WO2010084528A1 - 放射線断層撮影装置における較正データの収集方法 - Google Patents
放射線断層撮影装置における較正データの収集方法 Download PDFInfo
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- WO2010084528A1 WO2010084528A1 PCT/JP2009/000251 JP2009000251W WO2010084528A1 WO 2010084528 A1 WO2010084528 A1 WO 2010084528A1 JP 2009000251 W JP2009000251 W JP 2009000251W WO 2010084528 A1 WO2010084528 A1 WO 2010084528A1
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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
- G01T1/164—Scintigraphy
- G01T1/1641—Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras
- G01T1/1644—Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras using an array of optically separate scintillation elements permitting direct location of scintillations
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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
- G01T1/164—Scintigraphy
- G01T1/1641—Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras
- G01T1/1648—Ancillary equipment for scintillation cameras, e.g. reference markers, devices for removing motion artifacts, calibration devices
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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 collecting calibration data in a radiation tomography apparatus for imaging radiation, and more particularly to a method for collecting calibration data in a radiation tomography apparatus in which block-shaped radiation detectors are arranged in a ring shape.
- a radiation tomography that obtains a tomographic image of a radiopharmaceutical distribution in a region of interest of a subject by detecting an annihilation radiation pair (for example, ⁇ -rays) released from a radiopharmaceutical that is administered to the subject and localized in the region of interest Used in photographic equipment (ECT: Emission-Computed Tomography).
- ECT mainly includes a PET (Positoron Emission Tomography) apparatus, a SPECT (Single Photon Emission Computed Tomography) apparatus, and the like.
- the PET apparatus has a detector ring in which block-shaped radiation detectors are arranged in a ring shape. This detector ring is provided to surround the subject and is configured to detect the radiation that has passed through the subject.
- a conventional PET apparatus 50 includes a gantry 51 having an introduction hole for introducing a subject, and a block-shaped radiation detector 52 for detecting radiation inside the gantry 51.
- the detector ring 53 formed in such a manner and a support member 54 provided so as to surround the detector ring 53 are provided.
- a bleeder unit 55 having a bleeder circuit is provided at a position where the support member 54 is interposed, and this connects the support member 54 and the radiation detector 52.
- the PET device measures the annihilation radiation pair emitted from the radiopharmaceutical. That is, the annihilation radiation pair radiated from the inside of the subject M is a radiation pair whose traveling direction is opposite by 180 °.
- sensitivity unevenness used for image correction is acquired.
- a cylindrical phantom which is the source of the annihilation radiation pair, is inserted into the gantry 51 to cause the detector ring 53 to detect the annihilation radiation pair (see, for example, Patent Document 1).
- the detector ring 53 does not necessarily output a result that the annihilation radiation pair is uniformly emitted from the entire phantom. This is because the radiation detection sensitivity varies among the radiation detection elements constituting the detector ring 53.
- the conventional configuration has the following problems. That is, according to the conventional configuration, if the detector ring 53 is wide, it is difficult to adjust the phantom to be inserted into the detector ring 53. In recent years, radiation tomography apparatuses in which the detector ring 53 is wide enough to cover the whole body of the subject are being developed. In order to cancel the sensitivity unevenness inherent in such a radiation tomography apparatus, an elongated and huge phantom sufficient to block the through hole of the detector ring 53 is required.
- the phantom is pre-prepared before being inserted into the detector ring 53. That is, the phantom is a container filled with a solution, and first, the inside is filled with the solution. Next, radioactive material is added and the solution is stirred. As the detector ring 53 becomes wider, the amount of solution for filling the phantom increases, and it is not easy to stir the solution. The operation of inserting the phantom whose preparation has been completed into the detector ring 53 is also complicated.
- the present invention has been made in view of such circumstances, and an object thereof is to collect calibration data in a radiation tomography apparatus that can reliably collect calibration data even when the detector ring 53 is wide. Is to provide.
- the method of collecting calibration data in the radiation tomography apparatus includes a unit detection ring in which radiation detection elements for detecting radiation are arranged in a ring shape and the number of times two different radiation detection elements detect radiation simultaneously.
- a plurality of unit detection rings are stacked so as to share a central axis thereof, including a coincidence counting unit that counts the number of simultaneous events and a calibration data generation unit that generates calibration data based on the number of simultaneous events.
- the number of simultaneous events is acquired while moving the phantom that irradiates the annihilation radiation pair inside the inner hole of the detector ring It is characterized by that.
- the present invention acquires the number of simultaneous events while moving the phantom irradiating the annihilation radiation pair so as to pass through the inner hole of the detector ring.
