JP5355036B2 - Nuclear medicine image capturing device, nuclear medicine image reconstruction device, and nuclear medicine image reconstruction program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent degradation of an image due to decrease and weakening of gamma rays by a bone at some collection angles on the occasion of collecting data by detecting the gamma rays evolved from a subject. <P>SOLUTION: A collection condition deciding part 421 decides a collection conditions such as a collection starting angle, a collection ending angle, sequence of collection angles and a collecting time at each collection angle, based on an inspecting region predetermined by a user and a CT image thereof. Besides, a successive approximation processing part 433 specifies a projection angle at which the decrease and weakening of the gamma rays are large, by using the CT image, and performs successive approximation for the predetermined projection angle, by using the weight of which the value is smaller than those of the other projection angles. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a technique for improving the image quality of an image created by detecting radiation emitted from a subject.

  In a single photon emission computed tomography (SPECT) apparatus, data is collected around a patient (subject) at equiangular intervals of 360 degrees. In addition, in the case where the heart is the target site, some are collected at an equal angular interval of 180 degrees (see, for example, Non-Patent Document 1).

Eisner RL, Nowak DJ, Pettigrew R, Fajman W. Fundamentals of 180 degree acquisition and reconstruction in SPECT imaging.J Nucl Med. 1986; 27: 1717-1728.

  However, since gamma rays are greatly attenuated by bone, reconstructing an image using data collected at an angle that passes through bone in the same way as data collected at an angle that does not pass through bone results in gamma rays at an angle that passes through bone. There is an unsolved problem that image degradation occurs due to a decrease in the collection count.

  When the body part (myocardium, tumor, etc.) is the target site, data is also collected with the arm raised to avoid attenuation of gamma rays by the bone of the arm. However, such data collection has a problem that it is painful for the patient because the patient needs to keep the arm raised for a long time (20 minutes or more).

  The present invention has been made to solve the above-described problems caused by the prior art, and is a nucleus that can prevent image deterioration due to a decrease in the gamma ray collection count at an angle passing through a bone and improve the quality of a reconstructed image. It is an object to provide a medical image photographing apparatus, a nuclear medicine image reconstruction apparatus, and a nuclear medicine image reconstruction program.

In order to solve the above-described problems and achieve the object, the present invention is a nuclear medicine imaging apparatus that creates an image by detecting radiation emitted from a subject, and the radiation is attenuated below a predetermined threshold. Attenuation angle specifying means for specifying a projection angle, and a reconstruction for creating a reconstructed image by performing a sequential calculation with weighting lower than the other projection angles for the projection angle specified by the attenuation angle specifying means Means.

The present invention also relates to a nuclear medicine imaging apparatus for creating an image by detecting radiation emitted from a subject, and a collection time determining means for determining a time for collecting data from the subject for each collection angle. And data collection means for collecting data from the subject based on the collection time determined by the collection time determination means.

Further, the present invention is a nuclear medicine imaging apparatus that detects radiation emitted from a subject and creates an image, and a collection order determining unit that determines an order of angles for collecting data from the subject; And a data collection means for collecting data from the subject based on the order determined by the collection order determination means.

Further, the present invention is a nuclear medicine imaging apparatus for detecting radiation emitted from a subject to create an image, and an attenuation angle specifying means for specifying a projection angle at which the radiation is attenuated from a predetermined threshold; The projection angle data specified by the attenuation angle specifying means includes reconstructing means for creating a reconstructed image by performing sequential calculation with a reduced number of repetitions.

The present invention is also a nuclear medicine image reconstruction device that reconstructs data collected by detecting radiation emitted from a subject and creates an image, wherein the radiation is attenuated below a predetermined threshold value. Attenuation angle specifying means for specifying a projection angle, and a reconstruction for creating a reconstructed image by performing a sequential calculation with weighting lower than the other projection angles for the projection angle specified by the attenuation angle specifying means Means.

The present invention is also a nuclear medicine image reconstruction device that reconstructs data collected by detecting radiation emitted from a subject and creates an image, wherein the radiation is attenuated below a predetermined threshold value. An attenuation angle specifying unit that specifies a projection angle, and a reconstruction unit that creates a reconstructed image by sequentially calculating the projection angle data specified by the attenuation angle specifying unit by reducing the number of repetitions. It is characterized by that.

