JP2015001386A - Nuclear medicine diagnosis system and image processing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nuclear medicine diagnosis system and an image processing apparatus capable of reducing a data amount of PET projection data to be stored for generating a PET image.SOLUTION: The nuclear medicine diagnosis system includes: first acquisition means; second acquisition means; difference generating means; and storage means. The first acquisition means acquires first projection data relating to a first radiation detected by a first detector. The second acquisition means acquires second projection data relating to a second radiation detected by a second detector. The difference generating means generates difference data showing a difference between the first projection data acquired by the first acquisition means and the second projection data acquired by the second acquisition means. The storage means stores one of projection data of the first and second projection data, and the generated difference data.

Description

  Embodiments described herein relate generally to a nuclear medicine diagnostic apparatus and an image processing apparatus.

  Conventionally, a PET (Positron Emission Tomography) apparatus is known as a nuclear medicine diagnostic apparatus for imaging functional information in a living tissue of a subject.

  In recent years, an image diagnostic apparatus (hereinafter referred to as a PET-CT apparatus) in which a PET apparatus and an X-ray computed tomography apparatus (X-ray CT apparatus) for imaging morphological information in a living tissue of a subject are integrated. Notation) has been put to practical use.

  In this PET-CT apparatus, a pair of radiation (gamma rays) emitted in opposite directions due to the occurrence of positron pair annihilation (hereinafter referred to as an event) in a subject to which a drug (radioisotope) is administered. Are simultaneously measured by two gamma ray detectors out of a plurality of gamma ray detectors arranged so as to surround the subject. In the PET-CT apparatus, a nuclear medicine image (PET image) is generated by specifying a position where an event has occurred based on PET projection data relating to a pair of gamma rays measured simultaneously.

  In the PET-CT apparatus, X-rays radiated from the X-ray tube to the subject (X-rays transmitted through the subject) are detected by the X-ray detector, and the output (CT projection data) of the X-ray detector is detected. ) To generate an internal image (CT image) of the subject.

  In the PET-CT apparatus, the cross section of the PET image and the cross section of the CT image are set so as to physically match.

  That is, according to the PET-CT apparatus, as described above, the PET image and the CT image are generated, and the PET image (functional information obtained from the PET image) and the CT image (morphological information obtained from the image) are merged. (Fusion image) can be generated.

  By the way, for example, an event of about 10 G count occurs in a subject in one diagnosis (imaging) by a PET-CT apparatus (or PET apparatus). In the apparatus, the subject is used to generate a PET image. It is necessary to store PET projection data for each event occurring in the memory, that is, a large amount of data.

  The PET projection data includes the amount of gamma ray energy detected by the gamma detector. However, the energy resolution of the gamma ray tends to further improve in the future, and the amount of data related to the amount of energy in the PET projection data is large. Become.

  Accordingly, the problem to be solved by the present invention is to provide a nuclear medicine diagnostic apparatus and an image processing apparatus capable of reducing the data amount of PET projection data stored for generating a PET image.

  According to the embodiment, the first detector that detects the first radiation emitted from the radioisotope administered into the subject, and the first detector that is emitted from the radioisotope administered into the subject. There is provided a nuclear medicine diagnostic apparatus including a second detector that detects second radiation paired with one radiation.

  The nuclear medicine diagnosis apparatus according to the embodiment includes a first acquisition unit, a second acquisition unit, a difference generation unit, and a storage unit.

  The first acquisition means acquires first projection data relating to first radiation detected by the first detector.

  The second acquisition means acquires second projection data relating to second radiation detected by the second detector.

  The difference generation unit generates difference data indicating a difference between the first projection data acquired by the first acquisition unit and the second projection data acquired by the second acquisition unit.

  The storage means stores one projection data of the first and second projection data and the generated difference data.

The figure which shows schematically the structure of the PET-CT apparatus which concerns on embodiment. The block diagram which mainly shows a function structure of the image processing apparatus 40 with which the PET-CT apparatus 1 shown in FIG. 1 is provided. The flowchart which shows the process sequence of the image processing apparatus 40 with which the PET-CT apparatus 1 which concerns on this embodiment is provided. The figure for demonstrating one pair of gamma rays counted simultaneously. The figure for demonstrating the difference data memorize | stored in the memory | storage part.

  Hereinafter, embodiments will be described with reference to the drawings.

