be scanned and the high-energy radiation detector, with each detection element operative to detect high-energy radiation received at the high-energy radiation detector in a particular energy range.

Each of the two or more detection elements may comprise an array of detection pixels, of which the detection pixels may optionally comprise: a detector substrate for generating charge responsive to high-energy incident radiation, the detector substrate configured to form a high- energy radiation sense volume; and a circuit substrate supporting a read-out circuit corresponding to the sense volume and operative to collect charge from a corresponding sense volume, the read-out circuit including charge integration circuitry for integrating charge of a corresponding sense volume responsive to a radiation photon interaction event in a the corresponding sense volume; wherein the read-out circuit is operative to output a detection value corresponding to a charge of a corresponding sense volume.

A first of the two or more detection elements may be operative to detect radiation in a first energy range between a first energy level and a second energy level, and a second of the two or more detection elements is operative to detect radiation in a second energy range between the second energy level and a third energy level. Further, an nth of the two or more detection elements may be operative to detect radiation in an nth energy range between an nth energy level and an n+lth energy level. These n-lth and nth energy ranges may be adjacent and may also be contiguous.

Two or more detection elements may be configured in a columnar arrangement transverse to a direction of relative motion of the object to be scanned and the high-energy radiation detector.

The detection pixels forming the array may be configured in a linear arrangement. Also, the array may be located in a plane substantially parallel to a plane in which the object to be scanned is arranged to move relative to the high-energy radiation detector.

A speed at which the object to be scanned is advanced relative to the high-energy radiation detector may be substantially equal to one half of a width of a pixel.

A number of detection pixels in the array may comprise 256.

Output data from each one of the two or more detection elements at a particular time represents a particular energy range image of a particular part of the object to be scanned which is adjacent to the one of the two or more detection elements at the particular time.

Viewed from a third aspect, there is provided an image compiler for coupling to the high- energy radiation detector described above, wherein the image compiler is operative to receive output data from the high-energy radiation detector to prepare an image of an object scanned in the scanning system.

A number of spectral image components of the hyperspectral image may correspond to a number of detection elements of the high-energy radiation detector.

Viewed from a fourth aspect, there is provided a method of imaging one or more objects, comprising: moving an object to be scanned relative to an imaging element; the imaging element comprising a high-energy radiation emitter and a high-energy radiation detector spaced from the high-energy radiation emitter to allow passage of the object to be scanned between the high-energy radiation emitter and radiation detector; emitting high-energy radiation from the emitter; receiving, at the high-energy radiation detector, radiation emitted from the high-energy radiation emitter and incident on the object; wherein the high-energy radiation detector comprises two or more detection elements disposed in a direction of relative motion of the object to be scanned and the imaging element, with each detection element operative to detect high-energy radiation received at the high-energy radiation detector in a particular energy range.

The method may further comprise generating charge, in a detector substrate of each detection pixel of an array of detection pixels of the detection elements, responsive to high-energy incident radiation, the detector substrate configured to form a high-energy radiation sense volume; and incrementing, in a circuit substrate supporting a read-out circuit corresponding to the sense volume and operative to count photons incident upon a corresponding sense volume, a photon count of photons incident upon a corresponding sense volume responsive to a radiation photon interaction event in a the corresponding sense volume; outputting, from the read-out circuit a detection value corresponding to a number of photons incident upon a corresponding sense volume.

The method may further comprise generating charge, in a detector substrate of each detection pixel of an array of detection pixels of the detection elements, responsive to high-energy incident radiation, the detector substrate configured to form a high-energy radiation sense volume; collecting charge, in a circuit substrate supporting a read-out circuit corresponding to the sense volume and operative to collect charge from a corresponding sense volume; integrating, in charge integration circuitry of the read-out circuit, charge of a corresponding sense volume responsive to a radiation photon interaction event in a the corresponding sense volume; outputting, from the read-out circuit a detection value corresponding to a charge of a corresponding sense volume.

The method may further comprise detecting radiation in a first energy range between a first energy level and a second energy level, and detecting radiation in a second energy range between the second energy level and a third energy level. Further, the method may comprise detecting radiation in an nth energy range between an nth energy level and an n+lth energy level. These n-lth and nth energy ranges may be adjacent and may also be contiguous.

The method may further comprise advancing the object to be scanned relative to an imaging element at a speed substantially equal to one half of a width of a pixel.

The method may further comprise outputting data from the high-energy radiation detector to an image compiler, and, in the image compiler, preparing an image of a scanned object.