The present invention is also a nuclear medicine image reconstruction program for reconstructing data collected by detecting radiation emitted from a subject and creating an image, wherein the radiation is attenuated below a predetermined threshold value. Attenuation angle specifying procedure for specifying a projection angle, and a reconstruction for creating a reconstructed image by sequentially performing calculation by assigning a lower weight to the projection angle specified by the attenuation angle specifying procedure than other projection angles. And having the computer execute the procedure.

The present invention is also a nuclear medicine image reconstruction program for reconstructing data collected by detecting radiation emitted from a subject and creating an image, wherein the radiation is attenuated below a predetermined threshold value. An attenuation angle specifying procedure for specifying a projection angle, and a reconstruction procedure for creating a reconstructed image by sequentially calculating the projection angle data specified by the attenuation angle specifying procedure by reducing the number of repetitions. It is made to perform.

According to the present invention, the image quality of a reconstructed image can be improved.

Further, according to the present invention, it is possible to speed up the successive approximation process without degrading the image quality of the reconstructed image.

  Exemplary embodiments of a nuclear medicine image capturing device, a nuclear medicine image reconstruction device, and a nuclear medicine image reconstruction program according to the present invention will be described below in detail with reference to the accompanying drawings. In the present embodiment, the case where the present invention is applied to a SPECT-CT apparatus will be mainly described.

  First, the configuration of the SPECT / CT apparatus according to the present embodiment will be described. FIG. 1 is an explanatory diagram for explaining a configuration of a SPECT / CT apparatus according to the present embodiment. As shown in the figure, the SPECT / CT apparatus includes a SPECT 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, the SPECT / CT apparatus has buttons, a keyboard, and the like for the user to input instructions to the SPECT / CT apparatus.

  The SPECT scanner 1 moves a flat detector around a patient or arranges a plurality of flat detectors, detects gamma rays emitted from a patient's examination site from a plurality of directions, and based on the obtained gamma ray count values. An apparatus for generating projection data.

  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 SPECT scanner 1 and the CT scanner 2 to generate a SPECT 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 data collection planning unit 42, an OSEM reconstruction unit 43, a display unit 44, and an input receiving unit 45.

  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 is used for determination of data collection conditions to be described later, weighting in successive approximation processing, and the like.

  The data collection planning unit 42 is a processing unit that determines conditions for collecting data from a patient to create a SPECT image and sets the conditions in the SPECT scanner 1. The data collection planning unit 42 includes a collection condition determination unit 421 and a collection condition setting unit 422. Have.

  The collection condition determination unit 421 includes a collection start angle, a collection end angle, a collection time at each collection angle, an order of collection angles, that is, an order of data collection angles based on the examination region designated by the user and its CT image. It is a processing part which determines the collection conditions.

  As shown in FIG. 3, by appropriately selecting the range of angles for collecting data according to the shape of the examination site such as the heart, liver, and kidney, image distortion and non-uniformity can be reduced. Therefore, the collection condition determination unit 421 determines the collection start angle and the collection end angle based on the examination site designated by the user.

  In addition, the acquisition condition determination unit 421 identifies an imaging angle in which gamma rays are greatly attenuated by bone using a CT image of the examination site, and compares the data acquisition time of the specified imaging angle with the data acquisition time of other imaging angles. Then, the shooting time for each shooting angle is determined so as to shorten it.

  Here, the imaging angle where the attenuation of gamma rays is large is an imaging angle in which, for example, the length of the bone through which gamma rays pass is larger than a predetermined threshold. Alternatively, a plurality of threshold values can be provided to classify the attenuation of gamma rays into three or more, and three or more types of imaging time can be provided. In addition, by setting the shooting time to 0, it is possible not to collect data at a specific angle.

  FIG. 4 is a diagram illustrating a method for controlling the photographing time. As shown in FIG. 4, the imaging time at the Nth angle can be extended by slowing down the rotational speed of the detector at the Nth angle. Conversely, the imaging time at the Nth angle can be shortened by increasing the rotation speed of the detector at the Nth angle.

  As described above, the acquisition condition determination unit 421 uses the CT image to specify an imaging angle where the attenuation of gamma rays due to bone is large as the imaging condition of the examination site, and shortens the imaging time of the specified imaging angle. The image quality of the constituent image can be improved.

  In addition, the collection condition determination unit 421 determines the order of the collection angles so that data is continuously collected for each subset so that the movement of the examination site in the subset is minimized. Here, the subset is a subset of shooting angles.

