JP2015121407A - Nuclear medicine diagnosis device, image processing apparatus, and image processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nuclear medicine diagnosis device which properly applies an attenuation map, an image processing apparatus, and an image processing program.SOLUTION: A nuclear medicine diagnosis device includes: a map correction section which corrects displacement of an attenuation map with respect to a non-correction reconstructed image, by use of the non-correction reconstructed image formed by reconstructing projection data without correcting attenuation and the attenuation map; and an image reconstruction section which reconstructs the projection data by use of an attenuation map formed by correcting the displacement, to generate a reconstructed image with corrected attenuation.

Description

  Embodiments as one aspect of the present invention relate to a nuclear medicine diagnosis apparatus, an image processing apparatus, and an image processing program.

  Nuclear medicine diagnostic devices are distributed in the body using the property that drugs (blood flow markers, tracers) containing radioisotopes (RI) are selectively taken into specific tissues and organs in the body. This is a medical diagnostic imaging apparatus that detects gamma rays emitted from RI with a gamma ray detector disposed outside the living body. There are various types of nuclear medicine diagnosis apparatuses such as a SPECT (Single Photon Emission Computed Tomography) apparatus and a PET (Positron Emission Computed Tomography) apparatus. A nuclear medicine diagnostic apparatus generates a nuclear medicine image by imaging a dose distribution of detected gamma rays and is used for diagnosis of a function of a body organ or the like. For example, by using RI of an element accumulated in a specific organ such as a bone or a heart muscle (myocardium), the function of the organ can be examined. Unlike other modality devices such as X-ray CT (Computed Tomography) devices and MRI (Magnetic Resonance Imaging) devices, nuclear medicine diagnostic devices have inferior anatomical resolution, but blood flow measurement, metabolism, This is useful when examining functional information such as neurotransmitter activity.

  As described above, a nuclear medicine image is generated by detecting gamma rays emitted by RI accumulated in the body. However, gamma rays in the body are attenuated by the photoelectric effect and Compton scattering. The attenuation of gamma rays is expressed by an attenuation coefficient, and is greatly related to the atomic number of the RI used. The attenuation of gamma rays is expressed by Beer's law. For example, the ratio of 99mTc (technetium isotope) gamma rays often used in SPECT, which is detected by passing through a 5 cm thick water, has an attenuation coefficient of 0.15. Then, exp (−0.15 × 5) is obtained, and only 47% of the emitted gamma rays can be transmitted and detected. Since the human body can be considered as a water equivalent substance, many gamma rays will not be detected by absorption of the human body. As described above, the detection result of gamma rays includes the influence of attenuation in the living body. An attenuation coefficient map (hereinafter referred to as an attenuation map) showing the distribution of the attenuation coefficient of the gamma ray energy of the RI used is generated in a method often used as a method for correcting this kind of attenuation effect, and based on this attenuation map There is a method for correcting the detection result of gamma rays. According to this method, the influence of attenuation of gamma rays in the living body can be corrected (hereinafter referred to as attenuation correction). Attenuation correction using such an attenuation map is an essential process for reconstructing a nuclear medicine image with higher accuracy.

  Such an attenuation map raises the count number of gamma rays attenuated in the acquired projection data based on the attenuation coefficient specified in the attenuation map, and performs attenuation correction by bringing it closer to a true value ( For example, Patent Document 1).

  Such an attenuation map is roughly classified into a method of actually measuring the distribution of the attenuation coefficient by some method and a method of obtaining it simply by segmentation or the like. The former method includes a method of depicting the distribution of the attenuation coefficient in the body from the ratio of the X-ray dose transmitted using the X-ray CT apparatus, and a method of measuring the attenuation coefficient distribution of the γ-ray using an external γ-ray source. There is. The latter method does not perform X-ray CT, but obtains shape information from data such as scattered radiation when acquiring a nuclear medicine image and sets an average attenuation coefficient value, or MRI image or X-ray CT. There is a method of obtaining an organ outline from an image and setting an attenuation coefficient. In the case of the former, a more accurate attenuation map can be obtained than in the case of the latter, but the latter has the advantage of not costing.

  However, even if there is an attenuation map with high accuracy in the distribution of attenuation coefficients, accurate correction cannot be performed unless it can be applied to the correct position or range. In this way, a state where the attenuation map is not applied to the correct position or the correct range with respect to the SPECT or PET reconstructed image is simply referred to as a positional deviation.

  In a nuclear medicine diagnostic device, it takes several tens of minutes to obtain a sufficient number of counts, so it is difficult to avoid body movement of the subject during measurement. Misalignment is likely to occur in application.

  Therefore, a nuclear medicine diagnostic apparatus is provided that corrects body motion other than the body axis direction by generating estimated projection data when applying an attenuation map to projection data (for example, Patent Document 2).

Japanese Patent Laid-Open No. 2006-090752 JP 2006-250842 A

  As described above, misalignment is an important issue related to the accuracy of diagnosis in a nuclear medicine diagnostic apparatus. For example, when a tracer that accumulates in a tumor is used, the position of the attenuation map is misaligned by only a few millimeters. The location is not corrected correctly, and doctors may miss the findings. In addition, if the normal part becomes a high count or a low count in the reconstructed image as a result of the attenuation correction, it may cause a misdiagnosis.

