JP2008170183A - Tomography device, photographing system equipped with the same, and photographing data acquisition method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tomography device capable of determining an index independent of the physical quantity related to the size of an analyte in evaluating an image, a photographing system equipped with the same, and a photographing data acquisition method. <P>SOLUTION: A cross section calculation section 16c calculates the cross section of the analyte as a physical quantity related to the size of the analyte, and an NEC (Noise Equivalent Count) calculation section 16b calculates the noise equivalent count NEC as a physical quantity for evaluating the image. Based on the cross section of the analyte calculated by the section 16c and the noise equivalent count NEC calculated by the section 16b, C-NEC calculation section 16d calculates the noise equivalent count C-NEC per unit area as the physical quantity for evaluating the image per size of the analyte. Thus, by calculating the noise equivalent count C-NEC per unit area, the index independent of the cross section of the analyte can be determined in evaluating the image. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a tomographic apparatus that obtains a tomographic image by simultaneously counting radiation generated from a subject to which a radiopharmaceutical is administered, an imaging system including the same, and an imaging data acquisition method.

  The PET (Positron Emission Tomography) device detects a plurality of γ-rays generated by the annihilation of positrons, that is, positrons, and only detects γ-rays simultaneously with a plurality of detectors. Configured to reconfigure.

  In this PET apparatus, after a radiopharmaceutical is administered to a subject, the process of drug accumulation in the target tissue is measured over time, whereby quantitative measurement of various biological functions is possible. Therefore, the tomographic image obtained by the PET apparatus has functional information.

  By the way, in the technique of simultaneously detecting γ rays, that is, simultaneously counting γ rays, in addition to 2D-PET that detects γ rays two-dimensionally, in recent years, 3D-PET that detects γ rays three-dimensionally is used. It is used. In such 3D-PET, by arranging each detector in a large solid angle in the vicinity of the subject, the detection efficiency of γ rays can be improved, and the system sensitivity can be dramatically improved.

In order to simultaneously count γ-rays, each γ-ray is input to the coincidence counting circuit, and it is determined whether or not the time difference between the input γ-rays is within a predetermined time window. In an actual coincidence circuit, γ rays detected within a very short time window of about 4 ns to 20 ns (ns = 10 ⁻⁹ s) are generally regarded as “simultaneous”. Therefore, there is a possibility that one of γ rays generated at two different points is counted simultaneously. This is called “random coincidence”. FIG. 12A shows a schematic diagram schematically showing the state of the coincidence coincidence. On the other hand, when one or both of the pair of γ-rays are simultaneously counted after causing Compton scattering in the subject, this is called “scatter coincidence”. FIG. 12B is a schematic diagram schematically showing the state of the scattering coincidence counting. The hatched portion in the detector in FIG. 12 indicates the coincidence detector. In addition, when both of a pair of γ rays are counted simultaneously, this is called “true coincidence” (see, for example, Patent Documents 1 and 2).

  In order to improve the image quality of PET, it is necessary to increase the statistical accuracy by increasing the true coincidence (T), and further to suppress the noise amplitude in various corrections. As a technique for improving the statistical accuracy, it is conceivable to increase the dose of the radiopharmaceutical or to increase the collection time for simultaneous counting and collection. However, even if the true coincidence count (T) is doubled by doubling the dose, the random coincidence count (R) is quadrupled, and noise in the coincident coincidence correction is amplified. End up. Also included is a scattering coincidence (S) that varies depending on the size of the subject and the distribution of radioactivity. Therefore, a noise equivalent count (NEC) is used as an index that can easily evaluate the PET image quality from these counts T, S, and R (see Non-Patent Document 1, for example).

  When an accidental coincidence count is measured and corrected using a circuit (delayed coincidence count circuit) in which a delay circuit is combined with a coincidence circuit, the noise equivalent count NEC is expressed by the following equation (1). When the coincidence coincidence count is estimated and corrected from the single count rate, the noise equivalent count NEC is expressed by the following equation (2).

NEC = T ² / (T + S + 2 × f × R) (1)
NEC = T ² / (T + S + f × R) (2)
However, f in the above equations (1) and (2) is the ratio of the subject to the gantry in which the γ-ray detector is embedded. Specifically, it is the ratio of the subject to the opening diameter of the gantry (that is, the opening diameter of the γ-ray detector).
JP 2000-28727 A (page 3, FIG. 5) Japanese Patent Laid-Open No. 7-113873 (pages 1-7, 9-11, FIGS. 2, 5, 7, 8, 13) Junichi Matsumoto, 5 others “Evaluation of noise equivalent count and image quality of reconstructed images in 2D and 3D PET acquisition” Journal of Japanese Society of Radiological Technology, August 2006, Vol. 62, No. 8, p. 1111-1118

  However, the noise equivalent count NEC has a problem that the size of the subject is not taken into consideration. For example, when comparing PET images of large and small subjects having the same noise equivalent count, a situation occurs in which the small subject has higher image quality (for example, the standard deviation of the uniform region is smaller). This is because the noise equivalent count NEC is distributed within the reconstruction area, and as the reconstruction area is wider (that is, the subject size is larger), the noise equivalent count per unit area is smaller and the reconstruction area is smaller ( This is due to the fact that the noise equivalent count per unit area increases as the region (subject size is smaller). That is, there is a problem that the technique such as Non-Patent Document 1 that predicts the image quality from the noise equivalent count NEC of the prior art does not hold between different object sizes. As described above, the physical quantity for evaluating the image typified by the noise equivalent count is not an index for evaluating the image quality if the physical quantities related to the size of the subject typified by the area are different from each other.

  Further, since the noise equivalent count is calculated after the shooting from the total count information, it is only an index for examining the next shooting condition based on the calculated noise equivalent count. For this reason, it is necessary to determine how much image quality is ensured during shooting.

  The present invention has been made in view of such circumstances, and a tomography apparatus capable of obtaining an index independent of a physical quantity related to the size of a subject when an image is evaluated, and an imaging provided with the tomography apparatus It is an object of the present invention to provide a system and a photographing data acquisition method.

In order to achieve such an object, the present invention has the following configuration.
That is, the invention described in claim 1 is a tomographic apparatus that obtains a tomographic image by simultaneously counting radiation generated from a subject to which a radiopharmaceutical is administered, and calculates a physical quantity related to the size of the subject. Based on the physical quantity calculated by the first physical quantity calculating means, the second physical quantity calculating means for calculating the physical quantity for evaluating the image, the physical quantity calculated by the first physical quantity calculating means, and the physical quantity calculated by the second physical quantity calculating means And a third physical quantity calculating means for calculating a physical quantity for evaluating an image per size.

  [Operation / Effect] According to the invention described in claim 1, the tomography apparatus includes the first physical quantity computing means, the second physical quantity computing means, and the third physical quantity computing means. The first physical quantity calculator calculates a physical quantity related to the size of the subject, and the second physical quantity calculator calculates a physical quantity for evaluating the image. Based on the physical quantity calculated by the first physical quantity calculating means and the physical quantity calculated by the second physical quantity calculating means, the third physical quantity calculating means calculates a physical quantity for evaluating an image per size of the subject. In this way, by calculating the physical quantity for evaluating the image per size of the subject, an index independent of the physical quantity related to the size of the subject can be obtained when evaluating the image.

