The present invention relates to a radiation tomographic imaging apparatus for producing a radiation tomographic image of a body part moving in a subject, such as a heart, for example, and a program for controlling the radiation tomographic imaging apparatus.
In performing imaging of a heart in a radiation tomographic imaging apparatus, an EKG signal (ECG signal) is employed for image reconstruction of a radiation tomographic image using projection data collected in diastole or systole in which motion of the heart momentarily stops, as disclosed in Patent Document 1, for example (an electrocardiography-gated reconstruction method).
In the electrocardiography-gated reconstruction method employing an EKG signal, however, an apparatus or several settings for acquiring the EKG signal is required. Accordingly, the inventor of the present application has made a study of producing a radiation tomographic image of a heart without using an EKG signal.
Suppose here that a radiation tomographic image is to be produced in cardiac diastole or systole without using an EKG signal, it is necessary to produce a large number of radiation tomographic images and choose images with small motion from among them because the cardiac cycle is unknown. Accordingly, in producing a radiation tomographic image of a body part moving in a subject, such as a heart, at a time when it momentarily stops or its motion is small without using an EKG signal, it is desired to suppress the number of radiation tomographic images to produce.
The invention made for solving the aforementioned problem is a radiation tomographic imaging apparatus characterized in comprising: a first reconstructing section for reconstructing a plurality of temporally different first radiation tomographic images for a required slice position in a subject based on data obtained by scanning a required range in said subject in its body-axis direction with radiation; an information-on-movement acquiring section for acquiring information on movement of a body part in said subject in said required range based on said plurality of first radiation tomographic images; information creating section for creating information on a temporal change indicating a temporal change of said information on movement acquired by said information-on-movement acquiring section; an identifying section for identifying a time when motion of said body part in said subject stops or said motion is smaller than a predetermined amount based on said information on a temporal change; and a second reconstructing section for reconstructing a second radiation tomographic image for said subject at said time based on said data.
According to the invention in the aspect described above, information on movement of a body part in a subject is detected based on a plurality of temporally different first radiation tomographic images at a required slice position, and information on a temporal change indicating a temporal change of the information on movement is created. Then, a time at which motion of the body part in the subject stops or is smaller than a predetermined amount is identified based on the information on a temporal change, and the second radiation tomographic image described above at that time is reconstructed; hence, a radiation tomographic image at a time when motion stops or is small may be obtained without using an EKG signal while suppressing the number of radiation tomographic images to produce.
Now an embodiment of the invention will be described hereinbelow.
The gantry 2 has an X-ray tube 21, an aperture 22, a collimator device 23, an X-ray detector 24, a data collecting section 25, a rotating section 26, a high-voltage power source 27, an aperture driving apparatus 28, a rotation driving apparatus 29, and a gantry/table control section 30.
The X-ray tube 21 and X-ray detector 24 are disposed to face each other across a bore 2B.
The aperture 22 is disposed between the X-ray tube 21 and bore 2B. It shapes X-rays emitted from an X-ray focus of the X-ray tube 21 toward the X-ray detector 24 into a fan beam or a cone beam.
The collimator device 23 is disposed between the bore 2B and X-ray detector 24. The collimator device 23 removes scatter rays that would otherwise enter the X-ray detector 24.
The X-ray detector 24 has a plurality of X-ray detector elements two-dimensionally arranged in a direction of the span (referred to as channel direction) and a direction of the thickness (referred to as a row direction) of the fan-shaped X-ray beam emitted from the X-ray tube 21. Each respective X-ray detector element detects X-rays passing through a subject 5 laid in the bore 2B, and outputs an electric signal according to the intensity thereof. The subject 5 is an animate being, such as, for example, a human or an animal.
The data collecting section 25 receives the electric signal output from each X-ray detector element in the X-ray detector 24, and converts it into X-ray data for collection.