  For example, if the shooting angles are “angle 1” to “angle 6” in order and the number of subsets is 2, “angle 1”, “angle 3”, and “angle 5” are one subset, and “angle 2”. , “Angle 4”, “angle 6” are another subset. At this time, the order of photographing angles is such that “angle 1”, “angle 3”, “angle 5”, “angle 2”, “angle 4”, “angle 6”, and so on are the same subset of angles. To.

  Note that the collection condition determination unit 421 may specify an imaging angle with small attenuation of gamma rays using a CT image of the examination site, and determine the imaging order with priority on the specified imaging angle. By performing shooting using the priority order, shooting efficiency can be improved.

  The collection condition setting unit 422 is a processing unit that sets, in the SPECT scanner 1, collection conditions such as the collection start angle, the collection end angle, the order of collection angles, the collection time at each collection angle determined by the collection condition determination unit 421. is there.

  The OSEM reconstruction unit 43 is a processing unit that creates a reconstructed image (SPECT image) using an OSEM (ordered subset expectation maximization) method, and includes a SPECT image storage unit 431, a projection data acquisition unit 432, and a successive approximation process. Unit 433 and a reconstructed image creation unit 434.

  The SPECT image storage unit 431 is a storage unit that stores projection data, reconstructed images, and the like. The projection data acquisition unit 432 is a processing unit that acquires the projection data of the examination region from the SPECT scanner 1 and stores the acquired projection data in the SPECT image storage unit 431.

  The successive approximation processing unit 433 is a processing unit that calculates the pixel value Xj on the cross section by successive approximation. Here, j is an index corresponding to the pixel position on the cross section, and takes a value of 1 to 625 when the number of pixels is 625, for example.

  FIG. 5 is an explanatory diagram for explaining successive approximation of the pixel value Xj. As shown in FIG. 5, in the OSEM method, the n-th approximate value Xj (n) is multiplied by a weight Cij, and n + 1 so that the estimated value Zi (n) of the n-th projection data matches the projection data Yi. The approximate value Xj (n + 1) for the second time is calculated. Here, i is an index corresponding to the projection angle (imaging angle), and takes a value of 1 to m (number of projections).

  The successive approximation processing unit 433 identifies a projection angle with large attenuation of the gamma ray from the CT image of the examination region, and reduces the value of the specified projection angle weight Cij in comparison with the value of the weight Cij of other projection angles. To perform successive approximation. Alternatively, the attenuation of gamma rays can be classified into three or more, and three or more values can be provided as the value of the weight Cij. In addition, by setting the value of the weight Cij to 0, data of a specific projection angle can be prevented from being used in the sequential calculation.

  FIG. 6 is an explanatory diagram for explaining an example of assignment of the weight Cij by the successive approximation processing unit 433. In this example, the successive approximation processing unit 433 performs low weighting at a projection angle at which gamma rays emitted from the examination site 11 pass through the bone 12, and at a projection angle at which gamma rays emitted from the examination site 11 do not pass through the bone 12. Perform normal weighting.

  As described above, when the successive approximation processing unit 433 sequentially approximates the pixel value Xj on the cross section, the successive approximation is performed by reducing the value of the projection angle weight Cij where the attenuation of the gamma ray by the bone is large and performing the successive approximation. The image quality of the constituent image can be improved.

  Note that the successive approximation processing unit 433 may not perform calculation at a projection angle with large attenuation of gamma rays in a specific number of repetitions, instead of reducing the weight value of the projection angle with large attenuation of gamma rays. it can. By not performing calculation at a projection angle where the attenuation of gamma rays is large at a specific number of repetitions, it is possible to speed up the successive approximation process without degrading the image quality of the reconstructed image.

  The reconstructed image creation unit 434 is a processing unit that creates a reconstructed image using the pixel value Xj calculated by the successive approximation processing unit 433, and stores the created reconstructed image in the SPECT image storage unit 431.

  The display unit 44 is a processing unit that displays the reconstructed image stored in the SPECT image storage unit 431 on the display device 5.

  The input receiving unit 45 is a processing unit that receives a user instruction using a button, a keyboard, and the like, and notifies the received instruction to the data collection planning unit 42, the OSEM reconstruction unit 43, or the display unit 44. User instructions include examination site designation, reconstructed image creation instruction, image display instruction, and the like.

  Next, a processing procedure of data collection condition planning processing by the data collection planning unit 42 will be described. FIG. 7 is a flowchart showing a processing procedure of data collection condition planning processing by the data collection planning unit 42.

  As shown in FIG. 7, in this data collection condition planning process, the collection condition determination unit 421 determines the data collection start angle and collection end angle based on the examination site designated by the user (step S11).

