JP2007236446A - Tomographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tomographic apparatus capable of reducing exposure by radiation. <P>SOLUTION: Before performing tomography, a light receiving mechanism 13 receives a light from an examinee M and an irradiation condition setting part 6 sets an irradiation condition on the basis of an optical image (shadow of visible light beam) relating to the examinee M from the light receiving mechanism 13. Thus, the need of radiating X-rays in order to acquire an image (that is, scout image) for setting the irradiation condition as before is eliminated and the exposure by the X-rays is reduced for that. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a tomography apparatus used in the medical field, industrial fields such as non-destructive inspection and RI (Radio isotope) inspection, and more particularly to a technique for setting radiation irradiation conditions for an irradiation source.

Conventionally, as this type of apparatus, there is an X-ray CT (Computed Tomography) apparatus that rotates an X-ray tube and an X-ray detector around the body axis of a subject. In the X-ray CT apparatus, there is CT-AEC (Auto Exposure Control) as a mechanism for reducing X-ray exposure of a subject by reducing radiation applied to the subject. This mechanism obtains a scout image by irradiating X-rays prior to tomography with an X-ray CT apparatus, obtains a density map of X-ray absorption from the scout image, and based on that, for tomography X-ray irradiation is appropriately controlled (see, for example, Patent Documents 1 to 5). The scout image is a scano image in Patent Document 1, a scout image in Patent Document 2, a plane perspective image in Patent Document 3, a scout image in Patent Document 4, and a scano image in Patent Document 5.
JP-A-1-293844 (page 1-5, Fig. 1-3) Japanese Patent Laid-Open No. 11-104121 (page 1-6, FIG. 1-3) Japanese Patent Laid-Open No. 11-206755 (page 1-6, FIGS. 1-11, 13) JP 2002-306468 A (page 1-6, FIGS. 1 and 3-7) JP 2003-79611 A (page 1-11, FIG. 1-10)

  However, X-ray irradiation is performed in order to acquire scout images used in these CT-AEC mechanisms, and X-ray exposure occurs in the collection of scout images. Therefore, a configuration capable of reducing such X-ray exposure is desired.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a tomographic apparatus that can reduce exposure to radiation.

In order to achieve such an object, the present invention has the following configuration.
That is, an irradiation source that irradiates a subject with radiation, a radiation detection unit that detects the radiation that has been irradiated and transmitted through the subject, and an irradiation condition setting unit that sets irradiation conditions for the irradiation source A tomography apparatus for obtaining a tomographic image from a group of projection data detected by the radiation detection means under the irradiation condition set by the irradiation condition setting means, and receiving the light from the subject The irradiation condition setting means sets the irradiation condition based on the optical image relating to the subject from the light receiving means.

  [Operation / Effect] According to the first aspect of the present invention, the light receiving means for receiving the light from the subject is provided. Prior to tomography, the light receiving means receives light from the subject, and the irradiation condition setting means sets the irradiation conditions based on the optical image relating to the subject from the light receiving means. Thus, a tomographic image is acquired from a group of projection data detected by the radiation detection means under the irradiation conditions set by the irradiation condition setting means. In other words, instead of an image obtained by conventional radiation irradiation (ie, a scout image), the irradiation condition for tomography is set using an optical image related to the subject from the light receiving means. There is no need to irradiate radiation in order to acquire an image (scout image) for setting the conditions, and exposure by radiation can be reduced by that much.

  In the above-described invention, an example of light is infrared, and another example of light is visible light. In the case of infrared rays, the light receiving means receives infrared rays due to thermal radiation generated from the subject (the invention according to claim 2). Therefore, a light source for irradiating light is unnecessary. Note that the tomography apparatus may include a light source that irradiates the subject with light, and the light receiving means may be configured to receive the light that has been irradiated and reached the subject (the invention according to claim 3). . In the case of visible light, the above-described light source irradiates the subject with visible light, and the light receiving means receives the visible light that has reached the subject after being irradiated (the invention according to claim 4).

  In these inventions described above, there is provided body thickness deriving means for obtaining a body thickness that is the thickness of the subject based on an optical image relating to the subject from the light receiving means, and the irradiation condition setting means determines the irradiation condition based on the body thickness. It may be set (the invention according to claim 5). When the body thickness deriving unit is provided, the irradiation condition setting unit sets the increase or decrease of the irradiation amount based on the body thickness (the invention according to claim 6). For example, if the body thickness is thin, the irradiation amount is decreased, and if the body thickness is thick, the irradiation amount is increased.

