CA2277251A1 - High efficiency colour x-ray imaging system - Google Patents
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- CA2277251A1 CA2277251A1 CA 2277251 CA2277251A CA2277251A1 CA 2277251 A1 CA2277251 A1 CA 2277251A1 CA 2277251 CA2277251 CA 2277251 CA 2277251 A CA2277251 A CA 2277251A CA 2277251 A1 CA2277251 A1 CA 2277251A1
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B42/00—Obtaining records using waves other than optical waves; Visualisation of such records by using optical means
- G03B42/02—Obtaining records using waves other than optical waves; Visualisation of such records by using optical means using X-rays
Abstract
A line scan imaging system incorporating a source of ionizing electromagnetic radiation, such as X-rays or gamma rays, which use an improved microstrip gas counter as a detector. The microstrip gas counter detector provides very high efficiency to detect essentially all the incident radiation, and a simple and reliable inherent capability to discriminate and quantify the energy of the incident radiation. Thus, the microstrip gas counter detector provides colour images at low cost and complexity. The system may be used in a wide variety of applications including digital radiography, computed tomography, food inspection and grading, printed circuit board assembly inspection, wood processing, baggage inspection, and security systems.
Description
HIGH EFFICIENCY COLOUR X-RAY IMAGING SYSTEM
FIELD
The present invention relates to a high efficiency colour x-ray imaging system for use in detecting ionizing electromagnetic radiation.
BACKGROUND
X-ray images of objects are generally obtained by means whereby X-rays from a point-source, typically from an X-ray generator tube, are transmitted through the object. An X-ray detector located on the opposite side of the object from the source detects those X-rays which pass through the object.
Different portions of the object absorb, or fail to absorb, different portions of the incident X-rays, in a statistical manner which depends on a variety of factors including the elemental composition, density, and thickness of the portion of the object through which any X-ray photon passes, and which also depends on the wavelength of any particular photon. By providing many separate elements in the X-ray detector, an image may be formed of those X-rays which pass through the object, thereby providing an image which contains information relating to the interior composition of the object.
An example of the detector is photographic film used in the familiar X-ray image, where the photographic film is itself directly responsive to X-radiation. A second example is the well-known image intensifier tube. A third example is the recently introduced "amorphous silicon" detector. In these cases, the detector images simultaneously over the entire area of the detector, whereby each pixel of the image corresponds to the intensity of the transmitted radiation, providing a monochrome two dimensional "gray scale" image.
In another type of implementation, an X-ray detector is provided which is capable of generating a single multi-pixel line of the image. By moving the object past the detector, or vice versa, an image can be built up line by line. This type of imaging is generally referred to by the term "line scan", and can be considerably more cost-effective, since the detector has far fewer pixels than that for an "area scan" imaging system. An example of this type of system is that commonly used in baggage X-ray systems, using a line scan technique by means of a linear array of photodiodes coated with a scintillating material such as powdered phosphor or crystalline Cesium Iodide. Again, in this example, a monochrome gray scale image is the result.
The methods mentioned above, and many others, have several characteristics which are non-optimal. Among these characteristics are the fact that the resultant images are monochrome, and contain little or no information about the wavelength (i.e. energy) of the incident radiation, even though the X-ray generator tube produces X-rays over a range of energies.
In order to provide wavelength information two methods have been used, namely either taking two images one after the other, and using a different high voltage to the X-ray tube for the two successive images, or taking a single image on two detectors located one above the other, with an interposing X-ray filter (e.g. a sheet of metal) so that only the "hard" X-rays reach the second detector. Either method is costly and cumbersome.
Also, the above methods and others are essentially analog in nature, making them incompatible in their basic form with the widespread trend to digital image processing and storage.
Furthermore, such methods prove difficult, and sometimes impossible, to provide images at a combination of high resolution and high speed of rapidly moving objects. Finally, for a variety of reasons, they tend to have the feature that they fail to capture a significant portion of the incident radiation.
Therefore, compared to an ideal detector, a higher X-ray flux is required for a given image quality, thus increasing the cost of the source and the associated safety shielding, and in the case of X-ray images of living objects requiring a larger X-ray dose, at the expense of safety.
In 1968 the Multi-Wire Proportional Counter (MWPC) was developed by Charpak, among the work for which he won the Nobel Prize for Physics in 1992. Based fundamentally on the Geiger counter, it was fitted with multiple wires to provide spatial resolution. In the 1980's, Oed and others updated the technique by developing and refining the microstrip gas counter detector (MSGC), also called variously the gas microstrip counter (GMC) or the gas microstrip detector (GMD). Although this device was developed for use in high-energy particle physics research, it has been recognised that the principle could be used for X-ray imaging, and overcomes many of the disadvantages (enumerated above) of the methods currently in use.
The microstrip gas counter detector 10 shown in Fig 1A
comprises a sealed enclosure 12 filled with a gas mixture which absorbs X-rays resulting in ionization of the gas. The enclosure 12 is typically of such dimensions and/or is pressurized with gas to an extent that it absorbs a high proportion of the incident X-rays 14. Above the enclosure 12 is a collimator 16 with a slit 17, so that the X-ray beam width which interacts with the detector is limited to the dimension of the slit 17. After X-rays from a source il pass through slit 17 they impinge on a target 13 and enter enclosure 12. Inside the enclosure 12 is a drift electrode 18, constructed so that it is essentially transparent to X-rays.
The drift electrode 18 is held at a relatively large negative voltage by power supply 42 (see Fig. 1B), typically several thousand volts. Also inside the enclosure 12 is a substrate 20, typically made of glass, silicon, or plastic, upon which are deposited alternating cathodes 22 and anodes 24. Referring to Fig. 1B, all cathodes 22 are held at a common negative voltage by power supply 44, typically several hundred volts, while the anodes 24 are usually held at a voltage close to zero. Each anode 24 is connected to an amplifier 48 (see Fig. 1B) which transforms an electrical current pulse into a voltage pulse.
As an electromagnetic photon 15 (see Fig. 18) is absorbed by a gas molecule it ionizes the gas due to the photoelectric effect, and an electron cloud 36 is formed. The number of electrons and, therefore, the total charge is proportional to the energy of the incident X-ray photon 15. The cloud 36 is very small in dimension, and each electron in the cloud 36 is immediately and very quickly attracted down towards the substrate 20 because of the drift electric field. As the cloud approaches the anodes 24 and cathodes 22, the electric field gradient becomes intense due to the small spacing between the anodes 24 and cathodes 22 and the voltage difference between them, resulting in a rapid electron multiplication effect. Eventually the multiplied charge is captured at the anode 22, resulting in a brief electrical current whose magnitude is proportional to the original incident X-ray photon energy. A current to voltage amplifier 48 converts the current pulse to a voltage pulse 46.