  According to an eighth aspect of the present invention, there is provided a tomographic apparatus that obtains a tomographic image by simultaneously counting radiation generated from a subject to which a radiopharmaceutical has been administered, and a predetermined image obtained by performing predetermined imaging on the subject. A first physical quantity computing means for computing a physical quantity related to the size of a subject, a second physical quantity computing means for computing a physical quantity for evaluating an image, And a third physical quantity computing means for computing a physical quantity for evaluating an image per size of the subject based on the physical quantity computed by one physical quantity computing means and the physical quantity computed by the second physical quantity computing means. It is a feature.

  [Operation / Effect] According to the invention described in claim 8, the imaging system includes a tomography apparatus and an imaging apparatus, and the tomography apparatus is an invention related to the tomography apparatus (invention according to claim 1). ), First physical quantity computing means, second physical quantity computing means, and third physical quantity computing means are provided. The first physical quantity calculator calculates a physical quantity related to the size of the subject, and the second physical quantity calculator calculates a physical quantity for evaluating the image. Based on the physical quantity calculated by the first physical quantity calculating means and the physical quantity calculated by the second physical quantity calculating means, the third physical quantity calculating means calculates a physical quantity for evaluating an image per size of the subject. In this way, by calculating the physical quantity for evaluating the image per size of the subject, an index independent of the physical quantity related to the size of the subject can be obtained when evaluating the image.

  An example of these tomographic apparatuses described above and an imaging system including the tomographic apparatus includes an external radiation source that irradiates the subject with radiation of the same type as that of the radiopharmaceutical from the outside. The first physical quantity calculating means calculates a physical quantity related to the size of the subject based on the radiation that has been irradiated and transmitted through the subject (inventions according to claims 2 and 9). Data (for example, transmission data) acquired based on radiation irradiated from an external radiation source and transmitted through the subject has morphological information on the subject. Therefore, based on the radiation, the first physical quantity calculator can easily calculate the physical quantity related to the size of the subject.

  Another example of these tomographic apparatuses and an imaging system including the tomographic apparatus is an external apparatus viewed from the tomographic apparatus (external apparatus in the invention described in claim 1, and imaging apparatus in the invention described in claim 8). The first physical quantity calculation means calculates a physical quantity related to the size of the subject based on the form information of the subject acquired in (Inventions according to claims 3 and 10). Since the data acquired by the external device is the morphological information of the subject, the first physical quantity calculation means can easily calculate the physical quantity related to the size of the subject based on the morphological information.

  The data on which the first physical quantity calculation means calculates the physical quantity related to the size of the subject is not limited to the form information of the subject as in the inventions according to claims 2, 3, 9, and 10. Even if it is function information (for example, emission data) of the subject, the contour of the subject may be known by the distribution of the subject's radioactivity spread by the radiopharmaceutical, so the physical quantity related to the size of the subject is calculated. Is possible.

  Further, the above-mentioned external device (external device in the invention described in claim 1, and imaging device in the invention described in claim 8) viewed from the tomography apparatus is an X-ray CT apparatus. As in the described invention, when the first physical quantity calculating means calculates the physical quantity related to the size of the subject based on the form information of the subject, the calculation is performed as follows (claims 4 and 11). Invention). That is, when the X-ray CT apparatus acquires a CT image, the CT image becomes an image having morphological information. Based on the CT image, the first physical quantity calculation means calculates a physical quantity related to the size of the subject. Calculate.

  An external device viewed from a tomographic apparatus (an external device in the invention described in claim 1 and an imaging device in the invention described in claim 8) is an X-ray CT apparatus as in the invention described in claims 4 and 11. The shape information is not limited to the CT image. The present invention can be applied to an apparatus that obtains a predetermined image by performing predetermined imaging on a subject, and the data acquired by the apparatus has morphological information. For example, an image obtained by a nuclear magnetic resonance apparatus (MRI: Magnetic Resonance Imaging) has morphological information. Based on the morphological information obtained by MRI, the first physical quantity calculation means calculates a physical quantity related to the size of the subject. You may calculate.

  In these tomographic apparatuses described above and the imaging system including the tomographic apparatus, an example of the physical quantity relating to the size of the subject calculated by the first physical quantity calculating means is a cross-sectional area of the subject. Invention described in 1.). The cross-sectional area is an effective index for the size of the subject.

  The physical quantity related to the size of the subject calculated by the first physical quantity calculating means is not limited to the cross-sectional area of the subject as in the inventions according to claims 5 and 12. It may be the absorption rate of the subject. The absorptivity of the subject counts the radiation emitted from the external radiation source in the absence of the subject, and counts the radiation emitted from the external radiation source in the presence of the subject and transmitted through the subject, It is obtained by taking their counting ratio. The absorption rate of the subject is also an effective index regarding the size of the subject.

  Still another example of these tomographic apparatuses described above and an imaging system including the same includes a counting unit that counts radiation generated from a subject to which a radiopharmaceutical is administered, and is calculated by a second physical quantity calculating unit. The physical quantity for evaluating the image to be evaluated is a noise equivalent count based on the radiation counted by the counting means, and the third physical quantity calculating means is to calculate a noise equivalent count per size of the subject. 6 and 13). As described in the paragraph “Background Art”, the noise equivalent count is useful as an index for easily evaluating the image quality. In order to consider a physical quantity related to the size of the subject with respect to this noise equivalent count, noise that does not depend on the physical quantity related to the size of the subject is obtained by calculating a noise equivalent count per size of the subject. An equivalent count can be determined.

  In these tomographic apparatuses described above, and in an imaging system including the same, an imaging condition setting for setting an imaging condition based on a physical quantity that evaluates an image per size of a subject calculated by the third physical quantity calculating means. Means may be provided (inventions according to claims 7 and 14). Since the physical quantity for evaluating the image per subject size calculated by the third physical quantity calculating means does not depend on the physical quantity relating to the size of the subject and is an index for examining the next imaging condition, It is possible to determine how much image quality is ensured when shooting.

  The invention according to claim 15 is an imaging data acquisition method for acquiring imaging data by simultaneously counting radiation generated from a subject to which a radiopharmaceutical has been administered, wherein a physical quantity relating to the size of the subject is calculated. Based on the first physical quantity computing step, the second physical quantity computing step for computing the physical quantity for evaluating the image, the physical quantity computed in the first physical quantity computing step, and the physical quantity computed in the second physical quantity computing step, And a third physical quantity calculating step for calculating a physical quantity for evaluating an image per size of the subject.

  [Operation / Effect] According to the invention described in claim 15, in the first physical quantity calculation step, the physical quantity relating to the size of the subject is calculated, and in the second physical quantity calculation step, the physical quantity for evaluating the image is calculated. . Based on the physical quantity calculated in the first physical quantity calculating step and the physical quantity calculated in the second physical quantity calculating step, in the third physical quantity calculating step, a physical quantity for evaluating the image per size of the subject is calculated. In this way, by calculating the physical quantity for evaluating the image per size of the subject, an index independent of the physical quantity related to the size of the subject can be obtained when evaluating the image.

  The imaging data acquisition method described above may further include an imaging condition setting step for setting imaging conditions based on a physical quantity for evaluating an image per size of the subject calculated in the third physical quantity calculation step. 16). The physical quantity for evaluating the image per subject size calculated in the third physical quantity calculating step is an index for examining the next imaging condition without depending on the physical quantity related to the size of the subject. It is possible to determine how much image quality is ensured when shooting.

