JP4509507B2 - Radiation calculation tomographic image apparatus and tomographic image generation method - Google Patents

Description

  The present invention relates to a radiation computed tomography apparatus such as an X-ray CT (Computed Tomography) apparatus, and a tomographic image generation method using the radiation computed tomography apparatus.

In a computed tomography apparatus represented by an X-ray CT apparatus, projection data of a tomographic plane is acquired in a plurality of views around the tomographic plane of a subject whose image is to be generated, and the tomographic plane of the tomographic plane is acquired based on this projection data. An image (tomographic image) is generated. Such an X-ray CT apparatus is described in Patent Document 1, for example.
In the X-ray CT apparatus as described in Patent Document 1, an X-ray tube that radiates a fan-shaped X-ray beam and a plurality of channels are arranged in a row so that the X-ray beam can be detected within the above-described tomographic plane. The arranged detectors are arranged symmetrically with respect to a line connecting a radiation point of the X-ray beam and a predetermined rotation axis. Then, the X-ray tube and the detector are rotated around the rotation axis while maintaining a relative positional relationship to obtain projection data of a plurality of views.

In this way, when the projection data is obtained by rotating a detector in which a plurality of channels are arranged in a line around the subject, 1 is set in the portion outside the rotation axis than the portion on the rotation axis side even at the same view interval. The moving distance for the view increases. This means that it is necessary to generate an image having a larger area than the portion on the rotating shaft side with the same information amount in the portion outside the rotating shaft.
Since X-rays that pass through a region farther away from the rotation axis are detected in the channel outside the detector, the contribution ratio to the image of the portion outside the rotation axis is higher in the outer channel.
JP 2000-83946 A

As described above, in the configuration where it is necessary to generate an image of a larger area with the same information amount outside the rotation axis, there is a disadvantage that the resolution of the tomographic image decreases as the distance from the rotation axis increases.
Corrections for suppressing this decrease in resolution have also been proposed, but conventionally, the difference in contribution rate to the image for each channel as described above is not considered, and all detection values of each channel are uniformly set. In order to suppress the decrease in resolution, a correction was made. For this reason, for example, there is a tendency to overcorrect the portion on the rotating shaft side, resulting in the occurrence of artifacts and the like, and the image quality of the tomographic image may be deteriorated as a whole.

Therefore, an object of the present invention is to provide a radiation computed tomographic image apparatus capable of suppressing deterioration in image quality of a tomographic image caused by generating a tomographic image based on projection data of a subject around a certain rotation axis. There is.
Another object of the present invention is to reduce the degradation of tomographic image quality caused by generating a tomographic image based on projection data of a subject around a certain rotation axis using a radiation computed tomographic image apparatus. An object of the present invention is to provide a tomographic image generation method that can be suppressed.

  A radiation computed tomographic imaging apparatus according to the present invention includes a radiation source that emits a radiation beam in a fan shape, and a plurality of detection channels that are arranged to face the radiation source across a subject and detect the fan-shaped radiation beam. A radiation detector including at least one detection channel array arranged in a line, and the radiation beam emitted from the periphery of the subject around the rotation axis in the imaging tomographic plane and passed through the subject A projection data acquisition means for detecting a radiation beam with the radiation detector and acquiring projection data of the imaging tomographic plane of the subject in a plurality of views shifted by a predetermined angle around the rotation axis; and from the projection data Regarding the view data obtained for each view, the view data in a certain view and a predetermined number of views before and after the view are included in the view data. Reconstructing means for generating a reconstruction data for each view by performing a filtering process to give a predetermined weight, and calculating and reconstructing image data of the imaging tomographic plane based on the reconstruction data; And the weight to be given to the view data in the filtering process is determined individually for each detection channel of the plurality of detection channels.

