WO2013168778A1 - Méthode d'estimation du nombre de coïncidences aléatoires et dispositif d'estimation du nombre de coïncidences aléatoires - Google Patents

Méthode d'estimation du nombre de coïncidences aléatoires et dispositif d'estimation du nombre de coïncidences aléatoires Download PDF

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WO2013168778A1
WO2013168778A1 PCT/JP2013/063081 JP2013063081W WO2013168778A1 WO 2013168778 A1 WO2013168778 A1 WO 2013168778A1 JP 2013063081 W JP2013063081 W JP 2013063081W WO 2013168778 A1 WO2013168778 A1 WO 2013168778A1
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tof
data
sinogram
coincidence
count data
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PCT/JP2013/063081
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English (en)
Japanese (ja)
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ニュウ，シャオフォン
ワン，ウェンリー
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株式会社東芝
東芝メディカルシステムズ株式会社
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Priority claimed from US13/467,090 external-priority patent/US9241678B2/en
Application filed by 株式会社東芝, 東芝メディカルシステムズ株式会社 filed Critical 株式会社東芝
Priority to CN201380003466.0A priority Critical patent/CN103890609B/zh
Publication of WO2013168778A1 publication Critical patent/WO2013168778A1/fr

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    • 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)

Definitions

  • Embodiments described herein generally relate to estimation of random events in time-of-flight data acquired with a gamma ray detection system.
  • Positron Emission Tomography is a department of nuclear medicine that introduces positron-emitting radiopharmaceuticals into subjects. As radiopharmaceuticals decay, positrons are generated. Specifically, each of multiple positrons reacts with an electron in a phenomenon known as a positron pair annihilation event, producing a co-occurring pair of gamma photons that move in approximately opposite directions along the coincidence line. Is done. Gamma photon pairs detected within the coincidence time are typically recorded by the PET scanner as pair annihilation events.
  • time-of-flight (TOF) imaging the time within the coincidence interval at which each pair of gamma photons is detected is also measured.
  • the time-of-flight information indicates the position of the event detected along the coincidence line.
  • a plurality of pair annihilation event data is used to reconstruct or generate an image of the object or object to be scanned.
  • this image reconstruction or generation is generally performed using a statistical (iterative) or analytical reconstruction algorithm.
  • FIG. 1 shows the transverse and axial coordinates of the positrons emitted and the measured line-of-response (LOR) in a three-dimensional detector.
  • the coordinates (x e , y e , z e ) or (s e , t e , z e ) indicate the image coordinates of the emitted positron.
  • the delayed coincidence window can remove the correlation of two single events from each recorded paired event. Since a delayed coincidence window typically delays the size of the coincidence window by tens to hundreds of times, it is very unlikely that two recorded single events will result from one annihilation. Therefore, only random events are recorded in this method.
  • TOF mask in order to reduce random events in prompt data by filtering out these incidental coincidences that do not contribute to the field-of-view (FOV) completely.
  • TOF mask was designed. In this process, random events with TOF differences outside the mask are removed before reconstruction begins, resulting in a more accurate reconstructed image with list mode reconstruction and shorter computation time.
  • Non-TOF delay list mode data is first rebinned, interpolated into a 4D interpolated sinogram, smoothed, and then back-interpolated into a 4D raw sinogram.
  • a five-dimensional TOF raw sinogram is generated by spreading the LOR count evenly into bins in the tangential direction t and taking into account the range of t and the tilt angle along the radial direction of the LOR.
  • the problem to be solved by the present invention is to provide a random coincidence estimation method and a random coincidence estimation apparatus that can apply a TOF mask to random event estimation.
  • a random coincidence counting method for estimating random coincidence in positron emission tomography list mode data obtains TOF list mode count data including time-of-flight (TOF) information.
  • TOF time-of-flight
  • the four-dimensional interpolation sinogram count data is generated.
  • a low-pass filter is applied to the four-dimensional interpolation sinogram count data, and the four-dimensional interpolation sinogram count data to which the low-pass filter is applied is applied to the four-dimensional raw sinogram count data.
