JP6400436B2 - Tomography system - Google Patents

Description

  The present invention relates to a tomography system having a gantry.

  Examples of tomography systems having a gantry surrounding the measurement space include PET (Positron Emission Tomography), SPECT (Single Photon Emission Computed Tomography), X-ray CT (Computed Tomography), and MRI (Magnetic Resonance Imaging) systems. A system combining two or more types, such as a system combining SPECT and X-ray CT, or a system combining PET and MRI, may also be mentioned. Such a tomography system can acquire a tomographic image of the whole body or a part (for example, the head) of a subject (living body) arranged in a measurement space of the gantry.

  It takes several minutes to several tens of minutes of measurement time to acquire measurement data for reconstructing a tomographic image of a subject using such a tomography system. It is required that the subject does not move over the measurement time. Therefore, it is common to fix the measurement site of the subject. However, fixation of the subject (particularly fixation of the head as a measurement site) places a large physical and mental burden on the subject. Therefore, it is desirable to acquire measurement data without fixing the subject. Patent Documents 1 and 2 disclose an invention intended to meet such a requirement.

  The invention disclosed in Patent Literature 1 detects a body movement of a subject by attaching a marker to the head of the subject arranged in the measurement space of the gantry and imaging the marker from outside the measurement space of the gantry. Then, the measurement data is corrected based on the body motion detection result, and the tomographic image of the subject is reconstructed based on the corrected measurement data.

  In the invention disclosed in Patent Document 2, a plurality of distance sensors are arranged opposite to each other around an opening for inserting a subject in a measurement space of a gantry, and the body motion of the subject is detected by the distance sensor. The measurement data is corrected based on the body movement detection result, and the tomographic image of the subject is reconstructed based on the corrected measurement data.

JP-A-2-209133 Japanese Patent Laid-Open No. 4-128679

  The invention disclosed in Patent Document 1 can tolerate body movement of the subject to some extent. However, since it is necessary to attach a marker to the subject, there are still physical and mental constraints on the subject, and there is a possibility that optical continuous imaging of the marker cannot be performed appropriately. In particular, when the subject is a severe patient with dementia or the like, it is considered that the measurement is interrupted due to the burden of attaching the marker.

  The invention disclosed in Patent Literature 2 cannot be additionally provided in the gantry of the existing tomography system because it is necessary to attach a distance sensor simultaneously with the design and development of the gantry. In addition, since the subject can easily confirm the presence of the distance sensor arranged around the opening of the gantry, there is a possibility that the subject may feel mental restraint that the image is taken.

  The present invention has been made to solve the above-described problems, and provides a tomography system that can further reduce physical and mental restraints of a subject placed in a measurement space of a gantry. For the purpose.

  The tomography system of the present invention includes (1) a measurement unit that includes a gantry surrounding a measurement space around a predetermined axis and acquires measurement data from a subject arranged in the measurement space, and (2) a measurement space. A concave mirror having a reflecting surface that is disposed and has a reflecting surface facing the predetermined axis, the reflecting surface having a curvature in a cross section perpendicular to the predetermined axis, and (3) light emitted from a subject placed in the measurement space is a concave mirror. An optical system that compensates for distortion of the image formed by reflection, (4) an imaging unit that is placed outside the measurement space and that compensates for distortion by the optical system, and (5) is captured by the imaging unit. The body motion of the subject is detected based on the captured image, the measurement data acquired by the measurement unit is corrected based on the body motion detection result, and the tomographic image of the subject is regenerated based on the corrected measurement data. And a processing unit to be configured.

  In the tomography system of the present invention, it is preferable that the concave mirror is attached to the inner wall surface of the gantry. In addition, it is preferable that the concave mirror has a reflecting surface shape that is a part of a cylindrical surface having a central axis parallel to a predetermined axis.

  In the tomography system of the present invention, it is preferable that the optical system includes a curved mirror having a reflecting surface shape that is a part of a cylindrical surface having a central axis parallel to a predetermined axis. It is preferable that the optical system includes a curved mirror having a reflecting surface shape that is a part of a cylindrical surface having a central axis parallel to a predetermined axis, and the focal point of the curved mirror coincides with the focal point of the concave mirror. The optical system may further include a plane mirror that reflects the light incident from the concave mirror to the curved mirror. Further, at least a part of the optical system may be disposed outside the measurement space.

