WO2016203822A1 - 放射線検出素子の感度補正方法および放射線断層撮影装置 - Google Patents
放射線検出素子の感度補正方法および放射線断層撮影装置 Download PDFInfo
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- 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
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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
- G01T1/16—Measuring radiation intensity
- G01T1/161—Applications in the field of nuclear medicine, e.g. in vivo counting
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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
- G01T1/16—Measuring radiation intensity
- G01T1/17—Circuit arrangements not adapted to a particular type of detector
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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
- G01T1/16—Measuring radiation intensity
- G01T1/17—Circuit arrangements not adapted to a particular type of detector
- G01T1/172—Circuit arrangements not adapted to a particular type of detector with coincidence circuit arrangements
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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
- the present invention relates to a method for correcting the sensitivity of a radiation detection element that detects radiation generated from a radiopharmaceutical in a subject, and a radiation tomography apparatus that performs radiation tomography by detecting radiation generated from a radiopharmaceutical in a subject. .
- sensitivity correction Coefficients for sensitivity correction (hereinafter referred to as “sensitivity coefficients”) are calculated from actual data collected using a calibration source, and there are two methods for calculating sensitivity coefficients.
- the first is a direct method for obtaining sensitivity coefficients for all detector pairs.
- the direct method the sensitivity coefficients of all detector pairs can be obtained directly, but when there are many detectors, the number of detector pairs becomes enormous due to the square of the number of detectors. Therefore, the statistical accuracy per pair is lowered, and the number of sensitivity coefficients is enormous.
- NC uivj ⁇ ui ⁇ ⁇ vj ⁇ b uvk ⁇ d uvrk ⁇ g uvr ⁇ f uv (1)
- ⁇ ui and ⁇ vj are detector specific sensitivities
- d uvrk is a crystal interference factor
- f uv is a ring pair sensitivity
- b uvk is a block shape factor
- g uvr is a radial geometric factor.
- K is the relative crystal position in the block
- r is the radial position.
- g uvr , d uvrk and the like are geometrically determined elements (hereinafter referred to as “geometric system factors”). Note that ⁇ ui , ⁇ vj , and b uvk are non-geometric factors that change over time.
- the sensitivity correction method for each element is represented by the product of sensitivity coefficients, so the number of sensitivity coefficients is smaller than that of the direct method. Further, since the factors obtained by decomposing the sensitivity coefficient are added using geometric symmetry, the statistical accuracy can be improved. However, since the sensitivity coefficient is obtained indirectly by the product of factors, it is an approximate numerical value. In recent PET apparatuses, the element-specific sensitivity correction method has begun to be used for the purpose of high resolution, easy calibration, and improved statistical accuracy.
- FIG.1 is a calibration flow for calculating geometric factors using a conventional low-scattering calibration source
- Figure.2 is a calibration flow for calculating non-geometric factors using a conventional uniform cylindrical calibration source. It is. The geometric factor that does not change with time is calculated by the low scattering calibration source, and the non-geometric factor that changes with time is calculated by the data of the uniform cylindrical calibration source corrected by the coefficient of the geometric factor. And the sensitivity coefficient of a specific detector pair is calculated
- Such a conventional elemental sensitivity correction method has the following problems. That is, there is a problem that the multi-modality compatible flexible PET apparatus does not support the conventional elemental sensitivity correction method.
- the conventional sensitivity correction method for each element is established when the detector group has a circular arrangement and the positional relationship is fixed.
- the multi-modality-compatible flexible PET apparatus is composed of two detector heads 2A and 2B in which arc-shaped detector groups are arranged, and each detection is performed as shown by a two-dot chain line in FIG.
- the instrument heads 2A and 2B are close to each other.
- the positional relationship becomes variable and becomes elliptical, and the assumption of the elemental sensitivity correction method is broken and cannot be established (see AB in non-proximity and A′B in close proximity shown in FIG. 3).
- the sensitivity coefficient is unchanged if the detector pair is in the same detector head, but the distance between the detector heads facing each other changes, and ⁇ with respect to the detector changes. As the line incidence angle is different, the sensitivity of the geometric factor at the opposite detector head changes. As a result, artifacts are generated in the reconstructed image.
- the present invention has been made in view of such circumstances, and a reconstructed image free from artifacts can be obtained even when the arrangement of the plurality of radiation detection elements constituting the detector is variable and not circular. It is an object of the present invention to provide a sensitivity correction method for a radiation detection element and a radiation tomography apparatus.
- the present invention has the following configuration. That is, the sensitivity correction method according to the present invention is a sensitivity correction method for a radiation detection element that detects radiation generated from a radiopharmaceutical in a subject, and is based on coincidence count data collected by a plurality of the radiation detection elements.
- the sensitivity coefficient is obtained in the first sensitivity coefficient calculation step, and after the first sensitivity coefficient calculation step, the change in the arrangement of the plurality of radiation detection elements.
- the sensitivity coefficient is obtained in the second sensitivity coefficient calculation step before, and after the second sensitivity coefficient calculation step, the sensitivity coefficient is obtained in the third sensitivity coefficient calculation step in a state where the arrangement of the plurality of radiation detection elements is changed.
- the sensitivity coefficient is obtained separately for each sensitivity factor in the first sensitivity coefficient calculation step. Even if the arrangement of the plurality of radiation detection elements does not change, the non-geometric factor changes with time.