The entire process described in the foregoing is of a very brief duration, typically measured in tens of nanoseconds or less. Of course, for each electron there is a corresponding positive ion which moves in the opposite direction, and which contributes to the current. It may be noted in passing that it is the proximity of the anodes 24 to the cathodes 22 that permits the positive ions created in the avalanche to be rapidly removed prior to the next X-ray event, thus overcoming one of the limiting factors of the multi-wire proportional counter.
Referring to Fig. 1C, a number of parties (see US Patent 5,500,534 issued to Robinson et al.) have proposed that each anode 24 be connected to a current-to-voltage amplifier 48 followed by a multi-channel analyzer 32 to discriminate the pulses into multiple energy bands. Here the current-to-voltage amplifier 48 is combined with level discriminators 52, 54, and 56 and corresponding counters 58, 60, and 62 to provide a multi-channel analyzer 32. Each level discriminator 52, 54, and 56 receives the voltage pulse in analog form, and compares it to a threshold level T1, T2, ...TN for level discriminators 52, 54, and 56, respectively. The threshold levels T1, T2, ...TN represent minimum photon energy levels for passing a level discriminator and recording a count on a given counter. If a pulse exceeds a given threshold level Ti, it is passed onto a counter i where "i"
denotes a variable between 1 and N. Thus, the counter 1 contains a count for each voltage pulse exceeding a threshold voltage level T1. Similarly, counter 2 contains a count for each voltage pulse exceeding a threshold voltage T2 and counter N contains a count for each voltage pulse exceeding a threshold voltage TN. Either the counts in counter N can be subtracted from those in counter N-1 to give those signals exceeding threshold TN-1 and not TN.
Alternatively, logic can be used on the input to the counters to record only pulses exceeding a given threshold and not the higher thresholds. The counters 58, 60, and 62 are output on bus 64.
In brief, this technique results in a detector with a number of desirable characteristics. Firstly, with suitable gas dimensions and pressure, the efficiency in absorbing X-rays may be made very high without affecting the resolution, since the electrons are collected at the closest anode or anodes. Secondly, the response is extremely fast, since electrons flow freely through the gas, rendering the detector capable of imaging very fast targets. Thirdly, the resolution may be made very high by spacing the anodes and cathodes very close to each other.
Fourthly, the signal contains amplitude information relating to the energy of the incident X-ray. If the energy component is measured, a colour X-ray image may be formed, where visible colours may be used to represent different X-ray energy bands.
This may be extremely desirable in many applications where target object features of interest have different elemental composition.
Finally, since each individual photon event is captured, the device can be made inherently digital at the outset.
Since the original development of the microstrip gas counter detector, a variety of different adaptations have been developed, based on the same principle. In particular, the anodes and cathodes have been fabricated in different fashions. For example, in the gas microgap detector, the cathodes have been implemented as a plane surface, with the anode strips being deposited as pedestals on top of the cathode. In the gas microdot detector, the cathode has been similarly fabricated, with the anodes as small circular pedestal depositions on top. In another variant, in the Gas Electron Multiplier (GEM), there is an additional stage of amplification in the gas. However, these are details of fabrication, and the essential principle and characteristics are unchanged. Throughout the body of this document the term gas counter X-ray detector is to be understood as encompassing these, and potentially other, variants or derivatives based on the same principle of the microstrip gas counter detector.
The multi-channel analyzer technique described with respect to Fig. iC is a valid technique, but is relatively complex and expensive to implement in a practical commercial device. In particular, the multiple level discriminators 52, 54, and 56 require stable and precise analog circuitry capable of accurately detecting the amplitude of extremely short duration pulses. Each multiple level discriminator 52, 54, and 56 is complex and expensive, and the method requires a large quantity of such circuits, namely a number equal to the number of anodes multiplied by the number of energy bands.
It is often the aim of an X-ray imaging system to make the X-ray detector highly efficient, so that a high percentage of the incident X-rays are absorbed and detected. This reduces the necessary radiation dose in medical X-ray, also lowering the cost and increasing the reliability of the X-ray generator. This is normally done by increasing the gas pressure, and/or increasing the thickness of the gas. In the latter case, the effect is normally a penalty on resolution and spectral discrimination, since the electron avalanche has a greater probability of spreading further, thereby interacting with multiple anodes.
A disadvantage of the microstrip gas counter detector, as described above, is that incident radiation which is oblique to the plane of the detector may interact with the gas at any point in its travel through the gas, with a consequent penalty in resolution, as shown in Fig 1D. Radiation emanating from source 11 enters the detector gas enclosure 12 and interacts at point A.
The subsequent electron cloud provides a signal at anode A. If instead of interacting at point A it interacts at point B, the signal is produced primarily at anode B. Thus, the oblique rays have a lower precision of image resolution than those more normal to the detector substrate plane.
Accordingly, an object of the invention, is to provide an imaging system for ionizing electromagnetic radiation using gas microstrip gas counter detectors or their variants or derivatives, which provides a highly efficient detector to detect essentially all of the incident radiation, with minimal penalty in resolution and complexity, thereby improving the image quality for a given source radiation intensity, or conversely reducing the source intensity for a given image quality.
A further object of the invention is to provide an imaging system with a resolution which is essentially independent of the obliqueness of the incident radiation at any detection element of the detector.
It is yet a further object of the invention to achieve an improved simple method of providing spectral information in the image, in order to achieve low cost colour imaging.
SUMMARY OF THE INVENTION
According to the invention there is provided a gas counter for measuring radiation intensity from a radiation source along a linear segment. The gas counter has a collimator having an elongated slit in the path of the radiation which is operative to produce a thin fan-shaped beam, an enclosure for gas having a window for receiving the thin fan-shaped beam of radiation, a set of electrodes including anodes and a cathode both formed on a planar substrate and disposed parallel to and offset from a plane defined by the thin fan-shaped beam of radiation and electronic detecting and counting circuits operative to detect and count the electrical effect of a photon interaction with gas molecules in the enclosure so that the count per unit time is a measure of the radiation flux in a portion of the fan-shaped beam proximate an associated anode.
