JP5513900B2 - X-ray CT detector and X-ray CT apparatus - Google Patents

Description

  The present invention relates to an X-ray CT detector and an X-ray CT apparatus using the X-ray CT detector.

  An X-ray CT (Computed Tomography) apparatus rotates a bed on which a subject is placed, an X-ray tube, an X-ray CT detector, an X-ray tube and an X-ray CT detector around the bed It is comprised by the rotating mechanism etc. to be made.

  An X-ray tube irradiates a subject placed on a bed with X-rays from various directions.

  The X-ray CT detector is disposed at a position facing the X-ray tube across the subject on the bed, and detects X-rays transmitted through the subject after being irradiated from the X-ray tube. The X-ray CT detector includes a plurality of detection elements arranged in a channel direction substantially orthogonal to the body axis direction (slice direction) of the subject on the bed. Each detection element includes a scintillator that absorbs X-rays and emits light, and a photodiode that receives light emitted from the scintillator, converts it into an electrical signal, and outputs the electrical signal. The electrical signal output from the photodiode reflects the energy intensity of the X-ray that changes depending on which part of the subject the X-ray has transmitted, and the tomographic image is reconstructed based on the output electrical signal. And displayed on the display device.

  As shown in FIG. 6, the detection element 30 of such a detector for X-ray CT is opposite to a scintillator 31 that emits light when X-rays are incident and an incident surface 32 on which the X-rays are incident. And a photodiode 34 bonded to the side surface 33. The scintillator 31 is formed so that the dimension from the incident surface 32 to the opposite surface 33 is substantially uniform throughout the scintillator 31.

  The energy of the X-rays incident on the scintillator 31 differs depending on which part of the subject the X-rays have transmitted. The X-rays incident on the scintillator 31 have different light emission positions in the scintillator 31 depending on the energy of the X-rays. As shown in FIG. 6, the X-rays having high energy enter the deep position of the scintillator 31 and emit light. As the energy of X-rays decreases, the X-ray emission position in the scintillator 31 becomes shallower. The light emitted in response to these X-rays having different energies is received by one photodiode 34, and the received light is converted into an electrical signal and output from the photodiode 34. Each X-ray light emitted from the scintillator 31 is gradually attenuated from the light emission position until reaching the photodiode 34, so that the X-ray light emitted at a shallow position of the photodiode 34 is the photodiode 34. The amount of attenuation is larger than that of X-ray light emitted at a deep position.

  FIG. 7 is a graph showing the energy distribution of X-rays transmitted through the tissue A and tissue B of the subject. This graph is output from the photodiode 34 because the total amount of light received by one photodiode 34 after light emission is equal even if the energy distributions of the X-rays transmitted through the tissue A and the tissue B are different. This means that the electrical signals are the same.

  FIG. 8 shows a tomographic image of the tissue A and the tissue B reconstructed based on the electrical signal output from the photodiode 34. Even if the energy distributions of the X-rays transmitted through the tissue A and the tissue B are different as shown in FIG. 7, the electrical signals output from the photodiode 34 are the same. The CT values are displayed as the same.

  As an example of an X-ray CT apparatus that attempts to discriminate and collect X-rays of different energies, for example, the one disclosed in Patent Document 1 below is known. The X-ray CT apparatus disclosed in Patent Document 1 uses two detectors for X-ray CT in which a plurality of detection elements having different scintillator thickness dimensions are arranged in order to detect X-rays having different energy intensities. It has been.

Japanese Patent Laid-Open No. 06-296607

  However, the X-ray CT detector disclosed in Patent Document 1 and the like can detect the energy distribution of X-rays transmitted through the subject only in two stages. In addition to this, the high energy scintillator and the low energy scintillator must be manufactured as separate detector units, resulting in a problem of increased manufacturing costs. Further, it does not correspond to the multi-slice X-ray detector, and even if two types of scintillators are alternately arranged by the multi-slice X-ray detector, the X for one slice is detected by the detectors for two rows. Line detection is performed, and there is a problem that the resolution in the column direction is halved.

  The present invention has been made to solve such problems, and an object thereof is to accurately detect the energy distribution of X-rays transmitted through the subject.

