[go: up one dir, main page]

WO1993010472A1 - Detection de rayons gamma - Google Patents

Detection de rayons gamma Download PDF

Info

Publication number
WO1993010472A1
WO1993010472A1 PCT/AU1992/000620 AU9200620W WO9310472A1 WO 1993010472 A1 WO1993010472 A1 WO 1993010472A1 AU 9200620 W AU9200620 W AU 9200620W WO 9310472 A1 WO9310472 A1 WO 9310472A1
Authority
WO
WIPO (PCT)
Prior art keywords
scintillation
rays
crystals
signals
array
Prior art date
Legal status (The legal status 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 status listed.)
Ceased
Application number
PCT/AU1992/000620
Other languages
English (en)
Inventor
Geoffrey Norman Taylor
Gary Francis Egan
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
University of Melbourne
Original Assignee
University of Melbourne
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 University of Melbourne filed Critical University of Melbourne
Publication of WO1993010472A1 publication Critical patent/WO1993010472A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

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
    • G01T1/29—Measurement performed on radiation beams, e.g. position or section of the beam; Measurement of spatial distribution of radiation
    • G01T1/2914—Measurement of spatial distribution of radiation
    • G01T1/2985—In depth localisation, e.g. using positron emitters; Tomographic imaging (longitudinal and transverse section imaging; apparatus for radiation diagnosis sequentially in different planes, steroscopic radiation diagnosis)
    • 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
    • G01T1/2018—Scintillation-photodiode combinations
    • G01T1/20182—Modular detectors, e.g. tiled scintillators or tiled photodiodes
    • 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
    • G01T1/2018—Scintillation-photodiode combinations
    • G01T1/20184—Detector read-out circuitry, e.g. for clearing of traps, compensating for traps or compensating for direct hits
    • 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
    • G01T1/2018—Scintillation-photodiode combinations
    • G01T1/20185—Coupling means between the photodiode and the scintillator, e.g. optical couplings using adhesives with wavelength-shifting fibres

