WO2016077865A1 - Tomographie à rayons x/gamma à angle unique/limité - Google Patents

Tomographie à rayons x/gamma à angle unique/limité Download PDF

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Publication number
WO2016077865A1
WO2016077865A1 PCT/AU2015/000695 AU2015000695W WO2016077865A1 WO 2016077865 A1 WO2016077865 A1 WO 2016077865A1 AU 2015000695 W AU2015000695 W AU 2015000695W WO 2016077865 A1 WO2016077865 A1 WO 2016077865A1
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Prior art keywords
data
photons
radiation
scatter
tomography system
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PCT/AU2015/000695
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English (en)
Inventor
Jeremy Michael Cooney BROWN
Marcus John Kitchen
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Monash University
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Priority claimed from AU2014904708A external-priority patent/AU2014904708A0/en
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Publication of WO2016077865A1 publication Critical patent/WO2016077865A1/fr

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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
    • A61B6/42—Arrangements for detecting radiation specially adapted for radiation diagnosis
    • A61B6/4266—Arrangements for detecting radiation specially adapted for radiation diagnosis characterised by using a plurality of detector 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
    • A61B6/02—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
    • A61B6/42—Arrangements for detecting radiation specially adapted for radiation diagnosis
    • A61B6/4208—Arrangements for detecting radiation specially adapted for radiation diagnosis characterised by using a particular type of detector
    • A61B6/4258—Arrangements for detecting radiation specially adapted for radiation diagnosis characterised by using a particular type of detector for detecting non x-ray radiation, e.g. gamma radiation
    • 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
    • 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
    • A61B6/5258—Devices using data or image processing specially adapted for radiation diagnosis involving detection or reduction of artifacts or noise
    • A61B6/5282—Devices using data or image processing specially adapted for radiation diagnosis involving detection or reduction of artifacts or noise due to scatter
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR 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
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2211/00—Image generation
    • G06T2211/40—Computed tomography
    • G06T2211/436—Limited angle

Definitions

  • the present invention relates to the field of computed gamma/x-ray tomography.
  • Embodiments of the invention provide both a system and method for gamma/x-ray tomographic imaging and gamma/x-ray tomographic image reconstruction from either a single or limited number of angular gamma/x-ray projections.
  • An X-ray Computed Tomography (X-ray CT) scanner acquires between a few hundred and a few thousand x-ray images of an object/patient at multiple angles to reconstruct its/their three- dimensional structure via digital image processing.
  • the dose given to the object/patient during a clinical X-ray CT scan typically ranges between 1 mSv and 20 mSv. However, in the most extreme cases the level of dose can approach values of approximately 100 mSv.
  • X- ray CT spatial resolution is kept as low as possible to minimize the dose as it is inversely proportional to the fourth power of the spatial resolution.
  • shadowgraph an image created from the differences in x-ray absorption of the materials within the object.
  • Point by point, line by line and plane by plane CST systems utilise a collimated ⁇ - / x-ray source which is raster-scanned or swept over the object of interest.
  • the scattered photons are detected by a collimated energy resolving radiation detector and, in some cases, the attenuated beam of photons is detected by a position resolving radiation detector forming a partial shadowgraph.
  • the collimated scatter detectors are both energy and position resolving.
  • the energy dispersive CST modality utilises a wide area collimated point source and energy resolving radiation detector that are both directed at the object of interest.
  • Embodiments of the present invention employ an imaging modality that is able to reconstruct three-dimensional electron density estimates, i.e. volumetric imaging, of an object through the use of a single or limited number of wide area ⁇ - / x-ray field projections. This is achieved through the measurement and combination of both scattered and transmitted data types in the electron density reconstruction process.
  • the present inventors have identified a system geometry for large area ⁇ - / x-ray field imaging enabling single and limited angle X-ray computed tomography; a collimator design for scatter tomography with, in advantageous embodiments, position resolving radiation detectors; and a novel image reconstruction approach that enables the combination of both scatter and transmission datasets.
  • this novel imaging modality provides improved three-dimensional imaging and enables true four-dimensional imaging (time resolved volumetric imaging).
  • time resolved volumetric imaging time resolved volumetric imaging
  • this novel imaging modality allows the use of radiation doses up to thousands of times lower than today's scientific, pre-clinical and clinical CT systems.
