JP2004508544A - Multi-density multi-atomic number detector media with electron multiplier for imaging - Google Patents

Abstract

A multi-detector system that receives incident radiation through a subject consists of a gas microstrip detector in which anodes and cathodes are alternately formed on a substrate facing a voltage source, and a semiconductor detector arranged adjacent to the gas microstrip detector. Be composed. In a dual energy environment, an electric field is applied to both detectors when incident radiation is directed. Thereby, the detector generates a corresponding signal. The generated signals are compared to generate a signal having good contrast of the subject. These signals are generated for imaging, radiation monitoring, radiation measurement, and the like. The direction of the incident radiation and the direction of the electric field are adjusted for each application. The system can also be used in a single energy environment where two images are formed from incident radiation of the same energy on different detector media. By using various processing methods, the contrast between images can be increased.

Description

[0001]
Related application
This application is a continuation-in-part of U.S. application Ser. No. 09 / 078,991 filed May 14, 1998.
[0002]
Technical field
The invention relates to dual energy imaging, computed tomography (CT), digital tomography such as microtomography and X-ray microscopy, quantitative automatic radiography, single photon irradiation tomography (SPECT) And nuclear medicine such as positron emission tomography (PET), medical detection techniques such as monitoring, measuring, recording or projecting ionizing radiation in any energy range, bio-optical imaging such as optical confocal microscopy and optical tomography, and And industrial applications such as aerospace imaging security surveillance systems and non-destructive imaging. In particular, the present invention relates to a multi-density multi-atomic number detector medium that can be realized by performing kinestasis or time-delay integration as required for use in the above applications.
[0003]
Background art
Efficient capture and detection of ionizing radiation without significant loss or degradation of image information is extremely important in medical imaging. Recent advances in medical detection technology have resulted in superior images being created by digital electronic technologies such as digital radiography that compete with conventional film-screen technology. In fact, new radiographic imaging techniques that take advantage of advances in electronic and computer technologies have introduced new diagnostic modalities that have improved diagnostic quality and reduced patient exposure. In particular, digital radiography has many advantages over conventional radiography. For example, the dynamic range of the detector can be expanded and displayed, high-speed image acquisition and display are possible, convenient storage is provided, stored images can be transmitted and displayed without deterioration, data analysis function And the image processing function has been expanded, and the patient irradiation dose has been reduced.
[0004]
Different detector technologies and different beam shapes have been proposed for digital radiography. For example, a scintillator-photodiode system, a high pressure gas-filled detector, a scintillator-optical amplifier system, a kinetic static charge detector, a proximity image intensifier / CCD device, a phosphor screen-photodiode system, and a diode array. Was suggested.
[0005]
Problems with known digital radiographic systems include relatively high initial costs and low detector resolution. A major problem in digital radiography, computed tomography and related fields is how to efficiently detect x-ray radiation. Recent advances in medical detector technology suggest that digital electronic technology could be used to produce superior radiation images. In fact, recent advances in electronic and computer technology have made it possible to improve the quality and style of diagnosis while reducing the dose of incident radiation. Although several new detectors for digital radiography and computed tomography have been proposed, the only technique that overcomes all the problems of achieving optimal imaging is the appropriate choice. There is no such thing yet. Which technique you choose depends on several image quality criteria. That is, high quantum and energy absorption efficiency, high quantum efficiency (DQE) of the detector, high spatial resolution, little reception of scattered radiation, detector shape, high-speed reading, high dynamic range, image Correction and display functions, and one thing to keep in mind is that the costs are reasonable. One of the fundamental problems of digital radiography is how to detect scattered radiation that reduces the contrast of an image. Known line scanning methods do not use the X-ray tube output efficiently. This limitation is overcome by utilizing a wide slot x-ray beam to collect multiple lines simultaneously.
[0006]
One approach to overcoming the above problems is discussed in US patent application Ser. No. 60 / 011,499, which is incorporated herein by reference. In this disclosed strategy, a dual energy gas microstrip is used. Here, a low energy image and a high energy image are obtained, and these are compared to generate a high contrast image. Although this approach is effective, the two images are constructed using only a single medium, the gas surrounding the microstrip. Further research has led to the development of new devices that further enhance the above detection techniques. These devices are described in U.S. patent application Ser. No. 09 / 078,991, which is incorporated herein by reference. The invention has improved spatial and contrast resolution, lower noise, improved image quality and improved image contrast.
