JP4703150B2 - Radiation diagnostic apparatus and attenuation correction method - Google Patents

Description

  According to the present invention, X-rays (X-rays) irradiated to an object from an X-ray tube of an X-ray CT apparatus are detected by an X-ray detector to obtain a CT value, and reconfiguration in the PET apparatus is performed using the obtained CT value. The present invention relates to a radiation diagnostic apparatus and attenuation correction method for correcting a reconstructed image by obtaining an attenuation coefficient of an image, and in particular, an effective monochromatic photon energy of an X-ray spectrum detected by an X-ray detector can be obtained by calculation. The present invention relates to a radiological diagnostic apparatus and attenuation correction method.

  Conventionally, there are a positron emission computed tomography (PET) apparatus and an X-ray computed tomography (CT) apparatus as radiation diagnostic apparatuses using radiation.

  The PET device is one of nuclear medicine diagnostic devices, and a radioisotope (RI) that emits positrons is administered to a subject, and 511 keV emitted when positrons are emitted from the administered RI. Energy photons (gamma rays: gamma rays) are detected by a PET detector such as a pair of gamma cameras facing each other. RI has a property of being selectively taken into a specific tissue or organ within a subject. Therefore, by utilizing this RI property, a dose distribution of RI is obtained from γ rays detected by a PET detector, and imaged by image reconstruction processing by a computer, so that a subject to be scanned as a reconstructed image. A tomographic image at the site can be obtained.

  In tomography of a subject using a PET apparatus, if the projection data that is the original data of the reconstructed image is corrected using the distribution of the attenuation coefficient of γ rays on the scan target surface of the subject, the image quality of the reconstructed image is improved. It has been known. This is because γ rays are scattered or absorbed in the subject, and therefore the RI distribution obtained by using the γ rays detected by the PET detector does not necessarily reflect an accurate RI distribution. caused by. Although the attenuation coefficient is also called an absorption coefficient, it is a reaction cross section (reaction probability) of a certain substance with respect to photons, and depends on the energy of photons.

  Therefore, in the tomography of the subject by the PET apparatus, the attenuation coefficient distribution is created as an attenuation correction map and used for correcting the reconstructed image. The attenuation correction map can be created using RI. That is, using the RI as an external source, the subject is irradiated with γ rays emitted from the RI from the outside of the subject. Then, γ-rays that have passed through the scan target region of the subject can be detected by a PET detector, and an attenuation correction map can be created based on the detection data of the transmitted γ-rays.

  On the other hand, the X-ray CT apparatus detects X-rays that are irradiated on a subject from an X-ray tube and transmitted through the subject with an X-ray detector. A CT value is obtained from the X-ray detection data detected by the X-ray detector, and a tomographic image of the subject is reconstructed using the CT value.

  The CT value obtained by the X-ray CT apparatus is a value obtained based on the attenuation coefficient of water and the attenuation coefficient of air for X-rays according to the photon energy of X-rays transmitted through the subject. For this reason, the CT value corresponds to the attenuation coefficient of the scan target region with respect to X-rays.

  Therefore, an attenuation correction map for correcting the reconstructed image of the subject in the PET apparatus can be created from the CT value obtained by the X-ray CT apparatus without using RI. Therefore, in recent years, a PET-CT (positron-CT composite apparatus) in which an X-ray CT apparatus and a PET apparatus are combined is used as one of the radiation diagnostic apparatuses.

  That is, in the conventional PET-CT, X-rays irradiated to the subject from the X-ray tube of the X-ray CT apparatus are used as an external source instead of the RI external source, and the X-ray detected by the X-ray detector is used. An attenuation correction map for correcting the reconstructed image in the PET apparatus is created using the CT value obtained from the detection data. Then, the reconstructed image is corrected (attenuation correction) using the created attenuation correction map, and a final reconstructed image for diagnosis is obtained.

  Here, since X-rays used in the X-ray CT apparatus and γ-rays used in the PET apparatus are different from each other in photon energy, scaling of the attenuation coefficient is necessary. In other words, the attenuation coefficient obtained from the CT value corresponds to the photon energy of the X-ray, and therefore needs to be scaled to the attenuation coefficient corresponding to the γ-ray for correcting the reconstructed image in PET.

  Further, since the X-ray photon energy obtained in the X-ray CT apparatus has a continuous spectrum, the effective monochromatic photon energy is obtained by obtaining the effective photon energy of the monochromatic color from the photon energy of the X-ray continuous spectrum. It is necessary to obtain the attenuation coefficient for X-rays using.

  FIG. 7 is a flowchart showing an example of a procedure for creating an attenuation coefficient map and correcting attenuation of a reconstructed image in a conventional PET-CT, and the reference numerals with numerals in the figure indicate the steps of the flowchart.

  In FIG. 7, the scanning procedure by the PET apparatus is omitted.

  The attenuation correction of the reconstructed image in the PET apparatus can be performed by, for example, a hybrid attenuation correction method (see, for example, Non-Patent Document 1 and Non-Patent Document 2).

  First, in step S1, a CT scan is executed by an X-ray CT apparatus, and a CT value (HU) in a scan target portion of the subject is measured from X-ray detection data detected by an X-ray detector.

  Next, in step S2, a substance in the scan target part is provisionally identified from the obtained CT value (HU). That is, by comparing the CT value (HU) with the threshold value, the scan target region is divided into a bone region (b) and a water region (w) other than the bone.

Next, in step S3, the attenuation coefficient (μ _CT ) in the scan target region corresponding to the X-ray photon energy is calculated from the CT value (HU) in the scan target region and the X-ray photon energy detected by the X-ray detector. Is required. Here, since the photon energy of the X-ray detected by the X-ray detector is a continuous spectrum, the monochromatic effective monochromatic photon energy is obtained, and the attenuation coefficient (μ _CT ) for the X-ray is obtained using the effective monochromatic photon energy. There is a need.

  The continuous spectrum of X-rays detected by the X-ray detector differs depending on the tube voltage of the X-ray tube. However, the effective monochromatic photon energy of X-rays detected by an X-ray detector empirically has been fixed at about 70 keV regardless of the tube voltage of the X-ray tube.

Therefore, first, the attenuation coefficient (μ _w.CT ) for water X-rays when the effective monochromatic photon energy of X-rays is 70 keV is obtained, and the obtained water attenuation coefficient (μ _w.CT ) and CT value are obtained. From (HU), the attenuation coefficient (μ _CT ) in the case of X-rays at the scan target site is obtained.

Next, in step S4, a scaling factor for scaling the attenuation coefficient (μ _CT ) for X-rays to the attenuation coefficient (μ _PET ) for γ-rays is obtained.