- the phantom is shaped so as to uniformly irradiate the annihilation radiation pair toward the detector ring.
- the irradiation characteristics of actual annihilation radiation pairs are slightly different depending on the position of the phantom.
- the irradiation characteristics of the incident annihilation radiation pair differ depending on the position of the detector ring, so that the irradiation unevenness of the phantom annihilation radiation pair is superimposed on the calibration data.
- the irradiation unevenness of the annihilation radiation pair possessed by the phantom is blurred in the calibration data. With such characteristics, it can be considered that the annihilation radiation pair has been irradiated, and calibration data more suitable for false image removal can be acquired.
- phantom moving means for moving the phantom
- phantom control means for controlling the phantom moving means.
- the extending direction of the detector ring is the extending direction
- the direction in which the phantom moves relative to the detector ring is along the extending direction, and the length of the phantom in the extending direction is detected in the extending direction. It is more desirable if it is shorter than the length of the vessel ring.
- This configuration shows a specific mode of the radiation detector according to the present invention. As shown in this configuration, the calibration data collection method according to the present invention can be applied even when the detector ring extends in the extending direction from the phantom.
- the speed of the phantom described above is the fastest at the start of movement, and it is more desirable if it gradually becomes slower as the phantom moves.
- the coincidence counting unit counts the number of simultaneous events only when the distance between the two radiation detection elements in the extending direction is equal to or less than a predetermined length, and the length of the phantom in the extending direction is predetermined. Longer than the length is more desirable.
- the coincidence counting unit counts the number of simultaneous events only when the distance between the two radiation detection elements in the extending direction is equal to or less than a predetermined length. If the two radiation detection elements are too far apart in the extending direction, counting the number of simultaneous events between such radiation detection elements increases the burden on the coincidence counting means.
- the configuration is not performed. Further, the length of the phantom in the extending direction is longer than a predetermined length. That is, an annihilation radiation pair is reliably irradiated between two radiation detection elements that perform coincidence counting.
- the present invention acquires the number of simultaneous events while moving the phantom that irradiates the annihilation radiation pair so as to pass through the inner hole of the detector ring.
- the detector ring can be regarded as being irradiated with an annihilation radiation pair with uniform characteristics regardless of its position, and calibration data more suitable for removing false images can be acquired.
- the coincidence counting unit counts the number of simultaneous events only when the distance between the two radiation detection elements in the extending direction is equal to or less than a predetermined length. Moreover, between the two radiation detection elements that perform coincidence counting, the length in the extending direction of the phantom is longer than a predetermined length so that the annihilation radiation pair is reliably irradiated.
- FIG. 1 is a functional block diagram illustrating a configuration of a radiation tomography apparatus according to Embodiment 1.
- FIG. 1 is a perspective view illustrating a configuration of a radiation detector according to Embodiment 1.
- FIG. It is a figure explaining the structure of the detector ring which concerns on Example 1.
- FIG. 6 is a cross-sectional view illustrating an original map acquisition method according to Embodiment 1.
- FIG. 6 is a cross-sectional view illustrating an original map acquisition method according to Embodiment 1.
- FIG. 6 is a cross-sectional view illustrating a tomographic image acquisition method according to Embodiment 1.
- FIG. 6 is a cross-sectional view illustrating a tomographic image acquisition method according to Embodiment 1.
- FIG. 6 is a cross-sectional view illustrating a tomographic image acquisition method according to Embodiment 1.
- FIG. 1 is a functional block diagram illustrating a configuration of a radiation tomography apparatus according to Embodiment 1.
- FIG. 6 is a cross-sectional view illustrating a tomographic image acquisition method according to Embodiment 1.
- FIG. It is a figure explaining the structure concerning one modification of the present invention. It is a partially broken sectional view explaining the structure of the conventional radiation tomography apparatus.
- FIG. 1 is a functional block diagram illustrating the configuration of the radiation tomography apparatus according to the first embodiment.
- the radiation tomography apparatus 9 according to the first embodiment includes a top plate 10 that lies on the subject M and a gantry 11 having a through hole that surrounds the subject M.
- the top plate 10 is provided so as to pass through the opening of the gantry 11 and is movable back and forth along the direction in which the opening of the gantry 11 extends.
- Such sliding of the top plate 10 is realized by the top plate moving mechanism 15.
- the top plate moving mechanism 15 is controlled by the top plate movement control unit 16.
- a detector ring 12 for detecting an annihilation gamma ray pair emitted from the subject M is provided inside the gantry 11, a detector ring 12 for detecting an annihilation gamma ray pair emitted from the subject M is provided.
