JP4650324B2 - Nuclear medicine diagnostic equipment - Google Patents

Description

  The present invention detects γ-rays emitted by a radioisotope (RI = radioisotope) administered to a subject with a γ-ray detector, and distributes γ-ray detection signals output from the γ-ray detector to an RI distribution. The present invention relates to a nuclear medicine diagnostic apparatus that collects as emission data for image acquisition, and more particularly to a technique for photographing an RI distribution image with sufficient sensitivity.

  As shown in FIG. 18, a conventional PET (positron emission tomography) apparatus, which is one of useful nuclear medicine diagnostic apparatuses, has a top plate 91 on which a subject m is placed, and the top plate 91 is a subject. A large gantry 92 having an opening (tunnel) 92A that goes in and out while m is placed is disposed. The gantry 92 is provided with a ring-type γ-ray detector 93 shown in FIG. 19 or a flat-type γ-ray detector 94 shown in FIG. The γ-ray detectors 93 and 94 are composed of a scintillator, a photomultiplier (photomultiplier tube), and the like (see, for example, Non-Patent Documents 1 and 2).

When taking a RI distribution image with a conventional PET apparatus, the energy of 511 keV generated by the RI administered to the subject m that has entered the opening 92 </ b> A of the gantry 92 while the subject m is placed on the top 91. Γ rays (annihilation γ rays) are detected by the γ ray detector 93 or the γ ray detector 94. The γ-ray detection signals output from the γ-ray detector 93 and the γ-ray detector 94 are collected as emission data for acquiring RI distribution images, and a reconstruction process is performed based on the collected emission data. A tomographic image type or planar image type RI distribution image is acquired. In the case of a PET apparatus, two annihilation γ-rays that are simultaneously generated by the disappearance of an RI positron such as ¹¹ C administered to the subject m and proceed in the opposite direction are converted into a γ-ray detector 93 or a γ-ray detector 94. Emission data is collected when they are detected at the same time (when γ rays are counted simultaneously).

Seminars in Nuclear Medicine, vol.XXXIV, No.2,2004: 87-111 J Nucl Med 2003; 44: 756-769

However, the above-described conventional PET apparatus has a problem that the RI distribution image of the subject m cannot be captured with sufficient sensitivity.
The gantry 92 into which the subject m enters has a large diameter of the opening 92A, and the γ-ray detector 93 or the γ-ray detector 94 is located at a position considerably away from the subject m, and the γ-ray detector 93 or γ Since the number of γ rays incident on the line detector 94 is not so large and the detection sensitivity of γ rays becomes insufficient, the RI distribution image cannot be captured with sufficient sensitivity.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a nuclear medicine diagnostic apparatus capable of capturing an RI distribution image of a subject with sufficient sensitivity.

In order to achieve such an object, the present invention has the following configuration.
That is, in the nuclear medicine diagnostic apparatus according to the first aspect of the present invention, (A) γ-ray detection posture in which γ-ray incident surfaces face each other across the subject with respect to γ-rays generated by the radioisotope administered to the subject. And (B) collecting γ-ray detection signals output from the first and second γ-ray detectors as emission data for acquiring RI distribution images. In a nuclear medicine diagnostic apparatus comprising emission data collection means and (C) RI distribution image acquisition means for acquiring an RI distribution image based on emission data, (D) a first γ-ray detector attached to the tip The 1C-shaped arm member and the second C-shaped arm member to which the second γ-ray detector is attached at the tip are arranged in parallel, and the first γ-ray detector and the second γ-ray detector are placed between the subject. Relative Double arm type detector holding means arranged in an orientation; (E) arm member moving means for moving the first C-shaped arm member and the second C-shaped arm member in both directions along the bending of the arm; (F) The γ-ray detection posture in which the γ-ray incident surfaces of the first γ-ray detector and the second γ-ray detector face each other with the subject interposed therebetween by changing the inclination angle of the first γ-ray detector and the second γ-ray detector. And a detector angle adjusting means.

  [Operation / Effect] When an RI distribution image of a subject is photographed by the nuclear medicine diagnosis apparatus of the invention of claim 1, the interval between the first γ-ray detector and the second γ-ray detector is suitable for setting the subject. If it is not wide, first, the first C-shaped arm member with the first γ-ray detector attached to the tip and the second C-shaped arm member with the second γ-ray detector attached to the tip are moved to the arm member moving means. The distance between the first γ-ray detector and the second γ-ray detector is sufficiently widened by moving the first C-shaped arm member and the second C-shaped arm member away from each other along the bending of the arm. A subject to be imaged is set between the line detector and the second γ-ray detector.

