JP6292826B2 - Image processing apparatus, image processing method, and program - Google Patents

Description

  The present invention relates to an image processing apparatus, an image processing method, and a program.

  Conventionally, an X-ray computed tomography apparatus (X-ray CT) has been widely used as a powerful image diagnostic means. In X-ray CT, images are acquired at a plurality of angles around an imaging target over an angle of 180 degrees or more, and a tomographic image is created based on the obtained plurality of images.

  On the other hand, in the case of photographing a moving subject in X-ray CT, the occurrence of artifacts and image blur due to the movement of the photographing target becomes a problem. Therefore, it is necessary to estimate and correct artifacts and image blurs caused by such movements, and various methods have been devised for estimating and correcting artifacts and image blurs.

For example, in Patent Document 1, a motion map is created by calculating a difference between a reprojection image obtained by performing forward projection on a reconstructed image of a radiation projection image and a previous projection image, A technique for estimating the presence or absence and the amplitude of motion is disclosed.
In Patent Document 2, a series of transmitted X-ray images is divided into a plurality of sets, an X-ray distribution image is reconstructed from each set of transmitted X-ray images, and based on a set of transmitted X-ray images having the maximum sharpness. A technique for displaying an X-ray tomographic image or the like is disclosed.
Non-Patent Document 1 describes a feature point extraction and feature point matching method using the SIFT method. In Non-Patent Document 2, in the time difference method, global registration for detecting and correcting the rotation and movement of the entire image and local registration for detecting local deformation and the like are used. Techniques for matching geometric structures are disclosed.

Special table 2012-515592 gazette JP 2000-217810 A

Hiroyoshi Fujiyoshi. "Gradient-based feature extraction-SIFT and HOG-" Information Processing Society of Japan Research Report CVIM 160, pp. 211-224, 2007. Takayuki Ishida, Shigehiko Katsuragawa, Hiroshi Fujita, Shumi Takeo, “Medical Image Handbook”, Ohmsha, 2010

  However, as in Patent Document 1, when the whole of a plurality of projection images obtained by shooting is backprojected and reprojected, if there is a movement of the subject while the plurality of projection images are being shot, The image quality of the back-projected image is deteriorated. For this reason, there are cases where the motion cannot be estimated appropriately.

Therefore, the present invention provides a selection unit that selects a part of projection images from a plurality of projection images obtained by imaging a subject, and a tomographic image reconstructed based on the selection projection image selected by the selection unit. Based on the re-projection unit that generates a re-projection image by re-projecting, the non-selection projection image that is not selected by the selection unit among the plurality of projection images, and the re -projection image, A motion detecting means for detecting the movement of the subject in the image, a correcting means for correcting the non-selected projection image based on the detected movement, the selected projection image, and the corrected non-selected projection image. And an image generation means for generating a tomographic image .

  According to the present invention, it is possible to prevent the SN reduction of a tomographic image obtained from a series of projection images obtained in a certain period and the occurrence of artifacts.

It is a figure which shows the tomographic imaging apparatus concerning 1st Embodiment. It is a figure which shows the hardware structural example of the image processing apparatus which concerns on embodiment of this invention. It is a flowchart which shows the tomographic image generation process concerning 1st Embodiment. It is a figure which shows the tomographic imaging apparatus concerning 2nd Embodiment. It is a figure which shows the tomographic imaging apparatus concerning 3rd Embodiment. It is a flowchart which shows the tomographic image generation process concerning 3rd Embodiment. It is a figure which shows the tomographic imaging apparatus concerning 4th Embodiment. It is a flowchart which shows the tomographic image generation process concerning 4th Embodiment. It is a figure which shows the tomographic imaging apparatus concerning 5th Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram illustrating a photographing apparatus according to the first embodiment. The imaging apparatus according to this embodiment is a one-tube X-ray CT imaging apparatus, but as another example, the imaging apparatus may be an X-ray CT imaging apparatus having two or more tubes. Furthermore, the imaging apparatus may be an apparatus that images a tomogram of a subject, and other examples may include tomosynthesis, PET, SPECT, MRI, an ultrasonic apparatus, and the like.
The imaging apparatus includes an X-ray tube 101, a gantry 102, an X-ray detector 103, an apparatus control unit 104, and an image processing apparatus 105. The X-ray tube 101 emits X-rays from a plurality of angles. The X-ray detector 103 detects X-rays transmitted through the imaging target (subject) A on the gantry 102 and obtains a projected image of the X-ray image. The apparatus control unit 104 controls the X-ray tube 101, the gantry 102, and the X-ray detector 103.
In the above configuration, the apparatus control unit 104 makes a round of the X-ray tube 101 and the X-ray detector 103 around the imaging target A and captures a projected image over 360 degrees (imaging processing). Thereby, the apparatus control unit 104 obtains a projection image group including a plurality of projection images around the imaging target A. Note that the rotation angle at the time of obtaining the projection image group is not limited to 360 degrees. As another example, when the performance of the tube is insufficient, the apparatus control unit 104 may capture a projection image over two rotations (720 degrees) to obtain a projection image group.