[0007]
In particular, the interaction between ions and electrons in the detector makes the ion / electron movement random in the detector components. This movement is detected along with the primary ion / electron flow formed by the target. Since this movement is random, rather than completely blocking the image, it creates a ghosted image, a cloudy image (referred to as noise), resulting in poor image quality and reduced contrast. Let it. Therefore, there is a need for a detector that improves the image by reducing the detection of random ion / electron movement. Further, there is a need for a detector that amplifies the primary ion / electron flow, which improves the image signal, improves the signal-to-noise ratio, and improves the contrast between images.
[0008]
Disclosure of the invention
In view of the above, a first aspect of the present invention is to provide a multi-density multi-atomic number detector medium for applications such as, but not limited to, imaging, dosimetry, radiation monitoring, and combinations thereof. is there.
[0009]
Another aspect of the present invention is to provide an ionization apparatus or ionization source for projecting ionizing radiation (X-rays, gamma rays, fast particles, and neutrons) having an arbitrary energy range through a subject according to an application. Here, the radiation is received by a multiple detector.
[0010]
Yet another aspect of the invention described above provides a dual energy configuration multiple detector, wherein the dual energy detector receives a bimodal energy spectrum analyzed by two different media. In any case, the energy may be polychromatic or monochromatic. In the case of a polychromatic energy spectrum, the term monoenergetic is used to correspond to the "average" or "effective energy" of the polychromatic spectrum.
[0011]
Another aspect of the invention is to provide a multiple detector comprising a low energy detector and a high energy detector disposed adjacent thereto.
[0012]
Another aspect of the present invention is to apply an electric field separately to the low energy detector and the high energy detector when irradiated with incident radiation, wherein the low energy detector is a gas ionization detector. Or the semiconductor ionization detector, and the high energy detector is the other detector.
[0013]
In another embodiment of the present invention described above, an image is generated by the two detectors, so that the image is input to a microprocessor for imaging a subject, and an image signal with good contrast is generated.
[0014]
Another different form of the invention is that a high-pass energy filter is placed between the two detectors to facilitate the generation of a high-contrast image signal, where low-contrast is used for soft tissues and the like. In such a case, it is obtained by weighting and subtracting the two images.
[0015]
Another different aspect of the invention described above provides a mechanism for moving a multiple detector to receive ionizing radiation, wherein the kinetic or time lag is achieved by adjusting the applied electric field. To be able to implement the integration method, or both.
[0016]
According to another embodiment of the present invention described above, the gas ionization detector comprises a high voltage plate, and a substrate having a large number of anodes and cathodes opposed to the high voltage plate alternately interposed therebetween. A multiplex detector comprising a bias electrode formed on one side of a semiconductor substrate and a plurality of collecting electrodes facing the bias electrode.
[0017]
Another aspect of the invention described above is that the incident radiation is first absorbed by a low energy, low density, low Z material detector with the applied electric field orthogonal to the incident radiation, The detector is to provide a multiple detector arranged adjacent to a high energy, high density, high Z material detector in which the applied electric field is orthogonal to the incident radiation.
[0018]
According to another aspect of the invention described above, the incident ionizing radiation is first absorbed by a low energy detector in which the applied electric field is directly opposed to the incident radiation, and further the high energy detector comprises an applied electric field. Is to provide a multiple detector positioned adjacent to a low energy detector that is now orthogonal to the incident radiation.
[0019]
In another embodiment of the invention described above, the incident radiation is first absorbed by a low-energy detector with the applied electric field orthogonal to the incident radiation, and furthermore, the incident radiation has the same applied electric field as the incident radiation. It is to provide a multiple detector which is received by a high energy detector in a directionally aligned state.
[0020]
Another aspect of the present invention described above is to provide a multi-detector in which the incident radiation is firstly absorbed by the low energy detector and then absorbed by the high energy detector without restriction on the beam shape. Here, the electric field applied by each detector is aligned in the direction of the incident radiation.
[0021]
Another aspect of the invention described above is to provide a multiple detector in which the incident radiation is first absorbed by a low energy detector and then absorbed by a high energy detector, with no restriction on beam shape. Here, the electric field applied to each detector is aligned in the direction of the incident radiation.
[0022]
Another aspect of the invention described above is to configure multiple detectors to generate images and perform an association detection function.
[0023]
In another embodiment of the present invention described above, the detectors arranged adjacent to each other perform the same function or different functions. For example, both the detectors perform an imaging function. Alternatively, one adjacent detector performs an imaging function and the other adjacent detector performs a radiation monitoring function.
[0024]
Another aspect of the invention described above is that the ionizing radiation may be measured, monitored and displayed by one or both of the adjacent detectors at different energies, with the system geometry optimized. Here, each detector performs the same function or a different function, in the form of particles or different radiations (mixed fields).
