JP2009025035A - Nuclear medicine imaging apparatus and method for generating nuclear medicine image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely apply an attenuation correction to a moving part such as a diaphragm or the like in the attenuation correction of a PET image using a CT image. <P>SOLUTION: A table generating unit 422 of a correction table generating section 42 generates a correction table based on a weight which is specified by a user so as to approximate a weighted average CT image to a reference image for each CT image around the diaphragm. In a correction processing section 44, a weighted average processing unit 442 applies a weighted average process to the CT image around the diaphragm by using the weight defined in the correction table, and an attenuation map generating unit 443 generates an attenuation map by using the weighted average CT image, and a reconstructing unit 444 applies the attenuation correction to the PET image by using the attenuation map. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nuclear medicine imaging apparatus and a nuclear medicine image for imaging a radioisotope distribution in a subject by detecting γ-rays emitted from the subject administered with a drug labeled with a radioisotope. It relates to the creation method.

  Medical image diagnosis using an X-ray diagnostic apparatus, an MRI apparatus, an X-ray CT apparatus, a nuclear medicine imaging apparatus, etc. has made rapid progress along with the development of computer technology and has become indispensable in today's medical care. Yes.

  The above-mentioned X-ray diagnostic apparatus and X-ray CT apparatus are intended for so-called morphological diagnosis in which an outline of an organ, tumor, etc. is drawn, whereas a nuclear medicine imaging apparatus is selected as a living tissue. Γ-rays emitted from an isotope or its labeled compound taken in automatically are measured from outside the body, and the count (or numerical value) distribution is imaged to enable functional diagnosis on the subject.

  As this nuclear medicine imaging apparatus, a gamma camera, a single photon emission CT apparatus (SPECT apparatus), a positron emission CT apparatus (PET apparatus) and the like are used in clinical settings (for example, see Patent Document 1).

  The gamma camera measures the γ-rays emitted from within the subject using a flat detector placed facing the subject, thereby providing a two-dimensional image of the radioisotope distribution projected on the flat detector. The incident direction of γ rays is specified by a collimator attached to the front surface of the flat detector.

  In addition, the SPECT apparatus moves a flat detector similar to a gamma camera around a subject or arranges a plurality of flat detectors, and X-ray CT based on γ-ray information detected from a plurality of directions with respect to the subject. Image data is generated by performing a reconstruction process similar to that of the apparatus.

  On the other hand, a PET device administers a drug labeled with a nuclide that emits positrons (positrons) to a subject, and when the positrons combine with electrons and disappear, they emit a pair of 511 keV γ rays that are emitted in substantially opposite directions. For example, detection is performed by a ring-shaped detector disposed around the subject, and image data is generated by reconstructing the γ-ray information.

  In addition, by combining an X-ray CT apparatus and a PET apparatus, a PET / CT apparatus suitable for fusion of a morphological image created by the X-ray CT apparatus and a functional image created by the PET apparatus is also used.

JP 2007-107995 A

  In the PET apparatus and the PET / CT apparatus, it is necessary to correct the attenuation of γ rays generated in the subject. FIG. 10 is a diagram illustrating an example of PET images before and after attenuation correction. As shown in the figure, attenuation correction is indispensable because PET images differ greatly before and after attenuation correction. The SPECT / CT apparatus has the same problem.

  The attenuation correction includes a method using attenuation data collected by transmission scanning and a method using CT images. The attenuation correction using the CT image has an advantage that the inspection time is shortened and the accuracy of the attenuation map value is improved as compared with the case where attenuation data is collected by transmission scanning.

  However, the attenuation correction using the CT image has a problem that the SUV (Standardized Uptake Value) value greatly fluctuates in a moving part such as the periphery of the diaphragm whose position changes due to respiration.

  The present invention has been made to solve the above-mentioned problems caused by the prior art, and provides a nuclear medicine imaging apparatus and a nuclear medicine image creation method capable of accurately performing attenuation correction of a moving part such as the periphery of the diaphragm. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, the present invention according to claim 1 is a nuclear medicine imaging apparatus that performs attenuation correction of a nuclear medicine image using a CT image. Attenuation map creating means for creating an attenuation map using a CT image at the same position and a CT image obtained by weighted averaging of CT images before and after the CT image, and nuclear medicine using the attenuation map created by the attenuation map creating means An attenuation correction unit that performs image attenuation correction is provided.