  It is difficult for the attenuation map according to the shape and contour of the organ by segmentation technology or the like to set the boundary correctly due to the overlap of the organs. In particular, when the heart is observed in a cross section perpendicular to the body axis, it is difficult to determine the boundary because a part of the heart enters the lung field, and the attenuation map cannot be applied correctly in the overlapping area. There's a problem.

  Therefore, there is a demand for a nuclear medicine diagnostic apparatus, an image processing apparatus, and an image processing program that can correctly apply an attenuation map.

  The nuclear medicine diagnosis apparatus according to the present embodiment specifies a range that is a target of application correction of an attenuation map for the projection data, and an attenuation map according to the projection data of the target range. A correction unit that corrects an application range, an image reconstruction unit that generates an image by performing image reconstruction processing on the projection data in a state where the application range of the attenuation map is corrected, and the reconstructed image And a display unit for displaying.

The conceptual block diagram which shows an example of the nuclear medicine diagnostic apparatus which concerns on embodiment. The functional block diagram which shows the function structural example of the nuclear medicine diagnostic apparatus which concerns on embodiment. The figure explaining the problem in the conventional attenuation correction. The flowchart which shows an example of operation | movement of the nuclear medicine diagnostic apparatus which concerns on embodiment. The figure explaining the change of the superimposition ratio of the attenuation map in the nuclear medicine diagnostic apparatus which concerns on embodiment. The figure explaining the range designation | designated method in the nuclear medicine diagnostic apparatus which concerns on embodiment. The figure explaining the example of a display after range specification in the nuclear medicine diagnostic apparatus concerning an embodiment. The figure explaining the profile curve produced | generated in the position shift correction | amendment of the attenuation map in the nuclear medicine diagnostic apparatus which concerns on embodiment. The figure explaining the method of position shift amendment of the attenuation map in the nuclear medicine diagnostic device concerning an embodiment. The figure explaining the attenuation map after correction | amendment in the nuclear medicine diagnostic apparatus which concerns on embodiment.

  Embodiments of a nuclear medicine diagnosis apparatus, an image processing apparatus, and an image processing program according to the present invention will be described with reference to the accompanying drawings. The nuclear medicine diagnosis apparatus and image processing apparatus according to the present embodiment can be applied to various apparatuses including a gamma ray detector such as SPECT (Single Photon Emission Computed Tomography) and PET (Positron Emission Tomography). In the following description, an example in which a two-detector gamma ray detector rotating SPECT (Single Photon Emission Computed Tomography) apparatus is used as the nuclear medicine diagnostic apparatus according to the present invention will be described. In addition, as a gamma-ray detector rotation type SPECT apparatus, the number of detectors may be one, and two or more may be sufficient.

(1) Configuration FIG. 1 is a conceptual configuration diagram illustrating an example of a nuclear medicine diagnosis apparatus according to an embodiment. As shown in FIG. 1, the nuclear medicine diagnosis apparatus 1 mainly includes a scanner device 2 and an image processing device 3. The image processing apparatus 3 may be connected to the scanner apparatus 2 so as to be able to transmit and receive data, and may not be provided in the same room or building.

  The scanner device 2 includes gamma ray detection units 11 and 12, a gantry 14 having a rotation unit 13, a rotation drive device 15, and a data collection unit 16.

  The gamma ray detection unit 11 is a detection unit that detects gamma rays emitted from a radioisotope (RI) such as technesium administered to the subject P in a medicine. Since the gamma ray detection unit 12 has the same configuration and operation as the gamma ray detection unit 11, the description thereof is omitted.

  As the gamma ray detection unit 11, a scintillator type detector or a semiconductor type detector may be used.

  When the gamma ray detection unit 11 is configured using a scintillator type detector, the gamma ray detection unit 11 includes a collimator for defining an incident angle of the gamma ray, a scintillator that emits an instantaneous flash when the collimated gamma ray is incident, and a light A guide, a plurality of photomultiplier tubes arranged in a two-dimensional array for detecting light emitted from the scintillator, an electronic circuit for the scintillator, and the like. The scintillator is made of, for example, thallium activated sodium iodide NaI (Tl). The scintillator electronic circuit has information on the incident position of gamma rays in a detection plane constituted by a plurality of photomultiplier tubes based on the output of the plurality of photomultiplier tubes every time an event in which gamma rays are incident occurs. (Position information), incident intensity information, and incident time information are generated and output to the data collection unit 16. This position information may be information of two-dimensional coordinates in the detection surface, or the detection surface is virtually divided into a plurality of divided regions (primary cells) in advance (for example, divided into 1024 × 1024 pieces). In other words, it may be information indicating which primary cell is incident.