Definitions

  • the light emitted from at least one end of a scintillation crystal is detected and measured by the light detection means comprising an array of photodiodes.
  • X-ray or gamma ray detection apparatus comprising an array of elongate scintillation crystals, first light detection and measuring means at one end of each scintillation crystal, second light detection and measuring means at the other end of each scintillation crystal, and comparator means to receive and compare signals from the first and second light detection and measuring means whereby when an X-ray or gamma ray is absorbed by one of the scintillation crystals the signals from the first and second light detection means at both ends of that crystal are compared to determine the scintillation point within the crystal.
  • a preferred method of determining the longitudinal location of the scintillation point within an elongate crystal is to calculate the ratio of the number of photons detected at one end of the crystal to the sum of the number of photons measured by both detection means.
  • the signal output of each detector is proportional to the number of photons detected by that detector and so the ratio of the pulse height from one end to the total pulse heights can be used as a measurement of the required ratio of photons. This method is insensitive to the actual number of photons produced as only ratios are used.
  • the array of scintillation crystals are preferably arranged around the X-ray or gamma ray source in an annular or cylindrical arrangement so that a pair of gamma rays emitted from the source in opposite directions will be absorbed in generally opposed crystals of the array.
  • the light detectors at the inner ends of the crystals it is necessary for the light detectors at the inner ends of the crystals to be of a very thin construction, and a photodiode array satisfies this requirement so that the amount of material in front of the inner ends of the crystals does not distort the imaging capacity of the array to any significant extent.
  • the present invention therefore enables considerably smaller annular or cylindrical arrays to be used, and this substantially reduces: the manufacturing cost and complexity; the space needed to install an imaging camera; and the complexity and cost of maintenance.
  • the scintillation crystals may comprise crystals of any suitable scintillation material, for instance bismuth germanate (BGO).
  • BGO bismuth germanate
  • the light detection means at the ends of the crystals remote from the photodiode array may comprise any convenient form of detector, for instance, a photomultiplier tube, because in an annular arrangement of crystals it is not necessary for the detectors at the other ends of the crystals to be of a thin construction.
  • a method of determining the coincidence of X-rays or gamma rays in opposed or nearly opposed scintillation crystals of X-ray or gamma ray detection apparatus comprising a plurality of blocks of scintillation crystals and associated light detectors disposed around a source of X-rays or gamma rays, wherein the method comprises the steps of: supplying detection signals from each of the plurality of blocks of light detectors to logic gates of coincidence logic circuitry including a programmable memory; the logic gates being arranged to produce output trigger signals when detection signals from at least two detectors are received by a logic gate within a desired time interval; programming the memory to provide identification signals to respective logic gates of the coincidence logic circuitry; and using the identification signals to determine when trigger signals are produced by a coincidence of detection of X-rays or gamma rays absorbed in opposed or nearly opposed crystals.
  • apparatus for detecting X-rays or gamma rays comprising a plurality of blocks of scintillation crystals and associated light detectors disposed in an array around a source of X-rays or gamma rays, and coincidence logic circuitry connected to the light detectors associated with the blocks of crystals, wherein the coincidence logic circuitry includes a plurality of AND gates, each connected to at least two detectors, memory means programmed to provide respective identification signals to each of the AND gates, clock means to provide clock signals to the AND gates, and an OR gate connected to the outputs of the AND gates, wherein each AND gate provides an output signal when detection signals are received from at least two detectors within a predetermined time window determined by the clock signals, and the OR gate provides a trigger signal in response to the output signals from the AND gates to indicate a coincidence between X-rays or gamma rays detected by absorption in two or more blocks of scintillation crystals of the array, the identification signals
  • Figure 2 is a side view of part of the scintillator crystal and photodiode array of the apparatus of Figure 1 ;
  • Figure 4 is a graph of the number of photons detected at one end of a scintillation crystal plotted against distance along the crystal;
  • Figure 5 is a graph of the sum of the photons detected at both ends of the crystal plotted against distance along the crystal;
  • Figure 6 is a graph showing the ratio of the number of photons measured at one end to the sum of the number of photons measured at both ends plotted against distance along the crystal
  • Figure 7 is a schematic diagram of an analogue electronic circuit suitable for use with the diode array of the gamma imaging apparatus
  • Figure 8 is a schematic diagram of a crystal and detector arrangement with detectors on four sides of the gamma source under study
  • Figure 9 is a diagram of the coincidence logic circuitry associated with the crystal and detector arrangement of Figure 8.
  • Figure 10 is a schematic timing diagram for the electronic circuit of Figure 7.
  • FIG. 1 of the drawings there is shown a ring 10 of elongate scintillation crystals 12 forming an annular array of crystals surrounding an object 14 under study. It will, however, be appreciated that a plurality of rings of crystals may be provided to form a cylindrical array. If, for instance, positron annihilation takes place at point X in the object 14 two high energy X-rays or gamma rays ⁇ , ⁇ will be propagated in opposite directions from point X along flight path F.
  • the gamma rays ⁇ , ⁇ thus enter respective scintillation crystals 12a, 12b on opposite sides of the annular array 10 by passing through thin light detectors 16 on the inner ends of the crystals 12a and 12b at absorption points Z to generate photons of light which travel longitudinally in opposite directions within the crystals 12a and 12b.
  • Further light detectors 18 are provided on the outer ends of the crystals 12 so that light generated by absorption of the gamma rays in a crystal 12a or 12b is detected at each end of the crystal to enable the longitudinal position of the scintillation point Z within the crystal to be determined. Information on the transverse position of the scintillation points Z is obtained from the opposed or nearly opposed crystals in which scintillation takes place.
  • the region R 1( of possible trajectory of the gamma rays ⁇ , ⁇ is wider than the region R 2 of possible trajectory if information on both the longitudinal and transverse position of the scintillation points Z is determined.
  • Each of the graphs refers to data obtained from an elongate scintillation crystal of bismuth germanate (BGO) having a length of 20mm and a square cross-section of 3x3mm 2 .
  • BGO bismuth germanate
  • a diffuse reflector coating of 98% reflectance is applied to the side surfaces of the crystal and the index of refraction of the detectors is about 1.5.
  • the dip in the middle of Figure 5 is due to losses in reflections from the walls, where the distance from both ends is largest.