The method may further comprise performing, in the image compiler, time delay integration on the output data for preparation of a hyperspectral image comprising a combination of particular energy range images of each particular part of the object to be scanned from each of the two or more detection elements.

The number of spectral image components of the hyperspectral image may correspond to a number of detection elements.

Consider a particular aspect of the present invention where the high and low thresholds are organized on a columnar basis i.e. each column of the baggage ASIC is tuned to provide information between a particular high and low energy range. The potential advantage of this is that it allows for a simulated hyper-spectral TDI (time delayed integration) readout mode, where the number of components in the final hyper-spectral image is given by the number of rows or columns orthogonal to the direction of travel. If an ASIC is used that allows multiple energy bins per row or column then the number of components will be the multiple of the number of energy bins per row or column and the number of rows or columns.

According to an aspect of the present invention, there is provided an array of photon detection sensors for use in imaging scanning applications and that provide hyper-spectroscopic information about an imaged object. The array may be assembled from optimized configurations of pixelated sensors where each row or column is each assigned a specific energy sensing window, each of the pixels provide single photon detection capability and energy information about the photon interactions. The readout from the array is arranged to simulate a time delayed integration readout mode and thereby produces a continuous hyper- spectral image. The number of spectral image components relates to either the number of rows or columns of the linear array of photon detection sensors.

One or more embodiments of the present invention may also provide a scanning imaging system, apparatus and method for capturing contiguous spectral bands in the x-ray region of the electromagnetic spectrum.

In the case of an object moving on a conveyor relative to a scanner, the part of the object that was over pixel p(n) at time t(i) moves to be over pixel p(n+l), the next column along, at time t(i+l). For reasons of minimizing motion blur it is sensible to restrict the relative movement to half of one pixel per integration period. If the speed of the conveyor is synchronized in this way then information is collected from each pixel wide region of the transient object that relate to photon transmissions of the energy range specific to each column.

An ASIC may comprise 256 columns orthogonal to the direction of travel of the object to be imaged. In such a case the spectral range of interest may be divided into 256 discrete ranges and each column tuned to a specific range. As the object transits the ASIC, information is obtained on each of the 256 energy bins. Hence, 256 column wide image strips are obtained, each relating to a different energy bin. These can then be joined together to form a continuous hyper-spectral image of the transient object. These different images can be combined in various way so as to enhance the contrast between different materials e.g. to provide better discrimination of the contraband or potential terrorist related materials.

One or more embodiments of the present invention are arranged to provide apparatus, systems and methods which allow identification decisions to be based not only on extracted outline and shape parameters etc. but on estimates of material density and atomic number. In addition to then- potential as a basis for quantitative analysis, hyperspectral images may be useful in providing enhanced images for visual inspection. As incident photon energy increases the relative contrast between materials of different densities diminishes (merely as a side effect of their mass energy transmission coefficients). Increasing the x-ray peak energy in order to be able to see through denser material is problematic since there is a possibility of losing the ability to distinguish between materials whose attenuation characteristics are similar. However, by retaining the lower energy components, this relative contrast information is not discarded and optimum combinations of spectral images may be devised which emphasize these material differences. Therefore, one or more embodiments of the present invention can provide operators with displays in which the important differences are highlighted rather than masked as a side effect of the imaging process.

An aspect of the present invention relates to an X-ray scanning approach that greatly increases information available. This is particularly significant in security and baggage scanning applications, where there are competing demands for low false alarm rates and high detection accuracy. Due to the high sensitivity of the underlying hybrid imagers this additional information is acquired in the same time as current baggage scans and therefore maintains the throughput necessary for current levels of security operations.

Such a system, method and apparatus may provide increased detail about the X-ray imaged article by adding full spectrum transmission information to the standard density information normally gathered. Since the spectral transmission data of materials is characteristic, two new image analysis areas are enabled: 1) Analysis of an item's shape by similarity of spectral response; and 2) Analysis / identification of a material of concern by its characteristic spectral response. Analysis 1) may offer the potential for seeing items which have been deliberately hidden by higher density screening materials or whose density has been artificially modified to obscure an outline. Analysis 2) may allow for differentiation and selection for further analysis of items with similar density responses, but differing spectral responses.

The system, methods and apparatus according to one or more embodiments of the present invention also allow use of higher energy (more penetrating) X-rays, without the current drawback of reduction in contrast steps between materials of different densities. Hence the system can overcome efforts to mask or shield items while maintaining high contrast to help an operator.

