JP4275508B2 - X-ray CT system - Google Patents

Description

  The present invention relates to an X-ray CT apparatus, and more particularly to magnification control in an X-ray CT apparatus.

  An X-ray CT apparatus is an apparatus that rotates an X-ray beam that passes through a specimen and reconstructs a tomographic image or a three-dimensional image of the specimen based on data obtained thereby. In addition to being used for diagnosing human diseases, the X-ray CT apparatus is also used for measuring animals and other objects other than the human body for the purpose of research and experiments. For example, in a pharmaceutical company, an X-ray CT apparatus is used to verify the results of animal experiments. In this case, examples of the sample include small animals such as dogs, cats, birds, guinea pigs, rats, mice, and hamsters. In addition, a tissue piece separated from those small animals may be a specimen. Conventionally, when performing tomography of a small animal using an X-ray CT apparatus, for example, the small animal is placed on a simple horizontal bed.

Patent Document 1 listed below discloses a veterinary X-ray imaging apparatus (so-called X-ray imaging apparatus) including a table having a simple V-groove on which an animal such as a dog is placed. Patent Document 2 below discloses an industrial X-ray CT apparatus. According to this document, the enlarged projection image is obtained by rotating the sample side and changing the distance between the X-ray generator and the sample. In this apparatus, the sample to be measured is an industrial product. In this apparatus, it is recognized that the magnification is fixed when the CT scan is continuously performed on the measurement object.
JP 2001-299786 A JP-A-5-322802

  In a conventional X-ray CT apparatus, the magnification (resolution) cannot be changed, or even if it has a configuration capable of changing the magnification (for example, the configuration of Patent Document 2 above), CT scanning, A configuration that can sequentially acquire a plurality of CT images by switching magnification during moving scanning is not employed.

  For example, when a plurality of CT images are sequentially acquired for a head such as a dog (for example, a range from the nose to the jaw), that is, when a specimen whose form gradually increases is to be measured, However, when the measurement magnification is adjusted, the CT image near the nose becomes small (or it becomes difficult to observe a more detailed structure). There arises a problem that the image cannot be observed or the measurement itself cannot be performed due to physical interference between the specimen and the mechanism.

  Note that, as seen in the conventional X-ray CT apparatus, if the measurement is performed simply by placing a small animal on the horizontal bed, it is difficult to position the measurement site. If positioning is not appropriate, there is also a problem that a part of a small animal's body protrudes from the effective visual field. Also, if the small animal moves during the measurement, the image quality is significantly reduced. In addition, when the hair or tail of a small animal comes into contact with a gantry or other mechanism, hygiene problems are likely to occur. Each of the above problems can be pointed out for specimens other than small animals.

An object of the present invention is to make it possible to acquire a CT image at a favorable magnification in accordance with the size of a member containing a measurement target portion in a specimen.

Another object of the present invention is to make it possible to dynamically change the magnification in accordance with the scanning movement of the specimen (that is, the scanning scanning of the imaging position with respect to the specimen) .

(1) The present invention provides an X-ray generator that forms an X-ray beam in a direction that intersects the direction of the rotation center axis, and an X-ray detector that detects the X-ray beam; A holding member holding the specimen arranged on the rotation center axis, a moving mechanism for moving the holding member relative to the measurement unit in the direction of the rotation center axis, and the holding member A rotation mechanism that rotates the measurement unit around the rotation center axis; a displacement mechanism that displaces at least one of the X-ray generation unit, the X-ray detection unit, and the rotation center axis in the X-ray beam direction; wherein when scanning the imaging position by the relative movement of the holding member with respect to the measurement unit comprises a measurement magnification control unit for variable measurement ratio by controlling the operation of the displacement mechanism, the holding member, the analyte All of The housing member has a shape whose cross-sectional size changes continuously or stepwise in the direction of the rotation center axis, and the measurement magnification control unit When scanning the position, the measurement magnification is set according to a cross-sectional size at each photographing position in the housing member .

According to the above configuration, the holding member is moved and scanned relative to the measurement unit, and on the other hand, the measurement unit is rotated and scanned relative to the holding member. At that time, the measurement magnification at the time of each measurement can be individually set by controlling the displacement mechanism. Therefore, when a plurality of tomographic images are taken on the specimen, the measurement magnification is uniformly set. The problem can be solved. That is, according to the present invention, measurement in accordance with the size of the housing member housing the constant region, the measurement magnification can be set appropriately. Therefore, since the measurement magnification can be dynamically changed with the moving scanning of the imaging position , a CT image (tomographic image) can be acquired with a good resolution or magnification at each imaging position .

  Examples of the specimen include living organisms and non-living organisms, preferably animals other than human beings, particularly preferably small animals such as dogs and cats. For example, in a certain type of animal experiment, a dog's nasal cavity is used as a measurement target region, and a plurality of tomographic images are performed. In such a case, it is desirable to use the X-ray CT apparatus according to the present invention. At the time of the moving scanning, at least one of the holding member and the X-ray measuring unit is driven, and at the time of the rotating scanning, at least one of the holding member and the X-ray measuring unit is driven.

