JP4377468B2 - Radiation detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radiation detection apparatus.
[0002]
[Prior art]
A SPECT (Single Photon Emission Computed Tomography) device used as a nuclear medicine diagnostic device is to obtain a distribution of radioactive material (radiotracer) incorporated into a subject as an image, A radiation detection apparatus is provided that collects image data generated from a subject by detecting radiation emitted from the subject with a two-dimensional radiation detector.
[0003]
As this type of radiation detection apparatus, a two-dimensional radiation detector is used as a γ camera (scintillation camera), and the γ camera is rotated around the subject around the body axis of the subject. What detects the radiation to be radiated is described in, for example, Japanese Utility Model Publication No. 61-16537 and Japanese Patent Laid-Open No. 9-5442.
[0004]
In Japanese Patent Publication No. 4-34114, a number of two-dimensional radiation detectors are arranged so as to surround the entire circumference of the subject in an annular shape, and collimator portions of these detectors are attached to holding rings, respectively. A radiation detection apparatus is disclosed in which each detector uniformly scans a subject at the same scanning angle by rotating a holding ring.
[0005]
[Problems to be solved by the invention]
However, the apparatus described in Japanese Utility Model Publication No. 61-16537, Japanese Patent Application Laid-Open No. 9-5442, and Japanese Patent Publication No. 4-34114 has the following problems.
[0006]
That is, in a configuration in which the detector is rotated around the subject in a circular orbit, or arranged in an annular shape around the subject to collect data, the human body has an ellipsoidal cross section. The distance between the long axis direction and the short axis direction is greatly different from that of the subject. In particular, the short axis direction detector has a problem that the distance to the subject becomes long and the resolution is deteriorated. It was.
[0007]
Further, in the apparatus described in Japanese Utility Model Publication No. 61-16537, since the subject is photographed with one camera, the camera head is inevitably increased in size and weight, and the camera is rotated around the subject. There is a problem that the mechanism to be made becomes complicated and expensive. Further, since the weight is so heavy, it is not easy to swing the camera head and scan, and it is difficult to collect data in a short time.
[0008]
In the apparatus described in Japanese Patent Publication No. 4-34114, since each detector scans the subject uniformly at the same scanning angle, the length of the subject is detected by the detector on the short axis direction side of the subject. When scanning the entire axial direction (substantially 180 ° on one side of the subject), the detector on the long axis direction side of the subject scans a useless range (a range where the subject does not exist), and effective data is efficiently obtained. There is a problem that it cannot be collected.
[0009]
Further, in the subject, the path in the major axis direction is longer than that in the minor axis direction, and the absorption of radiation in the body in the major axis direction is increased. If the scanning angle is the same for the detector on the axial direction side (the measurement time per unit angle is the same), the radiation dose detected by the detector on the long axis direction side will be reduced, and the data in the long axis direction will be reduced. There is also a problem that the statistical noise is worse than that in the minor axis direction, and as a result, the signal-to-noise ratio (S / N) is deteriorated. Note that the noise referred to here is a statistical variation of the signal, and generally the count value follows Poisson statistics, so the square root of the count N is the standard deviation of the noise.
[0010]
The present invention has been made in order to solve such a problem, and can improve the resolution, reduce the cost by reducing the weight of the detector and shorten the data collection time. An object of the present invention is to provide a radiation detection apparatus that can efficiently collect effective data of a specimen and can improve S / N.
[0011]
[Means for Solving the Problems]
The radiation detection apparatus according to the present invention includes a plurality of two-dimensional radiation detectors capable of detecting radiation emitted from a subject around the subject and performing a swing motion for the purpose of scanning the subject to be measured. The detectors are arranged at least in part on a virtual elliptic curve that surrounds the subject in a substantially elliptical shape, and the swing angle varies depending on the measurement target of the subject at the same position on the virtual elliptic curve. It is characterized by that.
[0012]
According to the radiation detection apparatus configured as described above, the cross-sectional shape of the subject forms an approximately ellipsoid, and a plurality of detectors capable of detecting the radiation emitted from the subject include the subject as an approximately ellipse. Therefore, the distance between the subject and the detector is substantially the same regardless of the position of the detector on the virtual elliptic curve.