- the sensitivity coefficient of the non-geometric system factor is obtained in the second sensitivity coefficient calculation step based on the collected coincidence data.
- the third sensitivity coefficient calculation step the sensitivity coefficient derived from the geometric arrangement is obtained based on the coincidence count data collected in a state where the arrangement of the plurality of radiation detection elements is changed.
- the sensitivity coefficient when the arrangement of a plurality of radiation detection elements is changed is the arrangement for a combination whose positional relationship remains unchanged regardless of the arrangement of the radiation detection elements (for example, the same detector head). It is represented by the product of the sensitivity coefficient of the geometric factor obtained before the change and the sensitivity coefficient of the non-geometric factor. For combinations that are geometrically affected by the positional relationship of the radiation detection elements (for example, detector heads facing each other), the sensitivity factor of the geometric factor obtained after the change in arrangement and the non-geometric system It is expressed as the product of the factor's sensitivity coefficient.
- a correction coefficient from the ratio of coincidence count data collected at the same time using the same calibration source before and after the change of the arrangement of the plurality of radiation detection elements.
- the same calibration source the latter: the first: before and after the change of the arrangement of the plurality of radiation detection elements.
- the difference between the former before the change of the arrangement and the latter after the change of the arrangement is obtained by multiplying the obtained correction coefficient by the right side of the above equation (1). Can also be corrected.
- the coincidence data collected after the change in the arrangement of the plurality of radiation detection elements is a combination that is geometrically influenced by at least the positional relationship of the radiation detection elements. That is, based on the coincidence data collected after the change of the arrangement, sensitivity coefficient data for a combination (for example, detector heads facing each other) that is geometrically influenced by the positional relationship of the radiation detection elements can be obtained.
- the calibration rod radiation source can be regarded as a calibration ring radiation source by rotating along the plurality of radiation detection elements. Moreover, you may use the ring source for calibration provided along the some radiation detection element. In addition, when using a calibration plate source that can rotate along a plurality of radiation detection elements, the calibration plate source may be rotated along the plurality of radiation detection elements.
- the rotated calibration rod source that is, the calibration rod source regarded as the calibration ring source
- the calibration ring source or the rotated calibration plate source.
- the sensitivity coefficient is obtained separately for each sensitivity factor.
- the sensitivity coefficient of the non-geometric factor that changes with time can be obtained.
- each detector head composed of a plurality of radiation detection elements
- each detector head is configured such that the distance between the detector heads can be changed, the detector heads are brought close to each other. Therefore, when the arrangement of the plurality of radiation detection elements changes, it is preferable to obtain the sensitivity coefficient using a calibration radiation source as described below. That is, when trying to bring the detector heads close to each other, a calibration rod-shaped radiation source that can be rotated along a plurality of radiation detection elements and a calibration ring radiation source provided along the plurality of radiation detection elements respectively detect each detector head. May interfere with the instrument head.
- a calibration flat radiation source installed at the center of each detector head is used, or a calibration rod-shaped radiation source capable of reciprocating along the central axis of each detector head is used.
- the calibration rod-shaped radiation source is reciprocated along the central axis of each detector head to make it a calibration flat plate radiation source.
- the calibration flat plate source or the reciprocating calibration rod source that is, the calibration rod source assumed to be a calibration flat plate source
- the sensitivity coefficient derived from the geometry is obtained.
- a radiation tomography apparatus is a radiation tomography apparatus that performs radiation tomography by detecting radiation generated from a radiopharmaceutical in a subject, and includes a detector head comprising a plurality of radiation detection elements.
- a plurality of detector heads are configured such that the distances between the detector heads can be changed, and each of the detector heads includes a calculation unit that performs calculation processing.
- the calculation units are collected by the plurality of radiation detection elements.
- the first sensitivity coefficient calculation step for obtaining the sensitivity coefficient separately for each sensitivity factor, and after the first sensitivity coefficient calculation step and before the change of the arrangement of the plurality of radiation detection elements
- a second sensitivity coefficient calculation step for obtaining a sensitivity coefficient of the non-geometric factor, and an arrangement of the plurality of radiation detection elements is changed after the second sensitivity coefficient calculation step.
- a third sensitivity coefficient calculation step for obtaining a sensitivity coefficient derived from the geometric arrangement based on the coincidence data collected in a state where the first sensitivity coefficient is calculated, the second sensitivity coefficient calculation step, and the second sensitivity coefficient calculation step.
- the sensitivity correction of the radiation detection element is performed using the sensitivity coefficient obtained in the three sensitivity coefficient calculation step.
- the first sensitivity coefficient calculation step, the second sensitivity coefficient calculation step, and the third sensitivity coefficient calculation step as described in the sensitivity correction method according to the present invention are performed.
- Computation means for performing is provided.
- the sensitivity correction of the radiation detection element is performed using the sensitivity coefficients obtained in the first sensitivity coefficient calculation step, the second sensitivity coefficient calculation step, and the third sensitivity coefficient calculation step.