The rotating section 26 is rotatably supported around the bore 2B. The rotating section 26 has the X-ray tube 21, aperture 22, collimator device 23, X-ray detector 24, and data collecting section 25 mounted thereon.
The imaging table 4 has a cradle 41 and a cradle driving apparatus 42. The subject 5 is laid on the cradle 41. The cradle driving apparatus 42 moves the cradle 41 into/out of the bore 2B, i.e., an imaging volume, in the gantry 2.
The high-voltage power source 27 supplies high voltage and current to the X-ray tube 21.
The aperture driving apparatus 28 drives the aperture 22 and modifies the shape of its opening.
The rotation driving apparatus 29 rotationally drives the rotating section 26.
The gantry/table control section 30 controls several apparatuses and sections in the gantry 2, the imaging table 4, and the like.
The operation console 6 accepts several kinds of operation from an operator. The operation console 6 has an input device 61, a display device 62, a storage device 63, and a computational processing apparatus 64. In the present embodiment, the operation console 6 is constructed from a computer.
The input device 61 is configured to include a button, a keyboard, etc. for accepting an input of a command and information from the operator, and to further include a pointing device, and the like. The display device 62 is an LCD (Liquid Crystal Display), an organic EL (Electro-Luminescence) display, or the like.
The storage device 63 is an HDD (Hard Disk Drive), semiconductor memory, such as RAM (Random Access Memory) and ROM (Read Only Memory), and the like. The operation console 6 may have all of the HDD, RAM, and ROM as the storage device 63.
The computational processing apparatus 64 is a processor such as a CPU (central processing unit).
The operation console 6 may be configured to be connected with an external storage medium 90. The external storage medium 90 is a non-transitory storage medium having portability, such as a CD (Compact Disk), a DVD (Digital Versatile Disk), USB (Universal Serial Bus) memory, or a hard disk, for example.
As shown in
Referring to
The scan control section 71 controls the gantry/table control section 30 in response to an operation by the operator so that a scan is performed for a required range in the subject in its body-axis direction (z-direction). In the present embodiment, the required range in the subject is a heart. In the present embodiment, a helical scan is performed as the scan, and data at a plurality of slice positions in the subject are collected. The scan control section 71 is an exemplary embodiment of the control section in the present invention.
The first reconstructing section 72 reconstructs a plurality of temporally different first radiation tomographic images for required slice positions in the subject based on the data acquired by scanning the required range in the subject with X-rays. Details thereof will be discussed later. The first reconstructing section 72 is an exemplary embodiment of the first reconstructing section in the present invention.
The information-on-movement acquiring section 73 detects information on movement of a body part in the subject based on the plurality of first radiation tomographic images obtained by the first reconstructing section 72. Details thereof will be discussed later. The information-on-movement acquiring section 73 is an exemplary embodiment of the information-on-movement acquiring section in the present invention.
The information creating section 74 creates information on a temporal change indicating a temporal change of the information on movement acquired by the information-on-movement acquiring section 73. The information creating section 74 is an exemplary embodiment of the information creating section in the present invention.
The identifying section 75 identifies a time when the motion stops or is smaller than a predetermined amount based on the information on a temporal change created by the information creating section 74. The identifying section 75 is an exemplary embodiment of the identifying section in the present invention.
The second reconstructing section 76 reconstructs a second radiation tomographic image for the subject at the aforementioned time identified by the identifying section 75. The second reconstructing section 76 is an exemplary embodiment of the second reconstructing section in the present invention.
The display control section 75 controls the display device 62 to display several kinds of images and text on its screen.
Next, the flow of processing in the X-ray CT system in accordance with the present embodiment will be described based on the flow chart in
Next, at Step S2, the information creating section 74 creates a motion profile indicating a temporal change of motion of the heart. The motion profile is an exemplary embodiment of the information on a temporal change indicating a temporal change of the information on movement of the body part in the subject.