  On the other hand, when the gamma ray detection unit 11 is configured using a semiconductor detector, the gamma ray detection unit 11 includes a collimator and a plurality of gamma ray detection semiconductor elements (two-dimensionally arranged semiconductor elements for detecting collimated gamma rays). Hereinafter referred to as a semiconductor element) and a semiconductor electronic circuit. The semiconductor element is made of, for example, CdTe or CdZnTe (CZT). The semiconductor electronic circuit generates incident position information, incident intensity information, and incident time information based on the output of the semiconductor element and outputs the incident information to the data collecting unit 16 every time an event in which gamma rays are incident occurs. This position information is information indicating which semiconductor element is incident among a plurality of semiconductor elements (for example, 1024 × 1024). That is, the gamma ray detection unit 11 outputs incident position information, incident intensity information, and incident time information for each event. The position information is at least one of information indicating which position of the primary cell the gamma ray is incident on and information on the two-dimensional coordinates in the detection surface. In the following description, an example in which the gamma ray detection unit 11 outputs information indicating which position on the detection surface the gamma ray has entered as position information will be described.

  The gamma ray detection units 11 and 12 are controlled in imaging timing by the data collection unit 16.

  The rotation unit 13 is supported by the gantry 14 and holds the gamma ray detection units 11 and 12. The rotation unit 13 is controlled by the data collection unit 16 via the rotation driving device 15 and rotates around a predetermined rotation axis r (around the z axis), whereby the gamma ray detection units 11 and 12 rotate around the rotation axis r. To do.

  The rotation drive device 15 is controlled by the data collection unit 16 to rotate the rotation unit 13 around a predetermined rotation axis r (z axis).

  The subject P is placed on the top board 17. The top board drive device 18 is controlled by the data collection unit 16 to move the top board 17 up and down in the y-axis direction. In addition, the top plate driving device 18 is controlled by the data collection unit 16 to move the top plate 17 along the z-axis direction to the imaging region of the opening at the central portion of the rotation unit 13.

  The data collection unit 16 is controlled by the image processing device 3 to control the gamma ray detection units 11 and 12, the rotation drive device 15, and the top plate drive device 18, thereby executing the scan of the subject P. The data collection unit 16 collects the outputs of the gamma ray detection units 11 and 12 in a list mode, for example. In the list mode, gamma ray detection position information, intensity information, information indicating the relative positions of the gamma ray detection units 11 and 12 and the subject P (positions and angles of the gamma ray detection units 11 and 12), and gamma ray detection time include Collected for each incident event of gamma rays. The nuclear medicine image data collected in this way is called projection data.

  As illustrated in FIG. 1, the image processing apparatus 3 includes a control unit 21, a display unit 22, an input unit 23, and a storage unit 24. The image processing device 3 generates a nuclear medicine image reconstructed from the projection data.

  The control unit 21 includes a storage medium such as a CPU, a RAM and a ROM, and a hard disk, and controls the processing operation of the image processing apparatus 3 according to a program stored in the storage medium.

  The CPU of the control unit 21 loads an image processing program stored in a storage medium such as a ROM and a hard disk and data necessary for executing the program into the RAM, and corrects the displacement of the attenuation map according to the program. Etc. are executed.

  The RAM of the control unit 21 provides a work area for temporarily storing programs and data executed by the CPU. The storage medium such as the ROM of the control unit 21 stores a startup program for the image processing device 3, an image processing program, and various data necessary for executing these programs.

  A storage medium such as a ROM has a configuration including a recording medium readable by a CPU, such as a magnetic or optical recording medium or a semiconductor memory, and a part of programs and data in the storage medium. Or you may comprise so that all may be downloaded via an electronic network.

  The display unit 22 is configured by a general display output device such as a liquid crystal display or an OLED (Organic Light Emitting Diode) display, and displays various types of information such as a reconstructed image according to the control of the control unit 21.

  The input unit 23 includes a general input device such as a keyboard, a touch panel, and a numeric keypad, and outputs an operation input signal corresponding to a user operation to the control unit 21.

  The storage unit 24 has a configuration including a CPU-readable recording medium such as a magnetic or optical recording medium or a semiconductor memory, and part or all of the programs and data in the storage medium are stored in an electronic network. You may comprise so that it may be downloaded via. The storage unit 24 is controlled by the control unit 21 to store an attenuation map, a count value for each display pixel in the projection data, a nuclear medicine image, and the like.

  FIG. 2 is a functional block diagram illustrating a functional configuration example of the nuclear medicine diagnostic apparatus 1 according to the embodiment. As illustrated in FIG. 2, the nuclear medicine diagnosis apparatus 1 includes a data storage unit 241, a scan control unit 211, a superimposed image generation unit 212, a range specification unit 213, a map correction unit 214, and a reconstructed image generation unit 215. Among them, the scan control unit 211, the superimposed image generation unit 212, the range specification unit 213, the map correction unit 214, and the reconstructed image generation unit 215 are configured such that the program stored in the storage unit 24 is executed by the CPU of the control unit 21. Is a functional configuration realized by.

  The scan control unit 211 executes a scan by controlling the scanner device 2 based on the scan plan. As a result, information on gamma rays emitted from the subject P is given from the scanner device 2 to the data storage unit 241 via the data collection unit 16.