The displacement mechanism includes a distance between the rotation center axis and the X-ray generation unit and a distance between the rotation center axis and the X-ray detection unit in the X-ray beam direction (usually in the center axis direction of the X-ray beam). One or both of them is made variable. Although it is desirable to make the rotation center axis coincide with the specimen center axis, they may be inconsistent. As a result, when the X-ray beam is configured with a divergent shape, the subject passage width (or effective visual field range) of the X-ray beam changes, so that the magnification when a CT image is configured can be changed. In this case, the spatial resolution also varies. Usually, the magnification is varied so that the entire cross section of the subject is covered, but the magnification may be set so that a part of the cross section is magnified. In that case, it is desirable to position the specimen so that the center of the part coincides with the rotation center axis. The concept of the divergent shape includes a fan beam shape that spreads two-dimensionally. Anyway, according to the present invention, it is possible to perform variable measurement magnification with the movement scanning of the specimen (i.e. scanning movement of the imaging position for the analyte), in particular, the shape of the member housing the test body The measurement magnification can be changed according to the above. When such a method is used, the measurement magnification (image size, resolution) differs between a plurality of CT images obtained by one moving scan. Therefore, in image management, measurement magnification (scale information, etc. Or the information may be used in image processing.

Desirably, the X-ray CT apparatus has a gantry for accommodating the measurement unit, and the accommodating member is inserted into a cavity portion of the gantry.

  According to this configuration, a part to be measured (all or part of the specimen) in the specimen is accommodated in the accommodating member, and the accommodating member is inserted into the gantry. Therefore, it is possible to prevent the measurement site (for example, animal hair) from coming into contact with the measurement unit or the gantry that houses the measurement site by accommodating the measurement site in the housing member, and the measurement site is always within a certain volume. Since it is limited, the measurement magnification can be easily controlled. Furthermore, the specimen can be easily positioned by accommodating the specimen in the accommodating member, and the movement of the specimen can be prevented during the measurement by regulating the movement of the specimen. The housing member preferably has a rotationally symmetric shape with respect to the rotation center axis, and preferably has a shape corresponding to a shape change along the direction of the rotation center axis in the specimen.

  Preferably, the measurement magnification control unit sets a displacement amount by the displacement mechanism corresponding to the outer diameter of the X-ray beam passing position in the housing member. Although it is possible to adjust the amount of displacement according to the size of the sample itself, when the sample has a complicated shape, the adjustment becomes complicated and it is generally difficult to measure the shape of the sample. On the other hand, if the outer diameter of the housing member is used as a reference, the displacement amount can be easily adjusted. Therefore, it is desirable that the shape of the housing member is a simple shape that conforms to the shape of the specimen.

  Preferably, the housing member has a tapered shape. Desirably, the said accommodating member accommodates the part from the nose to a jaw in the small animal as the said test substance. Desirably, all or part of the housing member has transparency. If at least a part is transparent, the state of the specimen or measurement site can be visually observed therefrom.

  Preferably, the holding member has a mounting table connected to the housing member. According to this configuration, a part of the specimen (usually a measurement site) is stored in the storage member, and other non-measurement sites are placed on the mounting table. Here, the mounting table may be a flat member, may have a V-groove for positioning a non-measurement site, or may have a hollow cylinder or the like.

  Desirably, the data management means which associates and manages the information which specifies a measurement magnification with respect to the CT image acquired in each measurement position in the direction of the said rotation center axis | shaft is included. The information for specifying the measurement magnification is, for example, information representing the measurement magnification itself, scale information, resolution information, and the like.

  Preferably, data processing means for executing image processing on the CT image based on information specifying the measurement magnification is included. According to this configuration, appropriate image processing can be performed using the information for specifying the measurement magnification associated with image processing for a CT image. The image processing includes processing for making the display size of each CT image constant regardless of the measurement magnification, processing for separating each tissue (fat, bone, soft tissue, etc.) on the image inside the specimen, and the like.

  Desirably, it includes display processing means for displaying information for specifying the measurement magnification when displaying a CT image. According to this configuration, when the user observes the CT image of the specimen, the problem of misidentifying the size and the like can be prevented.

  Preferably, a storage unit in which shape data about the housing member is registered is included, and the measurement magnification control unit controls the operation of the displacement mechanism according to the shape data. According to this configuration, the shape data of the housing member is registered in advance, and the displacement amount is adjusted according to the shape data. The shape data may be composed of data representing the outer diameter of the housing member for each tomographic position, or may be composed of data representing all changes in the outer diameter of the housing member in the rotation center axis direction.

  Preferably, the measurement magnification control unit controls the operation of the displacement mechanism based on an X-ray intensity distribution obtained when the X-ray beam is transmitted through the housing member. According to this configuration, even if the shape of the housing member is not known, the shape data can be acquired by preliminary irradiation with X-rays. This preliminary irradiation can be performed in either a state where the specimen is accommodated in the accommodation member or a state where the specimen is not accommodated.

  Desirably, it includes shape measuring means for measuring the shape of the housing member and outputting shape data, and the measurement magnification control unit controls the operation of the displacement mechanism according to the shape data. According to this configuration, since the shape of the housing member is actually measured, it is accurate, and even when the housing member is replaced, the displacement amount can be appropriately controlled without error. Of course, it is also possible to directly or indirectly measure the shape of the specimen itself and to control the amount of displacement based on the obtained shape data.

(2) A method implemented in an embodiment to be described later is a method in which tomography is sequentially performed at a plurality of tomography positions on a sample other than a human body using an X-ray CT apparatus. When measuring tomographic images individually at the tomographic positions, performing tomographic imaging at the measurement magnifications individually set at the respective tomographic positions, and obtaining the tomographic images acquired at the respective tomographic positions the measurement magnification is intended for associating data identifying.

(3) In the later embodiment is used in X-ray CT apparatus for the animal's head tomography, there is provided a head receiving member for at least X-ray CT apparatus having a tapered shape to accommodate the head The

(4) As said accommodating member, various things are prepared according to a measurement site | part and its size, and you may make it selectively use them according to an actual specimen. When the specimen is accommodated in the accommodation member, the movement of the specimen may be regulated using a fixing member.

