WO2008115171A1 - Système et procédé de normalisation et de calibrage d'un système d'imagerie utilisant un filtre à épaisseur variable - Google Patents

Système et procédé de normalisation et de calibrage d'un système d'imagerie utilisant un filtre à épaisseur variable Download PDF

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Publication number
WO2008115171A1
WO2008115171A1 PCT/US2007/006623 US2007006623W WO2008115171A1 WO 2008115171 A1 WO2008115171 A1 WO 2008115171A1 US 2007006623 W US2007006623 W US 2007006623W WO 2008115171 A1 WO2008115171 A1 WO 2008115171A1
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WO
WIPO (PCT)
Prior art keywords
radiation
radiation beam
movable plates
plates
filter
Prior art date
Application number
PCT/US2007/006623
Other languages
English (en)
Inventor
Steven Jon Horstman
William M. Fries
William Adams Heindl
Original Assignee
Science Applications International Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Science Applications International Corporation filed Critical Science Applications International Corporation
Priority to PCT/US2007/006623 priority Critical patent/WO2008115171A1/fr
Publication of WO2008115171A1 publication Critical patent/WO2008115171A1/fr

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Classifications

    • 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
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T7/00—Details of radiation-measuring instruments
    • G01T7/005—Details of radiation-measuring instruments calibration techniques
    • 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
    • G21K1/02—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators
    • G21K1/04—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators using variable diaphragms, shutters, choppers
    • G21K1/046—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators using variable diaphragms, shutters, choppers varying the contour of the field, e.g. multileaf collimators