  • the 5D TOF raw sinogram count data is converted from the 4D sinogram count data to which the filter is applied. Generating.
  • FIG. 1 shows an example of the geometry of a PET imaging device.
  • FIG. 2 shows a cross-sectional view and a sagittal view of the new TOF mask.
  • FIG. 3A shows a (rad, t) diagram of GATE IEC phantom data obtained by performing a 5D random raw sinogram simulation without a 600 mm FOV and TOF mask.
  • FIG. 3B shows a (rad, t) diagram of GATE IEC phantom data for a 5D random raw sinogram simulation with a 600 mm FOV, TOF mask and 3 ⁇ TOF .
  • FIG. 4 shows a flowchart of a method for estimating a random event in PET according to an embodiment.
  • FIG. 5 shows the hardware of a PET system according to one embodiment.
  • the present application provides a random coincidence counting estimation method and a random coincidence estimation apparatus that can apply a TOF mask to random coincidence estimation.
  • a TOF mask is applied to the above-described prior art coincidence coincidence estimation (random estimation)
  • the random distribution changes with the introduction of an oval TOF mask, thereby causing a field-of-view (FOV). Random events collected in the central region of the FOV increase and random events collected in the periphery of the FOV decrease.
  • the above-described procedure without using the TOF mask cannot be applied. This is because (1) the random smoothing step changes the random distribution in the s dimension, which causes an estimation error in the inverse interpolation step.
  • a method for estimating random events in positron emission tomography list mode data which includes (1) time-of-flight (TOF) information.
  • a step of acquiring TOF list mode count data including, and (2) a step of converting the acquired TOF list mode count data into four-dimensional (4D) raw sinogram count data including random count values without using TOF information.
  • a TOF mask filter for filtering the pair annihilation points is effectively applied to the 4D raw sinogram count data to which the filter is applied by the processing device. Applying to generate five-dimensional (5D) TOF raw sinogram counting data from the filtered 4D raw sinogram counting data.
  • the TOF mask filter has a predetermined range of filter areas outside the reconstruction field along a line-of-response (LOR).
  • LOR line-of-response
  • the generating step includes 5D TOF raw sinogram count data for each TOF bin t according to the following formula: The step of generating is included.
  • t coin is the size in mm of the coincidence window
  • tof binsz is the size of the TOF bin in mm
  • r (rad, phi, slice) is the 4D raw sinogram random count data to which the filter is applied
  • Slice) is the LOR coordinate in the raw sinogram space
  • ⁇ is the inclination angle of the LOR.
  • slice is information related to a ring in which a pair annihilated gamma ray is detected, and includes ⁇ ring Diff, ring Sum ⁇ . “Ring Diff” indicates a difference between the detected rings (
  • the obtaining step obtains TOF list mode data having a data array ⁇ x a , z a , x b , z b , e a , e b , tof ⁇ for each simultaneous measurement event.
  • x a and x b are incident scintillator numbers in the transverse direction of event a and event b
  • z a and z b are incident scintillator numbers in the axial direction of event a and event b
  • e a , E b are the energy levels of event a and event b
  • tof is the difference in arrival time between event a and event b.
  • the method includes estimating a random count value in 4D raw sinogram count data using a delayed coincidence window method.
  • the non-TOF list mode data generally has a data array of ⁇ x a , z a , x b , z b , e a , e b ⁇ for each coincidence event.
  • x a and x b are incident scintillator numbers in the transverse direction of event a and event b
  • z a and z b are incident scintillator numbers in the axial direction of event a and event b
  • e a and e b are event a.
  • the energy level of event b is energy level of event b.
  • the TOF list mode data has a data array ⁇ x a , z a , x b , z b , e a , e b , tof ⁇ , where tof is the arrival time of event a and event b. It is a difference.
  • Random estimation in TOF list mode reconstruction by using a delayed coincidence window can be performed using a 5D or 4D approach.
  • the 5D method includes the following steps. (1) Rebind TOF delay window list mode data into 5D raw sinogram (rad, phi, slice, t) data. (2) Perform forward interpolation to convert LOR sinogram (rad, phi, slice, t) data into interpolated uniform sinogram (s, ⁇ , z, ⁇ , t) data. (3) Use a 5D low-pass filter based on a sinogram to reduce random data variation. (4) Obtain random estimates by back interpolation and convert the interpolated uniform sinogram (s, ⁇ , z, ⁇ , t) data to LOR sinogram (rad, phi, slice, t) data cure.