Advantageously, the cathode may be forked with its forks lying adjacent anodes, the anodes and cathode forks lying along a linear strip.
Preferably the anodes and cathode forks point towards the source of radiation.
The enclosure and the anodes and cathode forks may be sufficiently long so that substantially all of the incident radiation interacts with the gas and does not pass through the enclosure.
A drift electrode may be located parallel to the fan-shaped beam and offset therefrom on a side of the fan-shaped beam opposite from the electrodes.
Each of the anodes may be segmented into a plurality of segments with each segment having its own detecting and recording electronic circuit.
The length of the segments may be selected to detect incident radiation in a given energy band on a statistical basis.
In another aspect of the invention there is provided a method of forming an image of an object employing a source of ionizing electromagnetic radiation for use in irradiating the object and an elongated collimator intermediate the source and the object for producing a thin fan-shaped beam. The method includes moving the object relative to the source and substantially perpendicular to the radiation beam, positioning a detector selected from the group consisting of a microstrip, microgap and microdot gas counter and substitutes of microstrip, microgap and microdot gas counters comprising a gas enclosure in which is mounted a drift electrode. The anodes and cathodes are in close parallel proximity fabricated on a substrate, so as to intercept radiation after passing through the object and so that the orientation of anodes and adjacent cathode regions of the detector are substantially aligned with a direction of travel of the radiation and slightly offset therefrom. At each anode of the detector anode current is detected and recorded. The step of detecting and recording of anode current at each anode is repeated as the object moves. The detecting and recording of the position of the object is done at a sufficiently high rate such that the target object is imaged one cross-sectional slice at a time to build up a complete raster image of the object.
ADVANTAGES OF THE INVENTION
An advantage of the invention is that it may be used to produce high quality W, or X-ray, or gamma ray images with colour and high resolution, at high efficiency, low cost and with high reliability, in an essentially unlimited variety of applications, including digital radiography, computed tomography, food inspection and grading, printed circuit board assembly inspection, wood processing, baggage inspection, and security systems of many types, all of which benefit from the X-ray energy information, high resolution, high efficiency, and fast response speed at a relatively modest cost and compact package. The invention may be used in either one, two, or three dimensional imaging systems.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages will be apparent from the following detailed description, given by way of example, of a preferred embodiment taken in conjunction with the accompanying drawings, wherein:
Fig.lA is a perspective view of a microstrip gas counter detector;
Fig. 1B is front elevation view of a microstrip gas counter detector coupled with an anode current detector;
Fig. 1C is front elevation view of a microstrip gas counter detector coupled with a multi-channel analyzer;
Fig. 1D is a front elevation view of a microstrip gas counter detector showing the effect of early and late detection of an obliquely directed photon;
Fig. 2 is a perspective view of a microstrip gas counter detector with the electrodes oriented parallel to the plane of collimation of the radiation;
Fig. 3 is an end view of the assembly shown in Fig. 2;
Fig. 4 is front elevation view of a microstrip gas counter detector with its electrodes parallel to the plane of collimation of the radiation and the orientation of the anodes and adjacent cathode fingers pointing at the source of radiation;
Fig. 5 is front elevation view of a microstrip gas counter detector with its electrodes parallel to the plane of collimation of the radiation, the orientation of the anodes and adjacent cathode fingers pointing at the source of radiation and each anode split into two;
Fig. 6 is front elevation view of a microstrip gas counter detector with its electrodes parallel to the plane of collimation of the radiation, the orientation of the anodes and adjacent cathode fingers pointing at the source of radiation and the anodes split into three parts; and Fig. 7 is a top view of a microstrip gas counter detector which lies along a segment of a circle, whose electrodes are directed at a source and which is mounted together with the source for rotation about an object at diametrically opposite positions with respect to the object.
DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS
A preferred embodiment of the imaging system is depicted in various orientations in Figs 2, 3, and 4. The substrate is parallel to and slightly offset from the plane of the vertical collimated fan-shaped beam 14 passing through the slit 17 of the collimator 16. Note that although only a single collimator 16 is depicted, it is common in X-ray imaging systems, to employ more than one collimator. For example, referring to Fig. 3, one collimator 19 would be in front of the target 72 as shown by the dashed lines while the other collimator 16 is located on the other side as shown in Fig. 3. Two collimators are used to minimize the effects of radiation scattered from the target 72. On a planar substrate 78 located on one side of a gas enclosure 12 offset from a plane of fan-shaped beam 14 are individual anodes 76, and a furcated common cathode 74. The gas depth "d" and the anodes 76 and the forks, of cathode 74 are significantly longer than any previously used so that essentially all of the incident radiation undergoes interactions with the enclosed gas. A conveyor 73 moves the target or object 72 orthogonally to the direction of the incident beam 14. In Figure 4 a further refinement involves the anodes 76 pointing at the source 11 of radiation (e.g., the X-ray generator in the case of X-ray images). This gives two immediate advantages: First, because of the longer path through the gas, incident radiation is far more likely to interact with the gas and, therefore, be detected. Second, no matter where in the path through the enclosed gas chamber of any particular ionizing ray the gas interaction occurs, the same anode will detect the interaction, rendering the detector insensitive to the obliqueness of the radiation.
For any particular type of radiation, the gas enclosure depth "d" (as shown in Fig. 2) is made large enough that the probability of interaction is of the desired (high) value. As shown in Fig 3, the incident ray 14 interacts with the gas within the enclosure 12, and an electron cloud is produced, which then is drifted orthogonally to the incident ray 14 towards the substrate 78. Avalanching takes place in the vicinity of the anodes 76.
Because the beam 14 is collimated, the gas enclosure width "w"
(also known as the drift gap) can be made relatively small, and the time for the electron drift and avalanche phenomena is relatively brief and uniform, no matter where in the gas the interaction occurs.
An important advantage in the present geometry is that the incident radiation does not pass through the drift electrode, unlike the situation in a conventional MSGC. Therefore, the drift electrode 80 need not be transparent to X-rays, allowing it to be fabricated in a rugged fashion.
Fig. 5 shows a further refinement of the imaging system.
In this case, the anodes 84 are segmented into two pieces, and each segment is taken to its own signal processing circuit (not shown). Fig. 6 shows three anode segments 88a, 88b, and 88c with each segment also going to its own signal processing circuit consisting of amplifier 100, comparator 102 and counter 104. The value of the segments is to provide a spectral component to the received image, permitting in the case of visual images the assignment of arbitrary colours corresponding to energy bands.