  The data storage unit 241 stores projection data, which is gamma ray information collected by the data collection unit 16, and an attenuation map indicating the distribution of attenuation coefficients of the gamma ray energy of the RI to be used. Attenuation map is a method of drawing the distribution of attenuation coefficient in the body from the ratio of X-ray dose transmitted using an X-ray CT apparatus, a method of measuring the attenuation coefficient distribution of γ-rays using an external γ-ray source, and a nuclear medicine image Various methods such as obtaining shape information from data such as scattered radiation when acquiring the image and setting an average attenuation coefficient value, or obtaining an organ contour from an MRI image or X-ray CT image and setting the attenuation coefficient Can be obtained by various methods. Therefore, the attenuation map may be stored in advance in the data storage unit 241, information on gamma rays collected by the scanner device 2, CT images or MRI images collected at the same time or different timing from the collection of nuclear medicine images, etc. From this, the control unit 21 of the image processing apparatus 3 may generate the program stored in the storage unit 24.

  The superimposed image generation unit 212 acquires a reconstructed image (hereinafter referred to as an uncorrected reconstructed image) reconstructed without applying an attenuation map to the projection data from the reconstructed image generation unit 215. Then, the uncorrected reconstructed image and the attenuation map acquired from the data storage unit 241 are superimposed to generate a superimposed image and displayed on the display unit 22. In the generation of the superimposed image, it is possible to variously change the overlapping ratio between the uncorrected reconstructed image and the attenuation map. By changing the overlay ratio of the uncorrected reconstructed image and the attenuation map, it is possible to generate a superimposed image that facilitates correction of the displacement of the attenuation map. The overlapping ratio may be set in advance or may be input from the input unit 23 including a mouse or a keyboard. The adjustment of the overlay ratio will be described later.

  The range designating unit 213 determines a range for correcting the displacement of the attenuation map from the superimposed image displayed on the display unit 22. An uncorrected reconstructed image obtained by reconstructing projection data acquired by the nuclear medicine diagnostic apparatus 1 is composed of a plurality of slice image data. The range designation unit 213 selects one piece of slice image data from among a plurality of slice image data, and designates a range in which attenuation map correction is performed for the selected slice image. The range to be corrected is input from the input unit 23. A range designation method by the range designation unit 213 will be described later.

  The map correction unit 214 compares the count number distribution of the uncorrected reconstructed image with the attenuation coefficient distribution of the attenuation map in the designated range of the superimposed image, and the attenuation map distribution of the attenuation map is uncorrected. The position shift of the attenuation map is corrected so as to appropriately match the distribution of the count number of the reconstructed image. A method of correcting the displacement of the attenuation map by the map correction unit 214 will be described later.

  The reconstructed image generation unit 215 generates a nuclear medicine image reconstructed from the projection data. The reconstructed image generation unit 215 reconstructed the projection data by applying the uncorrected reconstructed image obtained by reconstructing the projection data without applying the attenuation map and the attenuation map subjected to the positional deviation correction. A corrected reconstructed image is generated.

(2) Operation FIG. 3 is a diagram for explaining a problem in the conventional attenuation correction. FIG. 3A is a view of the chest as viewed from the front, and the heart is observed at the upper right of FIG. FIG. 3B shows a reconstructed image in the cross section of the solid line A shown in FIG. FIG. 3C shows an attenuation map corresponding to the cross section shown in FIG. FIG. 3B is an uncorrected reconstructed image obtained by reconstructing projection data without applying the attenuation map as shown in FIG. FIG. 3C is an attenuation map that is not subjected to positional deviation correction. FIG. 3D shows a reconstructed image obtained by performing image reconstruction processing by applying the attenuation map of FIG. 3C to the projection data corresponding to the uncorrected reconstructed image of FIG. Show. The reconstructed image shown in FIG. 3A is composed of a plurality of slice images, and an attenuation map also exists corresponding to the slice image of the reconstructed image. Attenuation correction is performed using the attenuation map corresponding to the projection data of the corresponding slice, and the image illustrated in FIG. 3D is generated by the reconstruction process.

  In the uncorrected reconstructed image of FIG. 3B, the dark color indicates a high accumulation of gamma rays. As shown in FIG. 3B, in the nuclear medicine examination in the heart, a large amount of RI as a tracer is taken into the myocardium, so that high count accumulation is observed at the position where the myocardium is present. In a nuclear medicine examination, it can be determined that ischemia or infarction has occurred at a location where tracer uptake is poor, that is, where the gamma ray count is low. The reconstructed image shown in FIG. 3B shows an example of a nuclear medicine image in a normal heart.

  The contour of the heart is shown in the attenuation map of FIG. The attenuation map of FIG. 3C shows an example in which the range indicated by the contour defines the shape, position or range of the heart, and the attenuation coefficient of the heart is distributed in this range. That is, when the attenuation map illustrated in FIG. 3C is applied to the projection data of the uncorrected reconstructed image shown in FIG. 3B, the counts present in the range surrounded by the contour in FIG. Although the attenuation correction is properly performed, the heart attenuation correction is not properly performed for the count out of the contour.