  In addition, a tomographic image generation method according to the present invention includes a radiation source that emits a radiation beam in a fan shape, and a plurality of detection channels that are arranged to face the radiation source across a subject and detect the fan-shaped radiation beam. A radiation detector having at least one detection channel array arranged in a row, and calculating image data of the imaging tomographic plane of the subject based on projection data obtained from detection values of the radiation detector. A tomographic image generation method using a reconstructed radiation computed tomography apparatus, wherein the radiation has passed through the subject by emitting the radiation beam from around the subject around a rotation axis within the imaging tomographic plane Beams are detected by the radiation detector, and the projection data of the imaging tomographic plane of the subject in a plurality of views shifted by a predetermined angle about the rotation axis. A projection data obtaining step for obtaining a view, and a filtering process for assigning a predetermined weight to the view data in a certain view and a predetermined number of views before and after the view with respect to the view data for each view obtained from the projection data A tomographic image generating method for performing the filtering process using the weights individually determined for each of the plurality of detection channels in the filtering step.

In the present invention, the radiation source of the projection data acquisition means and the radiation detector are opposed to each other with the subject interposed therebetween in the imaging tomographic plane. A radiation detector having a detection channel array in which a plurality of detection channels are arranged in a row detects a fan-shaped radiation beam emitted from a radiation source in an imaging tomographic plane. Within the imaging tomographic plane, a radiation beam is emitted from the periphery of the subject around the rotation axis, and this radiation beam that has passed through the subject is detected by a radiation detector, so that a plurality of positions shifted by a predetermined angle around the rotation axis In this view, projection data of the tomographic plane of the subject is acquired. View data is generated for each view based on the projection data by the reconstruction means.
A filtering process for assigning this weight to view data in a certain view and views before and after this view is performed by the reconstruction means using weights individually determined for each of the plurality of detection channels. As a result, reconstruction data is generated for each view. The reconstruction unit generates image data of the imaging tomographic plane based on the reconstruction data.

  According to the present invention, in the image data generation of the tomographic plane based on the projection data of the subject for each of the plurality of views around the predetermined rotation axis, the influence on the image due to the rotation of each view around the rotation axis. Can be corrected for each channel of the radiation detector, so that deterioration of the image quality of the image of the tomographic plane can be suppressed.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The radiation in the present invention includes X-rays. Hereinafter, an X-ray CT apparatus using X-rays as radiation will be described as an example.

  FIG. 1 is a diagram showing a schematic configuration of an X-ray CT apparatus according to an embodiment of the present invention. An X-ray CT apparatus 10 shown in FIG. 1 has an X-ray CT apparatus main body 10A and a console 10B. An embodiment of the radiation computed tomography apparatus in the present invention is an X-ray CT apparatus 10 shown in FIG.

The X-ray CT apparatus main body 10A includes a projection data acquisition unit 2 and a data acquisition system (Data Acquisition System: DAS) 20, as shown in FIG.
One embodiment of the projection data acquisition means in the present invention corresponds to the projection data acquisition unit 2.
The projection data acquisition unit 2 includes an X-ray source XL that emits X-rays and an X-ray detector that detects X-rays emitted from the X-ray source XL.

The X-ray source XL emits a fan-shaped X-ray beam 5 from the X-ray focal point 3. As shown in FIG. 1, the emission surface of the fan-shaped X-ray beam is the xy plane. The axis orthogonal to the xy plane is taken as the z axis.
The projection data acquisition unit 2 detects the intensity of the X-ray beam 5 by the detection channel array 7 of the X-ray detector.

The detection channel array 7 has a plurality of detection channels ch arranged in a line in the direction of the spread of the X-ray beam 5 in the xy plane so that the intensity of the fan-shaped X-ray beam 5 can be detected. Each detection channel ch is configured by, for example, a combination of a scintillator and a photodiode.
X-ray intensity can be detected independently by each detection channel ch, and data of the number of detection channels ch can be obtained. The number Q of detection channels ch is about 1000, for example.
Further, in the present embodiment, the X-ray beam 5 and the detection channel array 7 are line-symmetric with respect to a line connecting the X-ray focal point 3 and the predetermined axis O as shown in FIG. A radiation source XL and a detection channel 7 are formed.
One embodiment of the rotating shaft in the present invention is the axis O.