Subsequently, the first C-shaped arm member and the second C-shaped arm member are moved in the direction in which the first C-shaped arm member and the second C-shaped arm member approach each other along the bending of the arm by the arm member moving means. To move the first γ-ray detector and the second γ-ray detector closer to the subject, and change the tilt angles of the first γ-ray detector and the second γ-ray detector by the detector angle adjusting means, and Imaging is started after the γ-ray detection posture in which the γ-ray incident surface of the second γ-ray detector faces each other with the subject interposed therebetween.
As the first C-shaped arm member and the second C-shaped arm member are moved by the arm member moving means, the inclination angles of the first γ-ray detector and the second γ-ray detector change, and the first γ-ray detector and the second γ-ray are changed. Since the γ-ray detection posture in which the γ-ray incident surfaces of the detector face each other with the subject sandwiched is destroyed, the detector angle adjustment means changes the inclination angle between the first γ-ray detector and the second γ-ray detector, thereby γ It returns to the line detection posture.

  Further, the first C-shaped arm member and the second C-shaped arm member are moved in the same direction along the bending of the arm by the arm member moving means, and the first γ-ray detector and the second γ-ray detection are detected by the detector angle adjusting means. If the γ-ray detection posture is such that the γ-ray incident surfaces of the first γ-ray detector and the second γ-ray detector face each other with the subject sandwiched between them by changing the tilt angle of the detector, the first γ-ray detector and the second γ-ray detection The instrument can change the imaging direction around the subject.

When imaging of the RI distribution image is started, the radioisotope is administered to the subject with the first γ-ray detector and the second γ-ray detector in the γ-ray detection posture in which the γ-ray incident surfaces face each other across the subject. Γ-rays generated by.
On the other hand, the emission data collection means collects γ-ray detection signals output from the first γ-ray detector and the second γ-ray detector as emission data for acquiring the RI distribution image, and the RI distribution image acquisition means includes the emission data collection means. An RI distribution image is acquired based on the emission data collected in (1).

  That is, in the case of the nuclear medicine diagnostic apparatus according to the first aspect of the present invention, before taking the RI distribution image, the first C-shaped arm member to which the first γ-ray detector is attached at the tip and the second γ-ray detector are at the tip. The second C-shaped arm member attached to the first γ-ray detector is moved by the arm member moving means in the direction in which the first C-shaped arm member and the second C-shaped arm member approach each other along the bending of the arm. And the second γ-ray detector can be brought close to the subject. In addition, the detector angle adjustment means changes the tilt angles of the first γ-ray detector and the second γ-ray detector so that the γ-ray incident surfaces of the first γ-ray detector and the second γ-ray detector face each other with the subject interposed therebetween. A gamma ray detection posture can be set. Therefore, an RI distribution image can be taken in a state where the first γ-ray detector and the second γ-ray detector are sufficiently close to the subject in advance.

As described above, if the first γ-ray detector and the second γ-ray detector are sufficiently close to the subject in advance, the γ-rays of the first γ-ray detector and the second γ-ray detector are captured during the acquisition of the RI distribution image. Since the number of γ rays incident on the incident surface increases, the detection sensitivity of γ rays increases.
Therefore, according to the nuclear medicine diagnostic apparatus of the first aspect, the RI distribution image of the subject can be taken with sufficient sensitivity.

  In addition to the first γ-ray detector, the second γ-ray detector and the double arm type detector holding means, the invention described in claim 2 includes an arm member moving means and a detector angle adjusting means (G ) It is mounted on a trackless truck that runs on the floor without a track.

  [Operation / Effect] In the apparatus of the invention of claim 2, in addition to the first γ-ray detector, the second γ-ray detector and the double-arm type detector holding means, the arm member moving means is caused by running of the trackless carriage. And the detector angle adjusting means can be moved to the imaging location to capture an RI distribution image of the subject.

  The invention described in claim 3 includes (H) vertical movement means for relatively moving the subject in the vertical direction of the apparatus.

  [Operation / Effect] In the case of the apparatus of the invention of claim 3, the vertical movement generated between the subject and the apparatus accompanying the movement of the first C-shaped arm member and the second C-shaped arm member by the arm member moving means, etc. The positional shift can be eliminated by moving the subject relative to the vertical direction of the apparatus by the vertical movement means.

  The invention according to claim 4 is the nuclear medicine diagnostic apparatus according to any one of claims 1 to 3, wherein the radioisotope administered to the subject is a positron type radioisotope, and the emission data The collecting means collects only γ-ray detection signals when emission γ-rays traveling in the opposite direction are simultaneously detected by the first γ-ray detector and the second γ-ray detector as emission data.

  [Operation / Effect] In the case of the apparatus of the invention of claim 4, the annihilation γ-ray generated by the emission data collecting means accompanying the annihilation of the positron emitted from the radioisotope administered to the subject and traveling in the opposite direction is γ Since only the γ-ray detection signals simultaneously detected by the ray detection means are collected as emission data, an RI distribution image of the positron-type radioisotope administered to the subject can be taken.