  Then, the collection condition determination unit 421 determines the order of collection angles so that data is collected continuously for each subset (step S12). Furthermore, the collection condition determination unit 421 determines whether or not the attenuation of the gamma ray at each collection angle is large using the CT image of the examination site, and determines the collection time based on the determination result (step S13). Then, the collection condition setting unit 422 sets the data collection condition in the SPECT scanner 1 (step S14).

  As described above, the collection condition determination unit 421 determines the collection conditions such as the collection start angle, the collection end angle, the order of the collection angles, and the collection time at each collection angle based on the examination region designated by the user and the CT image thereof. By doing so, the image quality of the reconstructed image can be improved.

  Next, a processing procedure of image reconstruction processing by the OSEM reconstruction unit 43 will be described. FIG. 8 is a flowchart showing a processing procedure of image reconstruction processing by the OSEM reconstruction unit 43.

  As shown in FIG. 8, in this image reconstruction process, the projection data acquisition unit 432 reads projection data from the SPECT scanner 1 (step S21), and the successive approximation processing unit 433 sets initial images, that is, Xj (0 ) Is set (step S22). As Xj (0), for example, the same value can be set for all.

  Then, the successive approximation processing unit 433 creates estimated projection data Zi (n) (step S23), estimates projection data Zi (n), current pixel value Xj (n), read projection data Yi (n), The next pixel value Xj (n + 1) is calculated using the weight Cij (step S24). Here, the value of the weight Cij is small for a projection angle where the attenuation of gamma rays is large.

  Then, it is determined whether or not the processing for the number of projections / the number of subsets has been performed, that is, whether or not the processing for one subset has been performed (step S25). Returning to S23, the next projection angle is processed.

  On the other hand, if processing for the number of projections / number of subsets has been performed, it is determined whether or not processing for the number of subsets has been performed (step S26). If processing has not been performed for the number of subsets, processing returns to step S23. Process the next subset.

  On the other hand, if processing for the number of subsets has been performed, it is determined whether or not processing has been performed for the number of repetitions (step S27). If processing has not been performed for the number of repetitions, the process returns to step S23 and the next iteration is performed. I do. On the other hand, when processing is performed for the number of repetitions, the reconstructed image creating unit 434 creates a reconstructed image using the final pixel value Xj (n) (step S28).

  In this way, in the successive approximation process, the image quality of the reconstructed image can be improved by using a weight having a small value for the projection angle where the attenuation of the gamma ray is large.

  As described above, in the present embodiment, the collection condition determination unit 421 performs collection at each collection angle, the collection start angle, the collection end angle, the order of the collection angles based on the examination region designated by the user and the CT image thereof. Determine collection conditions such as time. Therefore, it is possible to prevent image deterioration due to a decrease in the gamma ray count and improve the image quality of the SPECT image.

  In the present embodiment, the successive approximation processing unit 433 uses a CT image to specify a projection angle at which gamma ray attenuation is large, and the specified projection angle is a weight with a smaller value compared to other projection angles. Is used for successive approximation. Therefore, it is possible to prevent image deterioration due to a decrease in the gamma ray count and improve the image quality of the SPECT image.

  In the present embodiment, the case where the collection condition determination unit 421 determines the data collection condition and the successive approximation processing unit 433 performs the successive approximation process while changing the value of the weight Cij with respect to the projection angle has been described. However, the present invention is not limited to this, and only one of the collection condition determination unit 421 and the successive approximation processing unit 433 is used, and the other one is similarly applied to the case of using the prior art. Can do.

  In the present embodiment, the SPECT / CT apparatus has been described. However, the present invention is not limited to this, and a CT image is used for specifying an imaging angle and a projection angle in which gamma rays emitted from the examination site are greatly attenuated. The same applies to the SPECT apparatus to be used. It can also be applied to other nuclear medicine imaging devices.

  In this embodiment, the case where the OSEM reconstruction unit 43 performs the image reconstruction process has been described. However, the image reconstruction process performed by the OSEM reconstruction unit 43 may be realized by software.

  As described above, the present invention is useful for a SPECT / CT apparatus, a SPECT apparatus, or the like that creates an image by detecting radiation emitted from a subject.