The image processing apparatus 105 generates a tomographic image of the subject A based on a series of projection images. The image processing apparatus 105 includes an image processing unit 106, an image storage unit 107, an image selection unit 108, a reconstruction unit 109, a forward projection unit 110, a motion detection unit 111, and a motion correction unit 112. ing.
The image processing unit 106 processes the projection image acquired from the X-ray detector 103. Specifically, the image processing unit 106 performs preprocessing necessary for performing reconstruction, such as offset correction, gain correction, defect correction, and logarithmic conversion. The image storage unit 107 stores the projection image after processing by the image processing unit 106.

The image selection unit 108 selects some projection images from a plurality of projection images obtained by the X-ray detector 103 according to a predetermined condition based on a priori knowledge. Here, for example, it is assumed that the condition is such that a photographed projection image is selected at a timing at which the movement of the photographing object A is estimated to be small. Note that the conditions are set in advance in a ROM 202 or the like described later. In the present embodiment, in chest CT imaging, it is set as a condition that it is obtained for a certain time immediately after the start of imaging, that is, in a certain imaging order immediately after the imaging starts.
This is because in chest CT imaging, the breathing of the person to be inspected becomes a factor of movement, and there is a high possibility that the person to be inspected can hold his breath in the early stage of imaging. As described above, the condition may determine, for example, a part of the shooting order in the shooting order for obtaining a series of projection image groups.
Note that the number of projection images selected by the image selection unit 108 is two or more and may be any number that is smaller than the number of projection images included in the series of projection image groups. It is preferable that it is less than or equal to half of the number. Hereinafter, the projection image selected by the image selection unit 108 is referred to as a selected projection image. A projection image that is not selected by the image selection unit 108 is referred to as a non-selected projection image.

The reconstruction unit 109 reconstructs the selected projection image and obtains a tomographic image. Hereinafter, the tomographic image reconstructed using the selected projection image is referred to as a reference image. The reconstruction unit 109 also reconstructs the selected projection image and a non-selected projection image after motion correction described later is performed, and obtains a final tomographic image. Note that the algorithm used for reconstruction by the reconstruction unit 109 is not particularly limited, and general algorithms such as analytical reconstruction such as a filtered back projection method, algebraic reconstruction using an inverse matrix or a sequential method, etc. The method can be used.
The forward projection unit 110 forward-projects (reprojects) the reference tomographic image to obtain a reprojected image. Here, the reprojection image is compared with the projection image to be processed in the process described later. Therefore, the forward projection unit 110 performs forward projection so as to match the projection angle of the projection image to be processed. Note that the forward projection unit 110 selects a non-selected projection image as a projection image to be processed.