As described above, according to the present invention, a CT image can be acquired at a favorable magnification according to the size of a member that accommodates a measurement target portion in a specimen.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 shows an example of an X-ray CT apparatus. This X-ray CT apparatus is provided with a dynamic variable function of magnification, and is particularly intended for measuring the head (specifically, near the nasal cavity) of a dog (eg, a beagle dog) as a small animal. Of course, other specimens may be measured. For example, mice or guinea pigs may be measured. This X-ray CT apparatus is roughly divided into a measurement unit 10 and a calculation control unit 12.

  The measurement unit 10 has a main body 16 having a gantry 18. An arm 26 protrudes upward from the upper surface 16A of the main body 16. The arm 26 forms a part of a slide mechanism described later, and the arm 26 supports a holding member 400 described later, and slides it in the direction of the rotation center axis.

  On the other hand, measurement units (X-ray generator, X-ray detector), which will be described later, are accommodated in the gantry 18 and rotate around the rotation center axis. A hollow portion 18A is formed in the central portion of the gantry 18 in the direction of the rotation center axis.

  The holding member 400 includes a mounting table 402 and a housing member 401 in the present embodiment. The mounting table 402 is configured as a substantially flat pedestal, and both ends thereof are bent upward to form side walls. The housing member 401 is configured as a hollow member having a tapered shape, and has a substantially conical shape in the present embodiment. That is, the housing member 401 is configured as a horn shape having a large diameter at the rear and a small diameter at the front. The tip may be a vertical surface or a sharp shape having a vertex. The head of the dog (from the nose to the chin) as a specimen is housed in the housing member 401, and the parts other than the head (body, foot, tail, etc.) are placed on the mounting table 402. In the present embodiment, the housing member 401 is slid into the cavity 18A of the gantry 18 step by step or continuously, and CT imaging is performed at each slide position. Since the measurement site is confined in the housing member 401, the measurement site can be easily positioned, and the movement of the measurement site can be restricted in combination with the use of a fixing member such as padding. In addition, it is possible to prevent the problem of dog hair coming into contact with the gantry 18 and the problem of excrement such as dog drool dropping into the cavity 18A and contaminating it.

  The holding member 400 can be attached to and detached from the arm 26. After the holding member 400 is attached to the arm 26, a dog as a specimen is set on the holding member 400, and then the arm 26 is rotated about the center of rotation. Driven forward along the axial direction. As a result, the housing member 401 is inserted into the cavity 18 </ b> A of the gantry 18. At this time, the holding member 400 is positioned so that CT imaging is performed at a predetermined position on the specimen. The movement scanning of the holding member 400 is performed continuously or stepwise.

  An operation panel 20 is provided on the upper surface 16A of the main body 16, and the operation panel 20 includes a plurality of switches, indicators, and the like. Using this operation panel 20, the user can operate the operation of the apparatus at the measurement site. A plurality of casters 22 are provided below the main body 16. Incidentally, the height of the measurement unit 10 is, for example, 100 cm.

  Next, the arithmetic control unit 12 will be described. The arithmetic control unit 12 is electrically connected to the measurement unit 10 by a cable 14. The measurement unit 10 and the calculation control unit 12 may be provided in the same room, or may be installed in different places. The arithmetic control unit 12 is configured by a normal computer system or the like, and specifically includes a processor 30, a display 32, a keyboard 36, a mouse 38, a storage device 34, a printer 40, and the like. The operation control unit 12 controls the operation of the measurement unit 10, and a CT image is configured based on data transmitted from the measurement unit 10. Incidentally, in the apparatus of the present embodiment, the rotation speed of the measurement unit in the gantry 18 is, for example, 10 rotations per minute. Of course, such a rotation speed can be appropriately set according to the application.

  FIG. 2 is a block diagram showing the components of the X-ray CT apparatus shown in FIG. An X-ray generator 52 is provided on one side and an X-ray detector 60 is provided on the other side with the rotation center axis O therebetween. A collimator 54 is provided on the irradiation side of the X-ray generator 52. The X-ray generator 52 generates a divergent or fan-shaped (here, fan-beam shaped) X-ray beam 56 as shown. On the other hand, the X-ray detector 60 is configured as a plurality of (for example, 100) X-ray sensors arranged in a line, and an X-ray receiving opening is set according to the opening angle of the X-ray beam 56. Incidentally, the arrangement of the plurality of X-ray sensors may be linear or arcuate.

  In FIG. 2, the high voltage source used with the X-ray generator 52, the data processing circuit used with the X-ray detector 60, and the like are not shown.

  In FIG. 2, reference numeral 58 denotes an effective field of view. This is a circular region in which a CT image can be formed when the X-ray beam 56 is rotationally scanned. Incidentally, the effective visual field 58 is determined according to the positional relationship between the subject or the rotation center axis and the X-ray generator 52 and the X-ray detector 60. In the present embodiment, since a displacement mechanism 62 described below is provided, it is possible to change the positional relationship between them and mechanically vary the magnification of the CT image.

