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• • 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
  • A61B6/484—Diagnostic techniques involving phase contrast X-ray imaging
• • 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
  • A61B6/40—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
  • A61B6/42—Arrangements for detecting radiation specially adapted for radiation diagnosis
  • A61B6/4291—Arrangements for detecting radiation specially adapted for radiation diagnosis the detector being combined with a grid 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
  • A61B6/486—Diagnostic techniques involving generating temporal series of image data
• • 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
  • A61B6/52—Devices using data or image processing specially adapted for radiation diagnosis
  • A61B6/5205—Devices using data or image processing specially adapted for radiation diagnosis involving processing of raw data to produce diagnostic data
• • 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
  • G01N23/04—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 forming images of the material
  • G01N23/046—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 forming images of the material using tomography, e.g. computed tomography [CT]
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T1/00—General purpose image data processing
  • G06T1/0007—Image acquisition
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T11/00—2D [Two Dimensional] image generation
  • G06T11/003—Reconstruction from projections, e.g. tomography
  • G06T11/006—Inverse problem, transformation from projection-space into object-space, e.g. transform methods, back-projection, algebraic methods
• • 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
• • 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
  • G01N2223/60—Specific applications or type of materials
  • G01N2223/612—Specific applications or type of materials biological material
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2200/00—Indexing scheme for image data processing or generation, in general
  • G06T2200/04—Indexing scheme for image data processing or generation, in general involving 3D image data
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2210/00—Indexing scheme for image generation or computer graphics
  • G06T2210/41—Medical
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2211/00—Image generation
  • G06T2211/40—Computed tomography
  • G06T2211/424—Iterative

Definitions

• CT computed tomography
• Dark-field (or grating-based differential phase-contrast) imaging overcomes the above-noted contrast limitation.
• imaging utilizes X-ray gratings, which allow the acquisition of X-ray images in phase contrast, which provides additional information about the scanned object.
• dark- field imaging an image is generated that is based on the scatter components of the X-ray radiation diffracted by the scanned object. Very slight density differences in the scanned object then can be shown at very high resolution.
• An example imaging system configured for dark-filed imaging is discussed in application serial number 13/514,682, filed June 8, 2012, entitled “Phase Contrast Imaging," and assigned to Koninklijke Philips Electronics N.V., the entirety of which is incorporated herein by reference.
• the apparatus described in 13/514,682 is shown in FIGURE 1 and includes an X-ray source 102 and a detector array 104 located opposite each other across an examination region 106.
• a source grating 108 is adjacent to the source 102
• an absorber (or analyzer) grating 110 is adjacent to the detector array 104
• a phase grating 112 is between an object 114 and the absorber grating 110.
• the source grating 108 is separated from the phase grating 112 by a distance ("1") 116.
• the source grating 108 creates an array of individually coherent, but mutually incoherent sources.
• the object 114 in the beam path causes a slight refraction for each coherent subset of X-rays, which is proportional to the local phase gradient of the object. This small angular deviation results in changes of the locally transmitted intensity through the combination of the phase gratings 112 and the absorber grating 110.
• the phase grating 112 acts as a beam splitter and divides an incoming X-ray beam essentially into the two first diffraction orders.
• the diffracted beams interfere and form, in Talbot distances, linear periodic fringe patterns with a periodicity that equals half the phase grating times the geometric magnification factor defined by 1 / (1+d).
• Perturbations of the incident wave front such as those induced by refraction on the object 114 in the beam, lead to local displacement of the fringes.
• the absorber grating 110 acts as a transmission mask for the detector array 104 and transforms local fringe positions into signal intensity variations.
• the detected signal profile hence contains quantitative information about the phase shift induced by the object 114.
• phase-stepping approach To code and extract the phase information, a phase-stepping approach has been utilized. With this approach, the absorber grating 110, relative to the phase grating 112, is translated in a transverse direction, which is perpendicular to the lines of gratings, via predetermined step size movements over a grating lines period. At each grating step, a measurement is taken, and several (e.g., eight) grating steps and measurements are taken for a projection.
• the object 114 is rotated relative to the source 102, the gratings 108, 110 and 112, and the detector array 104, or the source 102, the gratings 108, 110 and 112, and the detector array 104 are rotated around the object 114 (over at least 180 degrees plus a fan angle), with a predetermined number of projections (e.g., 1000) acquired from different angular views of the rotation.
• a predetermined number of projections e.g. 1000
• Each pixel in the dark field image represents a line integral of the second moment of the small angle scattering distribution.
