JP2009216716A - Nuclear medicine diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nuclear medicine diagnostic apparatus including a two-dimensional semiconductor detector, improving spatial resolving power more than the center to center spacing of a semiconductor element and eliminating deficit in data due to gap between the elements. <P>SOLUTION: This nuclear medicine diagnostic apparatus includes the two-dimensional semiconductor detectors 1, 2; a moving mechanism 4 for moving the two-dimensional semiconductor detector in a predetermined direction substantially parallel to the body axis of a body to be examined; an inclining mechanism 16 for inclining the two-dimensional semiconductor detector to a predetermined direction; a reconfiguration means 13 for reconfiguring the concentration distribution of radioactive isotope related to the section of the body to be examined based on the output of the two-dimensional semiconductor detector; and a control part 7 for controlling the moving mechanism and the inclining mechanism, wherein the two-dimensional semiconductor detector is rotated around the body to be examined in the state of inclining to the predetermined direction under the control of the control part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention injects a radioisotope (radioisotope; hereinafter abbreviated as RI) into a living body, captures the concentration distribution of RI in the living body with a detector, and is useful for lesions, blood flow, and fatty acid metabolism. The present invention relates to a nuclear medicine diagnostic apparatus that can provide diagnostic information.

  In a nuclear medicine diagnostic device, the detector is one of the most important components on the front line for detecting gamma rays from the radioisotope (RI) injected into the subject, and this performance is the spatial resolution of the entire device. It is no exaggeration to say that it affects the performance such as energy resolution and counting characteristics.

  Currently, the scintillation type detectors occupy the mainstream, and as is well known, this is a method of increasing the number of photoelectrons that are densely arranged on the back of the light generated by the scintillator (phosphor) by the incidence of gamma rays. The detection is performed by a double tube (PMT) or a photodiode array, which is not only very large and heavy, but also has low energy resolution.

  On the other hand, semiconductor detectors have been in the spotlight in recent years, because they directly detect gamma rays, which is more than a conventional scintillation type detector that undergoes a two-step conversion process of gamma rays, light and electricity. However, it is expected that the energy resolution and the counting capability are remarkably improved since the conversion efficiency into the electric signal is high and the gamma rays can be individually detected by the semiconductor cell.

  As is well known, the structure of this semiconductor detector and the detection mechanism include, for example, an electrode formed on a compound semiconductor such as CdTe (cadmium telluride), and a bias electrode and a signal electrode are bonded to both surface electrodes. For such a structure, when a gamma ray is incident with a bias voltage applied, a large number of electron-hole pairs are generated, and the induced charge induced when each moves to the positive electrode and the negative electrode. It is accumulated in a charge amplifier installed on the positive electrode side, and this is output as a signal proportional to energy.

  In such a semiconductor detector, (1) the spatial resolution is limited by the size of the semiconductor element. Specifically, the spatial resolution is determined by the distance between the center points of adjacent semiconductor elements. (2) An insulator is sandwiched between adjacent semiconductor elements, but there is a problem to be improved that data cannot be obtained in this gap portion, that is, data is lost.

  As a technique for solving the problem (2), there is currently known a technique of minutely moving or vibrating a detector called wobbling. However, although it is much lighter than the Anger type, it is not easy to stably move the semiconductor detector to reach 20 kg, and an error occurs due to unstable movement. In addition, a mechanism and a stand having a large load resistance for realizing this may be expensive and large in size.

  An object of the present invention is to improve the spatial resolution rather than the distance between the central points of semiconductor elements and to eliminate data loss due to gaps between elements in a nuclear medicine diagnostic apparatus equipped with a two-dimensional semiconductor detector.

  One aspect of the present invention is that at least one two-dimensional semiconductor formed by two-dimensionally arranging semiconductor elements that administer a radioisotope to a subject and directly detect gamma rays emitted from the radioisotope. A detector, a rotation mechanism for rotating the two-dimensional semiconductor detector around a rotation axis substantially parallel to the body axis of the subject, and an inclination mechanism for tilting the two-dimensional semiconductor detector with respect to the rotation axis; Reconstructing means for reconstructing the concentration distribution of the radioisotope with respect to the cross section of the subject based on the output of the two-dimensional semiconductor detector; and control means for controlling the rotation mechanism and the tilt mechanism. In the nuclear medicine diagnosis apparatus, the nuclear medicine diagnosis apparatus is characterized in that the two-dimensional semiconductor detector is tilted with respect to the rotation axis under the control of the control means.

