JP4028209B2 - X-ray CT system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray CT apparatus that performs interpretation by comparing captured images that differ in time.
[0002]
[Prior art]
In general, in periodic medical examinations such as health checkups and medical checkups, there are cases in which interpretation is performed by comparing a photographed image taken before the current examination with a photographed image taken during the current examination. This is because, for example, a past photographed image in which a tumor or the like is not observed in the lung field is compared with a photographed image at the current examination, and is used to determine whether there is no abnormality at the present examination. Compared to finding abnormalities only with the images taken at the time of the current examination, it is easier to find out the occurrence of tumors, etc., by using past normal images as comparison targets. A tumor or the like is observed in the photographed image, and it is also useful for determining the degree of recovery after treatment by comparing the photographed image at the current examination after treatment.
[0003]
[Problems to be solved by the invention]
However, as described above, in the conventional diagnostic imaging method, it is a very useful diagnostic imaging method to compare the previous captured image with the captured image at the current examination, but interpretation is performed while comparing a plurality of captured images. In order to do this, doctors must be carefully discriminating and observing, which is a very laborious task. Whether it prints an image on a film and interprets it or compares it on a CRT monitor, it still requires a great amount of doctor's effort. In normal image diagnosis, diagnosis is performed based on one image at the time of imaging for one tomographic plane. However, as described above, since the past captured image and the captured image at the current screening are used, it is compared with normal image diagnosis. Thus, it is necessary to observe two or more images on one tomographic plane, and this increase in the number of interpretations causes a great effort on the doctor.
[0004]
An object of the present invention is to provide an X-ray CT apparatus capable of performing a highly reliable diagnosis by comparing a previously captured image with a captured image at the current examination while reducing the labor of a doctor. is there.
[0005]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present invention has a scanner and a bed, and the output from the scanner is converted into a photographed image by the reconstructed image processing means. In an X-ray CT apparatus that extracts a difference image from an image, an imaging position calculation unit that calculates a matching imaging position of both corresponding captured images and moves the bed based on the position information to match the imaging position; Further, the present invention is characterized in that there is provided a different portion extraction means for extracting the different portion by comparing the two photographed images after correcting the photographing position.
[0006]
An X-ray CT apparatus according to the present invention calculates a matching imaging position of both corresponding captured images, and uses the positional information to move the couch to match the imaging position, and to correct the imaging position. Since the difference part extraction means for comparing the two captured images and extracting the difference part is provided, it has been necessary to interpret a plurality of images of the past photographed image and the currently photographed image at the time of the examination. However, since it is sufficient to interpret only the difference image, a significant reduction in labor can be expected. The reliability of the difference image is obtained by using the imaging position calculation means so that the imaging position and the spatial position of the tomographic image are equal, and the difference image extraction means can obtain the difference screen as an abnormality in the body of the subject. It becomes an image of only a part and can be greatly improved.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 is a schematic configuration diagram of an X-ray CT apparatus according to an embodiment of the present invention.
An X-ray CT apparatus is configured by connecting a scanner unit 2 for imaging a tomographic plane of a subject located on the bed 1 to an image processing apparatus 3, and projection data of a human body imaged by the scanner unit 2 is image processing apparatus 3. The X-ray CT image of the tomographic plane is obtained through an operation called reconstruction image processing by this image processing apparatus 3.
[0008]
FIG. 1 is a block diagram showing the main part of the X-ray CT apparatus described above.
The image processing apparatus 3 compares the captured image obtained by the reconstructed image processing means 15 with the past captured image of the same subject stored in the storage means 16 and calculates a matching imaging position for both. Means 18 are connected. The photographing position calculation means 18 stores information including the photographing position of the image photographed before in time corresponding to the shape and position of at least one of the lumbar vertebra and the cervical vertebra in the current photographed image and the past photographed image. Based on this position information, the driving device 14 is operated to match the photographing position of the bed 1. A difference portion extraction means 17 is provided for extracting a difference portion by comparing the current photographed image corrected by the photographing position calculation means 18 with a past photographed image.
[0009]
In such an X-ray CT apparatus, when a subject having a headache subjective symptom is examined at a medical facility and a doctor is suspected of any disease in the head, as shown in FIG. As shown in Fig. 4, a site 4 that is likely to have a disease is imaged with an X-ray CT apparatus, and the tomographic plane image processed by the reconstructed image processing means is diagnosed while being displayed on the monitor 3A. Diagnosis of cerebral hemorrhage, cerebral infarction, brain tumor, etc. can be performed by interpretation.