- the detector ring 12 has a cylindrical shape extending in the body axis direction z (corresponding to the extending direction of the present invention) of the subject M, and its length is 1 m to 1.8 m. That is, the detector ring 12 extends to such an extent that at least the body portion of the subject M can be completely covered.
- the clock 19 sends time information to the detector ring 12.
- the detection data output from the detector ring 12 is given time information indicating when the ⁇ -rays were acquired, and is input to the filter unit 20 described later.
- the detector ring 12 is configured by arranging block-shaped radiation detectors 1 in a ring shape. Assuming that the width per one in the radiation detector 1 is about 5 cm, about 20 to 36 radiation detectors 1 are arranged on the detector ring 12 in the z direction. The configuration of the radiation detector 1 will be briefly described.
- FIG. 2 is a perspective view illustrating the configuration of the radiation detector according to the first embodiment. As shown in FIG. 2, the radiation detector 1 includes a scintillator 2 that converts radiation into fluorescence, and a photodetector 3 that detects fluorescence. A light guide 4 for transmitting and receiving fluorescence is provided at a position where the scintillator 2 and the photodetector 3 are interposed.
- the scintillator 2 is configured by arranging scintillator crystals two-dimensionally.
- the scintillator crystal is composed of Lu 2 (1-X) Y 2X SiO 5 (hereinafter referred to as LYSO).
- the photodetector 3 can specify the fluorescence generation position indicating which scintillator crystal emits fluorescence, and can also specify the intensity of fluorescence and the time when the fluorescence is generated. it can.
- the scintillator 2 having the configuration of the first embodiment is merely an example of an aspect that can be adopted. Therefore, the configuration of the present invention is not limited to this.
- FIG. 3 is a diagram illustrating the configuration of the detector ring according to the first embodiment.
- the radiation detectors 1 are arranged along a virtual circle (more precisely, a regular n-gon) in the detector ring 12.
- the scintillator crystals are also arranged along a virtual circle (precisely, a regular n-gon), and constitute a unit detection ring 12b as shown in FIG.
- the unit detection ring 12b is formed of scintillator crystals C (radiation detection elements) arranged at the same position in the z direction and arranged along an annular ring.
- the unit detection ring 12b is a concept in which scintillator crystals are arranged in a line and is independent of the radiation detectors 1 arranged along a virtual circle. As shown in FIG. 3B, the unit detection ring 12b is connected in the z direction to form the detector ring 12.
- the unit detection ring 12b has a through-hole at the center, and the unit detection ring 12b is arranged so that the through-holes of the unit detection ring 12b are connected, and the detector ring 12 is configured. You can also.
- the detector ring 12 is formed by arranging around 100 radiation detectors 1 in an annular shape. Therefore, when the through hole 12a is viewed from the z direction, the through hole 12a is, for example, It is a regular 100-gon. In this case, the plurality of unit detection rings 12b are connected so as to share the respective central axes, and the through hole 12a has a shape of a 100 prism.
- the radiation tomography apparatus 9 is further provided with various units for acquiring a tomographic image of the subject M as shown in FIG. Specifically, the radiation tomography apparatus 9 receives, from the detection data detected by the detector ring 12, a filter unit 20 that extracts valid data, and data that is regarded as valid by the filter unit 20.
- the coincidence counting unit 21 that performs simultaneous counting of annihilation ⁇ -ray pairs and the incident position of the ⁇ -rays on the detector ring 12 from the two ⁇ -ray detection data determined by the coincidence counting unit 21 to be annihilation ⁇ -ray pairs
- a LOR specifying unit 22 for discrimination, a data storage unit 23 for storing detection data, a mapping unit 24 for forming a tomographic image of the subject M, and a calibration unit 25 for calibrating the tomographic image of the subject M are provided.
- the calibration unit 25 refers to the original map stored in the calibration data storage unit 34 and removes the false image reflected in the tomographic image. The significance of providing the count target area setting unit 33 will be described later.
- the MRD storage unit 37 stores MRD described later.
- the input unit 38 is used to input a surgeon's operation, and for example, receives an MRD change.
- the above-mentioned coincidence counting unit corresponds to the coincidence counting unit of the present invention
- the calibration data generating unit corresponds to the calibration data generating unit of the present invention
- the top board moving mechanism corresponds to the phantom moving means of the present invention
- the top board movement control unit corresponds to the phantom movement control means.
- the radiation tomography apparatus 9 includes a main control unit 35 that performs overall control of each unit and a display unit 36 that displays a radiation tomographic image.