  In the case of the nuclear medicine diagnostic apparatus of the present invention, before taking the RI distribution image, the first C-shaped arm member to which the first γ-ray detector is attached at the tip and the second γ-ray detector are attached to the tip. By moving the second C-shaped arm member by the arm member moving means in the direction in which the first C-shaped arm member and the second C-shaped arm member approach each other along the bending of the arm, the first γ-ray detector and the second γ-ray The detector can be brought close to the subject. In addition, the detector angle adjustment means changes the tilt angles of the first γ-ray detector and the second γ-ray detector so that the γ-ray incident surfaces of the first γ-ray detector and the second γ-ray detector face each other with the subject interposed therebetween. A gamma ray detection posture can be set. Therefore, an RI distribution image can be taken in a state where the first γ-ray detector and the second γ-ray detector are sufficiently close to the subject in advance.

As described above, if the first γ-ray detector and the second γ-ray detector are sufficiently close to the subject in advance, the γ-rays of the first γ-ray detector and the second γ-ray detector are captured during the acquisition of the RI distribution image. Since the number of γ rays incident on the incident surface increases, the detection sensitivity of γ rays increases.
Therefore, according to the nuclear medicine diagnostic apparatus of the present invention, the RI distribution image of the subject can be taken with sufficient sensitivity.

  An embodiment of the nuclear medicine diagnosis apparatus of the present invention will be described. FIG. 1 is a block diagram showing the overall configuration of a mobile PET (positron emission tomography) apparatus according to an embodiment, FIG. 2 is a front view showing the apparatus of the embodiment, and FIG. 3 is a perspective view showing the apparatus of the embodiment. FIG.

  As shown in FIGS. 1 to 3, in the PET apparatus of the embodiment, the γ-ray incident surfaces 1 </ b> A and 2 </ b> A face each other with the subject M facing each other. A first γ-ray detector 1 and a second γ-ray detector 2 that detect the line detection posture are provided. The first γ-ray detector 1 and the second γ-ray detector 2 are composed of a scintillator that converts incident γ-rays into light, and a photomultiplier that is installed vertically and horizontally that converts the light emitted from the scintillator into electricity and outputs it. This is a substantially flat type two-dimensional detector. Further, as shown in FIG. 1, an external radiation source 3 that irradiates radiation when collecting transmission data for absorption correction is also disposed on the front side of the first γ-ray detector 1 and the second γ-ray detector 2. Yes.

  Further, the apparatus of the embodiment includes a double arm type detector holding mechanism 4 that holds the first γ-ray detector 1 and the second γ-ray detector 2. In the case of the double arm type detector holding mechanism 4, as shown in FIGS. 1 to 2, the first C-shaped arm member 5 to which the first γ-ray detector 1 is attached at the tip and the second γ-ray detector 2 are provided. The second C-shaped arm member 6 attached to the tip of the arm is extended along the longitudinal direction of the arm while the arm long axes 5A and 6A are adjacent to each other and arranged in parallel, and the first γ-ray detector 1 The second γ-ray detector 2 is arranged in a facing direction with the subject M in between.

  Furthermore, the apparatus of the embodiment includes an arm member moving mechanism 7 for moving the first C-shaped arm member 5 and the second C-shaped arm member 6 in both directions along the bending of the arm, the first γ-ray detector 1 and the second γ. A detector that changes the inclination angle of the line detector 2 to obtain a γ-ray detection posture in which the γ-ray incident surfaces 1A and 2A of the first γ-ray detector 1 and the second γ-ray detector 2 face each other with the subject M in between. An angle adjustment mechanism 8 is provided. In addition to this, in the case of the apparatus of the embodiment, the first γ-ray detector 1 and the second γ-ray detector 2, and the double arm type provided with the first C-shaped arm member 5 and the second C-shaped arm member 6. In addition to the detector holding mechanism 4, an arm member moving mechanism 7 and a detector angle adjusting mechanism 8 are mounted on a trackless traveling type carriage 9 that travels on the floor FL without a track.

  In the trackless traveling bogie 9, a wide arc-shaped arm member mounting base 11 is disposed on a bogie base 10 with the inner surface facing obliquely upward. As shown in FIG. 4, the arm member mounting base 11 is formed with two arm locking inner grooves 12 and 13 that continue in parallel along the longitudinal direction of the arm member receiving base 11. As shown in FIG. 5, the first C-shaped arm member 5 and the second C-shaped arm member 6 are provided with locking protrusions 5a and 6a extending along the longitudinal direction of the arm. Then, by inserting the locking protrusions 5a and 6a into the arm locking inner grooves 12 and 13, the first C-shaped arm member 5 and the second C-shaped arm member 6 are moved along the longitudinal direction of the arm. The arm member cradle 11 is attached in a slidable form. Several sliding rollers 12A and 13A are arranged on the side surfaces of the arm locking inner grooves 12 and 13, and the first C-shaped arm member 5 and the second C-shaped arm member 6 slide smoothly.

