WO2020144972A1

WO2020144972A1 - Image processing device, image processing method, and program

Info

Publication number: WO2020144972A1
Application number: PCT/JP2019/047019
Authority: WO
Inventors: 哲雄島田; 竹中　克郎
Original assignee: キヤノン株式会社
Priority date: 2019-01-09
Filing date: 2019-12-02
Publication date: 2020-07-16
Also published as: JP2020110264A

Abstract

This image processing device modifies the spatial frequency characteristic of at least one of multiple radiation images such that the spatial frequency characteristics of the multiple radiation images obtained by multiple different radiation energies approach each other, and uses the modified multiple radiation images to generate an image of the subject. This modification is performed by applying pre-set processing, which causes the measured spatial frequency characteristic of one of the multiple radiation energies to approximate the measured spatial frequency characteristic of another of the multiple radiation energies, to the radiation image obtained by said one radiation energy.

Description

Image processing apparatus, image processing method and program

The present invention relates to an image processing device, an image processing method, and a program for processing a radiation image.

Radiation imaging devices are widely used for medical image diagnosis and nondestructive inspection. A method is known in which a plurality of radiation images are acquired by using radiation having different energy components by using a radiation imaging apparatus, and an energy subtraction image in which a specific object portion is separated or emphasized is acquired from a difference between the plurality of radiation images. There is.

　To obtain energy subtraction images, multiple radiation images with different radiation energy are required for the same site. In Patent Document 1, scintillators are arranged on both surfaces of a substrate having optical transparency, and a photodiode for detecting light emitted by the scintillator on one side and a photodiode for detecting light emitted by the scintillator on the other side are arranged. Has been shown to do. The photodiodes that detect the light emitted by the different scintillators can acquire signals of two different energy components by one irradiation of radiation, and can generate an energy subtraction image.

JP, 2010-056396, A JP, 2011-227044, A

In the case of Patent Document 1, the first sensor unit for detecting the fluorescence obtained by converting the wavelength of the radiation by the scintillator arranged on the radiation incident surface side has a structure similar to that of a normal flat panel detector, which is favorable. It is possible to have spatial resolution. On the other hand, the second sensor section for detecting the fluorescence obtained from the scintillator arranged on the radiation incident surface side detects the fluorescence obtained by wavelength-converting the radiation that has reached through the light-transmissive substrate having a thickness. It will be. Therefore, the second sensor unit detects the fluorescence scattered by the light-transmissive substrate, which lowers the resolution. As a result, the image acquired by the first sensor unit and the image acquired by the second sensor unit have different spatial resolutions. When an energy subtraction image or a spectral imaging image is generated using these images with different spatial frequencies, the calculation is inconsistent particularly in a region including high frequency components of the spatial frequency, and the result is different from the actual structure.

The present invention provides a technique for improving the image quality of an image generated using a plurality of radiation images by reducing the difference in spatial frequency between the radiation images having different radiation energies.

A radiation image processing apparatus according to an aspect of the present invention has the following configuration. That is,
Changing means for changing the spatial frequency characteristics of at least one of the plurality of radiation images so that the spatial frequency characteristics of the plurality of radiation images obtained by different plurality of radiation energies approach each other;
Processing means for generating an image of a subject using the plurality of changed radiation images,
The changing unit preliminarily brings the spatial frequency characteristic measured for one radiation energy of the plurality of radiation energies close to the spatial frequency characteristic measured for another radiation energy of the plurality of radiation energies. The set process is applied to the radiation image obtained with the other radiation energy.

According to the present invention, by reducing the difference in spatial frequency between a plurality of radiation images having different radiation energies, the image quality of an image generated using these plurality of radiation images is improved.

Other features and advantages of the present invention will be apparent from the following description with reference to the accompanying drawings. Note that, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals.