- the main control unit 35 is constituted by a CPU, and executes various programs, thereby allowing the filter unit 20, the coincidence counting unit 21, the LOR specifying unit 22, the data storage unit 23, the mapping unit 24, and the calibration unit 25 to be included. Realized.
- each above-mentioned part may be divided
- the original map is mapping data in which unevenness of detection sensitivity of the annihilation radiation pair inherent to the detector ring 12 is mapped.
- a phantom 41 for irradiating radiation is prepared.
- the phantom 41 has a width that can be placed on the top board 10 and has a cylindrical shape that extends in the z direction.
- the length of the phantom 41 in the z direction is a characteristic configuration of the present embodiment and will be described later.
- the phantom 41 has a cylindrical shape following the shape of the opening of the gantry 11 and has a hollow filled with a solution.
- the direction of movement of the phantom 41 relative to the detector ring 12 coincides with the extending direction of the phantom 41.
- a radioactive substance is added.
- a nuclide that emits positrons that generate annihilation ⁇ -ray pairs is selected. More specifically, it is desirable to use the same nuclide as that used for the radiopharmaceutical injected into the subject M.
- the phantom 41 After adding a radioactive substance to the phantom 41 filled with the solution and sealing the hollow of the phantom 41, the phantom 41 is shaken. By doing so, annihilation gamma ray pairs are uniformly emitted from the entire phantom 41.
- the phantom 41 is attached to the top board 10.
- the top plate 10 is attenuated when arranged on the top plate 10, a collection system in which gamma rays emitted from the phantom directly reach the detector using a phantom mounting jig or the like is desirable.
- the length of the phantom 41 in the z direction is shorter than that of the detector ring 12.
- the top plate moving mechanism 15 slides the top plate 10 on which the phantom 41 is mounted.
- the front end 41 a of the phantom 41 passes through the unit detection ring 12 c existing at one end of the detector ring 12. This time is the initial position of the phantom 41.
- the radiation tomography apparatus 9 collects calibration data from the state of the initial position of the phantom 41 described above. Detection data (data relating to fluorescence emitted by the scintillator crystal) obtained by the detector ring 12 is sent to the filter unit 20.
- the filter unit 20 passes only the detection data obtained with the scintillator crystal existing in the counting target region R to the coincidence counting unit 21 and discards the other detection data. By doing in this way, useless calculation can be omitted in the coincidence counting section 21, and complicated coincidence calculation can be greatly simplified.
- the counting target region R at the initial position is only the scintillator crystal belonging to the unit detection ring 12c, and specifically, the hatched portion in FIG.
- the counting target area R is set by the counting target area setting unit 33, and the filter unit 20 sequentially reads the latest counting target area R from the counting target area setting unit 33.
- coincidence unit 21 when detection data derived from two different scintillator crystals falls within a time window having a predetermined time width, it is assumed that this is due to annihilation ⁇ -ray pairs, and this number of times is calculated. Count. This is the number of simultaneous events. This determination of simultaneity uses time information given to the detection data by the clock 19.
- the direction in which the annihilation ⁇ ray pair is emitted is determined.
- the detection data regarded as simultaneous by the coincidence counting unit 21 includes positional information indicating which scintillator crystal emits fluorescence.
- the LOR specifying unit 22 determines an LOR (Line of Response) which is a line segment connecting the two scintillator crystals, and sends the LOR and the number of simultaneous events corresponding to the LOR to the data storage unit 23.
- the top plate 10 is slid while detecting the radiation as described above. Accordingly, the relative position between the phantom 41 and the detector ring 12 is changed from the initial position, and the counting target region R is changed. That is, when the phantom 41 is moved from the initial position by the width of the unit detection ring 12b in the z direction, an area of the unit detection ring 12b adjacent to the unit detection ring 12c is added to the count target region R. That is, data indicating the movement status of the top board 10 is sent from the top board movement control section 16 to the counting target area setting section 33, and the counting target area setting section 33 counts based on this data.
- the region R is expanded.
- the count target area setting unit 33 moves the phantom 41 by the width of the unit detection ring 12b until the phantom 41 is completely covered with the detector ring 12 as shown in FIG.
- a single unit detection ring 12b is newly added, and the count target region R is expanded in the z direction.
- the scintillator crystal facing the phantom 41 exists in the counting target region R.
- the count target region R has a width corresponding to eight scintillator crystals. This number of 8 is obtained by adding 1 to the MRD described later.