  • the number of reflections off the surface of a crystal is large and hence losses become important where the point of interaction Z is at a maximum from the detectors at the ends of the crystals.
  • the method for obtaining information on the longitudinal position of interaction Z is to take the ratio of photons measured at one detector to the sum of the number of photons detected at both ends N A /(N A + N B ) as shown in Figure 6. This determination is insensitive to the number of photons produced because only ratios are used.
  • the signal output from a detector is proportional to the number of photons detected by that detector and so the ratios of pulse heights can be used as a measurement of the ratio of photons plotted in Figure 6.
  • the plot in that graph can then be used to convert the ratio to a measured position along the crystal.
  • each scintillation crystal 12 comprises an array of photodiodes 16 whereas the light detector 18 on the front or outer end of each crystal may comprise a photomultiplier tube (PMT) or a light guide in combination with a PMT.
  • PMT photomultiplier tube
  • Figure 4 a set of four quadrants each containing a sub-array of 4x4 crystals preferably of dimensions 3x3x20 mm 3 although it will be appreciated that different crystal configurations and dimensions of crystals may be used.
  • the diode arrays 16 and four 16-channel multiplexed preamplifier chips 20 are mounted on a substrate 22 (e.g. of machined ceramic).
  • the connections to the diode array active areas is made via metallised tracks on the silicon out to one edge where a wire bond connection 23 is made to the preamplifier chips 20.
  • the control signals, power and signal connections to the preamplifier 20 are made via flexible circuit 24 board which contains ancillary electronics, such a output driver circuits, before a connection to the data acquisition circuitry via a cable connector.
  • the electronics are attached in such a way that modules can be ganged together into the required annular formation for the purpose of PET imaging.
  • the entire module may be contained in a sheet metal case thin enough not to affect the required close packaging of modules into an annulus.
  • This metal case provides support to hold the crystals in their correct orientation and provides the necessary shielding against electromagnetic radiation noise.
  • FIG. 7 to 10 there is shown the associated electronic circuitry for the detectors of the gamma ray imaging system of the invention.
  • the design of the electronic circuitry to trigger the data acquisition system upon a coincidence between two annihilation X-rays or gamma rays interacting in two opposing or nearly opposing scintillation crystals is an important feature in the system of the invention.
  • An aim of the invention is to use a coincidence array capable of being remotely programmed for selection of specific combinations of inputs coincidentally within a predetermined time window, and to achieve this without the encumbrance and inflexibility of "hard wiring" specific combinations.
  • Figures 8 and 9 illustrate schematically how this is achieved in a simplified application with only four blocks of crystals 12 and associated detectors A,B,C and D around the object 14 under study.
  • the coincidence trigger circuitry comprises a respective amplifier 30 associated with each detector A, B, C and D, a matrix of six AND gates 32 a programmable RAM 34, and an OR gate 36.
  • Each amplifier 30 is connected to inputs of three of the AND gates 32 and the RAM 34 has six outputs 38, each of which is connected to an input of a respective AND gate 32.
  • the selection of the specific combinations that will register a trigger is made by loading the RAM, the set bits of which provide one of the inputs to the selected AND gates in the matrix, for a trigger to be flagged.
  • the corresponding element in the RAM must be set, providing one of the inputs to the AND gate with channels A and C as inputs.
  • the fourth input to all gates is a clock signal CK to provide the desired time window for the coincidence.
  • the outputs of all the AND gates 32 are logically summed by OR gate 36 to provide a trigger signal on any coincidence.
  • the identifiers of the elements that provided the trigger are clocked out for use by the data acquisition system.
  • This relatively simple "self-coincidence” idea is a far more flexible and economical logic circuit than any trigger electronics presently used in PET cameras. It is also ideally suited to implementation in very large scale integration (VLSI), electronics. An efficient trigger is desirable for the use of the high resolution gamma detector. The number of channels possibly containing data is high so for fast event rate capability is mandatory.
  • FIG. 7 Further details of the electronics circuitry are shown schematically in Figure 7 wherein similar "rear end" circuits are connected to each array of photodiodes 16.
  • Each circuit (only one of which is illustrated in Figure 7) comprises a pre-ampl ' ifier 42, a shaping amplifier 44, a buffer amplifier 46 and a multiplexer 48, all of which may be incorporated in a single integrated CMOS, low-noise amplifier chip 40, the output of which is connected to a flash analogue-digital converter 50 of data acquisition circuitry, with a clock input 52 from a real time clock 54.
  • the "front end” circuitry connected to the photomultiplier tube comprises amplifier 30 the output of which is connected both to the analogue-digital converter 50 via a sample and hold circuit 60 and, via a discriminator 62, to the coincidence logic circuitry illustrated in more detail in Figure 9.
  • the digital output from the discriminator 62 is put into coincidence with a not BUSY signal. If the BUSY signal is off, a signal from the photomultiplier tube is passed to the coincidence electronics. No signal is passed from the discriminator to the coincidence electronics when the BLOCK BUSY signal for the block is set.
  • a valid coincidence is required to trigger digitization of the photomultiplier tube signals and to commence the multiplex cycle for digitizing the diode array signals of the specific blocks involved in the coincidence.
  • Digitized signals are immediately clocked through a digital pedestal (noise) subtraction and zero suppression circuit into a local buffer memory. This process reduces the number of channels of data to be stored.
  • a readout request for the two blocks involved in the coincidence is posted to the data acquisition circuitry.
  • the queued requests to read the local buffer memories corresponding to the blocks in the trigger are handled in turn by the data acquisition circuitry.
  • the BLOCK BUSY signal is issued to the blocks in the coincidence and held in that state until after the data acquisition control circuitry has serviced the trigger and cleared the local memories of the blocks involved.
  • a RESET signal is sent to the blocks involved and BLOCK BUSY signal is dropped, enabling triggers from those blocks once more.
  • Clock speed for loading the digitized data into local memory is high (50- 100Mhz) as all diode channels must be processed.
  • Clock speed for loading data from local memory into the data acquisition control circuitry is slower f 10Mhz) as zero suppression has reduced the number of channels to data to be loaded.
  • the present invention provides not only an effective method and apparatus for detecting gamma rays in which a high degree of spacial resolution of the scintillation point within a crystal is achieved, but also reliable electronic circuitry for triggering a data acquisition system upon a coincidence between two gamma rays interacting in opposed or nearly opposed scintillation crystals so that the location of the source of the gamma rays can be determined more accurately. It will also be appreciated that various modifications or alterations may be made to the apparatus described above without departing from the scope of the invention.