  In addition, when a shooting condition setting step for setting shooting conditions is provided, the first physical quantity calculation is performed based on shooting data acquired by shooting after shooting under the shooting conditions set in the shooting condition setting step. Preferably, the step, the second physical quantity calculation step, and the third physical quantity calculation step are repeatedly performed (the invention according to claim 17). By repeating in this way, it is possible to determine how much image quality is ensured even during shooting related to repetition. More preferably, it is possible to determine how much image quality is ensured during photographing by performing this repetition during a series of photographing.

  According to the tomography apparatus, the imaging system including the tomography apparatus, and the imaging data acquisition method according to the present invention, the physical quantity related to the size of the subject is calculated and the physical quantity for evaluating the image is calculated. Based on the physical quantity relating to the size of the subject and the physical quantity for evaluating the image, the physical quantity for evaluating the image per size of the subject is calculated. In this way, by calculating the physical quantity for evaluating the image per size of the subject, an index independent of the physical quantity related to the size of the subject can be obtained when evaluating the image.

Embodiment 1 of the present invention will be described below with reference to the drawings.
FIG. 1 is a side view and a block diagram of a PET (Positron Emission Tomography) apparatus according to the first embodiment, and FIG. 2 is a layout diagram of γ-ray detectors in the PET apparatus.

  The PET apparatus according to the first embodiment includes a top plate 1 on which a subject M is placed as shown in FIG. The top plate 1 is configured to move up and down and translate along the body axis Z of the subject M. With this configuration, the subject M placed on the top 1 is scanned from the head to the abdomen and foot sequentially through the opening 2a of the gantry 2, which will be described later. Diagnostic data such as projection data and tomographic images are obtained.

  In addition to the top plate 1, the PET apparatus according to the first embodiment includes a gantry 2 having an opening 2a, a plurality of scintillator blocks (not shown) and a plurality of photomultipliers (not shown). The γ-ray detector 3 is provided. As shown in FIG. 2, the γ-ray detector 3 is arranged in a ring shape so as to surround the body axis Z of the subject M, and is embedded in the gantry 2. The photomultiplier is disposed outside the scintillator block. As a specific arrangement of the scintillator blocks, for example, two scintillator blocks are arranged in a direction parallel to the body axis Z of the subject M, and many scintillator blocks are arranged around the body axis Z of the subject M. Can be mentioned. The γ-ray detector 3 collects emission data to be described later.

  In addition, a point line source 4 and a γ-ray detector 5 for collecting absorption correction data (also referred to as “transmission data”) to be described later are provided. The γ-ray detector 5 for absorption correction data includes a scintillator block 5a (see FIG. 2) and a photomultiplier 5b (see FIG. 2) in the same manner as the γ-ray detector 3 for collecting emission data. Has been. The dotted line source 4 is a radiation source that irradiates a radioactive drug to be administered to the subject M, that is, a radiation of the same kind as the radioisotope (RI) (in this embodiment, γ rays), and is arranged outside the subject M. It is installed. The dotted line source 4 is embedded in the gantry 2. The dotted line source 4 rotates around the body axis Z of the subject M. The point source 4 corresponds to the external source in the present invention.

  In addition, in Example 1, including Example 2 described later, the γ-ray detector 5 has a plurality of scintillator blocks on the body axis Z of the subject M as shown in FIG. 5a and a photomultiplier 5b are provided. That is, a detector array composed of a large number of γ-ray detectors 3 arranged in a ring shape is stacked in the body axis Z direction so as to be stacked in multiple stages. In the first embodiment, there are six rows.

  In addition, the PET apparatus according to the first embodiment includes a top plate driving unit 6, a controller 7, an input unit 8, an output unit 9, a coincidence circuit 10, a projection data deriving unit 11, a PET reconstruction unit 12, and an absorption unit. A correction data deriving unit 13, an absorption correction data processing unit 14, a physical quantity calculation unit 16, an imaging condition setting unit 17, and a memory unit 18 are provided. The top plate driving unit 6 is a mechanism for driving the top plate 1 so as to perform the above-described movement, and is configured by a motor or the like not shown.

  The controller 7 comprehensively controls each part constituting the PET apparatus according to the first embodiment. The controller 7 includes a central processing unit (CPU).

  The input unit 8 sends data and commands input by the operator to the controller 7. The input unit 8 includes a pointing device represented by a mouse, a keyboard, a joystick, a trackball, a touch panel, and the like. The output unit 9 includes a display unit represented by a monitor, a printer, and the like.

  The memory unit 18 includes a storage medium represented by ROM (Read-only Memory), RAM (Random-Access Memory), and the like. In the first embodiment, the diagnostic data processed by the projection data deriving unit 11 and the PET reconstruction unit 12, the absorption correction data obtained by the absorption correction data deriving unit 13, and the absorption correction data processing unit 14 are processed. The acquired absorption correction data, the tomographic image corrected by the PET reconstruction unit 12 based on the absorption correction data, and various physical quantities described later obtained by the physical quantity calculation means 16 are written in the RAM and stored. Read from the RAM. The ROM stores in advance programs for performing various nuclear medicine diagnoses, and the controller 7 executes the programs to perform nuclear medicine diagnosis according to the programs.

  The projection data deriving unit 11, the PET reconstruction unit 12, the absorption correction data deriving unit 13, the absorption correction data processing unit 14, the physical quantity calculation unit 16, and the imaging condition setting unit 17 are represented by the memory unit 18 described above, for example. This is realized by the controller 7 executing a program stored in a ROM of a storage medium or a command input by a pointing device represented by the input unit 8 or the like.

  The γ-rays generated from the subject M to which the radiopharmaceutical is administered are converted into light by the scintillator block of the γ-ray detector 3, and the converted light is photoelectrically converted by the photomultiplier of the γ-ray detector 3. Output to electrical signal. The electric signal is sent to the coincidence counting circuit 10 as image information (pixel). The coincidence circuit 10 corresponds to the counting means in the present invention.

  Specifically, when a radiopharmaceutical is administered to the subject M, two γ rays are generated due to the disappearance of the positron of the positron emission type RI. The coincidence counting circuit 10 checks the position of the scintillator block and the incident timing of the γ-ray, and only when the γ-ray is simultaneously incident on two scintillator blocks that are opposed to each other with the subject M interposed therebetween, The information is determined as appropriate data. When γ rays are incident only on one scintillator block, the coincidence circuit 10 treats the image information sent at that time as noise instead of γ rays generated by the disappearance of the positron, and rejects it. To do.

  Actually, even if such processing is performed in the coincidence circuit 10, noise cannot be removed and noise components such as random coincidence or scattered coincidence count remain, but for these noises, the projection data deriving unit 11 together with true coincidence counts. And the physical quantity calculation unit 16 (the NEC calculation unit 16b). The projection data deriving unit 11 obtains the image information sent from the coincidence counting circuit 10 as projection data, and sends the projection data to the PET reconstruction unit 12. The PET reconstruction unit 12 reconstructs the projection data to obtain a tomographic image. The projection data obtained by the projection data deriving unit 11 and the tomographic image reconstructed by the PET reconstruction unit 12 are also referred to as “emission data”.