- the counting target area setting unit 33 When the phantom 41 is moved by the width of the unit detection ring 12b from the state of FIG. 4B, the counting target area setting unit 33 does not expand the counting target area R any more, and this time, The count target region R is shifted so as to follow 41. That is, the counting target region setting unit 33 removes the unit detection ring 12c from the counting target region R and adds a single unit detection ring 12b positioned on the front end 41a side of the phantom 41 so as to newly add. To reset. The count target area setting unit 33 shifts the count target area R every time the phantom 41 moves by the width of the unit detection ring 12b.
- FIG. 5A shows a state in which the phantom 41 is located in the middle of the detector ring 12. The count target region R always exists in a section sandwiched between the front end 41a and the rear end 41b of the phantom 41 in the z direction.
- the unit detection rings 12b positioned behind the rear end 41b are successively removed from the count target region R, and eventually, as shown in FIG.
- the rear end 41 b of 41 is located in the unit detection ring 12 d existing at one end of the detector ring 12. This state is the end position of the movement of the phantom 41.
- the data storage unit 23 stores the LOR and the number of simultaneous events corresponding to the LOR.
- the mapping unit 24 assembles this data and obtains an original map that visualizes the inside of the detector ring 12. Since the phantom 41 emits annihilation radiation pairs uniformly, it is expected that no false image will appear in the original map if simply considered. However, in reality, this is not always the case, and some spurious image appears in the original map due to the influence of sensitivity unevenness between the scintillator crystals.
- the radiation detector 1 has a characteristic that the scintillator crystal located on the side of the scintillator 2 is more difficult to detect radiation than that located at the center of the scintillator, and a false image due to the characteristic appears.
- a factor causing such a false image is called an in-plane block shape factor.
- another false image is generated due to the property that the detection sensitivity of ⁇ -rays decreases as the LOR length increases and the LOR width decreases.
- a factor causing such a false image is called a radial geometric factor.
- crystal interference factor there is a crystal interference factor as a factor different from the above-mentioned factors.
- the scintillator crystal on the side close to the phantom 41 passes through without being detected, and its vicinity, that is, a crystal far from the phantom 41 May be detected.
- the detection sensitivity of the scintillator crystal on the side far from the phantom 41 is lower than that on the near side, and a false image is generated. This is a crystal interference factor. In the original map, false images derived from these factors also appear.
- the calibration data is created in the calibration data generation unit 26 based on the original map and stored in the calibration data storage unit 34. If this calibration data is applied to the original map, the false image of the original map is cancelled.
- the maximum ring difference (MRD) which is an important concept when detecting an annihilation radiation pair, will be described.
- the original meaning of LOR is a line segment connecting different scintillator crystals. As shown in FIG. 6, when focusing on the scintillator crystal C8, a very large number of LORs can be considered. However, not all LORs are necessary for acquiring tomographic images. For example, the LOR 100g in FIG. 6 connects the scintillator crystal C8 and the scintillator crystal Dr. Both scintillator crystals are too far apart from each other in the z direction, and ⁇ rays enter the scintillator crystal from an oblique direction.
- LOR to be taken into account is LOR1g to LOR15g, and more generally, the scintillator crystals belonging to the region having a width of 15 scintillator crystals (for MRD ⁇ 2 + 1). Only the LOR connecting any one of the scintillator crystals C8 is the LOR relating to the scintillator crystal C8.
- Such selection of LOR is performed by the filter unit 20.
- the filter unit 20 passes detection data of the two scintillator crystals to the coincidence counting unit 21 when the distance between the two scintillator crystals in the z direction is equal to or less than MRD.
- the detection data is discarded.
- the filter unit 20 sends the detected data to the coincidence counting unit 21, the LOR specifying unit 22, the data storage unit 23, and the mapping unit 24. Since these operations are the same as described above, description thereof will be omitted.
- the tomographic image of the subject M assembled by the mapping unit 24 is output to the calibration unit 25.
- the calibration unit 25 performs data processing for removing the false image superimposed on the tomographic image of the subject M based on the calibration data stored in the calibration data storage unit 34.
- the completed image obtained in this way is displayed on the display unit 36. With this, the inspection using the radiation tomography apparatus 9 according to the configuration of the first embodiment is completed.
- the characteristic length of the phantom 41 in the configuration of the first embodiment will be described.
- the length of the phantom 41 is closely related to the maximum length of the count target region R as described with reference to FIG. Therefore, in the configuration of the first embodiment, if the appropriate maximum length of the count target region R is determined, the length of the phantom 41 is naturally determined.
- the LOR used for the coincidence counting is selected by the filter unit 20.
- the LOR is selected by designating the count target region R. Therefore, if the selection of the LOR at the time of the examination of the subject M and the selection of the LOR at the time of obtaining the calibration data are matched, the acquisition of the calibration data becomes the most effective.
