JP5784915B2 - Radiation detector and radiation image acquisition apparatus including the same - Google Patents

Description

  The present invention relates to a radiation detector and a radiation image acquisition apparatus including the radiation detector.

  Conventionally, with regard to X-ray image detection technology, a direct conversion method that directly detects radiation by detecting charges generated by radiation incident on a detector, and a radiation conversion member such as a scintillator material. An indirect conversion method is known, in which the light is converted into light using a light and then detected by a detector. These two conversion methods tend to limit the detection energy band of radiation. In order to deal with such problems, a radiation conversion film made of a scintillator material is provided on the detection surface of a radiation detection element that directly detects radiation, and the radiation that has passed through the radiation conversion film and the scintillation light converted by the radiation conversion film Has been devised (see Patent Document 1 below). According to such a configuration, radiation detection efficiency is improved, and image data with a good S / N can be acquired.

JP 2000-46951 A

  However, in the conventional configuration as described above, since radiation in a wide energy band is detected by the same detector, image blur tends to occur in the obtained image data. This is because radiation in a relatively low energy band is easily converted into scintillation light by the wavelength conversion film, and the radiation detection element detects the scintillation light transmitted through the radiation conversion film. In the case of radiation, the detection signal (S) tends to decrease, but in the high energy band, the noise to the detection signal is likely to increase due to the spread scintillation light, and the S / N of the detection signal of radiation in a wide energy band decreases. It is because it ends.

  Therefore, the present invention has been made in view of such problems, and provides a radiation detector capable of acquiring a radiation detection image with less blur over a wide energy band and a radiation image acquisition apparatus including the radiation detector. With the goal.

  In order to solve the above-described problems, a radiation detector according to the present invention includes a planar wavelength conversion member that generates scintillation light in response to incidence of radiation transmitted through an object, and radiation that detects radiation transmitted through the wavelength conversion member. A detection element; and a shielding member that is disposed between the wavelength conversion member and the radiation detection element and prevents scintillation light from entering the radiation detection element.

  According to such a radiation detector, the radiation in the relatively low energy band among the radiation transmitted through the object is converted into scintillation light by the wavelength conversion member and arranged on the radiation incident surface side of the wavelength conversion member. When the scintillation light is detected by the detector, it can be detected as an image signal. At the same time, of the radiation that has passed through the object, radiation in a relatively high energy band passes through the wavelength conversion member and the shielding member and is directly detected as an image signal by the radiation detection element. At this time, since the shielding member prevents the scintillation light from entering the radiation detection element, the S / N in the image signal in the high energy band is improved and the scintillation light is detected on the incident surface side of the wavelength conversion member. Therefore, it is possible to prevent image blur in an image signal in a low energy band. As a result, an image with a good S / N of the radiation detection signal can be acquired over a wide energy band. Note that “radiation in a relatively low energy band” and “radiation in a relatively high energy band” mean radiation having energy bands separated from each other or radiation having a common energy band.

  Alternatively, the radiation image acquisition apparatus of the present invention includes a radiation source that emits radiation, and a planar wavelength conversion member that generates scintillation light in response to incidence of radiation emitted from the radiation source and transmitted through the object; An imaging element that images the scintillation light emitted from the radiation incident surface of the wavelength conversion member, a radiation detection element that detects radiation transmitted through the wavelength conversion member, and the wavelength conversion member and the radiation detection element And a shielding member that prevents the scintillation light from entering the radiation detection element.

  According to such a radiation image acquisition apparatus, the radiation in the relatively low energy band out of the radiation transmitted through the object is converted into scintillation light by the wavelength conversion member and arranged on the radiation incident surface side of the wavelength conversion member. The scintillation light is detected by the image pickup device thus made, and can be detected as an image signal. At the same time, of the radiation that has passed through the object, radiation in a relatively high energy band passes through the wavelength conversion member and the shielding member and is directly detected as an image signal by the radiation detection element. At this time, since the shielding member prevents the scintillation light from entering the radiation detection element, the S / N in the image signal in the high energy band is improved and the scintillation light is detected on the incident surface side of the wavelength conversion member. Therefore, it is possible to prevent image blur in an image signal in a low energy band. As a result, the low energy band radiographic image captured by the imaging element and the high energy band radiographic image detected by the radiation detection element are separately acquired, so a wide energy band can be obtained by adding the acquired images. An image with a good S / N of the radiation detection signal can be obtained. Moreover, a favorable energy subtraction image can be acquired by subtracting the acquired images.

