Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/02—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
  • A61B6/03—Computed tomography [CT]
  • A61B6/032—Transmission computed tomography [CT]
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/06—Diaphragms
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/40—Arrangements for generating radiation specially adapted for radiation diagnosis
  • A61B6/4007—Arrangements for generating radiation specially adapted for radiation diagnosis characterised by using a plurality of source units
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/40—Arrangements for generating radiation specially adapted for radiation diagnosis
  • A61B6/4021—Arrangements for generating radiation specially adapted for radiation diagnosis involving movement of the focal spot
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/40—Arrangements for generating radiation specially adapted for radiation diagnosis
  • A61B6/4035—Arrangements for generating radiation specially adapted for radiation diagnosis the source being combined with a filter or grating
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/48—Diagnostic techniques
  • A61B6/482—Diagnostic techniques involving multiple energy imaging
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
  • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
  • G01N23/06—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and measuring the absorption
  • G01N23/083—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and measuring the absorption the radiation being X-rays
  • G01N23/087—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and measuring the absorption the radiation being X-rays using polyenergetic X-rays
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
  • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
  • G21K1/10—Scattering devices; Absorbing devices; Ionising radiation filters
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2223/00—Investigating materials by wave or particle radiation
  • G01N2223/40—Imaging
  • G01N2223/419—Imaging computed tomograph

Definitions

• the present disclosure relates to a method and an imaging system for generating spectrally different X-ray images with an X-ray source and an X-ray detector. More particularly, the present disclosure relates to including a filter providing different spectral filtration within an X-ray system in order to produce a spectrally modulated beam such that neighboring pixels of the X-ray detector receive different spectra, and using this spectral information to perform means of spectral X-ray imaging.
• Computed tomography is the science of recovering a three-dimensional representation of a patient or object by utilizing projection views with different orientations. From this volume, e.g., two-dimensional cross-sectional images can be displayed.
• CT systems typically include an X-ray source collimated to form a cone beam directed through an object to be imaged, i.e., a patient, and received by an X-ray detector array.
• the X-ray source, the cone beam, and the detector array may be rotated together on a gantry within the imaging plane, around the imaged object.
• an unwanted effect may be the radiation dose that a patient receives, as it may induce damage to cells and genes.
• the interaction of X-ray radiation with matter imposes scattered X-ray radiation, which adds in the detector to the signal of interest, i.e., the signal of the primary radiation.
• measures are taken to limit the amount of total X-ray exposure to a minimum, which is required to acquire images.
• a collimator defines a cone shape such that the cone beam covers exactly the whole detector area in order that each detector imaging element (denoted herein as a "pixel”) is exposed to the beam, but the overlap to the non-detector area is reduced to a minimum.
• a bowtie-shaped device known as a "beam shaper,” “bow tie” or sometimes also as a “wedge,” is placed in the path of the X-ray beam.
• the wedge functioning as an X-ray attenuation filter, is generally made of a light metal, such as aluminum, or a synthetic polymer, such as Teflon, having an X-ray absorption spectral characteristic near that of water, and, hence, the human body.
• the wedge is intended to compensate for the variation in thickness of the imaged body.
• the X-rays that pass through the center of the imaged body, normally the thickest part, are least attenuated by this filter, whereas the X-rays that pass through the periphery of the imaged body, normally the thinnest part, are more attenuated by this filter.
• the result of this selective attenuation is a better distribution of the X-ray dose.
• a spatially homogeneous filter (typically in the form of a metal plate, e.g., made of copper) is induced to absorb mainly the low energy components of the spectrum.
• the low energy components of the plain X-ray spectrum are typically that strongly attenuated by an object or a patient that they do not significantly contribute to a measured signal.
• the filter reduces the total dose a patient is exposed to with an acceptable reduction of the acquired detector signal.
• an X-ray imaging system includes an X-ray device having a single X-ray source for forming a plurality of X-ray beams, a filter positioned within the plurality of X-ray beams, an object space where the object to be imaged is accommodated, and an X-ray detector including an array of a plurality of pixels.
• the X-ray device, the filter, and the plurality of pixels are configured such that at least one pixel is exposed to the plurality of X-ray beams.
• X-ray radiation received by a particular pixel undergoes a same spectral filtration by the filter.