[0025]
Another aspect of the present invention described above is to operate at least one of the detectors like a frisch grid to increase the signal-to-noise ratio and improve the line spread function.
[0026]
Another aspect of the invention described above is that a gas electron multiplier is inserted in close proximity to a collection circuit that amplifies electrons without an induced current, increases the signal-to-noise ratio, and improves the line spread function. It is to be.
[0027]
Another aspect of the invention described above is to place a gas electron multiplier in the detector to improve ion generation.
[0028]
In general, the present invention provides a dual energy multiple detector that receives incident ionizing radiation through a subject, the multiple detector comprising a gas ionization detector, a semiconductor detector disposed adjacent thereto, and a gas ionization detector. A gas electron multiplier positioned within the vessel (where an electric field is applied to each detector to generate a corresponding signal, and the gas electron multiplier measures the performance of the gas ionization detector. To increase the electronic activity).
[0029]
The present invention also provides a method for obtaining an image of a subject exposed to incident radiation, the method comprising exposing multiple detectors to incident radiation illuminated through a specimen, and further comprising: Generating a first signal, generating a second signal from a second detector, arranging a gas electron multiplier near at least one of the detectors; And comparing the signal with Here, the multiple detector includes a first detector and a second detector arranged adjacent to the first detector.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
In the figure, and particularly in FIG. 1, a multi-density multi-atomic number detector imaging system is indicated generally by the numeral 10. As will be appreciated from the following discussion, to achieve a high contrast dual energy imaging system, the imaging system 10 must be configured with a high atomic number or high Z material, ie, a high density medium, and a low atomic number or low Z material, ie, a low density medium. Are used in combination. The system 10 acts as a slot scanning beam detector implemented by a kinestasis or time delay integration method. The imaging system 10 can also be used with application specific integrated circuits (ASICs) that act as charge coupled device cameras. As will be appreciated by those skilled in the art, the imaging system can also be used for large field imaging or micro imaging (microscopy) with dual energies.
[0031]
The system 10 includes an ionization device or source 12 for generating ionizing radiation 14 and transmitting it through a subject 16. Ionizing radiation includes, but is not limited to, X-rays, gamma rays, fast particles, neutrons, and the like. The radiation is irradiated in a mixed state or at different energies and is observed by multiple detectors that perform a predetermined function. The ionizer 12 is configured to generate a polychromatic energy spectrum of average energy E or a single energy beam from one frequency spectrum synchrotron. Alternatively, the ionizer 12 is configured to generate a polychromatic bimodal energy spectrum. The subject 16 is a human, biological or pharmaceutical specimen, and radiation is transmitted through the subject to generate radiation 18 that is received by a multi-density multi-atomic number multiplex detector 20. Generally, the multiple detector 20 is housed in a sealed aluminum container 21 that can move in a scanning direction 24 on a plane orthogonal to the incident image line 18. In order to appropriately obtain an observation image of the subject 16, the multiple detector 20 includes several components connected to the multiple detector 20. "Observing" with multiple detectors 20 refers to monitoring radiation, recording doses, and performing imaging to perform known functions performed by known ionization detectors. That is, each detector of the multiplex detector 20 performs a different function or the same function depending on a desired result and a system configuration.
[0032]
The pressurized gas 26 is a mixture of argon, xenon, krypton, a mixture thereof or another rare gas, or a mixture thereof and a magnetic compound or a quenching compound at an impurity concentration. , A fluid guided to the container 21 via the pressure line 28. A pressure gauge 30 is attached to the pressurized gas container and adjusts the pressure in the container of the multiple detector 20. Pressure signal 32 is generated by pressure gauge 30.
[0033]
A control system 30 communicates with the various components of system 10 to monitor and control their respective functions. Specifically, the control system 30 includes a microprocessor 40 having software, hardware, and a memory necessary for controlling the operation of the imaging system 10. The processor 40 receives the pressure signal line 32 and adjusts the pressure in the multiplex detector 20 to a low pressure, an atmospheric pressure, or a high pressure state according to the purpose of imaging.
[0034]
The processor 40 is connected to the detection circuit 44 via the signal line 42. The detection circuit 44 is connected to the multiplex detector 20 via a signal line 46. Similarly, a signal line 48 connects the processor 40 to the detection circuit 50, and the detection circuit 50 is connected to the multiplex detector 20 via a signal line 52. The processor 40 receives information from the detection circuits 44 and 50 and generates an image signal 54 with high contrast. The image signal with good contrast is received for display on the image display unit 56. In all embodiments involving dual energy imaging, the incident radiation is first received by a low energy detector. Unabsorbed radiation is received by the high energy detector.