It is explanatory drawing for demonstrating the structure of the SPECT / CT apparatus which concerns on a present Example. It is a functional block diagram which shows the structure of a data processor. It is a figure which shows the range of the angle which collects the data of a heart, a liver, and a kidney. It is a figure which shows the control method of imaging | photography time. It is explanatory drawing for demonstrating the successive approximation of pixel value Xj. It is explanatory drawing for demonstrating an example of allocation of the value of the weight Cij by a successive approximation process part. It is a flowchart which shows the process sequence of the data collection condition plan process by a data collection plan part. It is a flowchart which shows the process sequence of the image reconstruction process by an OSEM reconstruction part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 SPECT scanner 2 CT scanner 3 Bed 4 Data processing apparatus 5 Display apparatus 11 Test site 12 Bone 41 CT image memory | storage part 42 Data collection plan part 43 OSEM reconstruction part 44 Display part 45 Input reception part 421 Collection condition determination part 422 Collection conditions Setting unit 431 SPECT image storage unit 432 Projection data acquisition unit 433 Sequential approximation processing unit 434 Reconstructed image creation unit

Claims (9)

A nuclear medicine imaging apparatus that creates an image by detecting radiation emitted from a subject,
An attenuation angle specifying means for specifying a projection angle at which the radiation is attenuated below a predetermined threshold;
Reconstructing means for creating a reconstructed image by performing sequential calculation with weighting lower than other projection angles for the projection angle specified by the attenuation angle specifying means, and Medical imaging device.   The nuclear medicine image capturing apparatus according to claim 1, wherein the attenuation angle specifying unit specifies a projection angle at which the radiation is attenuated from a predetermined threshold using a CT image of a target region. A nuclear medicine imaging apparatus that creates an image by detecting radiation emitted from a subject,
An attenuation angle specifying means for specifying a projection angle at which the radiation is attenuated below a predetermined threshold;
Collection time determining means for determining the collection time of each projection angle so that the time for collecting data from the subject is shorter than the other projection angles for the projection angle specified by the attenuation angle specifying means ;
A nuclear medicine imaging apparatus comprising: a data collection unit that collects data from a subject based on the collection time determined by the collection time determination unit. A nuclear medicine imaging apparatus that creates an image by detecting radiation emitted from a subject,
An attenuation angle specifying means for specifying a projection angle at which the radiation is attenuated below a predetermined threshold;
For the projection angle specified by the attenuation angle specifying means, a collection order determining means for determining the order for each projection angle so that the order of collecting data from the subject is slower than other projection angles ;
A nuclear medicine imaging apparatus comprising: a data collection unit that collects data from a subject based on the order determined by the collection order determination unit. A nuclear medicine imaging apparatus that creates an image by detecting radiation emitted from a subject,
An attenuation angle specifying means for specifying a projection angle at which the radiation is attenuated below a predetermined threshold;
A nuclear medicine image photographing apparatus, comprising: reconstructing means for creating a reconstructed image by sequentially calculating the projection angle data identified by the attenuation angle identifying means by reducing the number of repetitions. A nuclear medicine image reconstruction device that reconstructs data collected by detecting radiation emitted from a subject to create an image,
An attenuation angle specifying means for specifying a projection angle at which the radiation is attenuated below a predetermined threshold;
Reconstructing means for creating a reconstructed image by performing sequential calculation with weighting lower than other projection angles for the projection angle specified by the attenuation angle specifying means, and Medical image reconstruction device. A nuclear medicine image reconstruction device that reconstructs data collected by detecting radiation emitted from a subject to create an image,
An attenuation angle specifying means for specifying a projection angle at which the radiation is attenuated below a predetermined threshold;
Reconstruction means for creating a reconstructed image by reducing the number of repetitions for the projection angle data specified by the attenuation angle specifying means and performing sequential calculation, and a nuclear medicine image reconstruction apparatus, comprising: . A nuclear medicine image reconstruction program that reconstructs data collected by detecting radiation emitted from a subject and creates an image,
An attenuation angle specifying procedure for specifying a projection angle at which the radiation is attenuated below a predetermined threshold;
A computer is caused to execute a reconstruction procedure for creating a reconstructed image by performing weighting lower than other projection angles for the projection angle specified by the attenuation angle specifying procedure and performing sequential calculation. A nuclear medicine image reconstruction program. A nuclear medicine image reconstruction program that reconstructs data collected by detecting radiation emitted from a subject and creates an image,
An attenuation angle specifying procedure for specifying a projection angle at which the radiation is attenuated below a predetermined threshold;
Reconstruction procedure for generating a reconstructed image by reducing the number of repetitions and performing a recalculation procedure on the projection angle data identified by the attenuation angle identifying procedure, Configuration program.

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