[0010]
However, in health checkups and screening facilities for the purpose of medical checkups, it is common for a subject to receive a health check once a year even if there is no subjective symptom such as physical pain. It is considered to be a very effective means for the early detection of cancer and other diseases. In such a screening facility or the like, since the subject often performs a medical checkup such as a medical checkup every year, the past X-ray CT images are often stored. Therefore, a past photographed image and a photographed image at the current examination are compared, and a change in the photographed image obtained by the current examination is identified. For example, as shown in FIG. 4, when a photographed image 5A of a tomographic plane with the abdomen of a subject last year is compared with a photographed image 5B at the current examination, new findings such as a tumor cannot be confirmed in both images. . On the other hand, as shown in FIG. 5, when a photographed image 6A of a tomographic plane on the abdomen of another subject last year is compared with a photographed image 6B at the time of the current examination, a tumor 7 is newly displayed. Here, this change is obtained by taking the difference between the past captured images 5A and 6A and the captured images 5B and 6B at the time of the current examination.
[0011]
However, the past captured images 5A and 6A shown in FIGS. 3 and 4 and the captured images 5B and 6B at the time of the current examination are not necessarily images of the same cross section. This is because the photographing conditions photographed in the past are strictly different from the photographing conditions photographed at the current examination. The imaging conditions described here are the position of the bed 1 on which the subject of the X-ray CT apparatus is placed. If the imaging tomographic plane is displaced depending on the imaging conditions, the comparative interpretation described in FIGS. 4 and 5 is also less reliable, but some positional deviation of the tomographic plane is recognized by the doctor himself, which is a clinical problem. There is no. However, when taking the difference between the above-described captured images 5A and 6A and the captured images 5B and 6B at the time of the current examination, it is necessary to correct the displacement of the tomographic plane.
[0012]
Therefore, first, the photographing position is adjusted by the photographing position calculating means. As shown in FIG. 6, if the photographed image 8A of the same person in the past and the photographed image 8B at the time of the current examination are not misaligned in the X and Y axis directions shown in the figure even during photographing, these two photographed images are taken. When the difference between 8A and 8B is taken, if there is no change over time, such as the occurrence of a tumor, the monitor 3A will obtain an image with one plane as shown in FIG. However, if there is no disease such as a tumor in the past captured image 8A and a tumor or the like is captured in the current captured image 8B, an image of only the tumor 7 is displayed as a difference image on the monitor 3A as shown in FIG. Will be obtained.
[0013]
On the other hand, if the past photographed image 8A and the current photographed image 8B are not equal in the X and Y axis directions shown in FIG. 6, in the difference image, the regions other than the temporal change in the past and the present also change over time. It is assumed that it has been made and is imaged. Therefore, at the time of X-ray CT imaging, an imaging position is stored with reference to at least one of the subject's cervical vertebra and lumbar vertebra, and the past stored in the storage means 16 even when a new imaging is performed. The photographing position calculation means 18 for controlling the position of the bed 1 by the bed driving device 14 is provided so as to have the same cross section as that of the photographing of FIG.
[0014]
When performing X-ray CT imaging, this imaging position calculation means 18 shows the imaging start position, the spatial position of the tomographic image, that is, the spatial position of the tomographic image, with reference to the cervical vertebrae and lumbar vertebrae, whose changes in shape, size and position are small in adults. The X and Y axes are memorized strictly. For example, as shown in FIG. 9, the position of the lumbar vertebra 9 obtained by a schematic diagram of a scanogram image from the side is used, and the imaging start position is indicated by the line segment 10, and the height of the bed 1 on which the subject 12 is placed is indicated by the line segment 11. Remember. Further, the position of the bed 1 of the subject 12 is stored and stored by the line segment 13 in the schematic diagram of the scanogram image of the front of the human body shown in FIG. The imaging position calculation means 18 storing these pieces of information accurately reproduces the X-ray CT imaging position and the spatial arrangement position of the subject 12 when the same subject 12 is imaged next time. Is possible. As a result, when the difference image extracting unit 17 processes the current captured image 8B corrected by the imaging position calculating unit 18 and the past captured image 8A, the obtained difference image has a space as shown in FIG. There is no misalignment, and it is possible to obtain only the part of the subject that has changed over time.