[0013]
In addition, since a plurality of detectors that can be swung in order to scan the subject or to direct a predetermined part of the subject are used, the detector is smaller than the device described in Japanese Utility Model Publication No. 61-16537. The weight can be reduced and the lighter can be easily swung by the detector.
[0014]
Further, each detector does not scan the subject uniformly at the same scanning angle as in the apparatus described in Japanese Patent Publication No. 4-34114, but each detector has a swing angle depending on the position on the virtual elliptic curve. Therefore, by setting the swing angle of the detector on the long axis side of the subject to be smaller than the swing angle of the detector on the short axis side (in this case, the scanning time is the same), The detector on the long axis direction side is prevented from scanning a useless range (the range in which the subject does not exist), and the measurement time per unit angle with the detector on the long axis direction side of the subject is short axis direction The measurement time per unit angle at the side detector is longer than the measurement time, and a decrease in the radiation dose detected by the detector on the long axis direction side of the subject is suppressed.
[0015]
Here, the detector is preferably movable on a virtual elliptic curve.
[0016]
When such a configuration is adopted, even if the detector is not arranged on the entire virtual elliptic curve, the detector is moved on the virtual elliptic curve, so that the image data generated from the subject has a direction of 360 °. Detected from.
Moreover, it is preferable that the swing angle of the detector on the long axis direction side on the virtual elliptic curve is larger than the swing angle of the detector on the short axis direction side. Thus, by making the swing angle of the detector on the long axis side of the subject smaller than the swing angle of the detector on the short axis side (in this case, the scanning time is the same), The detector is prevented from scanning a useless range (a range where the subject does not exist), and the measurement time per unit angle at the detector on the major axis side of the subject is measured on the minor axis side detector. Is longer than the measurement time per unit angle, and the decrease in the radiation dose detected by the detector on the long axis direction side of the subject is suppressed.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a radiation detection apparatus according to the invention will be described with reference to the accompanying drawings. Note that, in each drawing, the same elements are denoted by the same reference numerals, and redundant description is omitted.
[0018]
FIG. 1 is a perspective view showing an outline of a radiation detection apparatus according to an embodiment of the present invention. In FIG. 1, a subject table 1 is used to place a subject 2 to be examined, and is fixedly supported by a fixing unit (not shown) so as to be horizontal. An annular detector support ring 3 is disposed around the subject 2 on the subject table 1 so as to surround the subject 2. The detector support ring 3 is arranged substantially coaxially with the body axis of the subject 2 on the subject table 1 and is rotated by driving of a detector support ring rotating motor 4 fixedly supported by the fixing portion.
[0019]
A plurality of detector contact / separation motors 6 are fixed to the detector support ring 3 side by side along the circumferential direction, and the rotational driving force of each detector contact / separation motor 6 as shown in FIGS. 1 and 2. , And the feed screw 7 that rotates is screwed together. The feed screw 7 is arranged so that the axis thereof is generally directed to the body axis of the subject 2, and is in contact with and separated from the subject 2 individually by driving the corresponding detector contacting / separating motor 6 (see FIG. 1 and FIG. 1). It is moved while rotating in the direction of arrow A shown in FIG.
[0020]
A support arm 8 having a U-shape is provided at the subject side end of the feed screw 7. While the support arm 8 and the feed screw 7 are rotatably connected to each other, the support arm 8 is attached to the detector support ring 3 so as not to be rotated with the feed screw 7 by a detent member (not shown). Connected to each other. That is, the support arm 8 is moved in the direction A in which the support arm 8 contacts and separates from the subject 2 without rotating by the driving of the detector contact / separation motor 6.
[0021]
As shown in FIG. 2, a detector swing motor 9 is fixed to one end of the support arm 8 (the end on the near side in the figure). The dimensional radiation detector 5 is fixed. In the present embodiment, the two-dimensional radiation detector 5 is a γ camera that detects γ rays as radiation, and collects image data generated from the subject 2 by detecting γ rays emitted from the subject 2. To do. These two-dimensional radiation detectors (hereinafter simply referred to as detectors) 5 are individually smaller and lighter than the camera described in Japanese Utility Model Publication No. 61-16537.
[0022]
The detector 5 is arranged such that its detection surface faces the subject 2 and swings along the outer peripheral surface of the subject 2 by driving the detector swing motor 9, that is, in the direction of arrow B in the figure. It is configured to swing. A pin (not shown) that is coaxial with the output shaft 10 of the detector swing motor 9 and faces the detector 5 is located at the other end of the support arm 8 (the end on the far side in FIG. 2). It protrudes and is made into the structure which supports the said detector 5 rotatably from the other side.