  According to a first aspect of the present invention, there is provided an X-ray CT detector comprising: a scintillator that absorbs X-rays and emits light; and a photodiode that receives light emitted from the scintillators and converts the light into electric signals. The scintillator is formed with an inclined surface that is located on the opposite side of the incident surface on which X-rays are incident and is inclined in a direction in which a dimension from the incident surface gradually changes, and the photodiode includes the inclined surface of the scintillator It is that it is provided with two or more along the inclination direction.

  According to a second aspect of the present invention, in the X-ray CT apparatus, an X-ray tube that irradiates X-rays, and X-rays that are irradiated from the X-ray tube and transmitted through the subject absorb and emit light. A scintillator having an inclined surface formed on an opposite side of the incident surface where the light is incident and inclined in a direction in which the dimension from the incident surface gradually changes, and a plurality of scintillators provided along the inclination direction of the inclined surface of the scintillator A photodiode that receives light emitted from the scintillator and converts it into an electrical signal, and a reconstruction processing unit that reconstructs transmitted X-ray data based on the electrical signal converted by the photodiode and generates a tomographic image And providing.

  According to the present invention, the energy distribution of X-rays that have passed through the subject can be accurately detected.

It is a block diagram which shows schematic structure of a X-ray CT apparatus. It is the schematic which shows one detection element which comprises the detector for X-ray CT of one embodiment of this invention. 6 is a graph showing an energy distribution of X-rays transmitted through a tissue A and a tissue B of a subject. It is a tomographic image of the tissue A and the tissue B reconstructed based on an electric signal by a low energy X-ray. It is a tomographic image of the tissue A and the tissue B reconstructed based on an electric signal by high energy X-rays. It is the schematic which shows one detection element of the detector for X-ray CT of a prior art example. 6 is a graph showing an energy distribution of X-rays transmitted through a tissue A and a tissue B of a subject. It is a tomographic image of the tissue A and the tissue B reconstructed based on the electrical signal output from the photodiode.

  An X-ray CT apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing a schematic configuration of an X-ray CT apparatus. The X-ray CT apparatus includes a gantry 1, a bed 2, and an operation console 3.

  The gantry 1 is a part that irradiates the subject P with X-rays, detects X-rays transmitted through the subject P, and captures a tomographic image of the subject P. The gantry 1 includes a gantry control unit 4, a high voltage generation unit 5, a rotation driving unit 6, a tilt driving unit 7, an X-ray tube 8, an X-ray CT detector 9, and a data collecting unit 10. It has.

  The bed 2 is a part where the subject P is placed and the placed subject P is sent to an imaging position where X-rays are irradiated. The couch 2 includes a couch top 11 on which the subject P is placed, a couch base 12 that supports the couch top 11, and a couch drive unit 13 that moves the couch top 11 up and down and horizontally. I have.

  The operation console 3 is a part that controls input / output of the X-ray CT apparatus. The operation console 3 includes a console control unit 14, an input operation unit 15, a preprocessing unit 16, an X-ray projection data storage unit 17, a reconstruction processing unit 18, an image data storage unit 19, and an image processing unit. 20 and an image display unit 21.

  The gantry control unit 4 controls each unit in the gantry 1 in accordance with an input from the input operation unit 15 of the operation console 3.

  The high voltage generator 5 supplies a high voltage necessary for irradiating the X-ray from the X-ray tube 8 to the X-ray tube 8 according to a control signal transmitted from the gantry controller 4.

  The X-ray tube 8 emits X-rays with a high voltage supplied from the high voltage generator 5. X-rays radiated from the X-ray tube 8 are formed into a fan shape or a cone shape.

  The X-ray CT detector 9 detects X-rays that have been irradiated from the X-ray tube 8 and have passed through the subject P placed on the bedtop 11. In the case of a single slice CT apparatus, the X-ray CT detector 9 is configured by arranging, for example, 1000 channels of X-ray detection elements in a row in a fan shape or a linear shape. The X-ray CT detector 9 will be described in detail later.

  The data acquisition unit 10 has a plurality of data acquisition elements arranged in an array like the X-ray detection elements of the X-ray CT detector 9, and the X-rays detected by the X-ray CT detector 9 (Actually, an X-ray detection signal) is collected according to the data collection control signal output from the gantry control unit 4. This collected data becomes X-ray projection data.

  The rotation driving unit 6 drives a motor (not shown) by a control signal output from the gantry control unit 4 and holds an X-ray tube 8 and an X-ray CT detector 9 facing each other (see FIG. (Not shown) is rotated around its center line.