  According to the tomography according to the present invention, before the tomography is performed, the light receiving unit receives light from the subject, and the irradiation condition setting unit determines the irradiation condition based on the optical image related to the subject from the light receiving unit. Since the setting is performed, it is not necessary to irradiate the radiation to acquire the image for setting the irradiation condition (that is, the scout image) as in the prior art, and the exposure by the radiation can be reduced correspondingly.

Embodiment 1 of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic perspective view of an X-ray CT apparatus according to the first embodiment, and FIG. 2 is a side view and a block diagram of the X-ray CT apparatus according to the first embodiment.

  As shown in FIG. 1, the X-ray CT apparatus includes a visible light irradiation gantry 1, an X-ray irradiation gantry 2, and a top plate 3. The top plate 3 is configured in a bed shape. The visible light irradiation gantry 1 and the X-ray irradiation gantry 2 are arranged close to each other, and are placed on the top 3 when the top 3 is advanced in the direction of the arrow in the figure. The subject M (see FIG. 2) is arranged so as to pass through the opening 11 of the visible light irradiation gantry 1 and the opening 21 of the X-ray irradiation gantry 2 in this order. As shown in FIG. 2, the top 3 is configured to place the subject M, move up and down, and translate along the body axis Z of the subject M. Therefore, an image (optical image) for setting the X-ray irradiation condition is acquired by passing through the visible light irradiation gantry 1, and then the X-ray irradiation condition by passing through the X-ray irradiation gantry 2. A tomographic image under is acquired. In addition, it is preferable to comprise the top plate 3 with the transparent member which has translucency so that visible light may not be shielded by the top plate 3.

  In addition, the X-ray CT apparatus includes a top plate driving unit 4, a body thickness deriving unit 5, an irradiation condition setting unit 6, a memory unit 7, a controller 8, an input unit 9, and an output unit 10. The top plate drive unit 4 is a mechanism that drives the top plate 3 so as to perform the above-described movement, and includes a motor that is not shown in the figure.

  The body thickness deriving unit 5 obtains a body thickness, which is the thickness of the subject M, based on an optical image related to the subject M from the light receiving mechanism 13 described later (in the first embodiment, the shadow of visible light). The irradiation condition setting unit 6 sets the X-ray irradiation condition by setting the increase / decrease of the X-ray irradiation amount based on the body thickness. For example, as shown in FIGS. 6 and 7, if the body thickness h is thin, the X-ray intensity F is decreased to reduce the amount of X-ray irradiation, and if the body thickness h is thick, the X-ray intensity F is increased. And increase the dose. The body thickness deriving unit 5 corresponds to the body thickness deriving unit in the present invention, and the irradiation condition setting unit 6 corresponds to the irradiation condition setting unit in the present invention.

  The memory unit 7 is composed of a storage medium represented by a RAM (Random-Access Memory) or the like. In the first embodiment including the second embodiment described later, the memory unit 7 has an area of the correlation memory unit 7a. In the correlation memory unit 7a, a correlation between the body thickness h and the X-ray intensity F as shown in FIGS. 6 and 7 is stored in advance.

  The controller 8 comprehensively controls each component in the visible light irradiation gantry 1 and the X-ray irradiation gantry 2, the top board driving unit 4, the irradiation condition setting unit 6, and the like. The controller 8 includes a central processing unit (CPU). In the first embodiment including the second embodiment described later, the controller 8 is based on the correlation between the body thickness h and the X-ray intensity F stored in the correlation memory section 7a of the memory section 7 in advance. Then, control is performed to set an increase / decrease in the amount of X-ray irradiation in the irradiation condition via the irradiation condition setting unit 6.

  The input unit 9 sends data and commands input by the operator to the controller 8. The input unit 9 includes a pointing device represented by a mouse, a keyboard, a joystick, a trackball, a touch panel, and the like. The output unit 10 includes a display unit represented by a monitor, a printer, and the like.

  The visible light irradiation gantry 1 has the opening 11 as described above, and includes a visible light projecting mechanism 12 and a light receiving mechanism 13. The visible light projecting mechanism 12 and the light receiving mechanism 13 are arranged opposite to each other with the subject M interposed therebetween, and are embedded in the visible light irradiation gantry 1. However, in the vicinity of the visible light projecting mechanism 12 and the light receiving mechanism 13, visible light irradiation is performed so that visible light irradiated from the visible light projecting mechanism 12 can be applied to the subject M and the light receiving mechanism 13 can receive light. A passage for visible light or a transparent window is provided on the wall of the gantry 1 for use. The visible light projecting mechanism 12 corresponds to the light source in the present invention, and the light receiving mechanism 13 corresponds to the light receiving means in the present invention.