  Hereinafter, as a nuclear medicine diagnosis apparatus according to the present embodiment, an image diagnosis apparatus (hereinafter referred to as a PET-CT apparatus) in which a PET (Positron Emission Tomography) apparatus and an X-ray CT apparatus are integrated will be described as an example. To do.

  FIG. 1 is a diagram schematically showing a configuration of a PET-CT apparatus according to the present embodiment. As shown in FIG. 1, a PET-CT apparatus 1 includes an X-ray CT apparatus gantry (hereinafter referred to as a CT gantry) 10, a PET apparatus gantry (hereinafter referred to as a PET gantry) 20, a bed apparatus 30 and image processing. A device (console) 40 is provided.

  The CT gantry 10 and the PET gantry 20 are adjacent to each other while maintaining a predetermined positional relationship, and are detachably connected. A hollow portion 11 is formed in the CT mount 10. Further, a hollow portion 21 is formed in the PET mount 20. In the PET-CT apparatus 1, the CT gantry 10 and the PET gantry 20 are arranged so that the center line of the hollow portion 11 and the center line of the hollow portion 21 substantially coincide with each other.

  The CT gantry 10 performs CT imaging of the subject P in the imaging region with X-rays. Although not shown in FIG. 1, the CT mount 10 includes an X-ray tube, an X-ray detector, and a CT data acquisition unit. The X-ray tube, the X-ray detector, and the CT data collection unit are rotatably held around the hollow portion 11 by a rotating ring (not shown). The CT mount 10 is held so as to be tiltable around a horizontal axis passing through the center of the hollow portion 11.

  The X-ray tube and the X-ray detector are arranged so as to face each other with the hollow portion 11 interposed therebetween. The X-ray tube generates X-rays in response to application of a high voltage from a high voltage generator. The X-ray detector detects X-rays that have passed through the subject P. The X-ray detector generates an electrical signal corresponding to the detected X-ray intensity.

  The CT data collection unit collects the electrical signal generated by the X-ray detector and converts the electrical signal into digital data.

  The electrical signals (digital data) collected in the CT gantry 10 in this way are supplied to the image processing device 40.

  The PET gantry 20 performs PET imaging of the subject P with gamma rays (radiation) emitted in the subject P within the imaging region. At this time, a drug is administered to the subject P in advance. This drug is labeled with a radioisotope that emits positrons (positrons). A positron emitted from a drug (a radioisotope) annihilates with an electron and generates a pair of gamma rays (hereinafter referred to as first and second gamma rays). The pair of gamma rays includes a first gamma ray and a second gamma ray emitted in a direction opposite to the first gamma ray.

  Although not shown in FIG. 1, the PET gantry 20 includes a plurality of gamma ray detectors and a PET data collection unit. As described above, the PET gantry 20 has the hollow portion 21 having a substantially cylindrical shape into which the subject P on the top plate 31 is fed, and a plurality of gamma ray detectors are circular on the outer periphery of the hollow portion 21. It is arranged in a circle. A pair of gamma rays (first and second gamma rays) emitted from within the subject P is detected by a pair of gamma ray detectors (first and second detectors) out of a plurality of gamma ray detectors ( Simultaneous counting). Specifically, the first gamma ray of the pair of gamma rays emitted from the subject P is detected by the first gamma ray detector, and the second gamma ray is opposed to the first gamma ray detector. It is detected by a second gamma ray detector arranged at the position. Thus, when a gamma ray is detected by each gamma ray detector, an electrical signal corresponding to the intensity of the gamma ray is generated.

  The PET data collection unit collects the electrical signal generated by the gamma ray detector and converts the electrical signal into digital data.

  The electrical signals (digital data) collected in the PET gantry 20 in this way are supplied to the image processing apparatus 40.

  The couch device 30 supports the top plate 31 on which the subject P is placed so as to be movable in the longitudinal direction, the lateral direction, and the vertical direction, for example. As described above, the CT gantry 10 and the PET gantry 20 are arranged so that the central axis of the hollow portion 11 and the central axis of the hollow portion 21 are aligned in the same straight line. The subject P can be continuously passed through the hollow portion 11 and the hollow portion 21 by moving in one direction.

  The image processing apparatus 40 performs various data processing on the electrical signals (digital data) collected in the CT gantry 10 and the PET gantry 20.

  FIG. 2 is a block diagram mainly showing a functional configuration of the image processing apparatus 40 provided in the PET-CT apparatus 1 shown in FIG. As illustrated in FIG. 2, the image processing apparatus 40 includes a control unit 41, a storage unit (storage unit) 42, a CT image generation unit 43, a PET image generation unit 44, an operation unit 45, and a display unit 46.