  According to the present invention, in a nuclear medicine diagnostic apparatus equipped with a two-dimensional semiconductor detector, it is possible to improve the spatial resolution rather than the distance between the center points of the semiconductor elements and to eliminate data loss due to gaps between the elements.

The figure which shows the structure of the nuclear medicine diagnostic apparatus which concerns on preferable embodiment of this invention. The top view of the semiconductor detector of FIG. The flowchart which shows the operation | movement procedure at the time of the whole body imaging | photography of this embodiment. The figure which shows the track | orbit of the center point of a certain semiconductor element at the time of whole body imaging | photography. The figure which shows the spatial resolution by this embodiment. The figure which shows the inclination | tilt angle of a two-dimensional semiconductor detector. The figure which shows the center point track | orbit of the adjacent semiconductor elements A and B of FIG. 6 at the time of whole body imaging | photography. 6 is a flowchart showing an operation procedure during SPECT imaging according to the present embodiment. The figure which shows the track | orbit of the center point of a certain semiconductor element at the time of SPECT imaging | photography. The figure which shows the center point track | orbit of the adjacent semiconductor elements A and B of FIG. 6 at the time of SPECT imaging | photography.

  Hereinafter, a nuclear medicine diagnostic apparatus according to the present invention will be described with reference to the drawings according to a preferred embodiment. FIG. 1 shows the configuration of a nuclear medicine diagnostic apparatus according to this embodiment. In the two-dimensional semiconductor detectors 1 and 2, as shown in FIG. 2, for example, a semiconductor element formed by bonding a bias electrode and a signal electrode to a compound semiconductor piece such as CdTe (cadmium telluride) is two-dimensionally arranged. It becomes. Note that two two-dimensional semiconductor detectors 1 and 2 are not necessarily required, but only one, or three or more.

  The two-dimensional semiconductor detectors 1 and 2 are supported by a moving / tilting / shifting mechanism 16. Further, the moving / tilting / shifting mechanism 16 is supported by the rotating frame 4. The rotating frame 4 has a structure and a driving source necessary for rotating the two-dimensional semiconductor detectors 1 and 2 around a rotation axis substantially parallel to the body axis of the subject P. Controlled by

  The moving / tilting / shifting mechanism 16 includes a structure and a driving source necessary for moving and shifting the two-dimensional semiconductor detectors 1 and 2 along the rotation axis, and the two-dimensional semiconductor detectors 1 and 2 with respect to the rotation axis. And a structure and drive source necessary for shifting along an orthogonal axis substantially orthogonal to each other, and a structure and drive source necessary for tilting the two-dimensional semiconductor detectors 1 and 2 with respect to the rotation axis. The detector movement / tilt / shift control unit 7 controls the detector.

  The bed 3 has a structure and a driving source necessary for moving and shifting along the rotation axis in a state where the subject P is placed, and an orthogonality which is substantially orthogonal to the rotation axis in a state where the subject P is placed. It has a structure and a driving source necessary for shifting along the axis, and is controlled by the bed detector movement / tilt / shift control unit 7.

  The time control circuits 8 and 9 for each detector element are provided to control the start of the counting period for each semiconductor element when the two-dimensional semiconductor detectors 1 and 2 are imaged in an inclined state. Imaging is an operation for counting gamma rays from a radioisotope administered to a subject as the number of photons.

  The position / energy calculation circuits 10 and 11 generate, based on the outputs of the two-dimensional semiconductor detectors 1 and 2, each time a gamma ray is incident, a position signal indicating the incident position and angle and an energy signal indicating the energy. Output. Based on the position signal and the energy signal, the image memory 12 counts gamma rays as the number of photons for each incident position, angle, and energy. The data processing circuit 13 generates a planar concentration distribution (planar image) of a radioisotope based on the counting result stored in the image memory 12 during whole body imaging (in whole body imaging), and SPECT. At the time of imaging, the concentration distribution (tomographic image) of the radioisotope in the cross section of the subject is reconstructed. These planar images and tomographic images are sent to the display circuit 14 and displayed, for example, in shades. The controller 15 is provided for comprehensively controlling the movement of the entire apparatus.

  Such a nuclear medicine diagnostic apparatus according to the present embodiment can selectively perform whole body imaging and SPECT imaging. Hereinafter, each photographing operation will be described in order.