For computer-analysis of the images in machine vision applications the spectral energy component may permit improved feature extraction.
The physical explanation of the operation of the imaging system of Figure 6 is as follows. An incident ray of low energy (i.e., longer wavelength) has a higher probability of interacting with the gas early in its path through the gas, near the upper segment 88a of the anode, whereas higher energy rays will tend to penetrate the early part of the path and be absorbed on average later in the path, over the lower segment of the anode 88c.
Intermediate energy rays will tend to interact over the middle portion of the anode 88b. Thus, the interaction with the gas tends by itself to sort on a statistical basis the interactions over different segments of each of anodes 88a, 88b, and 88c. By fitting each segment with its own amplifier 100, comparator 102, and counter 104 then one obtains energy information with simplicity and economy. The number of segments will be dictated by the various desired environment, factors, and parameters, including type and wavelength of radiation source, target object features of interest, and cost and space constraints.
Relative orthogonal motion between the target and the MSGC (see Fig. 2) permits a line image to be acquired at regular frequent intervals, and after a number of lines a complete raster scan image is obtained. As shown in Figs 5 and 6, each anode 84 has one or more segments, and each segment is connected to an amplifier 100 which converts the brief current pulse to a voltage pulse. The voltage pulse is then sent to a comparator 102 which then converts the voltage pulse to a digital pulse. The digital pulse is recorded by a counter 104 which counts the photon events for that anode segment, corresponding to a spatial point and an energy window. After counting the events for the time corresponding to the interval allowed for one scan line, the counters are read out and reset using routine well-known digital multiplexing techniques. Each count corresponds to the radiation flux in the energy band for a particular spatial point, and the counts may be imaged as monochrome or colour images, and/or stored for subsequent automated computer-based image analysis.
Referring to Fig. 7, in a tomography application, the anodes and cathodes of a semi-circular gas detector 87 may be oriented along a sector of a circle and aligned so as to point towards a diametrically opposite source 11 so that the radiation 14 passes through a stationary object 72. As both the source 11 and the gas detector 87 rotate together around the object a 360 degree scan of the object by the fan-shaped beam 14 is obtained.
It is to be noted that the anodes 88 and cathodes 74 may be fabricated side-by-side on the substrate 78, or alternatively the anodes 88 may be deposited on a pedestal above a common cathode, commonly known as gas microgap geometry.
It is also noted that the substrate 78 need not be rectangular as shown. It may in some applications for example be shaped as the concave arc of a circle, centred on the radiation source, so that each anode is equidistant from the source. In this case all anodes receive a similar amount of radiation flux, which can have advantages in equalizing dynamic range, and which is also appropriate when providing images in tomography applications (Fig. 7).
Accordingly, while this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.
FIELD
The present invention relates to a high efficiency colour x-ray imaging system for use in detecting ionizing electromagnetic radiation.
BACKGROUND
X-ray images of objects are generally obtained by means whereby X-rays from a point-source, typically from an X-ray generator tube, are transmitted through the object. An X-ray detector located on the opposite side of the object from the source detects those X-rays which pass through the object.
Different portions of the object absorb, or fail to absorb, different portions of the incident X-rays, in a statistical manner which depends on a variety of factors including the elemental composition, density, and thickness of the portion of the object through which any X-ray photon passes, and which also depends on the wavelength of any particular photon. By providing many separate elements in the X-ray detector, an image may be formed of those X-rays which pass through the object, thereby providing an image which contains information relating to the interior composition of the object.
An example of the detector is photographic film used in the familiar X-ray image, where the photographic film is itself directly responsive to X-radiation. A second example is the well-known image intensifier tube. A third example is the recently introduced "amorphous silicon" detector. In these cases, the detector images simultaneously over the entire area of the detector, whereby each pixel of the image corresponds to the intensity of the transmitted radiation, providing a monochrome two dimensional "gray scale" image.
In another type of implementation, an X-ray detector is provided which is capable of generating a single multi-pixel line of the image. By moving the object past the detector, or vice versa, an image can be built up line by line. This type of imaging is generally referred to by the term "line scan", and can be considerably more cost-effective, since the detector has far fewer pixels than that for an "area scan" imaging system. An example of this type of system is that commonly used in baggage X-ray systems, using a line scan technique by means of a linear array of photodiodes coated with a scintillating material such as powdered phosphor or crystalline Cesium Iodide. Again, in this example, a monochrome gray scale image is the result.
The methods mentioned above, and many others, have several characteristics which are non-optimal. Among these characteristics are the fact that the resultant images are monochrome, and contain little or no information about the wavelength (i.e. energy) of the incident radiation, even though the X-ray generator tube produces X-rays over a range of energies.
In order to provide wavelength information two methods have been used, namely either taking two images one after the other, and using a different high voltage to the X-ray tube for the two successive images, or taking a single image on two detectors located one above the other, with an interposing X-ray filter (e.g. a sheet of metal) so that only the "hard" X-rays reach the second detector. Either method is costly and cumbersome.
Also, the above methods and others are essentially analog in nature, making them incompatible in their basic form with the widespread trend to digital image processing and storage.
Furthermore, such methods prove difficult, and sometimes impossible, to provide images at a combination of high resolution and high speed of rapidly moving objects. Finally, for a variety of reasons, they tend to have the feature that they fail to capture a significant portion of the incident radiation.
Therefore, compared to an ideal detector, a higher X-ray flux is required for a given image quality, thus increasing the cost of the source and the associated safety shielding, and in the case of X-ray images of living objects requiring a larger X-ray dose, at the expense of safety.
In 1968 the Multi-Wire Proportional Counter (MWPC) was developed by Charpak, among the work for which he won the Nobel Prize for Physics in 1992. Based fundamentally on the Geiger counter, it was fitted with multiple wires to provide spatial resolution. In the 1980's, Oed and others updated the technique by developing and refining the microstrip gas counter detector (MSGC), also called variously the gas microstrip counter (GMC) or the gas microstrip detector (GMD). Although this device was developed for use in high-energy particle physics research, it has been recognised that the principle could be used for X-ray imaging, and overcomes many of the disadvantages (enumerated above) of the methods currently in use.