  In the tomography system of the present invention, it is preferable that the imaging unit captures an image whose distortion is compensated by the optical system at each of a plurality of positions outside the measurement space.

  According to the present invention, it is possible to further reduce the physical and mental restraint of the subject arranged in the measurement space of the gantry.

1 is an overall configuration diagram of a tomography system 1 of the present embodiment. It is a figure which shows the 1st structural example of the tomography system 1 of this embodiment. It is a figure which shows the lens system equivalent to the 1st structural example of the tomography system 1 of this embodiment. It is a figure which shows the simulation result of the 1st structural example of the tomography system 1 of this embodiment. It is a figure which shows the 2nd structural example of the tomography system 1 of this embodiment. It is a figure which shows the simulation result of the 2nd structural example of the tomography system 1 of this embodiment. It is a figure which shows the 3rd structural example of the tomography system 1 of this embodiment. It is a figure which shows the 4th structural example of the tomography system 1 of this embodiment. It is a figure which shows the 5th structural example of the tomography system 1 of this embodiment. It is a figure which shows the image imaged with the cameras 41 and 42 as the imaging part 40 in the 5th structural example of the tomography system 1 of this embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is an overall configuration diagram of a tomography system 1 of the present embodiment. The tomography system 1 includes a measurement unit 10, a concave mirror 20, an optical system 30, an imaging unit 40, and a processing unit 50. The tomography system 1 corrects the body movement of the subject 90 arranged in the measurement space S to obtain a tomography of the subject 90. Images can be reconstructed. In the drawing, a cross-sectional view is shown for the measurement unit 10, the concave mirror 20, and the optical system 30, and a block diagram is shown for the imaging unit 40 and the processing unit 50.

  The tomography system 1 may be any system as long as the measurement unit 10 includes the gantry 11. The tomography system 1 may be any system of PET, SPECT, X-ray CT and MRI, a system combining PET or SPECT and X-ray CT, a system combining PET and MRI, and the like. A system combining two or more types may be used. In the following description, it is assumed that the tomography system 1 is a PET system.

  The measurement unit 10 includes a gantry 11 surrounding the measurement space S around the predetermined axis Ax, and acquires measurement data from the subject 90 arranged in the measurement space S. The measurement space S is included in a cylindrical region surrounded by the inner wall surface (cylindrical surface) of the gantry 11. A large number of detectors 12, a shield collimator 13, and a slice collimator 14 are provided in the gantry 11.

  Each detector 12 is a radiation detector that combines, for example, a scintillator and a photomultiplier tube. Each detector 12 detects 511 keV photons (γ-rays) generated as a result of electron-positron annihilation in the subject 90 into which a positron emission isotope (RI) has been introduced, and the energy of the detected photons. A signal having a value corresponding to the signal is output to the processing unit 50. A plurality of detectors 12 are arranged around a predetermined axis Ax to form a ring, and the plurality of rings are stacked in the direction of the predetermined axis Ax.

  The shield collimator 13 prevents leakage of γ rays to the outside. The slice collimator 14 allows the detector 12 to selectively detect photons flying in a direction substantially perpendicular to the predetermined axis Ax. The slice collimator 14 may not be provided.

  The concave mirror 20 is disposed in the measurement space S, has a reflective surface facing the predetermined axis Ax, and the reflective surface has a curvature in a cross section perpendicular to the predetermined axis Ax. The concave mirror 20 is preferably attached to the inner wall surface of the gantry 11. The concave mirror 20 preferably has a reflecting surface shape that is a part of a cylindrical surface having a central axis parallel to the predetermined axis Ax.

  The concave mirror 20 is made of a material that does not hinder acquisition of measurement data by the measurement unit 10. As the concave mirror 20, a film that reflects light (visible light or invisible light) may be used, or a heat ray reflective film that reflects infrared light may be used. The heat ray reflective film is used, for example, by being attached to a window glass in order to reduce the incidence of infrared light into the room, and has a reflectance of about 85% with respect to infrared light having a wavelength of 870 nm. It has been.