  As described above, the effective monochromatic photon energy of X-rays is empirically 70 keV. In addition, the photon energy of γ rays detected by scanning with a PET apparatus is caused by the disappearance of positrons emitted from FDG in a test in which fluorodeoxyglucose (FDG) commonly used as RI is administered to a subject. The photon energy of γ-rays that accompanies it is 511 keV.

When the scanning target site is the bone region (b), the scaling factor is the attenuation coefficient ( _μb.PET ) of the bone region (b) corresponding to the photon energy (511 keV) of γ rays and the effective X-ray. while determined as a ratio _(μ b.PET / μ b.CT) the attenuation coefficients of the bone region (b) corresponding to a single color photon energy _(70keV) (μ b.CT), water scanned sites other than bone In the case of the region (w), the water region corresponding to the attenuation coefficient ( _μw.PET ) of the water region (w) corresponding to the photon energy (511 keV) of γ-ray and the effective monochromatic photon energy (70 keV) of X-ray. It is obtained as the ratio of the attenuation coefficient of the _{(w) (μ w.CT) (} μ w.PET / μ w.CT).

In addition, the attenuation coefficient ( _μw.PET , _μw.CT , _μb.PET , _μb.CT ) of the water region and the bone region corresponding to the photon energy of X-rays or γ-rays when obtaining the scaling factor is Required from public database.

Next, in step S5, the attenuation coefficients for the γ-ray by multiplying the scaling factor (mu _PET) is determined for the attenuation coefficient for X-ray (mu _CT). Further, when the scanning target region is the water region (w), it is obtained from the CT value (HU) and the attenuation coefficient ( _μw.PET ) of the water region (w) corresponding to the photon energy (511 keV) of γ rays. You can also.

Next, in step S6, the attenuation data ( _μPET ) is used to attenuate and correct the projection data serving as the original data of the reconstructed image obtained by scanning with the PET apparatus.

  Next, in step S7, the reconstructed image is reconstructed by performing image reconstruction processing on the projection data after attenuation correction.

  Next, in step S8, a reconstructed image with improved image quality for diagnosis by attenuation correction is displayed on the monitor.

  On the other hand, in a single photo emission computed tomography (SPECT) apparatus, which is a typical nuclear medicine diagnostic apparatus along with a PET apparatus, attenuation correction of a reconstructed image is conventionally performed in the same manner as in a PET apparatus.

  The SPECT apparatus is an apparatus for reconstructing a tomographic image of a subject by detecting photons such as γ rays emitted from an RI administered to the subject. Also in this SPECT apparatus, conventionally, an RI source or an X-ray source is provided as an external source, and an attenuation coefficient distribution is obtained from detection data of radiation transmitted through the subject. Further, attenuation correction of the reconstructed image is performed using the obtained attenuation coefficient.

As another attenuation correction method in the SPECT apparatus, an RI that emits radiation of a plurality of different types of photon energy is administered to the subject without providing an RI source or an X-ray source outside the subject as an external source. However, a technique for obtaining an attenuation coefficient has been devised since the degree of the influence of the emitted radiation that is attenuated by passing through the subject differs depending on the photon energy (see, for example, Patent Document 1).
JP 2001-343461 A PE Kinahan, DW Townsend, T. Beyer, D. Sashin: Attenuation correction for a combined 3D PET / CT scanner. Med. Phys. 25 (10): 2046-2053, 1998 C. Burger, G. Goerres, S. Schoenes, A. Buck, AHR Lonn, GK von Schulthess: PET attenuation coefficients from CT images: experimental evaluation of the transformation of CT into PET 511-keV attenuation coefficients. Eur. J. Nuc Med. 29 (7): 923-927, 2002

  In the conventional PET-CT, the effective monochromatic photon energy of X-rays necessary for calculating the attenuation coefficient is empirically fixed at about 70 keV. For this reason, there exists a problem that restrictions arise in setting conditions, such as a tube voltage of an X-ray tube. That is, it is necessary to perform a condition setting operation for irradiating the subject so that the effective monochromatic photon energy of X-rays at the scan target site is actually about 70 keV. The occurrence of such work is a factor that reduces the convenience of PET-CT.

  Conversely, even if the tube voltage of the X-ray tube is adjusted, the effective monochromatic photon energy of the X-ray is also affected by the material and thickness of the filter and the body shape of the subject. The effective monochromatic photon energy is not always 70 keV. In such a case, if the effective monochromatic photon energy of X-rays is fixed at 70 keV, the accuracy of the attenuation coefficient obtained may be reduced.

  Furthermore, in the method of empirically obtaining the effective monochromatic photon energy of X-rays, data is collected by conducting tests whenever conditions such as the tube voltage of the X-ray tube, the filter material and thickness, and the body shape of the subject change. Therefore, it is inconvenient and economically disadvantageous.

  The present invention has been made in order to cope with such a conventional situation. An X-ray detector detects X-rays irradiated from a X-ray tube of an X-ray CT apparatus to obtain a CT value. Diagnosis capable of obtaining the effective monochromatic photon energy of the X-ray spectrum detected by the X-ray detector in the attenuation correction for correcting the reconstructed image by obtaining the attenuation coefficient in the PET apparatus using the obtained CT value An object is to provide an apparatus and an attenuation correction method.

  Another object of the present invention is to obtain a CT value by detecting an X-ray irradiated to a subject from an X-ray tube of an X-ray CT apparatus by using an X-ray detector, and using the obtained CT value, a PET apparatus In the attenuation correction in which the reconstructed image is corrected by obtaining the attenuation coefficient in the X-ray CT, the X-ray CT apparatus uses the X-ray CT apparatus so that the effective monochromatic photon energy of the X-ray spectrum detected by the X-ray detector becomes a desired value obtained by calculation. To provide a radiation diagnostic apparatus and attenuation correction method capable of setting conditions for CT scanning.

In order to achieve the above-described object, the radiological diagnostic apparatus according to the present invention, as described in claim 1, uses X-rays from the X-ray tube according to the tube voltage to effectively perform X-rays inside the subject. Irradiating the subject through a filter in which at least one of the material and the thickness is set so that the single-color photon energy becomes a desired value, transmitted through the subject, and detected by the X-ray detector An X-ray CT apparatus that performs a CT scan to obtain the CT value of the subject from the X-ray detection data, and γ-rays emitted from the radioisotope administered to the subject are detected by a γ-ray detector. And a nuclear medicine diagnostic apparatus for generating a nuclear medicine image by performing attenuation correction using the CT value on the detected γ-ray detection data, and the attenuation correction is effective for the X-ray having the desired value. It uses monochromatic photon energy And it is characterized in Rukoto.