Existing image processing techniques can be adapted by way of one or more embodiments of the present invention to take advantage of the full spectrum information available for use in the field of remote sensing and target identification. This may facilitate the automatic highlighting of contraband and may reduce false alarm rates. The hyperspectral X-ray imaging system, method and apparatus according to one or more embodiments of the present invention may provide an upgrade to X-ray baggage scanning capabilities, while maintaining the same infrastructure and operating procedures so that operator re-training is unnecessary, requiring merely a knowledge of the new capabilities that the system will provide, and establishing standard operating procedures for the new classes of alert which can be raised.

According to another aspect of the present invention, there is provided a scanning photon detection device comprising an array of photon detection cells wherein a set energy sensitivity range of the photon detection cells to incident photon energies may be adjustable on a columnar or row-wise basis.

The sensitivity of the photon detection cells may be set in accordance with a lower and upper threshold for each row and column.

Multiple sensitivity levels may be set per row and/or column.

A signal output from a sensitised photon detection ceil may be used to increment a digital counter to hold a digital representation of the number of photons incident within a period of time of interest that lie within the energy sensitivity range thereby forming a scanning photon counting device.

The readout of the device may be synchronized with the relative movement between a scanned object and the array of photon counting detection cells.

Further, a relative motion of an object to be scanned may be orthogonal to the rows or columns of the array of photon detection cells.

Also, the readout of the device may be synchronized where the relative movement of the scanned object is less than or equal to half the relative distance traversed across a photon counting detection cell.

The scanning photon detection device may comprise a linear array formed from a plurality of hybrid photon detection devices.

The linear array may be formed from a plurality of hybrid photon detection devices arranged in a stacked ladder configuration.

One or more embodiments of the present invention may also provide a scanning photon counting device, where a linear array is formed form a plurality of hybrid photon counting devices.

The present invention is described further hereinafter, by way of example only, with reference to the accompanying drawings.

Fig. 1 illustrates a schematic diagram of a scanning imaging apparatus employing a hyperspectral imaging scanning latter;

Fig. 2 illustrates a schematic view of a hybrid high-energy radiation detector and photon count graph for such a detector;

Fig. 3 illustrates the underside of a detector substrate and a cross section through a solder bump;

Fig. 4 illustrates a detective quantum efficiency (DQE) curve for a CdTe hybrid sensor;

Fig. 5 illustrates a tile (pixel) of a hyperspectral imaging ladder, the pixel energy response, and a schematic view of elements coupled to the pixel;

Fig. 6 illustrates a tile and column of a hyperspectral imaging ladder;

Fig. 7 illustrates a schematic view of a time delay integration (TDI) readout; and

Fig. 8 illustrates a schematic view of a TDI image view being built on a strip basis.

Fig. 1 illustrates the main components of a scanning imaging system 100 based on a hyperspectral imaging ladder. What is not shown is the illuminating x-ray source. The exact nature of the source will be application dependent; baggage scanning applications tend to use relatively low peak energy x-ray sources. Container and industrial inspection applications tend to use much higher peak energies. Importantly, the hyperspectral sensor imposes no particular constraints in relation to the x-ray source. Consequently, such sensors can be retrofitted to existing equipment.

Fig. 1 illustrates a conveyor system 102 on which an object 104 to be imaged is placed. This object is then translated by the conveyor over the imager, passing between the x-ray source (not shown) and an imaging ladder 106. The imaging ladder 106 is shown on the bottom of the configuration; however the position is arbitrary. Indeed multiple such sensors may be employed if required by system geometry or reconstruction requirements. The only requirement is that the imaged object passes between the ladder and the x-ray source. Thus, in an optional arrangement, the object to be imaged remains stationary and the x-ray source and imaging ladder are moved relative to the object. Further optionally, the object, X-ray source and imaging ladder may all move. The expanded section of Fig. 1 shows the side view of an imaging ladder which is fabricated by tiling multiple hybrid sensors (described further below).