  The visible light projecting mechanism 12 and the light receiving mechanism 13 are rotated around the body axis Z of the subject M in the visible light irradiation gantry 1 while maintaining the facing relationship with each other. The light receiving mechanism 13 receives visible light that has been irradiated onto the subject M from the visible light projecting mechanism 12 and outputs an optical image related to the subject M. This optical image is sent to the body thickness deriving unit 5 described above.

  The X-ray irradiation gantry 2 has the opening 21 as described above, and includes an X-ray tube 22 and an X-ray detector 23. The X-ray tube 22 and the X-ray detector 23 are disposed to face each other with the subject M interposed therebetween, and are embedded in the X-ray irradiation gantry 2. A large number of detection elements constituting the X-ray detector 23 are arranged in a fan shape around the body axis Z of the subject M. Note that the X-ray detector 23 may be a multi-detector composed of a large number of detector element arrays arranged in a fan shape, or may be a single detector composed of one detector element array. The X-ray tube 22 corresponds to the radiation detection means in this invention, and the X-ray detector 23 corresponds to the radiation detection means in this invention.

  The X-ray tube 22 and the X-ray detector 23 are rotated around the body axis Z of the subject M in the X-ray irradiation gantry 2 while maintaining the facing relationship with each other. The X-ray detector 23 detects X-rays irradiated from the X-ray tube 22 and transmitted through the subject M, and outputs them to an electrical signal. This electrical signal is projection data. This projection data is reconstructed to obtain a CT tomographic image.

  In this way, tomography is performed in which X-rays are emitted from the X-ray tube 22 and detected by the X-ray detector 23 to obtain a tomographic image. When tomography is performed, a tomographic image is obtained from a group of projection data detected by the X-ray detector 23 by irradiating X-rays from the X-ray tube 22 under the irradiation conditions set by the irradiation condition setting unit 6. To get.

  Actually, the visible light irradiation gantry 1 and the X-ray irradiation gantry 2 are integrally formed. As shown in FIG. 1, a visible light irradiation gantry 1 and an X-ray irradiation gantry 2 are arranged and integrated in a frame f (see a two-dot chain line in the figure).

  Next, an optical image when the subject M is irradiated with visible light will be described with reference to FIG. FIG. 3 is a diagram schematically illustrating a case where the subject M is irradiated with visible light and the light receiving mechanism 13 receives light. In the case of the first embodiment, since the visible light is irradiated toward the subject M, the visible light is shielded by the subject M in the portion irradiated to the subject M, and the contour of the subject M is visible. The light is projected onto the light receiving surface 13A of the light receiving mechanism 13 as a light shade 13M. The shade 13M corresponds to an optical image related to the subject M.

  Next, the relationship between the projection angles of visible light and X-rays and the relationship with the body thickness will be described with reference to FIGS. 4 and 5. FIG. 4A is a diagram schematically showing an irradiation state when the projection angle of visible light is 0 °, and FIG. 4B is a shadow 13M when the projection angle of visible light is 0 °. FIG. 4C is a diagram schematically showing an irradiation state when the X-ray projection angle is 270 °, and FIG. These are the figures which represented typically the body thickness h in the tomographic image when the projection angle of X-rays is 270 degrees. FIG. 5A is a diagram schematically illustrating an irradiation state when the projection angle of visible light is 90 °, and FIG. 5B is a diagram when the projection angle of visible light is 90 °. FIG. 5C is a diagram schematically showing the body thickness h at the shadow 13M, and FIG. 5C is a diagram schematically showing the irradiation state when the X-ray projection angle is 0 °. d) is a diagram schematically showing the body thickness h in the tomographic image when the X-ray projection angle is 0 °. 4 and 5, the subject M will be described as a human body.

  Here, an angle formed between a predetermined coordinate axis and the central axis of visible light or X-ray is referred to as “projection angle” or “rotation angle”. In the present specification, a vertical axis is used as a predetermined coordinate axis used for the projection angle (rotation angle). Therefore, the angle formed by the vertical axis and the central axis is referred to as “projection angle” or “rotation angle”. That is, when the central axis and the vertical axis are parallel, the projection angle is 0 ° or 180 °, and when the central axis and the horizontal axis are parallel (that is, the central axis and the vertical axis are orthogonal), the projection angle is 90 ° or 270 °.

  As shown in FIG. 4 (a), when visible light is irradiated when the projection angle is 0 °, as shown in FIG. 4 (b), the shadow 13M at that time becomes a projected image from the vertical direction, The body thickness h is the shoulder width of the subject M. On the other hand, as shown in FIG. 4C, when X-rays are irradiated when the projection angle is 270 ° (−90 °), the X-rays cross the shoulder of the subject M as shown in FIG. The path length, which is the transmission width, becomes the shoulder width of the subject M, and becomes equal to the body thickness h in the shadow 13M when the visible light projection angle in FIG. 4B is 0 °. Even when X-rays are irradiated when the projection angle is 90 °, the body thickness h and the path length at the shadow 13M when the visible light projection angle is 0 ° are equal.