On the other hand, the arm member moving mechanism 7 includes a first arm member moving mechanism 7A for moving the first C-shaped arm member 5 and a second arm member moving mechanism 7B for moving the second C-shaped arm member 6.
As shown in FIGS. 4 and 5A, the first arm member moving mechanism 7A includes an arm member in addition to the belt 7a1 having both ends fixed to one end side and the other end side of the C-shaped arm member 5. Guide pulleys 7a2, 7a3, drive pulley 7a4 and electric motor 7a5 for rotating the drive pulley 7a4 installed on the side of the cradle 11 are included, and the belt 7a1 is connected to the guide pulleys 7a2, 7a3 and the drive pulley. It is stretched between pulleys 7a4. Accordingly, as the electric motor 7a5 rotates, the belt 7a1 is transferred, and at the same time, the C-shaped arm member 5 is pulled by the belt 7a1 and moves along the bending of the arm as indicated by an arrow RA. The moving direction of the C-shaped arm member 5 is reversed if the rotation direction of the electric motor 7a5 is changed.

  As shown in FIGS. 4 and 5B, the second arm member moving mechanism 7B includes an arm member in addition to the belt 7b1 having both ends fixed to one end side and the other end side of the C-shaped arm member 6. The guide pulleys 7b2 and 7b3 installed on the cradle 11 side, the driving pulley 7b4, and the electric motor 7b5 for rotating the driving pulley 7b4 are included, and the belt 7b1 is connected to the guide pulleys 7b2 and 7b3. It is stretched between pulleys 7b4. Accordingly, the belt 7b1 is transferred as the electric motor 7b5 rotates, and at the same time, the C-shaped arm member 6 is pulled by the belt 7b1 and moves along the bending of the arm as indicated by an arrow RB. The moving direction of the C-shaped arm member 6 is reversed if the rotation direction of the electric motor 7b5 is changed.

  On the other hand, the detector angle adjustment mechanism 8 includes a first detector angle adjustment mechanism 8A and a second detector angle adjustment mechanism 8B. The first detector angle adjustment mechanism 8A and the second detector angle adjustment mechanism 8B have electric motors (not shown) that rotate the mounting shafts (not shown) of the first γ-ray detector 1 and the second γ-ray detector 2. As the electric motor rotates, the first γ-ray detector 1 and the second γ-ray detector rotate as shown by arrows ra and rb in FIG. 2 tilt angle changes. The direction of rotation of the first γ-ray detector 1 and the second γ-ray detector 2 is reversed if the rotation direction of the electric motor changes. That is, as the first C-shaped arm member 5 and the second C-shaped arm member 6 are moved by the arm member moving mechanism 7, the inclination angles of the first γ-ray detector 1 and the second γ-ray detector 2 are changed, and the first γ-ray detector 1 is changed. Since the γ-ray detection postures in which the γ-ray incident surfaces 1A and 2A of the line detector 1 and the second γ-ray detector 2 face each other with the subject M interposed therebetween are broken, the first γ-ray detector 1 is detected by the detector angle adjustment mechanism 8. Then, by changing the inclination angle of the second γ-ray detector 2, the γ-ray detection posture is restored.

  The trackless cart 9 is a four-wheeled vehicle in which a total of four wheels, two small front wheels 14A and two large rear wheels 14B, are arranged on the cart base 10, and the operator (photographer) is on the back side. This is a hand movement type in which the floor 15 is driven by turning the wheel by grasping and pushing or pulling the handle 15 provided at the upper part. Of course, the trackless cart 9 does not have to be a manual movement type, and may be an electric movement type in which wheels are driven by an electric motor.

  When an RI distribution image of the subject M is taken, the trackless carriage 9 is pushed or pulled to run on the floor FL and move to the location of the subject M. In other words, in the case of the apparatus of the embodiment, the first γ-ray detector 1, the second γ-ray detector 2, the first C-shaped arm member 5, and the second C-shaped arm member 6 are double-armed by traveling the trackless carriage 9. In addition to the type detector holding mechanism 4, the arm member moving mechanism 7 and the detector angle adjusting mechanism 8 can be moved to the imaging location to capture an RI distribution image of the subject M.