[0035]
Usually, the multiple detector 20 basically consists of two parts: a gas-filled detector and a solid or semiconductor substrate detector. Incident radiation 18 is partially dissipated in the first detector and then the remaining energy is dissipated by interaction in the second detector. In both cases, a charge pair is generated. The electric field applied to both detectors causes the charge pairs to have a constant drift velocity, and the charge pairs, ie, polar charges, are sent to their respective signal collectors. The different detector media used in the detector may be a solid semiconductor material, a gas or a liquid, and may be in any shape or a combination thereof, such as scintillation, regardless of the shape of the detector media. The signal is generated by ionization or indirect ionization.
[0036]
In the case of a two-energy multiplex detector, if a logarithmic expansion is applied to the signal generated from each medium, a desired image is generated by a difference between the two signals. An imaging method is also conceivable in which the direction of an electric field applied to the low energy detector and the high energy detector is changed to obtain a desired image contrast and spatial resolution or a result of another function.
[0037]
FIG. 2 shows one preferred embodiment of the multiple detector 20. More specifically, as an example of dual energy imaging, the multiple detector 20 includes a gas ionization detector 60 and a semiconductor ionization detector 62.
[0038]
The gas ionization detector 60 includes a high voltage plate 64 and a substrate 66 facing the high voltage plate. Substrate 66 is a conductive glass or plastic substrate with suitable electrical conductive properties. The substrate 66 has an electrically conductive layer provided on the surface of the insulator by ion implantation or deposition of a thin film of a semiconductor material. A plurality of insulated microstrip anodes 68 are alternately formed with similar insulated microstrip cathodes 70. Accordingly, an electric field 72 is generated between the high voltage plate 64 and the substrate 66. The high voltage plate 64, the substrate 66, the anode 68, and the cathode 70 are connected to the energy detection circuit 44 via the signal line 46.
[0039]
The semiconductor ionization detector 62 comprises a cubic semiconductor material 76 in which a bias electrode 78 is disposed on one surface of a cubic shape and a plurality of collecting electrodes 80 are disposed on an opposite surface. Accordingly, an electric field 82 is generated between the bias electrode 78 and the collection electrode 82. Both the bias electrode 78 and the collection electrode 80 are connected to the detection circuit 50 via the signal line 52.
[0040]
In all the embodiments of the present invention, the detection units of the energy detector, for example, the anode 68, the cathode 70, the collecting electrode 80, the low energy detection circuit 44, and the high energy detection circuit 50 are incorporated as a circuit integrated in the container 21. . The integrated circuit provides all the active and passive signal conditioning circuits and associated circuits integrated and produces a digital output that is received by the processor 40.
[0041]
As shown in FIG. 2, the detector 60 employs a high-pressure gas environment exhibiting high primary quantum detection efficiency and high charge conversion efficiency. As the pressure of the gas increases, the amount of incident photons that interact with the gas increases, thereby improving quantum efficiency. In addition, the amount of photon energy that acts on each photon and is deposited in the gas increases. Under high pressure, many electrons and fluorescence are blocked in the gas, and thus the sensitivity depends on the energy of the generated gamma photons. High pressure gas-filled ionization detectors operating in saturation are advantageous in many respects.
[0042]
In the preferred embodiment, xenon is employed as the gas because of its high x-ray stopping power. However, krypton is advantageous because it does not emit much fluorescence and does not reabsorb, and it allows the interaction that the incident radiation spreads from where it collides with the vessel 21 while limiting the range of emitted photoelectrons and Compton electrons. Therefore, the spatial resolution is improved.
[0043]
The response characteristics of the high pressure gas-filled detector 60 can be greatly improved by moving the enclosure 21 in a kinetic charged detection mode in synchronization with the ions, where the ion velocity The ion velocity is adjusted by adjusting the applied electric field such that has a direction equal or opposite to the scan speed 24 of the multiple detector 20. At any one time, 50 to 1000 image data lines are integrated simultaneously, depending on the scanning speed and the sampling rate. Only one line of the collector electrode needs to read the fully integrated image data.
[0044]
By using the microstrip substrate 66 as a collector, the performance of the multiple detector 20 and the imaging parameters can be improved. By using the anode 68 and the cathode 70 by using the light exposure method, a high gain can be obtained uniformly over a wide area. Thus, when the incident radiation is directed through the multiple detector 20, primary electrons generated by direct gamma ionization of the gaseous medium are directed toward the anode 68. When the electrons reach the electric field between the anode 68 and the cathode 70, the electrons drift toward the cathode 70 due to the pseudo-dipole anode-cathode structure and are avalanche if the electric field strength is high enough.
