WO2009111783A2 - Procédé et appareil de détection de rayonnement et d'imagerie - Google Patents

Procédé et appareil de détection de rayonnement et d'imagerie Download PDF

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Publication number
WO2009111783A2
WO2009111783A2 PCT/US2009/036521 US2009036521W WO2009111783A2 WO 2009111783 A2 WO2009111783 A2 WO 2009111783A2 US 2009036521 W US2009036521 W US 2009036521W WO 2009111783 A2 WO2009111783 A2 WO 2009111783A2
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WO
WIPO (PCT)
Prior art keywords
radiation
energy
scintillator detectors
gamma radiation
scattering layer
Prior art date
Application number
PCT/US2009/036521
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English (en)
Other versions
WO2009111783A3 (fr
Inventor
Rebecca Sue Detwiler
James Edward Baciak
Warnick J. Kernan
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University Of Florida Research Foundation, Inc.
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.)
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Application filed by University Of Florida Research Foundation, Inc. filed Critical University Of Florida Research Foundation, Inc.
Publication of WO2009111783A2 publication Critical patent/WO2009111783A2/fr
Publication of WO2009111783A3 publication Critical patent/WO2009111783A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/20—Measuring radiation intensity with scintillation detectors
    • G01T1/202—Measuring radiation intensity with scintillation detectors the detector being a crystal
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/29—Measurement performed on radiation beams, e.g. position or section of the beam; Measurement of spatial distribution of radiation
    • G01T1/2907—Angle determination; Directional detectors; Telescopes