  If the distance between the first γ-ray detector 1 and the second γ-ray detector 2 is not an appropriate width for setting the subject M, first, the first C-shaped arm member 5 and the second C-shaped arm member 6 are used. Are moved in the direction in which the first C-shaped arm member 5 and the second C-shaped arm member 6 are separated along the bending of the arm by the arm member moving mechanism 7, as shown in FIG. After sufficiently widening the interval between 1 and the second γ-ray detector 2, the subject M to be imaged is set between the first γ-ray detector 1 and the second γ-ray detector 2.

  In the case of the apparatus according to the embodiment, a top / bottom lift mechanism 16A that electrically lifts and lowers the top board 16 on which the subject M is placed is also provided. When there is a positional misalignment, the subject M can be moved in the vertical direction of the apparatus by moving the top / bottom plate 16 by operating the top / bottom lifting mechanism 16A at an appropriate time to eliminate the positional misalignment.

  Subsequently, as shown in FIGS. 6 and 7, the first C-shaped arm member 5 and the second C-shaped arm member 6 are reversed by the arm member moving mechanism 7 along the bending of the arm. 5 and the second C-shaped arm member 6 are moved toward each other to bring the first γ-ray detector 1 and the second γ-ray detector 2 sufficiently close to the subject M, and the detector angle adjusting mechanism 8 makes the first γ-ray. The γ-rays in which the γ-ray incident surfaces 1A and 2A of the first and second γ-ray detectors 1 and 2 face each other with the subject M sandwiched by changing the inclination angles of the detector 1 and the second γ-ray detector 2. Shooting is started in the detected posture. In the case of the gamma ray detection posture shown in FIGS. 6 and 7, the RI distribution image is taken from the front-rear direction.

The movement positions and inclination angles of the first C-shaped arm member 5, the second C-shaped arm member 6, the first γ-ray detector 1 and the second γ-ray detector 2 are adjusted, and the γ-rays shown in FIGS. With the detection posture, the RI distribution image can be taken from the body side direction.
As shown in FIGS. 10 and 11, the first C-shaped arm member 5, the second C-shaped arm member 6, the first γ-ray detector 1, and the second γ-ray detection according to the size of the subject M side. By adjusting the movement position and tilt angle of the vessel 2, it is possible to obtain a γ-ray detection posture corresponding to the size of the subject M side.

  In addition, the first C-shaped arm member 5 and the second C-shaped arm member 6 are moved in the same direction along the bending of the arm by the arm member moving mechanism 7, and the first γ-ray detector 1 is detected by the detector angle adjusting mechanism 8. Further, the inclination angle of the second γ-ray detector 2 is changed so that the γ-ray incident surfaces 1A and 2A of the first γ-ray detector 1 and the second γ-ray detector 2 face each other with the subject M in between. Then, the first γ-ray detector 1 and the second γ-ray detector 2 go around the subject M and change the imaging direction.

  The arm member moving mechanism 7 moves the first C-shaped arm member 5 and the second C-shaped arm member 6 while receiving movement control data according to an operator's operation and a preset program from the arm movement control unit 17. . The detector angle adjustment mechanism 8 changes the tilt angle of the first γ-ray detector 1 and the second γ-ray detector 2 while receiving angle control data according to an operator's operation and a preset program from the detector angle control unit 18. Let The top plate elevating mechanism 16A raises and lowers the top plate 16 while receiving elevating control data according to an operator's operation and a preset program from the top plate elevating control unit 19.

  Therefore, in the case of the apparatus of the embodiment, the arm member moving mechanism 7, the detector angle adjusting mechanism 8 and the top plate lifting mechanism 16A are all electrically driven, but these may be manually operated. For example, the operator pulls and moves the first C-shaped arm member 5 or the second C-shaped arm member 6 by hand or changes the tilt angle by grasping the first γ-ray detector 1 or the second γ-ray detector 2 by hand. But you can.

  Further, as shown in FIG. 1, the apparatus according to the embodiment includes an emission data collection unit 20, a transmission data collection unit 21, an absorption correction unit 22, and the second stage of the first and second γ-ray detectors 1 and 2. In addition to the provision of the RI distribution image acquisition unit 23, the display monitor 24 for displaying the RI distribution image, the X-ray CT image or the operation menu of the apparatus, and the operation for inputting data and commands necessary for the operation of the apparatus The unit 25 and the like are provided.

The emission data collection unit 20 collects γ-ray detection signals output from the first and second γ-ray detectors 1 and 2 as emission data for acquiring RI distribution images. In addition, in the case of the emission data collection unit 20, both the first and second γ-rays are generated by the disappearance of positrons emitted from the radioisotope administered to the subject M and proceeding in opposite directions. Only the γ-ray detection signals detected simultaneously by the detectors 1 and 2 are collected as emission data. That is, γ-ray detection when one of the annihilation γ-rays traveling in the opposite direction is detected by the first γ-ray detector 1 and at the same time the other γ-ray is detected by the second γ-ray detector 2. Only the signal is collected as emission data. Examples of the positron type RI administered to the subject M include ¹¹ C, ¹³ N, ¹⁵ O, ¹⁸ F and the like.