  The tilt drive unit 7 expands and contracts a tilt cylinder (not shown) according to a control signal output from the gantry control unit 4, and tilts the gantry 1 to a forward tilt state or a rear tilt state at an arbitrary angle.

  The couch driving unit 13 moves the couch top 11 in the vertical direction and the longitudinal direction (arrow X direction) in response to an input from the input operation unit 15 of the operation console 3. A subject P to be imaged by tomography by irradiation with X-rays is placed on the bed top 11 in a direction in which the body axis direction of the subject P coincides with the movement direction (arrow X direction) of the bed top 11. Is placed.

  The input operation unit 15 includes a keyboard, a touch panel, a mouse, and the like, and performs various input operations for driving the X-ray CT apparatus.

  The console control unit 14 generates a control signal corresponding to the input from the input operation unit 15, and transmits this control signal to the gantry control unit 4, the bed driving unit 13, and each unit in the operation console 3.

  The preprocessing unit 16 performs preprocessing such as sensitivity correction and X-ray intensity correction on the X-ray projection data output from the data collection unit 10.

  The X-ray projection data storage unit 17 stores the X-ray projection data subjected to preprocessing such as sensitivity correction by the preprocessing unit 16.

  The reconstruction processing unit 18 forms tomographic image data by back projecting the X-ray projection data stored in the X-ray projection data storage unit 17.

  The image data storage unit 19 stores the tomographic image data formed by the reconstruction processing unit 18 and transmits the stored tomographic image data to the image processing unit 20 in response to an input from the input operation unit 15.

  The image processing unit 20 performs various processes on the tomographic image data transmitted from the image data storage unit 19 according to the input from the input operation unit 15, such as a tomographic image at an arbitrary cross-sectional position, projection from an arbitrary direction. A process of converting the image data into image data such as an image or a three-dimensional image by rendering processing is performed, and the converted image data is transmitted to the image display unit 21. Further, the image processing unit 20 synthesizes tomographic images based on X-rays having different energies detected by the photodiodes 24 provided along the inclination direction of the inclined surface 26 of the scintillator 23 described later.

  The image display unit 21 displays an image corresponding to the image data transmitted from the image processing unit 20.

  The X-ray CT detector 9 is a device that detects X-rays irradiated from the X-ray tube 8 and transmitted through the subject P on the couch top 11 as described above. A plurality of detection elements 22 arranged in a channel direction substantially orthogonal to the slice direction). Each detection element 22 absorbs X-rays and emits light, and receives light emitted from the scintillators 23. And a plurality of photodiodes 24 for conversion into electrical signals. The X-ray CT detector 9 may be a multi-slice detector in which the detection elements 22 are two-dimensionally arranged in the channel direction and the slice direction.

  The scintillator 23 is formed using a high-luminance fluorescent material such as cesium iodide (CsI), for example. Further, in this scintillator 23, the surface facing the X-ray tube 8 across the subject P on the bed top plate 11 is an X-ray incident surface 25, and the side opposite to the incident surface 25 in the scintillator 23 is incident. An inclined surface 26 that is inclined in a direction in which the dimension from the surface 25 gradually changes is formed.

  The photodiode 24 is provided on the printed wiring board 27, and the photodiode 24 and the printed wiring board 27 are bonded to the inclined surface 26 of the scintillator 23 using an optical adhesive 28 having a property of transmitting light. . A plurality of photodiodes 24 are provided on the printed wiring board 27, and these photodiodes 24 are arranged along the inclination direction of the inclined surface 26 of the scintillator 23.

  Further, a plurality of electrical signals (for example, signal 1, signal 2, signal 3, signal 4) that are connected to each photodiode 24 and transmitted from each photodiode 24 are transmitted to the data collection unit 10 on the printed wiring board 27. Electrodes (not shown) are provided.

  In such a configuration, at the time of imaging by the X-ray CT apparatus, X-rays are irradiated from the X-ray tube 8 toward the subject P on the couch top 11 and the X-rays transmitted through the subject are incident on the scintillator 23. 25 is incident.

  The energy of the X-rays incident on the scintillator 23 differs depending on which part of the subject P the X-rays have transmitted. The X-rays incident on the scintillator 23 have different light emission positions in the scintillator 23 depending on the energy of the X-rays. As shown in FIG. 2, the X-rays having high energy enter a deep position in the scintillator 23. The X-ray emission position in the scintillator 23 becomes shallower as light is emitted and the energy of the X-ray becomes lower.