  In the present embodiment, the X-ray detector has only one detection channel row 7, but an X-ray detector having a plurality of detection channel rows 7 in the z-axis direction can also be used. In this case, it is preferable from the viewpoint of efficient data acquisition to emit an X-ray beam having a thickness in the z-axis direction by the X-ray source XL.

  As shown in FIG. 1, the X-ray source XL and the detection channel array 7 are arranged with the subject 1 interposed therebetween. The X-ray source XL and the detection channel array 7 of the X-ray CT apparatus 10 according to the present embodiment rotate around the axis O while maintaining their relative positional relationship. For example, the body axis direction from the head of the subject 1 toward the leg is matched with the direction of the axis O. The direction of the axis O coincides with the direction of the z axis in FIG.

  The X-ray source XL and the detection channel row 7 are rotated around the axis O, and the intensity of the X-ray beam 5 that has passed through the subject 1 is changed while the irradiation direction of the X-ray beam 5 on the subject 1 is sequentially changed. The X-ray intensity data is collected by the scan detected in. As a result, data in a plurality of directions shifted by a predetermined angle around the axis O per rotation around the axis O is obtained. The direction of data collection shifted by a predetermined angle about the axis O is called a view. The number of views R per rotation is about 1000, for example. In this case, the view interval Δθ between views shown in FIG. 1 is about 360 ° / 1000.

  As described above, in the present embodiment, the projection data of each view by irradiating the X-ray beam 5 around the axis O by rotating the X-ray source XL and the detection channel array 7 around the axis O is obtained. Obtained. However, the data of each view obtained by irradiating the fan-shaped X-ray beam 5 from multiple directions around the subject 1 may be obtained without rotating the X-ray source XL and the detection channel row 7 around the axis O. it can. For example, if a CT device such as an EBT (Electron-Beam CT) device is used, the projection data of multiple views rotating around the axis O can be acquired without physically rotating the X-ray source. be able to.

The DAS 20 collects a plurality of data obtained by the detection channel train 7. The DAS 20 converts the analog data of the X-ray intensity detected by the detection channel array 7 into digital data and transmits it to the console 10B.
Each piece of digital data transmitted to the console 10B is projection data of a tomographic plane through which the X-ray beam 5 passes in the subject 1.

As shown in FIG. 1, the console 10 </ b> B includes a calculation / control device 23 and a display device 25.
One embodiment of the reconstruction means in the present invention corresponds to the arithmetic / control device 23. The arithmetic / control device 23 is realized by, for example, hardware such as a CPU (Central Processing Unit) and software for driving the hardware.

  The arithmetic / control device 23 receives the projection data collected by the DAS 20. The calculation / control apparatus 23 performs reconstruction calculation such as back projection based on the received projection data, and generates image data. The image data generated based on the projection data is a tomographic image of the subject 1 through which the X-ray beam 5 passes, that is, image data of a tomographic image.

  When the projection data of each view is acquired by rotating the X-ray source XL and the detection channel row 7 around the axis O, as is apparent from FIG. 1, the outer portion away from the axis O even with the same view interval Δθ. The moving distance at is larger than the moving distance at the portion on the axis O side. In such a case, when the tomographic image is reconstructed by back projection, an image having a larger area in the portion outside the axis O than the portion on the axis O side is generated with substantially the same amount of information. As a result, due to the nature of back projection, the resolution of the tomographic image is reduced in the portion outside the axis O. However, since the principle and nature of back projection are well known, detailed description is omitted.

The calculation / control device 23 controls the view data of each view based on the projection data in view of a certain view and the previous and subsequent views in order to improve the image quality by suppressing a decrease in resolution of the tomographic image outside the axis O. A filtering process for giving a predetermined weight to the data is performed. Then, based on the view data after the filtering process, the calculation / control apparatus 23 performs a calculation such as back projection to generate tomographic image data.
Details of the filtering process by the arithmetic / control device 23 will be described later.