  Therefore, if the subject M is irradiated with visible light at a projection angle of 0 ° and the shadow 13M when the body thickness h is the shoulder width of the subject M is acquired, the case when the body thickness h is the shoulder width of the subject M is obtained. The irradiation condition setting unit 6 sets the X-ray intensity F and the X-ray irradiation amount at the X-ray intensity as an irradiation condition, and the X-ray is irradiated at a projection angle of ± 90 ° under the irradiation condition. It is possible to acquire a tomographic image by irradiating the specimen M.

  As shown in FIG. 5A, when visible light is irradiated when the projection angle is 90 °, the shadow 13M at that time becomes a projected image from the horizontal direction as shown in FIG. 5B. The body thickness h is the thickness of the abdomen or head of the subject M. On the other hand, as shown in FIG. 5C, when X-rays are irradiated when the projection angle is 0 °, the X-rays pass through the abdomen or head of the subject M as shown in FIG. The path length, which is the transmission width, becomes the thickness of the abdomen or head of the subject M, and is equal to the body thickness h in the shade 13M when the visible light projection angle in FIG. Become. Even when X-rays are irradiated when the projection angle is 180 °, the body thickness h and the path length in the shade 13M when the visible light projection angle is 90 ° are equal.

  Accordingly, if the subject M is irradiated with visible light at a projection angle of 90 ° and the shadow 13M is obtained when the body thickness h is the thickness of the abdomen or head of the subject M, the body thickness h is the subject M. The irradiation condition setting unit 6 sets the X-ray intensity F at the thickness of the abdomen or head of the subject and the X-ray irradiation amount at the X-ray intensity as an irradiation condition, and projects under the irradiation condition. It is possible to acquire a tomographic image by irradiating the subject M with X-rays at angles of 0 ° and 180 °.

  In summary, when the projection angle (rotation angle) of visible light is α, the projection is performed even if α is a general projection angle (0 ° to 360 °) other than 0 ° or 90 ° described above. If the subject M is irradiated with visible light at an angle α and a shadow 13M with a body thickness h at that time is obtained, the X-ray intensity F at the body thickness h and further X at the X-ray intensity are obtained. The irradiation condition setting unit 6 sets the irradiation dose as an irradiation condition, and acquires a tomographic image by irradiating the subject M with X-rays at a projection angle (α ± 90 °) under the irradiation condition. Is possible.

  As in the first embodiment, when performing a helical scan in which tomography is performed by moving the top plate 1, assuming that a certain tomographic position is A, it is preferable to control as follows. That is, when the tomographic position A first passes through the visible light irradiation gantry 1 and the subject M is irradiated with visible light at the projection angle α, then the tomographic position A passes through the X-ray irradiation gantry 2. So that the subject M is irradiated with X-rays at a projection angle (α ± 90 °), the rotational speed of the top 1, the rotational speed of the visible light projecting mechanism 12 and the light receiving mechanism 13, the X-ray tube 22, and The rotational speed of the X-ray detector 23 is controlled. By controlling in this way, it is possible to acquire a tomographic image by irradiation with visible light 13M and X-ray irradiation by a single helical scan. Of course, the helical scan may be performed by dividing the irradiation of visible light and X-ray irradiation into two times, and each irradiation without controlling the projection angle of visible light or X-rays at the above-described angle. You may go on.

  Next, the correlation between the body thickness h and the X-ray intensity F will be described with reference to FIGS. FIG. 6 is a graph schematically showing a linear correlation between the body thickness h and the X-ray intensity F, and FIG. 7 schematically shows a non-linear correlation between the body thickness h and the X-ray intensity F. It is a represented graph.

  As shown in FIGS. 6 and 7, the horizontal axis represents the body thickness h, and the vertical axis represents the X-ray intensity F. A phantom (for a body imitating the shape of the subject) is prepared in advance of tomography, and the X-ray intensity F at each body thickness is measured. At this time, in consideration of the S / N ratio of the tomographic image and the like, the X-ray intensity F that is the minimum within a range that does not adversely affect the image quality of the tomographic image is obtained, and the body thickness h at that time is associated. In the case of linearity, it becomes as shown in FIG. 6, and in the case of non-linearity, it becomes as shown in FIG. 7 (a) or FIG. 7 (b). As shown in FIGS. 6 and 7, if the body thickness h is thin, the X-ray intensity F is decreased to reduce the X-ray irradiation amount, and if the body thickness h is thick, the X-ray intensity F is increased. Increase the dose.