[0045]
In this embodiment, a multiple detector 20 utilizing high gas pressure was selected as a compromise between high quantum detection efficiency, limited electronic range and adequate gain. The gas microstrip substrate of the detector 60 is advantageous in that it has high spatial resolution and high contrast because of its small collector, high gas pressure and high gain. Further, the use of a low energy detector in the present invention is advantageous in that a high gain can be obtained even at a low applied voltage due to a high local electric field generated near the anode. Another advantage is that large signals are generated because of the high gain and quantum efficiency. Still another advantage is that the distance between the anode and the cathode is narrow, the drift speed is high due to the high electric field, and the capacitance of the microstrip is small, so that the signal collection time is very short. This suppresses the space charge effect. Another advantage is that a low cost detector with high mechanical stability is provided.
[0046]
As shown in FIG. 2, detector 62 receives image line 18, which is incident radiation unaffected by detector 60 and impinges on semiconductor material 76. Therefore, the detector 62 is optimal for digital X-ray imaging because it directly converts X-rays into electric signals. For example, Cd_1-XZn_X Te has a high density (5.8 g / cm³), The effective atomic number Z is 49.6 (Cd_0.9: 48, Zn_0.1: 30, Te: 52), which is one of the most suitable semiconductor materials for medical and industrial imaging purposes because of its high stopping power. If this material is used, the thickness of the detector can be reduced and the spatial resolution can be improved. Other potential semiconductor materials include a-Se, a-Si, CdTe with high atomic number and high density, and their equivalents. The advantage of this type of semiconductor ionization detector as realized as the multiple detector 20 is that the ionization line absorption efficiency is high, the linearity is excellent, the stability is high, the sensitivity is high, and the dynamic range is high. It is wide. High quality Cd using high pressure Bridgman method_1-X Zn_X Greater progress has been made in the development of Te semiconductor crystals. That is, by using an alloy of CdTe and Zn, the body resistivity of this semiconductor is about 10%.¹¹Ω-cm. The reason why the specific resistance is high is that the leak current is low and the noise characteristics are low because the band gap of the ternary compound semiconductor is wide. The imaging function of the solid state detector can be improved by using the time delay integration method. According to this method, the semiconductor material is configured as a pixel array consisting of N columns and M rows. The rate at which the collected charge is transferred in the column direction is synchronized with the rate at which the detector scans and translates parallel to the image plane. Thereby, the collected charge corresponding to a part of the observed object by providing a signal larger than the signal collected at the individual pixels is integrated during image acquisition.
[0047]
As radiation 18 passes through detector 60 and detector 62, corresponding signals 46 and 52 are generated and received by detection circuit 44 and detection circuit 50, respectively. Each of the circuits 44 and 50 controls the application of an electric field, monitors a collected signal, and performs signal filtering and signal processing by a known method as necessary. For example, the high voltage plate 64 and the substrate 66 are connected to the circuit 44 and control the application of the electric field 72. On the other hand, the anode 68 and the cathode 70 are connected to the circuit 44 to monitor the low energy absorption of the ionized gaseous medium. Similarly, the bias electrode 78 and the collection electrode 80 are connected to the circuit 50, control the application of the electric field 82, and monitor the energy absorption of the semiconductor substrate. Circuits 44 and 50 send corresponding signals 42 and 48 to processor 40. The processor receives these and generates a signal 54 with good contrast.
[0048]
In another embodiment, the position of the multimedia detector is changed according to the direction of the electric field. In each case, the gas ionization detector is always associated with the detection circuit 44 and the semiconductor ionization detector is always associated with the detection circuit 50.
[0049]
FIG. 3 shows another multiplex detector 100. The multiple detector 100 is housed in a container 21 and includes a first or low energy detector 102 as a gas ionization detector and a second or high energy detector 104 as a semiconductor ionization detector disposed adjacent thereto. Be composed. In this embodiment, the radiation 18 first strikes the detector 102 with the semiconductor substrate 103. In the detector 102, a bias electrode 106 to which the radiation 18 is directly applied is provided on one side of the substrate 103, and a pixel array detector 108 including a plurality of pixels 109 is provided on the other side of the substrate 103. Accordingly, an electric field 110 is generated to penetrate the substrate 103 and is directed in a direction opposite to the radiation 18. In the dual energy embodiment, the low energy radiation 18 is first absorbed by the substrate 103 and the unabsorbed energy is directed to the detector 104. The detector 104 includes a high voltage plate 112 and a substrate 114 facing the high voltage plate. As in the previous embodiment, a plurality of microstrip anodes 116 and a plurality of microstrip cathodes 118 are alternately arranged. Thus, the electric field 120 is directed in a direction orthogonal to the radiation 18 and opposite the scanning direction 24. The images generated by detector 102 and detector 104 are transferred to corresponding circuits 44 and 50 and processed by processor 40. The processor 40 generates a high-contrast image signal 54. As in the previous embodiment, the electrical leads and components associated with detectors 104 and 102 are connected to respective detection circuits, which are connected to processor 40.