  • the 4D method includes the following steps. (1) Rebind TOF delay window list mode data into 4D raw sinogram (rad, phi, slice) data. (2) Perform forward interpolation to convert LOR sinogram (rad, phi, slice) data into interpolated uniform sinogram (s, ⁇ , z, ⁇ ) data. (3) Using a 4D low-pass filter based on a sinogram, variations in random data are reduced. (4) Using inverse interpolation, the interpolated uniform sinogram (s, ⁇ , z, ⁇ ) data is converted back to LOR sinogram (rad, phi, slice) data. (5) The inverse interpolated event is equally divided into bins in the tangential direction t in (rad, phi, slice) along the t dimension to generate a random estimate in (rad, phi, slice, t) .
  • the above method may be difficult to use with the new time-of-flight mask (TOF mask) disclosed in this embodiment.
  • TOF mask time-of-flight mask
  • the random distribution changes.
  • the shape of the TOF mask is related to the radial distance s as shown in the following equation (2). Since the random distribution tends to change slowly and is almost uniform throughout the FOV, the random distribution is different before and after applying the TOF mask. For this reason, a new random correction method is required according to a new TOF mask.
  • the bin having zero t has the largest radius and a larger random distribution. Therefore, in the final step of the method, random counts cannot be distributed uniformly along the t dimension. That is, it is necessary to consider the shape of the TOF mask.
  • a new method for estimating the randomness of each event is used in the TOF list mode reconstruction using the TOF mask.
  • random list mode data not using the TOF mask is used.
  • this may be referred to as original random data.
  • the random distribution of the original random data does not depend on the size of the TOF, the random distribution is uniform along the t dimension in the tangential direction. As shown in FIG. 3A, the random distribution is substantially uniform along the t dimension for each radial distance s, except for statistical uncertainty. Even after applying the filter using the TOF mask, the random distribution is uniform along the t dimension in the TOF mask, but the range of the TOF mask is the radial direction of the LOR as shown by the s coordinate in FIG. Varies along.
  • TOF list mode count data including time-of-flight (TOF) information is obtained.
  • the TOF list mode data has the data array ⁇ x a , z a , x b , z b , e a , e b , tof ⁇ , where tof is the arrival of event a and event b. It is a difference in time.
  • non-TOF delay list mode data (without TOF mask filter) is first rebinned into a (rad, phi, slice) raw sinogram. In this step, the TOF portion of the data is ignored.
  • step 420 (rad, phi, slice) raw sinogram data is interpolated into 4D interpolation sinogram (s, ⁇ , z, ⁇ ) data.
  • step 430 a low-pass smoothing process based on a sinogram is applied to remove statistical noise in the data.
  • step 440 the smoothed sinogram (s, ⁇ , z, ⁇ ) data is inversely interpolated to 4D (rad, phi, slice) raw sinogram data r.
  • the 5D TOF raw sinogram data is obtained by spreading the LOR counts evenly in each of the tangential t bins and taking into account the difference in the range of t along the radial direction of the LOR and the tilt angle ⁇ . Is generated.
  • the random count estimated for each bin of t is determined by the following equation (3).
  • t coin represents the size in mm of the coincidence window
  • t binsz represents the size of the t bin in mm
  • t range (s) is defined as in Equation (2), and each s Represents the range of t. Note that the 5D TOF raw sinogram generated by equation (3) Has the effect of applying the TOF mask shown in FIG.
  • step 410 and / or step 440 can be omitted.
  • step 420 can be performed to obtain 4D interpolated sinogram data directly from list mode data.
  • the new random estimation method using the TOF mask can be applied not to list mode reconstruction but to image reconstruction based on sinogram.
  • the reconstruction engine may or may not use TOF information.
  • the estimated random is used in a 5D TOF interpolated sinogram. Even if the TOF information is not used in the reconstruction, a part of the random count can be rejected using the TOF mask.
  • the reconstruction engine itself does not use the TOF information, a 4D TOF interpolation sinogram is generated. Used.
  • the new random estimation method for TOF list mode reconstruction described above has several advantages.
  • random events in prompt data can be estimated by using non-TOF delayed list mode data that does not use a TOF mask filter.
  • the advantage of using a TOF mask during reconstruction is also valid here.
  • the new TOF mask shape does not increase the complexity of random correction.
  • Estimated random count scale factor value as shown in equation (3) Does not depend on the radial distance s.
  • FIG. 5 shows an exemplary PET hardware configuration that can be used with this embodiment.