  When a reflective film is used as the concave mirror 20, the reflective film may be affixed to the inner wall surface of the gantry 11 so that distortion and wrinkles do not occur. If it is difficult to attach the reflective film directly to the inner wall surface of the gantry 11, it is possible to attach a reflective film to a flexible sheet such as a flexible polyvinyl chloride sheet to the inner wall surface of the gantry 11. Good.

  In addition to the reflective film, the concave mirror 20 may be an ordinary mirror, a mirror coated with a reflection coating, or a mirror with reflection processing such as silver. The radius of curvature of the reflecting surface of the concave mirror 20 may not be the same as the inner radius of the gantry 11. The shape of the reflecting surface of the concave mirror 20 may be an aspherical surface such as a paraboloid. The concave mirror 20 may be directly attached to the inner wall surface of the gantry 11, or may be installed in the measurement space S by another holding jig.

  The optical system 30 compensates for distortion of an image formed by reflection of light emitted from the subject 90 disposed in the measurement space S by the concave mirror 20. The optical system 30 preferably includes a curved mirror (concave mirror or convex mirror) having a reflecting surface shape that is a part of a cylindrical surface having a central axis parallel to the predetermined axis Ax. Further, it is preferable that the focal point of the curved mirror coincides with the focal point of the concave mirror 20.

  The optical system 30 may include a plane mirror in addition to the curved mirror, or may include a cylindrical lens in addition to or instead of the curved mirror. The entire optical system 30 may be arranged in the measurement space S, the whole optical system 30 may be arranged outside the measurement space S, or a part thereof is arranged in the measurement space S and the remaining part is outside the measurement space S. It may be arranged. The optical system 30 may use a reflective film similarly to the concave mirror 20.

  The imaging unit 40 is arranged outside the measurement space S and captures an image whose distortion has been compensated for by the optical system 30. The imaging unit 40 may include one camera or may include a plurality of cameras. In the latter case, an image with distortion compensated at each of a plurality of positions outside the measurement space S is obtained. Take an image. Each camera has its installation position and camera lens adjusted according to the angle and size to be observed. Since the imaging position of the image compensated for distortion by the optical system 30 differs depending on the positional relationship of the subject 90, the concave mirror 20, and the optical system 30, each camera takes into account the assumed movement range of the subject 90. Installed.

  The camera lens of the imaging unit 40 may be a fisheye lens. The imaging unit 40 may be attached with a correction lens (such as a higher-order aspheric lens) for correcting distortion of a curved image. The imaging unit 40 may capture an image of the light emitted from the subject 90 reaching the concave mirror 20 and the optical system 30 multiple times.

  The processing unit 50 detects the body motion of the subject 90 based on the image captured by the imaging unit 40, corrects the measurement data acquired by the measurement unit 10 based on the body motion detection result, and performs this correction. A tomographic image of the subject 90 is reconstructed based on the measurement data. More specifically, it is as follows.

  The processing unit 50 receives the image captured by the imaging unit 40 and detects the position of the feature point in this image. The feature point is information that can be used for specifying the position of the subject 90, and may be, for example, a part (for example, eyes, nose, mouth, etc.) that the subject 90 has, It may be a three-dimensional shape of the specimen 90 (a group of points composed of a plurality of points), or may be a center of gravity point of the subject 90 calculated by calculation. The feature point may be a marker attached to the face or head of the subject 90.

  When the imaging unit 40 includes a plurality of cameras, if there is a common feature point in the plurality of images captured by each camera, the processing unit 50 is based on the correspondence between the feature points in the plurality of images by epipolar geometry. Thus, the body movement of the subject 90 can be detected. Further, the processing unit 50 calculates the conversion table or the like that represents the relationship between the three-dimensional position of the feature point estimated from the image and the three-dimensional position of the actual feature point. 3D position information can be obtained.

  The processing unit 50 inputs coincidence count information representing an event in which any two detectors 12 of the measurement unit 10 simultaneously detect photons having an energy of 511 keV from the measurement unit 10 as measurement data. The coincidence count information includes identification information of the two detectors 12 that simultaneously detect photons having an energy of 511 keV. The position where the pair annihilation of electrons and positrons occurs in the subject 90 into which the RI is input is on a line segment (simultaneous counting line) connecting the light receiving surfaces of these two detectors 12 to each other.