On the other hand, in the attenuation correction method according to the present invention, in order to achieve the above object, as described in claim 2 , when a CT scan is performed by an X-ray CT apparatus, X-rays inside the subject are detected. The CT value of the subject and the desired value obtained by performing a CT scan using a filter in which at least one of the material and the thickness is set so that the effective monochromatic photon energy becomes a desired value. A step of obtaining an attenuation coefficient for γ-rays from effective monochromatic photon energy of X-rays, and a step of performing attenuation correction on data obtained by scanning with a PET apparatus using the attenuation coefficient. Is.

  In the radiation diagnostic apparatus and attenuation correction method according to the present invention, an X-ray detector irradiates a subject from an X-ray tube of an X-ray CT apparatus to obtain a CT value, and obtains the calculated CT value. In attenuation correction in which the attenuation coefficient in the PET apparatus is used to correct the reconstructed image, the effective monochromatic photon energy of the X-ray spectrum detected by the X-ray detector can be calculated.

  Further, X-rays irradiated to the subject from the X-ray tube of the X-ray CT apparatus are detected by an X-ray detector to obtain a CT value, and an attenuation coefficient in the PET apparatus is obtained by using the obtained CT value for reconstruction. In attenuation correction for correcting an image, the conditions of CT scanning by the X-ray CT apparatus are set so that the effective monochromatic photon energy of the X-ray spectrum detected by the X-ray detector becomes a desired value obtained by calculation. Can do.

  Embodiments of a radiation diagnostic apparatus and attenuation correction method according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram showing a first embodiment of PET-CT which is a radiation diagnostic apparatus according to the present invention.

  The PET-CT 1 includes an X-ray CT apparatus 2, a PET apparatus 3 that is one of nuclear medicine diagnosis apparatuses, and an X-ray effective monochromatic energy calculation system 4. The X-ray effective monochromatic energy calculation system 4 is constructed by causing a computer to read an X-ray effective monochromatic energy calculation program. However, all or part of the X-ray effective monochromatic energy calculation system 4 may be configured by a circuit. Further, all or part of the X-ray effective monochromatic energy calculation system 4 may be built in the X-ray CT apparatus 2 or the PET apparatus 3.

  The X-ray CT apparatus 2 includes an X-ray tube 5, an X-ray detector 6, an X-ray detection data collection unit 7, and an X-ray detection data processing unit 8. The X-ray tube 5 has a function of irradiating the subject P with X-rays upon receiving application of tube voltage and supply of tube current from a high voltage generator (not shown). The X-ray tube 5 is configured by providing a tube 9 with a filter 10. Then, X-rays of photon energy corresponding to the tube voltage are generated from the tube 9 and the photon energy of the X-rays irradiated to the subject P can be controlled by adjusting the material and thickness of the filter 10. The

  The X-ray detector 6 has a function of detecting X-rays that are irradiated from the X-ray tube 5 to the subject P and transmitted through the subject P, and giving the X-ray detection data to the X-ray detection data collection unit 7.

  The X-ray detection data collection unit 7 has a function of digitizing the X-ray detection data received from the X-ray detector 6 to generate raw data and supplying the generated raw data to the X-ray detection data processing unit 8.

  The X-ray detection data processing unit 8 generates projection data by performing preprocessing and image processing on the raw data received from the X-ray detection data collection unit 7, and further generates a projection data from the generated projection data in the scan region of the subject P. It has a function for obtaining a CT value.

  The X-ray effective monochromatic energy calculation system 4 includes an incident X-ray spectrum calculation unit 11, a scan target modeling unit 12, an in-system X-ray spectrum calculation unit 13, an in-system X-ray spectrum averaging unit 14, and an X-ray effective monochromatic energy database. 15 is provided.

  The incident X-ray spectrum calculation means 11 is a system for calculating a photon energy spectrum of X-rays incident on the subject P from the X-ray tube 5 of the X-ray CT apparatus 2 and calculating the incident photon energy spectrum of the X-rays. A function to be provided to the inner X-ray spectrum calculation means 13. The photon energy spectrum of X-rays emitted from the X-ray tube 5 is a continuous spectrum depending on the imaging conditions such as the tube voltage applied to the X-ray tube 5 and the material and thickness of the filter 10. The photon energy spectrum of can be obtained by a method such as Birch, for example.

  For details of the method of Birch et al., For example, R. Birch, M. Marshall: Computation of Bremsstrahlung X-ray Spectra and Comparison with Spectra Measured with a Ge (Li) Detector. Phys. Med. Biol. 24 (3 ): It is described in documents such as 505-517, 1979.

  The scan target modeling unit 12 has a function of creating a system that simulates a CT scan by the X-ray CT apparatus 2 as a calculation model, and giving the created calculation model to the in-system X-ray spectrum calculation unit 13. The calculation model created by the scan target modeling unit 12 can be configured mainly by modeling the X-ray tube 5 of the X-ray CT apparatus 2 and the scan target portion of the subject P.

  Among the calculation models, the scan target model obtained by modeling the scan target portion of the subject P can be simulated by a water cylinder, for example, because the main component of the subject P is water. However, the scan target model may be created by simulating the subject P in detail. Furthermore, a plurality of scan target models can be created for each body type of the subject P such as weight, height, and chest circumference.

  Then, the scan target modeling unit 12 creates a plurality of scan target models in advance to construct a calculation model, and stores the calculation model in a systematic X-ray spectrum calculation unit 13 while saving each calculation model. Configured to be able to give to.

  The in-system X-ray spectrum calculation means 13 uses the X-ray incident photon energy spectrum received from the incident X-ray spectrum calculation means 11 to calculate the X-rays inside the subject P using the calculation model received from the scan target modeling means 12. And a function of giving the calculated X-ray photon energy spectrum to the in-system X-ray spectrum averaging means 14.

  That is, the in-system X-ray spectrum calculation means 13 calculates the X-ray photon energy spectrum inside the scan target model, for example, the center of the water cylinder, and the X-ray incident photon energy spectrum incident on the water cylinder from the outside of the water cylinder. It has a function of obtaining a continuous spectrum from an attenuation coefficient that is an interaction probability between a substance and a photon.

  It should be noted that attenuation coefficients of most substances including water with respect to photons are stored in a database as a function of photon energy. For example, MJ Berger, JH Hubbell, SM Seltzer, JS Coursey, and DS Zucker: XCOM: Photon Cross Sections Database, which are databases of the National Institute of Standards and Technology in the U.S. There are databases such as National Institute of Standards and Technology, USA 1999.