  • the first aspect of the present invention details a system geometry for large area ⁇ - / x-ray field imaging enabling single and limited angle X-ray computed tomography.
  • This system is composed of three basic elements: a large area ⁇ - / x-ray field source, a position resolving radiation detector (or a position and energy resolving radiation detector if desired) positioned to detect photons transmitted through the object, and either a single or multiple collimated position, and if desired energy, resolving radiation detectors for detecting scattered photons.
  • an object stage may be provided on which an object such as a patient can be positioned whilst exposed to radiation.
  • first radiation detectors each configured to resolve the positions of photons incident on a detection face of the first radiation detector
  • one or more large area sources of gamma rays or x-rays each configured to emit a beam of radiation towards at least one first radiation detector, whereby, in use, the one or more first radiation detectors detect photons transmitted through at least part of an object positioned in the path of the respective beam of radiation and output first data describing the positions on the detection face of the respective first radiation detector at which transmitted photons are received;
  • each scatter camera being positioned laterally of each beam of radiation to receive photons scattered from the object, each scatter camera comprising a collimator for filtering the photons scattered from the object and a second radiation detector configured to resolve the positions of photons incident on a detection face of the second radiation detector that pass through the collimator and output second data describing the positions on the detection face of the second detector at which scattered photons are received.
  • At least one of the first radiation detector and the second radiation detector is further configured to detect energy of incident photons.
  • the first and second radiation detectors are only configured to resolve the position of incident photons.
  • a tomography system as claimed in claim 6, comprising at least one pair of scatter cameras positioned opposing one another with their respective detection faces parallel to one another.
  • the transmission and single or multiple collimated radiation detectors measure two different types of shadowgraphs, obtained from transmission and scattered photons, respectively. These two data types contain complementary information about the electron density within the object and, through the application of the novel image reconstruction approach outlined, can be combined to generate true four-dimensional datasets, multiple frames per second volumetric imaging, or a volumetric estimate from very low dose radiation exposures.
  • a collimator is used in front of each scatter detector with the resulting advantage that the radiation detector only needs to be configured to resolve the positions of incident photons.
  • An advantage of this unique collimator design, in combination with the system geometry described above and image reconstruction approach outlined below, is that it removes the need for both energy and position resolving radiation detectors. At present, position only resolving detectors have a small fraction of detection dead time, have a higher spatial resolution and are able to record shadowgraphs at multiple frames per second. These factors increase the maximum frame rate of true four- dimensional volumetric imaging and further reduce the level of radiation exposure required to reconstruct a volumetric estimate of an object of interest.
  • the collimator filters the scattered photons to exclude photons incident on the scatter camera at greater than an acceptable scatter angle from reaching the detection surface.
  • the collimator comprises a grid of collimating cells.
  • the number of cells of the collimator corresponds to a number of detection elements on the detection surface of the second detector.
  • a collimator depth (/) and septal thicknesses between cells in x and y (t( X , y )) are optimised as a function of maximum acceptable scatter angle variation ( ⁇ ), minimum active detector pixel size ⁇ d ⁇ Xiy) ) and ⁇ - / X-ray energy attenuation length ( ⁇ ) in accordance with the following relationships: *.y ⁇ (d x>y /tan ( ⁇ ))-(3/ ⁇ ; ) ; and > d x,y
  • the second aspect of the present invention details a novel image reconstruction approach which is able to combine both scattered and transmission data types.
  • an iterative reconstruction framework the estimates of the electron density from transmission and scattered photons can be combined to calculate both true four-dimensional and three- dimensional volumetric estimates.
  • the key to this approach is the use of detailed physics models in the back and forward projection processes, which enable the replication of self- attenuation effects of the scattered photons within an object of interest.
  • the issue of self-attenuation of the scattered radiation was thought to be a limiting effect of CST; however, the present inventors have realised that these observed effects, seen in the scattered shadowgraphs, can be exploited to yield additional information about the electron density of an object of interest.
  • an electronic method of generating a volumetric estimate of an object comprising:
  • step (d) repeating steps (a) to (c) with the updated first and second data until a current volumetric estimate formed at step (b) meets a convergence condition with respect to a previous volumetric estimate;
  • Another embodiment provides computer program code for implementing the above method.