  The control unit 41 functions as the center of the PET-CT apparatus 1 and controls each part in the PET-CT apparatus 1.

  In addition, the control unit 41 pre-processes the electrical signals collected in the CT mount 10 as described above, and generates projection data related to CT imaging (hereinafter referred to as CT projection data). This preprocessing includes, for example, logarithmic conversion, sensitivity correction, beam hardening correction, and the like. The CT projection data generated by the control unit 41 is stored in the storage unit 42.

  Further, the control unit 41 performs signal processing on the electrical signals collected in the PET gantry 20 as described above, and generates projection data related to PET imaging (hereinafter referred to as PET projection data). This signal processing includes position calculation processing, energy calculation processing, coincidence counting processing, preprocessing, and the like. The preprocessing includes sensitivity correction, random correction, scattered radiation correction, and the like.

  The PET projection data generated by the control unit 41 includes projection data (hereinafter referred to as first projection data) relating to the first gamma rays emitted from the medicine (radioisotope) administered into the subject P. ) And second gamma ray projection data (hereinafter referred to as second projection data).

  The control unit 41 generates difference data indicating a difference between the first projection data and the second projection data included in the generated PET projection data.

  The control unit 41 stores, in the storage unit 42, one of the first and second projection data included in the acquired PET projection data and the generated difference data.

  In addition to the above-described data, the storage unit 42 stores a control program for the PET-CT apparatus according to the present embodiment. This control program is executed by the control unit 41.

  The CT image generation unit 43 generates CT image data related to a predetermined reconstructed cross section based on the CT projection data stored in the storage unit 42. The pixel value assigned to each pixel constituting the CT image has a CT value corresponding to the X-ray attenuation coefficient (absorption coefficient) related to the substance on the X-ray transmission path.

  The PET image generation unit 44 reconstructs the CT image at substantially the same position as the reconstructed cross section based on one of the first and second projection data stored in the storage unit 42 and the difference data. Data of a nuclear medicine image (hereinafter referred to as a PET image) relating to a cross section is generated. The pixel value assigned to each pixel constituting the PET image has a count value corresponding to the concentration of the radioisotope.

  The operation unit 45 receives an instruction or information input from an operator via an input device. As an input device, a keyboard, a mouse, various switches, a touch panel, and the like can be used.

  The display unit 46 includes a monitor such as a liquid crystal or a CRT. The display unit 46 displays the CT image generated by the CT image generation unit 43 and the PET image generated by the PET image generation unit 44 so as to overlap each other.

  Next, a processing procedure of the image processing apparatus 40 provided in the PET-CT apparatus 1 according to the present embodiment will be described with reference to the flowchart of FIG.

  First, the control unit 41 included in the image processing apparatus 40 performs preprocessing and the like on the electrical signals collected in the CT gantry 10 to acquire (generate) CT projection data (step S1). The CT projection data is acquired for each view based on the rotation angle (phase) between the X-ray tube and the X-ray detector.

  The CT projection data acquired by the control unit 41 is stored in the storage unit 42 (step S2).

  Next, the control unit 41 performs signal processing on the electrical signals collected in the PET gantry 20, and acquires (generates) PET projection data (step S3). Note that the PET projection data is acquired for each annihilation of positrons and electrons generated in the subject P as described above.

  The PET projection data acquired by the control unit 41 includes first and second gamma rays emitted in opposite directions when pair annihilation occurs in the subject P (that is, simultaneously by a pair of gamma ray detectors). First and second projection data for each of the counted pair of gamma rays) is included.

  Here, a pair of gamma rays that are simultaneously counted will be described with reference to FIG. As shown in FIG. 4, when the pair annihilation 100 occurs in the subject P, a pair of gamma rays composed of gamma rays 101 (first gamma rays) and gamma rays 102 (second gamma rays) are generated from the subject P. Released. As described above, the pair of gamma rays (gamma rays 101 and 102) emitted by the occurrence of the pair annihilation 100 is a plurality of gamma ray detectors arranged on the outer periphery of the hollow portion 21 of the PET mount 20 as described above. Are simultaneously counted (that is, detected simultaneously).