The microstrip gas counter detector 10 shown in Fig 1A
comprises a sealed enclosure 12 filled with a gas mixture which absorbs X-rays resulting in ionization of the gas. The enclosure 12 is typically of such dimensions and/or is pressurized with gas to an extent that it absorbs a high proportion of the incident X-rays 14. Above the enclosure 12 is a collimator 16 with a slit 17, so that the X-ray beam width which interacts with the detector is limited to the dimension of the slit 17. After X-rays from a source il pass through slit 17 they impinge on a target 13 and enter enclosure 12. Inside the enclosure 12 is a drift electrode 18, constructed so that it is essentially transparent to X-rays.
The drift electrode 18 is held at a relatively large negative voltage by power supply 42 (see Fig. 1B), typically several thousand volts. Also inside the enclosure 12 is a substrate 20, typically made of glass, silicon, or plastic, upon which are deposited alternating cathodes 22 and anodes 24. Referring to Fig. 1B, all cathodes 22 are held at a common negative voltage by power supply 44, typically several hundred volts, while the anodes 24 are usually held at a voltage close to zero. Each anode 24 is connected to an amplifier 48 (see Fig. 1B) which transforms an electrical current pulse into a voltage pulse.
As an electromagnetic photon 15 (see Fig. 18) is absorbed by a gas molecule it ionizes the gas due to the photoelectric effect, and an electron cloud 36 is formed. The number of electrons and, therefore, the total charge is proportional to the energy of the incident X-ray photon 15. The cloud 36 is very small in dimension, and each electron in the cloud 36 is immediately and very quickly attracted down towards the substrate 20 because of the drift electric field. As the cloud approaches the anodes 24 and cathodes 22, the electric field gradient becomes intense due to the small spacing between the anodes 24 and cathodes 22 and the voltage difference between them, resulting in a rapid electron multiplication effect. Eventually the multiplied charge is captured at the anode 22, resulting in a brief electrical current whose magnitude is proportional to the original incident X-ray photon energy. A current to voltage amplifier 48 converts the current pulse to a voltage pulse 46.
The entire process described in the foregoing is of a very brief duration, typically measured in tens of nanoseconds or less. Of course, for each electron there is a corresponding positive ion which moves in the opposite direction, and which contributes to the current. It may be noted in passing that it is the proximity of the anodes 24 to the cathodes 22 that permits the positive ions created in the avalanche to be rapidly removed prior to the next X-ray event, thus overcoming one of the limiting factors of the multi-wire proportional counter.
Referring to Fig. 1C, a number of parties (see US Patent 5,500,534 issued to Robinson et al.) have proposed that each anode 24 be connected to a current-to-voltage amplifier 48 followed by a multi-channel analyzer 32 to discriminate the pulses into multiple energy bands. Here the current-to-voltage amplifier 48 is combined with level discriminators 52, 54, and 56 and corresponding counters 58, 60, and 62 to provide a multi-channel analyzer 32. Each level discriminator 52, 54, and 56 receives the voltage pulse in analog form, and compares it to a threshold level T1, T2, ...TN for level discriminators 52, 54, and 56, respectively. The threshold levels T1, T2, ...TN represent minimum photon energy levels for passing a level discriminator and recording a count on a given counter. If a pulse exceeds a given threshold level Ti, it is passed onto a counter i where "i"
denotes a variable between 1 and N. Thus, the counter 1 contains a count for each voltage pulse exceeding a threshold voltage level T1. Similarly, counter 2 contains a count for each voltage pulse exceeding a threshold voltage T2 and counter N contains a count for each voltage pulse exceeding a threshold voltage TN. Either the counts in counter N can be subtracted from those in counter N-1 to give those signals exceeding threshold TN-1 and not TN.
Alternatively, logic can be used on the input to the counters to record only pulses exceeding a given threshold and not the higher thresholds. The counters 58, 60, and 62 are output on bus 64.
In brief, this technique results in a detector with a number of desirable characteristics. Firstly, with suitable gas dimensions and pressure, the efficiency in absorbing X-rays may be made very high without affecting the resolution, since the electrons are collected at the closest anode or anodes. Secondly, the response is extremely fast, since electrons flow freely through the gas, rendering the detector capable of imaging very fast targets. Thirdly, the resolution may be made very high by spacing the anodes and cathodes very close to each other.
Fourthly, the signal contains amplitude information relating to the energy of the incident X-ray. If the energy component is measured, a colour X-ray image may be formed, where visible colours may be used to represent different X-ray energy bands.
This may be extremely desirable in many applications where target object features of interest have different elemental composition.
Finally, since each individual photon event is captured, the device can be made inherently digital at the outset.
Since the original development of the microstrip gas counter detector, a variety of different adaptations have been developed, based on the same principle. In particular, the anodes and cathodes have been fabricated in different fashions. For example, in the gas microgap detector, the cathodes have been implemented as a plane surface, with the anode strips being deposited as pedestals on top of the cathode. In the gas microdot detector, the cathode has been similarly fabricated, with the anodes as small circular pedestal depositions on top. In another variant, in the Gas Electron Multiplier (GEM), there is an additional stage of amplification in the gas. However, these are details of fabrication, and the essential principle and characteristics are unchanged. Throughout the body of this document the term gas counter X-ray detector is to be understood as encompassing these, and potentially other, variants or derivatives based on the same principle of the microstrip gas counter detector.
The multi-channel analyzer technique described with respect to Fig. iC is a valid technique, but is relatively complex and expensive to implement in a practical commercial device. In particular, the multiple level discriminators 52, 54, and 56 require stable and precise analog circuitry capable of accurately detecting the amplitude of extremely short duration pulses. Each multiple level discriminator 52, 54, and 56 is complex and expensive, and the method requires a large quantity of such circuits, namely a number equal to the number of anodes multiplied by the number of energy bands.
It is often the aim of an X-ray imaging system to make the X-ray detector highly efficient, so that a high percentage of the incident X-rays are absorbed and detected. This reduces the necessary radiation dose in medical X-ray, also lowering the cost and increasing the reliability of the X-ray generator. This is normally done by increasing the gas pressure, and/or increasing the thickness of the gas. In the latter case, the effect is normally a penalty on resolution and spectral discrimination, since the electron avalanche has a greater probability of spreading further, thereby interacting with multiple anodes.
A disadvantage of the microstrip gas counter detector, as described above, is that incident radiation which is oblique to the plane of the detector may interact with the gas at any point in its travel through the gas, with a consequent penalty in resolution, as shown in Fig 1D. Radiation emanating from source 11 enters the detector gas enclosure 12 and interacts at point A.
