JP2003299643A - Tomographic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tomographic equipment capable of reducing the exposure of radiation ray to a subject. <P>SOLUTION: A set area 25 is determined on the basis of the past radiographing data of the subject, and corresponded to an actually radiographed scanogram 27, whereby a concerned area 31 as an actual radiographing area is determined, and the radiation ray passing through the external of the actual concerned area 31 is limited by a limiting means in radiographing. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tomography apparatus in which radiation to an object is limited by using limiting means such as a collimator.

[0002]

2. Description of the Related Art Usually, for example, when a liver region is imaged for postoperative observation in a patient whose liver has been excised, the entire tomographic image including the liver is imaged. Similarly, for patients with abnormalities observed by other modalities, X-ray C
Even when observing the abnormality detection unit using the T-apparatus, the region of interest cannot be specified, so that it is necessary to capture a fairly wide region including the region of interest. Similarly, in the case of percutaneously performing a tissue examination or treatment of a lesion, an X-ray CT apparatus displays an image in real time, and a fluoroscopic examination is performed using this image as a puncture guide. When the region of interest is imaged in this fluoroscopic inspection, Japanese Patent Laid-Open No. 2000-
Using the technique disclosed in Japanese Patent Laid-Open No. 300548 and Japanese Patent Laid-Open No. 2000-157534, first, a sufficient amount of a reference image is determined to determine a restriction region, and a region of interest is determined in the reference image. A procedure such as limiting the X-ray beam to the region of interest is required.

[0003]

By the way, in a tomography apparatus using radiation, the most important problem is the radiation exposure dose, which is pointed out to be harmful to the human body. MRI has the advantages of high spatial resolution and high temporal resolution of tomographic images.
It plays a central role in image diagnosis along with the equipment and ultrasonic diagnostic equipment. However, in the conventional tomography apparatus,
Since it is necessary to image a wider area than a desired region of interest, the amount of ineffective exposure increases, and in particular, X-rays using an image intensifier (II) in which the spatial resolution of a tomographic image changes depending on the size of the field of view. In the imaging apparatus, not only the amount of ineffective exposure increases but also the spatial resolution of the image decreases.

An object of the present invention is to provide a tomography apparatus which reduces the radiation exposure of the subject.

[0005]

In order to achieve the above object, the present invention provides a radiation source capable of irradiating radiation, a limiting means for limiting the radiation emitted from the radiation source to a region of interest of an object, and an object. In a radiation detector that detects radiation that has passed through an object, and in a tomography device that creates a tomographic image of a region of interest of an object from projection data detected by this radiation detector, refer to past data taken in the past It is characterized in that a determining means is provided which is used as an image and determines the region of interest from the set region of the reference image.

The tomography apparatus according to the present invention uses, as a reference image, the imaged data of the subject imaged in the past, and a deciding means for deciding a region of interest using this reference image, and radiation to the region of interest decided by this deciding means. By providing a limiting means for limiting the reference image, it is possible to determine the limited area which is the actual image capturing range without performing the conventional image capturing for the reference image and limit the radiation passing outside the limited area. Therefore, it is possible to reduce exposure in unnecessary areas.

According to the second aspect of the present invention, a scanogram is used as a reference image based on the past data captured in the first aspect.

According to the present invention, the reference image based on the past data photographed in the past according to claim 1 is a scanogram image, a two-dimensional tomographic image, a three-dimensional volume image, and a processed two-dimensional image obtained from the three-dimensional volume image. Although images and data obtained by different modalities can be used, in particular, since the scanogram image is used, alignment is easy.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is an external view of a tomography apparatus according to an embodiment of the present invention. A scanner 1 used for imaging, a bed 2 on which a subject is placed and moved, and a mouse, a keyboard, etc., for inputting measurement reconstruction parameters such as movement speed information and reconstruction position of the bed 2. The input device 3, an arithmetic device 5 for processing data obtained from the multi-row radiation detectors 4, a display device 6 for displaying a reconstructed image, and the like are configured.

FIG. 3 is a block diagram of the tomography apparatus described above. Here, the scanning method of the tomography apparatus is the rotate-rotate method (third generation),
It is mainly composed of a scanner 1 and an operation unit 7. The scanner 1 includes a bed 2 on which a radiation source including an X-ray generator 8, a high-voltage switching unit 9, a high-voltage generator 10, an X-ray controller 11, and the like, and a subject 17 are mounted.
A radiation detector 4 facing the radiation source with the subject 17 interposed therebetween; a limiting unit configured to control the collimator 12 disposed between the radiation source and the subject 17 by the collimator control device 13; A drive device 14 and a scanner control device 15 for rotating the scanner 1 located on the outer circumference of the scanner in the circumferential direction, and a preamplifier which converts the radiation detected by the radiation detector 4 into an electric current and amplifies it to input it to the arithmetic unit 5 as a projection data signal 16, a data collecting device for determining the sampling position for each rotation of the radiation source located in the preamplifier 16 and other means described later, and the sampling position in the circumferential direction of the preceding radiation source and the succeeding radiation source. Sampling adjusting means 17 for shifting the sampling position in the circumferential direction of the, and a central control device for controlling these It is composed 8 and the like.