  The point source 4 emits γ rays toward the subject M while rotating around the body axis Z of the subject M, and the irradiated γ rays are used as a scintillator block of the γ ray detector 5 for absorption correction data. The light 5a is converted into light, and the converted light is photoelectrically converted by the photomultiplier 5b of the γ-ray detector 5 and output to an electrical signal. The electric signal is sent to the absorption correction data deriving unit 13 as image information (pixel).

  Absorption correction data is obtained based on the image information sent to the absorption correction data deriving unit 13. The absorption correction data deriving unit 13 uses the calculation representing the relationship between the absorption coefficient of γ-rays or X-rays and the energy, so that the projection data for CT, that is, the distribution data of the X-ray absorption coefficients, is converted into By converting to distribution data, the distribution data of the γ-ray absorption coefficient is obtained as absorption correction data. The derived absorption correction data is sent to the absorption correction data processing unit 14. In addition, the absorption correction data processing unit 14 performs reconstruction. The absorption correction data obtained by the absorption correction data deriving unit 13 and the absorption correction data reconstructed by the absorption correction data processing unit 14 are also referred to as “transmission data”.

  The processed absorption correction data is sent to the PET reconstruction unit 12 and the physical quantity calculation unit 16 (the ratio calculation unit 16a and the cross-sectional area calculation unit 16c). The PET reconstruction unit 12 performs tomographic image absorption correction by obtaining a tomographic image taking into account the absorption of γ rays in the body of the subject M based on the absorption correction data. The absorption-corrected tomographic image is sent to the output unit 9 via the controller 7.

  Next, a specific configuration of the physical quantity calculation unit 16 will be described with reference to FIG. FIG. 3 is a block diagram of the physical quantity calculation unit and its peripheral part. The physical quantity calculator 16 includes a ratio calculator 16a, an NEC calculator 16b, a cross-sectional area calculator 16c, and a C-NEC calculator 16d. The ratio calculation unit 16 a calculates a ratio f occupied by the subject M in the gantry 2 based on the absorption correction data reconstructed by the absorption correction data processing unit 14. The NEC calculation unit 16b calculates a noise equivalent count NEC based on γ-ray data (image information) counted by the coincidence counting circuit 10 and including coincidence or scattering coincidence count. The cross-sectional area calculator 16 c calculates the cross-sectional area of the subject M based on the absorption correction data reconstructed by the absorption correction data processor 14. The C-NEC calculation unit 16d divides the cross-sectional area of the subject M calculated by the cross-sectional area calculation unit 16c from the noise equivalent count NEC calculated by the NEC calculation unit 16b to obtain a noise equivalent count per unit area (C -NEC: Computes Cross Section NEC). The NEC computing unit 16b corresponds to the second physical quantity computing unit in the present invention, the cross-sectional area computing unit 16c corresponds to the first physical quantity computing unit in the present invention, and the C-NEC computing unit 16d is the third physical quantity computing unit in the present invention. It corresponds to physical quantity calculation means. The cross-sectional area of the subject M corresponds to a physical quantity related to the size of the subject in the present invention, the noise equivalent count NEC corresponds to a physical quantity for evaluating an image in the present invention, and a noise equivalent count C per unit area. -NEC corresponds to a physical quantity for evaluating an image per size of the subject in the present invention.

  Next, a specific process of acquiring a series of shooting data will be described with reference to FIGS. FIG. 4 is a flowchart of a series of imaging data acquisition, FIG. 5 is a schematic diagram of a sinogram of transmission data, and FIG. 6 is a block of a circuit (delayed coincidence circuit) in which a delay circuit is combined with a coincidence circuit. FIG. 7 is a schematic diagram of a cross-sectional area, FIG. 8 is a schematic diagram of a cross-sectional area when soft tissue is taken into account, and FIG. 9 is a graph showing the imaging time and unit area during static collection. It is explanatory drawing which represented typically the relationship with a noise equivalent count.

  In the flow chart of FIG. 4, (1) the γ-ray detector 5 detects γ-rays that have been scanned from the foot to the abdomen and the head, and are irradiated from the point source 4 and transmitted through the subject M. In addition to collecting transmission data, the γ-ray detector 3 detects γ-rays generated from the subject M to which the radiopharmaceutical is administered, and collects emission data (collection of this (1) is “continuous whole body collection”) (2) or (2) after the γ-ray detector 5 detects γ-rays irradiated from the point source 4 and transmitted through the subject M at a predetermined site and collects transmission data, In contrast, the γ-ray detector 3 detects γ-rays generated from the subject M to which the radiopharmaceutical has been administered, and collects emission data (collection of (2) is called “static collection”). explain. Further, as shown in FIGS. 1 and 2, the emission γ-ray detector 3 is disposed on the foot rather than the transmission γ-ray detector 5 (for absorption correction data), so that In whole body collection, transmission data is collected first for the same site, and then emission data is collected.

(Step S1) Transmission Data Collection The transmission γ-ray detector 5 collects transmission data. Specifically, the γ rays irradiated from the point source 4 and transmitted through the subject M are converted into light by the scintillator block 5a, and the converted light is photoelectrically converted into an electric signal by the photomultiplier 5b. By outputting, the γ-ray detector 5 detects γ-rays. The electric signal is sent to the absorption correction data deriving unit 13 as image information (pixel).

(Step S2) Emission Data Collection The emission γ-ray detector 3 collects emission data for the same part where transmission data collection was performed in step S1. Specifically, the γ-rays generated from the subject M to which the radiopharmaceutical is administered are converted into light by the scintillator block, and the converted light is photoelectrically converted by the photomultiplier and output to an electrical signal. The γ-ray detector 3 detects γ-rays. The electrical signal is sent to the coincidence circuit 10 as image information (pixels), and γ rays are incident simultaneously on two scintillator blocks located opposite to each other across the subject M, including accidental coincidence and scattering coincidence. The coincidence circuit 10 determines that the sent image information is appropriate data only when the image information is sent. These pieces of image information are sent to the projection data deriving unit 11. The total number of image information per second is derived as count rate information (the number of image information per unit time) and is sent to the NEC calculation unit 16b of the physical quantity calculation unit 16.

(Step S12) Transmission sinogram calculation In parallel with step S2, the absorption correction data deriving unit 13 obtains absorption correction data based on the image information sent in step S1. Specifically, as shown in FIG. 5, a sinogram is created in which the vertical axis is the γ-ray irradiation direction θ and the horizontal axis is the surface direction perpendicular to the body axis Z of the subject M. The derived absorption correction data (sinogram here) is sent to the absorption correction data processing unit 14. A portion corresponding to the subject M, as well as illustrated in FIG. 5 C _M, the portion corresponding to the gantry 2, shown in C _G in FIG.

(Step S13) Transmission reconstruction The absorption correction data processing unit 14 reconstructs the absorption correction data (here sinogram) sent in step S12. Of the transmission data such as the sinogram processed in this way and the reconstructed absorption correction data, the sinogram obtained by the absorption correction data derivation unit 13 is sent to the ratio calculation unit 16a of the physical quantity calculation unit 16, and the absorption correction is performed. The absorption correction data reconstructed by the data processing unit 14 is sent to the PET reconstruction unit 12 and the cross-sectional area calculation unit 16c of the physical quantity calculation unit 16.