Definitions

  • the invention relates generally to the fields of cargo screening, non-intrusive inspection (Nil), non-destructive testing (NDT), and, more particularly, to systems and methods for calibrating such devices.
  • step wedge Most currently available normalization filters for use with high energy imaging systems are referred to as "step wedge" devices.
  • a step wedge is a single block of material which is cut into steps. Each step is a different thickness that may be placed into the radiation beam. To have many thicknesses one must have many steps. Since each step is in series the wedge is driven with a positioning system which can place each step in the beam. This requires a motion control capability.
  • the step wedge does not perform any of the collimation functions necessary for operation of an imaging system and thus represents yet another component to the source assembly which adds bulk, weight and expense.
  • the ultimate goal is to produce high quality images of the interior/contents of a target.
  • a collimated electromagnetic radiation beam e.g., x-ray or gamma
  • the detected radiation can be used to infer line of sight density information about the target and its contents.
  • Relative motion between the system and target is used to provide a multi-dimensional image.
  • step wedge of solid material, e.g., steel, that is moved in and out of the beam of the radiation source while readings are taken at the detector array.
  • the set of step thicknesses is generally chosen to cover the range of total densities that the system is capable of imaging.
  • a system intended for cargo container inspection may employ thicknesses ranging from VA" of steel (typical container wall thickness), up to the maximum thickness of steel the system can inspect (e.g. 12")-
  • VA of steel
  • a first exemplary embodiment of the present invention describes a system for calibrating a radiation imaging device.
  • the system includes: a variable thickness filter consisting of multiple movable plates for attenuating radiation and a radiation detector for measuring variations in the attenuated radiation.
  • a second exemplary embodiment of the present invention describes a method for calibrating an imaging device.
  • the method includes: directing a radiation beam at a detector; passing the radiation through a variable thickness filter including multiple movable plates, the radiation remaining unattenuated when each of the multiple movable plates is in a first position; attenuating the radiation in one or more increments dependent on the total thickness of the multiple movable plates that are in a second position; and detecting the radiation at the detector.
  • a third exemplary embodiment of the present invention describes a system for calibrating a radiation imaging device.
  • the system includes: a variable thickness filter including multiple steps and a slit through a thickest section of the variable thickness radiation filter and a radiation detector for measuring variations in radiation passing through the variable thickness filter.
  • Figure 1 shows an overall system design for implementing the preferred embodiments of the present invention within a transmission radiation imaging device
  • Figure 2 shows the source subassembly according to an embodiment of the present invention
  • Figure 3 shows a side view of the source subassembly according to an embodiment
  • Figure 4 shows a top, cut-away view collimator subassembly according to an
  • Figure 5 shows a side, partially cut-away view of a collimator subassembly
  • the exemplary device 10 for imaging the contents of a target, e.g., vehicle, shown in Figure 1.
  • the exemplary device 10 is a target, e.g., vehicle, shown in Figure 1.
  • a source assembly 15 includes, among other components, a source assembly 15 and at least one detector 20 for
  • the source assembly 15 is
  • source emits penetrating electromagnetic radiation, e.g., x-ray or gamma radiation. Included in source
  • the assembly 15 is a collimator subassembly 30 as shown in Figure 2.
  • the collimator subassembly 30 acts on x-ray or gamma radiation emitted from source 28.
  • source 28 For example, in a particular
  • x-rays are generated by a betatron.
  • the x-rays generated by the betatron result in a broad, cylindrically symmetric beam.
  • the device 10 requires a narrow, fan-shaped beam of x-rays. Accordingly, the system utilizes a collimator, usually in the form of a slit, that
  • the slit is located in front of the x-ray source, e.g., betatron, as described further herein and creates a window that blocks the broad beam of x-rays except for those x-rays
  • the x-ray source e.g., betatron
  • detector 20 which, in a preferred embodiment, is an array of detectors.
  • detector 20 which, in a preferred embodiment, is an array of detectors.
  • the larger device exemplified through Figure 1 is but one system that may benefit from the invention described herein. Those skilled in the art recognized that other portal, gantry, rail and mobile imaging systems may incorporate the invention.
  • FIGs 3 and 4 illustrate details of the collimator subassembly 30 according to a preferred embodiment of the present invention.
  • the collimator subassembly 30 includes the following principal components: beam flattening filter 40, primary collimator 45, beam monitoring device 47, secondary collimator 55 composed of parts 55a-55j, and normalization and calibration filter 50 composed of parts 50a- 5Oe.
  • Beam flattening filter 40 is used to flatten the radiation beam.
  • the intensity of the radiation beam from an x-ray source is strongly peaked in the forward direction, decreasing strongly away from that direction. Furthermore, the intensity of the beam decreases with the distance from the source.
  • the beam flattening filter 40 thickness is contoured to attenuate the radiation beam so that an approximately uniform radiation intensity is present on the full detector array 20. This is generally desirable for optimum performance of the device 10.
  • the beam flattening filter 40 is formed of a suitable material such as copper or other appropriate materials known to those skilled in the art. Additionally, though shown in the exemplified embodiment as being located prior to the primary collimator 45 in the radiation beam path, the beam flattening filter may be located after the primary collimator 45 or, alternatively, co-located with the primary collimator 45.
  • the primary collimator 45 has a main function of providing first, coarse collimation of the broad source beam. It is in the form of a monolithic block or a block built of multiple plates having a slot through which the desired radiation may pass.
  • the primary collimator is formed of a suitable material or combination of materials, such as copper and lead.
  • a beam monitoring detector 47 Located within the slit of the primary collimator is a beam monitoring detector 47. The beam monitoring detector 47 measures variability of the emitted radiation beam strength and is used to compensate signals measured in the detector array 20 for these variations.
  • the detector 47 may be of the same or similar construction to the individual detectors comprising the detector array 20 of the overall device, e.g., plastic scintillator, NaI, or other detectors well known to those skilled in the art for the detection of x-rays or gamma radiation.
  • a variable thickness normalization and calibration filter 50 is comprised of individual plates having a range of thicknesses of an appropriate material, e.g., copper.
  • an appropriate material e.g., copper.
  • five different filter plates 50a-50e are shown in Figure 4 ranging in size from 4.0 inches to .25 inches in thickness.
  • Each filter plate 50a-50e includes a slit 52 in the center thereof which can be co- located with the slits in all other major components of the collimator subassembly 30. When so aligned, the beam passes through the normalization and calibration filter 50 unimpeded.
  • the thickness of each plate may be moved in and out of the radiation beam path by virtue of actuators.
  • the filter plates may be supported by bearing rods allowing the plates to slide when acted upon by e.g., pneumatic piston actuators.
  • actuator 54a moves filter plate 50a in and out of the radiation beam path in the direction Y supported by rods 53a(i-iv).
  • actuator 54b moves 50b and rods 53b(i-iv);
  • actuator 54c moves 50c and rods 53c(i-iv);
  • actuator 54d moves 5Od and rods 53d(i-iv);
  • actuator 54e moves 5Oe and rods 53e(i-iv).
  • a single actuator serves to move each filter plate in both directions. This is exemplified most readily in Figure 3.
  • variable thickness normalization filter 50 there may be duplicate actuators on either side of the subassembly, one each to push the filter plate in opposite directions.
  • actuators on either side of the subassembly, one each to push the filter plate in opposite directions.
  • Anv combination of components known to those skilled in the art for positioning the i between positions of calibration and collimation is contemplated.
  • the combination of filter plates allows for variable thickness within the beam path ranging from .25 inches to 7.75 inches in .25 inch increments. This is but one exemplary configuration for the variable thickness normalization filter 50.
  • the number and thicknesses of filter plates may be increased or decreased.
  • the total thickness range and actual set of available thicknesses are appropriate to the performance range of the device.
  • an 8 inch filter could be added to the exemplary system to provide thicknesses from .25 inches to 15.75 inches if that were the maximum performance of the larger device.
  • the present invention contemplates additional or thicker filter plates to cover the increased range.
  • increments are exemplified as .25 inches, one skilled in the art recognizes that this is variable.
  • the filter plates extend in the Z direction as well as the X direction like the radiation beam 35 which expands in a fan shape from its source along the Z axis (See Figure 5).
  • the filter plates 50a-50e could be modified in shape and thickness, in order to best perform the normalization function.
  • the filter plates could be in parabolic, radius or stepped thickness profiles. Optimization can also be achieved by varying the material comprising the filter plates, i.e., steel, copper, lead, aluminum etc.
  • a still further embodiment of the invention contemplates a filter plate or set of filter plates, each having three possible positions: an open position for collimation, a first calibration position wherein the filter plate portion in the beam path is comprised of a low or moderate atomic number material (e.g., copper), a second calibration position wherein the filter plate portion in the beam path is comprised of a high atomic number material (e.g., tungsten).
  • a low or moderate atomic number material e.g., copper
  • a second calibration position wherein the filter plate portion in the beam path is comprised of a high atomic number material (e.g., tungsten).
  • This embodiment further includes the possibility of filter plates having more than three positions comprising an open position and multiple different atomic number materials.
  • This embodiment would be accompanied by a set of actuators, e.g. stepper motors, capable of positioning the filter plates in each of the multiple positions.
  • the filter plates could provide for the same approximate attenuation when the filter plates are in different positions,
  • a secondary collimator 55 Co-located with the variable thickness normalization filter 50 is a secondary collimator 55 which produces the final shape of the radiation beam.
  • the secondary collimator 55 is formed of a suitable material such as copper, steel, lead, tungsten or the like. In the embodiment shown, the secondary collimator 55 is formed of multiple stacked plates of approximately equal thickness 55a-55j. But the secondary collimator could be formed of a single, continuous block of material
  • the co-location feature of the present invention allows for a more compact overall source subassembly, which in turn reduces the amount of massive shielding that is required for high energy radiation sources and allows the source to be placed closer to the target and detector array.
  • a post- collimator or scatter trap may also be incorporated as part of the source subassembly.
  • the post-collimator incorporates an opening slit somewhat wider than the opening slit of the second collimator.
  • the post-collimator slit is of sufficient width to trap scattered radiation from the exit of the secondary collimator, but not impinge on the collimating beam thereby becoming an additional source of scatter.
  • the post-collimator is formed of a suitable material such as copper, lead, or tungsten.
  • FIG. 5 a partially cut-away side view of the collimator subassembly 30 is shown, illustrating a side view of the beam flattening filter 40, the primary collimator 45, variable thickness normalization filter 50, secondary collimator 55 and illustrating the path of the radiation fan beam 35.
  • variable thickness normalization filter 50 As an alternative to the variable thickness normalization filter 50 described and shown in Figure 4, the present invention also contemplates using a fixed step wedge filter having a slit through the thickest section, such that the wedge can be co-located with the remaining components during imaging.