  According to a seventh aspect of the present invention, there is provided a nuclear medicine image creation method for performing attenuation correction of a nuclear medicine image using a CT image, the CT image at the same position as the nuclear medicine image to be generated, and the CT image An attenuation map creating step for creating an attenuation map using a CT image obtained by weighted averaging of preceding and succeeding CT images; an attenuation correcting step for performing attenuation correction of a nuclear medicine image using the attenuation map created by the attenuation map creating step; It is characterized by including.

  According to the first or seventh aspect of the present invention, it is possible to improve the accuracy of the SUV value of a nuclear medicine image of a moving part such as the vicinity of the diaphragm.

  Exemplary embodiments of a nuclear medicine imaging apparatus and a nuclear medicine image creation method according to the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the case where the present invention is applied to a PET / CT apparatus will be mainly described. In the present embodiment, the description will focus on a case where attenuation correction is performed on a PET image near the diaphragm.

  First, the configuration of the PET / CT apparatus according to the present embodiment will be described. FIG. 1 is an explanatory diagram for explaining the configuration of the PET / CT apparatus according to the present embodiment. As shown in the figure, the PET / CT apparatus includes a PET scanner 1, a CT scanner 2, a bed 3, a data processing device 4, and a display device 5. Although not shown in FIG. 1, this PET / CT apparatus has buttons, a keyboard, and the like for the user to input instructions to the PET / CT apparatus.

  The PET scanner 1 is obtained by detecting a pair of γ-rays sequentially emitted from a diagnosis site of a patient in a predetermined monitoring period using a plurality of detector modules provided in a ring-shaped data detection unit. This is an apparatus that generates projection data based on a count value of γ rays in correspondence with a γ ray detection position and a γ ray incident direction in a detector module.

  The CT scanner 2 includes an X-ray generator that generates X-rays and a detector that detects X-rays. The patient is irradiated with X-rays generated by the X-ray generator, and X-rays transmitted through the patient are detected by the detector. An apparatus that detects and generates projection data.

  The bed 3 is a bed on which a patient is placed. The data processing device 4 is a device that processes the projection data generated by the PET scanner 1 and the CT scanner 2 to generate a PET image and a CT image, and displays them on the display device 5.

  FIG. 2 is a functional block diagram showing the configuration of the data processing device 4. As shown in the figure, the data processing device 4 includes a CT image storage unit 41, a correction table creation unit 42, a correction table storage unit 43, a correction processing unit 44, an input reception unit 45, and a PET image storage. Part 46.

  The CT image storage unit 41 is a storage unit that stores a CT image created from projection data generated by the CT scanner 2. The CT image storage unit 41 stores respiratory synchronous CT images and asynchronous CT images near various patient diaphragms as CT images for creating a correction table, which will be described later, and is used for correction of attenuation of PET images. Store asynchronous CT images.

  The correction table creation unit 42 is a processing unit that creates a correction table that defines weights for creating an attenuation map used when the correction processing unit 44 performs attenuation correction. The correction table creation unit 42 includes a comparison image display unit 421 and a table creation unit. 422.

  The comparative image display unit 421 is a processing unit that performs a weight definition process for defining a weight for creating an attenuation map. FIG. 3 is an explanatory diagram for explaining the weight definition processing by the comparative image display unit 421 for the diaphragm.

  As shown in FIG. 5A, the comparative image display unit 421 sets and displays a cursor at the position of the diaphragm on the whole body CT coronal image. Further, the respiratory synchronization CT image at that position is displayed as a reference image. Here, the respiratory-synchronized CT image is an image in which the movement of the diaphragm due to respiration is small. Then, the comparison image display unit 421 displays the CT images of N slices before and after the position of the cursor as shown in FIG. Note that N is a number that can be specified by the user, and in this example, N = 3. The reference uses the sum of all synchronized slices of respiratory synchronized CT.

  When the user designates the weight of the CT image of each slice, the comparison image display unit 421 creates and displays a weighted average CT image obtained by weighted averaging the CT images of each slice with the weight designated by the user. Here, the user designates the weight so that the weighted average CT image is close to the reference image. In this example, the user designates a weight of “1: 2: 1” for a CT image of three slices.