The motion detection unit 111 compares the projection image to be processed with the reprojection image having the same projection angle as the projection image to be processed. If the subject moves while taking a series of projected images, a difference occurs between the images. The motion detection unit 111 detects this difference as a motion.
The motion detection method includes feature point extraction, feature point matching, and motion vector derivation. As a method of feature point extraction and feature point matching, for example, a method based on the SIFT method is known. For example, Non-Patent Document 1 describes a feature point matching method based on the SIFT method. Using such a method, the motion detection unit 111 according to the present embodiment extracts feature points and feature amounts of the projection image and the reprojection image, and matches the feature points of the projection image and the reprojection image. Next, the motion detection unit 111 derives a motion vector. Specifically, the motion detection unit 111 can obtain a motion vector by subtracting the x coordinate and the y coordinate of the feature points of the corresponding projection image and reprojection image, respectively.
Further, when the feature point extraction fails because the number of feature points extracted falls below a threshold due to blurring of the image, the motion detection unit 111 divides the feature amount extraction method by, for example, a method based on centroid detection. Can be changed to In such a case, a part of the motion correction in the next motion correction unit may be restricted.
Based on the detected motion, the motion correction unit 112 corrects the projection image to be processed so that it becomes an image when there is no motion. The motion correction unit 112 performs, for example, global registration or local registration to deform the projected image. For details of this process, Non-Patent Document 2 can be referred to. Depending on the feature point extraction method, there are limitations on these motion correction methods.

FIG. 2 is a diagram illustrating a hardware configuration of the image processing apparatus 105. The image processing apparatus 105 includes a CPU 201, a ROM 202, a RAM 203, an HDD 204, a display unit 205, and an operation unit 206. The CPU 201 reads a control program stored in the ROM 202 and executes various processes. The RAM 203 is used as a temporary storage area such as a main memory and a work area for the CPU 201. The HDD 204 stores image data, various programs, various information to be described later, and the like. The display unit 205 displays various information. The display unit 205 displays a tomographic image finally obtained, for example. The operation unit 206 accepts various operations from the operator.
The functions of the image processing apparatus 105 described with reference to FIG. 1 are realized by the CPU 201 reading a program stored in the ROM 202 or the HDD 204 and executing this program. Similarly, the processing of the image processing apparatus 105 described with reference to FIG. 3 is realized by the CPU 201 reading a program stored in the ROM 202 or the HDD 204 and executing this program.

FIG. 3 is a flowchart showing tomographic image generation processing executed by the image processing apparatus 105. First, in step S <b> 301, the image selection unit 108 acquires a projection image group, that is, a plurality of projection images, from the image storage unit 107. Next, in S302, the image selection unit 108 selects a projection image from the group of projection images according to a predetermined condition (selection process). In the present embodiment, the image selection unit 108 meets the conditions according to the condition that two or more predetermined number of projected images shot in a certain shooting order (predetermined shooting order) immediately after the start of shooting is selected. Select a projected image.
Next, in S303, the reconstruction unit 109 reconstructs a tomographic image using a plurality of selected projection images to obtain a reference image. Here, the reference image is an example of a first tomographic image. The process of S303 is an example of a reconstruction process.

Next, in S304, the forward projection unit 110 performs forward projection (reprojection) on the reference image to generate a reprojection image (reprojection processing). Here, the forward projection unit 110 first specifies a non-selected projection image to be processed. Then, the forward projection unit 110 generates a reprojection image at a projection angle equal to the projection angle of the identified non-selected projection image.
The reprojection image is generated based on a projection image that is estimated to have little motion. Therefore, by comparing the reprojected image with the non-selected projection image having the same projection angle, it is possible to detect whether or not the non-selected projection image includes a motion. The reprojection image is a prediction of the non-selected projection image when a state with little movement such as respiration continues until the non-selection projection image is captured. That is, the coordinates of the feature point of the subject in the reprojected image become the predicted coordinates of the feature point of the subject when the case where the movement is small continues. In this case, since the movement of the coordinates for each feature point can be obtained, not only the amplitude of movement described in Patent Document 1, but also information on the direction of movement and deformation can be acquired. Can be done accurately.

Next, in S305, the motion detection unit 111 compares the non-selected projection image to be processed with the reprojected image, and detects the motion of the non-selected projection image to be processed based on the comparison result (motion detection). processing). Next, in S306, the motion correction unit 112 corrects the non-selected projection image to be processed based on the detected motion (correction processing).
Next, in S307, the reconstruction unit 109 reconstructs a final tomographic image using the selected projection image and the non-selected projection image after motion correction. Here, the reconstruction unit 109 reconstructs a tomographic image using all the projection images (selection projection image or non-selection projection image) included in the projection image group. Note that the tomographic image reconstructed in S307 is an example of a second tomographic image. Further, the process of reconstructing a tomographic image in S307 (reconstruction process) is an example of an image generation process.