- FIG. 7 is a schematic diagram for explaining the LOR in the unit detection ring existing at one end of the detector ring according to the configuration of the first embodiment.
- a unit detection ring that is separated from the unit detection ring 12c by seven unit detection rings (MRD) is defined as a unit detection ring 12e.
- the LOR used for the inspection is [1 from the scintillator crystal C8 and the unit detection ring 12c in the z direction.
- 7 types of LOR1g to LOR7g] and 1 type of LOR8g [connecting scintillator crystal C8 and scintillator crystal D8 belonging to unit detection ring 12c] are added. There are 8 types.
- a region K1 in FIG. 7A is a region occupied by the phantom 41 at one time when the calibration data is acquired. Since the phantom 41 is at least eight times as long as the width of the unit detection ring, all of the LOR1g to LOR8g pass through the region K1. If the phantom 41 is sometimes located in the region K1, the annihilation ⁇ -ray pairs along the LOR1g to LOR8g are reliably irradiated from the phantom 41. Note that a length eight times the width of the unit detection ring (the width of MRD + 1 unit detection rings 12b) corresponds to the predetermined length of the present invention.
- a unit detection ring separated from the unit detection ring 12d by 7 unit detection rings is defined as a unit detection ring 12f.
- the LOR used for the inspection is [1 from the scintillator crystal C8 and the unit detection ring 12d in the z direction.
- a region K2 in FIG. 7B is a region that the phantom 41 occupied at one time when acquiring calibration data. Since the phantom 41 is at least eight times as long as the width of the unit detection ring, all of the LORs 8g to LOR15g pass through the region K2. If the phantom 41 is sometimes located in the region K2, the annihilation ⁇ ray pair along the LOR 8g to LOR 15g is surely irradiated from the phantom 41.
- FIG. 8 is a schematic diagram for explaining the LOR in the unit detection ring existing in the central portion of the detector ring according to the configuration of the first embodiment. That is, as shown in FIG. 8A, among the LORs of the scintillator crystal C8, the LOR used for the inspection is (1) the scintillator crystal C8 and its left side (the other end side of the detector ring 12).
- LOR1g to LOR8g 7 types of LOR1g to LOR8g that connect to each of the unit detection rings 1 to 7 separated from the scintillator crystal C8 in the z direction and (2) connect the scintillator crystal C8 to the unit detection ring to which it belongs.
- a region K1 in FIG. 8A is a region occupied by the phantom 41 at a time when the calibration data is acquired.
- the eight types of LOR 1g to LOR 8g described in (1) and (2) the annihilation ⁇ -ray pairs along these LORs are reliably irradiated from the phantom 41.
- a region K2 in FIG. 8B is a region that the phantom 41 occupied at one time when acquiring the calibration data.
- the phantom 41 reliably irradiates annihilation ⁇ -ray pairs along these LORs.
- the configuration of the first embodiment acquires the number of simultaneous events while moving the phantom 41 that irradiates the annihilation gamma ray pair so as to pass through the inner hole of the detector ring 12.
- the phantom 41 has a shape that uniformly irradiates the annihilation gamma ray pair toward the detector ring 12.
- the irradiation characteristics of the actual annihilation ⁇ -ray pair may be slightly different depending on the position of the phantom 41 when the uniformity of the radiation source inside the phantom 41 is poor.
- the irradiation characteristics of the incident annihilation ⁇ -ray pair differ depending on the position of the detector ring 12. Will overlap.
- the configuration of the first embodiment since the phantom 41 is moved to the detector ring 12, the irradiation unevenness of the annihilation gamma ray pair possessed by the phantom 41 is blurred in the calibration data. Can be regarded as having been irradiated with an annihilation gamma ray pair with uniform characteristics regardless of the position, and calibration data more suitable for removing false images can be acquired.
- the coincidence counting unit 21 counts the number of simultaneous events only when the distance between the two scintillator crystals in the z direction is equal to or less than a predetermined length (the maximum length of the count target region R). If the two scintillator crystals are too far apart in the z direction, counting the number of simultaneous events between such scintillator crystals increases the burden on the coincidence counting unit 21, so such counting is performed. It has no structure. Further, the length of the phantom 41 in the z direction is longer than a predetermined length. That is, the annihilation ⁇ -ray pair is reliably irradiated between two scintillator crystals that perform coincidence counting.
- the present invention is not limited to the above configuration, and can be modified as follows.
- the radiation detector 1 in the above-described embodiment was provided with a single scintillator crystal layer.