(Step S3) NEC Calculation The projection data deriving unit 11 obtains the image information sent in step S2 as projection data. The projection data and the absorption correction data derived by the absorption correction data processing unit 14 in step S13 are sent to the PET reconstruction unit 12, and the PET reconstruction unit 12 absorbs γ rays in the body of the subject M. A tomographic image taking into account is obtained. A nuclear medicine diagnosis is performed based on the absorption-corrected tomographic image. On the other hand, based on the image information sent in step S2, NEC computation is performed using the true coincidence (T), random coincidence (R), and scattering coincidence (S) simultaneously counted by the coincidence circuit 10. The unit 16b calculates a noise equivalent count NEC. Although the noise equivalent count NEC may be calculated using the above formula (1) or (2), in the first embodiment, the noise equivalent count NEC is calculated using the following formula (3).

NEC = (T + S) ² / (T + S + 2 × f × R) (3)
In the actual coincidence circuit 10, since the total coincidence (T + S + R) and the delayed coincidence (R) are derived, it is difficult to distinguish the true coincidence (T) and the scattered coincidence (S). Therefore, (total coincidence count) − (delay coincidence count) = (T + S) is substituted into the above equation (3). The delayed coincidence count (R) is substituted with the delayed coincidence count as it is. As shown in FIG. 6, the delay coincidence is combined with the coincidence circuit 10 and a delay circuit 10 ', so that the delay circuit 10' causes a time delay for γ rays that would otherwise not fall within the time window, The time difference between the input γ rays is determined by the delay circuit 10 ′ as a component that is within the time window and is simultaneously counted by the coincidence counting circuit 10. The γ rays simultaneously counted by the coincidence counting circuit 10 by the delay circuit 10 ′ are noises that do not fall within the time window without the delay circuit 10 ′, and therefore can be distinguished as random coincidence (R).

Since f in the above equation (3) is the ratio f of the subject M to the gantry 2 as described above, it is obtained based on the sinogram obtained by the absorption correction data deriving unit 13 in step S12. Is possible. It is possible to determine the ratio f in the area of C _G area and C _M in FIG. Note that the ratio f may be obtained from the absorption correction data reconstructed by the absorption correction data processing unit 14 in step S13. The ratio f thus determined is sent to the NEC calculation unit 16b and substituted into the above equation (3), and the true coincidence (T) and coincidence coincidence (R) simultaneously counted by the coincidence circuit 10 are also obtained. Then, the noise equivalent count NEC is calculated by substituting the scattering coincidence count (S) into the above equation (3). The calculated noise equivalent count NEC is sent to the C-NEC calculation unit 16d. This step S3 corresponds to the second physical quantity calculation step in the present invention.

  Note that the noise equivalent count NEC is a true coincidence count (T) that is apparently the same as the image noise obtained when there is no coincidence coincidence (R) or scattering coincidence (S). Further, the noise equivalent count NEC is not limited to the above formulas (1), (2), and (3). Further, the count value (count value) to be counted depends on the radiation dose and does not take into account the size of the subject M. Therefore, a noise equivalent count C-NEC per unit area is calculated as in step S4 described later.

(Step S14) Cross-sectional area calculation The cross-sectional area calculation unit 16c calculates the cross-sectional area of the subject M based on the absorption correction data reconstructed by the absorption correction data processing unit 14 in step S13. From the reconstructed absorption correction data (absorption coefficient map), as shown in FIG. 7, the cross-sectional area S of the subject M having a cross section perpendicular to the body axis Z of the subject M is calculated. The calculated cross-sectional area S is sent to the C-NEC calculation unit 16d. When calculating the cross-sectional area S, soft tissue may be considered as shown in FIG. For example, in the case of the lung, since the gas other than the soft tissue is gas (for example, air) and the absorption of γ rays is small, only the cross-sectional area S ′ of the soft tissue of the lung may be considered. In addition, weighting is performed on the cross-sectional area S according to the absorbency, the weight at the portion having a small absorbency is reduced, and the cross-sectional area at the portion is multiplied by the reduced weight, thereby the portion having a large absorbency Alternatively, the weighting at may be increased, and the increased cross-sectional area may be multiplied by the increased weighting. This step S14 corresponds to the first physical quantity calculation step in this invention.

(Step S4) C-NEC Calculation From the noise equivalent count NEC calculated by the NEC calculation unit 16b in step S3, the cross-sectional area S calculated by the cross-sectional area calculation unit 16c in step S14 is calculated as shown in the following equation (4). By dividing, the C-NEC calculation unit 16d calculates a noise equivalent count C-NEC per unit area.

C-NEC = NEC / Cross Section
= {(T + S) ² / (T + S + 2 × f × R)} / Cross Section (4)
However, “Cross Section” in the above equation (4) is the value of the cross-sectional area S. This step S4 corresponds to the third physical quantity calculation step in this invention.

(Step S5) Imaging condition setting The noise equivalent count C-NEC per unit area calculated by the C-NEC calculating unit 16d in step S4 is sent to the imaging condition setting unit 17 via the controller 7 (see FIG. 3). . The shooting condition setting unit 17 sets shooting conditions based on the noise equivalent count C-NEC per unit area that is sent. In the first embodiment, the imaging condition setting unit 17 controls the top plate driving unit 6 (see FIG. 1) to control the moving speed of the top plate 1 or the stop time of the top plate 1. Therefore, in the first embodiment, the moving speed and the stop time of the top board 1 correspond to the photographing conditions in the present invention. The shooting condition setting unit 17 corresponds to the shooting condition setting means in the present invention.

  In the case of the continuous whole body collection (1) and the static collection (2) described above, the noise equivalent count C-NEC per unit area that does not affect the image quality is preset as a threshold value. In the case of continuous whole body collection, when the noise equivalent count C-NEC per unit area calculated in step S5 is higher than the set threshold value, the moving speed of the top board 1 is increased and the collection time is increased. If the noise equivalent count C-NEC per unit area calculated in step S5 is lower than the set threshold value, the moving speed of the top board 1 is reduced and collected. Set the time to be longer. In the case of static collection, as shown in FIG. 9, if the stop time of the top board 1 (that is, imaging time (collection time) in the case of static collection) becomes longer, the counted γ-rays (here, image information) ) Are accumulated and increased with time, and accordingly, the noise equivalent count C-NEC per unit area also increases. When the noise equivalent count C-NEC per unit area increased with this time becomes higher than the set threshold value, the imaging is terminated. This step S5 corresponds to the photographing condition setting step in this invention.

(Step S6) End of shooting?
In the case of continuous whole body collection, it is determined whether or not the scanning range has been reached, and if the scanning range has not been reached, it is determined that imaging has not been completed, and processing returns to step S1 and steps S1 to S6 are repeated. If the scanning range has been reached, it is determined that imaging has been completed, and a series of processing is terminated (the flowchart in FIG. 4 is for continuous whole body collection). In the case of static collection, it is determined whether or not the stop time (imaging time) of the top 1 set in step S5 based on the noise equivalent count C-NEC per unit area has been reached, and until the time is reached. In step S6, it waits and loops. If the time has been reached, it is determined that shooting has been completed, and the series of processing ends.