  The in-system X-ray spectrum averaging means 14 performs an effective process by averaging the photon energy spectrum of X-rays inside the subject P, which is a continuous spectrum received from the in-system X-ray spectrum calculation means 13. It has a function of obtaining monochromatic photon energy, that is, an effective monochromatic photon energy of X-rays, and a function of writing the obtained effective monochromatic photon energy in the X-ray effective monochromatic energy database 15.

  For this reason, the X-ray effective monochromatic energy database 15 stores the X-ray effective monochromatic photon energy. Further, the X-ray effective monochromatic energy database 15 stores any combination of imaging conditions such as the tube voltage applied to the X-ray tube 5 in advance, the material and thickness of the filter 10, or the body shape of the subject P. The effective monochromatic photon energy of X-rays obtained in accordance with each calculation model created in (1) can be stored in a table format in association with imaging conditions and calculation models. Then, when necessary, the effective single-color photon energy of a desired X-ray corresponding to various conditions can be read from the X-ray effective single-color energy database 15 in a shorter time without performing another calculation. .

  The PET apparatus 3 includes a γ-ray detector 16, a γ-ray detection data collection unit 17, an attenuation correction unit 18, an image reconstruction unit 19, and a monitor 20. The γ-ray detector 16 has a function of detecting γ-rays having energy of 511 keV emitted when positrons are emitted from the RI previously administered to the subject P, and the detected γ-ray detection data is used as γ-ray detection data. A function to be given to the collection unit 17.

  The γ-ray detection data collection unit 17 receives the γ-ray detection data from the γ-ray detector 16 as projection data, thereby giving the projection data of the subject P and the collected projection data to the attenuation correction unit 18. With functions.

  The attenuation correction unit 18 is based on the CT value in the scan region of the subject P received from the X-ray detection data processing unit 8 and the effective monochromatic photon energy in the X-ray scan region read from the X-ray effective monochromatic energy database 15. It has a function of obtaining an attenuation coefficient required when attenuation correction is performed by an arbitrary method, and a function of performing attenuation correction on the projection data received from the γ-ray detection data collection unit 17. Further, the attenuation correction unit 18 is configured to give the projection data after attenuation correction to the image reconstruction unit 19.

  For example, the attenuation correction unit 18 performs provisional identification of the substance in the scan region from the CT value in the scan region of the subject P and the effective monochromatic photon energy of the X-ray, and the attenuation coefficient for the X-ray and the attenuation coefficient for the X-ray Can be obtained by obtaining a scaling factor for converting γ to an attenuation coefficient for γ-rays, and multiplying the attenuation coefficient for X-rays by the scaling factor.

  The image reconstruction unit 19 performs an image reconstruction process on the projection data after attenuation correction received from the attenuation correction unit 18, thereby generating reconstruction image data, and the generated reconstruction image data to the monitor 20. The function of displaying the reconstructed image of the subject P, which is a nuclear medicine image, is provided.

  Next, the operation of PET-CT1 will be described.

  FIG. 2 shows the attenuation obtained based on the X-ray effective monochromatic photon energy obtained by calculating the X-ray effective monochromatic photon energy by the X-ray effective monochromatic energy calculation system 4 of PET-CT 1 shown in FIG. It is a flowchart which shows an example of the procedure at the time of carrying out attenuation correction | amendment of the reconstructed image obtained by the PET apparatus 3 using a coefficient, The code | symbol which attached | subjected the number to S in the figure shows each step of a flowchart.

  First, the X-ray effective monochromatic energy calculation system 4 uses the body shape of the subject P, the tube voltage applied to the X-ray tube 5 of the X-ray CT apparatus 2, and the filter 10 applied to the tube 9 of the X-ray tube 5. For each imaging condition such as material and thickness, the effective monochromatic photon energy of X-rays is obtained and stored in a table format.

  That is, in step S <b> 10, the incident X-ray spectrum calculation unit 11 calculates a photon energy spectrum of X-rays incident on the subject P from the X-ray tube 5 of the X-ray CT apparatus 2 by calculation. The photon energy spectrum of X-rays emitted from the X-ray tube 5 is a continuous spectrum that depends on the imaging conditions such as the tube voltage applied to the X-ray tube 5 and the material and thickness of the filter 10. Therefore, the incident X-ray spectrum calculation means 11 uses, for example, the method of Birch and the like, for each imaging condition such as the tube voltage applied to the X-ray tube 5 and the material and thickness of the filter 10, respectively. Ask for.

  Next, in step S <b> 11, the scan target modeling unit 12 creates a system that simulates CT scanning by the X-ray CT apparatus 2 as a calculation model, and gives the created calculation model to the in-system X-ray spectrum calculation unit 13. The calculation model can be configured mainly by modeling the X-ray tube 5 of the X-ray CT apparatus 2 and the scan target site of the subject P. The scan target modeling unit 12 is configured to scan the scan target site of the subject P. For example, a model to be scanned is created by simulating the above with a water cylinder.

  The calculation model created by the scan target modeling unit 12 is used for calculation of the X-ray photon spectrum in the subject P, but the main substance constituting the subject P which is a system is water, Regardless of the specimen P, it is almost constant. For this reason, it is considered that the behavior of X-rays in the subject P is mainly influenced by the width of the subject P. Therefore, when the subject P, which is a system, is simulated by a water cylinder, the behavior of the X-ray in the system is affected by the diameter of the water cylinder.

  That is, it can be considered that the behavior of X-rays in the subject P varies depending on the weight and chest circumference of the subject P. Therefore, the scan target modeling means 12 creates a plurality of scan target models for each body type such as the weight, height, chest circumference of the subject P.

  For example, the scan target model can be a water cylinder equivalent to the average cross-sectional area of the CT scan plane. That is, the body perimeter of the subject P including the scan target part such as the chest circumference of the subject P is measured, and the measured body perimeter is regarded as equivalent to the circumference of the scan target surface assumed to be a circle. Furthermore, the diameter of the circle can be obtained from the circumference of the scan target surface, and the scan target part can be simulated using the water cylinder of the determined diameter as the scan target model.

  Further, the scan target model may be a water column having a diameter obtained based on the weight and height of the subject P. That is, since the constituent material of the main subject P is water, the density of the scan target model can be regarded as equivalent to water. The diameter of the water cylinder can be obtained by regarding the height of the water cylinder simulating the scan target site as the height of the subject P while regarding the weight of the water cylinder as equivalent to the body weight of the subject P.