  • first radiation detectors each configured to resolve the positions of photons incident on a detection face of the first radiation detector
  • one or more large area sources of ⁇ rays or X-rays each configured to emit a beam of radiation towards the at least one first radiation detector, whereby, in use, the one or more first radiation detectors detect photons transmitted through at least part of an object positioned in the path of the respective beam of radiation and outputs first data describing the positions on the detection face of the respective first radiation detector at which transmitted photons are received;
  • each scatter camera being positioned laterally of the beam of radiation to receive photons scattered from the object, each scatter camera comprising a second radiation detector configured to resolve at least the positions of photons incident on a detection face of the second radiation detector, and output second data describing the positions on the detection face of the second detector at which scattered photons are received; and an image reconstruction module configured to process the first data in conjunction with the second data to generate a volumetric estimate of the object by: (a) forming a first backprojection from the first data and forming a second backprojection from the second data;
  • step (d) repeating steps (a) to (c) with the updated first and second data until a current volumetric estimate formed at step (b) meets a convergence condition with respect to a previous volumetric estimate.
  • Figure 1 is a schematic view of a tomography system according to an embodiment of the present invention
  • Figures 2A and 2B are side- and front-views of a pre-clinical single / limited angle ⁇ - / X-ray tomography system according to an embodiment of the present invention
  • Figures 3A and 3B are side- and front-views of a clinical single / limited angle ⁇ - / X-ray tomography system according to an embodiment of the present invention
  • Figures 4A and 4B are cross section and front-views of a collimator according to an
  • Figure 5 is a flow chart of an embodiment
  • Figure 6A is a schematic illustration of a sample used in a simulated example of the invention
  • Figure 6B is a standard x-ray of the sample of Figure 6A;
  • Figures 6C and 6D were formed by simulating radiation scattered by the sample; and Figures 7A to 7D show examples of slices of the 3D sample object volume reconstructed using filtered back projection, based solely on scattered photons.
  • Single/limited angle ⁇ - / X-ray tomography is an imaging modality applicable to the functional and structural volumetric imaging of any object.
  • Embodiments of the invention combine data from transmitted and scattered photons to obtain at least one volumetric estimate of an object.
  • the use of data from both transmitted and scattered photons has the advantage that a complete reconstruction of the object can be generated using much less radiation than conventional tomographic methods that use only the transmitted photons.
  • a plurality of images are obtained in order to advantageously allow the object to be observed as moving in three-dimensional space over time.
  • ⁇ - / X-rays penetrate through matter, some of them are absorbed whilst others pass through the object without interaction.
  • This selective absorption as measured by a transmission detector produces image contrast.
  • up to 90% of the non-absorbed photons can be scattered in random directions via processes including Rayleigh (elastic) and Compton
  • the transmitted X-rays are captured by a detector to form a single two-dimensional (2D) projection image (shadowgraph) of the object.
  • 2D projection image Located laterally of the object position, are one or more scatter cameras having detectors that capture these scattered X-rays.
  • a collimator is applied to the face of each detector to impose a spatial relationship between the object and pixels of the detector.
  • FIG. 1 is a schematic view of a single/limited angle ⁇ - / X-ray tomography system 10 according to an embodiment of the present invention.
  • Tomography system 10 includes a large area ⁇ - / X-ray field source 12, an object stage 14 (towards which ⁇ - / X-ray field source 12 directs a ⁇ - / X-ray field 15), a shielding ring (not shown) surrounding object stage 14, and a plurality of static radiation detectors (termed 'scatter cameras') 18 orientated with their active sensors directed towards object stage 14.
  • Tomography system 10 also includes a ⁇ - / X-ray field backstop (not shown) on the distal side of object stage 14 (relative to source 12) that includes a transmission detector 20 oriented towards ⁇ - / X-ray field source 12.
  • Transmission detector 20 is a position resolving radiation detector (or, optionally, a position and energy resolving radiation detector).
  • Transmission detector 20 comprises, for example, of a 100 mm x 100 mm x 1 mm thick silicon photon counting hybrid pixel detector with a 50 ⁇ pixel size, and is arranged to detect ⁇ -rays and X-rays transmitted through an object (such as a patient) on object stage 14, that is, radiation that has passed through that object, largely without interacting with the object.
  • transmission detector 20 is used by system 10 to form a transmission shadowgraph.
  • multiple transmission detectors could be used depending on the orientation of the ⁇ - / X-ray source/sources.