  FIG. 3D is a reconstructed image generated using the attenuation map illustrated in FIG. In FIG. 3D, the heart reconstructed image is distorted at the position indicated by the arrow B, as compared with the uncorrected reconstructed image shown in FIG. This is because there is a positional deviation between the range defined as the contour of the heart in FIG. 3C and the range in which the heart counts are accumulated in FIG.

  As illustrated in FIG. 3D, when the reconstruction process is performed using the attenuation map in which the positional deviation illustrated in FIG. 3C occurs, a reconstructed image having an incorrect RI distribution is generated. The As described above, the RI distribution in the nuclear medicine image of the heart is a criterion for determining whether an abnormality such as ischemia or infarction has occurred in the myocardium. Therefore, as illustrated in FIG. 3D, if the attenuation map is not applied to a part of the myocardium and the reconstructed image is generated without being accurately corrected, a misdiagnosis may occur. That is, due to the distortion generated in the reconstructed image of the heart, for example, if the myocardium is normal, the number of counts decreases at locations showing a high count, making it difficult to make a correct judgment in diagnosis.

  The positional deviation as shown in FIG. 3D is caused by factors such as the body movement of the subject P due to the long imaging time of the nuclear medicine image being several tens of minutes, or the contour extraction of the organ cannot be accurately performed. Occur. In particular, the heart is close to other organs such as the lung and liver, and it is difficult to extract the correct contour. As an attenuation map creation method, there is a method of acquiring anatomical form information using an X-ray CT apparatus or the like. However, it is difficult to perform alignment correctly by the above-described body movement of the subject. Further, in the method of obtaining the attenuation map from the scattered radiation at the time of acquiring the nuclear medicine image, there is a large error in the morphological information and the accurate movement of the organ due to the body movement of the subject P at the time of acquiring the nuclear medicine image. It is difficult to extract a simple contour.

  In addition, the data acquired by the nuclear medicine diagnosis apparatus 1 is volume data composed of a plurality of slice image data, and the uncorrected reconstructed image shown in FIG. 3B is one of them. Since attenuation maps corresponding to the slice image data exist, misalignment occurs for all slice images, and a reconstructed image having an incorrect RI distribution is generated.

  The nuclear medicine diagnosis apparatus 1 according to the present invention automatically resolves a state where such an attenuation map is not correctly applied.

  FIG. 4 is a flowchart illustrating an example of the operation of the nuclear medicine diagnostic apparatus 1 according to the embodiment.

  In ST101, the reconstructed image generation unit 215 generates an uncorrected reconstructed image that has not been corrected by the attenuation map, from the projection data stored in the data storage unit 241.

  In ST103, the superimposed image generation unit 212 generates a superimposed image obtained by superimposing the attenuation map before the positional deviation correction stored in the data storage unit 241 and the uncorrected reconstructed image generated by the reconstructed image generation unit 215. . The superimposed image generation unit 212 generates a superimposed image in which the overlapping ratio between the attenuation map before the positional deviation correction and the projection data is variously changed.

  In ST105, the display unit 22 displays a superimposed image. The display unit 22 displays an uncorrected reconstructed image, an attenuation map before misalignment correction, and the like together with the superimposed image.

  FIG. 5 is a diagram illustrating a change in the overlay ratio of the attenuation map in the nuclear medicine diagnosis apparatus 1 according to the embodiment. In FIG. 5A, the left figure shows the attenuation map before the positional deviation correction, and the right figure shows the uncorrected reconstructed image. When the superimposed image generation unit 212 generates a superimposed image obtained by superimposing the attenuation map before the positional deviation correction and the non-corrected reconstructed image, the positional deviation of the attenuation map is made clearer by adjusting the superposition ratio. A distinguishable superimposed image can be generated.

  FIG. 5B and FIG. 5C show examples of superimposed images obtained by adjusting Map Display Weight. A bar graph showing Map Display Weight is shown at the bottom of the superimposed image. Map Display Weight indicates a mixing ratio when the superimposed image generation unit 212 superimposes the uncorrected reconstructed image and the attenuation map before the position shift correction.

  FIG. 5B shows an example in which the map display weight is “1.5”. That is, an example is shown in which the ratio of the uncorrected reconstructed image is higher than the attenuation map before the positional deviation correction. On the other hand, FIG. 5C shows an example in which the map display weight is “0.5”. That is, an example is shown in which the ratio of the attenuation map before the positional deviation correction is higher than that of the uncorrected reconstructed image. As described above, when the ratio of the uncorrected reconstructed image is increased, the image count of the portion indicating the myocardium is displayed large as shown in FIG. 5B, and when the ratio of the attenuation map before the positional deviation correction is increased, As shown in FIG. 5C, the image count indicating the myocardium is displayed small. That is, FIG. 5B with a high ratio of the uncorrected reconstructed image is a superimposed image close to the right figure of FIG. 5A showing the uncorrected reconstructed image, but the ratio of the attenuation map before the positional deviation correction is high. FIG. 5C shows a superimposed image close to the left diagram of FIG. 5A showing the attenuation map before the positional deviation correction.