Now the processing at Step S2 will be described in detail based on the flow chart in
The reconstruction for a multi-time image group will now be described in detail. In general, a time and a position are in a one-to-one relationship in helical image reconstruction.
In helical cardiac imaging, consistent image reconstruction at a specific time is required.
On the other hand, the data used in image reconstruction at a specific position sometimes has a margin for a time shift in a temporal-axis direction taking account of the z-width of the X-ray detector. Especially in cardiac imaging, there is a sufficient margin because the helical pitch is low. This may be used to produce images at a plurality of times at the specific position.
A set of the image with no time shift and the two images temporally shifted forward and backward described above is referred to as a multi-time image group. The first reconstructing section 72 produces a multi-time image group for each of a plurality of slice positions in a range to be imaged (required range) in the subject. Each of images, i.e., first X-ray tomographic images, constituting the multi-time image group is an exemplary embodiment of the first radiation tomographic image in the present invention.
Next, a weighting function used in reconstruction of a multi-time image group will be described.
When a time shift is applied, the physical position of the X-ray detector, more particularly, a central position of the data region used in image reconstruction, coincides with the time of the image, but does not coincide with the position of the image. Moreover, the weighting function w(T0) here is shifted in the temporal-axis direction to become w(T0−ts) and w(T0+ts), although its profile shape is not modified according to the time shift in
Once a multi-time image group has been obtained for each of the plurality of slice positions at Step S21, the information-on-movement acquiring section 73 calculates a difference in the multi-time image group at Step S22. The difference is calculated for each of the plurality of slice positions. The difference may be calculated for a plurality of different times at one slice position.
Now calculation of the aforementioned difference will be particularly described. The information-on-movement acquiring section 73 first divides each of images constituting a multi-time image group into a plurality of local images. Next, the information-on-movement acquiring section 73 calculates, for each combination of local images at the same position in the subject but at different times, a difference value between local images in the combination.
The calculation of the difference value will be described in more detail. For example, as shown in
Note that the total sum obtained in each of the plurality of local images is an exemplary embodiment of the difference value between local images in the combination.
The information-on-movement acquiring section 73 calculates a feature quantity using the first total sum and second total sum as the aforementioned difference. For example, the information-on-movement acquiring section 73 may calculate a total difference value obtained by adding the first total sum and second total sum together as the aforementioned difference. Alternatively, it may calculate an average value of the first total sum and second total sum as the aforementioned difference. The total difference value or average value is calculated for each of the plurality of slice positions. It should be noted that the aforementioned difference is not limited to the total difference value or average value.
The total difference value and average value constitute an exemplary embodiment of the information on movement in a whole of the first radiation tomographic image.
The information-on-movement acquiring section 73 may also calculate an index value as the aforementioned difference based on the total difference value or average value using a required formula. In the present embodiment, a larger index value indicates a larger value of the aforementioned difference and a greater amount of movement.
It should be noted that the information-on-movement acquiring section 73 may take a difference between corresponding pixels (pixels whose positions are the same in the subject) in the image with no time shift and in the temporally forward time-shifted image without dividing the images into local images, and calculate a total sum thereof as the first total sum. Likewise, the information-on-movement acquiring section 73 may take a difference between corresponding pixels in the image with no time shift and in the temporally backward time-shifted image without dividing the images into local images, and calculate a total sum thereof as the second total sum.
Here, the aforementioned difference is larger as more motion of the heart is present between the image with no time shift and temporally shifted image, while it is smaller as less motion of the heart is present. Therefore, the aforementioned difference is an exemplary embodiment of the information on movement of the body part in the subject in the present invention.
Next, at Step S23, the information creating section 74 creates a motion profile based on the difference obtained at Step S22. Specifically, the information creating section 74 first plots the differences for a plurality of different times obtained at Step S22 against the temporal axis. The differences for a plurality of different times are differences obtained at each of a plurality of slice positions. The information creating section 74 plots the differences at times with no time shift described above (T0 described above, for example).