  • an object stage is not necessary, for example, in industrial applications, objects to be scanned could pass through the tomography system on a conveyor, or the object could be free standing and the tomography system could be moved into place around the object.
  • an object stage is advantageous as it makes it easier for the patient to stay still while the tomography system is operating.
  • Scatter cameras 18 comprise collimated position resolving radiation detectors (or optionally collimated position and energy resolving radiation detectors), and are provided to collect photons scattered from the object on object stage 14.
  • Each scatter camera 18 comprises, for example, a 100 mm x 100 mm x 1 mm thick silicon photon counting hybrid pixel detector with a 50 ⁇ pixel size.
  • Tomography system 10 is shown with two scatter cameras 18, but may include more or fewer scatter cameras. Desirably the scatter camera or cameras 18 subtend as large an angle as practical about object stage 14 in order to gather as much information about the scattered photons as practical, which will commonly be most convenient when plural, individual scatter cameras are employed. In particular, the use of multiple scatter cameras allows the detector bank to gain multiple views of an object.
  • this allows a complete three-dimensional tomographic reconstruction of the object to be created without moving the scatter cameras relative to the object.
  • the scatter cameras may be moved to improve the quality of the reconstruction of the image of the object.
  • multiple scatter cameras will be used and accordingly movement of the scatter detectors will be through a smaller angle than in conventional systems because movement will only be necessary to capture information not captured by another scatter camera.
  • angular movement will typically be through less than 90°. Obtaining images either from one angle or a limited range of angles has the advantage of reducing the radiation dose imparted by the scanner.
  • scatter cameras 18 are arranged around object stage 14 with their active sensors directed towards object stage 14, though without encroaching on the ⁇ - / X-ray field from ⁇ - / X-ray field source 12 or the field of view of transmission detector 20.
  • Scatter cameras 18 are arranged in respective pairs orientated towards object stage 14 such that the scatter cameras of each pair face each other with detection surfaces 19 mutually parallel. This mutual pairing yields additional information, on a voxel by voxel basis, due to co-linear measurement of scattered radiation self-absorption within the object.
  • Tomography system 10 includes a control system 22 that controls the operation of system 10, including in particular source 12 and detectors 18 and 20, and which receives the output of detectors 18 and 20. Control and data connections are shown schematically at 24a-e.
  • Tomography system 10 includes an image reconstruction module in the form of image reconstruction server 26, which receives image data from control system 22, reconstructs images of the subject (as described below) from that data, and outputs a Digital Imaging and Communications in Medicine (DICOM) file (or other appropriate image format) comprising the images.
  • DICOM Digital Imaging and Communications in Medicine
  • This file can be viewed using any conventional computer provided with the appropriate viewing software.
  • FIGS. 2A and 2B are side- and front-views of a specific implementation of tomography system 10, comprising a pre-clinical single/limited angle ⁇ - / X-ray tomography system 30 according to an embodiment of the present invention.
  • Tomography system 30 includes a large area ⁇ - / X- ray field source 32, an object stage 34 (towards which ⁇ - / X-ray field source 32 directs a y- I X- ray field 35), and a shielding ring 36 surrounding object stage 34.
  • the shielding ring 36 includes a plurality of scatter cameras 38 orientated with their active sensors directed towards object stage 34.
  • Tomography system 30 also includes a ⁇ - / X-ray field backstop 40 that includes a transmission detector 42 oriented towards ⁇ - / X-ray field source 32.
  • the ⁇ - / X-ray field source 32 of this embodiment is a microfocus liquid metal jet X-ray source, with a target of indium alloy and an approximate flux of 10 11 photons /(s mm 2 ).
  • X-ray and gamma ray sources could be used, for example, an Amercium 241 based ⁇ -ray source.
  • multiple sources could be used in a single system. Where multiple sources are used they could all be of the same type or composed of a mixture of X-ray and gamma ray sources.
  • an array of Americium 241 based ⁇ -ray sources, an array of microfocus liquid metal jet X-ray sources, or a combination of both, could be orientated around the patient stage.
  • Other possible sources include fixed or rotating anode X-ray generators, or ⁇ -ray sources Cobalt 57, Cobalt 60 and Caesium 137.
  • Transmission detector 42 is a position resolving radiation detector (or, optionally, a position and energy resolving radiation detector).