Landscapes

  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Molecular Biology (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Measurement Of Radiation (AREA)

Abstract

Un procédé et un appareil permettent de détecter des rayons X et gamma. L'appareil comporte des cristaux à scintillation (12) disposés en anneau ou en cylindre autour d'une source de rayons X ou gamma, ainsi que des détecteurs de lumière (16, 18) chargés de détecter et mesurer la lumière émise aux deux extrémités de chaque cristal (12) lorsque celui-ci absorbe un rayon X ou gamma. On peut ainsi déterminer la position (Z) d'un point de scintillation présent dans le cristal (12) en comparant les mesures de la lumière émise à chaque extrémité du cristal. On recourt à un arrangement de minces photodiodes (16) placées sur l'extrémité intérieure de chaque cristal (12) pour mesurer la lumière émise par ladite extrémité, ce qui permet de conférer à l'appareil un diamètre d'anneau réduit, d'où des coûts et une complexité moindres. La disposition des cristaux à scintillation peut se faire par blocs, l'appareil comportant alors des circuits logiques spécifiquement chargés de déterminer si une coïncidence entre rayons X ou gamma provient de blocs opposés ou quasiment opposés dans cette configuration.
PCT/AU1992/000620 1991-11-20 1992-11-20 Detection de rayons gamma Ceased WO1993010472A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AUPK959991 1991-11-20
AUPK9599 1991-11-20

Publications (1)

Publication Number Publication Date
WO1993010472A1 true WO1993010472A1 (fr) 1993-05-27

Family

ID=3775834

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/AU1992/000620 Ceased WO1993010472A1 (fr) 1991-11-20 1992-11-20 Detection de rayons gamma

Country Status (1)

Country Link
WO (1) WO1993010472A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5665971A (en) * 1993-04-12 1997-09-09 Massachusetts Institute Of Technology Radiation detection and tomography
WO2000025149A1 (fr) * 1998-10-28 2000-05-04 Koninklijke Philips Electronics N.V. Detecteur de tomodensitometre
CN100563575C (zh) * 2007-03-21 2009-12-02 中国科学院高能物理研究所 一种正电子断层扫描中符合系统及符合方法
CN110520760A (zh) * 2017-03-13 2019-11-29 通用电气公司 用于辐射检测器的像素设计