  Further, even when the body thickness h is the same, the X-ray absorption rate differs depending on the tomographic position, and when the X-ray intensity F is changed according to the absorption rate, the correlation may be obtained in consideration of the absorption rate. Specifically, phantoms having different absorption rates are prepared, the X-ray intensity F is similarly obtained, and the body thickness h at that time is associated with each phantom. When performing tomography, a correlation with an absorption rate closest to the absorption rate of the part is selected according to the part to be imaged, and irradiation conditions are selected based on the selected correlation. The setting unit 6 may set the X-ray irradiation amount based on the body thickness h at the absorption rate. For example, in the case of the lung, since it contains a lot of air, X-rays are easily transmitted and the absorption rate is small. In this case, the amount of X-ray irradiation is reduced. On the other hand, in the case of the abdomen, it contains an organ and the like, so that X-rays are hardly transmitted and the absorption rate is large. In this case, increase the amount of X-ray irradiation

  Based on FIG. 6 or FIG. 7, the X-ray intensity F corresponding to the body thickness h in the shadow 13M is obtained, and the irradiation condition setting unit 6 sets the X-ray irradiation amount. Under the irradiation condition that is the set irradiation amount, X-rays are irradiated from the X-ray tube 22 and a tomographic image is acquired from a group of projection data detected by the X-ray detector 23.

  Next, the flow of acquisition of a tomographic image by irradiation with a shadow 13M or irradiation with X-rays in the first embodiment will be described with reference to FIG. FIG. 8 is a flowchart illustrating a flow of acquiring a tomographic image by irradiation with a shadow 13M or irradiation with X-rays in the first embodiment.

(Step S <b> 1) Movement of the top plate With the subject M placed on the top plate 1, the top plate 1 is moved from the visible light irradiation gantry 1 toward the X-ray irradiation gantry 2. The movement of the top plate 1 is also performed after step S2.

(Step S2) Irradiation of Visible Light The light receiving mechanism 13 obtains a shadow 13M that reaches the light receiving surface 13A by irradiating the subject M with visible light from the visible light projecting mechanism 12 at the projection angle α. Actually, since the visible light projecting mechanism 12 and the light receiving mechanism 13 rotate around the body axis Z of the subject M, the projection angle α is 0 ° to 360 ° (or 0 in the case of tomography using a C-arm). The shadow M at the time of (° to 180 °) is obtained.

(Step S3) Derivation of body thickness The body thickness deriving unit 5 obtains a body thickness h at the shadow 13M based on the shadow 13M.

(Step S4) Setting of Increase / Decrease of Irradiation Dose The irradiation condition setting unit 6 sets the increase / decrease of the X-ray irradiation amount based on the body thickness h, thereby setting the X-ray irradiation condition.

(Step S5) X-ray irradiation The top plate 1 is moving from the visible light irradiation gantry 1 toward the X-ray irradiation gantry 2 between steps S2 and S4. Under the irradiation conditions set in step S4, tomography is performed by irradiating the subject M with X-rays from the X-ray tube 22 at a projection angle (α ± 90 °). Actually, since the X-ray tube 22 and the X-ray detector 23 rotate around the body axis Z of the subject M, the projection angle (α ± 90 °) is 0 ° to 360 ° (or tomography using a C-arm). In this case, tomographic images at 0 ° to 180 ° are respectively obtained.

(Step S6) Has the predetermined shooting range been reached?
It is determined whether or not the top board 1 has reached a predetermined photographing range set in advance. If not reached, the process returns to step S2, and steps S2 to S6 are repeated to acquire the shadow 13M and the tomographic image continuously, and if reached, the acquisition of the series of shadow 13M and the tomographic image is terminated.

  The X-ray CT apparatus according to the first embodiment described above includes the light receiving mechanism 13 that receives light from the subject M. Prior to tomography, the light receiving mechanism 13 receives light from the subject M, and irradiation conditions based on an optical image related to the subject M from the light receiving mechanism 13 (shading 13M of visible light in the first embodiment). The setting unit 6 sets irradiation conditions. Thus, a tomographic image is acquired from a group of projection data detected by the X-ray detector 23 under the irradiation conditions set by the irradiation condition setting unit 6. That is, the irradiation condition for tomography is set using the optical image related to the subject M from the light receiving mechanism 13 instead of the image obtained by the conventional X-ray irradiation (that is, the scout image). Thus, it is not necessary to irradiate X-rays in order to acquire an image (scout image) for setting the irradiation conditions, and exposure by X-rays can be reduced accordingly.