  In other words, the X-ray generator 52 and the X-ray detector 60 are connected to the displacement mechanism 62. In this embodiment, the displacement mechanism 62 is a distance between the X-ray generator 52 and the X-ray detector 60. The function of displacing them (that is, the measurement unit) in the direction of the beam axis of the X-ray beam 56 is maintained. In this case, the rotation center axis O is not changed, that is, the magnification can be changed by moving the measurement unit without moving the container described above. This will be described in detail later with reference to FIGS. The displacement mechanism 62 includes a motor 62A for generating a displacement force. In the present embodiment, the displacement amount can be individually set for each CT imaging, that is, the measurement magnification can be individually set. When such control is performed, the shape of the housing member (especially the outer diameter at the CT imaging position) is used as a reference, and the housing member is prevented from contacting or colliding with the gantry or the measurement unit when the magnification is variable. Has been.

  The gantry rotating mechanism 66 is a mechanism that rotates the entire structure including a displacement mechanism mounted thereon by rotating a rotating base described later. Since the measurement unit is mounted on the displacement mechanism 62, the measurement unit positioned at a desired position by the displacement mechanism 62 is rotationally driven while maintaining the position. The gantry rotating mechanism 66 has a motor 66A for generating the driving force. Note that the measurement magnification does not change during one rotation.

  The slide mechanism 68 is a moving mechanism that slides the arm 26 shown in FIG. 1, and the driving force is generated by the motor 68A. The operation panel 20 is provided on the upper surface of the main body as described above. The operation panel 20 may be connected to a local controller (not shown) provided on the measurement unit 10 side so that the local controller and the arithmetic control unit 12 communicate with each other.

  Incidentally, although various mechanisms 62, 66, 68 and the like are shown in FIG. 2, it is desirable to provide a sensor in order to detect a position or a change due to these mechanisms. Then, it is desirable that the arithmetic control unit 12 performs so-called feedback control based on the output signals of those sensors. In the example shown in FIG. 2, the slide mechanism 68 has the motor 68A as a drive source. However, the slide force may be artificially generated.

  Next, the arithmetic control unit 12 will be described. As described above, the display unit 32, the storage device 34, the keyboard 36, the mouse 38, the printer 40, and the like are connected to the processor 30. In addition, a communication unit 42 for communicating with an external device via a network is connected. The storage device 34 stores storage member shape data 34A as necessary.

  The processor 30 is configured by a CPU, an operation control program, an image processing program, and the like. FIG. 2 shows typical functions thereof. The processor 30 includes an operation control unit 44, a reconstruction calculation unit 46, a data management / processing unit 404, and the like.

  The operation control unit 44 controls the overall operation of the measurement unit 10. In particular, the displacement mechanism 62 is controlled to individually set the measurement magnification at each CT imaging position. The reconstruction calculation unit 46 executes a calculation for forming a CT image based on a lot of data obtained by rotational scanning of the X-ray beam. Various known methods can be used for the reconstruction operation. Note that, in changing the magnification described above, the arithmetic expression used in the reconstruction calculation can be basically used as it is. However, when a special variable magnification method is applied, a part of the reconstruction calculation expression may be changed as necessary.

  The data management / processing unit 404 manages each reconstructed CT image while associating information specifying the measurement magnification. Further, when image processing is performed on each CT image, the image processing is performed with reference to information for specifying the measurement magnification associated therewith as a parameter. For example, the image processing includes calculation of fat mass using a CT image, and in that case, a difference in scale in each CT image is considered. In addition, when the process of displaying each CT image with an apparently the same size is performed, an enlargement ratio (reduction ratio) or the like is set using the information specifying the measurement magnification.

  The display 32 displays a CT image. In this case, a numerical value or a scale representing the measurement magnification is displayed. According to this configuration, it is possible to correctly evaluate the size of an object when visually judging an image. That is, for example, the amount of fat and the size of a tumor can be determined quantitatively.

  The housing member is preferably composed of a transparent X-ray transmitting member as a whole. Examples of the material include resins such as acrylic and ABS. In addition, it is also possible to prepare a housing member having various shapes and sizes and select a housing member to be used according to the specimen and the measurement site. When fixing the specimen in the housing member, it is desirable to use a fixing member, but as such a fixing member, a material having an X-ray absorption coefficient equivalent to the air layer, or the housing member and the specimen can be used. It is desirable to use materials having different X-ray absorption coefficients. For example, cloth, sponge, air packing and the like. The outer diameter on the proximal end side of the housing member is, for example, 120 mm, the outer diameter on the distal end side is, for example, 30 mm, and the length in the rotation center axis direction is, for example, 100 mm. The wall thickness of the housing member is 3 mm, for example.

  When the above-described fixing member is used in combination, the movement of the specimen can be prevented, and the surface of the specimen can be separated from the inner surface of the housing member. That is, when the material constituting the housing member has an X-ray absorption coefficient equivalent to the fat or muscle of the specimen, if the specimen is in contact with the inner surface of the housing member, the housing member is a part of the specimen. There is a risk that it will be mistaken for data calculation as if it were. On the other hand, by inserting a material having a different X-ray absorption coefficient between the specimen and the housing member, it is possible to discriminate both on the image and prevent the above-described misidentification.

  Next, variable measurement magnification by the above-described displacement mechanism will be described with reference to the schematic diagrams of FIGS.

  In FIG. 3, reference numeral 100 indicates a rotation center axis. In the X-ray CT apparatus, the X-ray generator 52 and the X-ray detector 60 perform a rotation motion with the rotation center axis 100 as the rotation center. In this case, the effective visual field 102 is defined by an inscribed circle when the X-ray beam 101 is rotationally scanned. This effective visual field 102 corresponds to the photographing range. The X-ray beam 101 has a divergent shape, that is, a fan beam.

