JP2010204125A - Radiation detector unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that an annular gamma ray detector unit in a nuclear medicine diagnostic device for mammography cannot take a breast tissue around a breast of a subject into view. <P>SOLUTION: The annular detector unit is configured to have a notch which does not have a detector block in a part of its ring. By inserting a shoulder or the like into the notch, the vicinity of the breast can be taken into view. Moreover, by having a shield B1 for being shielded from gamma rays so as to cover the notch, the intrusion of gamma rays generated in the shoulder, an arm, etc. from the notch as accidental simultaneous factors from the outside of the view can be prevented. By having the shield on the outer peripheral surface and at front surface side of the annular detector unit in addition to the notch, the accidental simultaneous factors from the outside of the view can be further prevented. By forming the shield B1 into a shape on which the arm can be placed, the subject can maintain a stable position, and more favorable diagnostic images can be generated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radiation detector unit for detecting radiation emitted from breast tissue of a subject.

  Conventionally, a general nuclear medicine diagnostic apparatus is obtained from a radiation detector unit in which a plurality of radiation detectors for detecting radiation such as gamma rays are arranged in an annular shape having a circle or a polygon, and the radiation detector unit. And an image processing unit that generates an RI distribution image based on the emission data. The radiation detector includes a scintillator in which a large number of scintillator chips that emit light upon incidence of radiation are arranged, a photomultiplier tube that converts light emitted from the scintillator into an electrical signal, and the like.

  Then, the subject is placed in the hollow portion of the radiation detector arranged in an annular shape, and a radiopharmaceutical labeled with a positron radioisotope is administered to the subject. The positron radioactive isotope distributed in the body emits radiation such as two gamma rays in the opposite direction of 180 degrees. The radiation detector detects radiation emitted from the subject. Here, the image processing unit collects, as emission data, events in which a pair of radiations are simultaneously counted, and generates a two-dimensional or three-dimensional RI distribution image based on the emission data. The generated RI distribution image is suitably used mainly for diagnosis of the presence / absence of tumor, position, malignancy, and the like.

In addition, a nuclear medicine diagnostic apparatus for mammography, which is a nuclear medicine diagnostic apparatus exclusively for photographing breasts, has been developed. Especially in the case of breast cancer, early detection is important in the treatment, and in order to find a smaller tumor, the size of the scintillator chip is made smaller, and the detector is arranged close to the subject (for example, , See Patent Document 1).
JP 2003-325499 A

However, the conventional nuclear medicine diagnostic apparatus for mammography having such a configuration has the following problems.
That is, as shown in FIG. 1, when it is intended to obtain a diagnostic image of the breast of a subject (such as a human body) M with a detector unit 6 in which a plurality of detectors 21 are arranged in a ring shape, as shown in FIG. Since the detector unit 6 hits the arm or shoulder, the area where the breast tissue such as the armpit or the base of the shoulder exists (hereinafter simply referred to as the breast periphery) cannot be included in the field of view. However, even in the breast tissue around the breast, there is a possibility that breast cancer may develop like the breast, and the breast week should also be the site to be examined together with the breast, but in the conventional configuration, for the reasons described above, There is a problem that breast tissue around the breast cannot be diagnosed.

  Therefore, the inventors of the present application cut out a part of the annular detector as shown in FIG. 3 so that the breast and the periphery of the breast can be put into the field of view, and further shown in FIG. Thus, the detector unit 62 adapted to the breast shape is invented.

However, the radiopharmaceutical administered to the subject emits gamma rays not only from the breast and its surroundings, but also from the subject's shoulders, arms, torso, and other parts of the subject. Hereinafter, gamma rays (hereinafter simply referred to as “out of the field of view”) may be mixed into detection data from the breast and its vicinity as an accidental coincidence coefficient, which may adversely affect the generation of a target breast diagnostic image (RI distribution image).

  In addition, when the measurement is performed with the posture as shown in FIG. 3, since the subject is a living body such as a human body, it is necessary to maintain an unnatural posture such as raising the arm during the measurement. It may be forced or it may move unintentionally due to its unstable posture, and in such a case, it may adversely affect the generation of the intended breast diagnostic image.

  The present invention has been made in view of such circumstances, and eliminates the influence of radiation generated outside the field of view in a mammography detector unit having a notch for entering the breast and the periphery of the breast into the field of view. It is an object to provide a detector unit that can be used. It is another object of the present invention to provide a radiation detector unit for mammography that can perform stable measurement without imposing a load on the subject.

