Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/29—Measurement performed on radiation beams, e.g. position or section of the beam; Measurement of spatial distribution of radiation
  • G01T1/2914—Measurement of spatial distribution of radiation
  • G01T1/2921—Static instruments for imaging the distribution of radioactivity in one or two dimensions; Radio-isotope cameras
  • G01T1/2935—Static instruments for imaging the distribution of radioactivity in one or two dimensions; Radio-isotope cameras using ionisation detectors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/185—Measuring radiation intensity with ionisation chamber arrangements
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J47/00—Tubes for determining the presence, intensity, density or energy of radiation or particles
  • H01J47/02—Ionisation chambers

Definitions

• the present invention is directed to x-ray digital radiography, including dual- energy imaging, computed tomography (CT), microtomography and x-ray microscopy; nuclear medicine, including quantitative autoradiography, single photon emission tomography (SPECT) and positron emission tomography (PET); any medical detector technology involving monitoring, measuring, recording or projection of ionizing radiation of any energy range; bio-optical imaging, including optical confocal microscopy and optical tomography; and industrial applications, such as aerospace imaging, security surveillance systems, and non-destructive imaging.
• the invention is more particularly directed to multi-density and multi-atomic number detector media implemented, if needed, by kinestasis or time-delay integration for use in the above applications.
• the technology of choice depends upon several image quality criteria, such as high quantum and energy absorption efficiency, high detector quantum efficiency (DQE), high spatial resolution, negligible scattered acceptance, detector geometry, fast readout, high dynamic range, image correction and display capabilities, and, of course, acceptable cost.
• DQE detector quantum efficiency
• One of the primary problems with digital radiography is the detection of scattered radiation which reduces the contrast of the image.
• Known line scanning techniques inefficiently utilize the X-ray tube output. This limitation can be overcome by utilizing a wider slot-shaped X-ray beam and collection of multiple lines simultaneously.
• ion and electron interaction within the detector creates random ion/electron motion within the detector element.
• This motion is detected along with the primary ion/electron flow created by the target. Since the motion is random, it does not completely occlude the image, but reduces the image quality by creating ghost images, cloudiness, or reduced contrast, collectively referred to as "noise.” Therefore, a need exists for a detector that provides an improved image by reducing the detection of random ion/electron motion.
• Another aspect of the present invention is to provide an ionization device or source to project ionizing radiation (X-rays, gamma rays, fast particles, neutrons) of any energy range for any application through an object whereupon the rays are received by a multi- detector.
• a further aspect of the present invention is to provide the multi- detector in a dual-energy configuration, wherein the dual-energy detector receives a bimodal energy spectrum analyzed by two different physical media. In either case, the energy can be polychromatic or monochromatic. In the case of a polychromatic energy spectrum, the single energy term is used as equivalent to "average" or "effective energy" of the polychromatic spectrum.
• Yet another aspect of the present invention, as set forth above is to provide the multi-detector with a low-energy detector adjacent to a high-energy detector.
• Still another aspect of the present invention is to apply separate electric fields to both low and high-energy detectors as the incident radiation is projected therethrough, wherein the low-energy detector may either be a gas ionization detector or a semiconductor ionization detector and the high-energy detector is the other.
• a further aspect of the present invention is to generate images from the two detectors which are then received by a microprocessor to generate a subtracted image signal for display of the object.
• Yet another aspect of the present invention is to interpose a high pass energy filter needed between the two detectors to assist in developing the contrasted image signal, wherein a low contrast is obtained through weighted subtraction of the two images, such as for soft tissue.
• Yet a further aspect of the present invention is to provide a mechanism for moving the multi-detector as it receives the ionizing radiation and wherein the electric field applied is adjusted to allow for implementation of kinestatic, or time delay integration techniques, or both.
• An additional aspect of the present invention is to provide a multi-detector wherein the gas ionization detector includes a high voltage plate opposite a substrate with a plurality of interleaved anodes and cathodes and wherein a semiconductor ionization detector includes a bias electrode on one side of a semiconductor substrate opposite a plurality of collection electrodes.
• Yet another aspect of the present invention is to provide a multi-detector within two different physical media in which the incident radiation is first absorbed by a low-energy, low-density, low-Z material detector, with its applied electric field orthogonal to the incident radiation, and wherein the low-energy detector is adjacent a high-energy, high-density, high-Z material detector, with its applied electric field orthogonal to the incident radiation.