  Here, an inclined surface 26 is formed in the scintillator 23, and a plurality of photodiodes 24 are bonded to the inclined surface 26 along the inclination direction. For this reason, X-ray light emitted at different depth positions in the scintillator 23 is received by the photodiode 24 located near the light emission position, and an electric signal (for example, signal 1, signal 2, signal 3, signal 3) 4), the electric signal is collected by the data collecting unit 10, and the tomographic image is reconstructed based on the electric signal collected by the data collecting unit 10.

  In addition, since the inclined surface 26 is formed in the scintillator 23 and the some photodiode 24 is provided along the inclination direction of this inclined surface 26, the light is received from the light emission position in each X-ray which has different energy. The difference in distance to each photodiode 24 is reduced, and the variation in the amount of attenuation of light from when light is emitted until it is received by each photodiode 24 is reduced.

  FIG. 3 is a graph showing the energy distribution of X-rays transmitted through the tissue A and the tissue B of the subject P. In this graph, energy distributions of X-rays transmitted through the tissue A and the tissue B are different, and electrical signals (for example, signal 1, signal 2, signal 3, signal 4) corresponding to X-rays having different energy distributions are obtained. The output from a plurality of photodiodes 24 is shown.

  FIG. 4 shows a tomographic image of the tissue A and the tissue B reconstructed based on the signal 1 (electric signal by low energy X-rays). FIG. 5 shows a tomographic image of the tissue A and the tissue B reconstructed based on the signal 4 (electric signal by high energy X-rays). An image can be reconstructed based on such signals of X-rays having different energies, and an image in which a specific tissue is emphasized can be generated by combining the reconstructed images. For example, since calcium exhibits X-ray absorption characteristics that are significantly different from other tissues, an image in which bones and calcified portions are extracted is generated.

  Thus, by synthesizing tomographic images corresponding to the energy of the X-rays transmitted through the tissue A and the tissue B of the subject, a tissue that could not be conventionally distinguished because the difference in CT value was slight. It becomes possible to distinguish. This makes it possible to accurately detect the energy distribution of X-rays that have passed through each part of the subject (for example, tissue A and tissue B).

  Further, since X-rays having a plurality of energies can be discriminated and detected via one kind of scintillator 23, the manufacturing cost can be reduced compared to the case where a plurality of kinds of scintillators are required. Furthermore, since a plurality of energies can be detected using the scintillators 23 arranged in a line, the image quality resolution in the slice direction is not reduced compared to an X-ray CT apparatus that does not perform normal energy discrimination.

  In the present embodiment, the case where four photodiodes 24 are arranged along the inclination direction of the inclined surface 26 of the scintillator 23 is described as an example. However, the photo arranged along the inclination direction of the inclined surface 26 is described. The number of diodes 24 is not limited to four, and the energy distribution of X-rays can be accurately detected as the number increases.

8 X-ray tube 9 X-ray CT detector 18 Reconstruction processing unit 20 Image processing unit 23 Scintillator 24 Photodiode 25 Incident surface 26 Inclined surface

Claims (3)

In an X-ray CT detector having a scintillator that emits light by absorbing X-rays, and a photodiode that receives light emitted from the scintillator and converts it into an electrical signal,
The scintillator is formed with an inclined surface that is located on the opposite side of the incident surface on which X-rays are incident and is inclined in a direction in which a dimension from the incident surface gradually changes,
A plurality of the photodiodes are provided along the inclination direction of the inclined surface of the scintillator,
A detector for X-ray CT. An X-ray tube that emits X-rays;
Absorbs X-rays emitted from the X-ray tube and passes through the subject, emits light, and is positioned on the opposite side of the incident surface where the X-rays are incident and tilted in a direction in which the dimensions from the incident surface gradually change. A scintillator with an inclined surface formed,
A plurality of photodiodes provided along the inclination direction of the inclined surface of the scintillator, and receiving light emitted from the scintillator and converting it into an electrical signal; and
A reconstruction processing unit that reconstructs transmission X-ray data based on the electrical signal converted by the photodiode to generate a tomographic image;
An X-ray CT apparatus comprising:   The image processing unit according to claim 2, further comprising an image processing unit that synthesizes tomographic images based on X-rays having different energies detected by the photodiodes provided along an inclination direction of the inclined surface of the scintillator. X-ray CT system.

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