  Here, for example, a case is assumed where gamma rays are simultaneously counted by a gamma ray detector 201 (first gamma ray detector) and a gamma ray detector 202 (second gamma ray detector) among a plurality of gamma ray detectors. In addition, when the time (difference) at which the gamma rays are detected in the gamma ray detectors 201 and 202 is within a predetermined coincidence window (for example, 4.5 to 12 nanoseconds), the gamma ray detectors. Assume that gamma rays are simultaneously counted in 201 and 202.

  In this case, the gamma rays detected by each of the gamma ray detectors 201 and 202 are assumed to be a pair of gamma rays emitted by the generation of the pair annihilation 100 as described above. Here, PET projection data including first projection data relating to gamma rays 101) and second projection data relating to gamma rays detected by the gamma ray detector 202 (here, gamma rays 102) is generated.

  The first projection data included in the PET projection data includes position data indicating the position of the gamma ray detector 201 (first gamma ray detector) that detected the gamma ray 101 (first gamma ray) and the gamma ray 101. Energy data indicating the amount of energy is included. The position data included in the first projection data also includes time data indicating the time when the gamma ray 101 is detected by the gamma ray detector 201, for example.

  Similarly, the second projection data included in the PET projection data includes position data indicating the position of the gamma ray detector 202 (second gamma ray detector) that detected the gamma ray 102 (second gamma ray) and the gamma ray 102. Energy data indicating the amount of energy is included. The position data included in the second projection data also includes time data indicating the time when the gamma ray 102 is detected by the gamma ray detector 202, for example.

  Returning to FIG. 3 again, the control unit 41 determines one of the first and second projection data included in the acquired PET projection data as reference data (step S4). Here, it is assumed that the first projection data is determined as the reference data.

  Next, the control unit 41 generates difference data indicating a difference between the first projection data and the second projection data included in the acquired PET projection data (step S5). The difference data generated here is data capable of calculating the second projection data from the first projection data determined as the reference data, and has a data amount as compared with the second projection data. Assume that there is little data.

  The control unit 41 stores the projection data determined as the reference data and the generated difference data in the storage unit 42 (step S6).

  In the process of step S4 described above, for example, reference data is determined based on the amount of energy indicated by the energy data included in each of the first and second projection data. Specifically, the energy amount (hereinafter referred to as the first energy amount) indicated by the energy data included in the first projection data and the energy amount (hereinafter referred to as the energy data included in the second projection data). Projection data having a large amount of energy is determined as reference data. In this case, the difference between the energy data included in each of the first and second projection data is “first energy amount−second energy amount”, so that the difference becomes a negative value. And the amount of data in the difference can be further reduced.

  Here, projection data having a large amount of energy is determined as reference data. For example, projection data related to gamma rays detected earlier in the above-described coincidence window among the first and second projection data is used as a reference. The configuration may be data. According to this, it becomes possible to improve the processing speed of the difference data generation processing.

  That is, in the present embodiment, it is only necessary to determine the reference data from the viewpoint of reducing the data amount of the difference data or improving the processing speed of the difference data generation process. This reference data is not described in the present embodiment. It may be determined by the method.

  Further, in the process of step S5 described above, as shown in FIG. 5, for example, the difference between the position data included in each of the first and second projection data and each of the first and second projection data are included. The difference data including the difference of the energy data to be generated is generated. In the process of step S6, the first projection data determined as the reference data and the difference data are concatenated (that is, as one data) and stored in the storage unit 42.

  As described above, when the process of step S6 is executed, the CT image generation unit 43 acquires the CT projection data stored in the storage unit. The CT image generation unit 43 generates a CT image (data thereof) based on the acquired CT projection data (step S7).

  Next, the PET image generation unit 44 acquires reference data (here, first projection data) and difference data stored in the storage unit 42.

  The PET image generation unit 44 calculates second projection data based on the first projection data and the difference data included in the acquired PET projection data.

  The PET image generation unit 44 generates a PET image based on the acquired first projection data and the calculated second projection data (that is, PET projection data) (step S8).

  Here, it is assumed that the PET projection data used by the PET image generation unit 44 has been subjected to attenuation correction based on the above-described CT image. The attenuation-corrected PET projection data relates to the reconstructed cross section calculated to be a reconstructed cross section that is substantially the same as the reconstructed cross section of the CT image generated by the CT image generating unit 43. In this case, a gamma ray attenuation correction map is generated based on the CT image. The attenuation correction map is generated by calculating a gamma ray attenuation coefficient by applying a predetermined conversion formula to the CT value. The attenuation correction is performed by multiplying this attenuation correction map with the PET projection data.