The transmission data collection unit 21 receives the first and second radiations as the subject M is irradiated with radiation by the external radiation source 3 installed in front of the first and second γ-ray detectors 1 and 2. Radiation detection signals output from both γ-ray detectors 1 and 2 are collected as transmission data for absorption correction.
The absorption correction unit 22 corrects the absorption of the emission data collected by the emission data collection unit 20 using the transmission data collected by the transmission data collection unit 21.

The RI distribution image acquisition unit 23 acquires an RI distribution image based on the emission data subjected to the absorption correction. The display monitor 24 displays the RI distribution image acquired by the RI distribution image acquisition unit 23 on the screen.
The main control unit 26 is mainly composed of a computer and its operation program, and sends commands and data to each unit in accordance with commands input from the operation unit 25 and the progress of photographing, thereby normalizing the apparatus. To play a role.

  Further, as shown in FIG. 12, the apparatus of the embodiment can be a combined system combined with an X-ray CT apparatus 27. Specifically, the top plate 16 is shared by the PET apparatus of the embodiment and the X-ray CT apparatus 27, and after the RI distribution image is taken by the PET apparatus of the embodiment, the top board 16 is gantry of the X-ray CT apparatus 27. The PET-CT system can be configured such that an X-ray CT image at a position where the RI distribution image is taken by entering the image can be taken. In this case, the external radiation source 3 and the transmission data collection unit 21 can be dispensed with by using the X-ray CT image for emission absorption correction.

  As described above, in the case of the apparatus according to the embodiment, before taking the RI distribution image, the first C-shaped arm member 5 and the second γ-ray detector 2 to which the first γ-ray detector 1 is attached at the tip. Is moved to the direction in which the first C-shaped arm member 5 and the second C-shaped arm member 6 approach each other along the bending of the arm by the arm member moving mechanism 7. Thus, the first γ-ray detector 1 and the second γ-ray detector 2 can be brought close to the subject M. In addition, the detector angle adjusting mechanism 8 changes the inclination angles of the first γ-ray detector 1 and the second γ-ray detector 2 to change the γ-ray incident surfaces 1A and 2A of the first γ-ray detector 1 and the second γ-ray detector 2. A gamma ray detection posture that faces each other across the subject M can be achieved. Therefore, an RI distribution image can be taken in a state where the first γ-ray detector 1 and the second γ-ray detector 2 are sufficiently close to the subject in advance.

As described above, if the first γ-ray detector 1 and the second γ-ray detector 2 are sufficiently close to the subject M in advance, the first γ-ray detector 1 and the second γ-ray detection are performed during the radiography of the RI distribution image. Since the number of γ rays incident on the γ ray incident surfaces 1A and 2A of the vessel 2 increases, the detection sensitivity of γ rays increases.
Therefore, according to the PET apparatus of the embodiment, the RI distribution image of the subject M can be taken with sufficient sensitivity.

  In the apparatus of the embodiment, the tomogram is obtained by rotating the periphery of the subject 180 degrees with the first γ-ray detector 1 and the second γ-ray detector 2 facing each other and collecting emission data around the subject. You may comprise so that it may acquire. For example, in the “continuous rotation collection” shown in FIG. 13A, the first γ-ray detector 1 and the second γ-ray detector 2 are arranged in order to collect a necessary number of events that are the simultaneous detection of annihilation γ-rays. Reciprocating multiple times. According to this continuous rotation collection, even when the subject moves on the way, it can be imaged using the data up to that point. Further, data may be collected by “step collection” shown in FIG. In “step collection”, data is collected while the first γ-ray detector 1 and the second γ-ray detector 2 are kept stationary at a constant angle (for example, 6 degrees). The tomographic image reconstruction method is well known. For example, it is possible to generate a sinogram of a tomographic plane from emission data (projection data) at a certain angle and reconstruct the image by a filtered back projection method or a successive approximation method. it can.

  In the apparatus of the embodiment, in order to reduce the distance between the subject and the first and second γ-ray detectors 1 and 2 as much as possible, when rotating around the subject while changing the distance between the detectors, Since imaging also proceeds while the positions and orientations of the first and second γ-ray detectors 1 and 2 with respect to the origin are changed, the first and second γ-ray detectors 1 with respect to the mechanical origin of the apparatus will be described below. The reconstruction algorithm when the position and orientation of 2 change will be described.