[0050]
As another example, FIG. 4 shows another multiplex detector 140. In this embodiment, the radiation 18 first strikes the gas ionization detector 142 orthogonal to the electric field. Thereafter, the radiation 18 enters a semiconductor ionization detector 144 disposed adjacent to the detector 142. In this variation, however, the bias electrode 106 is located adjacent to a detector 142 that faces the pixel array detector 108. Alternatively, all the structural features of this embodiment are the same as those of the detector of the above-described embodiment. Thus, the electric field 110 is directed in the same direction as the incident radiation, and the signal is collected and generated as in the previous embodiment.
[0051]
If necessary, both of the multiple detectors 100 and 140 may be provided with a high-pass energy filter 150 between the detectors.
[0052]
FIG. 5 shows another multiplex detector 300. The multiple detector 300 includes a first or low energy detector 102 as a gas ionization detector and a second or high energy detector 104 as a semiconductor ionization detector disposed adjacent thereto. In this embodiment, the radiation 18 first strikes the detector 302 with the semiconductor substrate 303. In the detector 302, a bias electrode 306 to which the radiation 18 is directly applied is provided on one side of the substrate 303, and a pixel array detector 308 including a plurality of pixels 309 is provided on the other side of the substrate 303. Accordingly, an electric field 310 is generated to penetrate the substrate 303 and is directed in a direction opposite to the radiation 18. In the dual energy embodiment, the low energy radiation 18 is first absorbed by the substrate 303 and the unabsorbed energy is directed to the detector 304.
[0053]
The detector 304 includes a high voltage plate 312 and a substrate 314 facing the high voltage plate 312. As in the previous embodiment, a plurality of microstrip anodes 316 and a plurality of microstrip cathodes 318 are alternately arranged to form a collector circuit. An additional feature of this embodiment is that it includes a gas electron multiplier 330, an anode 316, and a cathode 318 located in close proximity to the collector circuit. As shown in the cross-section of FIG. 5, a gas electron multiplier (GEM) 330 is preferably located within the detector and located a few millimeters from the collector circuit. Gas electron multiplier 330 includes a thin composite mesh that functions as an amplifier proportional to gas in a gaseous medium. Preferably, the GEM 330 comprises a metal cladding with holes 336 forming a preferably rectangular matrix on the insulating foil 332, ie on both sides 334. The size of the holes is preferably in the micron range. The perforated foil 332 prevents the scattered electrons from moving and provides a path for the electrons along the formed electric field.
[0054]
An electric field 320 is directed in a direction orthogonal to the radiation 18 and opposite the scanning direction 24. The electrons in the electric field 320 contact the gas electron multiplier 330 and follow a path through the holes 336 in the matrix. The electrons collide with the gas particles in the hole 36, and the activity of the electrons increases. This increased activity will increase the electric field created at the adjacent detector anode 316. The increased electric field enhances the signal formed.
[0055]
In another embodiment, applying a potential difference to both sides 334 of the GEM improves signal quality and provides electron amplification in a dipole field formed between the edges of the hole. An avalanche phenomenon occurs and an increased electric field is formed at the anode 316. In any embodiment, the increased electric field improves the signal to noise ratio by forming an amplified signal. Any type of anode collector or shape (printed circuit board, pixel configuration board, strip board, etc.) can be used.
[0056]
To further improve the signal-to-noise ratio, the microstrip anode 316 and cathode 318 can be energized as described above and operated like an amplifier or a frisch grid. When they are operated like a frisch grid, the collecting electrodes are made much smaller than the non-collecting grid, and one of the strips is maintained at a slightly positive potential with respect to that of the second electrode. FIG. 5 shows a strip collector with frisch grid capability. As shown, the anode 316 of the low energy detector is much smaller than the non-collecting cathode. The non-collecting cathode strip functions to shield the collector. Larger induced charges occur at the strip collection anode. It should be noted that any shape of anode and cathode can be used as long as the anode is smaller than the cathode. This difference in magnitude minimizes the induced signal. For example, FIG. 7 shows another embodiment having a series of small anodes 317 and larger cathodes 319 disposed on a rectangular substrate 303. For strip 316 and cathode 318, a larger cathode 319 reduces the induced charge signal. Appropriate surface techniques, such as undercoating or overcoating, are applied to the strip to ensure optimal surface resistance. By operating the anode and cathode like a frisch grid, it is possible to detect signals resulting from the movement of charges, rather than induced charges. Therefore, the line spread function is very narrow, and an image with enhanced quality is obtained. The images formed by the high energy detectors 304 and 302 are then processed by the corresponding circuits 44 and 70 for processing by the processor 40 (which produces a high contrast image signal 74) as shown in FIG. Will be forwarded to As in the previously described embodiment, the electrical leads of the components associated with detectors 304 and 302 are each connected to a detector circuit, which is luckily connected to processor 40.