As described above, the imaging apparatus according to the present embodiment reconstructs a tomographic image using a larger number of projection images even when the projection image group includes a motion. Further, the imaging apparatus uses the projection image in which the motion is detected for the reconstruction of the tomographic image after correcting the motion.
Thereby, the imaging device can prevent the occurrence of SN degradation and artifacts. The imaging apparatus can reduce the occurrence of artifacts due to motion compared to a case where a tomographic image is generated using a projection image in which motion is detected as it is. In addition, the SN is improved because the number of projection images increases as compared to the case where a tomographic image is generated using only projection images in which no motion is detected.

Next, a first modification of the imaging device according to the first embodiment will be described. The imaging apparatus only needs to obtain a final tomographic image using the corrected non-selected projection image, and the processing for that purpose is not limited to the embodiment. In the second modified example, the imaging apparatus may reconstruct a final tomographic image using only a part of the projection images of the projection image group.
As another example, the imaging apparatus may perform motion detection and motion correction by comparing the selected projection image with the reprojection image. In this case, the imaging apparatus reconstructs a tomographic image using the corrected selected projection image and the corrected non-selected projection image.
As another example, the imaging apparatus may reconstruct a tomographic image using the corrected non-selected projection image and synthesize it with the reference tomographic image to generate a final tomographic image ( Image generation processing).

  Next, a second modification example will be described. The image selection unit 108 according to the embodiment selects a projected image shot at a timing when it is estimated that the movement of the shooting target A is small by selecting an image in accordance with a predetermined condition, but is not limited thereto. It is not something. In the second modification example, the image selection unit 108 may select images at random. Also in this case, it is possible to reduce SN degradation and occurrence of artifacts as compared to a case where a tomographic image is generated using a series of projection images as they are.

(Second Embodiment)
Next, a photographing apparatus according to the second embodiment will be described. The imaging apparatus according to the second embodiment monitors the movement of the imaging target A and selects a projection image with less movement based on the monitoring result. Hereinafter, the difference between the imaging device according to the second embodiment and the imaging device according to the first embodiment will be described.
FIG. 4 is a diagram illustrating an imaging apparatus according to the second embodiment. The photographing apparatus further includes a motion monitoring unit 401. The motion monitoring unit 401 is, for example, a video shooting camera, an acceleration sensor, an electrocardiograph, a respiratory monitoring device, or the like.

The motion monitoring unit 401 monitors the motion of the imaging target A as the subject while monitoring the projection image (monitoring process).
The image selection unit 402 identifies a period with less motion based on the monitoring result of the motion monitoring unit 401. Specifically, the image selection unit 402 specifically specifies a range in which the amount of motion obtained during a certain time is equal to or less than a threshold value as a period with less motion. Then, the image selection unit 402 selects a projection image obtained during a period with little motion. That is, the image selection unit 402 selects a projection image obtained at a timing when the motion is equal to or less than the threshold (selection process). The condition that the movement is equal to or less than the threshold is an example using a priori knowledge.
Thereby, the imaging device can reconstruct a reference image using a projection image with little motion in the reference image reconstruction process (S303) shown in FIG.
Note that other configurations and processes of the imaging apparatus according to the second embodiment are the same as the configurations and processes of the imaging apparatus according to the first embodiment.

  As described above, the imaging apparatus according to the second embodiment can perform motion detection and motion correction using a clearer reprojection image. Further, the photographing apparatus determines a projection image to be selected according to the projection image group. Therefore, even in a projection image group including irregular motion, a projection image with little motion can be selected. Thereby, the imaging device can prevent the SN degradation of the tomographic image obtained from a series of projection images obtained in a certain period and the occurrence of artifacts.

  As another example, the imaging apparatus may determine the presence or absence of movement of the subject based on a sinogram instead of the monitoring result of the movement of the subject.