  In this way, the scan target modeling means 12 converts a calculation model having a plurality of scan target models created for each body type such as the weight, height, and chest circumference of the subject P into a scan target model in a table format. Stored in the means 12. Then, a desired calculation model is given to the in-system X-ray spectrum calculation means 13 at a necessary timing.

  Next, in step S12, the in-system X-ray spectrum calculation unit 13 uses the incident photon energy spectrum of the X-rays received from the incident X-ray spectrum calculation unit 11 and uses the calculation model received from the scan target modeling unit 12. The behavior of X-rays inside the subject P is calculated, and the photon energy spectrum of X-rays at each scan site is obtained. In other words, the intra-system X-ray spectrum calculation means 13 refers to a known database, and attenuates the interaction probability between the incident photon energy spectrum of X-rays incident on the water cylinder from the outside of the water cylinder and the substance and photons. From the coefficient, for example, the photon energy spectrum of the X-ray at the center of the scan target model that is a water cylinder is obtained as a continuous spectrum.

  Since the incident photon energy spectrum of the X-rays given from the incident X-ray spectrum calculation means 11 to the in-system X-ray spectrum calculation means 13 has a plurality of sets with the tube voltage of the X-ray tube 5 and the material and thickness of the filter 10 as parameters. The photon energy spectrum of X-rays in the subject P is also obtained for each tube voltage of the X-ray tube 5, material of the filter 10, and thickness. Further, since there are a plurality of calculation models used for calculating the X-ray photon energy spectrum in the subject P for each body type of the subject P, the X-ray photon energy spectrum in the subject P is also different for each body type of the subject P. Each is required.

  FIG. 3 is a diagram showing an example of a photon energy spectrum of X-rays in the subject P obtained by the X-ray effective monochromatic energy calculation system 4 of PET-CT1 shown in FIG.

  In FIG. 3, the vertical axis indicates the intensity of X-rays (arbitrary unit), and the horizontal axis indicates the photon energy (keV) of X-rays.

  When the material and thickness of the filter 10 and the calculation model are specified, the X-ray photon energy spectrum can be obtained as a continuous spectrum for each tube voltage of the X-ray tube 5 as shown in FIG. A two-dot chain line in FIG. 3 is a photon energy spectrum of X-rays inside the subject P (a cylindrical phantom having a radius of 12 cm) when the tube voltage of the X-ray tube 5 is 80 kV. Also, the alternate long and short dash line, chain line, and solid line in FIG. 3 indicate the photon energies of the X-rays in the subject P (a cylindrical phantom having a radius of 12 cm) when the tube voltage of the X-ray tube 5 is 100 kV, 120 kV, and 140 kV, respectively. It is a spectrum.

On the other hand, the dotted line in FIG. 3 is the monochromatic photon energy E _PET (511 keV) of γ rays necessary for attenuation correction in the PET apparatus 3. Then, it is possible to determine the attenuation coefficient corresponding to the photon energy E _PET of γ rays by scaling the attenuation coefficient corresponding to the photon energy of X-rays obtained as a continuous spectrum. That is, as shown in FIG. 3, since the X-ray used in the X-ray CT apparatus 2 and the γ-ray used in the PET apparatus 3 are different in photon energy, scaling of the attenuation coefficient is necessary.

  However, since the X-ray photon energy has a continuous spectrum, the effective monochromatic photon energy obtained by setting the X-ray photon energy to an effective photon energy of a single color is obtained, and the attenuation coefficient for the X-ray is obtained using the effective monochromatic photon energy. There is a need.

  Therefore, the X-ray photon energy spectrum is supplied to the in-system X-ray spectrum averaging means 14.

  In step S13, the in-system X-ray spectrum averaging means 14 performs an averaging process on the X-ray photon energy spectrum inside the subject P, which is a continuous spectrum received from the in-system X-ray spectrum calculation means 13. As a result, the effective monochromatic photon energy of X-rays at the scan target site is obtained, and the obtained effective monochromatic photon energy is written in the X-ray effective monochromatic energy database 15.

  As a result, the X-ray effective monochromatic photon energy corresponding to the imaging conditions for each calculation model is stored in the X-ray effective monochromatic energy database 15. The effective monochromatic photon energy of the X-ray is stored in a table format for each tube condition applied to the X-ray tube 5, imaging conditions such as the material and thickness of the filter 10, or the body shape of the subject P. Then, the X-ray effective monochromatic photon energy corresponding to various conditions can be read from the X-ray effective monochromatic energy database 15 in a shorter time without recalculation when necessary.

  FIG. 4 is a diagram showing an example of the effective monochromatic photon energy of X-rays obtained by the PET-CT1 X-ray effective monochromatic energy calculation system 4 shown in FIG. 1 and stored in a table format.

As shown in the table of FIG. 4, the X-ray effective monochromatic energy database 15 can store the X-ray effective monochromatic photon energy in a table format. According to FIG. 4, it can be seen that the effective monochromatic photon energy E _CT of X-ray when the tube voltage CT applied to the X-ray tube 5 of the X-ray CT apparatus 2 is 80 kV is 54 keV.

Furthermore, the attenuation coefficient when the effective monochromatic photon energy E _{CT of} X-ray is 54 keV can be obtained from a public database. According to FIG. 4, when the tube voltage CT is 80 kV and the effective monochromatic photon energy E _CT of X-ray is 54 keV, the attenuation coefficient μ _w for water is 0.22 (1 / cm), and the attenuation for bone It can be seen that the coefficient μ _b is 0.60 (1 / cm).

Similarly, when the tube voltage CT is 100 kV and 120 kV, the effective monochromatic photon energy E _{CT of} X-rays is 62 keV and 70 keV, and the attenuation coefficient μ _w for water is 0.20 (1 / cm), 0, respectively. .19 (1 / cm), the attenuation coefficient μ _b for the bone is 0.50 (1 / cm) and 0.45 (1 / cm).

In other words, the X-ray effective monochromatic photon energy E _CT has been empirically set to 70 keV regardless of the tube voltage, whereas the X-ray effective monochromatic energy calculation system 4 uses not only the tube voltage but also the material of the filter 10. The effective monochromatic photon energy of X-rays is obtained by calculation using a calculation model according to the thickness and body shape of the subject P, and the effective monochromatic photon energy of X-rays corresponding to each condition is stored in a table format.

  As shown in FIG. 4, in addition to storing the effective monochromatic photon energy of X-rays in a tabular form, the tube voltage, the thickness and material of the filter 10 and the body shape of the subject P are formulated as parameters to obtain the effective X-ray monochromatic color. Photon energy can also be stored as an equation.