- the first sensitivity (determining the sensitivity coefficient for each sensitivity factor based on the coincidence data collected by the plurality of radiation detection elements) Coefficient calculation step (after the first sensitivity coefficient calculation step and before the change of the arrangement of the plurality of radiation detection elements, the sensitivity coefficient of the non-geometric system factor is obtained based on the collected coincidence data)
- a sensitivity coefficient calculation step and (after the second sensitivity coefficient calculation step, a sensitivity coefficient derived from the geometric arrangement is obtained based on coincidence data collected in a state where the arrangement of the plurality of radiation detection elements has changed)
- FIG. 1 It is the schematic perspective view and block diagram which show one embodiment of the detector head of the flexible PET apparatus for multi-modality which concerns on an Example.
- FIG. 1 It is a schematic perspective view of a gamma ray detector.
- A is the schematic which looked at the detector head from the depth direction
- (b) is the schematic which looked from the horizontal direction orthogonal to a depth direction.
- (a) is a schematic diagram of a ring radiation source when not approaching
- (b) is a schematic diagram of a cylindrical radiation source when not approaching
- (c) is It is a schematic diagram of the flat plate source at the time of proximity
- FIG. 1 is a schematic perspective view and a block diagram showing an embodiment of a detector head of a flexible PET apparatus for multi-modality according to an embodiment
- FIG. 2 is a schematic perspective view of a ⁇ -ray detector.
- (A) is the schematic which looked at the detector head from the depth direction
- FIG.3 (b) is the schematic which looked from the horizontal direction orthogonal to a depth direction.
- a multi-modality compatible PET apparatus (hereinafter simply referred to as “PET apparatus”) 1 includes detector heads 2A and 2B.
- PET apparatus As shown in FIG. 2, 18 detector blocks 31 ( ⁇ -ray detector 3) in which detector crystals arranged vertically and horizontally in 16 ⁇ 16 are stacked in four layers are arranged in an arc shape in the depth direction z (FIG. 1).
- a detector head is composed of a total of 18 ⁇ 3 detector blocks 31 arranged in three. A specific configuration of the ⁇ -ray detector 3 other than the detector block 31 will be described later with reference to FIG.
- the multi-modality flexible PET apparatus (PET apparatus) 1 corresponds to the radiation tomography apparatus in the present invention
- the detector heads 2A and 2B correspond to the detector head in the present invention
- the ⁇ -ray detector 3 It corresponds to the radiation detection element in the invention.
- the detector heads 2A and 2B are configured to face each other.
- the detector heads 2A and 2B are usually located on a circumference of a 48-gon.
- the total number of detector blocks 31 ( ⁇ -ray detectors 3) in the cross section of the two detector heads 2A and 2B is 48 squares for a total of 36 pieces (18 x 2 in an arc shape).
- Each gap region 4 exists.
- the detector heads 2A and 2B can be brought close to each other with the detector heads 2A and 2B facing each other.
- each detector head 2A, 2B is comprised so that the distance between each detector head 2A, 2B can be changed.
- the PET apparatus 1 includes a coincidence counting circuit 5 and an arithmetic circuit 6. Specific functions of the arithmetic circuit 6 will be described later with reference to FIG.
- the arithmetic circuit 6 corresponds to the arithmetic means in this invention.
- the coincidence counting circuit 5 checks the position of the detector block 31 (see FIG. 2) and the incident timing of ⁇ rays, and only when ⁇ rays are simultaneously incident on the two detector blocks 31 on both sides of the subject.
- the sent image information is determined as appropriate data (simultaneous counting data).
- the coincidence circuit 5 rejects.
- the coincidence counting circuit 5 detects that ⁇ rays are simultaneously observed (that is, coincidence counting) by the two ⁇ ray detectors 3 based on the above-described electrical signal.
- Image information (simultaneous counting data) collected by the coincidence circuit 5 is sent to the arithmetic circuit 6.
- the ⁇ -ray detector 3 includes a detector block 31, a light guide 32 optically coupled to the detector block 31, and an optically coupled to the light guide 32. And a photomultiplier tube (PMT: Photo Multiplier Tube) 33.
- PMT Photo Multiplier Tube
- Each detector crystal constituting the detector block 31 emits light with the incidence of ⁇ rays, thereby converting the ⁇ rays into light. By this conversion, the detector crystal detects ⁇ rays.
- the light emitted from the detector crystal is sufficiently diffused by the detector block 31 and input to a photomultiplier tube (hereinafter simply referred to as “PMT”) 33 through the light guide 32.
- the PMT 33 multiplies the light converted by the detector block 31 and converts it into an electrical signal.
- the electric signal is sent to the coincidence counting circuit 5 (see FIG. 1) as image information (simultaneous counting data) as described above.
- the ⁇ -ray detector 3 is a DOI detector composed of a plurality of layers in the depth direction.
- a four-layer DOI detector is illustrated, but the number of layers is not particularly limited as long as it is plural. Also, the number of detector crystals arranged vertically and horizontally is not particularly limited as long as it is plural.
- the DOI detector is constructed by laminating each detector crystal in the depth direction of the radiation, and the interaction depth (DOI: Depth of Interaction) direction and lateral direction (incident) Coordinate information with the direction parallel to the surface) is obtained by calculating the center of gravity.
- DOI Depth of Interaction
- lateral direction incident
- the number of DOI detector layers is the number of detector crystal layers stacked in the depth direction.
- FIGS. 4 (a) to 4 (c) are schematic diagrams of detector arrangements and types of calibration radiation sources
- FIG. 4 (a) is a schematic diagram of a ring radiation source when not in proximity.