The accompanying drawings are included in the specification and constitute a part of the specification, illustrate the embodiments of the present invention, and are used together with the description to explain the principle of the present invention.
The figure which shows the structural example of the radiation imaging system using the radiation imaging device which concerns on embodiment. The figure which shows the structural example of the imaging panel of a radiation imaging device. The figure which shows the structural example of the cross section of the pixel of a radiation imaging device. The figure which shows the structural example of the cross section of the pixel of a radiation imaging device. The figure which shows the example of arrangement|positioning of the pixel of a radiation imaging device. The timing chart which shows operation|movement of a radiation imaging device. The timing chart which shows operation|movement of a radiation imaging device. The figure which shows the operation|movement flow of a radiation imaging device. The figure which shows the operation|movement flow of a radiation imaging device. The figure which shows the example of pixel interpolation of a radiation imaging device. The figure which shows the spatial frequency characteristic of a low energy image and a high energy image. The figure explaining the example of the method of changing the spatial frequency characteristic by 1st Embodiment. The figure explaining the example of the change method of the spatial frequency characteristic by 2nd Embodiment. The figure explaining the example of the method of changing the spatial frequency characteristic by 3rd Embodiment. The figure explaining the other example of the change method of the spatial frequency characteristic by 3rd Embodiment.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiment, not all of the plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar components are designated by the same reference numerals, and duplicated description will be omitted.

In each of the following embodiments, an example will be described in which a radiation image pickup apparatus that picks up images of radiation having different energies of the same site in one image pickup is used. As such a radiation imaging apparatus, for example, the configuration of the radiation imaging apparatus described in Patent Document 2 can be used in addition to the configuration described in Patent Document 1 described above. A radiation imaging apparatus having a new configuration different from that of is used. These radiation imaging devices have a structure including two or more detection layers for detecting radiation in order to obtain images of different radiation energies by one irradiation of radiation. For example, a structure in which a first detection layer on the radiation irradiation side and a second detection layer behind the first detection layer are provided is used. In this case, since the second detection layer detects the radiation that has passed through the first detection layer, the radiation image detected by the first detection layer and the radiation image detected by the second detection layer are different from each other. Spatial frequency characteristics are different. In the following embodiments, the image quality of images (energy subtraction images, spectral imaging images, etc.) generated using radiation images of different radiation energies is improved by reducing such differences in spatial frequency characteristics. ..

Note that the following are examples of further factors that change the spatial frequency characteristics of a plurality of radiation images acquired by one-time imaging in the radiation imaging apparatus described above. For example, when a radiation-absorbing substance for increasing the energy difference between the radiations detected in the respective detection layers is provided between the two detection layers, such a radiation-absorbing substance is used as the radiation obtained in these two detection layers. Change the spatial frequency characteristics of the image. Similarly, if the material, thickness, etc. of the scintillator (phosphor layer) arranged in each detection layer change, the spatial frequency characteristic of the obtained radiation image changes. Further, the spatial frequency characteristic of the obtained radiation image changes even when pixel arrays having different array intervals are used for each detection layer, or when the size or shape of the light receiving surface of the conversion element is different. Further, not only the energy difference of radiation but also the noise characteristic of the image changes the spatial frequency characteristic of the radiation image. In the embodiment, the difference in spatial frequency characteristics caused by these factors is reduced.

Further, in the following embodiments, a description will be given using a radiation imaging apparatus that acquires a plurality of radiation images having different radiation energies at one time, but the present invention is limited to a configuration using such a radiation imaging apparatus. is not. For example, a method may be used in which one or more radiation imaging devices are used to image the same subject while changing the time and angle. That is, the present invention is not limited to the structure and technique of the radiation imaging apparatus as long as it is configured to collect a plurality of radiation images having different contrasts using a plurality of radiations having different energies and to perform energy subtraction and spectral imaging calculations. Not done.

Further, in the following embodiments, an indirect type imaging panel that uses a scintillator when converting radiation into electric charges is used, but the present invention is not limited to this, and a direct type that directly converts radiation into electric charges, or It may be a combination thereof. Furthermore, the energy of the radiation applied to the same radiation imaging apparatus may be changed in a short time to capture an image.

In addition, in the radiation in the present invention, in addition to α-rays, β-rays, γ-rays, etc., which are beams produced by particles (including photons) emitted by radiation decay, a beam having the same or higher energy, for example, X It may also include rays, particle rays, cosmic rays, etc.