The subsequent electron cloud provides a signal at anode A. If instead of interacting at point A it interacts at point B, the signal is produced primarily at anode B. Thus, the oblique rays have a lower precision of image resolution than those more normal to the detector substrate plane.
Accordingly, an object of the invention, is to provide an imaging system for ionizing electromagnetic radiation using gas microstrip gas counter detectors or their variants or derivatives, which provides a highly efficient detector to detect essentially all of the incident radiation, with minimal penalty in resolution and complexity, thereby improving the image quality for a given source radiation intensity, or conversely reducing the source intensity for a given image quality.
A further object of the invention is to provide an imaging system with a resolution which is essentially independent of the obliqueness of the incident radiation at any detection element of the detector.
It is yet a further object of the invention to achieve an improved simple method of providing spectral information in the image, in order to achieve low cost colour imaging.
SUMMARY OF THE INVENTION
According to the invention there is provided a gas counter for measuring radiation intensity from a radiation source along a linear segment. The gas counter has a collimator having an elongated slit in the path of the radiation which is operative to produce a thin fan-shaped beam, an enclosure for gas having a window for receiving the thin fan-shaped beam of radiation, a set of electrodes including anodes and a cathode both formed on a planar substrate and disposed parallel to and offset from a plane defined by the thin fan-shaped beam of radiation and electronic detecting and counting circuits operative to detect and count the electrical effect of a photon interaction with gas molecules in the enclosure so that the count per unit time is a measure of the radiation flux in a portion of the fan-shaped beam proximate an associated anode.
Advantageously, the cathode may be forked with its forks lying adjacent anodes, the anodes and cathode forks lying along a linear strip.
Preferably the anodes and cathode forks point towards the source of radiation.
The enclosure and the anodes and cathode forks may be sufficiently long so that substantially all of the incident radiation interacts with the gas and does not pass through the enclosure.
A drift electrode may be located parallel to the fan-shaped beam and offset therefrom on a side of the fan-shaped beam opposite from the electrodes.
Each of the anodes may be segmented into a plurality of segments with each segment having its own detecting and recording electronic circuit.
The length of the segments may be selected to detect incident radiation in a given energy band on a statistical basis.
In another aspect of the invention there is provided a method of forming an image of an object employing a source of ionizing electromagnetic radiation for use in irradiating the object and an elongated collimator intermediate the source and the object for producing a thin fan-shaped beam. The method includes moving the object relative to the source and substantially perpendicular to the radiation beam, positioning a detector selected from the group consisting of a microstrip, microgap and microdot gas counter and substitutes of microstrip, microgap and microdot gas counters comprising a gas enclosure in which is mounted a drift electrode. The anodes and cathodes are in close parallel proximity fabricated on a substrate, so as to intercept radiation after passing through the object and so that the orientation of anodes and adjacent cathode regions of the detector are substantially aligned with a direction of travel of the radiation and slightly offset therefrom. At each anode of the detector anode current is detected and recorded. The step of detecting and recording of anode current at each anode is repeated as the object moves. The detecting and recording of the position of the object is done at a sufficiently high rate such that the target object is imaged one cross-sectional slice at a time to build up a complete raster image of the object.
ADVANTAGES OF THE INVENTION
An advantage of the invention is that it may be used to produce high quality W, or X-ray, or gamma ray images with colour and high resolution, at high efficiency, low cost and with high reliability, in an essentially unlimited variety of applications, including digital radiography, computed tomography, food inspection and grading, printed circuit board assembly inspection, wood processing, baggage inspection, and security systems of many types, all of which benefit from the X-ray energy information, high resolution, high efficiency, and fast response speed at a relatively modest cost and compact package. The invention may be used in either one, two, or three dimensional imaging systems.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages will be apparent from the following detailed description, given by way of example, of a preferred embodiment taken in conjunction with the accompanying drawings, wherein:
Fig.lA is a perspective view of a microstrip gas counter detector;
Fig. 1B is front elevation view of a microstrip gas counter detector coupled with an anode current detector;
Fig. 1C is front elevation view of a microstrip gas counter detector coupled with a multi-channel analyzer;
Fig. 1D is a front elevation view of a microstrip gas counter detector showing the effect of early and late detection of an obliquely directed photon;
Fig. 2 is a perspective view of a microstrip gas counter detector with the electrodes oriented parallel to the plane of collimation of the radiation;
Fig. 3 is an end view of the assembly shown in Fig. 2;
Fig. 4 is front elevation view of a microstrip gas counter detector with its electrodes parallel to the plane of collimation of the radiation and the orientation of the anodes and adjacent cathode fingers pointing at the source of radiation;
Fig. 5 is front elevation view of a microstrip gas counter detector with its electrodes parallel to the plane of collimation of the radiation, the orientation of the anodes and adjacent cathode fingers pointing at the source of radiation and each anode split into two;
Fig. 6 is front elevation view of a microstrip gas counter detector with its electrodes parallel to the plane of collimation of the radiation, the orientation of the anodes and adjacent cathode fingers pointing at the source of radiation and the anodes split into three parts; and Fig. 7 is a top view of a microstrip gas counter detector which lies along a segment of a circle, whose electrodes are directed at a source and which is mounted together with the source for rotation about an object at diametrically opposite positions with respect to the object.
DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS
A preferred embodiment of the imaging system is depicted in various orientations in Figs 2, 3, and 4. The substrate is parallel to and slightly offset from the plane of the vertical collimated fan-shaped beam 14 passing through the slit 17 of the collimator 16. Note that although only a single collimator 16 is depicted, it is common in X-ray imaging systems, to employ more than one collimator. For example, referring to Fig. 3, one collimator 19 would be in front of the target 72 as shown by the dashed lines while the other collimator 16 is located on the other side as shown in Fig. 3. Two collimators are used to minimize the effects of radiation scattered from the target 72. On a planar substrate 78 located on one side of a gas enclosure 12 offset from a plane of fan-shaped beam 14 are individual anodes 76, and a furcated common cathode 74. The gas depth "d" and the anodes 76 and the forks, of cathode 74 are significantly longer than any previously used so that essentially all of the incident radiation undergoes interactions with the enclosed gas. A conveyor 73 moves the target or object 72 orthogonally to the direction of the incident beam 14. In Figure 4 a further refinement involves the anodes 76 pointing at the source 11 of radiation (e.g., the X-ray generator in the case of X-ray images). This gives two immediate advantages: First, because of the longer path through the gas, incident radiation is far more likely to interact with the gas and, therefore, be detected. Second, no matter where in the path through the enclosed gas chamber of any particular ionizing ray the gas interaction occurs, the same anode will detect the interaction, rendering the detector insensitive to the obliqueness of the radiation.