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4060730A (en) * 1973-09-07 1977-11-29 Elscint, Ltd. Scintillation camera for establishing the coordinates of a radiation stimuli produced by a radiation field
US4070581A (en) * 1975-07-10 1978-01-24 Emi Limited Detection of radiation
GB2007457A (en) * 1977-11-02 1979-05-16 American Science & Eng Inc Tomography apparatus using Bismuth germanate scintillators
GB2198620A (en) * 1986-09-18 1988-06-15 Hamamatsu Photonics Kk A scintillation detector and a positron ct apparatus incorporating it
GB2200205A (en) * 1986-12-11 1988-07-27 Hamamatsu Photonics Kk Radiation detector
US5103098A (en) * 1989-11-09 1992-04-07 Board Of Regents, The University Of Texas System High resolution gamma ray detectors for positron emission tomography (pet) and single photon emission computed tomography (spect)

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4060730A (en) * 1973-09-07 1977-11-29 Elscint, Ltd. Scintillation camera for establishing the coordinates of a radiation stimuli produced by a radiation field
US4070581A (en) * 1975-07-10 1978-01-24 Emi Limited Detection of radiation
GB2007457A (en) * 1977-11-02 1979-05-16 American Science & Eng Inc Tomography apparatus using Bismuth germanate scintillators
GB2198620A (en) * 1986-09-18 1988-06-15 Hamamatsu Photonics Kk A scintillation detector and a positron ct apparatus incorporating it
GB2200205A (en) * 1986-12-11 1988-07-27 Hamamatsu Photonics Kk Radiation detector
US5103098A (en) * 1989-11-09 1992-04-07 Board Of Regents, The University Of Texas System High resolution gamma ray detectors for positron emission tomography (pet) and single photon emission computed tomography (spect)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5665971A (en) * 1993-04-12 1997-09-09 Massachusetts Institute Of Technology Radiation detection and tomography
WO2000025149A1 (fr) * 1998-10-28 2000-05-04 Koninklijke Philips Electronics N.V. Detecteur de tomodensitometre
CN100563575C (zh) * 2007-03-21 2009-12-02 中国科学院高能物理研究所 一种正电子断层扫描中符合系统及符合方法
CN110520760A (zh) * 2017-03-13 2019-11-29 通用电气公司 用于辐射检测器的像素设计

Similar Documents

Publication Publication Date Title
US6407392B1 (en) Radiation detector
US3978337A (en) Three-dimensional time-of-flight gamma camera system
US4675526A (en) Method and apparatus for 3-D encoding
EP1627239B1 (fr) Module de detection destine a detecter un rayonnement ionisant
TWI638180B (zh) 成像器件及電子裝置
US6194726B1 (en) Semiconductor radiation detector with downconversion element
US4823016A (en) Scintillation detector for three-dimensionally measuring the gamma-ray absorption position and a positron CT apparatus utilizing the scintillation detector
EP3210042B1 (fr) Composant détecteur d'un détecteur de rayons x ou de rayons gamma
US4843245A (en) Scintillation detector for tomographs
US7709801B2 (en) Nuclear medicine diagnosis equipment
KR20040022437A (ko) Ｐｅｔ 스캐너
US6326624B1 (en) Device and method for determining the assumed position of a phenomenon relative to a set of photodetectors, and application to gamma-cameras
US8859976B2 (en) Radiation detector with multiple operating schemes
US5475225A (en) Autoradiographic digital imager
CN103245680A (zh) 基于飞行时间法的快中子成像方法及系统
US20040200966A1 (en) Gamma-ray detection apparatus and method for positron emission tomography
WO2018044606A1 (fr) Systèmes et procédés permettant de commander un couplage optique entre des cristaux scintillateurs
WO1993010472A1 (fr) Detection de rayons gamma
EP0829022B1 (fr) Appareil d'analyse scintigraphique, notamment mammographe, a resolution spatiale sous-millimetrique
US3825758A (en) Scintillation crystal
US4507733A (en) Photon emission imaging apparatus and method
JPH0452416B2 (fr)
JPH03108687A (ja) 放射線計測装置の放射線検出部
US4074135A (en) Gamma camera in which only the three largest signals are used for position determination
JP5060410B2 (ja) 放射線検出装置

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): AU CA JP US

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): AT BE CH DE DK ES FR GB GR IE IT LU MC NL SE

DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
122 Ep: pct application non-entry in european phase
NENP Non-entry into the national phase

Ref country code: CA