(Third embodiment)
Next, a photographing apparatus according to the third embodiment will be described. The imaging apparatus according to the third embodiment reconstructs a plurality of tomographic images and identifies a reference image from the reconstructed tomographic images. Hereinafter, the difference between the imaging device according to the third embodiment and the imaging device according to the first embodiment will be described.
FIG. 5 is a diagram illustrating an imaging apparatus according to the third embodiment. In addition, the same number is attached | subjected to the structure same as the imaging device concerning 1st Embodiment. The image processing apparatus 105 of the third photographing apparatus includes an image processing unit 106, an image storage unit 107, a forward projection unit 110, a motion detection unit 111, and a motion correction unit 112. The image processing apparatus 105 further includes a set creation unit 501, a reconstruction unit 502, and a reference image specifying unit 503.

The set creation unit 501 creates a plurality of sets having projection images included in the projection image group as constituent elements. Here, the projection images included in each set may overlap. For example, the set creation unit 501 specifies all possible sets as combinations of projection images of all images included in the projection image group. It is assumed that the number of projection images constituting the set created by the set creation unit 501 and the rules for the combination are set in advance. Note that the number of projection images constituting the set to be created and the rules for the combination are arbitrary.
The reconstruction unit 502 reconstructs a tomographic image using the projection images that constitute the group created by the group creation unit 501. The reconstruction unit 502 obtains a plurality of tomographic images corresponding to each of the plurality of sets. The reference image specifying unit 503 specifies one tomographic image as a reference image from among a plurality of tomographic images obtained by the reconstruction unit 502. The reference image is used as a reference for motion detection.

FIG. 6 is a flowchart showing a tomographic image generation process executed by the imaging apparatus according to the third embodiment. In FIG. 6, the same number is attached | subjected to the process same as each process in the tomographic image generation process concerning 1st Embodiment. After the projection image is acquired in S301, in S601, the set creation unit 501 creates a plurality of sets including a plurality of projection images (set creation processing). Next, in S602, the reconstruction unit 502 reconstructs a tomographic image using the projection images included in each created set. The tomographic image obtained in S602 is an example of a first tomographic image. Moreover, the process of S602 is an example of a reconstruction process.
In step S <b> 603, the reference image specifying unit 503 calculates the sharpness of the tomographic image obtained from each set. The reference image specifying unit 503 calculates the sharpness of a specific region (for example, a region of interest) in the image. More preferably, the reference image specifying unit 503 may calculate the overall sharpness from the sharpness of a plurality of regions. Here, the sharpness is a value indicating the contrast of an image, and is, for example, a pixel value of a tomographic image, an image level value, or the like. Note that Patent Document 2 can be referred to for the processing for calculating the sharpness.
Then, the reference image specifying unit 503 specifies the tomographic image having the maximum sharpness as the reference image (specific processing). Note that the reference image specifying unit 503 may specify the reference image based on the sharpness. As another example, the reference image specifying unit 503 may specify a tomographic image whose sharpness is equal to or greater than a threshold value as the reference image.

  Subsequently, in S304, the forward projection unit 110 generates a reprojection image using the reference image specified in S603. In the subsequent processing, the imaging apparatus proceeds with the projection image used for reconstructing the reference image as the selected projection image and the projection image not used for reconstructing the reference image as the non-selected projection image. The remaining configuration and processing of the imaging apparatus according to the third embodiment are the same as the configuration and processing of the imaging apparatus according to the first embodiment.

  As described above, the imaging apparatus according to the third embodiment can select a projection image with less motion based on the sharpness of the tomographic image, and can perform motion correction with high accuracy. In other words, the imaging apparatus can prevent a decrease in SN of a tomographic image obtained from a series of projection images obtained in a certain period and occurrence of artifacts.