  When the effective monochromatic photon energy of X-rays is obtained in this way, next, in step S14, a CT scan is executed by the X-ray CT apparatus 2, and a CT value (HU) at the scan target portion of the subject P is measured. The That is, a tube voltage is applied to the X-ray tube 5 from a high voltage generator (not shown) of the X-ray CT apparatus 2 and a tube current is supplied. Then, X-rays of photon energy corresponding to the tube voltage are radiated from the tube 9 of the X-ray tube 5, and the photon energy of the X-rays is adjusted via the filter 10 and irradiated to the subject P.

  X-rays irradiated to the subject P from the X-ray tube 5 and transmitted through the subject P are detected by the X-ray detector 6 and given to the X-ray detection data collection unit 7 as X-ray detection data. The X-ray detection data collection unit 7 digitizes the X-ray detection data received from the X-ray detector 6 to generate raw data, and gives the generated raw data to the X-ray detection data processing unit 8. The X-ray detection data processing unit 8 generates projection data by performing preprocessing and image processing on the raw data received from the X-ray detection data collection unit 7, and further generates a projection data from the generated projection data in the scan region of the subject P. A CT value (HU) is obtained.

As a result, the CT value (HU) at the scan target portion of the subject P can be obtained. The CT value (HU) at the scan target portion of the subject P is given to the attenuation correction unit 18 of the PET apparatus 3. Then, the attenuation correction unit 18 uses any method of the PET apparatus 3 based on the CT value (HU) obtained by the CT scan and the effective monochromatic photon energy of the X-ray obtained by the X-ray effective monochromatic energy calculation system 4. attenuation coefficient μ _PET for the γ-ray is required. In attenuation correction unit 18, for example, the following steps (Kinahan et al. Method, see Non-Patent Document 1) attenuation coefficient _{mu PET} in is required.

That is, in step S15, the attenuation correction unit 18 temporarily identifies a substance in the scan target site from the CT value (HU) in the scan target site of the subject P received from the X-ray detection data processing unit 8. That is, by comparing the CT value (HU) with the threshold value ε _CT , the scan target region is divided into a bone region (b) and a water region (w) other than the bone. The threshold ε _{CT with} respect to the CT value (HU) can be about 200 to 300.

In the case of HU> ε _CT , that is, when the CT value (HU) exceeds about ε _CT = 200 to 300, it can be temporarily identified that the scan target site is the bone region (b). On the other hand, when HU <ε _CT , that is, when the CT value (HU) is less than about ε _CT = 200 to 300, it can be temporarily identified that the scan target region is the water region (w).

Next, in step S <b> 16, the attenuation correction unit 18 responds to the X-ray photon energy from the CT value (HU) in the scan target region and the X-ray effective monochromatic photon energy read from the X-ray effective monochromatic energy database 15. The attenuation coefficient (μ _CT ) at the scanned site is obtained. The attenuation coefficient (μ _CT ) can be obtained from the CT value (HU) and the attenuation coefficient (μ _w.CT ) for water X-rays corresponding to the effective monochromatic photon energy of X-rays according to the equation (1).
[Equation 1]
_{μ CT = (1 + HU /} 1000) × μ W. _CT (1)
Next, in step S17, the attenuation correction unit 18 obtains a scaling factor for scaling the attenuation coefficient (μ _CT ) for X-rays to the attenuation coefficient (μ _PET ) for γ-rays.

The effective monochromatic photon energy of the X-ray is a value E _CT keV obtained depending on the imaging conditions such as the tube voltage, the material and thickness of the filter 10 and the body shape of the subject P. In addition, γ-ray photon energy detected by scanning by the PET apparatus 3 is generated in association with annihilation of positrons emitted from the FDG in a test in which FDG generally used as RI is administered to the subject P. The photon energy of the line, which is 511 keV.

Therefore, attenuation coefficient _(μ w.CT) in the water area where first corresponding to X-ray effective monochromatic photon energy _(E CT keV), the attenuation coefficients of the bone region corresponding to the effective monochromatic photon energy of X-ray _(E CT keV) (Μ _b.CT ), attenuation coefficient (μ _w.PET ) of water region corresponding to photon energy (511 keV) of γ ray, attenuation coefficient (μ _b.PET ) of bone region corresponding to photon energy (511 keV) of γ ray _{. PET} ) is determined based on the published database.

When the scanning target site is the bone region (b), the scaling factor is the attenuation coefficient ( _μb.PET ) of the bone region (b) corresponding to the photon energy (511 keV) of γ rays and the effective X-ray. While it is obtained as a ratio (μ _b.PET / μ _b.CT ) of the bone region (b) corresponding to the monochromatic photon energy (E _CT keV) with the attenuation coefficient (μ _b.CT ), the scanning target region is other than the bone In the case of the water region (w), the attenuation coefficient ( _μw.PET ) of the water region (w) corresponding to the photon energy (511 keV) of γ rays and the effective monochromatic photon energy (E _CT keV) of X-rays determined as the ratio _(μ w.PET / μ w.CT) the attenuation coefficients of the corresponding water area _(w) (μ w.CT).

Next, in step S18, the attenuation correction unit 18 determines an attenuation coefficient (X-ray attenuation coefficient) depending on whether the region to be scanned is a water region (w) or a bone region (b) as shown in Expression (2). attenuation coefficient for γ rays by multiplying a scaling factor (mu _PET) is determined for mu _CT). Further, when the scanning target region is the water region (w), it is obtained from the CT value (HU) and the attenuation coefficient ( _μw.PET ) of the water region (w) corresponding to the photon energy (511 keV) of γ rays. You can also.
[Equation 2]
When HU> ε _CT μ _PET = μ _CT × μ _{b. PET} / μb _{b. CT}
HU <ε _CT ε _{CT
μ PET = μ CT × μ w} . _PET / μw _{. CT} = (1 + HU / 1000) × μ _{w. PET}
... (2)
Then, the attenuation correction unit 18 determines the attenuation coefficient ( _μPET ) for each part to be scanned in this way and creates an attenuation correction map. When the attenuation correction map is created, attenuation correction can be performed on the reconstructed image obtained by the PET apparatus 3.

  Therefore, in step S19, in parallel with the creation of the attenuation correction map or when the creation of the attenuation correction map is completed, a scan by the PET apparatus 3 is executed and γ-ray projection data is collected. That is, when RI such as FDG is administered to the subject P, the RI is selectively taken into a specific tissue or organ in the subject P and then emits positrons. Then, positrons emitted from RI such as FDG emit γ-rays with photon energy of 511 keV as they disappear.