- the present invention is not limited to this. That is, as shown in FIG. 9A, a radiation detector 1 having a multilayer crystal layer can also be used. By doing in this way, the detection sensitivity of the gamma ray in the radiation detector 1 and the discrimination ability of an incident position are strengthened.
- the crystal layer in which the scintillator crystals are two-dimensionally arranged is provided in four layers so as to be stacked from the light guide 4. Not limited. Most of the description of the first embodiment can be used for the original map acquisition operation and the tomographic image generation operation of the subject M in this modification.
- a specific change is that the LOR is increased from the configuration of the first embodiment. That is, for example, when considering the LOR for the scintillator crystal C8 in FIG. 9B, the LOR corresponding to the LOR 15g in FIG. 8A is (1) LOR 15h connecting the scintillator crystal C8 and the uppermost crystal layer. , (2) LOR 15i connecting the scintillator crystal C8 and the second crystal layer, (3) LOR 15j connecting the scintillator crystal C8 and the third crystal layer, and (4) crystal of the scintillator crystal C8 and the fourth layer. Divides into four types of LOR15k connecting layers.
- the filter unit 20 passes the detection data to each subsequent unit without distinguishing the four layers, and the LOR specifying unit 22 performs data processing while distinguishing the four layers.
- the phantom 41 moves only in one direction, but the present invention is not limited to this configuration. That is, the phantom 41 may be moved from the state of FIG. 4A once as shown in FIG. 5B, and then moved back so as to be in the state of FIG. 4A. That is, the original map may be generated while the phantom 41 is reciprocated within the detector ring 12.
- the effects according to this modification are as follows. The phantom 41 is shaken before use, and is shaped so as to uniformly irradiate the annihilation gamma ray pair toward the detector ring 12.
- the irradiation characteristics of the actual annihilation ⁇ -ray pair are slightly different depending on the position of the phantom 41.
- the irradiation characteristics of the incident annihilation ⁇ -ray pair differ depending on the position of the detector ring 12. Will overlap.
- the irradiation unevenness of the annihilation ⁇ -ray pair that the phantom 41 has in the calibration data is blurred. Regardless of the position, it can be considered that the annihilation ⁇ -ray pair is irradiated with uniform characteristics, and calibration data more suitable for false image removal can be acquired.
- the speed of the phantom 41 is not particularly mentioned. However, when the original map is acquired, the speed of the phantom 41 is maximized at the start of movement, and the phantom 41 moves. It can also be configured to gradually slow down this. According to such a configuration, the detector ring 12 can be regarded as having been irradiated with the annihilation ⁇ -ray pair with more uniform characteristics. The annihilation gamma ray pair included in the phantom 41 is the strongest when the phantom 41 is set on the detector ring 12 and gradually attenuates due to the physical half-life, so that the detector ring 12 is irradiated per unit time.
- the dose of the annihilation ⁇ -ray pair that is generated differs between the movement start position and the movement end position of the phantom 41.
- the dose of the annihilation gamma ray irradiated to the detector ring 12 at the movement start position of the phantom 41 is decreased, and conversely, the movement end position of the phantom 41 In FIG. 4, the dose of the annihilation ⁇ -ray pair irradiated to the detector ring 12 can be increased.
- the scintillator crystal referred to in the above-described embodiments is composed of LYSO.
- the scintillator crystal may be composed of other materials such as GSO (Gd 2 SiO 5 ) instead. Good. According to this modification, it is possible to provide a method of manufacturing a radiation detector that can provide a cheaper radiation detector.
- the fluorescence detector is composed of a photomultiplier tube, but the present invention is not limited to this. Instead of the photomultiplier tube, a photodiode, an avalanche photodiode, a semiconductor detector, or the like may be used.
- the top plate is slidable.
- the present invention is not limited to this.
- the top plate may be fixed and the gantry 11 may slide.
- the present invention is suitable for a medical radiation tomography apparatus.