• Yet an additional aspect of the present invention is to provide a multi-detector in which the incident radiation is first absorbed by a low-energy detector, with its applied electric field facing directly into the incident radiation, and wherein a high-energy detector is adjacent the low-energy detector, with its applied electric field orthogonal to the incident radiation.
• Still an additional aspect of the present invention is to provide a multi-detector in which the incident radiation is first absorbed by a low-energy detector, with its applied electric field orthogonal to the incident radiation, and whereupon the incident radiation is received by a high-energy detector, with its applied electric field aligned in the same direction as the incident radiation or, in other words, a high-energy detector operating in a slot-scan geometry.
• Still another aspect of the present invention, as set forth above, is to configure, generate images, and perform related detector functions.
• Still yet another aspect of the present invention is to configure the adjacent detectors to perform the same or different functions noted above.
• both detectors could perform imaging functions, or, alternatively, one adjacent detector could perform an imaging function as the other adjacent detector performs a radiation monitoring function.
• the ionizing radiation may be presented in several particles or different radiations (mixed fields), at different energies which can be measured, monitored, or displayed by either one or both of the adjacent detectors upon proper optimization of the system geometries, wherein the detectors perform the same or different functions.
• Another aspect of the present invention is to operate at least one of the detectors as a Frisch Grid to increase signal-to-noise ratio and improve the line- spread function.
• Yet another aspect of the present invention is to interpose a gas electron multiplier close to the collector circuit producing electron amplification without induced current, increasing signal-to-noise ratio, and improving line-spread function.
• Still another aspect of the present invention is to place a gas electron multiplier within the detector volume to improve ion production.
• the present invention provides a dual-energy multi-detector which receives incident ionizing radiation through a subj ect, comprising an ionization detector, a semiconductor detector positioned adjacent the ionization detector, and a gas electron multiplier positioned within said gas ionization detector wherein electric fields are applied to each said detector to generate corresponding signals, and wherein said gas electron multiplier increases electron activity to enhance the performance of said gas ionization detector.
• the present invention also provides a method for obtaining an image of a subject exposed to incident radiation comprising the steps of exposing a multi-detector to incident radiation projected through a sample, wherein the multi-detector comprises a first detector adjacent a second detector; generating a first signal from the first detector; generating a second signal from the second detector; placing a gas electron multiplier near at least one of said detectors; and comparing the first and second signals.
• Fig. 1 is a schematic diagram of a multi-density and multi-atomic number detector imaging system
• Fig. 2 is a schematic diagram of a preferred detector employed in the imaging system
• Fig. 3 is a first alternative embodiment of a detector employed in the imaging system
• Fig. 4 is a second alternative embodiment of a detector employed in the imaging system
• Fig. 5 is a partially cutaway schematic diagram of an alternative embodiment employed in imaging.
• Fig. 6 is a partially cutaway schematic diagram of an alternative embodiment employed in imaging.
• Fig. 7 is a partially cutaway schematic diagram of an alternative embodiment employed in imaging.
• a multi-density and multi-atomic number detector imaging system is designated generally by the numeral 10.
• the imaging system 10 utilizes a high atomic number or high Z material, which is a high density media, in combination with a low atomic number or low Z material, which is a low density media, in order to provide a high-contrast or dual-energy imaging system.
• the system 10 may operate as a slot-scanning beam detector which may be implemented by kinestasis or time-delay integration techniques.
• the imaging system 10 may be used with an Application Specific Integrated Circuit (ASIC) to be operated as a charged couple device camera.
• ASIC Application Specific Integrated Circuit
• the imaging system may be used in large field view imaging or micro-imaging (microscopy) with dual-energy.
• the system 10 includes an ionization device or source 12 for generating and directing ionizing radiation 14 through a subject 16.
• the ionizing radiation 14 may include, but is not limited to, X-rays, gamma rays, fast particles, neutrons, and the like.
• the radiation 14 may be proj ected in the form of mixed fields or at different energies and observed by the multi-detector which performs its predetermined functions.
• the ionization device 12 may be configured to generate a polychromatic energy spectrum of mean energy E or a single energy beam generated by a one frequency spectrum synchrotron.