  FIG. 4 shows the positional relationship between the components. Here, the distance from the rotation center axis 100 to the X-ray generator 52 is defined as R, and the distance from the X-ray generator 52 to the X-ray detector 60 is defined as L. Incidentally, the distance from the rotation center axis 100 to the X-ray detector 60 is represented by T. Assuming the X-ray beam 101 having the fan beam shape described above, the magnification of the image is determined by L / R, and the larger the value, the larger the magnification, that is, the enlargement ratio. What can be said from this is that the measurement magnification can be varied by moving at least one of the X-ray generator 52, the rotation center axis, and the X-ray detector 60.

  In FIG. 5, a relatively large object (subject) 104 exists in the effective visual field 102. When the object 104 is imaged in the geometrical relationship as shown in FIG. 5, it becomes as shown by reference numeral 104A. That is, the object is displayed quite large on the screen. In this example, the center of the object 104 coincides with the rotation center axis, whereby the center of the image coincides with the center of the object 104A.

  On the other hand, as shown in FIG. 6, when a relatively small target object 106 is present with respect to the effective visual field 102, the size of the target object is very small on the screen as indicated by reference numeral 106A. As a result, there arises a problem that the diagnosis of the object cannot be accurately performed. Therefore, as shown in FIG. 7, for example, by reducing R while keeping L constant (in other words, by increasing T), even a small object 106 is displayed on the screen as indicated by reference numeral 106B. It becomes possible to express it greatly. That is, it is possible to realize zoom up. In this example, similarly to the above, the center of the object 106 coincides with the rotation center axis, and thus the center of the image and the center of the object 106A also coincide.

  Of course, in the case as shown in FIG. 6, the obtained data can be enlarged by image processing, but this cannot improve the spatial resolution itself. However, according to the technique as shown in FIG. 7, the spatial resolution itself can be increased, so that there is an advantage that a highly accurate enlarged image can be obtained.

  Here, considering the variable magnification method, at least one of the X-ray generator 52, the rotation center axis (in this example, coincides with the center of the object 106), and the X-ray detector 60 is arranged in the X-ray beam axis direction. It is understood that it is only necessary to move. Incidentally, when the distance L between the X-ray generator 52 and the X-ray detector 60 is varied, it is desirable to set a certain opening for the X-ray detector 60.

  In this embodiment, when scanning a certain specimen, the measurement magnification can be varied continuously or stepwise, so that tomography can be performed with good measurement magnification or resolution according to the specimen size at each tomography region.

  The principle described above will be further described with reference to FIGS. 8 and 9. In the case shown in FIG. 8, the distance between the X-ray generator 52 and the object 108 is R1, and in that case, the X-ray beam is used. Only a portion indicated by reference numeral 110 in 101 passes through the object 108. In this case, the X-ray intensity observed in the X-ray detector 60 is as illustrated. In other words, only the central sensor among many X-ray sensors (elements) acquires valid data.

  On the other hand, as shown in FIG. 9, when the object 108 is brought close to the X-ray generator 52 and the distance between the two is R2 (R1> R2), the range (reference numeral) of the X-ray beam 101 that passes through the object 108. 112) is enlarged, and a large part of the X-ray sensor in the X-ray detector 60 acquires valid data. It is understood from this that the spatial resolution is improved. Of course, even when the distance between the X-ray generator 52 and the X-ray detector 60 is not constant, the advantage of improving the spatial resolution can be obtained.

  Incidentally, the CT image may be formed so as to cover the entire specimen, or the measurement magnification may be set so that enlarged images of some organs in the specimen are acquired. That is, instead of aligning the rotation center axis with the center of the object, for example, the rotation center axis may be aligned with the center of the portion to be enlarged. For this purpose, a mechanism for moving the object not only in the direction of the X-ray beam but also in a direction orthogonal to both the X-ray beam and the rotation center axis is provided.

  Next, a specific configuration and operation of the measurement unit 10 illustrated in FIG. 1 will be described with reference to FIGS. First, the configuration of the measurement unit 10 will be described with reference to FIG. As described above, the X-ray generator 52 is provided on one side with respect to the rotation center axis, and the X-ray detector 60 is provided on the other side. Reference numeral 101 denotes a fan beam-shaped X-ray beam, and reference numeral 102 denotes the above-described effective visual field. Reference numeral 120 represents the shape of the cavity in the gantry.

  A belt 122 is wound around the motor 66A, and the rotational force of the belt 122 is transmitted by the rotational movement of the movable portion 50 by driving the belt 122 to rotate. The movable part 50 is constituted by various mechanisms mounted on the rotary base 123. Specifically, a displacement mechanism 62 is provided on the rotation base 123, and the displacement mechanism 62 is shown as a first mechanism 62L and a second mechanism 62R in FIG. Each of the first mechanism 62L and the second mechanism 62R has a member 134 fixed on the rotation base 123, and a guide 132 for slidably receiving the rail 130 fixed to the frame 124 is provided on the member 134. ing. Incidentally, the rails and guides of the first mechanism 62L are not shown.

  The rails 130 are provided on both sides of the frame 124, that is, the frame 124 is slidably held on both sides thereof. An X-ray generator 52 and an X-ray detector 60 are mounted on the frame 124.

  The first mechanism 62L has a motor 62A, and the rotational force thereof is transmitted to the feed screw 126. A bearing 128 is engaged with the feed screw 126. The bearing 128 is fixed to the rotating base 123. Therefore, when the feed screw 126 is rotated, the frame 124 moves forward or backward depending on the engagement relationship between the feed screw 126 and the bearing 128. That is, the measurement unit including the X-ray generator 52 and the X-ray detector 60 can be displaced with respect to the rotation center axis.