A hybrid high-energy radiation detector 108, as illustrated in Figs. 2 and 3, is constructed from a semi-conductor substrate 110 (e.g. CdTe, Si, CZT, GaAs) and a readout ASIC 1 12. In hybrid devices, such as that illustrated, the ASIC 112 is directly bonded (flipcm^'p bonded) to the underside of the detector substrate 110. A set of solder bumps 114 connect the input of the ASICs 112 to a pixelated underside of the substrate 110. Photons 116, such as, for example, those in the X-ray and gamma-ray regions of the electromagnetic (EM) spectrum, incident on the device, interact with the semi-conductor substrate creating a cloud of electron hole pairs. A drift potential (not shown) applied across the substrate 110 results in the movement of this charge, which in turn induces a charge in the collection station of the ASIC 112. Hence, the charge collected at the inputs to the ASIC 1 12 corresponds to the particular volume of detector substrate 110 lying directly above the input, i.e. each ASIC channel fields data from one pixel within the detector.

The ASICs on such hybrid radiation detectors are generally categorised in terms of how they deal with this induced charge. Charge integration ASICs merely collect the induced charge, whereas photon counting variants accrue the number of incident photons which lie between particular energy ranges (bins).

It will be appreciated that ladders of such devices can be formed by tiling both kind of hybrid devices one above the other.

In addition to the flexible nature of their construction, i.e. the ability to use different substrates for different applications, CZT (CdZnTe) hybrid detectors have a significant sensitivity advantage when compared with alternate digital x-ray sensors e.g. scintillators/ccd. Fig. 4 illustrates that the detective quantum efficiency (DQE) curve of a CdTe hybrid sensor approaches the theoretical maximum. For baggage scanning systems high sensitivity relate to an increased throughput while maintaining image quality, i.e. signal-to-noise ratio (SNR).

As discussed above in relation to Fig. 2, the ASICs on the hyperspectral ladders are optionally photon counting ASICs. One photon counting pixel is normally configured to provide information about photon hits that He in a particular energy range, i.e. between a high and low threshold. However, this need not be the case, and a plurality of photon counting pixels may be arranged in an array, with the array operative to provide information about photon hits that lie in the particular energy range. Other one or more arrays may be operative to provide information about photon hits that lie in other one or more particular energy ranges. Optionally, one or more arrays may be configured with pixels thereof in a columnar (e.g. linear or ladder) arrangement, and with such arrays located in a transverse direction to a direction of motion of the object to be scanned.

Fig. 5 illustrates a configuration of one tile of a hyperspectral imaging ladder 120 (or column of an ASIC). Each pixel 118 in the in the ASIC is configured to register incident photons thereat (or "hits") in a particular energy range of interest. Fig. 5 also illustrates a device for detecting the number of incident photons at a pixel 118. This device comprises a pre-amplifier 122 coupled to a pulse shaping unit 124, where the pulse shaping unit 124 is operative to remove depth of interaction effects. The pulse shaping unit 124 is coupled to a discriminator 126 which is operative to increment a digital counter 128. Following each exposure period, the digital counter 128 is read and reset to zero.

i s The device for detecting the number of incident photons is typically implemented in the ASIC, there generally being one device for each pixel. Examples of such detector tiles, ASICs and ladder arrangements are disclosed in EP 1801616, the teaching of which is incorporated herein by reference.

In an optional arrangement, a device for charge collection and integration is typically implemented in the ASIC, there generally being one device for each pixel. Examples of such detector tiles, ASICs and ladder arrangements are disclosed in WO 2007/144589, the teaching of which is incorporated herein by reference.

A map can be provided using this device illustrated in Fig. 5, on a pixel by pixel basis, of the incident photons between predefined energy ranges. The pixel energy response may be tuneable to respond to photons within a certain energy range.

In an optional arrangement of the hyperspectral imaging ladder, the high and low thresholds are organised on a columnar basis as illustrated in Fig, 6, where an nth column 130 and a pixel 131 of that column 130 are illustrated. Each column of the ASIC comprises a plurality of pixels, and each column 130 is tuned to provide information between a particular high and low energy range. Lines 132 and 132 represent the edges of column 130. This allows for a hyperspectral TDI (time delayed integration) readout mode by combining the outputs of each column.