[0023]
As shown in FIGS. 4 and 5, the detector 5 has a substantially rectangular parallelepiped shape as a whole. As shown in FIG. 4, the detector 5 arrives at the subject side portion from a direction perpendicular to the detector surface. It has a collimator 11 that allows gamma rays to pass through.
[0024]
The detector body is housed in a light shielding case 12 so that the collimator 11 protrudes outside, a scintillator 13 that receives γ-rays incident through the collimator 11 and emits photons according to the amount of received light; A photomultiplier-tube (hereinafter simply referred to as PMT) 16 that receives photons from the scintillator 13 on the photocathode 14 and outputs an electrical signal corresponding to the received light amount via a preprocessing circuit 15; Prepare.
[0025]
The collimator 11 is made of, for example, lead or tungsten. As the scintillator 13, for example, CsI (Na), CsI (Tl), YSO, NaI (Tl) or the like is employed. The scintillator 13 has a mosaic shape in which each is separated, and a reflecting material 17 is installed around each segment. Instead of using the reflector 17 between the segments, the segments may be separated using the refractive index difference between the air layer and the crystal.
[0026]
The PMT 16 is a position detection type PMT using a channel type dynode 18, and a multi-anode (possibly a cross-anode) 19 is disposed in the subsequent stage. In the light shielding case 12, a voltage supply line 20 for supplying power is connected and a signal output line 21 for outputting a signal from the preprocessing circuit 15 is connected, and a SPECT image is obtained according to this output. Has been made.
[0027]
1 and 2 again, each of the detector contact / separation motors 6 described above moves each detector 5 in the direction A to contact / separate the subject 2 so that each detector 5 moves to the subject 2. Is driven so as to be positioned on a virtual elliptic curve C (see FIG. 3) that surrounds substantially in an elliptical shape. This is because the cross-sectional shape of the subject 2 is substantially an ellipsoid as shown in FIG. 3, and the distance between the approximate ellipsoid and the detector 5 is substantially constant regardless of the position of the detector 5. It is. In this embodiment, the detector 5 is arranged approximately half a circumference around the subject 2 so as to cover approximately 180 ° in front of the subject 2 on the subject table 1 (see FIG. 3). In FIG. 1, in order to avoid complication of the drawing, a detector set including a detector 5, a detector swing motor 9, a support arm 8, a feed screw 7 and a detector contact / separation motor 6. Only three sets are shown.
[0028]
Further, each detector contact / separation motor 6 is always connected to each detector 5 even if the detector support ring 3 is rotated by driving the detector support ring rotation motor 4 and the position of each detector 5 is moved. It is driven so as to be positioned on the virtual elliptic curve C.
[0029]
Thus, the detector support ring rotation motor 4 and the detector support ring 3 correspond to a detector set rotation mechanism that rotates the detector set, and the detector contact / separation motor 6, feed screw 7, and support arm 8. Corresponds to a detector virtual elliptic curve arrangement mechanism that positions the detector 5 on the virtual elliptic curve C, and the detector virtual elliptic curve arrangement mechanism and the detector assembly rotation mechanism This corresponds to a detector elliptic trajectory forming mechanism that moves on the virtual elliptic curve C to draw a substantially elliptic trajectory, and a detector swing motor 6 connected to the detector 5 swings the detector 5. This corresponds to a detector swing mechanism.
[0030]
Then, by driving the detector swing motor 6, the swing scanning angle for swinging the detector 5 relative to the subject 2 is set in advance according to the position on the virtual elliptic curve C of the detector 5. Each of the detectors 5 is independently scanned and is configured not to scan a useless data collection range (details will be described later).
[0031]
In addition, in this embodiment, a parallel movement mechanism (not shown) that moves the detector assembly rotation mechanism in parallel over the entire length of the subject 2 is provided. As a result, the entire front surface of the subject 2 can be scanned.
[0032]
When the front side of the subject 2 is swung with the radiation detection apparatus configured in this way, first, each detector 5 is directed so as to direct the subject 2 at each preset orientation angle. Swing and set (see FIG. 3A). Next, the detector 5 is scanned at each preset swinging angle set in advance (see FIG. 3B). At this time, each detector 5 scans the subject 2 at a swing scanning angle that covers the subject 2, and each swing scanning angle varies depending on the position on the virtual elliptic curve C.