When the photographing conditions, that is, the bed moving speed, the tube current, the tube voltage, the slice position, the number of views, the number of photographing rotations, and the reconstruction conditions (reconstruction algorithm) are input from the input device 3 of the operation unit 7, the instruction is given. A control signal necessary for photographing is transmitted from the central controller 18 to the X-ray controller 11, the bed controller 19, and the scanner controller 1 based on
Then, the image pickup is started in response to the image pickup start signal. When imaging is started, a control signal is sent from the X-ray controller 11 to the high voltage generator 10, and a high voltage is applied to the X-ray generator 8 via the high voltage switching unit 9,
Radiation such as X-rays is emitted from the X-ray generator 8 to the subject 17.

At the same time, a control signal is sent from the scanner controller 15 to the driver 14, and the X-ray generator 8, the radiation detector 4, the preamplifier 16 and the like rotate around the outer periphery of the subject 17 in the circumferential direction. On the other hand, the bed 2 on which the subject 17 is placed by the bed control device 19 is stationary during the circular orbit scan, and moves in parallel in the circumferential axis direction of the X-ray generator 8 or the like during the spiral orbit scan. At this time, the moving speed of the couch 2 that moves in parallel is measured by the couch movement measuring device 20 and input to the computing device 5. The irradiation area of the radiation emitted from the X-ray generator 8 is limited by the collimator 12,
It is absorbed or attenuated by each tissue in the subject 17 and detected by the radiation detector 4. The radiation detected by the radiation detector 4 is converted into a current, amplified by the preamplifier 16 and input to the arithmetic unit 5 as a projection data signal. The projection data signal input to the arithmetic unit 5 is reconstructed by the reconstruction arithmetic unit 21 in the arithmetic unit 5 based on the number of views input by the input unit 3, and the reconstructed image processed by the image processing unit 22. Is stored in the storage device 23 and displayed as a tomographic image on the display device 6.

FIG. 1 is a flow chart showing the operation of the tomography apparatus described above. First, in step S1, a three-dimensional volume image previously imaged by the X-ray CT apparatus is used as a reference image, and a set area corresponding to a region of interest in main imaging in this reference image is determined. In the subsequent step S2, a new scanogram is imaged in order to match the reference image for grasping the positional deviation between the subject position at the time of photographing the past image and the current subject position. In step S3, a two-dimensional projection image such as a RAY SUM image similar to the scanogram is created from the reference image, and corresponding points in the scanogram and the two-dimensional projection image are determined.

In step S4, the image size and the image position of the image are corrected by using the affine transformation, and the two images are spatially associated with each other. After that, step S
In step 5, the actual spatial region of interest in the actual shooting is determined.
In the next step S6, the radiation is limited using the limiting means such as the collimator 12 and its control means based on the region of interest obtained here, and projection data is acquired by imaging. When the imaging range is a small part of the subject, a window function is applied to the projection data to correct the error at the time of reconstruction filtering, and reconstruction is performed by the well-known image reconstruction calculation device 21. The local image obtained by this reconstruction is the step S8.
The mode is switched by and displayed on the display device 6. This mode is for displaying only the obtained local image,
The mode is selected from a mode in which the reference image is displayed side by side, a mode in which a part of the reference image is replaced with a local image, and the like are displayed.

4A to 4C show step S in FIG.
4A shows an example of setting a setting area using a past reference image in FIG. 1, FIG. 4A is a coronal image or a projected image in the coronal direction, and FIG. 4B is an axial image or a projected image in the axial direction. 4C shows a sagittal image or a projection image in the sagittal direction. Here, as shown in FIGS. 4 (a) to 4 (c), the setting area 25 has a circular shape on the axial surface and a rectangular shape on the coronal surface and the sagittal surface, that is, the setting area 25 has a cylindrical shape extending in the body axis direction. It is set. The setting of the setting area 25 is input by the input device 3 while looking at the image displayed on the display device 6.

FIG. 5 shows steps S3 to S5 shown in FIG.
7 is an image flowchart showing an example of associating the spatial positions of the reference image 26 and the image 27 which is a scanogram obtained by the actual shooting in FIG. The reference image 26 is a scanogram in a past reference image or a scanogram (projection image) created from a two-dimensional volume image, or a projection image of a three-dimensional region of interest selected in a past image. Further, the image 27 is obtained by actual photographing.

First, in step S3, three corresponding points in both images 26 and 27 are determined. It is desirable that the corresponding three points be automatically determined, but in that case, it is necessary to automate the data in consideration of the case where data of another modality is used for the past reference image 26. Here, three corresponding points corresponding to both images 26 and 27 are determined by manual input. Next, in step S4, the corresponding points are extracted, and the transformation coefficient (movement amount, enlargement amount, rotation) for moving, enlarging, and rotating the triangle 28 obtained from these three points so as to have the same shape as the triangle 29. Amount). The conversion image is used to convert the past reference image 26 into an image 30.