- 4 (b) is a schematic diagram of a cylindrical radiation source at the time of non-proximity
- FIG. 4 (c) is a schematic diagram of a flat-plate radiation source at the time of proximity
- FIG. 5 is a sensitivity correction for each element according to the embodiment.
- FIG. 6 is a flowchart showing the flow of the processing procedure of the method
- FIG. 6 shows a state where a rod-shaped radiation source that can rotate along the ⁇ -ray detector of the detector head is rotated along the ⁇ -ray detector of the detector head.
- FIG. 4 (a) is a schematic diagram of a ring radiation source when not in proximity.
- 4 (b) is a schematic diagram of a cylindrical radiation source at the time of non-proximity
- FIG. 4 (c) is a schematic diagram of
- FIGS. 4 (a) code S R calibration ring-ray source in (hereinafter, abbreviated as “ring-ray source”) is a
- FIG. 4 (b) code S C is a calibration cylinder ray source in (hereinafter it is merely referred to as “cylinder-ray source”)
- FIG. 4 (c) code S P calibration flat plates ray source in (hereinafter, it is abbreviated as "flat-ray source”).
- a calibration rod-shaped radiation source (rotating along the ⁇ -ray detector 3 (see FIG. 2) (ie, radiation detection element) of the detector heads 2A and 2B ( hereinafter simply using abbreviated as “rod-shaped radiation source”) S L, shown in FIG.
- a rod-shaped radiation source S L detector heads 2A by rotating along the ⁇ -ray detectors 3 2B Mitateru to ring-ray source S R.
- the thickness of the ring-ray source S R is about 5 mm
- the diameter of the cylindrical ray source S C is about 15cm
- a thickness of the flat plate-ray source S P is approximately 5 mm
- the diameter of the rod-shaped radiation source S L is about 15cm.
- the non-illustrated in FIG. 4 rod-shaped radiation source during non-proximity shown in (a) S L ring-ray source likened to the ring is rotated (see Figure 6) S R, 4 (b) A uniform cylindrical source S C installed at the center of the apparatus (detector heads 2A, 2B) when approaching, and a flat plate installed at the center of the apparatus (detector heads 2A, 2B) shown in FIG. It provides three types of sources S P, to collect data, respectively.
- the calibration radiation source is made of acrylic resin, and a radioactive solution of uniform concentration is sealed inside.
- the long-axis block shape factor b uvk corresponds to “Transaxial Block Profile Factor” and the crystal interference factor d uvrk corresponds to “Crystal Interference Factor”.
- Block shape factor b uvk corresponds to “Axial Block Profile Factor”
- ring pair sensitivity f uv corresponds to “Ring Pair Factor”
- detector specific sensitivities ⁇ ui , ⁇ vj correspond to “Crystal Efficiency Factor”
- the crystal interference factor d Plate at the time of the flat plate source corresponds to “Crystal Interference (Plate) Factor”
- the ring pair sensitivity f Plate at the time of the flat plate source corresponds to “Ring Pair (Plate) Factor”.
- Step S1 As shown in the flowchart of FIG. 5, first use coincidence data collected by the ring-ray source S R shown in FIG. 4 (a), crystal interfering agents geometric system factors that change over time d uvrk ( “Crystal Calculated as “Interference Factor”. It is preferable to apply path length normalization (denoted as “Apply”) before calculating the crystal interference factor d uvrk (Crystal Interference Factor) of this geometric factor.
- the path length normalization is to normalize the coincidence count data on a predetermined path using the length that the path passes through the radiation source. By performing path length normalization, a difference in length that intersects the radiation source between predetermined paths is corrected in a pseudo manner.
- path length standardization refer to Japanese Patent Application Laid-Open No. 2008-170329.
- crystal interference factor d uvrk Crystal Interference Factor
- the coefficient of crystal interference factor d uvrk (Crystal Interference Factor) obtained as a result is output as a table.
- LOR Line Of Response
- This step S1 corresponds to the first sensitivity coefficient calculation step in the present invention.
- Step S2 Next, using the coincidence data crystalline interferer d uvrk (Crystal Interference Factor) cylindrical ray source shown in FIG. 4 (b) performing the correction of the geometric-based factors by S C, non-geometric-based time varying
- the detector's intrinsic sensitivities ⁇ ui and ⁇ vj (expressed as “Crystal Efficiency Factor”) are sequentially calculated.
- the block shape factor b uvk ( indicated by “Axial Block Profile Factor”) of the body axis section (cross section of the body axis) and the block shape factor b uvk (indicated by “Transaxial Block Profile Factor”) of the long axis calculated, it performs correction on coincidence data of the flat radiation source S P shown in FIG. 4 (c) in step S3.
- the ring pair sensitivity f uv (expressed as “Ring Pair Factor”) is calculated. Each factor obtained by calculation is output as a table.
- This step S2 corresponds to the second sensitivity coefficient calculation step in the present invention.
- Step S3 Finally, using the coincidence counting data of the flat plate-ray source S P shown in FIG. 4 (c), crystal interfering agents d Plate when the flat plate-ray source affected by changes in the geometry of the detector by adjacent (Represented by “Crystal Interference (Plate) Factor”) and ring pair sensitivity f Plate (represented by “Ring Pair (Plate) Factor”) at the time of a flat plate source are calculated.
- the crystal interference factor d uvrk Crystal Interference Factor
- Sensitivity f uv Sensitivity f uv (Ring Pair Factor) is not calculated.