  According to the PET apparatus according to the first embodiment having the above-described configuration, the PET apparatus includes the cross-sectional area calculation unit 16c, the NEC calculation unit 16b, and the C-NEC calculation unit 16d. The cross-sectional area calculation unit 16c calculates the cross-sectional area of the subject M as a physical quantity related to the size of the subject M, and the NEC calculation unit 16b calculates a noise equivalent count NEC as a physical quantity for evaluating the image. Based on the cross-sectional area of the subject M calculated by the cross-sectional area calculation unit 16c and the noise equivalent count NEC calculated by the NEC calculation unit 16b, the C-NEC calculation unit 16d calculates an image per size of the subject M. A noise equivalent count C-NEC per unit area is calculated as a physical quantity to be evaluated. Thus, by calculating the noise equivalent count C-NEC per unit area, an index that does not depend on the cross-sectional area of the subject M can be obtained when the image is evaluated.

  In the first embodiment, the PET apparatus includes a point source 4 that irradiates the subject M with the same type of γ rays as the radiopharmaceutical from the outside, and is based on the γ rays irradiated from the point source 4 and transmitted through the subject. Thus, the cross-sectional area calculation unit 16c calculates a physical quantity related to the size of the subject M (the cross-sectional area in the first embodiment). The data (transmission data in the first embodiment) acquired based on the γ rays irradiated from the point source 4 which is an external radiation source and transmitted through the subject has the form information of the subject M. Therefore, based on the γ-ray, the cross-sectional area calculation unit 16c can easily calculate a physical quantity related to the size of the subject M (the cross-sectional area in the first embodiment).

  In the first embodiment, the cross-sectional area of the subject M is taken as an example of the physical quantity related to the size of the subject M calculated by the first physical quantity calculating means (the cross-sectional area calculating unit 16c in the first embodiment) according to the present invention. The explanation is taken. The cross-sectional area is an effective index with respect to the size of the subject M.

  Further, the first embodiment includes a coincidence circuit 10 that counts γ rays generated from a subject to which a radiopharmaceutical is administered. The physical quantity for evaluating the image computed by the second physical quantity computing means (NEC computing unit 16b in the first embodiment) in this invention is a noise equivalent count NEC based on the γ-rays counted by the coincidence circuit 10, The third physical quantity computing means (C-NEC computing unit 16d in the first embodiment) in this invention computes a noise equivalent count C-NEC per size of the subject M (per unit area in the first embodiment). ing. The noise equivalent count NEC is useful as an index for easily evaluating the image quality, as described in the paragraph of “Background Art”. In order to consider a physical quantity related to the size of the subject M (cross-sectional area in the present embodiment 1) with respect to the noise equivalent count NEC, the per unit size of the subject M (per unit area in the present embodiment 1). By calculating and calculating the noise equivalent count C-NEC, the noise equivalent count C-NEC that does not depend on the physical quantity (cross-sectional area) related to the size of the subject M can be determined.

  In the first embodiment, the imaging condition setting unit 17 that sets the imaging condition is provided based on the noise equivalent count C-NEC per unit area calculated by the C-NEC calculation unit 16d. Since the noise equivalent count C-NEC per unit area calculated by the C-NEC calculation unit 16d does not depend on the cross-sectional area of the subject M and becomes an index for examining the next imaging condition, the next imaging is performed. Sometimes it is possible to determine how much image quality is ensured.

  In the first embodiment, in particular, in the case of continuous whole body collection, steps S3, S14, and S4 are included based on the shooting data acquired by shooting after shooting under the shooting conditions set in step S5. Steps S1 to S6 are repeated. By repeating in this way, it is possible to determine how much image quality is ensured even during shooting related to repetition. In addition, by performing this repetition during a series of imaging during continuous whole body collection, it is possible to determine how much image quality is ensured during imaging. Note that steps S1 to S6 may be repeated even during static collection. By repeatedly performing even during static collection, it is possible to update to the latest stop time (photographing time) of the top board, and it is possible to more accurately determine how much image quality is ensured during photographing.

Next, Embodiment 2 of the present invention will be described with reference to the drawings.
FIG. 10 is a side view and a block diagram of a PET-CT imaging system including a PET apparatus and an X-ray CT apparatus according to the second embodiment. The X-ray CT apparatus corresponds to the imaging apparatus in this invention.

  In the first embodiment described above, the PET apparatus includes the point source 4, the point source 4 emits the same γ-ray as the radiopharmaceutical and passes through the subject M, and the γ-ray detector 5 detects the γ-ray. Thus, although the absorption correction data is obtained as the form information based on the radiation, in the second embodiment, the projection data for CT is used as the absorption correction data. The absorption correction data corresponds to the CT image in the present invention.

  The X-ray CT apparatus includes a gantry 31 having an opening 31a, an X-ray tube 32, and an X-ray detector 33. The X-ray tube 32 and the X-ray detector 33 are arranged to face each other with the subject M interposed therebetween, and are embedded in the gantry 31. A large number of detection elements constituting the X-ray detector 33 are arranged in a fan shape around the body axis Z of the subject M.

  In addition, the X-ray CT apparatus includes a gantry driving unit 34, a high voltage generation unit 35, a collimator driving unit 36, and a CT reconstruction unit 37. The CT reconstruction unit 37 is realized by the controller 7 executing, for example, a program stored in a ROM of a storage medium represented by the above-described memory unit 18 or the like or an instruction input from the input unit 8. Note that CT projection data, which will be described later, and CT tomographic images processed by the CT reconstruction unit 37 are also written and stored in the RAM of the memory unit 18 in the same manner as in the first embodiment described above. Read from RAM. These CT projection data and CT tomographic images also correspond to the CT images in the present invention.

  The gantry drive unit 34 is a mechanism that drives the X-ray tube 32 and the X-ray tube detector 33 to rotate around the body axis Z of the subject M within the gantry 31 while maintaining the opposing relationship with each other. The motor is composed of a motor (not shown).

  The high voltage generator 35 generates a tube voltage or tube current of the X-ray tube 32. The collimator driving unit 36 is a mechanism that sets an X-ray irradiation field and drives the collimator (not shown) adjacent to the X-ray tube 32 to move in the horizontal direction. It consists of

  In the case of the indirect conversion type X-ray detector 33, the X-ray irradiated from the X-ray tube 32 and transmitted through the subject M is converted into light by a scintillator (not shown) in the X-ray detector 33. The light-sensitive film (not shown) photoelectrically converts the converted light and outputs it as an electrical signal. In the case of the direct conversion type X-ray detector 33, the X-ray is directly converted into an electric signal by a radiation sensitive film (not shown) and output. The electrical signal is sent to the CT reconstruction unit 37 as image information (pixels). The image information sent to the CT reconstruction unit 37 is transmitted as projection data for CT.

  The projection data for CT has the form information in the same way as the absorption correction data described in the first embodiment. In the second embodiment, the absorption correction data is used in order to use the projection data for CT as the absorption correction data. In addition to being sent to the deriving unit 13, it is also sent to the CT reconstruction unit 37. Image information (CT projection data) sent to the CT reconstruction unit 37 is reconstructed to obtain a CT tomographic image. This CT tomographic image is sent to the output unit 9 via the controller 7. Since the functions of the subsequent processing units (absorption correction data processing unit 14 and physical quantity calculation unit 16) of the PET apparatus including the absorption correction data deriving unit 13 are the same as those in the first embodiment, the description thereof is omitted. The PET tomographic image reconstructed by the PET reconstruction unit 12 and subjected to absorption correction, and the CT tomographic image reconstructed by the CT reconstruction unit 37 are superimposed and output by the output unit 9. May be.