Next, the setting area 25 determined in the past reference image 26 is also converted in the same manner, spatially associated with the image 27 obtained by the actual photographing in step S5, and the converted image 30 is converted. The correspondence setting area 25a is determined as the area of interest 31 of the image 27 in the actual shooting.

As can be seen from this description, the above-described tomographic imaging apparatus uses the past image captured in the past as the reference image 2
It can be seen that a determination means for determining the region of interest 31 of the main image 27 from the setting region 25 for the reference image 26 by using it as 6 is provided.

FIGS. 6 and 7 show the collimator 12 and the collimator controller 13 in step S6 shown in FIG.
6A and 6B are an axial cross-sectional view and a sagittal cross-sectional view showing an example of radiation control performed by a limiting unit configured by, for example, FIG. Figure 6
In the axial section shown in FIG. 3, the radiation emitted to the outside of the region of interest 31 is limited by using the collimator 12 that controls in the detector channel direction. The sagittal section shown in FIG. 7 is limited by using the collimator 12 that controls in the body axis direction.

Such a tomography apparatus uses the past data photographed in the past as the reference image 26 to generate the region of interest 3.
Since the determining means for determining 1 and the limiting means for limiting the radiation to the region of interest 31 determined by this determining device are provided, the same region of interest 31 as the conventional one can be obtained, and moreover, the conventional region of interest 31 can be obtained. It is not necessary to take a sufficient amount of reference image to determine the region of interest, and to determine the region of interest with this reference image, reduce the exposure dose when creating this reference image, and The burden can be reduced. Further, in the above-described embodiment, since the scanogram is used as the reference image 26 using the past data captured in the past, the alignment of steps S3 and S4 shown in FIG. 5 is easy.

In the above-described embodiment, the newly captured image 27 is a scanogram, but the image is not limited to a scanogram and may be any image at a position included in a past reference image. For example, it may be an axial image. Also, the image created from the past data is a two-dimensional projection image,
A three-dimensional volume image, a processed two-dimensional image obtained from the three-dimensional volume image, or a processed image such as a MIP image may be used. Further, in the present embodiment, the region of interest 31 extending in the body axis direction is set in a cylindrical shape, but may be a spherical shape. However, when a wide region is set as the region of interest 31 in the body axis direction and a spiral scan scan is performed, the columnar shape is preferable because the collimator 12 can be easily controlled. Further, the reference image is not limited to the imaging data captured by the tomography apparatus using X-rays,
Imaging data captured by the RI apparatus or the ultrasonic diagnostic apparatus may be used. In this case, the shooting condition setting at the time of shooting is not read from the past image, and is set to a general initial setting value. Further, in the present embodiment, the multi-row detector type three-dimensional tomographic apparatus is used, but it is needless to say that the present invention is applicable to a single row detector type tomographic apparatus as well. Further, in the present embodiment, a tomography apparatus using X-rays is used, but the present invention is not limited to this and is also applicable to a tomography apparatus using gamma rays or light.

[0023]

As described above, the tomography apparatus of the present invention can determine the region of interest to be actually photographed based on the image data photographed in the past, and the radiation outside the region of interest can be determined. Since it is possible to limit the exposure dose, it is possible to reduce the exposure dose of the subject and reduce the burden of exposure.

[Brief description of drawings]

FIG. 1 is a flowchart showing an operation of a tomography apparatus according to an embodiment of the present invention.

FIG. 2 is an external view showing the overall configuration of the tomography apparatus shown in FIG.

FIG. 3 is a block diagram of the tomography apparatus shown in FIG.

FIG. 4 is a cross-sectional view showing an example of setting a region of interest in a reference image in the tomography apparatus shown in FIG.

5 is an image flowchart showing association between a reference image and a spatial position of a scanogram in the tomography apparatus shown in FIG.

6 is an axial cross-sectional view showing control of radiation in the tomography apparatus shown in FIG.

FIG. 7 is a sagittal sectional view showing control of radiation in the tomography apparatus shown in FIG.

[Explanation of symbols]

1 scanner 4 Radiation detector 8 X-ray generator 12 Collimator 13 Collimator controller 25 setting area 26 Reference images 27 scanogram 31 Area of Interest

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Claims (2)

[Claims] 1. A radiation source capable of irradiating radiation, limiting means for limiting the radiation emitted from the radiation source to a region of interest of an object, a radiation detector for detecting radiation transmitted through the object, and this radiation. A tomography apparatus that creates a tomographic image of a region of interest of an object from projection data detected by a detector uses past data captured in the past as a reference image to determine the region of interest from the set region of this reference image. A tomography apparatus characterized in that a determining means is provided. 2. The tomography apparatus according to claim 1, wherein a scanogram is used as a reference image based on past data captured in the past.