(Fourth embodiment)
Next, a photographing apparatus according to the fourth embodiment will be described. The imaging apparatus according to the fourth embodiment reconstructs a plurality of tomographic images and performs motion detection based on the sharpness of the plurality of tomographic images. Then, the imaging apparatus synthesizes a plurality of tomographic images after motion correction to obtain a final tomographic image. Hereinafter, the difference between the imaging device according to the fourth embodiment and the imaging device according to the other embodiments will be described.
FIG. 7 is a diagram illustrating an imaging apparatus according to the fourth embodiment. In addition, the same number is attached | subjected to the structure same as the imaging device concerning other embodiment. The image processing apparatus 105 of the photographing apparatus according to the fourth embodiment includes an image processing unit 106, an image storage unit 107, a set creation unit 501, and a reconstruction unit 502. The image processing apparatus 105 further includes a reference image specifying unit 701, a motion detection unit 702, and an image composition unit 703.

The reference image specifying unit 701 specifies one tomographic image as a reference image from a plurality of tomographic images obtained by the reconstruction unit 502 according to a predetermined condition based on a priori knowledge. Here, it is assumed that the condition is such that, for example, a tomographic image reconstructed using a photographed projection image is selected at a timing when it is estimated that the movement of the photographing object A is small. Note that the conditions are set in advance in a ROM 202 or the like described later. In the present embodiment, in chest CT imaging, it is set as a condition that it is obtained for a certain time immediately after the start of imaging, that is, in a certain imaging order immediately after the imaging starts.
The reference image specifying unit 701 specifies, as a reference image, a tomographic image reconstructed using a predetermined number of two or more projected images taken in a fixed shooting order immediately after the start of shooting according to conditions.

The motion detection unit 702 compares the reference image with the target image and performs motion detection. Here, the target image is a tomographic image that has not been specified as a reference image, and is a tomographic image that is a target of motion detection processing. That is, the target image is a tomographic image other than the tomographic image specified as the reference image. The motion detection unit 702 detects blurring of the target image by comparison with the reference image.
Specifically, the motion detection unit 702 first divides the reference image and the tomographic image into small regions having the same size and the same shape. Next, the motion detection unit 702 selects a small region at the same position from the tomographic image and the target image, and calculates the sharpness of each small region. Then, the motion detection unit 702 calculates the difference in the sharpness of each small region. Here, the difference in sharpness is an index value indicating the presence or absence of motion.
The motion detection unit 702 calculates the weighting coefficient αi based on the sharpness difference. Here, αi is a weighting coefficient of the i-th small region of the target image. For example, the motion detection unit 702 calculates αi using a function in which the value of αi increases as the difference in sharpness decreases (where 0 ≦ αi ≦ 1). The motion detection unit 702 calculates the weighting coefficient of all the small regions by performing the above-described sharpness calculation and comparison for all the small regions.
When the deviation of the center of gravity of the subject between the reference image and the tomographic image is large, the adjustment is made as appropriate.
The motion detection unit 702 obtains the weighting coefficient αi in the small region and then obtains the weighting coefficient in each pixel. For this purpose, the weighting coefficient at a certain coordinate (for example, the center of gravity) in each small area is set as the weighting coefficient αi obtained in the small area. In addition, the motion detection unit 702 obtains a weighting coefficient at each coordinate of the image using an interpolation method such as bilinear interpolation. The weight coefficient α (x, y) obtained by interpolation is used. (X, y) represents the x coordinate and y coordinate of the image. As the weighting coefficient of the portion that cannot be obtained by interpolation, the nearest value among the weighting coefficients obtained by interpolation may be adopted. A single weighting factor can be adopted for the entire small area without obtaining a weighting factor for each pixel. In such a case, processing that does not require bilinear interpolation processing is performed at a high speed, but there is a problem in that the composition ratio is different at the small region boundary and the SN becomes discontinuous at the composition boundary.

The image composition unit 703 combines the reference image and the tomographic image with the weighting factor, and obtains a final tomographic image. Specifically, the image composition unit 703 synthesizes an image in units of pixels. For example, it is assumed that the pixel Ir (x, y) of the reference image Ir and the pixel Ia (x, y) of the tomographic image Ia are synthesized. (X, y) represents the x coordinate and y coordinate of the image. In this case, the image composition unit 703 obtains a final small area Io (x, y) of the tomographic image by (Equation 1).
Io (x, y)
= Α (x, y) × Ia (x, y) / 2 + (1−α (x, y) / 2) × Ir (x, y)
... (Formula 1)
Here, α (x, y) is a weighting coefficient calculated by the motion detection unit 702.
In (Expression 1), the coefficient relating to the pixel Ir (x, y) of the reference image Ir is 0.5 or more and 1 or less,
The coefficient relating to the pixel Ia (x, y) of the tomographic image Ia is 0 or more and 0.5 or less. That is, this expression means that a reference image that seems to have little motion is heavily weighted, and a priori information is reflected in the synthesis result.