• the ionization device 12 may be configured to generate a polychromatic bimodal energy spectrum.
• the subject 16 may be a person or a biological or pharmaceutical sample through which the radiation 14 passes to generate rays 18 that are received by a multi-density/multi-atomic number multi-detector 20.
• the multi-detector 20 is provided in a sealed aluminum enclosure 21 which is movable in a plane orthogonal to the incident image rays 18 in a scanning direction 24.
• the multi-detector 20 has several components which are connected to the multi-detector 20.
• the "observation" performed by the multi-detector 20 may be for imaging, monitoring radiation, recording dosage levels, or performing any known function performed by known ionization detectors.
• each detector within the multi-detector 20 may perform different functions or the same function, depending upon the desired results and system configuration.
• a pressure meter 30 is in operative engagement with the pressurized gas 26 so that the pressure within the enclosure 21 of the multi-detector 20 may be regulated.
• a pressure signal 32 is generated by the pressure meter 30.
• control system 36 communicates with various components of the system 10 to monitor and control each function thereof.
• control system 36 includes a microprocessor 40 which provides the necessary software, hardware, and memory to control operation of the imaging system 10.
• the processor 40 receives the pressure signal 32 so that pressure within the multi-detector 20 may be adjusted between low, atmospheric, and high pressures, depending upon the imaging application.
• the processor 40 is connected via a signal line 42 to a detector circuit 44 which is connected to the multi-detector 20 via a signal line 46.
• a signal line 48 com ects the processor 40 to a detector circuit 50 which is connected via a signal line 52 to the multi-detector 20.
• the processor 40 receives information from the detector circuit 44 and the detector circuit 50 and generates a contrasted image signal 54 which is received for display by an image display 56.
• the incident radiation is always first received by the low-energy detector. Any radiation that is not absorbed is then received by the high- energy detector.
• the multi-detector 20 has two basic components: a gas-filled detector volume and a solid state or semiconductor substrate detector volume.
• the incident rays 18 dissipate part of their energy in the first detector volume and then dissipate their remaining energy through interaction in the second detector volume, producing, in both cases, charge pairs.
• An applied electric field through both volumes imparts a constant drift velocity to these charge pairs and drives the charges of polarities toward their respective signal collectors.
• the different detector media used in the detectors may be a solid state semiconductor material, a gas, or a liquid that produces signals via direct or indirect ionization, such as by scintillation, in any geometry or combination thereof.
• logarithmic extractions may be applied to the signals generated by each media, whereupon the difference between the two signals generates the desired image. Additional imaging scenarios may be obtained by changing the orientations of the electric field applied to the low and high-energy detectors so as to achieve the desired image contrast and spatial resolution or other functional result.
• the multi-detector 20 includes a gas ionization detector 60 and a semiconductor ionization detector 62 for a dual-energy imaging embodiment.
• the gas ionization detector 60 includes a high- voltage plate 64 opposite a substrate 66.
• the substrate 66 may be a conductive glass or plastic substrate with suitable electrical conduction properties.
• the substrate 66 may be provided with an electrically- conductive layer on the surface of an insulator by means of ion implantation or deposition of a thin film of semiconductor material.
• a plurality of insulated microstrip anodes 68 are interleaved with a like plurality of 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 anodes 68, and the cathodes 70 are connected to the energy detection circuit 44 via the signal line 46.
• the semiconductor ionization detector 62 includes a substantially rectangular, slab-shaped semiconductor material 56 with a bias electrode 78 disposed on one surface of the cube while a plurality of collection electrodes 80 are disposed on an opposing surface. Accordingly, an electric field 82 is generated between the bias electrode 58 and the collection electrodes 80. Both the bias electrode 58 and the collection electrodes 80 are connected to the detection circuit 50 via a signal line 52.
• the detection components of the energy detectors such as the anodes 68, the cathodes 70, the collection electrodes 80, and even the low and high-energy detection circuits 44 and 50 may be incorporated on an integrated circuit contained within the enclosure 21.
• the integrated circuit would provide all the integrated active and passive signal conditioning and related circuits to generate a digital output received by the processor 40.
• the detector 60 employs a high-pressure gas environment to provide the advantage of a high primary quantum-detection efficiency together with an efficient conversion into charge carriers.