[0015]
Therefore, it has been necessary for doctors to interpret a plurality of images taken at the time of a medical examination in the past and an image taken at the time of a medical examination, but only a difference image needs to be interpreted, which greatly reduces labor. Connected. The reliability of the difference image is obtained by using the imaging position calculation means 18 so that the imaging position and the spatial position of the tomographic image become equal, and what is obtained as a difference screen by the different part extraction means 17 is in the body of the subject. It becomes an image of only a temporally changing part such as tumor occurrence, and can be greatly improved.
[0016]
The difference image may be projected on the monitor 3A or read as an X-ray film. In addition, when displaying on the monitor 3A, as a warning to the doctor, the part such as a tumor that appears in the difference image is painted with a warning color red or other colors other than black and white, or the surroundings such as a tumor that appears in the difference image are warned It is also effective to enclose it in red.
[0017]
By the way, the photographed image in the past and the photographed image at the time of the current examination differ not only strictly depending on the photographing position but also other factors. For example, it differs depending on the change in the body shape of the subject, growth, and a shift in respiratory phase, and it is considered that an extra pattern is generated due to such other elements in the difference image between the two. Therefore, an alignment processing unit is configured in the image processing apparatus 3, and these other elements are corrected by the alignment processing unit to further improve the display accuracy of the abnormal part based on the difference image. FIG. 11 is a flowchart showing the alignment processing procedure of the X-ray CT apparatus having the alignment processing means.
[0018]
First, in step S1, a corresponding image is selected or created. This associates the past photographed images A1 to An shown in FIG. 12 with the photographed images B1 to Bn at the current examination at the same photographing position. This may be performed by the method shown in FIGS. 1 to 10, or may be performed visually by the operator while viewing what is displayed on the monitor, or a photographed image having the smallest difference by taking the difference between the two. You may associate with each other. Subsequently, image deformation is performed in step S2. This will be described in detail later, but one captured image is deformed to match the other. Then, as shown in step S3, the two captured images are subtracted to obtain a difference image, and the subtraction result is multiplied by a constant in step S4 and displayed on the monitor.
[0019]
FIG. 13 is a flowchart showing details of the processing procedure of steps S2 to S4 described above.
First, in step S5, a blood vessel region and the like are extracted to create a binarized image. For example, as shown in FIG. 14, a small area 19 is set in the captured image, an average value of CT values in the small area 19 is obtained, and a coordinate average c2 of pixels having a value larger than the average value and an average value are obtained. A coordinate average c1 of pixels having a smaller value is set, and if the difference between the coordinate average c1 and the coordinate average c2 is larger than a preset set value, 1 is extracted and stored in the storage means. If it is smaller, 0 is stored in the memory means. In this way, when the past radiograph B5 shown in FIG. 15 and the radiograph A5 at the current examination are binarized, images B5a and A5a are obtained.
[0020]
Subsequently, in step S6, the image B5a and the image A5a are each divided as shown in FIG. At this time, the number of image divisions may be arbitrary. In subsequent step S7, alignment processing is performed for each corresponding divided image to obtain a transition vector in a matched state. The difference between the divided images is obtained by moving the divided images in parallel, and the amount of movement when the divided images are translated until the difference becomes the smallest becomes the transition vector. Here, in the divided images a1 to a3 of the image A5a obtained by binarizing the captured image at the time of the current examination, transition vectors V1 to V4 as illustrated are obtained, respectively.
[0021]
Subsequently, in step S8, image conversion using all transition vectors V is performed. This converts all pixel coordinates of the image A5a at the current examination using the transition vectors V1 to V4 and Affine transformation. From the description so far, the image processing apparatus 3 shown in FIG. 1 has an alignment processing means for performing a registration process by creating a binary extracted image from a corresponding past captured image and a captured image at the current examination. It can be seen that it is composed. Then, as shown in FIG. 17, using this converted image A5x, a difference image 20 is created by taking the difference between the converted image A5x and the past image B5 in step S9, and the difference image 20 is multiplied by a constant or increased in step S10. The area is emphasized and displayed on the monitor 3A.