• the contribution to the line integral depends on the relative position of the object 114 in the examination region 106 between the source 102 and detector array 104, due to inverse signal magnification.
• FIGURES 2 and 3 the object 114 is closer to the source 102 relative to the position of the object 114 in FIGURE 3.
• a maximum height 202 of a detector array profile 200 for the object location in FIGURE 2 will be smaller relative to a maximum height 302 of a detector array profile 300 for the object location in FIGURE 3.
• inverse signal magnification scales the height of the detected signal inversely with respect to the position of the object 114 between the source 102 and the detector array 104.
• / l Q e - lf ⁇ S+lr)dl
• I 0 the unattentuated detected signal
• /( ⁇ ) is the the distribution of the object property
• S is the source position
• r is a unit vector along the x- ray from the source 102 to the phase grating 112. Logging both sides of the equations renders a linear equation representing the line integral of the attenuation coefficient along a path, as shown in EQUATION 2:
• the goal is to reconstruct the distribution of the property "( ⁇ ) along the ray r.
• the imaging system must at least include a rotating frame that supports the source 102, the detector and the gratings 108, 110 and 112, a stationary frame and bearing to support the rotating frame, a belt, chain, magnetic or other drive system along with a motor and controller to rotate the rotating frame, and one or more encoders or the like to determine angular position information, which adds complexity and cost to the overall dark field imaging system.
• the rotating components are under g forces, which cause dynamic structural changes to the rotating components during each rotation, which may increase the mechanical requirements and tolerances of the phase stepping components so the grating is accurately stepped for each measurement.
• a method for dark-field imaging includes acquiring dark-field image projections of an object with an imaging apparatus that includes an x-ray
• interferometer applying a pressure wave having a predetermined frequency to the object for each acquired projection, wherein the predetermined frequency is different for each projection, and processing the acquired projections, thereby generating a 3D image of the object.
• an imaging system in another aspect, includes a scanner configured for dark- field imaging, the scanner including: a source/detector pair and a subject support, a pressure wave generator configured to generate and transmit pressure waves having predetermined frequencies, and a console that controls the scanner and the pressure wave generator to acquire at least two dark-field projection of an object with different pressure waves having different frequencies applied to the object.
• a method in another aspect, includes generating a 3D dark-field image of an object with data acquired without a relative movement between a source/detector pair of an imaging system scanning the object and the object and by applying pressure waves having different frequencies for each acquired projection.
• the invention may take form in various components and arrangements of components, and in various steps and arrangements of steps.
• the drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention.
• FIGURE 1 schematically illustrates a prior art apparatus configured for dark- field imaging.
• FIGURES 2 and 3 schematically illustrate how object position magnification along a ray affects dark-field imaging.
• FIGURE 4 schematically illustrates an imaging system configured for 3D dark-field grating-based DPCI imaging.
• FIGURE 5 illustrates an example method for 3D dark-field grating-based
• an imaging system 400 includes a scanner 401 configured for at least 3D dark- field imaging is schematically illustrated.
• the scanner 401 includes a radiation source 402 (e.g., an X-ray tube) with a focal spot 404 that emits radiation that traverse an examination region 406 and an object 417 or subject therein.
• a radiation sensitive detector array 408 is located opposite the radiation source 402 across the examination region 406. The radiation sensitive detector array 408 detects radiation traversing the examination region 406 and generates a signal indicative thereof, including a dark-field signal in connection with dark-field imaging.
• An X-ray imaging interferometer includes three grating structures, a source grating 410, a phase grating 412 and an absorber grating 414.
• the source grating 410, phase grating 412 and absorber grating 414 respectively have grating line periods and are separated by distances, e.g., as discussed in application serial number 13/514,682, filed June 8, 2012, entitled “Phase Contrast Imaging,” and assigned to Koninklijke Philips Electronics N.V., the entirety of which is incorporated herein by reference.
• the source grating 410 is adjacent to the focal spot 404 in the path of the radiation, acts as an absorbing mask with transmitting slits, filters the emitted radiation beam, and creates individual coherent (but mutually incoherent) sources.
• the object causes refraction of coherent x-rays that is proportional to the local gradient of the real part of the refractive index of the object, and the angular deviation results in changes of the locally transmitted intensity through the phase grating 412.
• the phase grating 412 is located adjacent to the object and acts as a beam splitter, dividing an incoming x-ray into diffracted beams that interfere and form linear periodic fringe patterns.