  The shielding member is preferably a planar member having a light shielding property against scintillation light. If such a shielding member is provided, S / N can be reliably improved over a wide energy band.

  The shielding member is also preferably a planar reflecting member that reflects scintillation light. In this case, the S / N ratio in the image signal in the high energy band can be improved, and the detection efficiency of the image signal in the low energy band can be improved.

  Furthermore, it is also preferable that the shielding member blocks a low energy band of radiation. By adopting such a configuration, it is possible to prevent the low energy band radiation incident from the wavelength conversion member side from entering the radiation detection element, and to further improve the S / N in the high energy band image signal.

  According to the present invention, a radiation detection image with little blur can be acquired over a wide energy band.

It is a front view of the radiographic image acquisition apparatus which concerns on suitable one Embodiment of this invention. It is a front view which expands and shows the radiation detector of FIG. It is a front view which shows the assembly state of the radiation detector of FIG. It is a front view which shows the assembly state of the radiation detector of FIG. It is a front view of the radiation detector which is a modification of this invention. It is a front view of the radiographic image acquisition apparatus which is a modification of this invention. It is a front view of the radiographic image acquisition apparatus which is a modification of this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a radiation detector according to the present invention and a radiation image acquisition apparatus using the same will be described in detail with reference to the drawings. In the description of the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted. Each drawing is made for the purpose of explanation, and is drawn so as to particularly emphasize the target portion of the explanation. Therefore, the dimensional ratio of each member in the drawings does not necessarily match the actual one.

  FIG. 1 is a front view showing a schematic configuration of a radiation image acquisition apparatus 1 according to a preferred embodiment of the present invention. FIG. 2 is an enlarged front view showing the radiation detector 3 of FIG. 4 is a front view showing an assembled state of the radiation detector 3 of FIG. As shown in FIG. 1, the radiation image acquisition apparatus 1 is emitted from a radiation source 2 that emits radiation such as X-rays toward an object A such as an electronic component such as a semiconductor device or a food product, and the radiation source 2. A radiation detector 3 for detecting the radiation transmitted through the object A and a photodetector (imaging device) 4 for imaging the light converted by the radiation detector 3. The radiation detector 3 is a direct conversion type detector that directly detects incident radiation and generates an image signal indicating a detection image of the object A, and the photodetector 4 converts based on the incident radiation. Indirect conversion type detectors such as a CMOS sensor and a CCD sensor that detect the emitted light and generate an image signal.

  As shown in FIGS. 1 and 2, the radiation detector 3 includes a direct conversion detector (radiation detection element) 5 that directly detects radiation emitted from the radiation source 2 and transmitted through the object A. Examples of the direct conversion detector 5 include a semiconductor detector whose main material is a semiconductor material such as amorphous selenium, CdTe, silicon (Si), or Ge. The direct conversion detector 5 internally converts the radiation that has passed through the object A and entered from the planar radiation detection surface 5a on the radiation source 2 side into charges, and detects the charges to detect the object A. An image signal indicating a two-dimensional radiation transmission image is output.