FIG. 8 is a flowchart showing a tomographic image generation process executed by the imaging apparatus according to the fourth embodiment. In FIG. 8, the same number is attached | subjected to the process same as each process in the tomographic image generation process concerning other embodiment.
A plurality of sets of two or more projection images are created by the processing of S601 and S602 (set creation processing), and a plurality of tomographic images are reconstructed (reconstruction processing). Thereafter, in S801, the reference image specifying unit 701 specifies a reference image from among a plurality of tomographic images (specific processing). In the present embodiment, the reference image specifying unit 701 is a tomographic image reconstructed using two or more predetermined number of projection images that have been shot in a certain shooting order (predetermined shooting order) immediately after the start of shooting. Is specified as a reference image.

Next, in S802, the motion detection unit 702 performs motion detection using the reference image specified in S801. Specifically, the motion detection unit 702 calculates the sharpness of each small area of the tomographic image (target image) to be processed and the reference image, and calculates the difference between the sharpness of the target image and the reference image. Then, the motion detection unit 702 calculates a weighting coefficient based on the difference. Here, the weighting coefficient is an example of a weight value. The process of S802 is an example of a weight value calculation process that calculates the weight value of the target image based on the motion.
In step S <b> 803, the image composition unit 703 performs processing based on all tomographic images (including reference images and tomographic images not specified as reference images) generated by the reconstruction unit 502 and weighting factors. Then, the final tomographic image is synthesized (synthesis process). The other configurations and processes of the imaging apparatus according to the fourth embodiment are the same as the configurations and processes of the imaging apparatus according to the other embodiments.

  As described above, the imaging apparatus according to the fourth embodiment detects a motion by comparing the sharpness between tomographic images. Then, the imaging apparatus corrects the motion by multiplying each tomographic image by a weighting factor, synthesizes the tomographic image after the motion correction, and obtains a final tomographic image. Therefore, the photographing apparatus can perform motion detection with high accuracy and can perform motion correction with high accuracy. In other words, the imaging apparatus can prevent a decrease in SN of a tomographic image obtained from a series of projection images obtained in a certain period and occurrence of artifacts.

  As a first modification of the fourth embodiment, the reference image specifying unit 701 may specify a reference image based on the sharpness of each tomographic image. Specifically, the reference image specifying unit 701 specifies a tomographic image having the maximum sharpness, that is, a tomographic image with little motion, as the reference image. Note that the reference image specifying unit 701 may determine based on, for example, the sharpness in the region of interest, or as another example, may determine based on the sharpness in a plurality of regions of interest. The reference image specifying unit 701 may specify a tomographic image whose sharpness is equal to or greater than a threshold value as a reference image.

  Next, a second modification of the fourth embodiment will be described. The reference image specifying unit 701 according to the embodiment specifies the reference image according to a predetermined condition, but is not limited thereto. In the second modification example, the reference image specifying unit 701 may select images at random. Also in this case, the occurrence of SN and artifacts can be reduced as compared with the case where a tomographic image is generated using a series of projection images as they are.