  FIG. 11 shows a state where the movable part 50 is rotated from the state shown in FIG.

  On the other hand, FIG. 12 shows a state in which the feed screw 126 is rotated as described above and the frame 124 is pulled upward from the engagement relationship between the lead screw 126 and the bearing 128. Since the X-ray beam 101 has a divergent shape, the effective visual field 102 is extremely small in the state of FIG. That is, this means that the magnification has been increased. FIG. 13 shows a state where the movable unit 50 is rotated from the state shown in FIG. During the rotation, the displacement state of the measurement unit once set is maintained.

  In the above embodiment, the driving force for changing the magnification is generated by the motor 62A. However, it may be generated by an artificial force. Even in such a case, a mechanism for sliding the measurement unit in the beam axis direction of the X-ray beam and maintaining the displacement state once set is necessary.

  FIG. 14 schematically shows the holding member 400. The holding member 400 holds a dog 406 under anesthesia as a specimen. Specifically, the head 406 </ b> A is inserted into the housing member 401, and a portion (such as a body) below the head 406 </ b> A is placed on the mounting table 402. The housing member 401 has a conical shape as described above, and the head portion 406A is inscribed on the inner surface thereof. The X direction is the rotation axis direction (actually, the holding member 400 slides in the minus direction), and the Y direction is a direction orthogonal to the X direction.

  When capturing a plurality of tomographic images for the head 406A, generally, a scout image of the entire head 406A is acquired. That is, the holding member 400 is slid without being rotated while irradiating the X-ray beam, whereby a scout image as a two-dimensional transmission image such as an X-ray X-ray image is acquired (described later). FIG. 16A). The scout image is displayed on the screen, and a plurality of CT imaging positions are designated by the user. In this example, a plurality of coordinates in the X direction are designated. Then, the holding member located at the slide origin in the X direction (which may be the slide end point) is slid to position the holding member 400 at each designated CT imaging position. Then, CT imaging is sequentially performed at each CT imaging position. In this case, the displacement amount of the measurement unit, that is, the measurement magnification is individually set according to the diameter (outer diameter) of the housing member at the imaging position. The

  In the example in FIG. 14, the displacement state of the measurement unit when a CT image is acquired for the nose tip region and the central region in the head 406 </ b> A is shown. When measuring the nose tip region, the X-ray generator 52 is close to the housing member 401, while the X-ray detector 60 is retracted from the housing member 401. Since the X-ray beam 101 has a fan shape, the measurement magnification becomes large. Next, when measuring the central part, the X-ray generator 52 ′ moves backward from the housing member 401 in the Y direction, while the X-ray detector 60 ′ approaches the housing member 401. Since the X-ray beam 101 'has a fan-like shape as described above, the measurement magnification is small. In any case, after avoiding physical contact between the housing member 401 and the measurement unit, the displacement amount is controlled so that a CT image can be acquired with the best resolution.

  In the above, it is also possible to perform the same measurement as described above with the head 406A exposed. However, considering the positioning of the head 406A, the sanitary viewpoint, and the complicated shape measurement of the head 406A, it is desirable to use the housing member 401. In the above example, the X-ray generator 52 and the X-ray detector 60 are integrally displaced with a constant distance therebetween, but the measurement magnification may be varied by other methods. .

  Therefore, for example, in the case where CT measurement is performed at a plurality of imaging positions for a sample accommodated in a conical-shaped accommodation member, the result is generally as shown in FIG. That is, (A) shows the displacement state when the measurement magnification is large, (B) shows the displacement state when the measurement magnification is medium, and (C) shows that the measurement magnification is small. The displacement state in some cases is shown. Here, 100 indicates a rotation center axis, 102 indicates an effective visual field, and 410 indicates the shape of the housing member.

  FIG. 16 shows measurement results for the head of a dog as a specimen. (A) shows a scout image of the head, and the shooting positions x1, x2, and x3 are designated by the user on the scout image. The number of designations is arbitrary, and the photographing position may be automatically determined without performing such designation. Alternatively, a large number of CT images may be acquired by repeatedly performing imaging at a constant pitch, and a necessary CT image may be selected from among them. The CT image shown in (B) is the imaging result at x1, the CT image shown in (C) is the imaging result at x2, and the CT image shown in (D) is the imaging result at x3. . Since the scale of each CT image is different because the measurement magnification is variable (for example, there is a difference in the expression of the thickness of the housing member), the resolution can be improved particularly with respect to the CT image on the distal end side, and the image size can be increased.

  FIG. 23 shows a comparative example. In this comparative example, the enlargement ratio is kept constant using a cylindrical housing member (see (A)). As can be understood from (B), (C), and (D), the scales of the respective CT images can be matched, but the display size is reduced and the resolution is reduced near the tip. On the other hand, according to the present embodiment, as shown in FIG. 16, an image can be displayed in a sufficiently large size near the tip, and the resolution can be improved.

  Next, an operation example of the X-ray CT apparatus will be described with reference to FIGS.

  First, with reference to FIGS. 17 and 18, a case will be described in which shape data of a housing member is registered in advance and operation control is performed using the data.

In FIG. 17, reference numeral 102 represents the above-described effective visual field, and reference numeral 410 represents a housing member. The radius of the effective field of view 102 is represented by r, and the radius of the housing member 410 is represented by r _f . Α is a margin distance.

Here, the radius r of the effective visual field 102 is defined by the following equation (1) using each symbol shown in FIG.

On the other hand, the relationship between the radius r _f of the radius r and the housing member of the effective field of view is represented as the following equation (2) using the margin distance alpha. Here, D is the length of the X-ray detector.