  As described above, in the second embodiment, the projection data for CT obtained by being detected by the X-ray detector 33 of the X-ray CT apparatus is sent to the CT reconstruction unit 37, and also to the absorption correction data deriving unit 13. Infeed and CT projection data are used as absorption correction data.

  According to the PET-CT imaging system according to the second embodiment having the above-described configuration, as in the first embodiment, the cross-sectional area of the subject M is calculated as a physical quantity related to the size of the subject M, and the image The noise equivalent count NEC is calculated as a physical quantity for evaluating. Based on the cross-sectional area of the subject M and the noise equivalent count NEC, a noise equivalent count C-NEC per unit area is calculated as a physical quantity for evaluating an image per size of the subject M. Thus, by calculating the noise equivalent count C-NEC per unit area, an index that does not depend on the cross-sectional area of the subject M can be obtained when the image is evaluated.

  In the second embodiment, the form information of the subject M acquired by the imaging apparatus according to the present invention (X-ray CT apparatus in the second embodiment) (CT projection data used as the absorption correction data in the second embodiment). ), The first physical quantity computing means (cross-sectional area computing unit 16c in the second embodiment) in this invention computes a physical quantity related to the size of the subject M (cross-sectional area of the subject M in the second embodiment). is doing. Since the data acquired by the imaging apparatus (X-ray CT apparatus in the second embodiment) is the morphological information of the subject M, the first physical quantity calculating means (the cross-sectional area calculation in the second embodiment) is based on the morphological information. The unit 16c) can easily calculate a physical quantity related to the size of the subject (cross-sectional area in the second embodiment).

  In the second embodiment, the imaging apparatus according to the present invention is an X-ray CT apparatus, and the morphological information of the subject M (in this second embodiment, CT projection data used as CT images, that is, absorption correction data). ), When the first physical quantity computing means (cross-sectional area computing unit 16c in the second embodiment) in the present invention computes a physical quantity related to the size of the subject M (cross-sectional area in the second embodiment), Calculate as follows. That is, when the X-ray CT apparatus acquires a CT image, the CT image becomes an image having morphological information. Based on the CT image, the first physical quantity calculation means according to the present invention (in the second embodiment, the processing is interrupted). The area calculation unit 16c) calculates a physical quantity related to the size of the subject M (cross-sectional area in the second embodiment).

  In the second embodiment, the PET apparatus and the X-ray CT apparatus are integrated into one imaging system. However, the X-ray CT apparatus is configured as an external apparatus of the PET apparatus, and the subject acquired from the X-ray CT apparatus. M form information (CT projection data used as absorption correction data in the second embodiment) may be transferred to the PET apparatus. In this case, the X-ray CT apparatus is an external apparatus when viewed from the PET apparatus. Therefore, the X-ray CT apparatus corresponds to the external apparatus in the present invention.

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) In each of the embodiments described above, the PET apparatus has been described as an example. However, the present invention is a tomographic apparatus that obtains a tomographic image by simultaneously counting radiation generated from a subject to which a radiopharmaceutical is administered. If there is, it can be applied without being limited to the PET apparatus.

  (2) In each of the above-described embodiments, the γ-ray detector 5 for transmission is a stationary type that detects γ-rays while still, but the γ-ray detector 5 rotates around the subject M. A rotary type that detects γ rays may be used.

  (3) In the second embodiment described above, the imaging apparatus in the present invention is an X-ray CT apparatus, and the morphological information of the subject M (in the second embodiment, a CT image used as a CT image, that is, a CT projection used as absorption correction data) Based on the data), the first physical quantity computing means (cross-sectional area computing unit 16c in the second embodiment) in the present invention computes a physical quantity related to the size of the subject M (cross-sectional area in the second embodiment). It is not limited to the X-ray CT apparatus as in the second embodiment, and the shape information is not limited to the CT image. The present invention can be applied to an apparatus that obtains a predetermined image by performing predetermined imaging on a subject, and the data acquired by the apparatus has morphological information. For example, since an image obtained by a nuclear magnetic resonance apparatus (MRI: Magnetic Resonance Imaging) has morphological information, based on the morphological information obtained by MRI, first physical quantity computing means (in the second embodiment, a cross-sectional area computing unit 16c). ) May calculate a physical quantity related to the size of the subject (cross-sectional area in the second embodiment).

  (4) In each of the above-described embodiments, the first physical quantity calculation means (in each embodiment, the cross-sectional area calculation unit 16c) is data serving as a basis for calculating a physical quantity related to the size of the subject M (in each embodiment, the cross-sectional area). Is the morphological information of the subject M (transmission data in the first embodiment, CT image in the second embodiment, that is, CT projection data used as absorption correction data). Such data is as in each embodiment. The shape information of the subject M is not limited. Even in the case of function information (for example, emission data) of the subject M, the contour of the subject may be known by the distribution of the subject's radioactivity spread by the radiopharmaceutical, so the physical quantity related to the size of the subject is calculated. Is possible.

  (5) In each of the above-described embodiments, the cross-sectional area of the subject M is used as a physical quantity related to the size of the subject M calculated by the first physical quantity calculating means (the cross-sectional area calculating unit 16c in each embodiment) in the present invention. Although described as an example, the physical quantity is not limited to the cross-sectional area as in each embodiment. It may be the absorption rate of the subject. The absorptance of the subject is determined by counting the radiation irradiated from the external radiation source in the absence of the subject and irradiating from the external radiation source (the point source 4 in the first embodiment) in the presence of the subject. It is obtained by counting the radiation that has passed through and taking their count ratio. The absorption rate of the subject is also an effective index regarding the size of the subject.

  (6) In each of the above-described embodiments, a noise equivalent count NEC will be described as an example of a physical quantity for evaluating an image calculated by the second physical quantity calculation means (NEC calculation unit 16b in each embodiment) in the present invention. In addition, as a physical quantity for evaluating an image per size of the subject M calculated by the third physical quantity calculation means (C-NEC calculation unit 16d in each embodiment) in the present invention, a noise equivalent count per unit area C- Although NEC has been described as an example, the physical quantity is not limited to the noise equivalent count as in each embodiment. There is no particular limitation as long as it is a physical quantity for evaluating an image. For example, the ratio of random coincidence (R) to total coincidence, including true coincidence (T), random coincidence (R), and scatter coincidence (S) (R / (T + S + R)) Since it can be a physical quantity to be evaluated, R / (T + S + R) per size of the subject may be obtained by using R / (T + S + R) as a physical quantity to evaluate the image.

  (7) In each of the above-described embodiments, the moving speed and the stop time of the top board 1 are taken as examples of shooting conditions, but the shooting conditions are not limited to this. A case where imaging is performed in synchronization with expansion and contraction of the myocardium will be described with reference to FIG. As shown in FIG. 11, the period of the myocardium is T, the number of divisions for time division of the period T is the number of gates, the number of gates is N, and the number of frames corresponding to each period is F. Accordingly, the photographing time (collection time) is time per unit gate × number of gates N × number of frames F. The noise equivalent count C-NEC per unit area in the first embodiment will be described as an example. When the noise equivalent count C-NEC per unit area is high, the number of frames is set so that the entire acquisition time is shortened. If the number of gates is increased or the number of gates is increased so that the time per unit gate is shortened and the noise equivalent count C-NEC per unit area is low, the number of frames is increased so that the total acquisition time is increased, or Reduce the number of gates to increase the time per unit gate. In this case, the collection time, the number of gates, the number of frames, etc. correspond to the photographing conditions in the present invention.