  Further, the calculation / control device 23 controls the X-ray CT apparatus 10 to generate a tomographic image, and rotates the X-ray source XL and the X-ray detector in the projection data acquisition unit 2 and acquires projection data via the DAS 20. Etc. are executed.

FIG. 2 is a functional block diagram showing a schematic configuration of functions related to a calculation function for generating tomographic image data of the calculation / control apparatus 23.
As illustrated in FIG. 2, the arithmetic / control device 23 includes a view data generation unit 30, a weight selection unit 32, a reconstruction data generation unit 34, and an image data generation unit 36.
The hardware of each of these units can be appropriately realized by a plurality of processors.

The projection data transmitted from the DAS 20 is input to the view data generation unit 30. The view data generation unit 30 performs predetermined processing such as offset correction on the projection data of each view around the axis O, and generates view data for each view.
The offset correction is to correct an offset value mixed in projection data mainly due to a drift of an A / D (Analog to Digital) converter provided in the DAS 20.

  As described above, the view interval Δθ between views is set to, for example, about 360 ° / 1000, but the view interval Δθ may vary depending on the shooting conditions. If the shooting condition changes and the view interval Δθ increases, for example, the resolution of the image of the outer portion away from the axis O decreases accordingly.

In consideration of such properties, the weight selection unit 32 displays a group of weights to be given to the view data of each detection channel ch at the time of filtering processing by the reconstruction data generation unit 34 described later based on the view interval Δθ. 3 is selected from a plurality of groups Gp1, Gp2,..., Gpn,. The weight values included in the weight groups Gp1, Gp2,..., Gpn,... Are different values that can improve the image quality of the tomographic image corresponding to the difference in the view interval .DELTA..theta.
FIG. 3 is a diagram illustrating a correspondence relationship between each detection channel ch in the detection channel row 7 and a weight value assigned to each view data. For convenience, each detection channel ch in the detection channel row 7 is numbered 1, 2,..., Q sequentially from the left in the figure. Further, in the detection channel row 7, a detection channel positioned at the center in the direction in which the detection channels ch are arranged, that is, the direction along the width direction of the X-ray beam 5 is defined as a detection channel ct. The number of detection channels ct may be one or two, but here, there are two detection channels ct, which are represented as detection channels ct1 and ct2, respectively.
As shown in FIG. 3, in the present embodiment, the weight to be given to each view data during the filtering process in the reconstruction data generation unit 34 is individually determined for each detection channel ch.

  The reconstruction data generation unit 34 receives the view data generated by the view data generation unit 30. Then, the reconstruction data generation unit 34 uses the weight of the group selected by the weight selection unit 32 to weight the view data in a certain view and the view data in a predetermined number of views before and after each detection channel ch. Is applied to perform filtering processing to generate new view data.

An example of the filtering process performed by the reconfiguration data generation unit 34 is shown in FIG. 3 by weight α _in (i is a channel number, i = 1,..., Q. n is a weight. As a general formula using weights generally described as a group number.

Eij = (1 + 2α _in ) Dij−α _in Dij−1−α _in Dij + 1
... (1)

In the expression (1), the view data Dij represents view data based on projection data detected in the j-th (j = 1, 2,..., R) view of the i-th detection channel ch. The view data Eij represents view data newly generated corresponding to the view data Dij by the filtering process of the expression (1).
For example, in the case where there is no front or rear view data and the view data used for the filtering process is insufficient, such as the first detection channel ch and the last Qth detection channel ch, the available view data Just generate new view data.
Note that the value of the weight α _in may be positive or negative.

The above expression (1) is an expression representing a filtering process for generating new view data from three view data of a certain view data for each detection channel ch and the view data immediately before and after the view data. However, the number of view data used for the filtering process need not be three. Filtering processing can be performed using a predetermined number of view data before and after certain view data.
If the weight to be given to each view data can be individually determined for each detection channel ch, a filtering process represented by an expression other than Expression (1) may be performed.