  As described above, the superimposed image generation unit 212 adjusts the mixing ratio of the respective data to be superimposed, thereby changing the display of the superimposed image in various ways so that it is easy to determine whether or not a positional deviation has occurred in attenuation correction and where it occurs. Can be generated. Such an adjustment may be performed by displaying an image as illustrated in FIG. 5B on the display unit 22 and adjusting the indicator shown in the bar graph indicating the Map Display Weight via the input unit 23. Alternatively, it may be performed by arranging superimposed images whose mixing ratios have been adjusted at predetermined intervals and displaying them on the display unit 22. The superimposed image generation unit 212 generates a superimposed image that can clearly determine the positional deviation of the attenuation map by superimposing the uncorrected reconstructed image and the attenuation map before the positional deviation correction with a certain mixing ratio and performing reconstruction processing. Is done.

  In ST107 of FIG. 4, a slice image for which a range is designated is determined from the superimposed images displayed on the display unit 22.

  In ST109, based on the content input from the input unit 23, the range specifying unit 213 sets a slice range for specifying the range. In addition, a region of interest (ROI) is set for the slice image for which the range is specified by the range specification.

  FIG. 6 is a diagram for explaining a range specifying method in the nuclear medicine diagnosis apparatus 1 according to the embodiment. FIG. 6A shows a nuclear medicine image in which the chest is observed from the front as in FIG. The nuclear medicine image includes a plurality of slice image data. When heart attenuation correction is performed, slice image data included in a region sandwiched between alternate long and short dash lines shown in FIG. As shown in the left diagram of FIG. 6B, the display unit 22 displays a plurality of slice images side by side. Each image is a superimposed image as shown in the right diagram of FIG. The superimposed image generation unit 212 creates a superimposed image for a plurality of slice image data included in the heart region, and displays it on the display unit 22. The range designation unit 213 selects one slice image from the superimposed images of the slice range to be corrected displayed in this way, and a range in which attenuation map position shift correction is performed on the selected slice image is a rectangular ROI. specify.

  The right view of FIG. 6B shows a ROI surrounded by a rectangle in a portion where the heart count is observed. As illustrated in the right diagram of FIG. 6B, the range designating unit 213 sets a portion surrounded by a rectangular shape as a range for correcting the displacement of the attenuation map. This range designation is set by, for example, inputting information selected by the user using an input device such as a mouse from the input unit 23 based on the slice image displayed on the display unit 22. For the area designated as a range, a rectangular frame may be displayed on the slice image as illustrated in FIG.

  FIG. 7 is a diagram for explaining a display example after range designation in the nuclear medicine diagnosis apparatus 1 according to the embodiment. FIG. 7 shows an example in which a plurality of slice images of the chest shown in FIG. 6A are displayed in order from the upper left to the lower right. A slice image indicated by a thick frame in the upper right of FIG. 7 is a selected slice. In the selected slice, a rectangular ROI designated by the range designation unit 213 is displayed by a one-dot chain line. A frame indicated by a broken line indicates a selected slice range, and the range designation is performed using a slice image in which the myocardium is observed most greatly among the selected slice ranges as a selected slice.

  As illustrated in FIG. 7, the rectangular ROI set in the selected slice indicated by the thick frame in the upper right is automatically set in all the slice images in the selected slice range. In FIG. 7, the automatically set ROI is indicated by a two-dot chain line. The ROI that is automatically set in this way is selected from the slice images in which the selected slice is included in the slice range, so that the myocardium is included in the ROI also in other slice images by selecting the slice in which the myocardium is observed most greatly. To be set. If the position and size of the ROI specified by the range specifying unit 213 does not match in other slice images, a slice image that does not match the position or size is selected, and the position of the ROI or the ROI specified according to the input from the input unit 23 The size can be corrected as appropriate.

  In ST111 of FIG. 4, the map correction unit 214 detects the displacement of the attenuation map for the area designated in the range and performs correction. In the attenuation map misalignment correction, the map correction unit 214 generates a profile curve relating to the distribution of the number of counts of the uncorrected reconstructed image and the distribution of the attenuation map for the region designated in the range. If the displacement map correction is performed so that the profile curve related to the distribution of the attenuation map includes the profile curve related to the distribution of the count number of the uncorrected reconstructed image, the attenuation correction is performed for all the counts of the uncorrected reconstructed image. It will be.

  In ST113, the projection data is reconstructed in a state in which the image reconstructed image 215 has corrected the position shift of the attenuation map by the map correcting unit 214, and a reconstructed image after correction is generated.

  In ST115, the display unit 22 displays the reconstructed image after correction.

  FIG. 8 is a diagram for explaining a profile curve generated in the position correction of the attenuation map in the nuclear medicine diagnosis apparatus 1 according to the embodiment. FIG. 8A is an image similar to the superimposed image shown in FIG. FIG. 8B is an uncorrected reconstructed image superimposed on the superimposed image of FIG. 8A, and FIG. 8C is a misalignment correction superimposed on the superimposed image of FIG. 8A. It is the previous attenuation map. Each of FIG. 8A to FIG. 8C shows a rectangular ROI and an arrow C. The ROI is an area specified by the range specifying unit 213 described with reference to FIG.