Fig. 7 illustrates an object 136 imaged on a conveyor 138. The object 136 is irradiated with radiation 140 from a high-energy radiation emitter (not shown). The conveyor 138 is operative to convey the object in a direction indicated by arrow A. Thus, the part 142 of the object 136 that was over column p(n) of a high-energy radiation detector at time t(n) (illustrated in upper figure of Fig. 7) moves to be over column/? (71+/,) of the high-energy radiation detector(i.e. the next column along), at time t(n+J) (illustrated in lower figure of Fig. 7). For reasons of minimizing motion blur, the relative movement between readouts of the high-energy radiation detector may optionally be limited to half of one pixel per integration period. If the speed of the conveyor 138 is synchronized in this way then information is collected from each pixel per column of the radiation detector of the transient object that relate to photon transmissions of the energy range specific to each column. For an ASIC with 256 columns orthogonal to the direction of travel of the object to be imaged, the spectral range of interest may be divided into 256 discrete ranges and each column tuned to a specific range. As the object transits the ASIC, information is obtained on each of the 256 energy bins. Hence, 256 column wide image strips are obtained, with each relating to a different energy bin. As illustrated in Fig. 8, these can then be joined together to form a continuous hyperspectral image 144 of the transient object. In the example given above this hyperspectral image will contain 256 images of the imaged object, each image corresponding to a different range of incident photon energies. These different images can be combined in various way so as to enhance the contrast between different materials e.g. to provide better discrimination of the contraband or potential terrorist related materials, material identification, back-scatter explosive detection etc.

As described above, images are combined to form a continuous hyperspectral image 144 (or hyperspectral imaging datacube) of the transient object. Established approaches for the analysis of hyperspectral imaging datacubes, principal component analysis, PLS-DA (partial least squares discriminate analysis) and SIMCA (Soft Independent Modelling of Class Analogy)) are described in, for example, "Segmented Principal Components Transformation for Efficient Hyperspectral Remote-Sensing Image Display and Classification", by Xiuping Jia, John A. Richards, (IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 37, NO. 1, JANUARY 1999), and in "Near- infrared hyperspectral reflectance imaging for detection of bruises on pickling cucumbers" by Diwan P, Arianaa, Renfu Lua and Daniel E. Guyerb, (Computers and Electronics in Agriculture Volume 53, Issue 1, August 2006, Pages 60-70).

The above scanning imaging system is described with a high-energy, i.e. an illuminating X-ray emission source. However, this need not be the case and other types of high-energy radiation emission sources may be used. For example, other types of high-energy EM radiation source, such as gamma-ray sources or sources which emit EM radiation in a Tera-Hertz (THz) frequency range. Also, alpha-ray and/or beta-ray and/or neutron emission sources may optionally or additionally be used.

As will be appreciated, one or more objects can be imaged using the system descried above. Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the scope of protection sought is not limited to those precise embodiments. As such, many modifications and variations will be apparent to practitioners skilled in this art. Accordingly, it is intended that the scope of the protection sought be defined by the following claims and their equivalents. Furthermore, it is contemplated that a particular feature described either individually or as part of an embodiment can be combined with other individually described features, or parts of other embodiments, even if the other features and embodiments make no mention of the particular feature. Thus, the absence of describing combinations should not preclude the inventor from claiming rights to such combinations.

Insofar as embodiments of the invention described above are implement able, at least in part, using a software- controlled programmable processing device such as a general purpose processor or special-purposes processor, digital signal processor, microprocessor, or other processing device, data processing apparatus or computer system it will be appreciated that a computer program for configuring a programmable device, apparatus or system to implement the foregoing described methods, apparatus and system is envisaged as an aspect of the present invention. The computer program may be embodied as any suitable type of code, such as source code, object code, compiled code, interpreted code, executable code, static code, dynamic code, and the like. The instructions may be implemented using any suitable high- level, low-level, object-oriented, visual, compiled and/or interpreted programming language, such as C, C++, Java, BASIC, Perl, Matlab, Pascal, Visual BASIC, JAVA, ActiveX, assembly language, machine code, and so forth. A skilled person would readily understand that term "computer" in its most general sense encompasses programmable devices such as referred to above, and data processing apparatus and computer systems.

Suitably, the computer program is stored on a carrier medium in machine readable form, for example the carrier medium may comprise memory, removable or non-removable media, erasable or non-erasable media, writeable or re-writeable media, digital or analog media, hard disk, floppy disk, Compact Disk Read Only Memory (CD-ROM), Company Disk Recordable (CD-R), Compact Disk Rewriteable (CD-RW), optical disk, magnetic media, magneto -optical media, removable memory cards or disks, various types of Digital Versatile Disk (DVD) subscriber identify module, tape, cassette solid-state memory. The computer program may be supplied from a remote source embodied in the communications medium such as an electronic signal, radio frequency carrier wave or optical carrier waves. Such carrier media are also envisaged as aspects of the present invention.