• the absorber grating 414 acts as a transmission mask for the detector 408 and transforms local fringe positions into signal intensity variations.
• the phase/absorber gratings 412/414 can be considered a multi-collimator translating the angular deviations into changes of the locally transmitted intensity, which can be detected with a standard or other imaging detector array.
• the phase grating 412 and the absorber grating 414 are configured to translate, relative to one another, in a transverse direction, perpendicular to the z-axis. This includes translating one or both (in a same direction with different speeds or an opposing direction with the same or different speed) of the phase grating 412 and the absorber grating 414 in the transverse direction.
• a grating stepper 418 controls translation (i.e., stepping) of the absorber grating 414 at least based on a phase stepping algorithm which moves the absorber grating 414 in predetermined discrete step size increments.
• a pressure wave generator 420 generates and transmits a pressure wave that traverses the examination region 406 and the object 417 therein.
• the pressure wave generator 420 may include a transducer or the like that can convert one form of energy (e.g., electrical) into a pressure wave of a predetermined frequency. Suitable frequencies are frequencies between one Hertz (1 Hz) and one thousand Hertz (1000 Hz), which cause compression and/or vibration of the material of the object 417 that results in physical deformation of the object 417 in the examination region 406 which is similar to actual physical displacement of the object 417 in the examination region 406.
• a general-purpose computing system or computer serves as an operator console 424.
• the console 424 includes a human readable output device such as a monitor and an input device such as a keyboard, mouse, etc.
• Software resident on the console 424 allows the operator to interact with and/or operate the imaging system 400. Such interaction includes selecting a dark- field imaging scan protocol which utilizes the pressure wave generator 420, initiate scanning, etc.
• a subject support 416 supports the object 417 in the examination region 406.
• the pressure wave generator 420 is invoked to transmit a pressure wave that traverses the object 417 and the grating stepper 418 steps the absorber grating 414 through phase coding steps for acquisition of a projection, a pressure wave having a different frequency is generated for different projections, and the projections are acquired with no relative movement between the source/detector pair 402/408 and the object 417.
• the number of phase coding steps and/or projections can be default, user defined, and/or otherwise determined.
• the pressure waves interacts with the material of the object 417 and such interactions result in different material deformations of the object 417 for each projection, which, effectively, is similar to physically moving the object 417 along a ray path between the source 402 and the detector array 408.
• the dark field signal A is a function of distance of the object 417 from the source 402
• the resulting set of projections include information that can be used to determine attenuation along each ray, which is described is greater detail next.
• a j a e -i .tk t +(S+lf)k 7 ) ⁇
• a is the amplitude of the displacement
• i sqrt(-l)
• k t is the frequency of the sound wave
• k r is the wavelength
• t time.
• the dark field imaging measurement h as a function of local displacement, and based on EQUATIONS 2 and 4, can be expressed as shown in in EQUATION 5:
• h(M) j( l + A )f(S + lr)dl.
• EQUATION 6 With a set of modulations, EQUATION 6 becomes a Fourier transformation.
• a dark- field signal processor 422 processes the dark-field signals generated and output by the detector array 408, producing 3D data of the scanned object 417. This includes inverting the Fourier transformation and reconstructing the distribution of the property /( ⁇ ) along the ray r, creating a 3D image of the object. Where inhomogeneous elastic properties of the tissue disturb the displacement field, an iterative reconstruction and a discrete formulation of the measurement can be used to solve for an elasticity field and the dark field in one combined reconstruction.
• FIGURE 5 illustrates an example dark field imaging method with no physical movement of the source/detector pair 402/480 and the object 417 between projections.
• a reference projection of a dark- field scan of the object 417 is acquired with no relative movement between the source/detector pair 402/480 and the object 417.
• a pressure wave having a predetermined frequency is applied to the object, which causes a deformation of the object 417 similar to actual physical displacement of the object 417 along a ray path between the source 402 and the detector 408.
• a next projection of the dark- field scan of the object 417 under the first deformation is acquired with no relative movement between the source/detector pair 402/480 and the object 417.
• acts 504 and 506 are repeated with a pressure wave having a next different frequency.
• the projections are processed to generate a 3D image of the object 417.
• the above methods may be implemented by way of computer readable instructions, encoded or embedded on computer readable storage medium, which, when executed by a computer processor(s), cause the processor(s) to carry out the described acts. Additionally or alternatively, at least one of the computer readable instructions is carried by a signal, carrier wave or other transitory medium.

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• 2013
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