- the combination of the detector heads facing each other is geometrically influenced by the positional relationship of the ⁇ -ray detector 3 (radiation detection element), so that the crystal interference factor d Plate (Crystal Interference ( Plate) Factor) and the ring pair sensitivity f Plate (Ring Pair (Plate) Factor) at the time of a flat plate source.
- step S3 path length normalization is preferably applied before calculating these factors.
- the solid angle correction is performed with the coordinates at the time of proximity to the crystal interference factor d Plate (Crystal Interference (Plate) Factor) at the time of the flat plate source.
- Output the calculated crystal interference factor d Plate (Crystal Interference (Plate) Factor) and flat pair source coefficient f Plate (Ring Pair (Plate) Factor) coefficients for a flat plate source as a table.
- This step S3 corresponds to the third sensitivity coefficient calculation step in the present invention.
- Non-Patent Document 1 for specific calculation of each factor.
- the flexible PET apparatus uses a fan-sum method because there is a gap between the detector heads.
- Patent Document 2 International Publication No. 2010/013356 Please refer to.
- N near is the coincidence count data (count value) collected using the flat plate source at the time of proximity
- N normal is the coincidence count collected using the plate source at the time of non-proximity.
- Data (count value) L near is the detector distance when close
- L normal is the detector distance when not close.
- a sensitivity coefficient is obtained in the first sensitivity coefficient calculation step (step S1), and after the first sensitivity coefficient calculation step (step S1), a plurality of radiation detection elements.
- the sensitivity coefficient is obtained in the second sensitivity coefficient calculation step (step S2) before the change of the arrangement of the ( ⁇ -ray detector in the present embodiment) (in the case of non-proximity in the present embodiment), and the second sensitivity coefficient calculation step (step After S2), the sensitivity coefficient is obtained in the third sensitivity coefficient calculation step (step S3) in a state where the arrangement of the plurality of radiation detection elements has changed (in this embodiment, the detector heads 2A and 2B are close to each other).
- the sensitivity coefficient is obtained separately for each sensitivity factor in the first sensitivity coefficient calculation step (step S1). Even if the arrangement of the plurality of radiation detection elements ( ⁇ -ray detectors) does not change, the non-geometric factor changes with time. Therefore, the non-geometric system is used in the second sensitivity coefficient calculation step (step S2) based on the collected coincidence data before the change of the arrangement of the plurality of radiation detection elements ( ⁇ -ray detectors) (when not in proximity). Find the sensitivity factor of the factor. Then, in the third sensitivity coefficient calculation step (step S3), the geometric arrangement is based on the coincidence count data collected in a state where the arrangement of the plurality of radiation detection elements is changed (the detector heads 2A and 2B are close to each other).
- the radiation detection element (step S1), the second sensitivity coefficient calculation step (step S2), and the third sensitivity coefficient calculation step (step S3) are used to obtain the radiation detection element (
- a reconstructed image is obtained based on the data after sensitivity correction.
- a reconstructed image free from artifacts can be obtained even when the arrangement of the plurality of radiation detection elements ( ⁇ -ray detectors) constituting the detector is variable and not circular.
- the sensitivity coefficient when the arrangement of the plurality of radiation detection elements is changed has the same positional relationship regardless of the arrangement of the radiation detection elements ( ⁇ -ray detectors).
- the sensitivity factor of the geometric factor obtained before the change of arrangement in the present embodiment in the case of non-proximity
- the sensitivity of the non-geometric factor It is expressed as a product with a coefficient.
- the PET apparatus 1 determines whether the detector pair is the same detector head or the detector heads facing each other. )) Determines. If the opposing detector head, switching to the sensitivity coefficients in the nearby obtained from flat plate-ray source S P shown in FIG. 4 (c).
- CPU central processing unit
- the same calibration source (same flat plate source in this embodiment) is used before and after the change of the arrangement of the plurality of radiation detection elements ( ⁇ -ray detectors) (when approaching or not approaching) as in the above formula (2). It is preferable to obtain the correction coefficient ⁇ from the ratio of the coincidence count data collected at the same time (the left side of the above equation (2)).
- a plurality of radiation detection elements are used.
- the same calibration source (the latter: the second calibration source, in the present embodiment, the flat plate source) is used before and after the change of arrangement (at the time of proximity or non-proximity)
- the obtained correction coefficient ⁇ is used as the former.
- the coincidence data collected after the change of the arrangement of multiple radiation detection elements ( ⁇ -ray detectors) (at the time of proximity) has a geometrical influence due to the positional relationship of at least the radiation detection elements ( ⁇ -ray detectors). It is a combination that receives. That is, combinations that are geometrically influenced by the positional relationship of the radiation detection elements ( ⁇ -ray detectors) based on the coincidence data collected after the change in arrangement (at the time of proximity) (in the present embodiment, face each other) Sensitivity coefficient data for the detector head) can be obtained.
- the first sensitivity coefficient calculation step (step S1) it is preferable to obtain the sensitivity coefficient using a calibration source as described below. That is, as in the present embodiment, when a rod-shaped radiation source S L (see FIG. 6) that can rotate along a plurality of radiation detection elements ( ⁇ -ray detectors) is used, a plurality of rod-shaped radiation sources S L are provided. Mitateru by rotating along a radiation detection element (gamma ray detector) in a ring-ray source S R shown in Figure 4 (a).