  As shown in FIGS. 14 and 15, the first and second γ-ray detectors 1 and 2 are aggregates of minute γ-ray detection elements a and b. An image reconstruction area S having a center coordinate OC defined by a vector VC starting from the mechanical origin OM is set. Vectors VA and VB from the mechanical origin OM of the apparatus to the center coordinates OA and OB of the respective γ-ray detectors 1 and 2 are obtained based on the above-described transport position data, rotation angle data, and position variation data. The vectors WA and WB from the center coordinates WA and WB of the γ-ray detectors 1 and 2 to the γ-ray detection elements a and b are based on the addresses (coordinates) of the γ-ray detection elements a and b in the γ-ray detectors 1 and 2. Is required.

Accordingly, when a phenomenon occurs in which γ rays emitted from the subject M are simultaneously counted (hereinafter abbreviated as “event” as appropriate), a γ ray detecting element a that simultaneously detects γ rays from the mechanical origin OM of the apparatus. , B, the vectors uA and uB are also obtained according to the following equations (1) and (2).
uA = VA + WA (1)
uB = VB + WB (2)

On the other hand, when a phenomenon (event) in which γ rays emitted from the subject M are simultaneously counted occurs, address pair data of the γ ray detection elements a and b that detect the γ rays, and γ that detects the γ rays. Address pair data of vectors uA and uB for the line detection elements a and b are collected and stored as list mode type data for each event.
On the other hand, a straight line LOR (Line of Response) connecting γ-ray detection elements a and b that simultaneously detect γ-rays is obtained for each event from address pair data of vectors uA and uB collected and stored as list mode type data. The positron emitting species is above the straight line LOR.

The vector uA is obtained according to the following equation (3) and information on the position and orientation of the γ-ray detectors 1 and 2 as the γ-ray detection mechanism 3 stored as list mode type data. The position and orientation data of the γ-ray detectors 1 and 2 may be stored as tag information only when there is a change.
uA = R _X , R _Y , R _Z , T, WA (3)
However, as shown below, R _X , R _Y , R _Z are rotations of the γ-ray detectors 1, 2 around the X, Y, and Z axes orthogonal to each other with the mechanical origin OM of the apparatus as the origin, T Is the position in each direction of the X axis, Y axis, and Z axis (ie, VA).
Further, the vector uB can be obtained in the same manner as the vector uA.

  In this way, when a straight line LOR (Line of Response) connecting γ-ray detection elements a and b that simultaneously detect γ-rays is obtained for each event, a successive approximation list mode reconstruction algorithm is applied [ For example, see J Reader et al 1998 Phys. Med Bial. 43 835-846 (non-patent literature). The image update formula of this list mode reconstruction algorithm is as shown in formula (4). The RI distribution image is obtained by repeating the updating formula (4).

Here, f ^k _j is the pixel value of the pixel j in the k-th iteration, a _ij is the probability that the γ-ray emitted from the pixel j is detected by LORi, M is the number of measured events, and I is the main imaging condition It is the number of all LORs in (detector arrangement). The update formula used in the image reconstruction algorithm applied to the apparatus of the embodiment is not limited to the formula (4).

The present invention is not limited to the above embodiment, and can be modified as follows.
(1) In the apparatus of the embodiment, as shown in FIGS. 16 and 17, the first γ-ray detector 1 includes two detector pieces 1a and 1b, and the second γ-ray detector 2 includes two detector pieces 2a. , 2b, and the detector pieces 1a, 1b, 2a, 2b can be modified as an example of a modification which is substantially the same as the embodiment except that the inclination angle of each detector piece 1a, 1b, 2a, 2b can be changed. In the case of the modified apparatus, the front-rear direction and the body-side direction of the subject can be imaged at once.

  When the subject M is large, as shown in FIG. 16, the γ-ray detection posture is such that the distance between the detector pieces 1a and 1b and the detector pieces 2a and 2b is wider, and the subject M is small. As shown in FIG. 17, the distance between the two detector pieces 1a and 1b and the two detector pieces 2a and 2b is a narrow gamma ray detection posture.

  (2) In the case of the apparatus of the embodiment, when there is a vertical displacement between the subject M and the apparatus, the subject M is moved vertically by moving the top plate 16 up and down. However, when the carriage base 10 or the arm member cradle 11 of the trackless carriage 9 can be moved up and down and there is a vertical misalignment between the subject M and the apparatus, A configuration may be adopted in which the position difference is eliminated by moving the apparatus up and down by moving the carriage base 10 or the arm member cradle 11 up and down.

  (3) In the case of the apparatus of the embodiment, the arm member cradle 11 is provided on the cart base 10 of the trackless bogie 9, but the arm member cradle 11 travels along a rail laid on the ceiling or floor. An apparatus having the same configuration as that of the embodiment except that it is provided on the substrate to be used is given as a modification.

  (4) Although the apparatus of the example was a PET apparatus, the present invention can also be applied to a non-positron type nuclear medicine diagnostic apparatus such as a SPECT apparatus.