  • the photomultiplier tubes 135 and 140 are disposed on the light guide 130, and the scintillator array 105 is disposed below the light guide 130.
  • a second scintillator array 125 is disposed opposite the scintillator 105 so as to overlap the light guide 115 and the photomultiplier tubes 195 and 110.
  • the gamma ray timing detection system detects gamma rays simultaneously with the scintillators 100 and 120.
  • gamma detection at the scintillator 100 will be described here.
  • the description of the scintillator 100 can be similarly applied to gamma ray detection in the scintillator 120.
  • Each photomultiplier tube 110, 135, 140, 195 is connected to the data acquisition device 150.
  • Data acquisition device 150 includes hardware configured to process signals from a photomultiplier tube. The data acquisition device 150 measures the arrival time of gamma rays. The data acquisition device 150 is for the combination of two outputs (one photomultiplier tube (PMT) 135/140) that encodes the time of the identification pulse with respect to the system clock (not shown). For PMT110 / 195 combination). In a time-of-flight PET system, the data acquisition device 150 generates a time stamp with an accuracy of typically 15-20 picoseconds. The data acquisition device measures the magnitude of each PMT signal (four outputs from the data acquisition device 150).
  • PMT photomultiplier tube
  • the output of the data acquisition device is sent to the CPU 170 for processing.
  • the process consists of estimating the energy and position from the output of the data acquisition device, and the arrival time from the time stamp output for each event, in order to improve the accuracy of the estimated values of energy, position, and time. Furthermore, it may include the application of a number of correction steps based on prior calibration.
  • the CPU 170 is configured to execute a random event estimation method according to the flowchart shown in FIG. 4 and the above contents.
  • the CPU 170 is an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or a complex programmable logic device (Complex Programmable Logic Device). It can be implemented as an individual logic gate such as CPLD). FPGA or CPLD implementations may be coded in VHDL, Verilog, or other hardware description languages, and the code stored directly in the electronic memory in the FPGA or CPLD or as another electronic memory. Also good.
  • ASIC application specific integrated circuit
  • FPGA field programmable gate array
  • CPLD complex programmable logic device
  • the electronic memory may be a nonvolatile memory such as a ROM, an electrical PROM (electrically programmable read only memory: EPROM), an electrically erasable PROM (electrically erasable programmable read only memory: EEPROM), or a flash memory.
  • the electronic memory may be volatile such as static or dynamic RAM.
  • a processing device such as a microcontroller or a microprocessor may be provided to manage the electronic memory.
  • the CPU 170 may be implemented as a series of computer-readable instructions stored in either or both of the electronic memory and a known storage medium such as a hard disk, CD, DVD, or flash drive.
  • the computer readable instructions are provided as a utility application, background daemon, or operating system component, or a combination thereof, a processing device such as an Intel Xeon processor or an AMD Opteron processor, and It is executed in conjunction with an operating system known to those skilled in the art, such as Microsoft Vista, UNIX (registered trademark), Solaris, LINUX (registered trademark), and Apple MAC-OS.
  • the processed signal is stored in the electronic storage device 180 and / or displayed on the display 145.
  • the electronic storage device 180 may be an electronic storage device known in the art, such as a hard disk drive, a CD-ROM drive, a DVD drive, a flash drive, a RAM, and a ROM.
  • the display 145 is a liquid crystal display (LCD), a cathode ray tube (CRT), a plasma display, an organic light emitting diode (OLED), a light emitting diode (LED), or the like in this technical field. It may be implemented as a known display.
  • the description of the electronic storage device 180 and the display 145 described here is merely an example, and does not limit the scope of progress of the present embodiment in any way.
  • FIG. 5 also includes an interface 175 for connecting the gamma ray detection system to other external devices and / or users.
  • the interface 175 is known in the art such as a universal serial bus (USB) interface, a personal computer memory card international association (PCMCIA) interface, an Ethernet (registered trademark) interface, and the like.
  • Interface. Interface 175 may also be wired or wireless and may include a human interface for interacting with the user, such as a keyboard and / or mouse.