(Fifth embodiment)
Next, a photographing apparatus according to the fifth embodiment will be described. The imaging apparatus according to the fifth embodiment obtains a final tomographic image by synthesizing tomographic images, similarly to the imaging apparatus according to the fourth embodiment. Furthermore, the imaging apparatus according to the present embodiment monitors the movement of the imaging target A and identifies the target image based on the monitoring result, similarly to the imaging apparatus according to the second embodiment. Using monitoring results is an example of using a priori knowledge.
FIG. 9 is a diagram illustrating an imaging apparatus according to the fifth embodiment. In addition, the same number is attached | subjected to the structure same as the imaging device concerning other embodiment. The photographing apparatus has a motion monitoring unit 401. Further, the reference image specifying unit 901 of the image processing apparatus 105 specifies a tomographic image reconstructed using a projection image obtained during a period of low motion as a reference image based on the monitoring result of the motion monitoring unit 401. . Accordingly, the imaging apparatus can detect the motion of each tomographic image with reference to the tomographic image obtained from the projection image with little motion in the motion detection processing (S802) shown in FIG. The other configurations and processes of the imaging apparatus according to the fifth embodiment are the same as the configurations and processes of the imaging apparatus according to the other embodiments.

  As described above, the imaging apparatus according to the fifth embodiment, like the imaging apparatus according to the other embodiments, reduces SN of artifacts obtained from a series of projection images obtained in a certain period, and artifacts. Occurrence can be prevented.

  As another example, the imaging apparatus may determine the presence or absence of motion based on a sinogram instead of having the motion monitoring unit 401.

<Other embodiments>
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media. Then, the computer (or CPU, MPU, etc.) of the system or apparatus reads and executes the program.

  As mentioned above, according to each embodiment mentioned above, SN fall of the tomographic image obtained from a series of projection images obtained in a fixed period, and generation of an artifact can be prevented.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such specific embodiments, and various modifications can be made within the scope of the gist of the present invention described in the claims.・ Change is possible.

101 X-ray tube, 102 frame, 103 X-ray detector, 104 device control unit, 105 image processing device, 106 image processing unit, 107 image storage unit, 108 image selection unit, 109 reconstruction unit, 110 forward projection unit, 111 motion detection unit, 112 motion correction unit

Claims (7)

Selection means for selecting a part of the projection images from a plurality of projection images obtained by imaging the subject;
Reprojection means for generating a reprojection image by reprojecting a tomographic image reconstructed based on the selected projection image selected by the selection means;
A motion detection unit that detects a motion of the subject in the non-selected projection image based on the non-selected projection image that has not been selected by the selection unit and the reprojection image among the plurality of projection images;
Correction means for correcting the non-selected projection image based on the detected movement ;
An image processing apparatus comprising: an image generation unit configured to generate a tomographic image using the selected projection image and the corrected non-selected projection image . The image processing apparatus according to claim 1, wherein the selection unit selects the partial projection image according to a predetermined condition. The image processing apparatus according to claim 2 , wherein the selection unit selects the part of the projection images captured in a predetermined imaging order. The selection unit selects the partial projection image obtained at a timing when the movement of the subject monitored by the monitoring unit that monitors the movement of the subject is equal to or less than a threshold based on the projection image of the subject. The image processing apparatus according to claim 2 , wherein: An image processing apparatus according to any one of claims 1 to 4 ,
Photographing means for photographing a projected image of the subject;
An imaging apparatus comprising: monitoring means for monitoring the movement of the subject during imaging by the imaging means. An image processing method executed by an image processing apparatus,
A selection step of selecting some projection images from a plurality of projection images obtained by imaging the subject;
A reprojection step of generating a reprojection image by reprojecting a tomographic image reconstructed based on the selected projection image selected in the selection step;
A motion detection step of detecting a motion of the subject in the non-selected projection image based on the non-selected projection image not selected in the selection step and the reprojection image among the plurality of projection images;
A correction step of correcting the non-selected projection image based on the detected movement ;
An image processing method comprising: an image generation step of generating a tomographic image using the selected projection image and the corrected non-selected projection image . Computer
Selection means for selecting a part of the projection images from a plurality of projection images obtained by imaging the subject;
Reprojection means for generating a reprojection image by reprojecting a tomographic image reconstructed based on the selected projection image selected by the selection means;
A motion detection unit that detects a motion of the subject in the non-selected projection image based on the non-selected projection image that has not been selected by the selection unit and the reprojection image among the plurality of projection images;
Correction means for correcting the non-selected projection image based on the detected movement ;
A program for functioning as an image generation means for generating a tomographic image using the selected projection image and the corrected non-selected projection image .

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