For example, it is assumed that the weight selection unit 32 selects the weight group Gp1 shown in FIG. It is considered that new view data E12 corresponding to the view data D12 of the second detection channel ch is generated for the view data of the first view using the filtering process of Expression (1).
The weight α ₂₁ assigned to the second detection channel ch in the group Gp1 is, for example, α ₂₁ = 0.1. At this time, new view data E12 is obtained by the calculation of E12 = 1.2D12−0.1D11−0.1D13. This equation corresponds to applying an enhancement process for applying an enhancement filter to enhance the view data in the vicinity of the view data D12.

For example, when the 500th detection channel ch is the detection channel ct1 in the center of the detection channel row 7, new view data corresponding to the view data D1500 of the detection channel ct1 is obtained for the view data of the first view. Consider generating E1500.
At this time, the weight α ₅₀₀₁ assigned to the 500th detection channel ch in the group Gp1 is, for example, α ₅₀₀₁ = −0.15 different from the weight α ₂₁ . At this time, new view data E1500 is obtained by calculation of E1500 = 0.7D1500 + 0.15D1499 + 0.15D1501. This equation corresponds to performing a smoothing process for smoothing view data in the vicinity of the view data D1500 by applying a smoothing filter.

As described above, in the filtering process using Equation (1), the enhancement process is performed when the value of the weight α _in is α _in > 0, and the smoothing process is performed when α _in <0. It will be.
As described above, the resolution of the tomographic image tends to decrease in the portion outside the axis O. Since the X-ray beam 5 that passes through a region farther away from the axis O as the detection channel ch outside the detection channel row 7 is detected, the contribution ratio to the resolution of the outer portion is as high as the detection channel ch outside. large. Accordingly, the value of the weight α _in associated with each detection channel ch in the detection channel row 7 is set to a value such that stronger enhancement processing is performed toward the outer detection channel ch, and the effect of substantially improving the resolution is obtained. It is preferable from the viewpoint of improving the image quality of the tomographic image.

On the other hand, in the portion close to the axis O, the resolution of the tomographic image is originally higher than the portion outside the axis O. Therefore, in order to make the resolution of the tomographic image uniform throughout, the value of the weight α _in is applied to the detection channel ch on the central side of the detection channel row 7 having a high contribution ratio to the axis O side portion of the tomographic image. It is preferable to set the value so that a stronger smoothing process is performed as it goes.

By performing the filtering process as described above, the view data Dij (i = 1,..., Q, j = 1,..., R) before the filtering process as shown in FIG. ) New view data Eij (i = 1,..., Q, j = 1,..., R) after filtering processing as shown in FIG.
In FIG. 4 (a), (b) , both the vertical axis represents the channel number i of the detection channel row 7, both the horizontal axis represents the view number j.

For example, when detecting the fan-shaped X-ray beam 5 irradiated around the axis O using the detection channel row in which the detection channels ch are arranged in a ring shape and do not rotate around the axis O, each detection channel ch is detected. The X-ray beam 5 having the same incident angle is not always incident on.
In such a case, the reconstruction data generation unit 34 irradiates the detection channel ch portion of the ring-shaped detection channel array with the X-ray beam 5 used for acquiring projection data of a certain view. Judging.
The reconstruction data generation unit 34 is based on the X-ray intensity detected by each detection channel ch in correspondence with the distance from the center in the width direction of the fan-shaped X-ray beam 5 irradiated while rotating around the axis O. Arrange the projection data. Thereby, the same view data array as that shown in FIG. 4A can be obtained.
Thereafter, as in the filtering process described above, if the weight α _in is individually determined in correspondence with the direction of the number of detection channels in the array of view data, the fan-shaped X-ray beam is the same as described above. Thus, it is possible to obtain new view data Eij that has been subjected to the filtering process in consideration of the influence of the rotation of 5.

Note that the value of the weight α _in used for the filtering processing described so far is stored in a storage device such as a memory (not shown). The weight selection unit 32 and the reconfiguration data generation unit 34 appropriately access the storage device and obtain the value of the weight α _in .