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Molecular Biology (AREA)
  • Apparatus For Radiation Diagnosis (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)

Abstract

L'invention concerne un système et un procédé de calibrage d'un système d'imagerie par rayonnement qui inclut un filtre de rayonnement à épaisseur variable à double fonction comportant une fente sur une partie de sorte que dans une première position un faisceau de rayonnement passant au travers ne soit pas atténué et que dans une seconde position le faisceau de rayonnement soit atténué suivant l'épaisseur totale du filtre dans la trajectoire du faisceau de rayonnement. Le filtre peut être formé de multiples plaques mobiles ou d'une seule pièce de matériau haute densité à échelons.
PCT/US2007/006623 2007-03-16 2007-03-16 Système et procédé de normalisation et de calibrage d'un système d'imagerie utilisant un filtre à épaisseur variable WO2008115171A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/US2007/006623 WO2008115171A1 (fr) 2007-03-16 2007-03-16 Système et procédé de normalisation et de calibrage d'un système d'imagerie utilisant un filtre à épaisseur variable

Applications Claiming Priority (1)

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PCT/US2007/006623 WO2008115171A1 (fr) 2007-03-16 2007-03-16 Système et procédé de normalisation et de calibrage d'un système d'imagerie utilisant un filtre à épaisseur variable

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109924996A (zh) * 2017-12-18 2019-06-25 上海西门子医疗器械有限公司 调节准直器和过滤片的方法和装置

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5668847A (en) * 1995-07-20 1997-09-16 Siemens Medical Systems, Inc. Apparatus and method for adjusting radiation in a radiation-emitting device
US5771272A (en) * 1993-11-22 1998-06-23 Hologic, Inc. X-ray densitometer detector calibration by beam flattening and continuous dark scanning
US6389108B1 (en) * 1999-02-03 2002-05-14 Moshe Ein-Gal Moving collimator system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5771272A (en) * 1993-11-22 1998-06-23 Hologic, Inc. X-ray densitometer detector calibration by beam flattening and continuous dark scanning
US5668847A (en) * 1995-07-20 1997-09-16 Siemens Medical Systems, Inc. Apparatus and method for adjusting radiation in a radiation-emitting device
US6389108B1 (en) * 1999-02-03 2002-05-14 Moshe Ein-Gal Moving collimator system

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109924996A (zh) * 2017-12-18 2019-06-25 上海西门子医疗器械有限公司 调节准直器和过滤片的方法和装置
CN109924996B (zh) * 2017-12-18 2023-08-22 上海西门子医疗器械有限公司 调节准直器和过滤片的方法和装置

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