  FIG. 8D shows a profile curve corresponding to the position of the arrow C in the uncorrected reconstructed image in FIG. 8B and the attenuation map in FIG. In the profile curve of FIG. 8D, the vertical axis represents the pixel value, and the horizontal axis represents the distance of the arrow C. The pixel value indicates the RI count number and the attenuation coefficient stored for each pixel of the uncorrected reconstructed image and the attenuation map before the positional deviation correction. The solid line indicates the profile curve of the attenuation map before the positional deviation correction, and the broken line indicates the profile curve of the uncorrected reconstructed image.

  In FIG. 8A, as in FIG. 6B and the like, there is a positional shift between the position of the heart in the uncorrected reconstructed image and the position of the heart in the attenuation map. Therefore, also in the profile curve shown in FIG. 8D, a positional deviation occurs between the uncorrected reconstructed image and the attenuation map. In the profile curve shown in FIG. 8D, the region indicated by the profile curve of the uncorrected reconstructed image is the region G, the region indicated by the arrow D, and the region indicated by the profile curve of the attenuation map in the range indicated by the arrow E, respectively. In the attenuation map, the region D indicates a range where the attenuation coefficient of the heart shows an appropriate value, and the region E shows a range where the attenuation coefficient of the heart shows an inappropriate value. The discrepancy between the region G and the region D is due to the displacement of the attenuation map.

  As a result, in region D in FIG. 8D, an appropriate attenuation coefficient (almost flat attenuation coefficient) is applied to the count of the heart in the uncorrected reconstructed image, whereas in region E, An inappropriate attenuation coefficient (coefficient that excessively attenuates) is applied to the count in the uncorrected reconstructed image. Therefore, if the projection data is reconstructed using the attenuation map (that is, the attenuation map that is not corrected for positional deviation), a reconstructed image in which the heart region corresponding to the region E is excessively attenuated may be generated. become. Therefore, in the nuclear medicine diagnosis apparatus 1 according to the embodiment, the positional deviation correction described below is performed on the attenuation map.

  FIG. 9 is a diagram for explaining a method for correcting the displacement of the attenuation map in the nuclear medicine diagnosis apparatus 1 according to the embodiment. FIG. 9A is the same as the profile curve of FIG. As described with reference to FIG. 8, attenuation correction is not correctly applied to the range indicated by the arrow E due to the displacement of the attenuation map.

  FIG. 9B shows an example in which the map correction unit 214 corrects the profile curve of the attenuation map according to the count of uncorrected reconstructed images. In FIG. 9B, the profile curve indicated by the alternate long and short dash line indicates the profile curve of the attenuation map after the positional deviation correction. The profile curve of the attenuation map after the misalignment correction shown in FIG. 9B covers the profile curve of the uncorrected reconstructed image at the portion indicated by the arrow E. In FIG. An example is shown in which attenuation correction is performed for a range that has not been applied correctly.

  As described above, the map correction unit 214 corrects the profile curve of the attenuation map so that the profile curve of the attenuation map covers the profile curve of the uncorrected reconstructed image. The attenuation map profile curve may be corrected by, for example, correcting the attenuation map profile curve so that the count number in the profile curve of the uncorrected reconstructed image is greater than or equal to a threshold value, or uncorrected. For example, in the graph of FIG. 9B, attenuation is performed so that the falling portion of the attenuation map covers the falling portion of the profile curve of the uncorrected reconstructed image with reference to the falling portion of the profile curve of the reconstructed image. You may correct | amend so that the falling part of a map may be located in the right side of the profile curve of an uncorrected reconstruction image. The attenuation map may be corrected by extending the upper flat part of the attenuation map profile curve, or by interpolating the extension part with the data immediately before the falling edge of the attenuation map profile curve. You may carry out by shifting the position of a falling part.

  In this way, the map correction unit 214 automatically performs correction so that the profile curve of the attenuation map overlaps the profile curve of the uncorrected reconstructed image. Such correction is performed not only on the slice image with the range specified in FIG. 9 but also on other slice images. At this time, the correction is performed so that the profile curve of the uncorrected reconstructed image overlaps the profile curve of the attenuation map in the same manner for the other slice images.

  Further, the map correction unit 214 moves the position of a part of the profile curve of the attenuation map when correcting the displacement of the profile curve of the attenuation map. As shown in FIG. 9B, the map correction unit 214 calculates the position where the profile curve is moved, for example, as a distance, as indicated by an arrow F, thereby causing a position generated in the attenuation map of another slice image. The displacement may be calculated as a numerical value to correct the displacement.

  FIG. 10 is a diagram for explaining a corrected attenuation map in the nuclear medicine diagnosis apparatus 1 according to the embodiment. FIG. 10A illustrates an attenuation map before misalignment correction illustrated in FIG. FIG. 10B shows a corrected attenuation map obtained by correcting the attenuation map shown in FIG. 8C and the like based on the profile curve shown in FIG.