  In this way, the comparison image display unit 421 displays the CT images of N slices before and after the center of the cursor position and the CT images obtained by weighted averaging the CT images with the weights specified by the user, thereby allowing the user to perform a reference. A weight for obtaining a CT image closest to the image can be defined. The definition of the weight by the user is performed not only for the slices of the diaphragm but also for the M slices before and after the diaphragm. Here, M is a number designated by the user. Moreover, the definition of the weight by the user is classified into a plurality based on the patient's body type, age, and sex.

  Here, the respiratory synchronization CT image is used as the reference image, but a transmission image can be used instead of the respiratory synchronization CT image. Here, the user selects the weighted average CT image closest to the reference image. However, the comparison image display unit 421 may specify the weighted average CT image closest to the reference image.

  FIG. 4 is an explanatory diagram for explaining a method in which the comparative image display unit 421 specifies the weighted average CT image closest to the reference image. As shown in the figure, the ROI (Region of Interest) is taken at the same location of the reference image and the weighted average CT image, and the pixel value in the ROI is compared to identify the weighted average CT image closest to the reference image. it can.

  However, when the reference image is a transmission image, the absolute value of the pixel value cannot be compared, so the pixel value is compared with a relative value based on one pixel value in the ROI. Alternatively, the weighted average CT image closest to the reference image can be specified together with the user's selection. In addition, the comparison result of the pixel value can be displayed and the user can select it.

  Returning to FIG. 2, the table creation unit 422 is a processing unit that creates a correction table using the weights defined by the weight definition processing by the comparison image display unit 421 and writes the correction table in the correction table storage unit 43.

  The correction table storage unit 43 is a storage unit that stores the correction table created by the table creation unit 422. The correction table storage unit 43 stores a plurality of correction tables defining weights for M slices based on the patient's body type, age, sex, and the like.

  FIG. 5 is a diagram illustrating an example of a correction table stored in the correction table storage unit 43. As shown in the figure, this correction table includes a label indicating the patient's body type, age, and gender, the number of tables indicating the number of tables defining weight (M), and the number of CT images used for the weighted average. The number of frames (N) to be shown and the weight of each slice are defined.

  The correction table in FIG. 5 defines the weights of obese boys from the age of 20 to 24, three tables are defined, the number of CT images used for the weighted average is 5, and for each slice, Five weights are defined. In FIG. 5, “Slice 2” is a correction table centered on the slice at the cursor position (diaphragm position), and “Slice 1” is a correction table centered on the slice immediately before the cursor position. , “Slice 3” is a correction table centered on the slice immediately after the cursor position.

  Here, only the weight is defined in the correction table. However, depending on the part, it may be more appropriate to obtain the weighted average by enlarging / reducing or translating the CT image. It is also possible to define a rate and a translation amount.

  The correction processing unit 44 is a processing unit that performs attenuation correction of the PET image using the correction table stored in the correction table storage unit 43, and includes a confirmation image display unit 441, a weighted average processing unit 442, and an attenuation map creation unit 443. And a reconfiguration unit 444.

  The confirmation image display unit 441 is a processing unit that displays a confirmation image to the user regarding attenuation correction. FIG. 6 is an explanatory diagram for explaining an image displayed by the confirmation image display unit 441. As shown in the figure, the confirmation image display unit 441 displays the set position of the cursor at the position of the diaphragm on the whole body CT coronal image. In addition, a cursor is set at the same position and displayed for a PET coronal image (without attenuation correction). Further, a CT image and a PET image at the diaphragm position are displayed. In addition to the image shown in FIG. 6, the confirmation image display unit 441 also displays a weighted average CT image using the weights defined in the correction table and a PET image after attenuation correction.

  The weighted average processing unit 442 is a processing unit that takes a weighted average of CT images using the correction table stored in the correction table storage unit 43. FIG. 7 is a diagram showing a distribution of weights used by the weighted average processing unit 442 for weighted average of CT images, and shows peak values (center slices) and weight ranges. The weighted average processing unit 442 performs smoothing processing in which the number of weighted averages for each slice and the weights are changed in the slice direction. However, as illustrated in FIG. Smoothing process with a large weight spread while using the CT image (with a large number of images), and the movement becomes smaller as the distance from the diaphragm increases. Perform smoothing.

  In addition, the weighted average processing unit 442 displays the CT image obtained by the weighted average on the confirmation image display unit 441 together with the CT image before the weighted average. The user can confirm the influence of the correction by comparing the CT images before and after the weighted average.