  • Transmission detector 42 comprises, for example, a 100 mm x 100 mm x 1 mm thick silicon photon counting hybrid pixel detector with a 50 ⁇ pixel size, and is arranged to detect ⁇ -rays and X-rays transmitted through an object (such as a patient) on object stage 34, that is, radiation that has passed through that object, largely without interacting with the object.
  • the output of transm ' detector 42 is used by the system 30 to form a transmission shadowgraph.
  • Scatter cameras 38 like those of system 10, comprise collimated position resolving radiation detectors (or optionally collimated position and energy resolving radiation detectors), and are provided to collect photons scattered from the object on object stage 34.
  • each scatter camera 38 comprises, for example, a 100 mm x 100 mm x 1 mm thick silicon photon counting hybrid pixel detector with a 50 ⁇ pixel size.
  • Tomography system 30 includes eight such scatter cameras 38, but tomography system 30 may include more or fewer scatter cameras. Indeed, in a variant embodiment only one such scatter camera is used, though desirably the scatter camera or cameras subtend as large an angle as practical about object stage 34, which will commonly be most convenient when plural, individual scatter cameras are employed.
  • Scatter cameras 38 are arranged around object stage 34 with their active sensors directed towards object stage 34, without encroaching on the ⁇ - / X-ray field from ⁇ - / X-ray field source 32 or the field of view of transmission detector 42. Scatter cameras 38 are arranged in respective pairs orientated towards object stage 34 such that the scatter cameras of each pair face each other with detection surfaces 39 mutually parallel. Alternatively, since each scatter camera comprises a plurality of detection elements or pixels (as described below), the outputs of respective pairs of opposed detection elements or pixels may be paired during analysis, irrespective of the actual number of scatter cameras 38 into which they are assembled.
  • the output of scatter cameras 38 is used by the system 30 to form one or more scatter shadowgraphs.
  • Figures 3A and 3B are side- and front-views of another specific implementation of tomography system 10, comprising a clinical single/limited angle ⁇ - / X-ray tomography system 50.
  • Tomography system 50 includes an object stage 52 and a shielding ring 54 surrounding an object stage 52.
  • Tomography system 50 further includes, mounted to a rotatable annular mount 56 within shielding ring 54, a large area ⁇ - / X-ray field source 58 directed towards object stage 52 and six scatter cameras 60 with their active sensors also directed towards object stage 52 and with respective pairs of detection surfaces 61 facing each other.
  • ⁇ - / X-ray field source 58 of this embodiment is a rotating anode X-ray source, with a target of tungsten and an approximate flux of 10 9 photons /(s mm 2 ).
  • Tomography system 50 includes a ⁇ - / X-ray field backstop 62 that includes a transmission detector 64 (in the form of, for example, a 750 mm x 750 mm x 1 mm thick Csl(TI) flat panel detector with a 200 ⁇ effective pixel size), also located on annular mount 56, with a transmission detector 64 (in the form of, for example, a 750 mm x 750 mm x 1 mm thick Csl(TI) flat panel detector with a 200 ⁇ effective pixel size), also located on annular mount 56, with a transmission detector 64 (in the form of, for example, a 750 mm x 750 mm x 1 mm thick Csl(TI) flat panel detector with a 200 ⁇ effective pixel size), also located on annular mount 56, with a transmission detector 64 (in the form of, for example, a 750 mm x 750 mm x 1 mm thick Csl(TI) flat panel detector with a 200 ⁇ effective
  • transmission detector 64 directed towards ⁇ - / X-ray field source 58.
  • Annular mount 56 hence rotates source 58, scatter cameras 60, backstop 62 and transmission detector 64 in unison.
  • Scatter cameras 60 each comprise, for example, a 500 mm x 500 mm x 2 mm thick Cadmium Zinc Telluride photon counting hybrid pixel detector with 250 ⁇ pixel size.
  • Clinical tomography system 50 is able to operate in both a single shot and limited angle tomography modes.
  • each scatter camera 18, 38, 60 in anembodiment includes a grid pattern collimator 70, as shown schematically in cross section (figure 4A, shown with detection surface 72 comprising a plurality of detection elements 74) and from the front (figure 4B).
  • Each cell 76 corresponds to a respective detection element or pixel 74.
  • the illustrated exemplary collimator 70 comprises a 10 x 10 grid of cells 76 but it will be appreciated that this is for illustrative purposes to show that the collimator has a distance between walls d(x,y) (here corresponding to active detector pixel size (d(x,y)), collimator depth (/), and a septal thicknesses in x and y ⁇ t(x,y)) leading to a scatter angle variation ( ⁇ ).