For example, the information creating section 74 plots the index values against the temporal axis.
Next, the information creating section 74 creates a motion profile MP indicated by a dashed line in
The motion profile obtained at Step S2 may be displayed on the display device 62.
Once the motion profile has been obtained at Step S2 as described above, the identifying section 75 identifies a time when motion of the heart stops or is smaller than a predetermined amount based on the motion profile at Step S3.
For example, the identifying section 75 identifies a time when the index value is equal to or lower than a predefined threshold in the motion profile to identify the aforementioned time. The following description will be made exemplifying the motion profile MP shown in
A portion (upward-convex portion) in the motion profile MP in which the index value is at a local maximum is a portion in which motion of the heart is at its peak. On the other hand, a portion (downward-convex portion, the time Ts) in which the index value is at a local minimum in the motion profile MP is a portion in which motion of the heart momentarily stops.
While only one time zone TR is shown in
As for the heart, its motion momentarily stops at diastole and systole. The diastole and systole are alternately repeated. The identifying section 75 identifies whether the aforementioned time identified in the motion profile is in diastole or systole based on, for example, data of the image produced by the first reconstructing section 72.
More specifically, a plurality of times Ts are identified as the aforementioned time in a motion profile MP shown in
Next, at Step S4, the second reconstructing section 76 reconstructs a second X-ray tomographic image for the subject at the aforementioned time identified at Step S3. Since systole and diastole are distinguished from each other as the aforementioned time, a second X-ray tomographic image at systole and that in diastole are obtained at Step S4 here.
This will be described in more detail. The second reconstructing section 76 reconstructs a second X-ray tomographic image at the time identified at Step S3 based on the data collected at Step S1 and obtained at that time.
The second reconstructing section 76 reconstructs second X-ray tomographic images for a plurality of slice positions at one time. This will be particularly described based on
It should be noted that the data obtained at the times Ts1, Ts2 are data over a predefined temporal width around the times Ts1, Ts2. The predefined temporal width is a temporal width in which data required to produce one image are collected.
The second reconstructing section 76 reconstructs the second X-ray tomographic images in a region of the whole heart, which is the body part to be imaged. Thus, second X-ray tomographic images at the time of diastole and those at the time of systole are obtained.
According to the present embodiment described above, an X-ray tomographic image at a time when motion of the heart stops or is small may be obtained without using an EKG signal while suppressing the number of X-ray tomographic images to produce.
Next, a variation of the embodiment will be described. In the variation, the information creating section 74 may create a motion profile on a local image-by-local image basis. This will be described in detail. A difference is taken between corresponding pixels in each of local images Idt0 in an image It0 with no time shift and in each of local images Id(t0−ts) in a temporally forward time-shifted image I(t0−ts) to calculate a difference value, and a total sum of absolute values of the difference values within the local image is taken as a third total sum. That is, the third total sum is a total sum of absolute values of difference values obtained in each of the local images. Moreover, a difference is taken between corresponding pixels in each of the local images Idt0 in the image It0 with no time shift and in each of local images Id(t0+ts) in a temporally backward time-shifted image (t0+ts) to calculate a difference value, and a total sum of absolute values of the difference values within the local image is taken to as a fourth total sum. That is, the fourth total sum is also a total sum of absolute values of difference values obtained in each of the local images.
The information-on-movement acquiring section 73 calculates a feature quantity using the third total sum and fourth total sum, in place of the first total sum and second total sum, as the aforementioned difference at Step S22 described above. For example, the information-on-movement acquiring section 73 may calculate a total difference value in which the third total sum and fourth total sum are added together as the aforementioned difference between corresponding local images. The total difference value here is obtained on a local image-by-local image basis. Alternatively, the information-on-movement acquiring section 73 may calculate an average value of the third total sum and fourth total sum as the aforementioned difference between corresponding local images. The average value here, again, is obtained on a local image-by-local image basis. Note that the total difference value and average value here are calculated for each of a plurality of slice positions, as in the embodiment described earlier.