• Pixels receiving the X-ray radiation undergoing the same spectral filtration are summarized to a pixel subset. At least two subsets of pixels exist.
• the X-ray device includes a collimator positioned between the X-ray device and the filter, the collimator having a plurality of openings for directing the plurality of X-ray beams generated by the X-ray source.
• the X-ray source includes an X-ray emission area with a spatially modulated X-ray intensity profile such that the plurality of X-ray beams originate from one or more pronounced intensity maxima of the X-ray emission area.
• the plurality of pixels have
• the X-ray imaging system and the collimator are configured to reduce X-ray intensity in the X-ray insensitive regions between the plurality of pixels.
• the filter includes at least two different materials.
• one of the filter materials is air.
• the filter includes one material having a spatial modulation.
• the filter is a combination of at least two spatially separated filters.
• the filter has a spatially alternating pattern of spectral filtration.
• the filter is a grating having grating lines or a pattern of tiles representing different spectral filtration.
• the filter is replaceable and can be chosen from a set of a plurality of different filters.
• the subsets of pixels of the X- ray detector form an interlacing and alternating pattern of rows, columns, or tiles.
• a smallest effective size of a row, a column, or a tile of the alternating pattern of a subset of pixels of the X- ray detector corresponds to the effective size of one pixel.
• the filter is configured such that at least one pixel subset represents an opaque filtration of X-rays such that at least one pixel subset of the plurality of pixels of the X-ray detector is shadowed from any direct X-ray radiation from the X-ray source of the X-ray device.
• a method for measuring an intensity of scattered X-ray radiation for at least one pixel subset of an X-ray imaging system as described above including generating a plurality of X-ray beams via the X-ray device, transmitting the plurality of X-ray beams through a combination of one or more filters and collimators, as well as an object included in the X-ray imaging system, and detecting the scattered X-ray intensity for at least one pixel subset representing an opaque filtration of direct X-ray radiation from the X-ray device.
• a method for generating at least one X-ray projection data set including at least two subsets of spectrally different X-ray projections with an X-ray imaging system including generating a plurality of X-ray beams via the X-ray device, transmitting the plurality of X-ray beams through a combination of one or more filters and collimators, as well as an object included in the X-ray imaging system, detecting the X-ray beams via the X-ray detector of the X-ray imaging system, and logically assigning the acquired data of the pixel subsets of the plurality of pixels of the X- ray detector to subsets of spectrally different X-ray projections.
• FIG. 1 illustrates an imaging geometry of an imaging system, according to the present disclosure
• FIGs. 2a and 2b illustrate a side view and a top view, respectively, of the filter, according to the present disclosure
• FIGs. 3a and 3b illustrate possible configurations of the X-ray filter passed by a plurality of X-ray beams, according to the present disclosure
• Fig. 3c illustrates an alternative arrangement of the filter passed by a plurality of
• FIG. 4 illustrates an alternative positioning of the filter grating, according to the present disclosure.
• Fig. 5 illustrates an alternative of the filter grating being replaced by a combination of two or more filters, according to the present disclosure.
• the present disclosure relates to an x-ray device, particularly in the form of a Computed Tomography (CT) scanner, which includes at least a radiation source, a beam filter, and a radiation-sensitive detector array, described below.
• CT Computed Tomography
• each point emitter projects the filter array onto the detector, such that the overlay of each particular image (using the periodicity of the arrays) produces a congruently superposed image of the filtered array.
• a system and method is suggested that includes introducing a filter which spatially and spectrally modulates the X-ray beam.
• This filter may be, for example, constructed from two different materials within an X-ray system in order to produce a spectrally modulated beam such that, for example, neighboring pixels of the X-ray detector receive different spectra.
• an imaging geometry of an imaging system having at least one
• the X-ray imaging system 100 includes at least one X-ray device 110 emitting X- rays from a number of locations 106, a filter grating 120, an optional collimator grating 130, an object space 140, and an X-ray detector 150 including an array of a plurality of pixels 151 to 155, which may be separated by X-ray insensitive gaps 170.
• the X-ray device 110 generates a plurality of X-ray beams 104, each beam 104 characterized by connecting one of the locations 106 with one of the pixels 151 to 155, respectively.
• the X-ray beams 104 pass through a filter 120.
• the filter 120 may be referred to as a "filter grating" configured to apply a specific filtration to each of the X-ray beams 104.