  The attenuation map creation unit 443 is a processing unit that creates an attenuation map using the weighted average CT image created by the weighted average processing unit 442. The attenuation map creation unit 443 creates an attenuation map using the weighted average CT image, so that the accuracy of the SUV value can be improved for a PET image of a portion having a large movement such as the vicinity of the diaphragm affected by respiration.

  The reconstruction unit 444 is a processing unit that performs attenuation correction of a PET image using the attenuation map created by the attenuation map creation unit 443. In addition, the reconstruction unit 444 causes the confirmation image display unit 441 to display the PET images before and after attenuation correction.

  The input reception unit 45 is a processing unit that receives a user instruction using a button, a keyboard, and the like and notifies the correction table creation unit 42 or the correction processing unit 44 of the received instruction. User instructions include correction table creation instructions, weight instructions, attenuation correction execution instructions, and the like.

  The PET image storage unit 46 is a storage unit that stores a PET image, and stores a PET image before attenuation correction and a PET image after attenuation correction.

  Next, a processing procedure of correction table creation processing by the correction table creation unit 42 will be described. FIG. 8 is a flowchart showing a processing procedure of correction table creation processing by the correction table creation unit 42. Here, a case where a correction table is created for one slice position will be described.

  As shown in FIG. 8, in this correction table creation process, the correction table creation unit 42 aligns the breath-synchronized CT image and the CT image of the PET / CT apparatus at a portion where there is little organ movement due to respiration ( Step S11). Note that this processing is not necessary when there is no positional deviation.

  Then, the comparative image display unit 421 sets and displays a cursor at the diaphragm position on the whole body CT coronal image (step S12), and displays the breath synchronization CT image at the diaphragm position as a reference image (step S13). Further, the comparative image display unit 421 displays the CT images of N slices before and after the diaphragm position as a center (step S14).

  When the user designates the weight of the CT image of each slice, the comparison image display unit 421 accepts the weight designated by the user (step S15), performs weighted averaging of the CT image using the accepted weight, and weighted average CT An image is displayed (step S16).

  When the user designates the weighted average CT image closest to the reference image, the table creation unit 422 creates a correction table (step S17) and writes it in the correction table storage unit 43.

  Thus, the correction table creation unit 42 creates the correction table that defines the weight of the CT image centered on the diaphragm by displaying the reference image and the weighted average CT image and allowing the user to specify the weight of the CT image. be able to.

  Next, a processing procedure of PET image correction processing by the correction processing unit 44 will be described. FIG. 9 is a flowchart illustrating the processing procedure of the PET image correction processing by the correction processing unit 44. As shown in FIG. 9, in this PET image correction process, the confirmation image display unit 441 sets and displays a cursor at the diaphragm position on the whole body CT coronal image (step S21), and displays the PET coronal image. Is also set and displayed at the same position (step S22). Also, a CT image and a PET image at this position are displayed.

  Then, the weighted average processing unit 442 creates a weighted average CT image using the correction table (step S23), and the confirmation image display unit 441 displays the CT images before and after the weighted average (step S24). Then, after allowing the user to confirm the influence of the correction using the CT images before and after the weighted average, the attenuation map creation unit 443 creates an attenuation map using the weighted average CT image (step S25). Then, the reconstruction unit 444 attenuates and corrects the PET image using the attenuation map (step S26), and the confirmation image display unit 441 displays the PET images before and after the attenuation correction (step S27).

  As described above, the correction processing unit 44 performs the attenuation correction using the CT image weighted and averaged with the weight defined in the correction table, thereby improving the accuracy of the SUV value of the PET image near the diaphragm. The confirmation image display unit 441 may display the SUV values before and after attenuation correction in addition to the PET images before and after attenuation correction.

  As described above, in the present embodiment, the table creation unit 422 of the correction table creation unit 42 based on the weight specified by the user so that the weighted average CT image is close to the reference image for each CT image near the diaphragm. Creates a correction table. Then, the weighted average processing unit 442 of the correction processing unit 44 performs weighted averaging of CT images near the diaphragm using the weights defined in the correction table, and the attenuation map creation unit 443 creates an attenuation map using the weighted average CT images. Then, the reconstruction unit 444 performs attenuation correction on the PET image using the attenuation map. Therefore, the PET image attenuation correction can be performed without the influence of the movement of the diaphragm due to respiration, and the accuracy of the SUV value of the PET image near the diaphragm can be improved.