As used herein any reference to "one embodiment" or "an embodiment" means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

In addition, use of "a" or "an" are employed to describe elements and components of the invention. This is done merely for convenience and to give a general sense of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

Claims

1. A scanning system for imaging one or more objects, comprising: an imaging element; a conveyor for providing relative movement between an object to be scanned and said imaging element; said imaging element comprising a high-energy radiation emitter and a high-energy radiation detector spaced from the high-energy radiation emitter to allow passage of the object to be scanned between the high-energy radiation emitter and radiation detector, and the high-energy radiation detector operative to receive radiation emitted from said high-energy radiation emitter and incident on said object; wherein said high-energy radiation detector comprises two or more detection elements disposed in a direction of relative motion of the object to be scanned and said imaging element, with each detection element operative to detect high-energy radiation received at the high- energy radiation detector in a particular energy range.

2. A scanning system according to Claim 1, wherein each of said two or more detection elements comprises an array of detection pixels.

3. A scanning system according to Claim 2, wherein each of said detection pixels comprise: a detector substrate for generating charge responsive to high-energy incident radiation, said detector substrate configured to form a high-energy radiation sense volume; and a circuit substrate supporting a read-out circuit corresponding to said sense volume and operative to count photons incident upon a corresponding sense volume, said read-out circuit including count incrementing circuitry for incrementing a photon count of photons incident upon a corresponding sense volume responsive to a radiation photon interaction event in a said corresponding sense volume; wherein said read-out circuit is operative to output a detection value corresponding to a number of photons incident upon a corresponding sense volume.

4. A scanning system according to Claim 2, wherein each of said detection pixels comprise: a detector substrate for generating charge responsive to high-energy incident radiation, said detector substrate configured to form a high-energy radiation sense volume; and a circuit substrate supporting a read-out circuit corresponding to said sense volume and operative to collect charge from a corresponding sense volume, said read-out circuit including charge integration circuitry for integrating charge of a corresponding sense volume responsive to a radiation photon interaction event in a said corresponding sense volume; wherein said read-out circuit is operative to output a detection value corresponding to a charge of a corresponding sense volume.

5. A scanning system according to any of the preceding claims, wherein a first of said two or more detection elements is operative to detect radiation in a first energy range between a first energy level and a second energy level, and a second of said two or more detection elements is operative to detect radiation in a second energy range between said second energy level and a third energy level.

6. A scanning system according to Claim 5, wherein an nth of said two or more detection elements is operative to detect radiation in an nth energy range between an nth energy level and an n+lth energy level.

7. A scanning system according to Claim 5 or 6, wherein n-lth and nth energy ranges are adjacent.

8. A scanning system according to any of Claims 5 to 7, wherein n-lth and nth energy ranges are contiguous.

9. A scanning system according to any of the preceding claims, wherein said two or more detection elements are configured in a columnar arrangement transverse to a direction of relative motion of the object to be scanned and said imaging element.

10. A scanning system according to Claim 9, when directly or indirectly dependent upon Claim 2, wherein detection pixels forming said array are configured in a linear arrangement.

1 1. A scanning system according to Claim 10, wherein said array is located in a plane substantially parallel to a plane in which said object to be scanned is arranged to move relative to the imaging element.

12. A scanning system according to Claim 2, and any of Claim 3 to 1 1, when directly or indirectly dependent upon Claim 2, wherein a speed at which the object to be scanned is advanced relative to the imaging element is substantially equal to one half of a width of a pixel.

13. A scanning system according to Claim 2, and any of Claim 3 to 12, when directly or indirectly dependent upon Claim 2, wherein a number of detection pixels in said array comprise 256.

14. A scanning system according to any of the preceding claims, wherein radiation emitted by said high-energy radiation emitter comprises one or more of the following: high- energy electro-magnetic (EM) radiation; or neutron radiation.

15. A scanning system according to Claim 14, wherein said high-energy EM radiation comprises: EM radiation in an X-ray region and/or a gamma-ray region of an EM spectrum.

16. A scanning system according to any of the preceding claims, wherein the particular energy range over which each one of the two or more detection elements is operative to detect radiation is adjustable.

17. A scanning system according to any of the preceding claims, wherein the high-energy radiation detector is arranged for coupling to an image compiler, and where the image compiler is operative to receive output data from the high-energy radiation detector to prepare an image of an object scanned in the scanning system.