- the first sensitivity coefficient calculating step (Step S1) (in this example ⁇ -rays) radiation from the rotating rod-like radiation source S L (i.e.
- the rod-shaped radiation source is likened to a ring-ray source S R S L) for detecting the Based on the coincidence data collected in this way, the sensitivity coefficient is obtained separately for each sensitivity factor.
- the second sensitivity coefficient calculation step (step S2) it is preferable to obtain the sensitivity coefficient using a calibration source as described below. That is, in the second sensitivity coefficient calculating step (step S2), and prior to the change of the arrangement of a plurality of radiation detecting elements (gamma ray detector) (non-proximity state), model and from the cylinder-ray source S C to the actual subject Based on the coincidence data collected by detecting the radiation ( ⁇ rays), the sensitivity coefficient of the non-geometric factor that changes with time can be obtained.
- a plurality of detector heads (two in this embodiment) including a plurality of radiation detection elements ( ⁇ -ray detectors) are provided, and each detector head is configured such that the distance between the detector heads can be changed.
- the sensitivity coefficient can be obtained using the following calibration radiation source. preferable. That is, when each detector head is brought close to each other, it is provided along a rod-shaped radiation source that can be rotated along a plurality of radiation detection elements ( ⁇ -ray detectors) or a plurality of radiation detection elements ( ⁇ -ray detectors). There is a possibility that the generated ring source interferes with each detector head.
- the third sensitivity coefficient calculating step (step S3) and in a state of being close to the detector head one another, based on the coincidence count data collected by detecting radiation (gamma rays) from the flat plate-ray source S P Then, the sensitivity coefficient derived from the geometric arrangement is obtained.
- Computation means (arithmetic circuit 6 in FIG. 1) that performs the sensitivity coefficient calculation step (step S2) and the third sensitivity coefficient calculation step (step S3) is provided.
- it was obtained in the first sensitivity coefficient calculation step (step S1), the second sensitivity coefficient calculation step (step S2), and the third sensitivity coefficient calculation step (step S3).
- a cylindrical radiation source with a uniform radioactivity concentration of 300 mm in diameter is installed at the center of the device (detector heads 2A, 2B) in the proximity of the device (detector heads 2A, 2B) to a diameter of 778mm to 250mm. Collected.
- the reconstruction result incorporating the conventional elemental sensitivity correction method using the geometric factor of the ring source and the non-geometric system factor of the cylindrical source uses the non-proximate geometric factor. Artifacts occur. Non-geometric factors for cylindrical sources, events in the same detector head are derived from ring sources, events in opposite detector heads are derived from flat sources, and correction factor ⁇ It was confirmed that artifacts disappeared and the image quality improved as a result of the included reconstruction.
- the present invention is not limited to the above embodiment, and can be modified as follows.
- the radiation is ⁇ rays, but may be radiation such as ⁇ rays and ⁇ rays.
- the DOI detector is used.
- the DOI detector may be applied to a radiation detector that does not distinguish the depth direction.
- each detector head 2A and 2B has been described, but the number of detector heads is not limited to two. If there is a structure in which a plurality of detector heads each including a plurality of radiation detection elements (gamma ray detectors in the embodiment) are provided and the distance between the detector heads can be changed, each detector head is 3 There may be more than one.
- the rod-shaped radiation source S L is formed by using the rod-shaped radiation source S L (see FIG. 6) that can rotate along a plurality of radiation detection elements ( ⁇ -ray detectors in the embodiment).
- S R by rotating along a plurality of radiation detecting elements (gamma ray detector), S R and itself ring-ray source shown in FIG. 4 (a)
- S P may be rotated along a flat plate-ray source S P a plurality of radiation detecting elements (gamma ray detector) shown in Figure 7 (a). That may be a ring-ray source S R provided along the plurality of radiation detecting elements (gamma ray detector), as shown in Figure 4 (a).
- FIG. 7 in the case of using a rotatable flat-ray source S P along a plurality of radiation detecting elements as shown in (a) (gamma ray detector)
- the flat-ray source S P a plurality of radiation detecting elements You may rotate along (gamma ray detector).
- FIG. 4 A rod-shaped source S L that can reciprocate along the center axis of each detector head shown in FIG. That is, in the case of using a reciprocable rod-shaped radiation source S L along the central axis of each detector head as shown in FIG. 7 (b), along the rod-shaped radiation source S L to the central axis of each detector head Mitateru flat plate-ray source S P by reciprocating Te.
- the arrangement before the change of the arrangement of the plurality of radiation detection elements is not close, and after the change of the arrangement, the arrangement is close. In other words, before the change of arrangement, it may be close, and after the change of arrangement, it may be non-close. Therefore, the first sensitivity coefficient calculating step (step S1), the based on the coincidence count data collected at proximity with ring-ray source S R oval shown in FIG. 7 (c), the sensitivity coefficient by the sensitivity factor Ask separately. Then, in the third sensitivity coefficient calculation step (step S3), the sensitivity coefficient derived from the geometric arrangement is obtained based on the coincidence data collected at the time of non-proximity.
- the shape of the calibration radiation source in the first sensitivity coefficient calculation step (step S1), the second sensitivity coefficient calculation step (step S2), and the third sensitivity coefficient calculation step (step S3) is not particularly limited.