  The reconstruction data generation unit 34 performs predetermined predetermined processing for reconstruction on the generated new view data Eij as necessary, and finally generates reconstruction data.

The image data generation unit 36 illustrated in FIG. 2 performs reconstruction calculation processing such as back projection using the reconstruction data generated by the reconstruction data generation unit 34, and generates image data of the tomographic plane of the subject 1. Generate.
The image data generation unit 36 performs predetermined image processing as necessary based on the generated image data.
The image generated by the above processing is displayed on a display device 25 such as a CRT (Cathode-Ray Tube) or a liquid crystal display panel.

  The procedure of the tomographic image generation method according to the present invention using the X-ray CT apparatus 10 will be briefly summarized with reference to FIG. 5A and 5B are diagrams showing the procedure of the tomographic image generation method according to the present invention. As shown in FIGS. 5A and 5B, the procedure of the tomographic image generation method according to the present invention can be modified in various ways, but FIGS. 5A and 5B are pre-processing stages. Since only a part of the procedure is replaced, the procedure will be described with reference to FIG. 5A, and detailed description of FIG. 5B will be omitted.

In order to obtain a tomographic image of the subject 1, first, projection data of the tomographic plane of the subject 1 is acquired (step ST1).
As described above, by scanning the subject 1 by rotating the X-ray source XL and the X-ray detector around the axis O, projection data of tomographic planes in a plurality of views can be obtained.

The view data generation unit 30 of the calculation / control apparatus 23 performs first preprocessing such as offset correction on the projection data obtained in step ST1 (step ST2).
The reconstruction data generation unit 34 performs the filtering process described above based on the view data obtained as a result of the first preprocessing by the view data generation unit 30 (step ST3).
In step ST3, the reconstruction data generation unit 34 performs filtering using weights individually determined for each detection channel ch in the weight group selected by the weight selection unit 32 based on the view interval Δθ between views. Execute the process.
As a result of the filtering process by the reconstruction data generation unit 34, new view data Eij as shown in FIG. 4B is generated.

The reconstruction data generation unit 34 performs second preprocessing such as beam hardening (BH) correction on the generated new view data Eij to generate reconstruction data (step ST4).
The beam hardening correction is a correction for correcting a non-linear relationship between the path length through which the X-ray passes through the subject 1 and the detected X-ray intensity resulting from the difference in X-ray absorption rate depending on the substance. is there.
Steps ST2, 3, and 4 are referred to as pre-processing steps before generating tomographic image data.

The image data generation unit 36 performs image reconstruction calculation processing using the reconstruction data obtained in step ST4, and generates image data of the subject 1 (step ST5).
The image data generation unit 36 also performs post-processing such as rendering based on the generated image data (step ST6).
By post-processing in step ST6, for example, processing such as color conversion of tomographic images and switching between two-dimensional display and three-dimensional display is executed.

  A tomographic image based on the image data that has been post-processed in step ST6 is displayed on display device 25 (step ST7).

As described above, it is possible to obtain a tomographic image that has been subjected to the filtering process according to the distance from the axis O and corrected in consideration of the influence of the rotation of the fan-shaped X-ray beam 5.
As shown in FIG. 5B in which the order of step ST3 and step ST4 is changed, the filtering process according to the present embodiment is an arbitrary pre-processing stage prior to image data generation. This can be done in steps.

FIG. 6 is a schematic diagram of a verification image 50 for showing a difference between a tomographic image obtained by using the X-ray CT apparatus 10 according to the present embodiment and a tomographic image obtained by a conventional X-ray CT apparatus.
FIG. 6 shows an image of a tomographic plane in the xy plane shown in FIG. 1 using a cylindrical phantom having a radius of 125 [mm] as the subject 1. In the verification image 50 shown in FIG. 6, the portion above the line LL represents the channel-specific weight image 50a obtained by performing the filtering process in which the weight is set for each detection channel ch according to the present embodiment. ing. The lower part of the line L-L represents the same weight image 50b obtained as a result of correction by applying the same weight to all the detection channels ch as in the prior art.
FIG. 6 shows the result of photographing with the center of the axis along the longitudinal direction of the cylindrical phantom aligned with the axis O shown in FIG.