  The processing unit 50 corrects the coincidence line obtained from the measurement data (simultaneous counting information) according to the body movement detection result based on the measurement data and the body movement detection result obtained at the same timing. 90 is converted into a coincidence line passing through the electron / positron pair annihilation position. Then, the processing unit 50 accumulates the measurement data corrected in this way, and reconstructs a tomographic image of the subject 90 based on the accumulated measurement data after correction.

  The tomography system 1 of this embodiment may include an illumination light source for irradiating the subject 90 with illumination light, or may not include an illumination light source. When the subject 90 is a self-luminous body or when a light emitting body is attached to the subject 90 as a marker, an illumination light source is not necessary. The light emitted from the light emitter may be in any wavelength region such as visible light and invisible light (infrared region / ultraviolet region), but is imaged by the imaging unit 40 from the subject 90 via the concave mirror 20 and the optical system 30. It is necessary to be in the wavelength range to obtain.

  When the illumination light source is provided, the illumination light may be in any wavelength region such as visible light and invisible light (infrared region / ultraviolet region), but the reflected light generated in the subject 90 due to illumination light irradiation is It is necessary that the wavelength range can be picked up by the imaging unit 40 from the subject 90 via the concave mirror 20 and the optical system 30. The installation position of the illumination light source is arbitrary. An illumination light source may be installed at a position where the subject 90 can be directly irradiated with illumination light. Further, an illumination light source may be installed outside the measurement space S, and the subject 90 may be irradiated with illumination light through the optical system 30 and the concave mirror 20.

  The illumination light source may be any light emitting diode, fluorescent lamp, incandescent lamp, laser light source, and the like. The illumination light applied to the subject 90 may be applied over a certain range of the subject 90, or may be a pattern light such as a slit light or a lattice. The illumination light may be a broadband, a single wavelength, or a plurality of wavelengths. When the illumination light is broadband light or a plurality of wavelengths, an optical filter that selectively transmits light of a specific wavelength may be provided in front of the imaging unit 40.

  Next, specific configuration examples of the concave mirror 20, the optical system 30, and the imaging unit 40 in the tomography system 1 of the present embodiment will be described.

  FIG. 2 is a diagram illustrating a first configuration example of the tomography system 1 of the present embodiment. Assume an xyz orthogonal coordinate system in which the predetermined axis Ax that is the center of the measurement space S is the z-axis. Let d be the diameter of the measurement space S surrounded by the gantry 11. The concave mirror 20 has a part of a cylindrical surface with a diameter d having a central axis parallel to the predetermined axis Ax as a reflection surface, and is attached to the inner wall surface of the gantry 11. The concave mirror 31 as the optical system 30 has a part of a cylindrical surface with a diameter d having a central axis parallel to the predetermined axis Ax as a reflecting surface, and is arranged so that the cylindrical surface is in contact with the predetermined axis Ax. Yes. The focal length f of each of the concave mirror 20 and the concave mirror 31 is d / 4. The concave mirror 20 and the concave mirror 31 are arranged so that their focal points coincide with each other on the yz plane. The camera of the imaging unit 40 is located on the yz plane.

  FIG. 3 is a diagram showing a lens system equivalent to the first configuration example of the tomography system 1 of the present embodiment. The concave mirror 20 is equivalent to a cylindrical lens 20A having a focal length f, and the concave mirror 31 is equivalent to a cylindrical lens 31A having a focal length f. The first configuration example is equivalent to a configuration in which the cylindrical lens 20A and the cylindrical lens 31A are separated from each other by a distance 2f.

  When the distance between the subject 90 and the cylindrical lens 20A is shorter than the focal length f, a virtual image 91 is formed by the cylindrical lens 20A, and a real image 92 is formed from the virtual image 91 by the cylindrical lens 31A. Conversely, if the distance between the subject 90 and the cylindrical lens 20A is longer than the focal length f, a real image is formed by the cylindrical lens 20A, and another real image is formed from the real image by the cylindrical lens 31A. As described above, in any case, the X-axis direction is the reverse image of the same magnification based on the same principle as the relay lens, and the Z-axis direction is the same as normal specular reflection. That is, the real image formed by the concave mirror 31 becomes a reverse image of the subject 90 in the X-axis direction at an equal magnification.