  In the first embodiment, visible light is used as light. Therefore, the X-ray CT apparatus according to the first embodiment includes the visible light projecting mechanism 12 that irradiates the subject M with visible light, and the light receiving mechanism 13 receives the visible light that has been irradiated by the subject M. Is configured to do.

  Further, the X-ray CT apparatus according to the first embodiment including the second embodiment to be described later calculates the body thickness h that is the thickness of the subject M based on the optical image related to the subject M from the light receiving mechanism 13. A thickness deriving unit 5 is provided, and the irradiation condition setting unit 6 sets irradiation conditions based on the body thickness h. Specifically, the irradiation condition setting unit 6 sets the increase / decrease of the irradiation amount based on the body thickness h. For example, as shown in FIGS. 6 and 7, the X-ray irradiation amount is decreased when the body thickness h is thin, and the X-ray irradiation amount is increased when the body thickness h is thick.

Next, Embodiment 2 of the present invention will be described with reference to the drawings.
FIG. 9 is a side view and a block diagram of the X-ray CT apparatus according to the second embodiment. The parts common to the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

  In the second embodiment, the X-ray CT apparatus includes an infrared gantry 15 instead of the visible light irradiation gantry 1 of the first embodiment. As in the first embodiment, as shown in FIG. 9, the infrared gantry 15 and the X-ray irradiation gantry 2 are disposed close to each other, and the top plate 3 is arranged in the direction of the arrow in the figure. When the advancing to, the subject M placed on the top 3 is arranged so as to pass through the opening 16 of the infrared gantry 15 and the opening 21 of the X-ray irradiation gantry 2 in this order.

  Since the top plate 3, the top plate drive unit 4, the body thickness deriving unit 5, the irradiation condition setting unit 6, the memory unit 7, the controller 8, the input unit 9, and the output unit 10 are the same as those in the first embodiment described above, the description thereof is omitted. Is omitted.

  The infrared gantry 15 has the opening 16 as described above, and includes an infrared monitor 17. The infrared monitor 17 receives infrared rays generated by thermal radiation generated from the subject M. The infrared monitor 17 is rotated around the body axis Z of the subject M in the infrared gantry 15. The infrared monitor 17 corresponds to the light receiving means in this invention.

  Next, an optical image when infrared rays are received will be described with reference to FIG. FIG. 10 is a diagram schematically illustrating a case where the infrared monitor 17 receives light. In the case of the second embodiment, since infrared rays due to thermal radiation generated from the subject M are received, the temperature distribution image 17M of the subject M caused by thermal radiation is projected onto the light receiving surface (monitor surface) 17A of the infrared monitor 17. The This temperature distribution image 17M corresponds to an optical image related to the subject in the present invention. At this time, the width of the temperature distribution image 17M becomes the body thickness h.

  As in the first embodiment, when the tomographic position A first passes through the infrared gantry 15, the infrared monitor 17 receives infrared rays at the projection angle α, and then the tomographic position A becomes the X-ray irradiation gantry 2. So that the subject M is irradiated with X-rays at a projection angle (α ± 90 °) when passing through, the rotational speed of the top board 1, the rotational speed of the infrared monitor 17, the X-ray tube 22 and the X-ray detection. It is preferable to control the rotational speed of the vessel 23 and the like. In the case of the second embodiment, the central axis used for the projection angle α is an axis connecting the central point of the top plate 1 and the central point on the light receiving surface 17A of the infrared monitor 17. Since the correlation between the body thickness h and the X-ray intensity F is the same as that in the first embodiment, the description thereof is omitted.

  Next, the flow of acquiring the temperature distribution image 17M by infrared light reception and the tomographic image by X-ray irradiation in the second embodiment will be described with reference to FIG. FIG. 11 is a flowchart illustrating a flow of acquiring a temperature distribution image 17M by infrared light reception and a tomographic image by X-ray irradiation in the second embodiment.

(Step S11) Movement of the top plate Since it is the same as the movement of the top plate in step S1 of the first embodiment, the description thereof is omitted.

(Step S12) Infrared light reception The infrared monitor 17 receives infrared rays generated by thermal radiation generated from the subject M at a projection angle α, and obtains a temperature distribution image 17M of the subject M due to thermal radiation. Actually, since the infrared monitor 17 rotates around the body axis Z of the subject M, the projection angle α is 0 ° to 360 ° (or 0 ° to 180 ° in the case of tomography with a C-arm). Temperature distribution images 17M are obtained.

(Step S13) Derivation of body thickness Since this is the same as the derivation of body thickness in step S3 of Example 1, the description thereof is omitted.