  The present invention has been made in order to achieve such an object, and is configured in an annular shape having a hollow portion, and in a radiation detector unit having the hollow portion as a field of view, a portion of the annular shape is cut out. And a shielding shield for suppressing an accidental coincidence coefficient from the outside of the field of view is provided at least in the notch. Alternatively, the shielding shield can be provided on the outer peripheral surface and the front side of the annular detector unit in addition to the notch.

According to the radiation detector unit of the present invention, when the detector is annularly arranged so as to surround the breast, even if the inspection target external position is in the way and the desired arrangement cannot be performed, If the position is combined with the notch, the external position to be examined does not get in the way, and the detector can be placed around the breast or around the breast. As a result, the breast or breast tissue existing around the breast Can be diagnosed efficiently. At the same time, since the cutout portion includes a shielding shield for suppressing the coincidence coincidence coefficient from the outside of the field of view, a good diagnostic image can be generated. In addition, by making the arm in a shape that allows the arm to be placed, the subject can maintain a stable posture, and a better diagnostic image can be generated.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 5 is a block diagram showing the overall configuration of a mammography nuclear medicine diagnostic apparatus. This is a device for nuclear medicine diagnosis of the breast tissue of a subject (here, assuming a human body) that is a mammal having a breast. A radiation detector unit (hereinafter referred to as a gamma ray detector unit is shown as an example, but the rest 1), an image processing unit 3, and a monitor 4 are provided.

Similar to a general nuclear medicine diagnostic apparatus, this apparatus places a subject in a hollow portion of a gamma ray detector configured in an annular shape, and administers a radioactive drug labeled with a positron radioisotope to the subject. Positron radioisotopes distributed in the body emit two gamma rays in the opposite direction of 180 degrees. The gamma ray detector 2 detects gamma rays emitted from the subject. The gamma ray detector 2 is mainly composed of a scintillator in which a large number of scintillator chips that emit light upon incidence of gamma rays are arranged, a photomultiplier tube that converts light emitted from the scintillator into an electric signal, and the like. On the other hand, the image processing unit 3 is realized by a central processing unit (CPU) that reads and executes a predetermined program, a RAM (Random-Access Memory) that stores various information, a storage medium such as a fixed disk, and the like. The emission data collection unit 31 collects the events in which the gamma rays are simultaneously counted, and the RI distribution image generation unit 32 generates a two-dimensional or three-dimensional RI distribution image based on the emission data.

The configuration of the gamma ray detector unit 1 will be described with reference to FIG. 6 which is a horizontal sectional view.
The gamma ray detector unit 1 includes a detector 2 that is a generic name of a group of detectors in which a plurality of detector blocks 21 that detect gamma rays are arranged in a ring shape having a hollow portion A. The detector 2 can further include a housing that houses a group of detectors. The term “annular” as used in the present invention encompasses all shapes having a closed curve or a polygon having a hollow portion. Horseshoe shape, U-shape, teardrop shape, ellipse shape, rugby ball shape, and other various contour shapes can be selected.

  The configuration of each detector block 21 will be described with reference to FIG. A scintillator 211 that converts gamma rays into light, a photomultiplier 212 that converts light into an electrical signal, a light guide 213 that guides light from the scintillator 211 to the photomultiplier 212, and the like. The scintillator 211 is an aggregate in which scintillator chips 211a are arranged in a matrix (for example, 8 rows × 8 columns) and stacked in a plurality of stages (for example, 2 stages), and the upper surface is the detection surface of the detector block 21. It becomes. That is, the direction in which the detection surface faces (detectable direction) becomes the “field of view” for detection. Thus, as shown in FIG. 6, the detection surfaces C of the plurality of detector blocks 21 are arranged in an annular shape so as to face the hollow portion A, thereby forming a detection surface C as shown in FIG. 5. Strictly speaking, the hollow portion A has a polygonal shape approximated to a substantially circular shape as shown in FIG.

The detector 2 can also be a multilayer ring in which the detector blocks 21 are stacked. FIG. 8 is a cross-sectional view along the line aa indicated by a broken line in FIG. Now, the detection surface C of the detector 2 is a surface perpendicular to the bottom surface of the hollow portion A, but is not limited to this. Here, the hollow portion A has a columnar shape having a substantially cylindrical shape (strictly, a polygonal column shape). The hollow portion A, which is the column space, serves as a field of view in the detector 2, and a breast or a breast tissue around the breast is inserted into the hollow portion A for measurement. In addition, the detector 2 can block the outside of the visual field on one side by providing the front plate D as necessary, can prevent the breast from protruding from the visual field, and can appropriately diagnose the entire breast.