よって、上記の（３）式にしたがってＲを定めれば最も良好な分解能かつサイズで検体についてＣＴ画像を取得することが可能となる。ここで、Ｒ_fは、収容部材の形状データから求めることができ、すなわち撮影位置の関数として導くことができる。 Here, α is a margin distance for reliably accommodating the accommodating member within the effective visual field, and may be zero when the positioning error of the accommodating member can be regarded as zero. From the above equations (1) and (2), R that defines the amount of displacement is defined as follows.

Therefore, if R is determined according to the above equation (3), a CT image can be acquired for the specimen with the best resolution and size. Here, R _f can be obtained from the shape data of the housing member, that is, can be derived as a function of the photographing position.

  FIG. 18 is a flowchart showing an example of the operation of the apparatus when performing measurement based on the principle shown in FIG.

  First, in S101, the housing member is positioned automatically or at a tomographic position designated by the user. In S102, the outer diameter of the housing member at the tomographic position is obtained. In S103, R defining the amount of displacement is calculated using the above-described equation (3). That is, the amount of displacement by the displacement mechanism is specified. In S104, the measurement unit is displaced so that the above R is realized. In S105, tomography is executed under an appropriate measurement magnification. In S106, it is determined whether or not the final tomography has been completed, and if the tomography is to be continued, the processes from S101 are repeatedly executed.

  Next, a method for adjusting the amount of displacement using the X-ray intensity distribution will be described with reference to FIGS. 19 and 20.

  In FIG. 19, reference numeral 412 indicates the arrangement relationship of measurement units and the like, and reference numeral 414 indicates an X-ray intensity distribution. The first axis corresponds to the element number, and the second axis represents the X-ray attenuation. When the X-ray beam 101 is formed in a state where the rotation positions of the measurement unit, that is, the X-ray generator 52 and the X-ray detector 60 are fixed, the reference numeral 414 is derived from the relationship between the effective visual field 102 and the size of the housing member 410. An X-ray intensity distribution as shown in FIG. That is, if the accommodating member 410 is smaller than the effective visual field 102, peaks or edges 412A and 412B are generated on both sides in the X-ray intensity distribution, and it is possible to determine whether or not the measurement magnification is appropriate from such feature amounts. . For example, when the accommodating member 410 becomes larger than the effective visual field, the edges 412A and 412B as described above are not generated, and it can be determined that the measurement magnification is too large. On the other hand, when the two edges 412A and 412B occur at a position close to the center from the viewpoint of the element number, it can be determined that the measurement magnification is too small.

  Therefore, if the displacement amount is adjusted so that the two edges 412A and 412B are generated at the most desirable positions while changing the measurement magnification stepwise, that is, while increasing or decreasing the displacement amount, an optimum measurement magnification is set as a result. It becomes possible. Incidentally, as the condition, for example, when the detection element array is composed of N elements, the X-ray attenuation rates of the first element and the Nth element are not more than a predetermined threshold value, and the second element It can be determined that the measurement magnification is optimum when the condition that the X-ray attenuation rate of the element and the (N−1) th element is equal to or greater than a predetermined threshold is satisfied. Various conditions can be set as such conditions, and in any case, the shape data of the housing member is registered in advance by performing the preliminary X-ray irradiation as described above prior to the CT measurement. Even if it is not, that is, even if its shape is unknown, it is possible to always set an optimum measurement magnification.

  FIG. 20 is a flowchart showing an operation example of the apparatus according to the above principle.

  In S201, the housing member is positioned at the tomographic position. In S202, it is determined whether or not the housing member (the outer edge thereof) is housed in an effective field of view with an appropriate relationship. If NO, the measurement unit is displaced in S203. In that case, as described above, it is determined whether the two edges are outside or inside the effective field of view. If they are outside, the amount of displacement is adjusted so as to increase R. The amount of displacement is adjusted to make it smaller. In this case, a desired value can be set as the increment of the displacement amount.

  Therefore, when the processes of S202 and S203 are repeatedly executed, an optimum measurement magnification is finally obtained. In this state, tomography is executed in S204, and whether or not the final tomography is determined in S205. Is determined, and if tomography is to be performed, each step after S201 is repeatedly executed.

FIG. 21 shows a method for directly measuring the outer diameter of the housing member. That is, a laser displacement meter 430 is provided adjacent to the X-ray generator 52, and the laser displacement meter 430 measures the distance r ₁ from the measurement origin to the surface of the housing member. In FIG. 1, d indicates the distance between the measurement origin and the beam center axis. R ′ indicates the distance between the X-ray generator 52 and the rotation center axis when the outer diameter of the housing member is measured.

In the relationship as described above, the diameter r _f of the housing member is obtained by the following equation (4).

  If the outer diameter of the housing member is directly obtained in this way, the optimum R can be calculated from the above equation (3).

  FIG. 22 is a flowchart showing an operation example of the apparatus based on the above principle.

  In S301, the housing member is positioned during tomography. In S302, the measurement unit is positioned so that the distance between the X-ray generator and the rotation center axis is R '. In this case, R ′ may be directly obtained without performing such positioning.

In S303, the outer diameter r _f of the housing member is measured by the laser displacement meter. In S304, R is calculated by executing the above equation (3). In step S305, the measurement unit is positioned so that R is calculated as described above. In S306, tomography is executed. In S307, it is determined whether or not the final tomography has been completed. If it has not been completed, the processes from S301 described above are repeatedly executed.