• the gas pressure is increased, the amount of incident photons which interact with the gas increases, therefore increasing the quantum efficiency. Additionally, the amount of photon energy deposited in the gas per interacting photon increases.
• a high-pressure gas-filled ionization detector operating in a saturation regime offers many advantages.
• the gas of choice is xenon because of its high X-ray stopping power.
• krypton may provide an advantage since it has less emitted and re-absorbed fluorescence and allows the interactions to spread out from where the incident radiation impinges on the enclosure 21 while restricting the ranges of the emitted photo electrons and Compton electrons, thereby improving spatial resolution.
• the response of a high-pressure gas-filled detector 60 may be greatly improved by moving the enclosure 21 in synchrony with the ions, wherein the ion speed is adjusted by adjusting the applied electric field so that the ion speed is equal and opposite to the scan speed 24 of the multi-detector 20.
• the ion speed is adjusted by adjusting the applied electric field so that the ion speed is equal and opposite to the scan speed 24 of the multi-detector 20.
• An improvement of the multi-detector 20 and imaging parameters is obtained by utilizing the microstrip substrate 66 as a collector.
• the anodes 68 and cathodes 70 with photolithographic techniques, high gain uniformity over large areas is attainable. Accordingly, as the incident radiation is directed through the multi-detector 20, the primary electrons produced by direct gamma-ray ionization of the gas medium are directed toward the anodes 68. When the electrons reach the electric field between the anodes 68 and cathodes 70, the electrons drift toward the cathodes 70 and experience an avalanche amplification at sufficiently high field strength due to the quasi-dipole anode-cathode configuration.
• the multi-detector 20 utilizing a high operating gas pressure has been chosen as a compromise among high quantum detective efficiency, reduced electron range, and adequate gain.
• Advantages of the gas-microstrip substrate for the detector 60 include high spatial and contrast resolution, resulting from the fine collector size, high gas pressure, and high gain.
• a further advantage of utilizing the low- energy detector in the present invention is that a high gain is achieved with a low applied voltage due to the high local electric fields generated near the anodes.
• a further advantage is that large signals are produced due to the high gain and high quantum efficiency.
• Yet another advantage is that an extremely small signal collection time is needed due to the small anode/cathode separation, high drift velocity caused by the high electric fields, and a small value of microstrip capacitance, which thereby eliminates space-charge effects. Still another advantage is that ahigh mechanical stability, low cost detector is provided.
• the detector 62 receives the image rays 18 which are not affected by the detector 60 and are impinged upon the semi-conductor material 56. Accordingly, the detector 62 is optimally used for digital radiography because of the direct conversion of X-rays to electrical signals.
• Cd ! . x Zn x Te is one potential semiconductor material for medical and industrial imaging applications because it has a high stopping power due to its high mass of density (5.8 g/cm 3 ) and an effective atomic number Z of 49.6 (Cd 09 :48, Zn 0 1 :30, Te:52). This allows for a decreased detector thickness and consequently, good spatial resolution.
• Other potential semi-conductor materials are a- Se, a-Si, CdTe, and the like, which provide a high atomic number and high density.
• the primary advantages of such a semiconductor ionization detector 62, as embodied in the multi-detector 20, is evident by its efficient radiation absorption, good linearity, high stability, high sensitivity, and wide dynamic range. Significant progress has been achieved in the growth of high-quality Cd ⁇ Zn x Te semiconductor crystals using a High Pressure Bridgman technique. Specifically, by alloying CdTe with Zn, the bulk resistivity ofthis semiconductor is approximately 10 u ⁇ -cm.
• the imaging potential of the solid state detector can be improved if a time-delay integration technique is utilized.
• the semiconductor material is organized into an array of pixels consisting of N columns and M rows.
• the speed with which the collective charge is transferred along the columns is synchronized with the speed with which the detector is scanned or translated parallel to the image plane.
• the collected charge corresponding to one portion of the observed subject, is integrated during image acquisition providing a larger signal than that collected in any individual pixel.
• each circuit 44 and 50 controls application of the respective electric fields and monitors the collected signals and if required, performs signal filtering and processing as known in the art.
• the high-voltage plate 64 and the substrate 66 are connected to the circuit 44 to control application of the electric field 72, while the anodes 68 and the cathodes 70 are connected to the circuit 44 to monitor the low energy absorption of the ionized gas medium.