(Step S14) Setting of Increase / Decrease of Irradiation Dose Since it is the same as the setting of increase / decrease of irradiation dose in Step S4 of Example 1, the description thereof is omitted.

(Step S15) X-ray irradiation Since it is the same as the X-ray irradiation in step S5 of the first embodiment, the description thereof is omitted.

(Step S16) Has the predetermined shooting range been reached?
Has the predetermined shooting range in step S6 of Example 1 been reached? The explanation is omitted because it is the same.

  According to the X-ray CT apparatus according to the second embodiment described above, before performing tomography, the infrared monitor 17 receives light from the subject M, and an optical image regarding the subject M from the infrared monitor 17 ( In the second embodiment, since the irradiation condition setting unit 6 sets the irradiation condition based on the temperature distribution image 17M), X-rays are used to acquire an image (that is, a scout image) for setting the irradiation condition as in the past. Therefore, exposure by X-rays can be reduced accordingly.

  In the second embodiment, infrared light is used as light. In the case of infrared rays, the infrared monitor 17 receives infrared rays due to thermal radiation generated from the subject M. Therefore, the X-ray CT apparatus according to the second embodiment does not need a light source (visible light projecting mechanism 12 in the first embodiment) that emits light as in the first embodiment.

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) In each of the embodiments described above, X-rays have been described as examples of radiation. However, the present invention can also be applied to tomography using radiation other than X-rays (for example, γ-rays).

  (2) In each of the above-described embodiments, the X-ray irradiation gantry 2 that houses the X-ray tube 22 and the X-ray detector 23 is provided, and the subject M is caused to enter the opening 11 of the X-ray irradiation gantry 2. In the X-ray irradiation gantry 2, the X-ray tube 22 and the X-ray detector 23 were rotated around the body axis Z of the subject M, and tomography was performed. The X-ray tube 22 and the X-ray detector 23 may be rotated around the body axis Z of the subject M to perform tomography.

  (3) In each of the above-described embodiments, the helical scan in which tomography is performed by moving the top board 1 has been described as an example, but the imaging mode in which tomography is performed while being fixed at a predetermined tomographic position is exemplified. As described above, the shooting mode is not particularly limited.

  (4) In the first embodiment described above, the visible light irradiation gantry 1 and the X-ray irradiation gantry 2 are provided one by one. In the second embodiment described above, the infrared gantry 15 and the X-ray irradiation gantry 2 are provided. Although one is provided, the arrangement and number of gantry are not particularly limited. For example, as shown in FIG. 12, two visible light irradiation gantry 1 (or infrared gantry 15) is provided, and two visible light irradiation gantry 1 (or infrared gantry 15) is used to form X-ray irradiation gantry 2. It may be disposed in a sandwiched manner. In FIG. 12, when the top board 1 is moved in the right direction in the drawing as viewed from the drawing, the optical image is obtained by receiving light with the visible light irradiation gantry 1 (or infrared gantry 15) at the left end. Later, a tomographic image is obtained with the central X-ray irradiation gantry 2. When the top plate 1 is moved in the left direction in the figure, the optical image is obtained by receiving light with the visible light irradiation gantry 1 (or the infrared gantry 15) at the right end, and then the X-ray irradiation at the center. A tomographic image is obtained with the gantry 2.

  (5) In the above-described first embodiment, description has been made by taking visible light as an example, and in the above-described second embodiment, infrared has been described as an example, but the present invention is also applicable to light other than visible light and infrared light. be able to.

  (6) As shown in FIG. 13, the present invention can also be applied to a tomography apparatus including a laser light source 18 that emits a laser and a laser detector 19 that receives the laser light by detecting the laser. In FIG. 13, a transmissive optical sensor is used as the laser detector 19. That is, when the laser is shielded by the subject M, the laser does not reach the laser detector 19 at the position facing the laser light source 18, and the laser detector 19 detects that the subject M exists. To do. Conversely, when the laser reaches the laser detector 19, the laser detector 19 detects that the subject M does not exist. As shown in FIG. 13, when the laser detector 19 is composed of a single light receiving element, the laser light source 18 and the laser detector 19 are moved from one end where the subject M does not exist to the other end. Is moved in parallel with respect to the scanning. After scanning, when the laser signal reaches the laser detector 19 without being shielded by the subject M and when the electrical signals output from the laser detector 19 when shielded by the subject M are arranged in the scanning direction, an optical image is output. Will be. Further, since the scanning range of the portion shielded by the subject M becomes the body thickness h of the subject M, the body thickness deriving unit 5 as in each embodiment is not necessary, and only the detection result from the laser detector 19 is used. Thus, the body thickness h can be obtained. The laser light source 18 corresponds to the light source in the present invention, and the laser detector 19 corresponds to the light receiving means in the present invention.