  The 511 keV γ-rays emitted from the RI are detected by the γ-ray detector 16 and supplied to the γ-ray detection data collecting unit 17 as γ-ray detection data. The γ-ray detection data collecting unit 17 collects γ-ray projection data of the subject P by receiving the γ-ray detection data from the γ-ray detector 16 as γ-ray projection data.

  Next, in step S <b> 20, the projection data collected by the γ-ray detection data collection unit 17 is given to the attenuation correction unit 18. Then, the attenuation correction unit 18 performs attenuation correction on the projection data received from the γ-ray detection data collection unit 17 in accordance with the already created attenuation correction map. Further, the attenuation correction unit 18 gives the projection data after attenuation correction to the image reconstruction unit 19.

  Next, in step S21, the image reconstruction unit 19 performs image reconstruction processing on the projection data after attenuation correction to generate reconstructed image data.

  Next, in step S <b> 22, the reconstructed image data is given from the image reconstruction unit 19 to the monitor 20. As a result, a reconstructed image having improved image quality for diagnosis by attenuation correction is displayed on the monitor 20.

  That is, the PET-CT 1 as described above is an apparatus that performs attenuation correction by obtaining an attenuation coefficient for image reconstruction in the PET apparatus 3 from the CT value obtained by CT scanning by the X-ray CT apparatus 2. Then, in the calculation of the attenuation coefficient for correcting the reconstructed image obtained by the PET apparatus 3, the effective monochromatic photon energy of X-rays that has been given in the past is simulated by the scanning target site in the X-ray CT scan. It is configured to be obtained by calculation using a calculation model.

  For this reason, according to PET-CT1 shown in FIG. 1, since the effective monochromatic photon energy of X-rays is obtained according to the tube voltage applied to the X-ray tube 5, even if the tube voltage is changed, the tube voltage The scaling factor and the attenuation coefficient reflecting the change can be obtained. Therefore, a reconstructed image with good image quality can be obtained by obtaining the attenuation coefficient with higher accuracy and appropriately performing the attenuation correction as compared with the conventional attenuation coefficient calculation method in which the tube voltage value is not reflected.

  In other words, the tube voltage of the X-ray CT apparatus 2 could not be changed because there is an influence on the scaling factor and the attenuation coefficient in the past, but according to the PET-CT1 shown in FIG. Since the tube voltage can be arbitrarily changed without restriction, the convenience of PET-CT1 can be improved. That is, the degree of freedom in setting the tube voltage increases, and the operational restrictions on PET-CT1 decrease. In particular, by reducing the tube voltage of the X-ray CT apparatus 2, it becomes possible to operate the PET-CT 1 in which the exposure dose of the subject P is reduced.

  In addition, the effective monochromatic photon energy of X-rays at the scan target site can be accurately obtained for each condition such as not only the tube voltage of the X-ray CT apparatus 2 but also the filter 10 and the body shape of the subject P. As a result, the quality of the reconstructed image can be improved.

  Furthermore, according to the PET-CT1 shown in FIG. 1, the effective monochromatic photon energy of X-rays obtained by calculation in advance for each condition such as the tube voltage, the filter 10, and the body shape of the subject P is used in an arbitrary timing in a table format. Since it is configured to be able to do so, there is no need to collect data for empirically obtaining the effective monochromatic photon energy of X-rays by performing a test or the like every time the conditions change as in the prior art. Thereby, according to PET-CT1 shown in FIG. 1, it becomes possible to reduce the effort and cost of a test compared with the past, and it is advantageous in terms of convenience and economy.

  In addition, it is not necessary to calculate the effective monochromatic photon energy of X-rays every time a scan is executed in the PET apparatus 3, so that the time required to obtain a reconstructed image after attenuation correction is shortened. can do.

  In particular, if the subject P is simulated by a simple water cylinder and the scan target model is created so that the body shape of the subject P is reflected as the diameter of the water cylinder, the process for obtaining the effective monochromatic photon energy of X-rays The effective monochromatic photon energy of the X-ray can be obtained with higher accuracy while shortening the time.

  Similarly, even when the material and thickness of the filter 10 of the X-ray tube 5 are changed, X-rays that are obtained easily and accurately according to the material and thickness of the filter 10 and stored in a table format. By using the effective single color photon energy, it is possible to obtain a reconstructed image having a good image quality with attenuation correction performed in a shorter time.

  FIG. 5 is a block diagram showing a second embodiment of PET-CT which is a radiation diagnostic apparatus according to the present invention.

  In the PET-CT 1A shown in FIG. 5, the X-ray effective monochromatic energy calculation system 4 is provided with the filter condition setting means 30 and the tube voltage applied to the X-ray tube 5 of the X-ray CT apparatus 2 is CT scanned. 1 is different from the PET-CT1 shown in FIG. Since other configurations and operations are not substantially different from those of the PET-CT 1 shown in FIG. 1, the same configurations are denoted by the same reference numerals and description thereof is omitted.

  The PET-CT 1A X-ray effective monochromatic energy calculation system 4 is provided with a filter condition setting means 30. The filter condition setting means 30 refers to the X-ray effective monochromatic photon energy stored in the X-ray effective monochromatic energy database 15 in a table format, and the X-ray CT when the X-ray effective monochromatic photon energy becomes a desired value. It has a function of setting the material and thickness of the filter 10 of the apparatus 2 as a filter condition, and a function of giving the effective monochromatic photon energy of X-rays to the attenuation correction unit 18 of the PET apparatus 3 under the set filter condition.

  Furthermore, the filter condition setting means 30 has a function of controlling the filter 10 as necessary so that the material and thickness of the filter 10 of the X-ray CT apparatus 2 become the material and thickness of the filter 10 according to the filter conditions. Provided. In this case, the X-ray CT apparatus 2 is provided with a filter control mechanism for arranging a desired filter 10. However, the user may install the filter 10 in the X-ray CT apparatus 2 according to the filter condition set by the filter condition setting means 30.

  Next, the action of PET-CT1A will be described.

  FIG. 6 is a flowchart showing an example of a procedure for attenuation correction of the reconstructed image obtained by the PET apparatus 3 by obtaining the attenuation coefficient by the PET-CT 1A shown in FIG. The reference numerals indicate the steps of the flowchart.

  In FIG. 5, the same steps as those in FIG.

  First, in steps S10 to S13, the X-ray effective monochromatic photon energy is obtained for each tube voltage, the material and thickness of the filter 10, and the body shape of the subject P, and is stored in the X-ray effective monochromatic energy database 15 in a table format. Saved.