<First Embodiment>
The configuration and operation of the radiation imaging apparatus according to the first embodiment will be described with reference to FIGS. FIG. 1 is a diagram showing a configuration example of a radiation imaging system 200 using the radiation imaging apparatus 210 according to the first embodiment. The radiation imaging system 200 is configured to electrically capture an optical image converted from radiation and obtain an electrical signal (radiation image data) for generating a radiation image. The radiation imaging system 200 includes, for example, a radiation imaging apparatus 210, a radiation source 230, an exposure controller 220, and a computer 240.

The radiation source 230 starts emitting radiation according to the exposure command (radiation command) from the exposure control unit 220. Radiation emitted from the radiation source 230 is applied to the radiation imaging apparatus 210 through an unillustrated body. The radiation source 230 also stops the emission of radiation according to a stop command from the exposure controller 220.

The radiation imaging apparatus 210 includes an imaging panel 212 and a control unit 214 that controls the imaging panel 212. The control unit 214 generates a stop signal for stopping the radiation of the radiation from the radiation source 230 based on the signal obtained from the imaging panel 212. The stop signal is supplied to the exposure control unit 220, and the exposure control unit 220 sends a stop command to the radiation source 230 in response to the stop signal. The control unit 214 includes, for example, a PLD (abbreviation of Programmable Logic Device) such as an FPGA (abbreviation of Field Programmable Gate Array), or an ASIC (abbreviation of Application Specific) or a program for integrated general purpose integrated circuit (ASIC). It may be configured by a computer or a combination of all or a part thereof.

The computer 240 controls the radiation imaging device 210 and the exposure control unit 220. The computer 240 also includes an image processing unit 241 that receives the radiation image data output from the radiation imaging apparatus 210 and processes the radiation image data. The image processing unit 241 can generate a radiation image from the radiation image data.

The exposure control unit 220 has an exposure switch (not shown) as an example. When the user turns on the exposure switch, the exposure control unit 220 sends an exposure command to the radiation source 230 and also indicates the start of radiation emission. Send notification to computer 240. The computer 240 that has received the start notification notifies the control unit 214 of the radiation imaging apparatus 210 of the start of radiation emission in response to the start notification.

FIG. 2 shows a configuration example of the image pickup panel 212. The imaging panel 212 includes the pixel array 112. The pixel array 112 includes a plurality of pixels PIX each including a conversion element S arranged in a two-dimensional array for detecting radiation. The pixel array 112 also has a plurality of column signal lines Sig1 to Sig4 along the column direction (vertical direction in FIG. 2) for outputting the signal generated by the conversion element S. Further, the image pickup panel 212 includes a drive circuit (row selection circuit) 114 that drives the pixel array 112, and a readout circuit 113 that detects a signal that appears on the column signal line Sig of the pixel array 112. In the configuration shown in FIG. 2, for simplification of description, the pixel array 112 is composed of 4 rows×4 columns of pixels PIX, but in reality, more pixels PIX can be arrayed. In one example, the imaging panel 212 has dimensions of 17 inches and may have about 3000 rows by about 3000 columns of pixel PIX.

Each pixel PIX includes a conversion element S for detecting radiation and a switch T that connects the conversion element S and the column signal line Sig (the signal line Sig corresponding to the conversion element C among the plurality of signal lines Sig). including. Each conversion element S outputs a signal corresponding to the amount of incident radiation to the column signal line Sig. The conversion element S may be, for example, a MIS type photodiode that is arranged on an insulating substrate such as a glass substrate and has amorphous silicon as a main material. Further, the conversion element S may be a PIN photodiode. In the present embodiment, the conversion element S may be configured as an indirect element that detects light after converting radiation into light with a scintillator. In the indirect type element, the scintillator can be shared by the plurality of pixels PIX (the plurality of conversion elements S).

The switch T can be composed of, for example, a transistor such as a thin film transistor (TFT) having a control terminal (gate) and two main terminals (source and drain). The conversion element S has two main electrodes, one main electrode of the conversion element S is connected to one of the two main terminals of the switch T, and the other main electrode of the conversion element S has a common electrode. It is connected to the bias power supply 103 via the bias line Bs. The bias power supply 103 supplies the bias voltage Vs. The control terminal of the switch T of each pixel PIX arranged in the first row is connected to the gate line Vg1 arranged in the row direction (horizontal direction in FIG. 2). Similarly, the control terminals of the switches SW of the pixels PIX arranged in the second to fourth rows are connected to the gate lines Vg2 to Vg4, respectively. A gate signal is supplied to the gate lines Vg1 to Vg4 by the drive circuit 114.