[0057]
Further, another multiplex detector is shown generally in FIG. As described above, the multiple detector 400 includes the first detector 402 and the second detector 404. In this embodiment, GEM 430 is located in the detector. Primary electrons generated by X-rays drift to GEM 430 as described above. An increase in electrons occurs at GEM 430. When this occurs, the generated ions drift to the cathode 416. The cathode 416 is used as a frisch grid. As mentioned above, the collecting electrodes are much smaller than those of the non-collecting grid, and one of the strips is maintained at a slightly positive potential with respect to that of the second electrode. Amplification occurs by maintaining one of the strips at a slightly positive potential. Appropriate surface treatment techniques such as undercoat or overcoat are used to ensure optimum sheet resistance.
[0058]
Preferably, the manufacture of the microstrip detector utilizes a light exposure method, replacing the anode-cathode wire with a very thin layer of conductive strip. The use of these techniques improves the accuracy of the anode-cathode pattern and ensures high gain uniformity over a large area within the microstrip detector. Using these techniques, the conductive strips are placed in an anode-cathode pattern on an insulating or partially insulating glass substrate.
[0059]
Primary electrons generated by direct X-ray ionization of gas drift to the microstrip. When these electrons arrive at the microstrip substrate, they drift toward the positively charged strip and undergo avalanche amplification. With the quasi-dipole anode-cathode structure, a high field strength of amplification is achieved. The ions rapidly collect on the adjacent cathode which provides the detected image signal. The generated image is then transferred to corresponding circuits 44 and 70 for processing by processor 40 (which produces a high contrast image signal 74), as shown in FIG. As in the previous embodiment, the electrical leads of the components associated with the detectors 404 and 402 are each connected to a detector circuit, which is luckily connected to the processor 40.
[0060]
As can be seen from the foregoing discussion, the system 10 with multiple detectors 20, 100, 140, 300, or 400 provides high energy absorption efficiency of solid-state ionization detectors and high spatial resolution and low energy detection of fine microstrip collectors. High gain of the vessel is realized at the same time. Therefore, excellent spatial resolution and contrast are realized at a low radiation dose. In addition, the system 10 allows free design and optimization of a dual energy system. All of the detectors disclosed in the present invention can operate with scan slot beams or with pixel configurations. These detectors can also operate as large area detectors. The kinetic static principle is used for generating an imaging signal by a low energy detector. On the other hand, the high-energy detector uses a time-lag integration method to generate an observation signal according to the shape of the scanning slot beam.
[0061]
The object of the present invention is achieved by the above structure and method. In accordance with the patent statutes, only the best mode and appropriate embodiment of the present invention has been described in detail, but the present invention is not limited thereto. Therefore, reference should be made to the appended claims for an understanding of the true scope and breadth of the present invention.
[Brief description of the drawings]
FIG.
FIG. 1 is a schematic diagram of a multi-density multi-atomic number detector imaging system.
FIG. 2
FIG. 2 is a schematic diagram of a suitable detector used in an imaging system.
FIG. 3
FIG. 3 is a first alternative embodiment of the detector used in the imaging system.
FIG. 4
FIG. 4 is a second alternative embodiment of the detector used in the imaging system.
FIG. 5
FIG. 5 is a schematic partial cross-sectional view of another embodiment used for imaging.
FIG. 6
FIG. 6 is a schematic partial cross-sectional view of another embodiment used for imaging.
FIG. 7
FIG. 7 is a schematic partial cross-sectional view of another embodiment used for imaging.