For any particular type of radiation, the gas enclosure depth "d" (as shown in Fig. 2) is made large enough that the probability of interaction is of the desired (high) value. As shown in Fig 3, the incident ray 14 interacts with the gas within the enclosure 12, and an electron cloud is produced, which then is drifted orthogonally to the incident ray 14 towards the substrate 78. Avalanching takes place in the vicinity of the anodes 76.
Because the beam 14 is collimated, the gas enclosure width "w"
(also known as the drift gap) can be made relatively small, and the time for the electron drift and avalanche phenomena is relatively brief and uniform, no matter where in the gas the interaction occurs.
An important advantage in the present geometry is that the incident radiation does not pass through the drift electrode, unlike the situation in a conventional MSGC. Therefore, the drift electrode 80 need not be transparent to X-rays, allowing it to be fabricated in a rugged fashion.
Fig. 5 shows a further refinement of the imaging system.
In this case, the anodes 84 are segmented into two pieces, and each segment is taken to its own signal processing circuit (not shown). Fig. 6 shows three anode segments 88a, 88b, and 88c with each segment also going to its own signal processing circuit consisting of amplifier 100, comparator 102 and counter 104. The value of the segments is to provide a spectral component to the received image, permitting in the case of visual images the assignment of arbitrary colours corresponding to energy bands.
For computer-analysis of the images in machine vision applications the spectral energy component may permit improved feature extraction.
The physical explanation of the operation of the imaging system of Figure 6 is as follows. An incident ray of low energy (i.e., longer wavelength) has a higher probability of interacting with the gas early in its path through the gas, near the upper segment 88a of the anode, whereas higher energy rays will tend to penetrate the early part of the path and be absorbed on average later in the path, over the lower segment of the anode 88c.
Intermediate energy rays will tend to interact over the middle portion of the anode 88b. Thus, the interaction with the gas tends by itself to sort on a statistical basis the interactions over different segments of each of anodes 88a, 88b, and 88c. By fitting each segment with its own amplifier 100, comparator 102, and counter 104 then one obtains energy information with simplicity and economy. The number of segments will be dictated by the various desired environment, factors, and parameters, including type and wavelength of radiation source, target object features of interest, and cost and space constraints.
Relative orthogonal motion between the target and the MSGC (see Fig. 2) permits a line image to be acquired at regular frequent intervals, and after a number of lines a complete raster scan image is obtained. As shown in Figs 5 and 6, each anode 84 has one or more segments, and each segment is connected to an amplifier 100 which converts the brief current pulse to a voltage pulse. The voltage pulse is then sent to a comparator 102 which then converts the voltage pulse to a digital pulse. The digital pulse is recorded by a counter 104 which counts the photon events for that anode segment, corresponding to a spatial point and an energy window. After counting the events for the time corresponding to the interval allowed for one scan line, the counters are read out and reset using routine well-known digital multiplexing techniques. Each count corresponds to the radiation flux in the energy band for a particular spatial point, and the counts may be imaged as monochrome or colour images, and/or stored for subsequent automated computer-based image analysis.
Referring to Fig. 7, in a tomography application, the anodes and cathodes of a semi-circular gas detector 87 may be oriented along a sector of a circle and aligned so as to point towards a diametrically opposite source 11 so that the radiation 14 passes through a stationary object 72. As both the source 11 and the gas detector 87 rotate together around the object a 360 degree scan of the object by the fan-shaped beam 14 is obtained.
It is to be noted that the anodes 88 and cathodes 74 may be fabricated side-by-side on the substrate 78, or alternatively the anodes 88 may be deposited on a pedestal above a common cathode, commonly known as gas microgap geometry.
It is also noted that the substrate 78 need not be rectangular as shown. It may in some applications for example be shaped as the concave arc of a circle, centred on the radiation source, so that each anode is equidistant from the source. In this case all anodes receive a similar amount of radiation flux, which can have advantages in equalizing dynamic range, and which is also appropriate when providing images in tomography applications (Fig. 7).
Accordingly, while this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.
Claims (21)
1. A gas counter for measuring radiation intensity from a radiation source along a linear segment after passing through a target, the gas counter used in combination with a collimator having an elongated slit in the path of the radiation so as to produce a thin fan-shaped beam, said gas counter comprising:
(a) an enclosure for gas having a window for receiving the thin fan-shaped beam of radiation;
(b) a set of electrodes including anodes and a cathode both formed on a planar substrate and disposed parallel to and offset from a plane defined by the thin fan-shaped beam of radiation; and (c) electronic detecting and counting circuits operative to detect and count the electrical effect of a photon interaction with gas molecules in said enclosure so that the count per unit time is a measure of the radiation flux in a portion of the fan-shaped beam proximate an associated anode.
(a) an enclosure for gas having a window for receiving the thin fan-shaped beam of radiation;
(b) a set of electrodes including anodes and a cathode both formed on a planar substrate and disposed parallel to and offset from a plane defined by the thin fan-shaped beam of radiation; and (c) electronic detecting and counting circuits operative to detect and count the electrical effect of a photon interaction with gas molecules in said enclosure so that the count per unit time is a measure of the radiation flux in a portion of the fan-shaped beam proximate an associated anode.
2. A gas counter according to claim 1, wherein the cathode is forked with its forks lying adjacent anodes, the anodes and cathode forks lying along a linear strip.
3. A gas counter according to claim 2, wherein said anodes and cathode forks point towards the source of radiation.
4. A gas counter according to claim 3, wherein said enclosure and said anodes and cathode forks are sufficiently long so that substantially all of the incident radiation interacts with the gas and does not pass through the enclosure.
5. A gas counter according to claim 1, including a drift electrode parallel to the fan-shaped beam and offset therefrom on a side of said fan-shaped beam opposite from said electrodes.
6. A gas counter according to claim 1, wherein each of said anodes are segmented into a plurality of segments with each segment having its own detecting and recording electronic circuit.