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Abstract

Selon un mode de réalisation de la présente invention, une méthode d'estimation du nombre de coïncidences aléatoires consiste à : acquérir des données chiffrées de temps de vol (TOF) en mode liste qui contiennent des informations de TOF; convertir les données chiffrées de TOF en mode liste acquises en données chiffrées de fistulographie brutes quadridimensionnelles (4D), qui comprennent des valeurs chiffrées aléatoires, sans utiliser les informations de TOF; interpoler les données chiffrées de fistulographie brutes 4D afin de produire des données chiffrées de fistulographie interpolées 4D; appliquer un filtre passe-bas aux données chiffrées de fistulographie interpolées 4D afin d'éliminer le bruit; convertir les données chiffrées de fistulographie interpolées 4D auxquelles le filtre passe-bas a été appliqué en données chiffrées de fistulographie brutes 4D filtrées; et produire des données chiffrées de TOF de fistulographie brutes pentadimensionnelles (5D) à partir des données chiffrées de fistulographie brutes 4D en appliquant efficacement un filtre masque de TOF permettant de filtrer les paires de points d'annihilation aux données chiffrées de fistulographie brutes 4D filtrées.
PCT/JP2013/063081 2012-05-09 2013-05-09 Méthode d'estimation du nombre de coïncidences aléatoires et dispositif d'estimation du nombre de coïncidences aléatoires WO2013168778A1 (fr)

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US13/467,090 US9241678B2 (en) 2012-05-09 2012-05-09 Random estimation in positron emission tomography with tangential time-of-flight mask
US13/467,090 2012-05-09
JP2013-093004 2013-04-25
JP2013093004A JP6125309B2 (ja) 2012-05-09 2013-04-25 偶発同時計数推定方法及び偶発同時計数推定装置

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07113873A (ja) * 1993-10-14 1995-05-02 Univ Tohoku 陽電子断層撮影装置におけるγ線吸収体による散乱同時計数測定法及び陽電子断層撮影装置
JP2007071858A (ja) * 2005-08-11 2007-03-22 Shimadzu Corp 放射線同時計数処理方法、放射線同時計数処理プログラムおよび放射線同時計数処理記憶媒体、並びに放射線同時計数装置およびそれを用いた核医学診断装置、記憶媒体
WO2011117990A1 (fr) * 2010-03-25 2011-09-29 独立行政法人放射線医学総合研究所 Procédé et dispositif de détermination de coïncidence dans un dispositif de type pet

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07113873A (ja) * 1993-10-14 1995-05-02 Univ Tohoku 陽電子断層撮影装置におけるγ線吸収体による散乱同時計数測定法及び陽電子断層撮影装置
JP2007071858A (ja) * 2005-08-11 2007-03-22 Shimadzu Corp 放射線同時計数処理方法、放射線同時計数処理プログラムおよび放射線同時計数処理記憶媒体、並びに放射線同時計数装置およびそれを用いた核医学診断装置、記憶媒体
WO2011117990A1 (fr) * 2010-03-25 2011-09-29 独立行政法人放射線医学総合研究所 Procédé et dispositif de détermination de coïncidence dans un dispositif de type pet

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