Definitions

  • Gamma ray imaging and detection are used in many scientific and commercial applications, including medical imaging, nuclear spectroscopy, and gamma ray astronomy
  • a traditional Compton imaging design includes two position sensitive detector layers, as shown in Figure 1. In the top level, the gamma ray Compton scatters off an electron in the detector material, where some energy is lost and energy is transferred to the electron off of which the scattering occurs. The energy transferred to the electron creates multiple electron-hole pairs, which combine to create light that is detected.
  • the light can be detected by, for example, a scintillator detector.
  • the instrument is read out.
  • G 1 is the Compton scattering angle of the incident gamma ray
  • m e is the mass of an electron
  • c is the speed of light
  • Ei is the energy of the scattered gamma ray.
  • G 1 and the position of the two interactions a cone can be drawn that includes the direction of the incident gamma ray. As shown in Figure 1, the overlap of cones from multiple events gives the original source position (U.S. Patent No. 6,528,795). While typical Compton imaging devices using Si as the absorber layer provide high angular resolution, it would be advantageous to have a method and apparatus for detection of energy and incident angle of gamma radiation that improves on detection efficiency and/or image resolution of current techniques.
  • Embodiments of the invention relate to a method and apparatus for measuring energy and incident angle of gamma radiation of an external source.
  • Embodiments can incorporate a radiation scattering layer and a radiation absorbing layer.
  • the radiation scattering layer includes a one-dimensional array of a plurality of scintillator detectors or the radiation absorbing layer includes a one-dimensional array of a plurality of scintillator detectors, where the radiation absorbing layer is spaced from the radiation scattering layer.
  • the radiation scattering layer includes a first two- dimensional array of a first plurality of scintillator detectors and the radiation absorbing layer includes a two-dimensional array of a plurality of scintillator detectors, where the second radiation absorbing layer is spaced from the radiation scattering layer.
  • the spacing between the radiation absorbing layer and the radiation scattering is adjustable.
  • lanthanum halide scintillator detectors in the radiation scattering layer and/or the radiation absorbing layer.
  • a lanthanum halide scintillator detector that can be utilized with embodiments of the invention include a lanthanum tri-bromide (LaBr 3 ) crystal scintillator detector and a lanthanum tri-chloride (LaCl 3 ) crystal scintillator detector.
  • a system using LaBr 3 as both detector and absorber can provide higher imaging efficiency than typical Compton imaging devices using Si as the absorber layer.
  • Figure 2 shows a comparison of single Compton scattering efficiency as a function of detector thickness, for two energies. As shown, at energies near 500 keV, LaBr 3 provides a higher efficiency than Si as a scatter detector for detector material thicknesses less than 1.2cm, and this "cutoff thickness increases with photon energy (at 2 MeV the "cut off thickness is greater than 3cm as shown).
  • the scatter detector should be thinner than 1.2cm to allow a single scatter, but not the absorption of the entire energy of the photon for photon energies above 500 keV, using LaBr 3 as both scatter and absorber detector allows a higher Compton efficiency for the energy range 0.5 MeV and higher, as compared to using Si for the scatter detector.
  • Specific embodiments of the subject detector which are advantageous in detection of photons under 500 keV of energy, can incorporate scattering layers less than or equal to 1.5cm. Further embodiments can utilize absorbing layers less than or equal to 6.62cm, and more particularly in the range 5.08cm to 5.62cm.
  • Figures 3, 4A and 4B illustrate the use Of LaBr 3 in a Compton imaging array system, with parallel two-dimensional arrays for both scatter and absorber detector layers and adjustable spacing between the layers.
  • an embodiment of the subject invention is directed to a hybrid imaging routine involving traditional Compton imaging methods for photon energies above 500 keV, and use of a coded aperture method for energies below 500 keV.
  • the coded aperture method uses a shielding element and a position sensitive photon detector, such as a radiation absorbing layer.
  • the shielding element, or coded aperture is composed of "mask elements" that are distributed in a predetermined pattern, which is placed on a grid.
  • the mask elements can be of an equal size.
  • the position sensitive detector has a spatial resolution that is sufficient to resolve the mask-pattern grid. Photons from a given direction project the mask pattern on the detector; this projection has the same coding as the mask pattern, but is shifted relative to the central position over a distance uniquely correspondent to this direction of the photons, as seen in Figure 6.
  • the image of the incident photons is reconstructed via a decoding algorithm, using the accumulated distribution of shifts and intensities from a source.
  • an embodiment of the invention uses a hybrid approach in which the coded aperture incorporates active detection elements Of LaBr 3 (Ce) in the scatter detector layer, as shown in Figure 7.
  • the detector elements of the radiation scattering layer can act as the shielding element to implement the coded aperture technique.
  • embodiments of the subject gamma radiation detection device can utilize a hybrid detection scheme, where for photon energies at or below 500 keV, the shift in the mask pattern of the radiation scattering layer can be used to determine the angle of incidence and absorption in the radiation absorbing layer can be used to determine the photon energy and count (note, absorption in the radiation scattering layer can also be used to determine photon energy and count), and for photon energies above 500 keV Compton imaging using the radiation scattering layer and radiation absorbing layer can be used to determine incident angle, photon energy, and photon count.
  • Figure 1 shows a schematic diagram of a Compton imaging device.
  • Figure 2 shows a comparison of single Compton scattering efficiency as a function of detector thickness for Silicon (Si) and lanthanum tri-bromide (LaBr 3 ) for photon energies of 0.511 MeV and 2 MeV.
  • Figure 3 shows a three-dimensional view of a second lanthanum tri-bromide (LaBr 3 ) radiation absorbing array adjustably spaced from a first lanthanum tri-bromide (LaBr 3 ) radiation scattering array.
  • Figures 4A-4B show a three-dimensional view of a LaBr 3 array and the adjustable array angle (90°).
  • Figure 5 shows a plot from the National Institute for Standards and Technology (NIST) Photon Cross Section Database (XCOM) of photon interaction probabilities as a function of energy in lanthanum tri-bromide (LaBr 3 ).
  • NIST National Institute for Standards and Technology
  • XCOM Photon Cross Section Database
  • Figure 6 shows a schematic diagram of an imaging detector system in accordance with the subject invention using a coded aperture mask.
  • Figure 7 shows a three-dimensional view of a second lanthanum tri-bromide (LaBr 3 ) radiation absorbing array adjustably spaced from a first lanthanum tri-bromide (LaBr 3 ) radiation scattering array, with the first lanthanum tri-bromide (LaBr 3 ) array also functioning as an active Coded Aperture mask element.
  • Embodiments of the invention relate to a method and apparatus for measuring energy and incident angle of gamma radiation of an external source. Specific embodiments relate to a method and apparatus for gamma ray detection. Further embodiments relate to a method and device for directional imaging of gamma radiation. Embodiments of the subject invention can also be used for nuclide identification. Standard methods can be utilized, in conjunction with the detector materials and structures described herein, to accomplish isotope identification, where detector energy signals can be processed via electronics such as analog- to-digital converters and multi-channel analyzers. A gross count detector can also be implemented. Embodiments can incorporate a radiation scattering layer and a radiation absorbing layer.
  • the radiation scattering layer includes a one-dimensional array of a plurality of scintillator detectors or the radiation absorbing layer includes a one- dimensional array of a plurality of scintillator detectors, where the radiation absorbing layer is spaced from the radiation scattering layer.