  • Collimator 70 in combination with the image reconstruction approach described below, removes the need for energy resolution in detection elements 74. If these detection elements 74 are in the form of position only resolving radiation detectors (i.e. not energy resolving) it enables the use of high flux, high spatial resolution radiation detectors, such as photon counting hybrid pixel detectors, which possess spatial resolutions of tens of microns and individual pixel maximum photon counting rates of 100,000 counts per second.
  • Equation 2 tan(A0)
  • energy resolving radiation detectors can be employed with the advantage that additional information can be obtained about the materials that are present but typically with the disadvantage of a slower counting rate.
  • transmission and scattered datasets are combined through the use of an iterative reconstruction method. In these embodiments, this is in the form of Maximum
  • ML-EM Likelihood Expectation Maximisation
  • This approach is implemented in the present embodiments with the use of a back-projection (BP) approach that has been developed to combine the two complementary transmission and scatter datasets.
  • BP back-projection
  • Conventional techniques are employed in the calculation of Systems Matrices and modelling of the forward projection (P) process on a specific system-by-system basis.
  • One back-projection approach suitable for modification in accordance with the present approach is the Siddon's line backprojection method.
  • Both transmission and scatter datasets are back-projected using Siddon's Line of Response (LoR) approach in which, for the present embodiments, the effective electron density within the region of the projected ⁇ - / X-ray field is estimated.
  • LiR Siddon's Line of Response
  • I / 1 0 is the measured normalised beam intensity
  • ⁇ is the energy dependent attenuation coefficient
  • f is the thickness of the material.
  • Equation 5 p P A
  • p the material density
  • N A is Avogadro's number
  • A the relative atomic mass of the element
  • ⁇ the atomic cross-section
  • o e is the cross-section of an electron
  • nZ is the number of electrons per unit volume
  • N g is the number of electrons per unit mass.
  • V- ⁇ p N g) ⁇ i i a ⁇ Equation 12
  • (pA/ g ) is the electron density of the material.
  • Equation 14 s,e where a s e is the combined coherent scattering (CS) and incoherent scattering (ICS) cross- section for a single electron and ⁇ f E is the photoelectric absorption cross-section.
  • This combined scattering cross-section is dependent on the orientation of each scatter camera 18, 40 with respect to the incident ⁇ - / X-ray field and angular acceptance of the collimator opening ⁇ .
  • a description of an exemplary iterative image reconstruction method 500 for the above electron density mapping approach follows. For a given x-ray/gamma-ray exposure of arbitrarily length, two datasets, scatter data (SD) 501 and transmission data (TD) 502, are recorded. These datasets are piped into the update scatter data estimate (USDE) function 51 1 and update transmission data estimate (UTDE) function 512 which compare 550 the forward projection 545 of the volumetric estimate of the systems active volume with the current value of the volumetric estimate. In the first iteration the current value of the volumetric estimate is a map of the system sensitivity, and the USDE function 51 1 and UTDE function 512 are divided by the current normalised estimate of the systems active volume.
  • USDE update scatter data estimate
  • UTDE update transmission data estimate
  • the current value of the volumetric estimate consists of the current electron density estimate of the systems active volume.
  • the outputs of USDE function 51 1 and UTDE function 512 are then backprojected 520 into individual volumetric estimates and combined into a single dataset through the use of a system specific weighting function 525.
  • This weighting function combines the two temporary volumetric estimates through the fractional ratio of each dataset electron density maps corresponding cross-sectional estimate with respect to the sum of both cross-sectional estimates (derived from Equations 13 and 14). The result is a single electron density volumetric estimate that is then used to update the current estimate of the systems active volume 530.
  • the volumetric estimate is assessed for convergence 535, i.e. has the current volumetric estimate after update changed less than a specific defined measure with respect to the previous estimate. If the volumetric estimate has converged, the iterative loop is broken and a final volumetric estimate of the systems active volume 570 is returned. In the case of where convergence has not been reached, the iterative process continues to the start of the loop with the current estimate forward projected 545 and compared 550 with the last iterations respective scatter and transmission datasets. This process will continue until either convergence or a user defined number of iterations is reached.
  • the method may be embodied in program code.