- a calibration radiation source having a shape suitable for the detector arrangement may be used.
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Abstract
Description
ただし、上記(1)式中のεui,εvjは検出器固有感度、duvrkは結晶干渉因子、fuvはリングペア感度、buvkはブロック形状因子、guvrは動径方向幾何学因子、kはブロック内の結晶相対位置、rは動径方向位置である。これらの要素のうち、guvr,duvrkなどは幾何学的に決まる要素(以下、「幾何学系因子」と呼ぶ)である。なお、εui,εvj,buvkは経時変化する非幾何学系因子である。
すなわち、マルチモダリティ対応フレキシブルPET装置は従来の要素別感度補正法に対応していないという問題がある。従来の要素別感度補正法は検出器群が円形配置で、位置関係が固定である場合に成立する。
すなわち、この発明に係る感度補正方法は、被検体内の放射性薬剤から発生した放射線を検出する放射線検出素子の感度補正方法であって、複数の前記放射線検出素子で収集された同時計数データに基づいて、感度係数を感度要因別に分けて求める第1感度係数算出工程と、前記第1感度係数算出工程の後で、前記複数の放射線検出素子の配置の変化前に、収集された同時計数データに基づいて、非幾何学系因子の感度係数を求める第2感度係数算出工程と、前記第2感度係数算出工程の後で、前記複数の放射線検出素子の配置が変化した状態で収集された同時計数データに基づいて、幾何学配置由来の感度係数を求める第3感度係数算出工程とを備え、前記第1感度係数算出工程,前記第2感度係数算出工程および前記第3感度係数算出工程で求められた感度係数を用いて、放射線検出素子の感度補正を行うことを特徴とするものである。
また、第2感度係数算出工程では、下記のような校正用線源を用いて感度係数を求めるのが好ましい。すなわち、第2感度係数算出工程では、複数の放射線検出素子の配置の変化前に、実際の被検体に模した校正用円筒線源からの放射線を検出することで収集された同時計数データに基づいて、経時変化する非幾何学系因子の感度係数を求めることができる。
図1は、実施例に係るマルチモダリティ対応フレキシブルPET装置の検出器ヘッドの一実施態様を示す概略斜視図およびブロック図であり、図2は、γ線検出器の概略斜視図であり、図3(a)は、検出器ヘッドを奥行き方向から見た概略図であり、図3(b)は、奥行き方向に直交する水平方向から見た概略図である。
図5のフローチャートに示すように、最初に図4(a)に示すリング線源SRで収集された同時計数データを使って、経時変化しない幾何学系因子の結晶干渉因子duvrk(「Crystal Interference Factor」で表記)を計算する。この幾何学系因子の結晶干渉因子duvrk(Crystal Interference Factor)を計算する前にパス長規格化を適用(「Apply」で表記)するのが好ましい。
次に、結晶干渉因子duvrk(Crystal Interference Factor)による幾何学系因子の補正を行った図4(b)に示す円筒線源SCの同時計数データを使って、経時変化する非幾何学系因子の検出器固有感度εui,εvj(「Crystal Efficiency Factor」で表記)を順に計算する。このときに、体軸断面(体軸横断面)のブロック形状因子buvk(「Axial Block Profile Factor」で表記)や長軸断のブロック形状因子buvk(「Transaxial Block Profile Factor」で表記)も計算し、ステップS3で図4(c)に示す平板線源SPの同時計数データに対して補正を行う。
最後に、図4(c)に示す平板線源SPの同時計数データを使って、近接したことによって検出器の幾何学配置の変化による影響を受ける平板線源の時の結晶干渉因子dPlate(「Crystal Interference(Plate) Factor」で表記)および平板線源の時のリングペア感度fPlate(「Ring Pair(Plate) Factor」で表記)のみを計算する。
また、第2感度係数算出工程(ステップS2)では、下記のような校正用線源を用いて感度係数を求めるのが好ましい。すなわち、第2感度係数算出工程(ステップS2)では、複数の放射線検出素子(γ線検出器)の配置の変化前(非近接時)に、実際の被検体に模した円筒線源SCからの放射線(γ線)を検出することで収集された同時計数データに基づいて、経時変化する非幾何学系因子の感度係数を求めることができる。
装置(検出器ヘッド2A,2B)の直径778mmから直径250mmに近接させて、装置(検出器ヘッド2A,2B)中心に直径300mmの均一放射能濃度の円筒線源を設置して、同時計数データを収集した。リング線源の幾何学因子と円筒線源の非幾何学系因子とを使った従来の要素別感度補正法を組み込んだ再構成結果では、非近接の幾何学因子を使うので、再構成画像にアーティファクトが生じる。円筒線源の非幾何学系因子,同一の検出器ヘッド内のイベントはリング線源由来,互いに対向する検出器ヘッド内のイベントは平板線源由来に切り替える幾何学系因子,さらに補正係数αを入れた再構成結果でアーティファクトがなくなり画質が改善したのが確認された。
2A,2B … 検出器ヘッド
3 … γ線検出器
SR … 校正用リング線源(リング線源)
SC … 校正用円筒線源(円筒線源)
SP … 校正用平板線源(平板線源)
SL … 校正用棒状線源(棒状線源)
α … 補正係数
Claims (10)