  • the radiation scattering layer includes a first two-dimensional array of a first plurality of scintillator detectors and the radiation absorbing layer includes a second two-dimensional array of a second plurality of scintillator detectors, where the radiation absorbing layer is spaced from the radiation scattering layer.
  • the spacing between the radiation absorbing layer and the radiation scattering is adjustable.
  • Specific embodiments incorporate lanthanum halide scintillator detectors in the first radiation absorbing layer and/or the second radiation absorbing layer.
  • a lanthanum halide scintillator detector that can be utilized with embodiments of the invention include a lanthanum tri-bromide (LaBr 3 ) crystal scintillator detector and a lanthanum tri- chloride (LaCl 3 ) crystal scintillator detector.
  • a specific embodiment, as shown in Figure 7, relates to a Compton imaging and radiation detector incorporating two lanthanum tri-bromide (LaBr 3 ) two-dimensional arrays.
  • the arrays are nxn scalable substantially planar element arrays with lanthanum bromide (LaBr 3 ) cylindrical crystals having photomultiplier tubes.
  • n 8.
  • Each detector can be monitored separately.
  • Specific embodiments can incorporate photodiodes with the crystals.
  • the detector crystals can have other cross-sectional shapes as well, such as square, rectangular, and hexagonal.
  • each layer of scintillator detectors is of fixed geometry and incorporates separate, relatively large-area crystals.
  • the crystal dimensions are 5.08 cm in diameter by 1.27 cm for the top or "scattering" layer, and 5.08 cm in diameter by 5.08 cm for the bottom or "absorbing" layer.
  • the separation between the layers is approximately 30 cm initially but is adjustable to enable fine-tuning of angular resolution and efficiency.
  • the unit can operate with custom multi-channel signal shaping and read-out electronics. Embodiments can be used, for example, for both Department of Homeland Security
  • Homeland Security related embodiments include portable, vehicle based or portal radiation monitoring, detection and identification systems.
  • Embodiments can have the higher gamma-ray detection and nuclide identification performance than commonly used room-temperature gamma-ray detectors for DHS work.
  • a smaller package can be used and simultaneously provide imaging and directional capability.
  • the higher Z Of LaBr 3 can provide detectors with an efficiency 60% greater than detectors using NaI(Tl), a common detector material for DHS and NNSA applications.
  • Specific embodiments can use crystals of sufficient size and thickness in both layers, and/or hybrid imaging routines, to provide gamma-ray detection, and/or imaging capability, in the energy range 0-20 MeV, which is often of interest for DHS applications and medical physics applications. Further embodiments can operate in the 0-3 MeV energy range. Specific embodiments operate in the 20 keV-5MeV range. Specific embodiments can provide imaging capability with a resolution of 0.1 radians. LaBr 3 can provide improved energy resolution as compared to NaI, for example, 3% at 662 keV for LaBr 3 compared to 6% with NaI. Thus, embodiments can provide a compact, fieldable unit with higher detection efficiency, better energy resolution, and position-sensitive imaging capability.
  • Embodiments of the subject device can detect radiation emanating from a source and can measure energy and angle of incident gamma radiation from the external source. Specific embodiments measure the quantity of radiation and provide spectral information.
  • the two array layers when operated in a summed mode, can provide high efficiency gamma- ray detection and spectral identification data by summing the individual crystals.
  • the two layers can also be operated in coincidence mode (coincidence between layers) to provide angular and directional information.
  • LaBr 3 can be used in a device in accordance with the subject invention for providing angular and directional information due to its excellent timing properties as compared to other high-efficiency room-temperature gamma-ray detector materials.
  • Medical physics embodiments include medical imaging of photons in the 0-20 MeV range. Medical imaging embodiments include 3 -dimensional image reconstruction with proton therapy and other medical imaging applications. Specific embodiments using position sensitive LaBr 3 detectors can provide 3 -dimensional image reconstruction of high energy photons from proton therapy as well in the energy range of 0 - 20 MeV, with a resolution of, for example, 5mm or less for 2 MeV photons.
  • a solid layer of LaBr 3 crystal for example, a 3" x 3" crystal, can be used. Smaller individual crystals in an array layout can allow the system to be used for nuclide identification as well as gamma-ray detection and directional imaging.
  • LaBr 3 is superior to NaI for both gamma-ray detection (NaI has almost a factor of 2 lower detection efficiency for gamma-rays at 662 keV)
  • LaBr 3 is superior for nuclide identification as it has a superior energy resolution (below 3% at 662 keV as compared to 6% or higher in NaI)
  • LaBr 3 also is superior for Compton imaging applications due to its much faster timing (18ns compared to 180 ns for NaI).
  • a Compton imager or "Compton camera” in accordance with embodiments of the subject invention can use a thinner radiation scattering layer detector thickness, oriented at the "top" of the system, or pointing toward the desired detection direction.
  • the gamma-ray will scatter first in the detector of the radiation scattering layer, but not be completely absorbed or stopped in this detector as it is too thin. This allows the gamma-ray to enter the detector of the radiation absorbing layer where is scatters again, and is absorbed.
  • the two scattering positions and partial energy loss in the first detector allow determination of its incoming angle or direction, and its absorption in the second thicker detector allows determination of its energy.
  • a smaller spacing can increase the detection efficiency, the spacing can be adjusted in real time, depending on the situation.
  • Spacing of detectors and distance between the arrays, as well as the distance of the source, can affect both angular resolution and detection efficiency. Larger spacing between absorber and scatterer planes in general produce greater angular resolution. In specific embodiments, the spacing between the planes can be adjusted in real time to optimize resolution and efficiency for a specific source distance. The Compton efficiency increases in general with radius of the detectors, but angular error can also increase with a larger error in position for larger detector (if non-position sensitive detectors are used). A larger spacing between detectors increases angular error and reduces efficiency. A larger spacing between detector planes in general reduces angular error (increases angular accuracy) but as a function of detector dimensions.
  • Position sensitive detectors can be used in the arrays. Such an array design can be implemented with either standard non-position sensitive detectors with photo-multiplier tubes
  • PMT's and associated standard shaping and read-out electronics, or with position- sensitive detectors and a type of ASICs (Application Specific Integrated Circuit) electronics, for example having compact, multi-channel read-outs, and shaping electronics.
  • ASICs Application Specific Integrated Circuit
  • the counts from all detectors can be read out at once, allowing the detectors to function like one large detector, for use with gamma-ray detection.
  • a "coincidence” read-out between two or more detectors can be incorporated, where detector information is recorded if a trigger occurred within a given time window. This can allow read-out for detector hits related to a specific gamma-ray.
  • Nuclide identification can be implemented in accordance with embodiments of the invention, using LaBr 3 as the detector material and can also utilize either single read-out of detectors or coincidence read-out.
  • Four-pi imaging techniques can be utilized and can use a single position-sensitive crystal for both scatter and absorber detector, to provide the gamma-ray direction and energy, thus allowing a solid angle or field-of-view of 4-pi. Imaging efficiencies may vary with incoming angle due to the dimensions of the crystal.