  (7) In the modified example (6) described above, the case where the laser detector 19 is composed of one light receiving element has been described as an example. However, as shown in FIG. 14, the laser is fan-shaped by an optical system (not shown). When the laser beam is spread and irradiated, the laser detector 19 may be composed of a plurality of light receiving elements.

  (8) In the modification (6) described above, the laser detector 19 is a transmissive optical sensor, but may be a reflective optical sensor. In this case, the laser detector 19 includes a light projecting element and a light receiving element, and the above-described light projecting element is used instead of the laser light source 18. When the laser irradiated from the light projecting element is reflected by the subject M, the reflected light reaches the light receiving element on the same side as the light projecting element, so that the laser detector 19 detects that the subject M exists. To do. On the contrary, when the laser irradiated from the light projecting element does not reach the light receiving element, the laser detector 19 detects that the subject M does not exist.

1 is a schematic perspective view of an X-ray CT apparatus according to Embodiment 1. FIG. 1 is a side view and block diagram of an X-ray CT apparatus according to Embodiment 1. FIG. It is the figure which represented typically the case where a subject is irradiated with visible light and the light-receiving mechanism received light. (A) is a diagram schematically showing an irradiation situation when the projection angle of visible light is 0 °, and (b) shows the body thickness in the shade when the projection angle of visible light is 0 °. It is the figure typically represented, (c) is a figure which represented typically the irradiation condition when the projection angle of X-rays is 270 degrees, (d) is the projection angle of X-rays 270 degrees. It is the figure which represented typically the body thickness in the tomographic image at the time of. (A) is the figure which represented typically the irradiation condition when the projection angle of visible light is 90 degrees, (b) is the body thickness in the shadow when the projection angle of visible light is 90 degrees. It is the figure represented typically, (c) is a figure which represented typically the irradiation condition when the projection angle of X-rays is 0 degree, (d) is the projection angle of X-rays 0 degree. It is the figure which represented typically the body thickness in the tomographic image at the time of. 3 is a graph schematically showing a linear correlation between body thickness and X-ray intensity. It is the graph which represented typically the nonlinear correlation of body thickness and X-ray intensity. 6 is a flowchart illustrating a flow of acquiring a tomographic image by irradiation with visible light or irradiation with X-rays in the first embodiment. 6 is a side view and a block diagram of an X-ray CT apparatus according to Embodiment 2. FIG. It is the figure which represented typically the case where an infrared monitor received light. 10 is a flowchart illustrating a flow of acquiring a temperature distribution image by infrared light reception and a tomographic image by X-ray irradiation in the second embodiment. It is a side view of the X-ray CT apparatus which concerns on a modification. It is the figure which represented typically the irradiation and light reception condition of a laser when a laser detector consists of one light receiving element. (A), (b) is the figure which represented typically the irradiation of a laser, and the light reception condition when a laser detector consists of a some light receiving element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 5 ... Body thickness deriving part 6 ... Irradiation condition setting part 12 ... Visible light projection mechanism 13 ... Light receiving mechanism 13M ... Shadow 17 ... Infrared monitor 17M ... Temperature distribution image 22 ... X-ray tube 23 ... X-ray detector M ... Subject

Claims (6)

  An irradiation source that irradiates a subject with radiation, a radiation detection unit that detects the radiation irradiated and transmitted to the subject, and an irradiation condition setting unit that sets irradiation conditions for the irradiation source The tomography apparatus for obtaining a tomographic image from a group of projection data detected by the radiation detection means under the irradiation condition set by the irradiation condition setting means, comprising a light receiving means for receiving light from the subject. A tomography apparatus, wherein the irradiation condition setting means sets the irradiation condition based on an optical image relating to the subject from the light receiving means.   The tomography apparatus according to claim 1, wherein the light is an infrared ray, and the light receiving unit receives an infrared ray due to thermal radiation generated from a subject.   The tomography apparatus according to claim 1, further comprising a light source that irradiates the subject with light, wherein the light receiving unit receives the light that has been irradiated and reached the subject.   4. The tomography apparatus according to claim 3, wherein the light is visible light, the light source irradiates the subject with visible light, and the light receiving means irradiates the subject with visible light that has reached. A tomography apparatus characterized by receiving light.   5. The tomography apparatus according to claim 1, further comprising a body thickness deriving unit that obtains a body thickness that is a thickness of the subject based on an optical image related to the subject from the light receiving unit. The tomography apparatus is characterized in that the condition setting means sets the irradiation condition based on the body thickness. 6. The tomography apparatus according to claim 5, wherein the irradiation condition setting means sets an increase / decrease in the dose based on the body thickness.

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