• Locations 106, filter grating 120, and detector pixels 151 to 155 are configured such that all X-ray beams 104 connected to a particular single pixel undergo the same spectral filtration by filter grating 120.
• the spectral and also spatial separation of X-ray beams 104 may be supported by an optional collimator grating 130 which includes a plurality of openings 108.
• the openings 108 are configured such that they allow for the passage of photons propagating along the center of each of the X-ray beams 104, or stated differently, each photon propagating from the center of a location 106 to the center of any pixel 151 to 155 passes an opening 108 of the optional collimator grating 130.
• blockings 131 of the optional collimator 130 are configured to suppress to a maximum amount of X-ray photons, which propagate from one of the locations 106 towards the gaps 170 in between the pixels 151 to 155.
• not illuminating the pixel gaps 170 means that an object or patient placed in the object space 140 receives less dose compared to a configuration in which the optional collimator grating 130 is not present. For ideal opaque gratings, even a total shadowing of the pixel gaps 170 can be achieved. It can be shown that the dose saving is about 20% for current CT geometries. It is contemplated that the collimator grating 130 is constructed or formed from highly opaque materials, such as, for example, Tungsten or Lead of appropriate thickness, such that the amount of transmitted radiation through the blockings 131 is reduced to a minimum.
• An object to be imaged is positioned in the object space 140 located (from the viewpoint of the X- ray source) behind the filter grating 120 and the optional collimator 130, but before the X-ray detector 150.
• the filter grating 120 and the optional collimator 130 In this exemplary embodiment, five pixels 151 to 155 are shown. However, one skilled in the art may envision several more pixels forming the array of the X-ray detector 150.
• Fig. 2a and Fig. 2b show two possible configurations of the X-ray device 110.
• the X-ray device 110 contains a single area 112 from which X-ray photons emerge. This area may be the common focal spot of a common X-ray tube.
• the emitted X-rays are collimated by a grating 114, which is configured to transmit X-rays only through its openings 106, which are therefore identical to the locations 106 of the X-ray device 110.
• the grating 114 is constructed or formed from highly opaque materials, such as, for example, Tungsten or Lead of appropriate thickness, such that the amount of transmitted radiation through the blockings 231 is reduced to a minimum.
• the X-ray beams 104 received by a particular pixel of detector 150 may pass only a particular number of locations 106, i.e., those locations 106 which are in the line-of-sight between a corresponding pixel of detector 150 and the X-ray emission area 112. Also it may be that X-ray beams 104 assigned to different pixels of detector 150 are assigned to completely different locations 106 of the X-ray device 110.
• the X-ray device 110 includes a single area 116 from which X-ray photons emerge in a spatially modulated intensity such that the locations 106 are represented by local intensity maxima of the X-ray area 116.
• the area 116 may be the focal spot of an X-ray tube for which the modulation of X-ray intensity is performed by a correspondingly varying density of electrons hitting the metal anode.
• the electrons may be generated from a spatially modulated electron source, and a common electron lens optics produces an "image" of the electron source, such that the focal spot displays the same spatial X-ray intensity pattern as the electron source area.
• the filter 120 forms a characteristic pattern of different X-ray filtration.
• this pattern may be in the form of alternating stripes that extend a horizontal (or vertical) length of the filter 120.
• the filter 120 is shown in a side view in Fig. 3a, where a first grating 210 and a second grating 220 are shown both differing from each other by different X-ray filtration properties.
• the filter 120 is shown in a top view in Fig. 3b, where the first grating 210 and the second grating 220 are shown extending a length of the filter 120.
• This alternating pattern design of the filter 120 allows for alternating pixels of the plurality of pixels 151 to 155 to be illuminated with different X-ray spectra. For example, as shown in all of Fig. 1, Fig. 4, and Fig. 5, the first pixel 151 receives a first spectra 180 and the second pixel 152 receives a second spectra 182. Additionally, the third pixel 153 and the fifth pixel 155 receive the first spectra 180, whereas the fourth pixel 154 receives the second spectra 182. Stated differently, the odd pixels (i.e., pixels 151, 153, and 155) receive the first spectra 180, whereas the even pixels (i.e., pixels 152 and 154) receive the second spectra 182.