  Next, in step S30, the filter condition setting means 30 refers to the X-ray effective monochromatic photon energy stored in the table format in the X-ray effective monochromatic energy database 15, and the X-ray effective monochromatic photon energy is a desired value. The material and thickness of the filter 10 of the X-ray CT apparatus 2 are set as filter conditions. Then, the filter condition setting means 30 gives the X-ray effective monochromatic photon energy for the set filter condition to the attenuation correction unit 18 of the PET apparatus 3.

  Next, in step S31, a CT scan is executed with the material and thickness of the filter 10 of the X-ray CT apparatus 2 as the material and thickness of the filter 10 in accordance with the filter condition set by the filter condition setting means 30. The filter 10 of the X-ray CT apparatus 2 may be automatically controlled by a filter control mechanism (not shown) or installed by a user. Thereby, the CT value of the subject P is measured.

  Next, in step S15, the attenuation correction unit 18 performs tentative identification of the substance in the scan target site according to the CT value measured by the CT scan.

Next, in step S32, the attenuation correction unit 18 corresponds to the X-ray photon energy from the CT value in the scan target region and the X-ray effective monochromatic photon energy of the desired value received from the filter condition setting means 30. An attenuation coefficient (μ _CT ) at the scan target site is obtained.

  In steps S17 to S22, scaling factor calculation, attenuation coefficient calculation for γ rays, scanning by the PET apparatus 3, attenuation correction, and image reconstruction processing are performed in the same procedure as in FIG. The reconstructed image is displayed on the monitor 20.

  That is, in the PET-CT 1A as described above, the PET-CT 1 shown in FIG. 1 obtains the effective monochromatic photon energy of the X-ray according to the CT scan condition by the X-ray CT apparatus 2 and attenuates according to the CT scan condition. In contrast to an apparatus that performs attenuation correction using a coefficient, conversely, a CT scan condition is set so that the effective monochromatic photon energy of X-rays becomes a desired value, and CT scan is performed to obtain an attenuation coefficient. It is.

  In such PET-CT1A, the effective monochromatic photon energy of X-rays can be set to an arbitrary value. For example, if the effective monochromatic photon energy of X-rays is set to 70 keV that has been used empirically, even if attenuation correction is performed in the attenuation correction unit 18 of the PET apparatus 3 by the conventional attenuation correction method, a problem in accuracy occurs. do not do.

  Furthermore, since the effective monochromatic photon energy of X-rays can be set to a desired value depending on the material and thickness of the filter 10 that is put on the tube 9 of the X-ray tube 5, the X-ray tube 5 of the X-ray CT apparatus 2 can be obtained. The tube voltage applied to can be arbitrarily set. For this reason, the convenience of PET-CT1 can be improved.

  In addition, you may abbreviate | omit a part of function and process of PET-CT1,1A in each above embodiment. For example, the effective single-color photon energy of X-rays may be obtained by calculation whenever necessary without being stored in a table format. Furthermore, the processing order of PET-CT1, 1A may be changed. For example, the X-ray effective monochromatic photon energy may be obtained by calculation by the X-ray effective monochromatic energy calculation system 4 after scanning by the PET apparatus 3. Further, for example, the order of attenuation correction and image reconstruction processing of the PET apparatus 3 may be changed. For this reason, the attenuation correction unit 18 and the image reconstruction unit 19 can process arbitrary data including intermediate data obtained from the γ-ray detection data detected by the γ-ray detector 16.

  Moreover, PET-CT which has both functions of PET-CT1, 1A can also be comprised.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram which shows 1st Embodiment of PET-CT which is a radiation diagnostic apparatus based on this invention. The PET-CT X-ray effective monochromatic energy calculation system shown in FIG. 1 calculates the effective monochromatic photon energy of X-rays by using the attenuation coefficient obtained based on the obtained effective monochromatic photon energy of X-rays. The flowchart which shows an example of the procedure at the time of carrying out attenuation correction | amendment of the reconstructed image obtained with the apparatus. The figure which shows an example of the photon energy spectrum of the X-ray inside the subject calculated | required by the X-ray effective monochromatic energy calculation system of PET-CT shown in FIG. The figure which shows an example of the effective monochromatic photon energy of the X-ray calculated | required by the X-ray effective monochromatic energy calculation system of PET-CT shown in FIG. 1, and preserve | saved in the table format. The block diagram which shows 2nd Embodiment of PET-CT which is a radiation diagnostic apparatus which concerns on this invention. The flowchart which shows an example of the procedure at the time of carrying out attenuation correction | amendment of the reconstructed image obtained by the PET apparatus by calculating | requiring an attenuation coefficient by PET-CT shown in FIG. The flowchart which shows an example of the procedure of preparation of the attenuation coefficient map in conventional PET-CT, and attenuation correction of a reconstructed image.

Explanation of symbols

1,1A PET-CT
2 X-ray CT apparatus 3 PET apparatus 4 X-ray effective monochromatic energy calculation system 5 X-ray tube 6 X-ray detector 7 X-ray detection data collection unit 8 X-ray detection data processing unit 9 Tube 10 Filter 11 Incident X-ray spectrum calculation Means 12 Scan target modeling means 13 In-system X-ray spectrum calculating means 14 In-system X-ray spectrum averaging means 15 X-ray effective monochromatic energy database 16 γ-ray detector 17 γ-ray detection data collecting section 18 Attenuation correcting section 19 Component 20 Monitor 30 Filter condition setting means P Subject

Claims (2)

The X-ray corresponding to the tube voltage from the X-ray tube is passed through a filter in which at least one of the material and the thickness is set so that the effective monochromatic photon energy of the X-ray inside the subject becomes a desired value. An X-ray CT apparatus for performing a CT scan for irradiating the subject and transmitting the subject and detecting a CT value of the subject from X-ray detection data detected by an X-ray detector; and the subject A nuclear medicine image is generated by detecting γ-rays emitted from a radioisotope administered to a gamma ray detector with a γ-ray detector and performing attenuation correction using the CT value on the obtained γ-ray detection data A radiation diagnostic apparatus comprising: a medical diagnostic apparatus, wherein the attenuation correction uses effective monochromatic photon energy of the X-ray having a desired value. When a CT scan is performed by an X-ray CT apparatus, a filter in which at least one of a material and a thickness is set so that an effective monochromatic photon energy of X-rays inside the subject becomes a desired value is used. A step of obtaining an attenuation coefficient for γ-rays from the CT value of the subject obtained by executing the CT scan and the effective monochromatic photon energy of the X-ray of the desired value, and a PET apparatus using the attenuation coefficient And a step of performing attenuation correction on the data obtained by the scan according to the above.

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