(Hole body shooting)
FIG. 3 shows an operation procedure at the time of hole body photographing according to the present embodiment, and FIG. 4 shows a trajectory of a central point of a certain semiconductor element at the time of hole body photographing. First, the basic movement at the time of whole body imaging is the continuous movement of the two-dimensional semiconductor detectors 1 and 2 relative to the subject P along the rotation axis (body axis) direction. The counting operation is repeated in a certain counting period T in parallel with the movement, and by such movement, gamma rays can be counted at a large number of positions for almost the whole body of the subject P.

  In this embodiment, such basic movement is repeated while reciprocating the two-dimensional semiconductor detectors 1 and 2 with a fixed stroke. In particular, the moving direction from the forward path to the backward path and vice versa is reversed. In the meantime, the distance is shifted by a distance of d / n in the direction of the orthogonal axis substantially orthogonal to the rotation axis. Here, d is the distance between the center points of adjacent semiconductor elements in the direction of the orthogonal axis, and n is an integer of 2 or more.

  As a result of such a shift, the spatial resolution in the direction of the orthogonal axis is improved to 1 / n as compared with the spatial resolution d in the case of no shift, as shown in FIG.

  Next, the operation when the two-dimensional semiconductor detectors 1 and 2 are inclined only with respect to the rotation axis (body axis) as shown in FIG. 6 will be described. In this way, the two-dimensional semiconductor detectors 1 and 2 are tilted by θ ° with respect to the rotation axis (body axis), and the above-mentioned basic movement of the whole body photographing is performed, whereby the direction of the orthogonal axis Is improved from d to cos θ from the spatial resolution d when not inclined. For example, when θ = 11.5 °, the spatial resolution in the direction of the orthogonal axis is substantially d / 5.

  In such tilt photography, as in basic hole body photography, when the counting operation is repeated in a uniform manner for all semiconductor elements, the semiconductor element moves during the counting period T as shown in FIG. In the range (thick line) to be produced, a deviation occurs between the semiconductor elements A and B adjacent to each other in the direction of the orthogonal axis. As shown in FIG. 7 (b), the time control circuits 8 and 9 start the counting period T at the start of the semiconductor so that this shift is eliminated and the counting ranges are matched between the adjacent semiconductor elements A and B. Between the elements A and B, the start time of the counting period T is set to the semiconductor so as to be shifted by a time according to the moving speed V, the distance d between the center points, and the inclination angle θ, specifically, (d · cos θ) / V. Each element is controlled individually.

  Note that the two-dimensional semiconductor detectors 1 and 2 may be reciprocated while the two-dimensional semiconductor detectors 1 and 2 are tilted, and a movement that slightly shifts in the orthogonal axis direction may be performed during the reversal. . In this case, the shifting distance is (d · cos θ) / n, and the spatial resolution in this direction can also be improved to (d−cos θ) / n.

(SPECT photography)
FIG. 8 shows an operation procedure at the time of SPECT imaging according to this embodiment, and FIG. 9 shows a trajectory of a center point of a certain semiconductor element at the time of SPECT imaging. First, the basic movement at the time of SPECT imaging is that the two-dimensional semiconductor detectors 1 and 2 are continuously rotated around the subject P, and the counting operation is performed in a constant counting period T in parallel with the continuous rotation. Thus, gamma rays can be counted with respect to the subject P from multiple directions.

  In the present embodiment, such basic movement is repeated while rotating the two-dimensional semiconductor detectors 1 and 2 around the subject a plurality of times. Each time the sample is rotated once around the sample, it is characterized in that it is shifted by a distance of d / n along the direction of the rotation axis (body axis). In this case, d is the distance between the center points of adjacent semiconductor elements in the direction of the rotation axis.

  By such a shift, the spatial resolution in the direction of the rotation axis (body axis) is improved to 1 / n as compared with the spatial resolution d in the case of no shift, as shown in FIG.

  Also in this SPECT imaging, as shown in FIG. 6, the two-dimensional semiconductor detectors 1 and 2 are tilted by θ ° with respect to the rotation axis (body axis), and the above-described basic SPECT imaging is performed. By performing the movement, the spatial resolution in the direction of the rotation axis is improved from the spatial resolution d when not tilted to d · cos θ. Again, when θ = 11.5 °, the spatial resolution in the direction of the rotation axis is approximately d / 5.