The phantom used for photographing is made of polypropylene and has a thickness of 80 [mm] in the z-axis direction.
A plurality of voids exist inside the phantom, and in these voids, as shown in FIG. 6, air AR, Teflon (registered trademark) TF, and water equivalent material WT having the same X-ray absorption rate as water, Are appropriately filled.

In the present embodiment, as described above, the weighting is individually determined for each detection channel ch in the detection channel row 7 and the filtering process for correction is performed in consideration of the influence of the rotation of the X-ray beam 5. For this reason, it is possible to perform appropriate correction according to the position of the tomographic plane such as the outer side and the inner side of the verification image 50 in the radial direction. As a result, as shown in FIG. 6, the image blurs like the same weight image 50 b on the outer side away from the axis O, for example, in a portion where the material changes and the X-ray absorption rate changes. Deterioration can be suppressed, and the resolution can be substantially improved like the weighted image 50a for each channel. Further, on the axis O side, it is possible to prevent occurrence of an artifact that is overcorrected and a portion where an image according to the material is originally displayed is depressed and displayed in white.
As described above, the resolution can be made uniform over the entire tomographic image. If the resolution is uniform over the entire tomographic image, the image has no sense of incongruity and becomes very easy to see, so it can be said that the image quality is improved overall.
In addition, since the weight value is adjusted so that the image quality is uniform along the radial direction as in the channel-specific weight image 50a, the same material is used even in the direction along the radial direction as in the regions Re1 and Re2. If so, the standard deviations of the values of the pixels in the regions Re1 and Re2 are substantially the same. Thus, since the standard deviation of the values of the pixels in the region of the same material becomes uniform, the image quality of the image obtained by this embodiment is improved.
By using the tomographic image generation method according to the present embodiment, when the standard deviation of the value of each pixel is not uniform as in the prior art, more radiation (in the region where the standard deviation is smaller than the weight of each detection channel ch) X-rays) can be irradiated so that the standard deviation of each pixel need not be made uniform, and the radiation exposure dose of the subject can be reduced.

In addition, the content described in the said embodiment and drawing is an example for demonstrating this invention, and this invention is not limited to said content. For example, the position of the axis O can be appropriately changed between the X-ray focal point 3 and the center portion of the detection channel row 7. Further, other radiation such as γ rays other than X-rays may be used as long as it can be used for tomographic image generation.
Also, for example, when the view interval Δθ is changed, if the amount of change does not significantly affect the resolution of the image, the same weight value is used for different view intervals Δθ. Also good. In this case, however, the weight value is different for each detection channel ch.

  The present invention can be used in a CT apparatus that generates a tomographic image of a living body. Further, the present invention can be used not only for living bodies but also for non-living tomographic image generation using projection data.

1 is a diagram showing a schematic configuration of an X-ray CT apparatus according to an embodiment of the present invention. FIG. 2 is a functional block diagram showing a schematic configuration of functions related to a calculation function for generating tomographic image data in the calculation / control apparatus of the X-ray CT apparatus shown in FIG. 1. It is a figure which shows the correspondence of each detection channel of a detection channel row | line | column, and the value of the weight provided to each view data. It is a figure which shows the view data obtained using the X-ray CT apparatus shown in FIG. 1, (a) has shown the view data before filtering processing, (b) has shown the view data after filtering processing . (A) is a figure which shows the procedure of the tomographic image generation method which concerns on this invention, (b) is a figure which shows the modification. It is a typical figure of the verification image for showing the difference of the tomogram obtained using the X-ray CT apparatus concerning this embodiment, and the tomogram by the conventional X-ray CT apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Subject 2 ... Projection data acquisition part 5 ... X-ray beam 7 ... Detection channel 10 ... X-ray CT apparatus (radiation tomography apparatus)
DESCRIPTION OF SYMBOLS 10A ... X-ray CT apparatus main body 10B ... Console 23 ... Calculation / control apparatus 30 ... View data generation part 32 ... Weight selection part 34 ... Reconstruction data generation part 36 ... Image data generation part
XL ... X-ray source
ch: Detection channel