  (8) In each of the above-described embodiments, a physical quantity (each implementation) for evaluating an image per size of the subject M calculated by the third physical quantity calculation means (C-NEC calculation unit 16d in each embodiment) in the present invention. In the example, the photographing condition setting means (the photographing condition setting unit 17 in each embodiment) for setting the photographing condition is provided and the photographing condition is automatically set based on the noise equivalent count per unit area (C-NEC). However, it is not always necessary to provide photographing condition setting means. For example, a physical quantity for evaluating an image typified by a noise equivalent count C-NEC or the like is graphically output and displayed on an output unit typified by a monitor or the like, and an operator (operator) makes an imaging condition based on the displayed physical quantity. May be set manually.

1 is a side view and block diagram of a PET (Positron Emission Tomography) apparatus according to Embodiment 1. FIG. FIG. 3 is a layout diagram of γ-ray detectors in a PET apparatus. It is a block diagram of a physical quantity calculation part and its peripheral part. It is a flowchart of a series of imaging data acquisition. It is a schematic diagram of a sinogram of transmission data. It is a block diagram of a circuit (delayed coincidence circuit) in which a delay circuit is combined with a coincidence circuit. It is a schematic diagram of a cross-sectional area. It is a schematic diagram of a cross-sectional area when considering soft tissue. It is explanatory drawing which represented typically the relationship between the imaging | photography time at the time of static acquisition, and the noise equivalent count per unit area. FIG. 6 is a side view and a block diagram of a PET-CT imaging system including a PET apparatus and an X-ray CT apparatus according to a second embodiment. It is a timing chart with which it uses for description which image | photographs synchronizing with expansion and contraction of a myocardium. (A) is the schematic which showed the mode of the coincidence coincidence typically, (b) is the schematic which showed the mode of the scattering coincidence typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 4 ... Point source 10 ... Simultaneous counting circuit 16b ... NEC calculating part 16c ... Cross-sectional area calculating part 16d ... C-NEC calculating part 17 ... Imaging condition setting part S ... Cross-sectional area M ... Subject

Claims (17)

  A tomography apparatus for obtaining a tomographic image by simultaneously counting radiation generated from a subject to which a radiopharmaceutical is administered, a first physical quantity calculating means for calculating a physical quantity related to the size of the subject, and a physical quantity for evaluating an image Based on the physical quantity calculated by the second physical quantity calculating means, the physical quantity calculated by the first physical quantity calculating means, and the physical quantity calculated by the second physical quantity calculating means, A tomography apparatus comprising: a third physical quantity calculation means for calculating.   The tomography apparatus according to claim 1, further comprising an external radiation source that irradiates the subject with radiation of the same type as that of the radiopharmaceutical from the outside, and based on radiation that is irradiated from the external radiation source and transmitted through the subject. The tomography apparatus, wherein the first physical quantity computing means computes a physical quantity related to the size of the subject.   The tomography apparatus according to claim 1, wherein the first physical quantity calculation means calculates a physical quantity related to the size of the subject based on the form information of the subject acquired by an external device. Shooting device.   The tomography apparatus according to claim 3, wherein the morphological information is a CT image acquired by an X-ray CT apparatus which is the external apparatus, and the first physical quantity calculation unit is configured to perform processing based on the CT image. A tomography apparatus that calculates a physical quantity related to the size of a specimen.   5. The tomography apparatus according to claim 1, wherein the physical quantity related to the size of the subject calculated by the first physical quantity calculating means is a cross-sectional area of the subject. Shooting device.   6. The tomography apparatus according to claim 1, further comprising a counting unit that counts radiation generated from the subject to which the radiopharmaceutical is administered, and an image calculated by the second physical quantity calculating unit. The physical quantity to be evaluated is a noise equivalent count based on the radiation counted by the counting means, and the third physical quantity calculating means calculates a noise equivalent count per size of the subject. apparatus.   7. The tomography apparatus according to claim 1, wherein imaging conditions are set based on a physical quantity that evaluates an image per size of a subject calculated by the third physical quantity calculation means. A tomography apparatus comprising a condition setting means.   Imaging provided with a tomography apparatus that obtains a tomographic image by simultaneously counting radiation generated from a subject to which a radiopharmaceutical has been administered, and an imaging apparatus that performs a predetermined imaging on the subject to obtain a predetermined image A system comprising: a first physical quantity computing unit that computes a physical quantity related to the size of an object; a second physical quantity computing unit that computes a physical quantity for evaluating an image; the physical quantity computed by the first physical quantity computing unit; An imaging system comprising: third physical quantity computing means for computing a physical quantity for evaluating an image per size of the subject based on the physical quantity computed by the second physical quantity computing means.   9. The imaging system according to claim 8, wherein the tomography apparatus includes an external radiation source that irradiates the subject with the same type of radiation as the radiopharmaceutical from the outside, and is irradiated from the external radiation source and passes through the subject. The imaging system according to claim 1, wherein the first physical quantity calculation means calculates a physical quantity related to the size of the subject based on the radiation.   9. The imaging system according to claim 8, wherein the imaging apparatus acquires morphological information of the subject, and based on the morphological information, the first physical quantity calculating means calculates a physical quantity related to the size of the subject. A characteristic shooting system.   The imaging system according to claim 10, wherein the imaging apparatus is an X-ray CT apparatus, and the form information is a CT image acquired by the X-ray CT apparatus, and the first information is based on a CT image. The physical quantity calculating means calculates a physical quantity related to the size of the subject.   12. The imaging system according to claim 8, wherein the physical quantity related to the size of the subject calculated by the first physical quantity calculating means is a cross-sectional area of the subject. .   13. The imaging system according to claim 8, wherein the tomography apparatus includes a counting unit that counts radiation generated from a subject to which a radiopharmaceutical has been administered, and the second physical quantity calculation unit includes: The physical quantity for evaluating the calculated image is a noise equivalent count based on the radiation counted by the counting means, and the third physical quantity computing means calculates a noise equivalent count per size of the subject. A characteristic shooting system.   14. The imaging system according to claim 8, wherein the tomography apparatus performs imaging based on a physical quantity that evaluates an image per size of a subject calculated by the third physical quantity calculation means. An imaging system comprising imaging condition setting means for setting conditions.   An imaging data acquisition method for acquiring imaging data by simultaneously counting radiation generated from a subject to which a radiopharmaceutical is administered, the first physical quantity calculating step for calculating a physical quantity related to the size of the subject, and evaluating the image An image per size of the subject is evaluated based on the second physical quantity calculating step for calculating the physical quantity to be calculated, the physical quantity calculated in the first physical quantity calculating step, and the physical quantity calculated in the second physical quantity calculating step. A shooting data acquisition method comprising: a third physical quantity calculation step of calculating a physical quantity.   The imaging data acquisition method according to claim 15, further comprising an imaging condition setting step for setting imaging conditions based on a physical quantity for evaluating an image per size of the subject calculated in the third physical quantity calculation step. An imaging data acquisition method characterized by:   The imaging data acquisition method according to claim 16, wherein after performing imaging under the imaging conditions set in the imaging condition setting step, based on imaging data acquired by the imaging, the first physical quantity calculation step, the first An imaging data acquisition method characterized by repeatedly performing a second physical quantity calculation step and a third physical quantity calculation step.

Images