  FIG. 10B is expanded in the direction of arrow F compared to the attenuation map shown in FIG. An arrow F indicates a portion obtained by extending the profile curve of the attenuation map in order to correct the position shift of the attenuation map in FIG. 9B. In this way, the influence of the positional deviation can be reduced by extending the attenuation map by the amount of the arrow F indicating the positional deviation of the attenuation map.

  This misalignment correction can be relatively corrected by converting the misalignment indicated by the arrow F from the slice position for all other slices for which the ROI is set. If such a method is taken, the correction process based on the profile curve can be omitted, and the positional deviation can be easily corrected for all the slice images.

  Collecting images in the nuclear medicine diagnostic apparatus takes time, and it is difficult to align the attenuation map in the reconstructed image due to the body movement of the subject P. Attenuation map misalignment is noticeable in just a few pixels, leading to missed findings and misdiagnosis. The nuclear medicine diagnosis apparatus, the image processing apparatus, and the image processing program according to the present invention generate a superimposed image, and the position shift of the attenuation map in the superimposed image is semi-automatically according to the count number distribution of the uncorrected reconstructed image. Can be corrected. As described above, since the position shift of the attenuation map can be automatically corrected for a plurality of slice images, it is possible to avoid misdiagnosis and oversight of findings in diagnosis and interpretation, and to perform diagnosis with higher accuracy. Moreover, since the position shift of the attenuation map can be automatically corrected, the time for image interpretation can be greatly shortened.

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

DESCRIPTION OF SYMBOLS 1 Nuclear medicine diagnostic apparatus 2 Scanner apparatus 3 Image processing apparatus 11, 12 Gamma ray detection part 13 Rotation part 14 Gantry 15 Rotation drive apparatus 16 Data collection part 17 Top board 18 Top board drive apparatus 21 Control part 22 Display part 23 Input part 24 Memory | storage Unit 211 scan control unit 212 superimposed image generation unit 213 range designation unit 214 map correction unit 215 reconstructed image generation unit 241 data storage unit

Claims (10)

A map correction unit that corrects a positional shift of the attenuation map with respect to the uncorrected reconstructed image using an uncorrected reconstructed image obtained by reconstructing projection data without attenuation correction, and an attenuation map;
An image reconstruction unit that reconstructs the projection data using an attenuation map after correction in which the positional deviation is corrected, and generates a reconstructed image that has been corrected for attenuation.
A nuclear medicine diagnostic apparatus comprising: A superimposed image generating unit that generates a superimposed image by superimposing the uncorrected reconstructed image and the attenuation map;
A display unit for displaying the superimposed image;
A range designating unit for designating a range to be subjected to the misalignment correction for the superimposed image displayed on the display unit when performing the misalignment correction of the attenuation map with respect to the uncorrected reconstructed image;
Further provided,
The nuclear medicine diagnosis apparatus according to claim 1. The map correction unit is configured to change an application range of the attenuation map according to a distribution threshold of the count number of the uncorrected reconstructed image;
The nuclear medicine diagnostic apparatus according to claim 1, wherein The map correction unit changes the application range of the attenuation map according to the distribution of the count number of the uncorrected reconstructed image and the distribution of the attenuation coefficient of the attenuation map.
The nuclear medicine diagnosis apparatus according to any one of claims 1 to 3. The map correction unit compares the distribution of the count number of the uncorrected reconstructed image in the target range with the distribution of the attenuation coefficient of the attenuation map, and the distribution of the attenuation coefficient of the attenuation map is the target Changing the application range to interpolate the distribution of the uncorrected reconstructed image in the range to be
The nuclear medicine diagnosis apparatus according to claim 3 or 4, wherein The uncorrected reconstructed image is composed of a plurality of slice image data,
The map correction unit applies the change of the application range of the attenuation map to all of the plurality of slice image data;
The nuclear medicine diagnostic apparatus according to claim 1, wherein: The projection data is composed of a plurality of slice image data,
The map correction unit applies a change in an application range of the attenuation map to a part of the slice image data selected from the plurality of slice image data;
The nuclear medicine diagnostic apparatus according to claim 1, wherein: The map correction unit detects a positional shift between the uncorrected reconstructed image and the attenuation map based on one slice image data in which the target range is specified, and based on the positional shift, Correcting the position shift of the attenuation map for the slice image data of
The nuclear medicine diagnosis apparatus according to claim 6 or 7, wherein A map correction unit that corrects a positional shift of the attenuation map with respect to the uncorrected reconstructed image using an uncorrected reconstructed image obtained by reconstructing projection data without attenuation correction, and an attenuation map;
An image reconstruction unit that reconstructs the projection data using an attenuation map after correction in which the positional deviation is corrected, and generates a reconstructed image that has been corrected for attenuation.
An image processing apparatus. Computer
Means for correcting a positional shift of the attenuation map with respect to the uncorrected reconstructed image using an uncorrected reconstructed image obtained by reconstructing projection data without attenuation correction and an attenuation map;
Means for reconstructing the projection data using an attenuation map after correction in which the positional deviation is corrected, and generating a reconstructed image with attenuation correction;
Image processing program to function as