In each pixel PIX arranged in the first column, the main terminal of the switch T that is not connected to the conversion element S is connected to the column signal line Sig1 of the first column. Similarly, in each of the pixels PIX arranged in the second to fourth columns, the main terminals of the switch T not connected to the conversion element S are connected to the column signal lines Sig2 to Sig4 in the second to fourth columns, respectively. ..

The read circuit 113 has a plurality of column amplification units CA so that one column amplification unit CA corresponds to one column signal line Sig. Each column amplification unit CA may include an integrating amplifier 105, a variable amplifier 104, a sample hold circuit 107, and a buffer circuit 106. The integrating amplifier 105 amplifies the signal appearing on the column signal line Sig. The integrating amplifier 105 may include an operational amplifier and an integrating capacitor and a reset switch connected in parallel between the inverting input terminal and the output terminal of the operational amplifier. The reference potential Vref is supplied to the non-inverting input terminal of the operational amplifier. By turning on the reset switch, the integration capacitance is reset and the potential of the column signal line Sig is reset to the reference potential Vref. The reset switch can be controlled by the reset pulse RC supplied from the control unit 214.

The variable amplifier 104 amplifies the signal output from the integrating amplifier 105 at a set amplification factor. The sample hold circuit 107 samples and holds the signal output from the variable amplifier 104. The sample hold circuit 107 can be composed of a sampling switch and a sampling capacitor. The buffer circuit 106 buffers (impedance-converts) the signal output from the sample hold circuit 107 and outputs it. The sampling switch may be controlled by a sampling pulse supplied from the controller 214.

The read circuit 113 also includes a multiplexer 108 that selects and outputs signals from a plurality of column amplification units CA provided corresponding to the respective column signal lines Sig in a predetermined order. The multiplexer 108 includes, for example, a shift register. The shift register performs a shift operation according to the clock signal CLK supplied from the control unit 214, and the shift register selects one signal from the plurality of column amplification units CA. The read circuit 113 further includes a buffer 109 that buffers (impedance-converts) the signal output from the multiplexer 108, and an AD converter 110 that converts an analog signal output from the buffer 109 into a digital signal. sell. The output of the AD converter 110, that is, the radiation image data is transferred to the computer 240.

In the present embodiment, as will be described later, a scintillator that converts the radiation into visible light is provided on both the incident surface side for allowing the radiation of the substrate to enter and the back surface on the side opposite to the incident surface, respectively. It is arranged to cover the surface of. The conversion element S included in each pixel PIX includes two types of conversion elements S. In the configuration shown in FIG. 2, the conversion elements S12, S14, S21, S23, S32, S34, S41, S43 are arranged to receive light from the two scintillators. In the following, when these conversion elements that receive light from two scintillators of the conversion elements S are specified, they are referred to as a first conversion element 901. Further, in the conversion elements S11, S13, S22, S24, S31, S33, S42, S44, a light shielding layer 903 is arranged between one scintillator and each of the conversion elements S. Thereby, the conversion elements S11, S13, S22, S24, S31, S33, S42, S44 are arranged so that the light from one scintillator is blocked and the light from the other scintillator is received. In the following, in the case of specifying those conversion elements in which light from one scintillator of the conversion elements S is blocked, they are referred to as a second conversion element 902. The light-blocking layer 903 is a layer that blocks light emitted from the scintillator, and may block light between the second conversion element 902 and either of the scintillator that covers the incident surface side or the back surface side of the substrate. At this time, in the second conversion element 902, the light from one scintillator may not be completely blocked. One of the scintillator that covers the incident surface side and the back surface side of the substrate and the second conversion element 902 so that the amount of light that can be received from one scintillator is smaller than that of the first conversion element 901. The light shielding layer 903 may be provided between them.