• the bias electrode 78 and the collection electrodes 80 are connected to the circuit 50 to control application of the electric field 82 and to monitor the energy absorption of the semiconductor substrate 76.
• the circuits 44 and 50 then pass corresponding signals 42 and 48 to processor 40, which in turn generates the contrasted signal 54.
• the positioning of the multi-media detectors may be interchanged along with the orientation of their respective electric fields.
• the gas ionization detector 60 is always associated with detection circuit 44 and the semiconductor ionization detector 62 is always associated with detection circuit 50.
• an alternative multi-detector is generally designated by the numeral 100.
• the multi-detector 100 which is received in the enclosure 21 , provides a first or low-energy detector 102 adj acent a second or high- energy detector 104.
• the rays 18 are first impinged upon the detector 102 which employs a semiconductor substrate 103.
• the detector 102 provides a bias electrode 106 on one side of the substrate 103 which directly faces the rays 18 while the opposite side of the substrate 103 provides a pixel array detector 108 made up of a plurality of pixels 109. Accordingly, an electric field 110 is generated across the substrate 103 and is oriented in a direction opposite the rays 18.
• the low energy of the rays 18 is first absorbed in the substrate 103, and any energy that is not absorbed thereby is directed to the detector 104.
• the detector 104 includes a high- voltage plate 112 opposite a substrate 114.
• a plurality of microstrip anodes 116 are interleaved with a plurality of microstrip cathodes 118.
• an electric field 120 is orthogonal to the rays 18 and opposite the scan direction 24.
• the images generated by the detector 102 and the detector 104 are then transferred to their corresponding circuits 44 and 50 for processing by the processor 40, which in turn generates a contrasted image signal 54.
• the electrical leads and components associated with the detectors 104 and 102 are connected to their respective detection circuits, which are in turn connected to the processor 40.
• an alternative multi-detector is generally designated by the numeral 140.
• the rays 18 first impinge upon a gas ionization detector 142, with its electric field is orthogonal thereto.
• the rays 18 are received by a semiconductor ionization detector 144 adj acent to the detector 142.
• the bias electrode 106 is adjacent the detector 142, with the pixel array detector 108 being opposed thereby.
• all the structural features of this embodiment are the same as that of the detector of the previous embodiment. Therefore, the electric field 110 is oriented in the same direction as the impinging rays, and the signals are then collected and generated as in the previous embodiments.
• both of the multi-detectors 100 and 140 may be provided with a high- pass energy filter 150 disposed between the detectors.
• a multi-detector is generally designated by the numeral 300.
• the multi-detector 300 provides a first or low-energy detector 302, which is a gas ionization detector, adjacent a second or high- energy detector 304 in the form of a semiconductor ionization detector.
• the rays 18 are first impinged upon detector 302, which employs a semiconductor substrate 303.
• the detector 302 provides a bias electrode 306 on one side of the substrate 303 which directly faces the rays 18 while the opposite side of the substrate 303 provides a pixel array detector 308 made up of a plurality of pixels 309. Accordingly, an electric field 310 is generated across the substrate 303 and is oriented in a direction opposite the rays 18.
• the low energy of the rays 18 is first absorbed in the substrate 303 , and any energy that is not absorbed thereby is directed to the detector 304.
• the detector 304 includes a high- voltage plate 312 opposite a substrate 314.
• the substrate 314 provides a plurality of microstrip anodes 316 interleaved with a plurality of microstrip cathodes 318, which forms a collector circuit.
• An added feature of this embodiment is the inclusion of gas electron multiplier 330 placed close to the collector circuit, anodes 316, and cathodes 318.
• the gas electron multiplier (GEM) 330 is preferably placed within the detector volume and positioned a few millimeters from the collector circuit.
• Gas electron multiplier 330 comprises a thin composite mesh acting as a gas proportional amplifier in gas media.
• GEM 330 is constructed of an insulating foil 332, metal-clad on both sides 334 and perforated by a regular matrix of holes 336.
• the holes' size preferably, is in the micron range.
• the perforated foil 332 inhibits scattered electron motion and provides a path for those electrons flowing within the produced field.