[0022]
In this way, there is provided an alignment processing means for creating a binary extracted image from the corresponding past captured image and the captured image at the current examination and performing alignment processing, and the image after the alignment processing by this alignment processing means is displayed. Since the difference image is obtained by using this, it is possible to correct the body shape change, growth, breathing phase shift, etc. of the subject, and to reduce the extra pattern generated in the difference image, thereby reducing the abnormal region 21 due to the difference image. Display accuracy can be improved.
[0023]
【The invention's effect】
As described above, according to the X-ray CT apparatus of the present invention, it has been necessary to interpret a plurality of images of a past photographed image and a photographed image at the time of a medical examination so far, but only a difference image is interpreted. Therefore, a significant reduction in labor can be expected. The reliability of the difference image is obtained by using the imaging position calculation means, so that the imaging position and the spatial position of the tomographic image become equal, and what is obtained as a difference screen by the different part extraction means is the occurrence of an abnormality in the body of the subject. It becomes an image of only a part and can be greatly improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a main part of an X-ray CT apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of the X-ray CT apparatus shown in FIG.
FIG. 3 is a front view showing a usage state of the X-ray CT apparatus shown in FIG. 2;
4 is a front view showing a comparison state of captured images by the X-ray CT apparatus shown in FIG. 2. FIG.
5 is a front view showing a comparison state of other captured images by the X-ray CT apparatus shown in FIG. 2. FIG.
6 is a front view showing a comparison state of still other captured images by the X-ray CT apparatus shown in FIG. 2. FIG.
7 is a front view of a monitor displaying a difference image by the X-ray CT apparatus shown in FIG. 1. FIG.
FIG. 8 is a front view of a monitor displaying another difference image by the X-ray CT apparatus shown in FIG. 1;
FIG. 9 is a side view of a lumbar vertebra obtained by a scanogram image.
FIG. 10 is a front view of a lumbar vertebra obtained by a scanogram image.
FIG. 11 is a flowchart showing the alignment processing procedure by the X-ray CT apparatus shown in FIG. 1;
FIG. 12 is a plan view of a past photographed image and a photographed image at the current examination.
13 is a flowchart showing details of a main part of an alignment processing procedure by the X-ray CT apparatus shown in FIG.
FIG. 14 is a front view of a monitor showing a state in which a small region is set in a captured image.
FIG. 15 is a plan view showing a comparison between binarized images of a past captured image and a captured image at the time of a current examination.
FIG. 16 is a plan view showing a comparison of a state in which a transition vector between a past photographed image and a photographed image at the current examination is obtained.
FIG. 17 is a plan view showing a state in which a difference image is obtained from a past photographed image and a transition image at the time of a current examination.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Bed 2 Scanner 3 Image processing apparatus 3A Monitor 17 Difference part extraction means 18 Shooting position calculation means

Claims (4)

In an X-ray CT apparatus that generates a difference image between two imaging tomographic images having different acquisition times,
The position of the physical feature in the scanogram image acquired at the first time, the imaging position of the tomographic image acquired on the basis of the position of the physical feature in the scanogram image, and the tomographic image; Means for storing
Based on the difference between the stored physical feature position and the physical feature position of the scanogram image acquired at the second time, and the stored tomographic image capturing position, a new one should be acquired. Positioning means for setting the imaging position of the tomographic image;
Extracting means for obtaining a difference image between the tomographic image taken at the set position and the stored tomographic image;
An X-ray CT apparatus comprising: The X-ray CT apparatus according to claim 1,
The X-ray CT apparatus, wherein the physical feature is either a cervical vertebra or a lumbar vertebra . The X-ray CT apparatus according to claim 1 or 2,
The extraction means has an image deformation means, and before the difference image is obtained by the deformation means, either the stored tomographic image or a new tomographic image captured and acquired at the set position is used. An X-ray CT apparatus which is deformed by coordinate transformation so as to be matched with the other in position and / or shape and obtains a difference image between the tomographic image after deformation and the other tomographic image which is not deformed . The X-ray CT apparatus according to claim 3.
The image transformation means divides each stored binarized image, a binarized image generating means for binarizing the stored tomographic image, and a newly acquired tomographic image taken at the set position. An image dividing unit, a shift vector calculating unit for obtaining a shift vector of each of the corresponding divided images in both images, and at least one of the two tomographic images is matched with the other using the shift vector. An X-ray CT apparatus comprising: pixel coordinate conversion means for performing coordinate conversion as described above .

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