  If the imaging unit 40 captures an image reflected by the concave mirror 20 without providing the concave mirror 31 as the optical system 30, the image is not only greatly distorted, but also the subject 90 and the concave mirror 20. Depending on the magnitude relationship between the distance between and the focal length f, the images may differ, and the imaging unit 40 may not be able to capture images. On the other hand, in this embodiment, by providing the optical system 30 in addition to the concave mirror 20, the imaging unit 40 can perform appropriate imaging.

  FIG. 4 is a diagram showing a simulation result of the first configuration example of the tomography system 1 of the present embodiment. Here, a flat plate on which a checker pattern such as a chess board is drawn is used as the subject 90. As shown in the figure, the imaging unit 40 can acquire an image that substantially matches the checker pattern of the subject 90, has a small curved surface distortion, and is close to a plane reflection image.

  FIG. 5 is a diagram illustrating a second configuration example of the tomography system 1 of the present embodiment. In the second configuration example, a convex mirror 32 is provided as an optical system 30 in place of the concave mirror 31. The convex mirror 32 uses a part of a cylindrical surface having a central axis parallel to the predetermined axis Ax and having a diameter less than d as a reflecting surface. The focal length f of the concave mirror 20 is d / 4, and the focal length f2 of the convex mirror 32 is shorter than d / 4. The concave mirror 20 and the concave mirror 31 are arranged so that their focal points coincide with each other on the yz plane. The camera of the imaging unit 40 is located on the yz plane.

  FIG. 6 is a diagram illustrating a simulation result of the second configuration example of the tomography system 1 of the present embodiment. Here, a flat plate on which a checkered pattern such as a chess board is drawn is used as the subject 90. The focal length of the convex mirror 32 is set to one half of the focal length of the concave mirror 20. As shown in the figure, the imaging unit 40 can acquire an image that substantially matches the checker pattern of the subject 90, has a small curved surface distortion, and is close to a plane reflection image. Compared to the first configuration example, in the second configuration example, the size of the image acquired by the imaging unit 40 is halved in the X-axis direction.

  FIG. 7 is a diagram illustrating a third configuration example of the tomography system 1 of the present embodiment. In the third configuration example, a flat mirror 33 is provided as the optical system 30, and a concave mirror 34 is provided as an extension of the concave mirror 20. Similar to the concave mirror 20, the concave mirror 34 has a part of a cylindrical surface with a diameter d having a central axis parallel to the predetermined axis Ax as a reflecting surface, and is affixed to the inner wall surface of the gantry 11. Is on the yz plane. The plane mirror 33 is in the focal position of each of the concave mirror 20 and the concave mirror 34 and is provided in parallel to the xz plane. In the third configuration example, light emitted from the subject 90 is sequentially reflected by the concave mirror 20, the plane mirror 33, and the concave mirror 34 and received by the imaging unit 40. The third configuration example is substantially equivalent to the first configuration example although the plane mirror 33 is provided.

  FIG. 8 is a diagram illustrating a fourth configuration example of the tomography system 1 according to the present embodiment. In the fourth configuration example, a cylindrical lens 35 is provided as the optical system 30. The focal point of the cylindrical lens 35 coincides with the focal point of the concave mirror 20. In the fourth configuration example, light emitted from the subject 90 is reflected by the concave mirror 20 and is received by the imaging unit 40 via the cylindrical lens 35. As described above, since the cylindrical lens 35 in the fourth configuration example has a function equivalent to the concave mirror 31 in the first configuration example, the fourth configuration example is substantially equivalent to the first configuration example. Note that the camera lens and the cylindrical lens 35 of the imaging unit 40 may be an integrated lens system.

  FIG. 9 is a diagram illustrating a fifth configuration example of the tomography system 1 according to the present embodiment. In the fifth configuration example, two cameras 41 and 42 are provided as the imaging unit 40 in the first configuration example. These two cameras 41 and 42 capture images with distortion compensated by the concave mirror 31 at each of two positions outside the measurement space S. The same figure (a), (b) is the figure seen from the different direction.