• An electric field 320 is orthogonal to the rays 18 and opposite the scan direction 24. Electrons within the electron field 320 come into contact with the gas electron multiplier 330 and seek passage through the matrix of holes 336. The electrons collide with gas particles inside the holes 336, causing increased electron activity. This increased activity is seen as an increased electric field produced at the anode 316 of the adjacent detector. The increased electric field strengthens the produced signal.
• signal quality is further improved by applying a potential difference between the GEM' s two sides 334, and electron amplification takes place through a dipole field developed between the hole edges. Avalanching takes place, and an increased electric field is produced at the anode 316. In each embodiment, the increased electric field improves the signal-to-noise ratio by producing an amplified signal.
• Any kind of anode collector or geometry can be used, such as printed circuit board, pixelated, or stripped.
• the microstrip anodes 316 and cathodes 318 may be operated as an amplifier, applying a potential as above, or as a
• Fig. 5 shows a strip collector with Frisch Grid capabilities.
• the low-energy detector anode 316 is much smaller than the noncollecting cathode strip.
• the noncollecting cathode strip serves to shield the collector. Large induced charge results on the strip collector anode 316.
• any geometry of anode and cathode can be utilized as long as the anode is smaller than the cathode. This size difference minimizes the induced signal. For example, Fig.
• FIG. 7 shows an alternative embodiment having a series of smaller anodes 317 and larger cathodes 319 placed on the substrate 303 utilizing a square geometry.
• the larger cathodes 319 reduce the induced charge signal.
• appropriate surface techniques such as undercoating or overcoating are applied to the strips.
• Operating the anode and cathode as a Frisch Grid allows detection of the signal resulting from charge motion and not from induced charge. Accordingly, the line spread function is significantly narrowed, and enhanced image quality is obtained.
• the images generated by the high-energy detector 304 and the detector 302 are then transferred to their corresponding circuits 44 and 70, Fig.
• the processor 40 for processing by the processor 40, which in turn generates a contrasted image signal 74.
• the electrical leads in components associated with the detectors 304 and 302 are connected to the respective detection circuits, which are in turn connected to the processor 40.
• an alternative multi-detector is generally designated by the numeral 400.
• the multi-detector 400 as described above, is provided with a first detector 402 and a second detector 404.
• the GEM 430 is placed within the detector volume. The primary electrons, produced by the
• X-ray ionization of the gas drift toward the GEM 430, as above. Electron multiplication occurs at the GEM 430. As this is occurring, the produced ions drift toward the cathode 416.
• the cathode 416 is used as a Frisch Grid.
• the collector electrode is much smaller of that of the non-collecting grid, and one of the strips is maintained at a potential slightly positive with respect to that of the second electrode. By maintaining one of the strips at a slightly positive potential, amplification occurs.
• appropriate surface treatment techniques, undercoating or overcoating are employed.
• fabrication for the microstrip detector utilizes photolithographic techniques to replace anode-cathode wires with ultra fine layers of conductive strips. Using these techniques improves accuracy in the anode-cathode pattern and ensures high gain uniformity over large areas within the microstrip detector.
• the conductive strips are arranged in an anode-cathode pattern on an insulating or partially insulating glass substrate. The primary electrons produced by direct x-ray ionization of the gas drift towards the microstrip plate. When these electrons reach the microstrip substrate, the electrons drift towards the positively charged strip and experience an avalanche amplification.
• the quasi-dipole anode-cathode configuration causes high field strength that motivates amplification.
• Ions are collected rapidly on the adjacent cathode giving rise to the detected image signal.
• the generated image is then transferred to the corresponding circuits 44 and 70, Fig. 1, for processing by the processor 40, which in turn generates a contrasted image signal 74.
• the electrical leads in the components associated with the detectors 404 and 402 are connected to the respective detection circuits, which are in turn connected to the processor 40.
• the system 10 allows freedom to design and optimize a dual-energy system.
• All of the detectors disclosed herein may operate in a scanning slot beam or pixelated geometry. These detectors may also operate as large area detectors. Using these geometries is more economical than open beam geometry because the detector does not have to be large enough to cover the entire object to be imaged.
• Kinestatic principles are utilized in generating the imaging signals by the low-energy detectors, while the high-energy detectors employ time-delay integration techniques to generate the corresponding observation signals for the scanning slot beam geometries.

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