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Abstract
Description
すなわち、従来の構成によれば、検出器リング53を幅広なものとすると、これに挿入させるファントムを調整することが困難となるという問題点がある。近年において、被検体の全身を覆う程度に検出器リング53が幅広となっている放射線断層撮影装置が開発されつつある。この様な放射線断層撮影装置が固有に有する感度ムラを打ち消すためには、検出器リング53の有する貫通孔を塞ぐのに十分な細長状で巨大なファントムが必要となる。
12 検出器リング
12b 単位検出リング
15 天板移動機構(ファントム移動手段)
16 天板移動制御部(ファントム移動制御手段)
21 同時計数部(同時計数手段)
26 較正データ生成部(較正データ生成手段)
41 ファントム
以下、本発明に係る放射線断層撮影装置の実施例を図面を参照しながら説明する。図1は、実施例1に係る放射線断層撮影装置の構成を説明する機能ブロック図である。実施例1に係る放射線断層撮影装置9は、図1に示すように、被検体Mを仰臥させる天板10と、被検体Mを包囲する貫通穴を有するガントリ11を有している。天板10は、ガントリ11の開口を貫通するように備えられているとともに、ガントリ11の開口の伸びる方向に沿って進退自在となっている。この様な天板10の摺動は、天板移動機構15によって実現される。天板移動機構15は、天板移動制御部16によって制御される。
次に、較正データ記憶部34にて記憶されているオリジナルマップの取得方法について説明する。オリジナルマップは、検出器リング12が固有に有する消滅放射線対の検出感度のムラ等をマッピングしたマッピングデータである。オリジナルマップを作成するには、まず、放射線を照射するファントム41を準備する。このファントム41は、天板10に載置できる程度の幅を有し、z方向に延伸した円柱状である。ファントム41のz方向の長さについては、本実施例の特徴的な構成であり、後述のものとする。
次に、実施例1に係る放射線断層撮影装置9の動作について説明する。実施例1に係る放射線断層撮影装置9で検査を行うには、まず、放射線薬剤を予め注射投薬された被検体Mを天板10に載置する。そして、天板10を摺動させ、被検体Mをガントリ11の開口に導入する。この時点より、被検体Mから発せられる消滅γ線対が検出される。
次に、実施例1の構成において特徴的なファントム41の長さについて説明する。ファントム41の長さは、図5(a)を用いて説明したように、計数対象領域Rの最大長さと密接に関係している。そこで、実施例1の構成において、ふさわしい計数対象領域Rの最大長さが決定されれば、自ずとファントム41の長さが決定されることになる。
Claims (6)
- 放射線を検出する放射線検出素子が環状に配列された単位検出リングと、2つの異なる放射線検出素子が同時に放射線を検出した回数である同時イベント数を計数する同時計数手段と、前記同時イベント数を基に較正データを生成する較正データ生成手段とを備え、複数の単位検出リングがそれらの中心軸を共有するようにして積層されることにより構成された検出器リングを備えた放射線断層撮影装置における較正データの収集方法において、
消滅放射線対を照射するファントムを前記検出器リングの有する内穴の内部で移動させながら、前記同時イベント数が取得されることを特徴とする放射線断層撮影装置における較正データの収集方法。 - 請求項1に記載の放射線断層撮影装置における較正データの収集方法において、
前記ファントムの移動は、前記ファントムを移動させるファントム移動手段と、前記ファントム移動手段を制御するファントム制御手段とによって実現されることを特徴とする放射線断層撮影装置における較正データの収集方法。 - 請求項1または請求項2に記載の放射線断層撮影装置における較正データの収集方法において、
前記検出器リングの伸びる方向を延伸方向としたとき、
前記ファントムが前記検出器リングに対して移動する方向は、前記延伸方向に沿っており、
前記延伸方向における前記ファントムの長さは、前記延伸方向における前記検出器リングの長さよりも短いことを特徴とする放射線断層撮影装置における較正データの収集方法。 - 請求項1ないし請求項3のいずれかに記載の放射線断層撮影装置における較正データの収集方法において、
前記ファントムは、前記検出器リングに対して往復移動することを特徴とする放射線断層撮影装置における較正データの収集方法。 - 請求項1ないし請求項4のいずれかに記載の放射線断層撮影装置における較正データの収集方法において、
前記ファントムの速度は、移動の開始時に最も速く、前記ファントムが移動するにつれ、次第に遅くなることを特徴とする放射線断層撮影装置における較正データの収集方法。 - 請求項1ないし請求項5のいずれかに記載の放射線断層撮影装置における較正データの収集方法において、
前記同時計数手段は、前記延伸方向における2つの放射線検出素子間の距離が所定の長さ以下となっているときのみ同時イベント数を計数し、
前記ファントムの前記延伸方向における長さは、前記所定の長さよりも長いことを特徴とする放射線断層撮影装置における較正データの収集方法。
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PCT/JP2009/000251 WO2010084528A1 (ja) | 2009-01-23 | 2009-01-23 | 放射線断層撮影装置における較正データの収集方法 |
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WO2014180734A2 (en) | 2013-05-08 | 2014-11-13 | Koninklijke Philips N.V. | Apparatus and method for the evaluation of gamma radiation events |
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