  FIG. 10 is a diagram illustrating images captured by the cameras 41 and 42 as the imaging unit 40 in the fifth configuration example of the tomography system 1 of the present embodiment. Here, a flat plate on which a checkered pattern such as a chess board is drawn is used as the subject 90. FIG. 4A shows an image obtained by the camera 41, and FIG. 4B shows an image obtained by the camera. As described above, by using a plurality of cameras, a stereo image necessary for three-dimensional measurement can be acquired, and the body movement of the subject 90 can be easily detected.

  In the present embodiment, it is not necessary to attach a marker or the like to the subject 90. The body motion of the subject 90 is detected in a non-contact / non-constraint manner, and the measurement data is corrected based on the body motion detection result to obtain a tomographic image. Can be reconfigured. Since the imaging unit 40 is disposed outside the measurement space S, the subject 90 is not aware of the existence of the imaging unit 40 and does not feel the mental restraint that the imaging is being performed. There is little mental restraint. In the present embodiment, physical and mental restraint of the subject 90 arranged in the measurement space S of the gantry 11 can be further reduced.

  In the present embodiment, in addition to the concave mirror 20, an optical system 30 (a convex mirror 32, a plane mirror 33, a concave mirror 34, and a cylindrical lens 35) that compensates for distortion of an image formed by being reflected by the concave mirror 20 is provided. The imaging unit 40 can acquire an image with small distortion. Further, since the optical system 30 is provided in addition to the concave mirror 20, the imaging unit 40 can acquire an image that is not affected by the relationship between the subject 90 and the focal position.

  Further, in the present embodiment, even when the measurement space S is narrow as in the case where the gantry 11 is for the head, the body movement of the subject 90 can be detected and the measurement data can be corrected.

DESCRIPTION OF SYMBOLS 1 ... Tomography system, 10 ... Measuring part, 11 ... Gantry, 12 ... Detector, 13 ... Shield collimator, 14 ... Slice collimator, 20 ... Concave mirror, 30 ... Optical system, 31 ... Concave mirror, 32 ... Convex mirror, 33 ... Plane mirror , 34 ... concave mirror, 35 ... cylindrical lens, 40 ... imaging unit, 41, 42 ... camera, 50 ... processing unit, 90 ... subject.

Claims (8)

A measurement unit including a gantry surrounding a measurement space around a predetermined axis, and acquiring measurement data from a subject arranged in the measurement space;
A concave mirror disposed in the measurement space and having a reflecting surface facing the predetermined axis, the reflecting surface having a curvature in a cross section perpendicular to the predetermined axis;
An optical system that compensates for distortion of an image formed by reflection of light emitted from the subject arranged in the measurement space by the concave mirror;
An imaging unit that is arranged outside the measurement space and captures an image whose distortion is compensated by the optical system;
Based on the measurement data obtained by detecting the body motion of the subject based on the image captured by the imaging unit, correcting the measurement data acquired by the measurement unit based on the detection result of the body motion, and A processing unit for reconstructing a tomographic image of the subject,
A tomography system comprising: The concave mirror is attached to the inner wall surface of the gantry,
The tomography system according to claim 1. The concave mirror has a reflecting surface shape that is a part of a cylindrical surface having a central axis parallel to the predetermined axis.
The tomography system according to claim 1. The optical system includes a curved mirror having a reflecting surface shape that is a part of a cylindrical surface having a central axis parallel to the predetermined axis.
The tomography system of any one of Claims 1-3. The optical system includes a curved mirror having a reflecting surface shape that is a part of a cylindrical surface having a central axis parallel to the predetermined axis, and the focal point of the curved mirror coincides with the focal point of the concave mirror;
The tomography system according to claim 3. The optical system further includes a plane mirror that reflects light incident from the concave mirror to the curved mirror;
The tomography system according to claim 4 or 5. At least a part of the optical system is disposed outside the measurement space;
The tomography system of any one of Claims 1-6. The imaging unit captures an image in which distortion is compensated by the optical system at each of a plurality of positions outside the measurement space;
The tomography system of any one of Claims 1-7.