Further, the radiation detector 3 includes a wavelength conversion plate (wavelength conversion film / wavelength conversion member) 6 and a light shielding plate (light shielding film / shielding member) 7 disposed on the radiation detection surface 5 a side of the direct conversion detector 5. ing. The wavelength conversion plate 6 is a flat member disposed so as to cover the radiation detection surface 5a along the radiation detection surface 5a of the direct conversion detector 5, and responds to the incidence of radiation transmitted through the object A. To generate scintillation light. Examples of such wavelength conversion plate 6 include Gd ₂ O ₂ S: Tb, Gd ₂ O ₂ S: Pr, CsI: Tl, CdWO ₄ , CaWO ₄ , Gd ₂ SiO ₅ : Ce, Lu _0.4 Gd _1.6 SiO ₅ , Examples include scintillators such as Bi ₄ Ge ₃ O ₁₂ , Lu ₂ SiO ₅ : Ce, Y ₂ SiO ₅ , YAlO ₃ : Ce, Y ₂ O ₂ S: Tb, YTaO ₄ : Tm, and the thickness is several μm to It is set to an appropriate value depending on the energy band of the radiation detected within a range of several mm. The light shielding plate 7 is disposed between the wavelength conversion plate 6 and the direct conversion detector 5 so as to cover the radiation detection surface 5a, and the scintillation light generated by the wavelength conversion plate 6 is directly converted into the detector. 5 is a flat plate-like member for preventing the light from being incident on 5. Specifically, the light shielding plate 7 is a member that has a light shielding property against light in the wavelength region of the scintillation light and has a property of transmitting radiation emitted from the radiation source 2. Examples of the material of the light shielding member 7 include metal members such as beryllium, aluminum, copper, and titanium, non-metal members such as carbon (carbon) and silicon (silicon), polypropylene, polyimide, and polyethylene terephthalate. Examples thereof include a member in which a molecular organic substance has a light shielding property. Here, the wavelength conversion member 6 and the light shielding member 7 may be in the form of a film.

  When the light shielding member 7 and the wavelength conversion member 6 are assembled to the direct conversion type detector 5 as described above, the light shielding member 7 and the wavelength conversion member 6 are placed on the radiation detection surface 5a of the direct conversion type detector 5. The light shielding member 7 and the wavelength conversion member 6 may be deposited in advance, and the light shielding member 7 and the wavelength conversion member 6 may be bonded on the radiation detection surface 5a. Further, as shown in FIG. 3, holder members 8 and 9 for holding the light shielding member 7 and the wavelength conversion member 6 are prepared, and the light shielding member 7 and the wavelength conversion member 6 are prepared by the holder members 8 and 9. May be held on the radiation detection surface 5 a of the direct conversion detector 5. Further, as shown in FIG. 4, the light shielding member 7 and the wavelength conversion member 6 may be directly fixed on the radiation detection surface 5 a of the conversion type detector 5 using a fixing member such as a bolt.

  Next, the positional relationship between the radiation detector 3 having such a configuration, the radiation source 2 and the photodetector 4 will be described. As shown in FIG. 1, in the radiation source 2, the optical axis of radiation is substantially perpendicular to the radiation detection surface 5a of the direct conversion detector 5 (perpendicular to the radiation detection surface 5a and the optical axis of radiation). And is disposed so as to face the center of the radiation detection surface 5a. Further, the optical detector 4 obliquely intersects the radiation incident surface 6a of the wavelength conversion plate 6 with the optical axis of the built-in imaging lens 4a so that the scintillation light emitted from the wavelength conversion plate 6 can be imaged. (The surface perpendicular to the optical axis and the radiation incident surface 6a have an angle). The imaging lens 4 a condenses the scintillation light emitted from the radiation incident surface 6 a toward an imaging element (not shown) inside the photodetector 4. With such an arrangement, the photodetector 4 is arranged so as to be out of the radiation emission region from the radiation source 2.