7. A gas counter according to claim 6, wherein the length of the segments is selected to detect incident radiation in a given energy band on a statistical basis.
8. A gas counter according to claim 7, wherein detected radiation from said segments provides a colour image, each colour representing the proportion of the energy in the various energy bands at each spatial point in the image.
9. A gas counter assembly for measuring radiation intensity from a radiation source along a linear segment after passing through a target, said gas counter comprising:
(a) a collimator having an elongated slit in the path of the radiation so as to produce a thin fan-shaped beam impinging on said target;
(b) an enclosure for gas having a window for receiving the thin fan-shaped beam of radiation after passing through said target;
(c) a set of electrodes including anodes and a cathode both formed on a planar substrate and disposed parallel to and offset from a plane defined by the thin fan-shaped beam of radiation; and (d) electronic detecting and counting circuits operative to detect and count the electrical effect of a photon interaction with gas molecules in said enclosure so that the count per unit time is a measure of the radiation flux in a portion of the fan-shaped beam proximate an associated anode.
(a) a collimator having an elongated slit in the path of the radiation so as to produce a thin fan-shaped beam impinging on said target;
(b) an enclosure for gas having a window for receiving the thin fan-shaped beam of radiation after passing through said target;
(c) a set of electrodes including anodes and a cathode both formed on a planar substrate and disposed parallel to and offset from a plane defined by the thin fan-shaped beam of radiation; and (d) electronic detecting and counting circuits operative to detect and count the electrical effect of a photon interaction with gas molecules in said enclosure so that the count per unit time is a measure of the radiation flux in a portion of the fan-shaped beam proximate an associated anode.
10. A gas counter assembly according to claim 9, a conveyor operative to convey said target in a direction orthogonal to said fan-shaped radiation beam.
11. A gas counter according to claim 9, wherein the cathode is forked with its forks lying adjacent anodes, the anodes and cathode forks lying along a linear strip.
12. A gas counter according to claim 9, wherein said anodes and cathode forks point towards the source of radiation.
13. A gas counter according to claim 11, wherein said enclosure and said anodes and cathode forks are sufficiently long so that substantially all of the incident radiation interacts with the gas and does not pass through the enclosure.
14. A gas counter according to claim 9, including a drift electrode parallel to the fan-shaped beam and offset therefrom on a side of said fan-shaped beam opposite from said electrodes.
15. A gas counter according to claim 9, wherein each of said anodes are segmented into a plurality of segments with each segment having its own detecting and recording electronic circuit.
16. A gas counter according to claim 9, wherein the length of the segments is selected to detect incident radiation in a given energy band on a statistical basis.
17. A gas counter according to claim 16, wherein detected radiation from said segments provides a colour image, each colour representing the proportion of the energy in the various energy bands at each spatial point in the image.
18. A method of forming an image of a target employing a source of ionizing electromagnetic radiation for use in irradiating the target and an elongated collimator intermediate the detector and the target for producing a thin fan-shaped beam, comprising:
(a) moving the object relative to the source and substantially perpendicular to the radiation beam;
(b) positioning a detector selected from the group consisting of a microstrip, microgap and microdot gas counter and substitutes of microstrip, microgap and microdot gas counters comprising a gas enclosure in which is mounted a drift electrode, and anodes and a cathode in close proximity to said anodes, both said anodes and said cathode fabricated on a substrate, so as to intercept radiation after passing through the object and so that the orientation of anodes and adjacent cathode regions of said detector are substantially aligned with a direction of travel of said radiation and slightly offset therefrom;
(c) detecting and recording anode current of each anode of said detector; and (d) repeating the detecting and recording of anode current at each anode as said target moves and recording the position of the object with each step of detecting and recording at a sufficiently high rate such that the target object is imaged one cross-sectional slice at a time to build up a complete raster image of the object.
(a) moving the object relative to the source and substantially perpendicular to the radiation beam;
(b) positioning a detector selected from the group consisting of a microstrip, microgap and microdot gas counter and substitutes of microstrip, microgap and microdot gas counters comprising a gas enclosure in which is mounted a drift electrode, and anodes and a cathode in close proximity to said anodes, both said anodes and said cathode fabricated on a substrate, so as to intercept radiation after passing through the object and so that the orientation of anodes and adjacent cathode regions of said detector are substantially aligned with a direction of travel of said radiation and slightly offset therefrom;
(c) detecting and recording anode current of each anode of said detector; and (d) repeating the detecting and recording of anode current at each anode as said target moves and recording the position of the object with each step of detecting and recording at a sufficiently high rate such that the target object is imaged one cross-sectional slice at a time to build up a complete raster image of the object.
19. A method according to claim 18, wherein the moving is continuous.
20. A method according to claim 18, wherein the moving is done in steps.
21. A method according to claim 18, wherein each of said anodes and cathode regions are elongated strips and each anode is split into at least two portions with separate detecting and recording electronics coupled to each so that statistically different energy spectra are recorded by each of said portions.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2277251 CA2277251A1 (en) | 1999-07-09 | 1999-07-09 | High efficiency colour x-ray imaging system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2277251 CA2277251A1 (en) | 1999-07-09 | 1999-07-09 | High efficiency colour x-ray imaging system |
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| Publication Number | Publication Date |
|---|---|
| CA2277251A1 true CA2277251A1 (en) | 2001-01-09 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2277251 Abandoned CA2277251A1 (en) | 1999-07-09 | 1999-07-09 | High efficiency colour x-ray imaging system |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7127029B2 (en) * | 2004-03-30 | 2006-10-24 | Xcounter Ab | Arrangement and method for obtaining tomosynthesis data |
| JP2007530212A (en) * | 2004-03-30 | 2007-11-01 | エックスカウンター アーベー | Structure and method for acquiring imaging data |
-
1999
- 1999-07-09 CA CA 2277251 patent/CA2277251A1/en not_active Abandoned
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7127029B2 (en) * | 2004-03-30 | 2006-10-24 | Xcounter Ab | Arrangement and method for obtaining tomosynthesis data |
| US7164748B2 (en) | 2004-03-30 | 2007-01-16 | Xcounter Ab | Arrangement and method for obtaining imaging data |
| JP2007530212A (en) * | 2004-03-30 | 2007-11-01 | エックスカウンター アーベー | Structure and method for acquiring imaging data |
| JP4874232B2 (en) * | 2004-03-30 | 2012-02-15 | エックスカウンター アーベー | Structure and method for acquiring imaging data |
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