  In the present invention, as shown in FIG. 6, the detector 2 has a shape in which a notch B is formed in a part of the ring in the annular arrangement of the detector block 21. The diameter of the hollow portion A is exemplified as a value within the range of 160 mm to 250 mm, and the length of the inner arc of the cutout portion B is exemplified as 50 mm to 150 mm. However, each dimension is not limited to these numerical ranges. The notch B is provided to insert the base of the arm or / and the shoulder on the same side as the breast of the subject M, thereby surrounding the detector 2 at the lower part of the breast. One end side of the breast is located in the range up to the base of the shoulder above the breast, and the other end side can be placed in the range up to the armpit on the side of the breast. In this way, not only the breast but also breast tissue around the breast such as the armpit and shoulder base that could not be put in the field of view in the past can be put in the field of view of the detector 2.

  Furthermore, the present invention is characterized in that a gamma ray shielding shield B1 is disposed in the notch B. The radiopharmaceutical administered to the subject emits gamma rays not only from the breast and its surroundings, but also from the shoulder, arm, torso of the subject, and other parts. The main purpose of the shield B1 for shielding gamma rays is to prevent such gamma rays from outside the field of view from entering the detector from the notch B as an accidental coincidence coefficient. In FIGS. 5 and 6, the gamma ray shielding shield B1 is formed of a plate-like object curved convexly with respect to the hollow portion A, and both ends thereof are connected to both ends of the detector with the notch B interposed therebetween. The notch B is configured to be closed. Alternatively, in order to shield not only gamma rays from the base of the shoulder and arm but also out-of-view gamma rays from the elbow and the entire arm, the length may be extended along the arm as shown in FIG. The length of the shield B1 is exemplified by a value within the range of 100 mm to 600 mm, but is not limited to this numerical range, and is appropriately selected according to the body shape of the subject. Alternatively, as shown in FIG. 10, it may be configured to be integrated with the housing of the detector 2 as shown in FIG. 10, and the shape is not semi-cylindrical as long as the cutout portion B can be shielded. Of course, it does not matter even if it consists of a plane.

  When the gamma-ray shielding shield B1 has a shape on which an arm can be placed, the subject can take a comfortable posture, so that the posture can be easily maintained stably. In addition to reducing the burden, stable measurement is possible and a good breast diagnostic image can be obtained.

  Further, not only the gamma ray shielding shield B1, but also a gamma ray shielding shield can be provided so as to cover the outer periphery of the detector 2, or the entire casing (excluding the detection surface C) covering the entire detector 2 can be shielded. By using a shield material, or by configuring the front plate D or member 22 shown in FIG. 8 from a shield material capable of gamma ray shielding, it is possible to further reduce the occurrence of random coincidence coefficients from outside the field of view. .

It is more preferable that the gamma ray detector unit 1 further includes a rotation support portion 22 for changing the posture of the detector unit 1 so that the left and right breasts can be easily diagnosed. For example, as illustrated in FIGS. 5 and 8, the gamma ray detector unit 1 is fixed to the gamma ray detector unit 1. Adjust the position. In this embodiment, the uniaxial P is coincident with the central axis of the substantially circular hollow portion A, but is not limited thereto. The rotation operation is not limited to manual operation and does not prevent the use of a power source such as a motor. By attaching the rotation support part 22, the left and right breasts can be easily diagnosed.

  Next, the operation of the mammography nuclear medicine diagnostic apparatus provided with the gamma ray detector unit according to the above embodiment will be described.

  As shown in FIGS. 5 and 9, either the left or right breast of the subject M is placed in the hollow portion A of the detector 2, and the root of the arm on the same side as the breast of the subject M or the notch B / And the shoulder is inserted, and the arm or the like is brought into contact with the shield B1 for shielding gamma rays. The detector 2 surrounds the lower part of the breast, one end side of the detector 2 is located in a range up to the base of the shoulder above the breast, and the other end side of the detector 11 is located in a range up to the armpit on the side of the breast. . The periphery of the breast, such as the armpit or the base of the shoulder, and the breast are sandwiched by the detection surface C of the detector 2 and enter the field of view of the detector 2. In addition, since there is the gamma ray shielding shield B1, the external position to be inspected such as the arm and the shoulder does not enter the visual field of the detector 2 too much.