• each adjacent or neighboring pixel may receive different spectra (i.e., creation of an alternating configuration of spectra). Stated differently, spectrum separation may be achieved. Moreover, the first spectra 180 may have a strong weight on high energy photons, whereas the second spectra 182 may have a strong weight on low energy photons, and vice versa.
• the filter 120 causes the generation of at least two spectra, such that no spatial overlap between the spectrum occurs, or the spatial spectrum overlap is reduced to a minimum for particular locations on the X-ray detector 150.
• a pattern used for a filter grating 120 needs to be aligned to the pattern of the X-ray emission locations 106 of the X-ray device 110, to the pattern of the optional collimator grating 130, and the geometry of the pixel array of the X-ray detector 150.
• subsets of pixels are assigned for the X-ray detector 150, which are aligned to the pattern of different X-ray spectra.
• the grating-line pattern of the filter grating 120 reported in Fig.
• 3a and 3b would be used together with a similar grating-line pattern of the X-ray emission locations 106 of the X-ray device, optionally a grating-line pattern of the collimator grating 130, and a rectangular pattern of detector pixels of the X-ray detector 150 where subsets of pixels form an interlacing grating-line pattern.
• Figs. 3a and 3b An alternative arrangement is, for example, shown in Fig. 3c where the filter grating 120 is formed by a two-dimensional pattern of rectangular tiles 230, 240. This tile pattern is used together with an X-ray device 110 having X- ray emission locations 106 arranged in rectangular array of almost point emitters, optionally with a collimator grating 130 having a rectangular array of openings 108, and an X-ray detector 150 with a rectangular pixel matrix with pixel subsets forming interlacing tile patterns.
• a detector pixel array configured to detect the alternating pattern of spectral filtration, i.e., each pixel detects a spectrum different from its direct neighboring pixel.
• the X-ray device 110, the filter grating 120, and the optional collimator grating 130 may be configured in a way that the first spectra 180 and second spectra 182 form an interlacing partem with a larger periodicity such that a column, a row, or a tile of the pattern covers an detector area with size dimensions larger than that of a single detector pixel.
• the subsets of pixels may contain sequences of directly neighboring pixels.
• the size of a column, a row or a tile of the pattern represented by the subsets of pixels may correspond to the size of one pixel, but it is not limited to the size of one pixel and may therefore have a larger size.
• the X-ray device 110, the filter grating 120, and the optional collimator grating 130 and the detector 150 may be configured in a way that interlacing patterns with more than two spectra can be generated. For example, by choosing a filter grating providing means for three or more different X-ray filtrations and having appropriate grating pitches, it is possible to generate an alternating and interlacing sequence of three or more different spectra on the detector 150.
• a filter 120 fulfilling the configuration may be placed at different positions between X-ray device 110 and detector 150.
• Fig. 4 shows an alternative positioning of the filter grating 120 (it is noted that the grating pitch needs to be adapted according to the total system geometry).
• the filter grating 120 and the optional collimator grating 130 have to be mounted into the system.
• the filter grating 120 may be replaced by a combination of two or more filters 122 and 124 as shown, for example, in Fig. 5.
• One skilled in the art may envision several more arrangements and patterning of an effective grating 120.
• the filter 120 may include or be formed of two or more different materials.
• the filter 120 may be formed from a single material providing different filtration by a modulation of the material thickness.
• One of the filter materials may be air or another weakly attenuating material. Effectively, this weakly attenuating material represents an effective zero attenuation of X-rays such that one of the subsets of pixels is assigned to an effectively unfiltered spectrum.
• one or more of the materials of the filter grating 120 may be formed of materials with relatively large K-edge energies, such as tantalum, tungsten, or lead which results in spectra filtration with a relatively enhanced transmission of photons with energies below the K-edge.
• the K-edge may be chosen high enough such that photons with energies below the K- edge may still pass the object placed in the object space 140.
• materials with a relatively low K-edge such as aluminum, copper or tin are also contemplated to create spectra which put more relative weight to "high" energies, since it is assumed that their K-edge energy is that low that photon energies below their K-edge will effectively not be able to transmit the object placed into the object space 140.
• one or more materials (or their thickness) of filter grating 120 may be made opaque for X-rays, such that at least one subset of pixels does not get illuminated by primary radiation. Consequently, radiation received by these pixels consists of scattered radiation only. By interpolation, the intensity received by the fully illuminated pixels may be corrected for by its scatter content.

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• 2015
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