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  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
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Abstract

La présente invention concerne un dispositif destiné à mesurer l'énergie et l'angle d'incidence du rayonnement gamma d'une source externe; il comprend une couche de diffusion de rayonnement et une couche d'absorption de rayonnement. La couche de diffusion de rayonnement comprend un premier réseau bidimensionnel d'une première pluralité de détecteurs à scintillation aux cristaux de tribromure de lanthane. La couche d'absorption de rayonnement comprend un second réseau bidimensionnel d'une seconde pluralité de détecteurs à scintillation aux cristaux de tribromure de lanthane. La seconde couche d'absorption de rayonnement est espacée de la première couche de diffusion de rayonnement.
PCT/US2009/036521 2008-03-07 2009-03-09 Procédé et appareil de détection de rayonnement et d'imagerie WO2009111783A2 (fr)

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US3475508P 2008-03-07 2008-03-07
US61/034,755 2008-03-07

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9201160B2 (en) 2013-11-08 2015-12-01 Baker Hughes Incorporated Measurement of downhole gamma radiation by reduction of compton scattering
WO2020075106A3 (fr) * 2018-10-10 2020-07-30 Ebamed Sa Moniteur gamma instantané pour thérapie par hadron
CN111880211A (zh) * 2020-06-08 2020-11-03 中国科学院高能物理研究所 一种利用康普顿散射事例统计进行放射性核素识别的方法

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US5773829A (en) * 1996-11-05 1998-06-30 Iwanczyk; Jan S. Radiation imaging detector
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US20060202125A1 (en) * 2005-03-14 2006-09-14 Avraham Suhami Radiation detectors
US20070284534A1 (en) * 2006-06-07 2007-12-13 General Electric Company Scintillators for detecting radiation, and related methods and articles

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Publication number Priority date Publication date Assignee Title
US3944835A (en) * 1974-09-25 1976-03-16 General Electric Company High energy radiation detector having improved reflective backing for phosphor layer
US5665971A (en) * 1993-04-12 1997-09-09 Massachusetts Institute Of Technology Radiation detection and tomography
US5773829A (en) * 1996-11-05 1998-06-30 Iwanczyk; Jan S. Radiation imaging detector
US6541836B2 (en) * 2001-02-21 2003-04-01 Photon Imaging, Inc. Semiconductor radiation detector with internal gain
US20060202125A1 (en) * 2005-03-14 2006-09-14 Avraham Suhami Radiation detectors
US20070284534A1 (en) * 2006-06-07 2007-12-13 General Electric Company Scintillators for detecting radiation, and related methods and articles

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9201160B2 (en) 2013-11-08 2015-12-01 Baker Hughes Incorporated Measurement of downhole gamma radiation by reduction of compton scattering
WO2020075106A3 (fr) * 2018-10-10 2020-07-30 Ebamed Sa Moniteur gamma instantané pour thérapie par hadron
US11506801B2 (en) 2018-10-10 2022-11-22 Ebamed Sa Prompt gamma monitor for hadron therapy
CN111880211A (zh) * 2020-06-08 2020-11-03 中国科学院高能物理研究所 一种利用康普顿散射事例统计进行放射性核素识别的方法

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