18. A scanning system according to Claim 17, wherein said output data from each one of said two or more detection elements at a particular time represents a particular energy range image of a particular part of the object to be scanned which is adjacent to the said one of said two or more detection elements at the particular time,

19. A scanning system according to Claim 17 or 18, wherein said image compiler is operative to perform time delay integration on said output data for preparation of a hyperspectral image comprising a combination of particular energy range images of each particular part of the object to be scanned from each of said two or more detection elements.

20. A scanning system according to Claim 19, wherein a number of spectral image components of said hyperspectral image corresponds to a number of detection elements.

21. A high-energy radiation detector for a scanning system for imaging one or more objects, the high-energy radiation detector operative to receive radiation emitted from a high- energy radiation emitter and incident on said object; wherein said high-energy radiation detector comprises two or more detection elements disposed in a direction of relative motion of the object to be scanned and said high-energy radiation detector, with each detection element operative to detect high-energy radiation received at the high-energy radiation detector in a particular energy range.

22. A high-energy radiation detector according to Claim 21, wherein each of said two or more detection elements comprises an array of detection pixels.

23. A high-energy radiation detector according to Claim 22, wherein each of said detection pixels comprise: a detector substrate for generating charge responsive to high-energy incident radiation, said detector substrate configured to form a high-energy radiation sense volume; and a circuit substrate supporting a read-out circuit corresponding to said sense volume and operative to count photons incident upon a corresponding sense volume, said read-out circuit including count incrementing circuitry for incrementing a photon count of photons incident upon a corresponding sense volume responsive to a radiation photon interaction event in a said corresponding sense volume; wherein said read-out circuit is operative to output a detection value corresponding to a number of photons incident upon a corresponding sense volume.

24. A high-energy radiation detector according to Claim 22, wherein each of said detection pixels comprise: a detector substrate for generating charge responsive to high-energy incident radiation, said detector substrate configured to form a high-energy radiation sense volume; and a circuit substrate supporting a read-out circuit corresponding to said sense volume and operative to collect charge from a corresponding sense volume, said read-out circuit including charge integration circuitry for integrating charge of a corresponding sense volume responsive to a radiation photon interaction event in a said corresponding sense volume; wherein said read-out circuit is operative to output a detection value corresponding to a charge of a corresponding sense volume.

25. A high-energy radiation detector according to any of Claims 21 to 24, wherein a first of said two or more detection elements is operative to detect radiation in a first energy range between a first energy level and a second energy level, and a second of said two or more detection elements is operative to detect radiation in a second energy range between said second energy level and a third energy level.

26. A high-energy radiation detector according to Claim 25, wherein an nth of said two or more detection elements is operative to detect radiation in an nth energy range between an nth energy level and an n+lth energy level.

27. A high-energy radiation detector according to Claim 26, wherein n-lth and nth energy ranges are adjacent.

28. A high-energy radiation detector according to any of Claims 25 to 27, wherein n-lth and nth energy ranges are contiguous.

29. A high-energy radiation detector according to any of the preceding claims, wherein said two or more detection elements are configured in a columnar arrangement transverse to a direction of relative motion of the object to be scanned and said high-energy radiation detector.

30. A high-energy radiation detector according to Claim 29, when directly or indirectly dependent upon Claim 22, wherein detection pixels forming said array are configured in a linear arrangement.

31. A high-energy radiation detector according to Claim 30, wherein said array is located in a plane substantially parallel to a plane in which said object to be scanned is arranged to move relative to the high-energy radiation detector.

32. A high-energy radiation detector according to Claim 22, and any of Claim 23 to 31, when directly or indirectly dependent upon Claim 22, wherein a speed at which the object to be scanned is advanced relative to the high-energy radiation detector is substantially equal to one half of a width of a pixel.

33. A high-energy radiation detector according to Claim 22, and any of Claim 23 to 32, when directly or indirectly dependent upon Claim 22, wherein a number of detection pixels in said array comprise 256.

34. A high-energy radiation detector according to any one of Claims 21 to 33, wherein radiation emitted by said high-energy radiation emitter comprises one or more of the following: high-energy electro -magnetic (EM) radiation; or neutron radiation.

35. A high-energy radiation detector according to Claim 34, wherein said high-energy EM radiation comprises EM radiation in an X-ray region and/or a gamma-ray region of an EM spectrum.

36. A high-energy radiation detector according to any of Claims 21 to 35, wherein the particular energy range over which each one of the two or more detection elements is operative to detect radiation is adjustable.