  According to the radiographic image acquisition apparatus 1 described above, the radiation in the relatively low energy band among the radiation transmitted through the object A is converted into scintillation light by the wavelength conversion plate 6, and the radiation incident surface of the wavelength conversion plate 6. When the scintillation light is detected by the photodetector 4 arranged on the 6a side, it can be detected as an image signal indicating a radiation transmission image of the object A. At the same time, of the radiation transmitted through the object A, radiation in a relatively high energy band passes through the wavelength conversion plate 6 and the light shielding plate 7 and is directly detected by the direct conversion detector 5 as an image signal. This is because radiation in the low energy band is easily converted into scintillation light on the radiation incident surface 6 a side inside the wavelength conversion plate 6, whereas radiation in the high energy band is easy to pass through the wavelength conversion plate 6. is there. At this time, since the incidence of the scintillation light on the direct conversion detector 5 is prevented by the light shielding plate 7, the S / N in the high energy band image signal detected by the direct conversion detector 5 is improved. Further, in a direct conversion type detector, when a plurality of radiations are incident in a time shorter than the time resolution of the detector, it tends to be detected as energy higher than actual energy (this phenomenon). Is called “Sum Peak”). According to the present embodiment, low-energy radiation incident on the direct conversion type detector is reduced, and as a result, pseudo signals can be reduced. At the same time, since the scintillation light is detected on the radiation incident surface 6 a side of the wavelength conversion plate 6, image blur in the low energy band image signal detected by the photodetector 4 can also be prevented. As a result, it is possible to acquire a dual energy detection image with good S / N by separating into a high energy band and a low energy band.

  In addition, the direct conversion type detector has a limit in energy sensitivity, and a detector having sensitivity in a high energy band may have low sensitivity in a low energy band. Therefore, the radiological image acquisition apparatus 1 can acquire a low-energy band radiographic image with high sensitivity by imaging the scintillation light by the indirect conversion method using the photodetector 4. As a result, a highly sensitive detection image can be acquired in a wide energy range including a high energy band and a low energy band.

  Further, since the photodetector 4 is arranged so as to be out of the radiation emission region from the radiation source 2, the shadow of the photodetector 4 is not reflected in the radiation transmission image of the object A, and noise in the image signal. Therefore, it is possible to detect low-energy radiation. Furthermore, generation of noise including a direct conversion signal of radiation due to exposure inside the photodetector 4 is also prevented.

  Furthermore, the target object is obtained by performing predetermined arithmetic processing on the image signal in the low energy band and the image signal in the high energy band acquired by the radiation image acquisition device 1 by one shot (single imaging or detection). A contrast-enhanced energy difference (energy subtraction) and energy-separated radiation transmission image regarding A can be obtained.

  In addition, this invention is not limited to embodiment mentioned above. That is, the light shielding member 7 may be a reflection plate or a reflection film that reflects the scintillation light generated by the wavelength conversion plate 6. For example, like a radiation detector 103 which is a modification of the present invention shown in FIG. 5, a flat reflector 107 is interposed between the wavelength conversion plate 6 and the direct conversion detector 5 instead of the light shielding plate 7. You may do it. The reflection plate 107 is disposed so as to cover the radiation detection surface 5a of the direct conversion detector 5, has a reflection surface 107a that reflects light in the wavelength region of the scintillation light on the wavelength conversion plate 6 side, and The member has a property of transmitting the radiation emitted from the radiation source 2. Examples of the material of the reflecting member 107 include a material in which a reflecting surface is formed by polishing the surface of a flat plate member such as aluminum, nickel, copper, silver, or gold. As a method for forming the reflection surface, in addition to polishing, a method of forming a metal layer by vapor deposition, spraying, coating, or the like on the surface of a support that transmits radiation, or on the back surface of the radiation incident surface 6a of the wavelength conversion member Examples thereof include a method of forming a metal layer by vapor deposition, spraying, coating, or the like. By providing such a reflector 107, it is possible to improve the S / N in the high energy band image signal detected by the direct conversion type detector 5, and to efficiently generate scintillation light by the photodetector 4. Since it can detect, the detection efficiency of the image signal of a low energy zone can be improved.

  Further, the light shielding plate 7 and the reflection plate 107 may have a filtering function that further blocks low energy band components of the radiation transmitted through the object A. Examples of the material of the light shielding plate 7 and the reflection plate 107 having such a filtering function include copper, aluminum, carbon, silicon (silicon), nickel, silver, gold, stainless steel (iron), and titanium. By providing the light shielding plate 7 and the reflection plate 107 with a filtering function, it is possible to prevent the low energy band radiation incident from the wavelength conversion plate 6 side from directly entering the conversion type detector 5, and thus the high energy band image. S / N in the signal can be further improved.