Claims (23)

A multiple detector for receiving incident ionizing radiation through a subject,
Gas ionization detector,
A semiconductor ionization detector disposed adjacent to the gas ionization detector;
A gas electron multiplier arranged in the gas ionization detector;
Including
An electric field is applied to each of the detectors to generate a corresponding signal, and the gas electron multiplier increases the activity of the electrons to enhance the performance of the gas ionization detector, multiple detection. vessel. 2. The multi-detector according to claim 1, wherein the gas electron multiplier is an insulating foil having metal lads on both sides and perforated to form a rectangular matrix. further,
A sealed container containing the detector;
A control system connected to each of said detectors;
3. The multiplex detector of claim 2, wherein the control system controls the application of the electric field and monitors the signal. further,
A gas ionization detector circuit connected to said gas ionization detector for controlling application of an electric field and generating a gas ionization detector signal;
A semiconductor ionization detector circuit connected to said semiconductor ionization detector for controlling application of an electric field and generating a semiconductor ionization detector signal;
A processor for receiving the detector signal and generating a high-contrast signal received by a display unit;
The multiplex detector according to claim 3, comprising: The gas ionization detector comprises:
A high voltage plate,
A substrate supporting a plurality of alternating anodes and cathodes;
Including
The substrate is disposed so as to face the high voltage plate, the gas electron multiplier is disposed between the substrate and the high voltage plate, and the high voltage plate is provided in a hole forming the matrix. 5. The multi-detector of claim 4, wherein electrons are generated to collide with the gas particles and the electrons are accelerated to enhance the gas ionization detector signal. The multiplex detector of claim 5, wherein the anode is larger than the cathode. The multiplex detector of claim 5, wherein the cathode is larger than the anode. A method for obtaining an image of a subject exposed to incident radiation, the method comprising:
Exposing a multiple detector comprising a first detector and a second detector adjacent thereto to incident radiation irradiated through the subject;
Generating a low energy signal from the first detector;
Generating a high energy signal from the second detector;
Disposing a gas electron multiplier near at least one of the two detectors;
Comparing the first and second signals;
A method that includes 9. The method of claim 8, wherein the gas electron multiplier is located within a few millimeters of at least one of the two detectors. further,
Storing the multiple detector in a gas-filled container;
Applying an electric field to each of the first detector and the second detector;
Wherein the gas is ionized by incident radiation in one of the first and second detectors, and the other of the first and second detectors converts the first and second signals. A semiconductor substance that is ionized by incident radiation to produce
The method according to claim 8. The method according to claim 10, wherein the gas electron multiplier is disposed in the gas-filled container. 12. The method of claim 11, wherein the gas electron multiplier is a perforated insulating foil having metal lads on both sides and forming a rectangular matrix. The electric field is applied so that electrons drift to the gas electron multiplier and amplify the electron flow, so as to positively charge the gas electron multiplier, and the increased electron current is applied to the gas electron multiplier. 13. The method of claim 12, wherein at least one of the detectors produces a stronger signal. further,
Applying respective electric fields to form an electron flow;
Disposing the gas electron multiplier in front of the electron flow so that the gas electron multiplier removes the movement of scattered electrons;
The method of claim 11, comprising: further,
The method according to claim 10, comprising operating at least one of the two detectors as a frisch grid. further,
Scanning the multiple detector in a plane orthogonal to the incident radiation;
13. The method of claim 12, wherein the electric field applied to one of the first and second detectors is adjusted such that the ion velocity is approximately equal to and opposite to the scan rate of the multiple detector. further,
Scanning the multiple detector in a plane orthogonal to the incident radiation;
An electric field applied to one of the detectors generates a collected charge on a surface of the semiconductor material arranged in rows and columns, and the collected charge is transferred along one of the rows and columns. The method of claim 10, wherein a speed is synchronized with a scanning speed of the detector. further,
Orienting the gas ionization detector to first receive incident radiation;
Directing an electric field generated by the gas ionization detector and the semiconductor ionization detector in a plane direction orthogonal to incident radiation;
The method of claim 10 comprising: further,
Orienting the semiconductor ionization detector first to receive incident radiation;
Directing the electric field generated by the semiconductor ionization detector in a direction opposite to the incident radiation;
Directing the electric field generated by the gas ionization detector in a plane direction orthogonal to the incident radiation;
The method of claim 10 comprising: further,
Orienting the gas ionization detector to first receive incident radiation;
Directing the electric field generated by the gas ionization detector in a plane direction orthogonal to the incident radiation;
Directing an electric field generated by the semiconductor ionization detector in a direction coincident with incident radiation;
The method of claim 10 comprising: further,
Orienting the semiconductor ionization detector first to receive incident radiation;
Directing the electric field generated by the gas ionization detector and the semiconductor ionization detector in the same direction as the incident radiation;
The method of claim 10 comprising: further,
Orienting the gas ionization detector to first receive incident radiation;
Directing the electric field generated by the gas ionization detector and the semiconductor ionization detector in the same direction as the incident radiation;
The method of claim 10 comprising: further,
13. The method of claim 12, comprising selectively utilizing said first and second signals for imaging, radiation monitoring and radiation measurement.

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