37. A high- energy radiation detector according to any of Claims 21 to 36, wherein the high- energy radiation detector is arranged for coupling to an image compiler, and where the image compiler is operative to receive output data from the high-energy radiation detector to prepare an image of an object scanned in the scanning system.

38. A high-energy radiation detector according to Claim 37, wherein said output data from each one of said two or more detection elements at a particular time represents a particular energy range image of a particular part of the object to be scanned which is adjacent to the said one of said two or more detection elements at the particular time,

39. A high-energy radiation detector according to Claim 37 or 38, wherein said image compiler is operative to perform time delay integration on said output data for preparation of a hyperspectral image comprising a combination of particular energy range images of each particular part of the object to be scanned from each of said two or more detection elements.

40. A high-energy radiation detector according to Claim 39, wherein a number of spectral image components of said hyperspectral image corresponds to a number of detection elements.

41. An image compiler for coupling to the high-energy radiation detector of any of Claims 21 to 40, wherein the image compiler is operative to receive output data from the high- energy radiation detector to prepare an image of an object scanned in the scanning system.

42. An image compiler according to Claim 41, wherein said image compiler is operative to perform time delay integration on said output data for preparation of a hyperspectral image comprising a combination of particular energy range images of each particular part of the object to be scanned from each of said two or more detection elements.

43. An image compiler according to Claim 42, wherein a number of spectral image components of said hyperspectral image corresponds to a number of detection elements of said high-energy radiation detector.

44. A method of imaging one or more objects, comprising: moving an object to be scanned relative to an imaging element; said imaging element comprising a high-energy radiation emitter and a high-energy radiation detector spaced from the high-energy radiation emitter to allow passage of the object to be scanned between the high-energy radiation emitter and radiation detector; emitting high-energy radiation from said emitter; receiving, at said high-energy radiation detector, radiation emitted from said high-energy radiation emitter and incident on said object; wherein said high-energy radiation detector comprises two or more detection elements disposed in a direction of relative motion of the object to be scanned and said imaging element, with each detection element operative to detect high-energy radiation received at the high-energy radiation detector in a particular energy range.

45. A method according to Claim 44, further comprising generating charge, in a detector substrate of each detection pixel of an array of detection pixels of said detection elements, responsive to high-energy incident radiation, said detector substrate configured to form a high-energy radiation sense volume; and incrementing, in a circuit substrate supporting a read-out circuit corresponding to said sense volume and operative to count photons incident upon a corresponding sense volume, a photon count of photons incident upon a corresponding sense volume responsive to a radiation photon interaction event in a said corresponding sense volume; outputting, from said read-out circuit a detection value corresponding to a number of photons incident upon a corresponding sense volume.

46. A method according to Claim 44, further comprising generating charge, in a detector substrate of each detection pixel of an array of detection pixels of said detection elements, responsive to high-energy incident radiation, said detector substrate configured to form a high-energy radiation sense volume; collecting charge, in a circuit substrate supporting a read-out circuit corresponding to said sense volume and operative to collect charge from a corresponding sense volume; integrating, in charge integration circuitry of said read-out circuit, charge of a corresponding sense volume responsive to a radiation photon interaction event in a said corresponding sense volume; outputting, from said read-out circuit a detection value corresponding to a charge of a corresponding sense volume.

47. A method according to any of Claims 44 to 46, comprising detecting radiation in a first energy range between a first energy level and a second energy level, and detecting radiation in a second energy range between said second energy level and a third energy level.

48. A method according to Claim 47, further comprising detecting radiation in an nth energy range between an nth energy level and an n+lth energy level.

49. A method according to Claim 47 or 48, wherein n-lth and nth energy ranges are adjacent.

50. A method according to any of Claims 47 to 49, wherein n-lth and nth energy ranges are contiguous.

51. A method according to scanning system according to Claim 45 or 46, and any of Claim 47 to 50, when directly or indirectly dependent upon Claim 45 or 46, comprising advancing said object to be scanned relative to an imaging element at a speed substantially equal to one half of a width of a pixel.

52. A method according to any of Claims 44 to 51, further comprising outputting data from the high-energy radiation detector to an image compiler, and, in the image compiler, preparing an image of a scanned object.

53. A method according to Claim 52, further comprising performing, in said image compiler, time delay integration on said output data for preparation of a hyperspectral image comprising a combination of particular energy range images of each particular part of the object to be scanned from each of said two or more detection elements.

54. A method according to Claim 53, wherein a number of spectral image components of said hyperspectral image corresponds to a number of detection elements.