  Moreover, regarding the positional relationship between the radiation source 2 and the photodetector 4 with respect to the radiation detector 3, various modifications can be adopted. That is, it is only necessary that the light detector 4 be arranged so as to be away from the radiation emission region from the radiation source 2, and the radiation source 2 is arranged so that the radiation detection surface 5 a of the direct conversion type detector 5 is shown in FIG. 6. Are arranged so that the optical axis of the radiation is inclined obliquely, the optical detector 4 has the optical axis of the imaging lens 4a substantially perpendicular to the radiation incident surface 6a of the wavelength conversion plate 6, and the radiation incident surface 6a. You may arrange | position so that the center part may be opposed. Further, as shown in FIG. 7, a reflecting plate 11 that reflects the scintillation light generated from the wavelength conversion plate 6 is disposed on the optical axis of the radiation emitted from the radiation source 2, and the imaging lens 4 a of the photodetector 4 is provided. The photodetector 4 may be arranged so that the scintillation light reflected by the reflector 11 can be collected. Even in this case, the photodetector 4 can be separated from the radiation emission region.

  DESCRIPTION OF SYMBOLS 1 ... Radiation image acquisition apparatus, 2 ... Radiation source, 4 ... Photodetector (imaging element), 5 ... Direct conversion type detector (radiation detection element), 6 ... Wavelength conversion plate, wavelength conversion film (wavelength conversion member), 7: light-shielding plate, light-shielding film (shielding member), 107: reflector, reflective film (shielding member).

Claims (15)

A planar wavelength conversion member that generates scintillation light in response to the incidence of radiation transmitted through the object;
A direct conversion type radiation detection element for directly detecting the radiation transmitted through the wavelength conversion member;
A shielding member that is disposed between the wavelength conversion member and the radiation detection element and prevents the scintillation light from entering the radiation detection element;
A radiation detector comprising: The shielding member is a planar member having a light shielding property against the scintillation light.
The radiation detector according to claim 1. The shielding member is a planar reflecting member that reflects the scintillation light.
The radiation detector according to claim 1. The shielding member blocks a low energy band of the radiation;
The radiation detector of any one of Claims 1-3 characterized by the above-mentioned. A radiation source that emits radiation; and
A planar wavelength conversion member that generates scintillation light in response to incidence of the radiation emitted from the radiation source and transmitted through the object;
An imaging device that images the scintillation light emitted from the radiation incident surface of the wavelength conversion member;
A direct conversion type radiation detection element for directly detecting the radiation transmitted through the wavelength conversion member;
A shielding member that is disposed between the wavelength conversion member and the radiation detection element and prevents the scintillation light from entering the radiation detection element;
A radiological image acquisition apparatus comprising: The shielding member is a planar member having a light shielding property against the scintillation light.
The radiological image acquisition apparatus according to claim 5. The shielding member is a planar reflecting member that reflects the scintillation light.
The radiological image acquisition apparatus according to claim 5. The shielding member blocks a low energy band of the radiation;
The radiographic image acquisition device according to any one of claims 5 to 7, wherein   The shielding member and the wavelength conversion member are deposited in this order on the detection surface of the radiation detection element,
The radiation detector of any one of Claims 1-4 characterized by the above-mentioned.   The shielding member and the wavelength conversion member are adhered in this order on the detection surface of the radiation detection element,
The radiation detector of any one of Claims 1-4 characterized by the above-mentioned.   The shielding member and the wavelength conversion member are held by a holder member on the detection surface of the radiation detection element,
The radiation detector of any one of Claims 1-4 characterized by the above-mentioned.   The shielding member and the wavelength conversion member are fixed by a fixing member on the detection surface of the radiation detection element,
The radiation detector of any one of Claims 1-4 characterized by the above-mentioned.   The imaging element is disposed so as to be separated from an emission region of radiation from the radiation source.
The radiographic image acquisition apparatus according to any one of claims 5 to 8, wherein   The radiographic image acquisition apparatus according to claim 5, further comprising an imaging lens that condenses the scintillation light on the imaging element.   The object is an electronic component.
The radiographic image acquisition apparatus according to any one of claims 5 to 8, wherein

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