  In this embodiment, the case where attenuation correction is performed on a PET image near the diaphragm has been described. However, the present invention is not limited to this, and the case where attenuation correction is performed on a PET image where an organ moves due to breathing or the like. Can be applied to as well.

  In this embodiment, the PET / CT apparatus has been described. However, the present invention is not limited to this, and can be similarly applied to a PET apparatus that uses a CT image for attenuation correction. The present invention can also be applied to a SPECT / CT apparatus and a SPECT apparatus that uses a CT image for attenuation correction.

  In this embodiment, the case where attenuation correction is performed has been described. However, in the PET apparatus and the SPECT apparatus, when the CT image and the functional image are fused, the CT image and the functional image at the same slice position mismatch when the position of the organ is shifted due to respiration or the like. As described above, even when the CT image and the functional image have a mismatch, the influence of the movement of the organ can be reduced by using the CT image obtained by weighted averaging of the preceding and succeeding CT images.

  As described above, the present invention is useful for a PET / CT apparatus, a PET apparatus, a SPECT / CT apparatus, a SPECT apparatus, or the like that uses a CT image for attenuation correction, and in particular, a PET image or a SPECT image of a site where an organ moves. This is suitable for correcting attenuation.

It is explanatory drawing for demonstrating the structure of the PET / CT apparatus which concerns on a present Example. It is a functional block diagram which shows the structure of a data processor. It is explanatory drawing for demonstrating the weight definition process by the comparative image display part for the diaphragm. It is explanatory drawing for demonstrating the method for a comparative image display part to specify the weighted average CT image nearest to a reference image. It is a figure which shows an example of the correction table which a correction table memory | storage part memorize | stores. It is explanatory drawing for demonstrating the image which a confirmation image display part displays. It is a figure which shows distribution of the weight which a weighted average process part uses for the weighted average of CT image. It is a flowchart which shows the process sequence of the correction table preparation process by the correction table preparation part. It is a flowchart which shows the process sequence of the PET image correction process by a correction process part. It is a figure which shows the PET image example before and behind attenuation correction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 PET scanner 2 CT scanner 3 Bed 4 Data processing apparatus 5 Display apparatus 41 CT image storage part 42 Correction table creation part 43 Correction table storage part 44 Correction processing part 45 Input reception part 46 PET image storage part 421 Comparison image display part 422 Table Creation unit 441 Confirmation image display unit 442 Weighted average processing unit 443 Attenuation map creation unit 444 Reconstruction unit

Claims (7)

A nuclear medicine imaging apparatus that performs attenuation correction of nuclear medicine images using CT images,
An attenuation map creating means for creating an attenuation map using a CT image obtained by weighted averaging of a CT image at the same position as the nuclear medicine image to be generated and CT images before and after the CT image;
A nuclear medicine imaging apparatus comprising: attenuation correction means for performing attenuation correction of a nuclear medicine image using the attenuation map created by the attenuation map creating means.   2. The nuclear medicine imaging apparatus according to claim 1, further comprising a correction table creating unit that creates a correction table that defines a weight used by the attenuation map creating unit for a weighted average of CT images.   The correction table creating means includes a CT image that is the same position as the nuclear medicine image to be generated and a CT image weighted and averaged with a weight designated by the user for the CT images before and after the CT image, together with a reference image for creating an attenuation map The nuclear medicine imaging apparatus according to claim 2, wherein the correction table is created by using a weight specified by the user by displaying.   The nuclear medicine imaging apparatus according to claim 3, wherein the attenuation map creating reference image displayed by the correction table creating means is a respiratory synchronization CT image or a transmission image.   5. The nuclear medicine imaging apparatus according to claim 2, wherein the correction table creating means creates a plurality of correction tables based on body type, age, and sex.   The nuclear medicine imaging apparatus according to claim 1, wherein the correction table creating unit creates a correction table that defines an enlargement / reduction ratio and a translation amount of an image in addition to a weight. A nuclear medicine image creation method for performing attenuation correction of a nuclear medicine image using a CT image,
An attenuation map creating step of creating an attenuation map using a CT image obtained by weighted averaging of a CT image at the same position as the nuclear medicine image to be generated and CT images before and after the CT image;
A nuclear medicine image creation method comprising: an attenuation correction step of performing attenuation correction of a nuclear medicine image using the attenuation map created by the attenuation map creation step.

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