  • the program code could be supplied in a number of ways, for example on a tangible computer readable storage medium, such as a disc or a memory device or as a data signal (for example, by transmitting it from a server). Further different parts of the program code can be executed by different devices, for example in a client server relationship. Persons skilled in the art, will appreciate that program code provides a series of instructions executable by the processor. Simulation
  • Single shot X-ray tomography was simulated in order to show the quantity of X-rays that would be detected at 90° to the main X-ray beam upon scattering from an object.
  • the Monte Carlo radiation transport toolkit Geant4 (trade mark) was employed. Geant4 enables accurate simulation of the transport of X-rays as they travel through a user defined volume. At each point along the X-ray path, the likelihood of the numerous possible physical interactions is calculated. This includes the probability of X-rays being photo- electrically absorbed, being redirected elastically via Rayleigh scattering, or redirected inelastically by Compton scattering.
  • Geant4 For photons within the diagnostic x-ray energy regime, Geant4 utilises the interaction cross-sections for the given materials from the Evaluated Nuclear Data Library of the OECD Nuclear Energy Agency.
  • a simple phantom sample was simulated, the sample comprising a cylinder of lung tissue 10 mm in diameter and 10 mm in height. Inside this were two smaller cylinders running parallel to the long axis, the first comprising a bone equivalent plastic 3 mm in diameter and 8 mm in height, the second an air-filled cavity 1 .5 mm in diameter and 10 mm in height.
  • Figure 6A is a schematic illustration of this sample 100, showing the lung tissue 102, air-filled cavity 104 and bone equivalent plastic 106.
  • the simulation included a tomography system comparable to the embodiment shown in Figures 2A and 2B, although with eight scatter cameras, each comprising silicon based photon-counting detectors with a depth of 500 ⁇ and a pixel size of 250 ⁇ . These scatter cameras 100 were arranged in an equal angular spacing of 45° to obtain 8 different projections. The scatter cameras collected photons scattered by sample 100 at 90° to the main beam.
  • IMBL IMBL
  • the exposure was set to 20 ms (assuming 10 12 photons / (s mm 2 )) to show the potential for performing dynamic imaging at this spatial resolution. This simulation took approximately 410 thousand CPU hours to run on the MASSIVE supercomputer cluster housed at the Australian Synchrotron and Monash University.
  • Figures 6B to 6D The results of this Monte Carlo based simulation are shown in Figures 6B to 6D.
  • Figure 6B shows the standard X-ray image 1 10 that would be formed by the transmission detector, so may be regarded as a standard radiograph.
  • Figures 6C and 6D were formed by using radiation scattered by the sample and subsequently incident on the collimated photon-counting detectors. The cross-hatching evident in figures 6C and 6D is caused by the cross-hatched collimator design used for this simulation. These results show that scattered X-rays can be used to form a clear image of a sample when using collimated, photon counting detectors.
  • the direct (i.e. transmission) detector produces an attenuation map (shadowgraph) of the sample object in which all three cylinders 102, 104, 106 can be clearly seen.
  • the scatter cameras cf. Figures 6C and 6D
  • the lateral scatter image shows the two internal cylinders overlapping in projection, making them difficult to distinguish.
  • the vertical scatter camera projections Figure 6C
  • bone equivalent plastic cylinder 104 can be seen above the image noise.
  • the air-filled cavity 104 is very easily seen in most projections owing to the larger difference in density between it and the lung tissue 102, than between the bone equivalent plastic 106 and lung tissue 102.
  • Figures 7A to 7D show examples of slices of the 3D sample object volume reconstructed using simple backprojection, based solely on scattered photons.
  • Figures 7A and 7B show axial and coronal slices, respectively, reconstructed using four projections, while figures 7C and 7D show the same axial and coronal slices, respectively, reconstructed with eight projections.
  • Figures 7A to 7D nonetheless show the clear potential for the method, but also that a small number of scatter cameras using standard algorithms may produce images of less than diagnostic quality.
  • Medical applications include diagnostic, prognostic or predictive applications such as scanning the patient to detect abnormalities such as tumours (benign or malignant), oedema, internal haemorrhaging, tissue necrosis, heart defects, cardiovascular disease (including
  • thrombosis thrombosis
  • inflammation e.g. inflammation caused by arthritis, such as rheumatoid arthritis
  • bronchopulmonary dysplasia Other diagnostic applications include obtaining images of complex fractures, blocked blood vessels and obstructions of the bowel.