  In the embodiment described above, a part of the specimen is accommodated in the accommodating member, but the whole specimen may of course be accommodated in the accommodating member. Further, the shape of the housing member is not limited to the conical shape as described above, and various shapes can be adopted corresponding to the shape of the measurement site housed therein. Desirably, it is desirable that the housing member has a rotationally symmetric shape with respect to the rotation center axis, but other shapes may be employed. In any case, when continuously taking a tomographic image of a certain specimen, it is desirable to set an appropriate measurement magnification according to the size of the specimen or a member accommodating the specimen. Therefore, the configuration of the above embodiment can be used even when measurement is performed by exposing the specimen without accommodating the specimen in the housing member. In addition, tomography is usually performed with the specimen fixed horizontally, but it is also possible to perform tomography with the specimen standing upright.

1 is a perspective view showing an overall configuration of an X-ray CT apparatus according to the present invention. 1 is a block diagram showing an overall configuration of an X-ray CT apparatus according to the present invention. It is a figure for demonstrating the effective visual field defined by rotation operation of a X-ray beam. It is a figure for demonstrating the geometric relationship of the three of an X-ray generator, an X-ray detector, and a rotation center. It is a figure which shows the state in which the sample is suitably accommodated in the effective visual field. It is a figure which shows the state whose sample is very small with respect to an effective visual field. It is a figure which shows the state which raised the measurement magnification and matched the effective visual field and the magnitude | size of the sample. It is a figure which shows X-ray intensity distribution in case a measurement magnification is small. It is a figure which shows X-ray intensity distribution in case a measurement magnification is moderate. It is a figure which shows the operation state in case a measurement magnification is small. It is a figure which shows the operation state in case a measurement magnification is small. It is a figure which shows the operation state in case a measurement magnification is large. It is a figure which shows the operation state in case a measurement magnification is large. It is a schematic diagram which shows a holding member. It is a figure for demonstrating the change of the measurement magnification by adjusting the displacement amount of a measurement unit. It is a figure which shows three CT images in the case of changing a measurement magnification. It is a figure for demonstrating the system which controls displacement amount using shape data. It is a flowchart which shows the operation example based on the principle shown in FIG. It is a figure for demonstrating the system which adjusts the displacement amount using X-ray intensity distribution. It is a flowchart which shows the operation example based on the principle shown in FIG. It is a figure for demonstrating the system which measures the outer diameter of a storage member directly, and controls a displacement amount. It is a flowchart for demonstrating the operation example based on the principle shown in FIG. It is a figure which shows three CT images with a fixed measurement magnification as a comparative example.

Explanation of symbols

  10 measurement unit, 12 calculation control unit, 44 operation control unit, 46 reconstruction calculation unit, 52 X-ray generator, 60 X-ray detector, 62 displacement mechanism, 400 holding member, 401 housing member, 402 mounting table, 404 data Management and processing department.

Claims (11)

A measurement unit comprising: an X-ray generator that forms an X-ray beam in a direction that intersects the direction of the rotation center axis; and an X-ray detector that detects the X-ray beam;
A holding member holding a specimen arranged on the rotation center axis;
A moving mechanism for moving the holding member relative to the measurement unit in the direction of the rotation center axis;
A rotation mechanism for rotating the measurement unit around the rotation center axis with respect to the holding member;
A displacement mechanism that displaces at least one of the X-ray generation unit, the X-ray detection unit, and the rotation center axis in the X-ray beam direction;
Upon scanning of the imaging position by the relative movement of the holding member with respect to the measuring unit, a measurement ratio controller for variable measurement ratio by controlling the operation of the displacement mechanism,
Including
The holding member has an accommodating member that accommodates all or a part of the specimen,
The housing member has a shape whose cross-sectional size changes continuously or stepwise in the direction of the rotation center axis,
The measurement magnification control unit sets the measurement magnification according to a cross-sectional size at each photographing position in the housing member when scanning the photographing position.
An X-ray CT apparatus characterized by that. The apparatus of claim 1.
A gantry that houses the measurement unit;
The housing member is inserted into a cavity portion of the gantry,
An X-ray CT apparatus characterized by that. The apparatus of claim 1 .
The X-ray CT apparatus, wherein the measurement magnification control unit sets a displacement amount by the displacement mechanism corresponding to an outer diameter of an X-ray beam passing position in the housing member. The apparatus of claim 1 .
The X-ray CT apparatus, wherein the housing member has a tapered shape. The apparatus of claim 4.
The X-ray CT apparatus, wherein the accommodating member accommodates a portion from a nose to a jaw in a small animal as the specimen. The apparatus of claim 1.
An X-ray CT apparatus comprising: data management means for managing information specifying a measurement magnification in association with a CT image acquired at each measurement position in the direction of the rotation center axis. The apparatus of claim 6.
An X-ray CT apparatus comprising: data processing means for performing image processing on the CT image based on information specifying the measurement magnification. The apparatus of claim 1.
An X-ray CT apparatus comprising display processing means for displaying information for specifying a measurement magnification when displaying a CT image. The apparatus of claim 1 .
Including a storage unit in which shape data about the housing member is registered;
The X-ray CT apparatus, wherein the measurement magnification control unit controls the operation of the displacement mechanism according to the shape data. The apparatus of claim 1 .
The X-ray CT apparatus, wherein the measurement magnification control unit controls the operation of the displacement mechanism based on an X-ray intensity distribution obtained when the X-ray beam is transmitted through the housing member. The apparatus of claim 1 .
Including shape measuring means for measuring the shape of the housing member and outputting shape data;
The X-ray CT apparatus, wherein the measurement magnification control unit controls the operation of the displacement mechanism according to the shape data.

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