[0033]
Here, the reason why the swing scanning angle can be varied depending on the position of each detector 5 on the virtual elliptic curve C will be described below.
[0034]
FIG. 6 is a schematic diagram showing detectors arranged in an annular shape with respect to the circular body P, and FIG. 7 is a diagram in which the horizontal axis is the distance T between the center of the visual field (center of inspection object) and an arbitrary point R, This is a sinogram display when the vertical axis is the angle θ with respect to the center of the visual field of an arbitrary point R and the moving range of the arbitrary point R is a circular body P, and the rectangular inner portion X surrounded by a bold line is the data existence of the circular body P Indicates the range. FIG. 8 is a schematic diagram showing detectors arranged in an annular shape with the ellipsoid Q as an object, and FIG. 9 is a sinogram display of the ellipsoid object, where the hyperbolic portion Y surrounded by a thick line is the data existence range of the ellipsoid. Indicates.
[0035]
FIG. 7 shows the data ranges collected by the detectors J to N shown in FIG. 6, and FIG. 9 shows the data ranges collected by the detectors J to N shown in FIG. Yes. As shown in FIG. 7, in order to cover the data existence range X of the circular body P, it is necessary to scan all the detectors with a wide swing scanning angle Δθ1, but as shown in FIG. In order to cover the data existence range Y, the swing scanning angle Δθ3 of the detector K on the long axis side is smaller than the swing scanning angle Δθ2 of the detector J on the short axis direction side of the ellipsoid Q. good.
[0036]
That is, when the cross-sectional shape is substantially an ellipsoid like a subject, the swing scanning angle can be varied depending on the position of each detector. Here, in the prior art (Japanese Patent Publication No. 4-34114), since the scanning angles of all the detectors are the same, the detector on the long axis direction side of the subject 2 has a useless range (of the subject 2). However, in this embodiment, as described above, the swing of the detector on the long axis direction side of the subject 2 is not possible. The scanning angle is different from the oscillation scanning angle of the detector on the short axis direction side so that the oscillation scanning angle of the detector on the long axis side is smaller than the oscillation scanning angle of the detector on the short axis direction side. Therefore, the detector on the long axis direction side is prevented from scanning a useless range, and effective data of the subject 2 can be collected efficiently.
[0037]
In addition, in the present embodiment, each detector 5 is arranged on a part of the virtual elliptic curve C that surrounds the subject 2 in a substantially elliptical shape, so that the distance between the subject 2 and the detector 5 is small. Regardless of the position of the detector 5 on the virtual elliptic curve C, it is substantially the same, so that the resolving power can be improved.
[0038]
In addition, the swing scanning angle of each detector 5 varies depending on the position on the virtual elliptic curve C, and as described above, the swing angle of the detector 5 on the major axis side of the subject 2 is detected on the minor axis side. The measuring time per unit angle at the detector 5 on the long axis direction side of the subject 2 is set to be smaller than the swing angle of the detector 5 (in this case, the scanning time is the same). The measurement time per unit angle in 5 is longer than the measurement time, and the decrease in the radiation dose detected by the detector 5 on the long axis direction side of the subject 2 is suppressed. As a result, the S / N can be improved. It is also possible to collect data depending on the passage thickness of γ rays by controlling the angular scanning speed nonlinearly.
[0039]
In addition, since a large number of detectors 5 are used, the detector 5 is reduced in size and weight as compared with the apparatus described in Japanese Utility Model Publication No. 61-16537, and the detector 5 can be swung by the weight reduction. It is easy to implement. As a result, it is possible to reduce the cost and shorten the data collection time (speed up the data collection).
[0040]
In addition, since each detector 5 is moved on the virtual elliptic curve C, the image data generated from the subject 2 can be detected from a direction of 360 °, and the detector 5 is not present on the virtual elliptic curve C. Also, data around 360 ° around the subject can be obtained.