Claims (12)

A radiation source that emits a radiation beam in a fan shape; and
A radiation detector comprising at least one detection channel array arranged in a row with a plurality of detection channels for detecting the fan-shaped radiation beam arranged opposite to the radiation source with the subject interposed therebetween, In the plane, the radiation beam is emitted from the periphery of the subject around the rotation axis, and the radiation beam passing through the subject is detected by the radiation detector, and shifted by a predetermined angle around the rotation axis. Projection data acquisition means for acquiring projection data of the imaging tomographic plane of the subject in a plurality of views;
Relates view data for each of the views obtained from the projection data, the view of the view data in a predetermined number of views before and after a certain view and the view, respectively subjected to filtering processing for adding by applying a predetermined weight Reconstructing means for generating reconstruction data every time, calculating image data of the imaging tomographic plane based on the reconstruction data, and reconstructing
The radiation calculation tomographic image apparatus, wherein the weight to be given to the view data in the filtering process is individually determined for each of the detection channels of the plurality of detection channels. The radiation computed tomography apparatus according to claim 1, wherein the weight for each detection channel in the detection channel array changes according to a distance from a center along a width direction of the fan-shaped radiation beam. The radiation computed tomography apparatus according to claim 2, wherein the weight is a value for performing stronger emphasis processing from the center side toward an outer portion of the detection channel row by the filtering processing. The radiation computed tomography apparatus according to claim 2, wherein the weight is a value for performing a stronger smoothing process from the outer part of the detection channel sequence toward the center by the filtering process. The weight is a value for performing a smoothing process by the filtering process on the center side, and a value for performing an emphasizing process by the filtering process on an outer portion of the detection channel sequence. The radiation computed tomography apparatus according to claim 2. The radiation computed tomography apparatus according to claim 1, wherein different weights are used as the weights for the detection channels with respect to different view intervals with respect to the plurality of views. A radiation source that emits a radiation beam in a fan shape and at least one detection channel row that is arranged to face the radiation source with a subject interposed therebetween and in which a plurality of detection channels that detect the fan-shaped radiation beam are arranged in a row. And a tomography using a radiation calculation tomographic apparatus that calculates and reconstructs image data of the imaging tomographic plane of the subject based on projection data obtained from detection values of the radiation detector. An image generation method comprising:
Within the imaging tomographic plane, the radiation beam is emitted from the periphery of the subject around the rotation axis and passed through the subject, and the radiation detector detects the radiation beam, and the predetermined angle around the rotation axis. A projection data acquisition step of acquiring the projection data of the imaging tomographic plane of the subject in a plurality of shifted views;
A filtering step of applying a filtering process for adding the view data in a certain view and a predetermined number of views before and after the view with respect to the view data obtained from the projection data by adding a predetermined weight; Have
A tomographic image generation method for performing the filtering processing using the weights individually determined for each of the plurality of detection channels in the filtering step. 8. The filtering process is performed in the filtering step by changing the weight for each of the detection channels in the detection channel row according to a distance from the center along the width direction of the fan-shaped radiation beam. The tomographic image generation method described. The tomographic image generation method according to claim 8, wherein the weight is set to a value for performing stronger emphasis processing from the center side toward an outer portion of the detection channel sequence by the filtering processing. The tomographic image generation method according to claim 8, wherein the weight is a value for performing a stronger smoothing process from the outer part of the detection channel sequence toward the center side by the filtering process. The weight is a value for performing smoothing processing by the filtering processing on the center side, and a value for performing enhancement processing by the filtering processing on an outer portion of the detection channel sequence. Tomographic image generation method. In the filtering step, when the view intervals of the plurality of views are different for each detection channel, one different weight is selected from the plurality of weights, and the filtering process is performed using the selected weight. Item 12. The tomographic image generation method according to any one of Items 7 to 11.

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