- 被検体内の放射性薬剤から発生した放射線を検出する放射線検出素子の感度補正方法であって、
複数の前記放射線検出素子で収集された同時計数データに基づいて、感度係数を感度要因別に分けて求める第1感度係数算出工程と、
前記第1感度係数算出工程の後で、前記複数の放射線検出素子の配置の変化前に、収集された同時計数データに基づいて、非幾何学系因子の感度係数を求める第2感度係数算出工程と、
前記第2感度係数算出工程の後で、前記複数の放射線検出素子の配置が変化した状態で収集された同時計数データに基づいて、幾何学配置由来の感度係数を求める第3感度係数算出工程と
を備え、
前記第1感度係数算出工程,前記第2感度係数算出工程および前記第3感度係数算出工程で求められた感度係数を用いて、放射線検出素子の感度補正を行うことを特徴とする感度補正方法。 - 請求項1に記載の感度補正方法において、
前記複数の放射線検出素子の配置が変化した場合の感度係数は、放射線検出素子の配置によらず位置関係が不変の組み合わせに対しては、配置変化前に求められた幾何学系因子の感度係数と、非幾何学系因子の感度係数との積で表され、放射線検出素子の位置関係により幾何学的な影響を受ける組み合わせに対しては、配置変化後に求められた幾何学系因子の感度係数と、非幾何学系因子の感度係数との積で表されることを特徴とする感度補正方法。 - 請求項1に記載の感度補正方法において、
前記複数の放射線検出素子の配置の変化前後で同じ校正用線源を用いて同時間にそれぞれ収集された同時計数データの比から補正係数を求めることを特徴とする感度補正方法。 - 請求項3に記載の感度補正方法において、
前記複数の放射線検出素子の配置の変化前に所定の校正用線源を第1校正用線源として用いた後に、前記第1校正用線源とは別の校正用線源を第2校正用線源としたときに、前記複数の放射線検出素子の配置の変化前後で同じ第2校正用線源を用いて同時間にそれぞれ収集された同時計数データの比から補正係数を求め、
前記第1校正用線源での感度補正に関する各因子の積で表された式に、前記補正係数を乗算することを特徴とする感度補正方法。 - 請求項1に記載の感度補正方法において、
前記複数の放射線検出素子の配置の変化後に収集された同時計数データは、少なくとも放射線検出素子の位置関係により幾何学的な影響を受ける組み合わせであることを特徴とする感度補正方法。 - 請求項1に記載の感度補正方法において、
前記第1感度係数算出工程では、複数の前記放射線検出素子に沿って回転可能な校正用棒状線源,複数の前記放射線検出素子に沿って設けられた校正用リング線源または複数の前記放射線検出素子に沿って回転可能な校正用平板線源からの放射線を検出することで収集された同時計数データに基づいて、感度係数を感度要因別に分けて求めて、
前記第2感度係数算出工程では、前記複数の放射線検出素子の配置の変化前に、校正用円筒線源からの放射線を検出することで収集された同時計数データに基づいて、非幾何学系因子の感度係数を求めることを特徴とする感度補正方法。 - 請求項1に記載の感度補正方法において、
同時計数する2つの検出器を結ぶ仮想上の直線であるLORの結晶干渉因子に対して、当該LORの検出器距離の二乗で割ることによって、検出器距離を補正するための立体角補正を行うことを特徴とする感度補正方法。 - 請求項1から請求項7のいずれかに記載の感度補正方法において、
複数の前記放射線検出素子からなる検出器ヘッドを複数備え、各当該検出器ヘッド間の距離が変更可能に各々の検出器ヘッドは構成されており、
各検出器ヘッドの中心に設置された校正用平板線源または各検出器ヘッドの中心軸に沿って往復可能な校正用棒状線源であって、
前記第3感度係数算出工程では、各検出器ヘッドを互いに近接させた状態で、当該校正用平板線源または往復した当該校正用棒状線源からの放射線を検出することで収集された同時計数データに基づいて、幾何学配置由来の感度係数を求めることを特徴とする感度補正方法。 - 被検体内の放射性薬剤から発生した放射線を検出して放射線断層撮影を行う放射線断層撮影装置であって、
複数の放射線検出素子からなる検出器ヘッドを複数備え、各当該検出器ヘッド間の距離が変更可能に各々の検出器ヘッドは構成されており、
演算処理を行う演算手段を備え、
当該演算手段は、
複数の前記放射線検出素子で収集された同時計数データに基づいて、感度係数を感度要因別に分けて求める第1感度係数算出工程と、
前記第1感度係数算出工程の後で、前記複数の放射線検出素子の配置の変化前に、収集された同時計数データに基づいて、非幾何学系因子の感度係数を求める第2感度係数算出工程と、
前記第2感度係数算出工程の後で、前記複数の放射線検出素子の配置が変化した状態で収集された同時計数データに基づいて、幾何学配置由来の感度係数を求める第3感度係数算出工程と
を行い、
前記第1感度係数算出工程,前記第2感度係数算出工程および前記第3感度係数算出工程で求められた感度係数を用いて、放射線検出素子の感度補正を行うことを特徴とする放射線断層撮影装置。 - 請求項9に記載の放射線断層撮影装置において、
前記検出器ヘッドは、円弧状に各々の前記放射線検出素子を配置して構成されていることを特徴とする放射線断層撮影装置。
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JP6607256B2 (ja) | 2019-11-20 |
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US20180196151A1 (en) | 2018-07-12 |
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