[0041]
By the way, when the radioactive substance administered to the subject 2 accumulates only in a specific organ (for example, accumulation of the myocardium), as shown in FIG. The individual detector head motors 9 are preferably driven toward the target organ (heart in FIG. 10) 2a. Thus, even when the radioactive substance administered to the subject 2 accumulates only in the specific organ 2a, each detector 5 is directed to a specific organ by varying the swing angle depending on the position on the virtual elliptic curve C. By doing so, the S / N can be improved.
[0042]
As described above, the present invention has been specifically described based on the embodiment. However, the present invention is not limited to the above embodiment. For example, in the above embodiment, the plurality of detectors 5 include the virtual elliptic curve C. Although it is arranged only approximately half the circumference around the upper subject, it may of course be arranged all around. In addition, each detector 5 may be installed at an angle of 180 ° or less, or each detector 5 may be discretely installed around the subject apart from each other.
[0043]
The detector (γ camera) 5 may be a semiconductor detector such as CdZnTe.
[0044]
【The invention's effect】
A radiation detection apparatus according to the present invention includes at least a plurality of detectors capable of detecting radiation emitted from a subject (whose cross-sectional shape forms a substantially ellipsoid) on a virtual elliptic curve that surrounds the subject in a substantially elliptic shape. Because it is arranged in part and the distance between the subject and the detector is configured to be substantially the same regardless of the position on the virtual elliptic curve of the detector, the resolution can be improved. Become. In addition, a plurality of detectors capable of scanning the subject or swinging to direct a predetermined part of the subject are used, and the detector is reduced in size and weight as compared with the apparatus described in Japanese Utility Model Publication No. 61-16537. In addition, since it is configured so that the scanning of the detector can be easily performed by reducing the weight, the cost can be reduced and the data collection time can be shortened. Further, each detector does not scan the subject uniformly at the same scanning angle as in the device described in Japanese Patent Publication No. 4-34114, but the swing angle of each detector is determined by the position on the virtual elliptic curve. Differently, by setting the swing angle of the detector on the major axis side of the subject to be smaller than the swing angle of the detector on the minor axis side (in this case, the scanning time is the same), the major axis direction of the subject The measurement time per unit angle with the detector on the long axis direction of the subject is measured as the measurement time per unit angle with the detector on the short axis direction. Since it is configured to be longer and to suppress a decrease in the radiation dose detected by the detector on the long axis direction side of the subject, it becomes possible to efficiently collect effective data of the subject, It is possible to improve the S / N.
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing a radiation detection apparatus according to an embodiment of the present invention.
FIG. 2 is an enlarged perspective view showing a detector virtual elliptic curve arrangement mechanism and a detector swing mechanism constituting the radiation detection apparatus.
FIG. 3 is an operation explanatory diagram when a detector constituting the radiation detection apparatus swings and scans a subject.
FIG. 4 is a configuration diagram showing a detector.
FIG. 5 is an external perspective view showing the detector with the collimator and the light shielding case removed.
FIG. 6 is a schematic diagram showing detectors arranged in a ring for a circular body.
7 is an explanatory diagram showing a data range collected by each detector shown in FIG. 6; FIG.
FIG. 8 is a schematic diagram showing detectors arranged in an annular shape for an ellipsoid.
9 is an explanatory diagram showing a data range collected by each detector shown in FIG. 8. FIG.
FIG. 10 is an operation explanatory diagram when the detector is directed to a predetermined part of the subject.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Subject table, 2 ... Subject, 2a ... Heart (predetermined part of subject), 3 ... Detector support ring, 4 ... Detector support ring rotation motor, 5, JN ... Two-dimensional radiation detector, 6 ... Detector contact / separation motor, 7 ... Feed screw, 8 ... Support arm, 9 ... Detector swing motor, C ... Virtual elliptic curve.

Claims (3)

A plurality of two-dimensional radiation detectors capable of detecting radiation emitted from the subject around the subject and performing a swing motion for the purpose of scanning the subject to be measured;
Each detector is arranged on at least a part of a virtual elliptic curve that surrounds the subject in a substantially elliptical shape, and has a swing angle in accordance with the measurement target of the subject at the same position on the virtual elliptic curve. A radiation detection apparatus characterized by being different.   The radiation detector according to claim 1, wherein the detector is movable on the virtual elliptic curve. 3. The radiation detection apparatus according to claim 1, wherein a swing angle of the detector on the long axis direction side on the virtual elliptic curve is larger than a swing angle of the detector on the short axis direction side. .

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