The information creating section 74 creates a motion profile for each local image by creating a motion profile based on the feature quantity calculated using the third total sum and fourth total sum.
In the case that the motion profile is created on a local image-by-local image basis, the identifying section 75 identifies a time when motion of the heart stops or is smaller than a predetermined amount on a local image-by-local image basis based on the motion profile at Step S3 described earlier. Then, at Step S4 described earlier, the second reconstructing section 76 reconstructs a partial second X-ray tomographic image at the aforementioned time for each part corresponding to the local image, and then, produces one second X-ray tomographic image comprised of the partial second X-ray tomographic images for a required slice position. It should be noted that the partial second X-ray tomographic image is also obtained at one time for a plurality of slice positions.
When the motion profile is created on a local image-by-local image basis as described above, the identifying section 75 may identify a local image Idm in which motion of the heart is detected. A region hatched by dots in
The identifying section 75 detects motion of the heart based on the motion profile. The identifying section 75 identifies that the heart is in motion when the index value is greater than a predefined threshold Ith in the motion profile, for example.
The identifying section 75 may identify that the heart is in motion when the index value is greater than the predefined threshold Ith only in the case that the waveform of the motion profile is periodic. It may also detect motion of the heart at a plurality of different times, and identify a region of the local images Idm at each time.
The identifying section 75 may identify the region of the local images Idm in which motion of the heart is detected as a region of the heart, and identify whether the aforementioned time identified in the motion profile is in diastole or systole based on the size of the region of the heart.
In the case that a region of the heart is identified as described above, regions of air used for identifying diastole and systole in the embodiment described earlier may be identified within the region of the heart.
The display control section 77 may display an image Ic indicating that motion of the heart is detected on the display device 62, although not particularly shown. The display control section 77 may display the image in the first X-ray tomographic image I1, for example. The image Ic is a color image through which a background black-and-white image passes, for example. The image Ic is displayed in a portion in the first X-ray tomographic image I1 corresponding to local images in which motion of the heart is detected by the information creating section 74, for example.
The display control section 77 may display an image Idt indicating a temporal difference in motion of the heart, as shown in
The display control section 77 displays a first image Idt1, a second image Idt2, and a third image Idt3 as the image Idt. The first image Idt1 indicates a region having a time at which motion of the heart starts from its momentary stop later than the second image Idt2. The third image Idt3 indicates a region having a time at which motion of the heart starts from its momentary stop earlier than the second image Idt2.
The first image Idt1 is displayed in a portion in the second X-ray tomographic image I2 corresponding to local images having a first motion profile MP1 shown in
The first motion profile MP1 has a waveform whose phase is behind that of the second motion profile MP2. The third motion profile MP3 has a waveform whose phase is in advance of that of the second motion profile MP2.
The first image Idt1, second image Idt2, and third image Idt3 are displayed with mutually different display patterns. While in
While the present invention has been described with reference to the embodiments, it will be easily recognized that the invention may be practiced with several modifications without changing the spirit and scope thereof. For example, a case in which three images are produced as a multi-time image group is described in the embodiment above, it is sufficient that the multi-time image group is comprised of at least two images.
Moreover, the technique of identifying a time by the identifying section 75 described in the embodiment above is exemplary and is not limited to that described above.
Furthermore, the weighting function described in the embodiment above is exemplary and is not limited to that described above. For example, the weighting function may be a weighting function W1 shown in
While the present embodiment is an X-ray CT apparatus, the invention is also applicable to tomographic imaging apparatuses using radiation other than X-rays, for example, those using gamma rays.
In addition, a program for causing a computer to function as several means for performing control and/or processing in the X-ray CT apparatus described above and a recording medium in which such a program is stored each constitute an exemplary embodiment of the invention as well.
Number | Date | Country | Kind |
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2016-063470 | Mar 2016 | JP | national |