  • Such technology would also be useful for surgical procedures where implants need to be accurately positioned within the body (e.g. stents).
  • This imaging technology may also be used for imaging patients during radiation therapy to aid in alignment of the x-ray beam with the position of the tumour. In such uses the radiation beam could be used as the radiation source for imaging the three- dimensional structure of the patient.
  • Embodiments of the invention may also be used in fluoroscopy.
  • Embodiments of the present invention are particularly suited to diagnostics in respect of parts of the body that move during normal operation such as the heart or the lungs where it is desired to capture images of one or more operation cycles of the organ. Imaging such body parts with prior art techniques is difficult due to the need to rotate the source and detector around the object to obtain sufficient projections for volumetric reconstruction. This process typically results in object misalignment from projection to projection and/or motion blur from either the movement of the object or movement within the object and rapid movement of the gantry. To obtain time resolved volumetric estimates in this manner, a number of shadowgraphs are measure at each projection which encompasses the entire operation cycle leading to a significant dose of radiation.
  • time resolved volumetric information can be gathered more quickly than in conventional techniques with a resultant reduction in radiation dosage. Further, as no breath or heart beat is exactly the same, gathering data more quickly reduces the complexity of integrating data from a number of different cycles.
  • embodiments of the invention may also be used in industrial applications such as flaw detection, failure analysis, material analysis, and security scanning.
  • an advantage of embodiments of the invention is that information can be gathered more quickly than in conventional techniques allowing for more efficient throughput.
  • a further advantage in industrial applications is that the lower dose requirements of the technique can lead to power savings.

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Abstract

L'invention concerne un système de tomographie (30) qui comprend un ou plusieurs premiers détecteurs de rayonnement (42) et une ou plusieurs sources de grande surface de rayons gamma ou rayons X (32). En utilisation, le ou les premiers détecteurs de rayonnement (42) détectent des photons transmis à travers au moins une partie d'un objet positionné dans le trajet du faisceau de rayonnement respectif et fournissent les premières données décrivant les positions sur la face de détection du premier détecteur de rayonnement respectif (42), au niveau de laquelle les photons transmis sont reçus. Le système comprend également au moins un appareil de prise de vues de la dispersion (38). Chaque appareil de prise de vues de la dispersion (38) est positionné latéralement par rapport à chaque faisceau de rayonnement pour recevoir des photons dispersés par l'objet.
PCT/AU2015/000695 2014-11-21 2015-11-17 Tomographie à rayons x/gamma à angle unique/limité WO2016077865A1 (fr)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112512427A (zh) * 2018-08-07 2021-03-16 美国西门子医疗***股份有限公司 用于医学成像的自适应康普顿摄像机
CN114113173A (zh) * 2021-11-18 2022-03-01 上海联影医疗科技股份有限公司 一种x射线设备、应用于x射线设备中的散射校正方法
CN112512427B (zh) * 2018-08-07 2024-05-24 美国西门子医疗***股份有限公司 用于医学成像的自适应康普顿摄像机

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4887285A (en) * 1986-03-18 1989-12-12 U.S. Philips Corporation Method and device for determining the spatial distribution of chemicals in an object
US5696806A (en) * 1996-03-11 1997-12-09 Grodzins; Lee Tomographic method of x-ray imaging
US20120140887A1 (en) * 2009-06-02 2012-06-07 Mundy Daniel W System and method for dose verification radiotherapy

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4887285A (en) * 1986-03-18 1989-12-12 U.S. Philips Corporation Method and device for determining the spatial distribution of chemicals in an object
US5696806A (en) * 1996-03-11 1997-12-09 Grodzins; Lee Tomographic method of x-ray imaging
US20120140887A1 (en) * 2009-06-02 2012-06-07 Mundy Daniel W System and method for dose verification radiotherapy

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112512427A (zh) * 2018-08-07 2021-03-16 美国西门子医疗***股份有限公司 用于医学成像的自适应康普顿摄像机
CN112512427B (zh) * 2018-08-07 2024-05-24 美国西门子医疗***股份有限公司 用于医学成像的自适应康普顿摄像机
CN114113173A (zh) * 2021-11-18 2022-03-01 上海联影医疗科技股份有限公司 一种x射线设备、应用于x射线设备中的散射校正方法

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