  Next, a radiopharmaceutical labeled with a positron radioisotope is administered to the subject M. The positron radioactive isotope emits two gamma rays in the subject M in directions opposite to each other by 180 degrees. The detector 2 detects gamma rays emitted from the breast and the periphery of the breast and reaching the detection surface C, and outputs an electrical signal.

  The emission data collection unit 31 collects emission data from the detection result of the detector 2. Specifically, each electrical signal output from the detector 2 is once recorded in the memory together with its position information and time information, and when the detection by the detector 2 is completed, the data is read from the memory and counted simultaneously. A certain event is judged, and this event is counted to obtain emission data.

  The RI distribution image generation unit 32 performs a reconstruction process based on the collected emission data, and generates a two-dimensional or three-dimensional RI distribution image. As an example of reconstruction processing, a successive approximation image reconstruction method (for example, OSEM (Ordered Subset Expectation Maximization) algorithm (see Takayuki Nakamura, Hiroyuki Kudo IEEE Nuclear Science Symposium Conference Record 2005 pp. 1950-54)) is preferable. According to this method, it is possible to generate an RI distribution image in which the influence of the cutout portion B is sufficiently suppressed.

  Now, twelve detector blocks in which 32 scintillator chips with a length and width of 1.5 mm and a length of 4.5 mm are stacked in four layers in the length direction and arranged in rows and columns of 32 are arranged in a circle with a diameter of 208 mm. As a result of the simulation by the reconstruction method using the OSEM algorithm when one of the detector blocks is not extracted as the notch B, the spatial resolution at 70 mm from the center of the field of view is the notch In the case where B is not present, 1.3 mm is obtained, whereas in the case where the notch B is present, 1.6 mm is obtained, and it was found that the notch B is hardly affected by the present reconstruction method.

  Note that, instead of the reference successive approximation image reconstruction method, an existing method such as a 3D Fourier transform method, a 3D-FBP method, a rebinning method (rebinning), a 3D reprojection method, or a FORE method (Fourier rebinning) may be selected. Good.

  The generated RI distribution image is output to the monitor 4 as appropriate.

  When the diagnosis of one of the left and right breasts is completed, an operator or the like manually operates the rotation support unit 22 to rotate the detector unit 1 around one axis P. Thereby, the posture of the detector unit 1 is changed so that the other breast can be easily diagnosed. Then, the other breast is diagnosed in the same procedure.

The present invention is not limited to the above embodiment, and can be modified as appropriate.

It is a figure which shows the use condition of the annular detector unit 6 in the conventional nuclear medicine diagnostic apparatus for mammography. It is the figure which looked at the use condition shown in FIG. 1 from the side. It is a figure which shows the use condition of the annular detector unit 61 which has a notch part. It is a figure which shows the use condition of the cyclic | annular detector unit 62 which has a notch part. It is a figure which shows the whole structure of the nuclear medicine diagnostic apparatus for mammography provided with the radiation detector unit which concerns on this invention. It is a horizontal sectional view of a radiation detector unit concerning the present invention. It is a perspective view of a detector block. FIG. 7 is a vertical sectional view taken along the line aa shown in FIG. 6. It is a figure which shows the use condition of the radiation detector unit which concerns on this invention. It is a figure which shows the modification Example of the radiation detector unit which concerns on this invention.

DESCRIPTION OF SYMBOLS 1 Radiation detector unit 2 Radiation detector 21 Detector block 211 Scintillator 211a Scintillator chip 212 Photomultiplier 213 Light guide 22 Rotation support part 3 Image processing part 31 Emission data collection part 32 RI distribution image generation part 4 Monitor A Hollow part B Notch B1 Radiation shielding shield C Detection surface D Front plate

Claims (5)

A plurality of radiation detector blocks are arranged in an annular shape having a hollow portion, provided with a radiation detector having the hollow portion as a field of view, and a notch portion without a radiation detector block is formed in a part of the ring, at least A radiation detector unit comprising a radiation shielding shield at the notch. The radiation detector unit according to claim 1, wherein the notch is formed to have a size that allows insertion of a base or shoulder of an arm of a subject. The radiation detector unit according to claim 1, wherein the radiation shielding shield is formed in a size and shape on which an arm of a subject can be placed. The radiation detector unit according to claim 3, further comprising a housing for accommodating the radiation detector, wherein the radiation detector unit is formed integrally with the radiation shielding shield. The radiation detector unit according to claim 1, wherein the shielding shield is provided on an outer peripheral surface and / or a front surface of the annular radiation detector.

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