  Also in such SPECT tilt imaging, as in basic SPECT imaging, when the counting operation is repeated in a uniform manner for all semiconductor elements, the semiconductor elements are counted during the counting period T as shown in FIG. The angular range (thick line) in which the rotation of the semiconductor element is shifted due to the adjacent semiconductor elements A and B with respect to the direction of the rotation axis. As shown in FIG. 10B, the time control circuits 8 and 9 start the counting period T at the start of the semiconductor so that the deviation is eliminated and the angle ranges coincide between the adjacent semiconductor elements A and B. The start of the counting period T is shifted between the elements A and B by a time corresponding to the rotational speed ω, the distance d between the center points, and the inclination angle 0, specifically, (d · cos θ) / ω. Each element is controlled individually.

  Note that the two-dimensional semiconductor detectors 1 and 2 may be rotated a plurality of times while the two-dimensional semiconductor detectors 1 and 2 are tilted, and a movement that slightly shifts in the rotation axis direction may be performed every round. In this case, the shifting distance is (d · cos θ) / n, and the spatial resolution in this direction can also be improved to (d · cos θ) / n.

  It goes without saying that the present invention is not limited to the above-described embodiment, and can be implemented with various modifications.

  The present invention has potential applications in the field of

  DESCRIPTION OF SYMBOLS 1, 2 ... Two-dimensional semiconductor detector, 3 ... Bed, 4 ... Rotation frame, 5 ... Bed movement / shift / up / down control unit, 6 ... Whole rotation control unit, 7 ... Detector movement / tilt / shift control unit, 8 , 9 ... Time control circuit, 10, 11 ... Position / energy calculation circuit, 12 ... Image memory, 13 ... Data processing circuit, 14 ... Display circuit, 15 ... Controller, 16 ... Moving / tilting / shifting mechanism

Claims (6)

At least one two-dimensional semiconductor detector formed by two-dimensionally arranging semiconductor elements that administer a radioisotope to a subject and directly detect gamma rays emitted from the radioisotope;
A moving mechanism for moving a relative position of the two-dimensional semiconductor detector with respect to the subject;
An inclination mechanism for inclining the two-dimensional semiconductor detector with respect to a moving direction of the relative position;
Reconstructing means for reconstructing a concentration distribution of the radioisotope with respect to a cross section of the subject based on an output of the two-dimensional semiconductor detector;
In a nuclear medicine diagnostic apparatus comprising a control means for controlling the moving mechanism and the tilt mechanism,
The nuclear medicine diagnosis apparatus according to claim 1, wherein the two-dimensional semiconductor detector is moved in the predetermined direction while being inclined with respect to the movement direction of the relative position by the control by the control means. Counting means for counting gamma rays incident within a predetermined counting period as the number of photons for each semiconductor element based on the output of the two-dimensional semiconductor detector, and control for individually controlling the start of the counting period for each semiconductor element The nuclear medicine diagnosis apparatus according to claim 1, further comprising: means. The moving mechanism rotates at least one of the two-dimensional semiconductor detector and the subject, and a rotational movement mechanism that rotates the two-dimensional semiconductor detector around a rotation axis substantially parallel to the body axis of the subject. A first translation mechanism that moves along the axis,
By the control by the control means, at least one of the two-dimensional semiconductor detector and the subject moves a distance of d / n along the rotation axis every time it rotates around the subject. The nuclear medicine diagnosis apparatus according to claim 1. 4. The nuclear medicine diagnosis apparatus according to claim 3, wherein the two-dimensional semiconductor detector rotates around the subject while being tilted with respect to the rotation axis under the control of the control means. The moving mechanism includes: a first parallel moving mechanism that moves at least one of the two-dimensional semiconductor detector and the subject along the rotation axis; and at least one of the two-dimensional semiconductor detector and the subject. And a second translation mechanism that moves the axis along an orthogonal axis that is substantially orthogonal to the rotation axis,
By the control by the control means, the two-dimensional semiconductor detector reciprocates along the rotation axis, and the two-dimensional semiconductor detector moves along the orthogonal axis when the direction of movement is reversed during the reciprocation. 4. The nuclear medicine diagnosis apparatus according to claim 3, wherein the distance is d / n. An inclination mechanism for inclining the two-dimensional semiconductor detector with respect to the rotation axis;
6. The nuclear medicine diagnosis apparatus according to claim 5, wherein the two-dimensional semiconductor detector reciprocates along the rotation axis while being inclined with respect to the rotation axis by the control by the control means.

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