  When the CT image and the PET image are generated as described above, the display unit 46 displays an image (fusion image) obtained by superimposing the CT image and the PET image (step S9).

  As described above, in the present embodiment, the first projection data related to the first gamma rays emitted from the radioisotope administered into the subject P is acquired, and the second projection data is paired with the first gamma rays. Second projection data relating to the gamma rays of the first is acquired, difference data indicating a difference between the first projection data and the second projection data is generated, and one of the first and second projection data is projected. Compared with the case where the first and second projection data (including the PET projection data) are stored by the configuration in which the data and the generated difference data are stored in the storage unit 42, a PET image is generated. Therefore, it is possible to reduce the data amount of the PET projection data stored for the purpose. Thereby, in this embodiment, it becomes possible to store more PET projection data.

  In the present embodiment, the processing shown in FIG. 3 described above has been described as being executed in the image processing apparatus 40. However, for example, even if the processing in steps S3 to S5 shown in FIG. I do not care. In this case, the reference data and the difference data generated in the PET gantry 20 may be stored in the storage unit 42 included in the image processing apparatus 40.

  Although the present embodiment has mainly described the PET-CT apparatus, the present embodiment can be applied to any nuclear medicine diagnostic apparatus that needs to store PET projection data related to a pair of gamma rays as described above. It is.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... PET-CT apparatus, 10 ... CT mount, 20 ... PET mount, 30 ... Bed apparatus, 40 ... Image processing apparatus, 41 ... Control part, 42 ... Memory | storage part, 43 ... CT image generation part, 44 ... PET image generation Part, 45 ... operation part, 46 ... display part.

Claims (7)

A first detector for detecting a first radiation emitted from a radioisotope administered into the subject; and a pair with the first radiation emitted from a radioisotope administered into the subject. A nuclear medicine diagnostic apparatus comprising: a second detector for detecting second radiation comprising:
First acquisition means for acquiring first projection data relating to first radiation detected by the first detector;
Second acquisition means for acquiring second projection data relating to second radiation detected by the second detector;
Difference generation means for generating difference data indicating a difference between the first projection data acquired by the first acquisition means and the second projection data acquired by the second acquisition means;
A nuclear medicine diagnosis apparatus comprising: storage means for storing one projection data of the first and second projection data and the generated difference data.   The other projection data of the first and second projection data is calculated from one of the first and second projection data stored in the storage means and the difference data, and the first projection data is calculated. 2. The nuclear medicine diagnosis apparatus according to claim 1, further comprising image generation means for generating a nuclear medicine image based on the second projection data. A gantry device including the first and second detectors, and an image processing device that generates a nuclear medicine image based on the first and second projection data;
The nuclear medicine diagnosis apparatus according to claim 1, wherein the image processing apparatus includes the first acquisition unit, the second acquisition unit, the difference generation unit, and the storage unit. A gantry device including the first detector and the second detector; and an image processing device that generates a nuclear medicine image based on the first and second projection data;
The gantry device includes the first acquisition unit, the second acquisition unit, and the difference generation unit,
The nuclear medicine diagnosis apparatus according to claim 1, wherein the image processing apparatus includes the storage unit. Further comprising a determining means,
The first projection data includes energy data indicating an energy amount of the first radiation detected by the first detector;
The second projection data includes energy data indicating an amount of energy of the second radiation detected by the second detector,
The determining means is configured to determine the first and second projections based on an energy amount indicated by energy data included in the first projection data and an energy amount indicated by energy data included in the second projection data. One projection data of the data is determined as reference data,
The nuclear medicine diagnosis apparatus according to claim 1, wherein the storage unit stores projection data determined as the reference data and the generated difference data. Of the first and second projection data, based on the time when the first radiation is detected by the first detector and the time when the second radiation is detected by the second detector. One of the projection data is determined as reference data,
The nuclear medicine diagnosis apparatus according to claim 1, wherein the storage unit stores projection data determined as the reference data and the generated difference data. First acquisition means for acquiring first projection data relating to first radiation emitted from a radioisotope administered into a subject;
Second acquisition means for acquiring second projection data relating to the second radiation paired with the first radiation emitted from the radioisotope administered into the subject;
Difference generation means for generating difference data indicating a difference between the first projection data acquired by the first acquisition means and the second projection data acquired by the second acquisition means;
An image processing apparatus comprising: storage means for storing one projection data of the first and second projection data and the generated difference data.

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