It is a block diagram which shows the structure of the mobile PET apparatus which concerns on an Example. It is a front view which shows the PET apparatus of an Example. It is a perspective view which shows the PET apparatus of an Example. It is a horizontal sectional view which shows the attachment structure of both the 1st, 2nd C-shaped arm members of the apparatus of an Example. It is a schematic diagram which shows the structure of the arm member moving mechanism of the apparatus of an Example. It is the schematic which shows the condition when image | photographing a test object from the front-back direction with the apparatus of an Example. It is a perspective view which shows the condition at the time of image | photographing a test object from the front-back direction with the apparatus of an Example. It is the schematic which shows the condition at the time of image | photographing a test object from a body side direction with the apparatus of an Example. It is a perspective view which shows the condition at the time of image | photographing a subject from a body side direction with the apparatus of an Example. It is the schematic which shows the condition at the time of image | photographing a big test subject from the body side direction with the apparatus of an Example. It is the schematic which shows the condition at the time of image | photographing a small test object from a body side direction with the apparatus of an Example. It is a perspective view which shows the composite system which combined the PET apparatus and X-ray CT apparatus of an Example. It is explanatory drawing of the data collection method in the case of obtaining a tomogram with the apparatus of an Example. It is a schematic diagram which shows the arrangement | positioning relationship of both the 1st, 2nd gamma-ray detector and image reconstruction area | region in the apparatus of an Example. It is a graph which shows the coordinate system of both the 1st, 2nd gamma-ray detector and the image reconstruction area | region in the apparatus of an Example. It is the schematic which shows the condition at the time of image | photographing a big test subject with the apparatus of a modification. It is the schematic which shows the condition at the time of image | photographing a small test object with the apparatus of a modification. It is a front view which shows the conventional PET apparatus. It is an elevation view which shows an example of the gantry in the conventional PET apparatus. It is an elevational view showing another example of a gantry in a conventional PET apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st gamma ray detector 1A ... Gamma ray incident surface (of 1st gamma ray detector) 2 ... 2nd gamma ray detector 2A ... Gamma ray incidence surface (of 2nd gamma ray detector) 4 ... Double arm type detector Holding mechanism (double arm detector holding means)
DESCRIPTION OF SYMBOLS 5 ... 1st C-shaped arm member 5A ... Arm long axis (of 1st C-shaped arm member) 6 ... 2nd C-shaped arm member 6A ... Arm long axis (of 2nd C-shaped arm member) 7 ... Arm member moving mechanism (Arm member moving means)
8 ... Detector angle adjustment mechanism (detector angle adjustment means)
9 ... Trackless type truck 16A ... Top plate lifting mechanism (up and down movement means)
20 ... Emission data collection unit (Emission data collection means)
23 ... RI distribution image acquisition unit (RI distribution image acquisition means)
M… Subject

Claims (4)

  (A) a first γ-ray detector and a second γ-ray detector for detecting γ-rays generated by a radioisotope administered to a subject in a γ-ray detection posture in which a γ-ray incident surface is opposite to the subject; B) Emission data collection means for collecting γ-ray detection signals output from the first γ-ray detector and the second γ-ray detector as emission data for acquiring RI distribution images, and (C) an RI distribution image based on the emission data. (D) a first C-shaped arm member having a first γ-ray detector attached to the tip and a second γ-ray detector attached to the tip. And a second arm detector holding means in which the first γ-ray detector and the second γ-ray detector are arranged facing each other with the subject in between. When,( ) Arm member moving means for moving the first C-shaped arm member and the second C-shaped arm member in both directions along the bending of the arm; and (F) changing the inclination angle of the first γ-ray detector and the second γ-ray detector. And a detector angle adjusting means for setting a γ-ray detection posture in which the γ-ray incident surfaces of the first γ-ray detector and the second γ-ray detector face each other across the subject. Diagnostic device.   In the nuclear medicine diagnostic apparatus according to claim 1, in addition to the first γ-ray detector and the second γ-ray detector, and the double arm type detector holding means, the arm member moving means and the detector angle adjusting means include: (G) A nuclear medicine diagnostic apparatus mounted on a trackless traveling vehicle that travels on a floor without a track.   The nuclear medicine diagnostic apparatus according to claim 1 or 2, further comprising (H) a vertically moving means for moving the subject relative to the vertical direction of the apparatus. 4. The nuclear medicine diagnostic apparatus according to claim 1, wherein the radioisotope administered to the subject is a positron type radioisotope, and the emission data collection means proceeds in the opposite direction. A nuclear medicine diagnostic apparatus that collects only γ-ray detection signals as emission data when is detected simultaneously by the first γ-ray detector and the second γ-ray detector.

Images