Here, it is assumed that the light shielding layer 903 is arranged between the scintillator arranged on the incident surface side of the substrate and the second conversion element 902. Of the radiation incident from the incident surface side of the substrate, the low energy component is absorbed by the scintillator covering the incident surface side of the substrate, converted into visible light, and incident on each pixel PIX. Since the second conversion element 902 is shielded from the incident surface side of the substrate, light emitted from the incident surface side of the substrate does not enter. Therefore, the light converted from the low energy component of the radiation does not enter the second conversion element 902. On the other hand, in the first conversion element 901, since the light shielding layer 903 is not arranged, the light converted from the component of low radiation energy is incident.

Also, of the radiation, high-energy components not absorbed by the scintillator arranged on the incident surface side of the substrate are absorbed by the scintillator covering the rear surface side of the substrate and converted into visible light. In the first conversion element 901 and the second conversion element 902, the back surface side of the substrate is not shielded, so that light converted from a component having a high energy in the radiation is converted into the first conversion element 901 and the second conversion element 902. It enters both of the conversion elements 902.

As described above, in the first conversion element 901, the signal due to the high energy component and the low energy component of the radiation and the signal due to the high energy component of the radiation in the second conversion element 902 are You can get each. That is, the information of different radiation energies can be held in the pixels PIX adjacent to each other. By holding the information acquired from the radiation of different energy components in the adjacent pixels PIX in this way, energy subtraction can be performed using a method described later.

3A and 3B schematically show an example of a cross-sectional structure of a pixel PIXA having a first conversion element 901 and a pixel PIXB and a pixel PIXC having a second conversion element 902. Here, the radiation is described as being incident from the upper side of the drawing, but the radiation may be incident from the lower side of the drawing. In FIGS. 3A and 3B, the first conversion element 901 and the second conversion element 902 are arranged between the substrate 310 and the scintillator 904 arranged on the incident surface side of the substrate 310. In FIG. 3A, in the pixel PIXB, the case where the light shielding layer 903 is arranged between the second conversion element 902 and the scintillator 904 is shown. On the other hand, in FIG. 3B, in the pixel PIXC, the case where the light shielding layer 903 is arranged between the second conversion element 902 and the scintillator 905 arranged on the back surface side opposite to the incident surface of the substrate 310 is shown. Has been done.

The conversion element S of each pixel PIX is disposed on an insulating substrate 310 such as a glass substrate that transmits the light emitted by the

scintillators

904 and 905. Each pixel PIX includes a conductive layer 311, an insulating layer 312, a semiconductor layer 313, an impurity semiconductor layer 314, and a conductive layer 315 on a substrate 310 in this order. The conductive layer 311 forms a gate electrode of a transistor (for example, TFT) that forms the switch T. The insulating layer 312 is arranged so as to cover the conductive layer 311, and the semiconductor layer 313 is arranged over the portion of the conductive layer 311 which forms the gate electrode with the insulating layer 312 interposed therebetween. The impurity semiconductor layer 314 is arranged on the semiconductor layer 313 so as to form two main terminals (source and drain) of the transistor forming the switch T. The conductive layer 315 forms a wiring pattern that is connected to the two main terminals (source and drain) of the transistor that forms the switch T, respectively. A part of the conductive layer 315 forms the column signal line Sig, and another part of the conductive layer 315 forms a wiring pattern for connecting the conversion element S and the switch T.

Each pixel PIX further includes an interlayer insulating film 316 covering the insulating layer 312 and the conductive layer 315. The interlayer insulating film 316 is provided with a contact plug 317 for connecting to a portion of the conductive layer 315 that constitutes the switch T. In addition, each pixel PIX includes a conversion element S arranged on the interlayer insulating film 316. In the example illustrated in FIGS. 3A and 3B, the conversion element S is configured as an indirect conversion element that converts light converted from radiation by the

scintillators

904 and 905 into an electric signal. The conversion element S includes a conductive layer 318, an insulating layer 319, a semiconductor layer 320, an impurity semiconductor layer 321, a conductive layer 322, and an electrode layer 325 that are stacked on the interlayer insulating film 316. The protective layer 323 and the adhesive layer 324 are disposed on the conversion element S. The scintillator 904 is arranged on the adhesive layer 324 so as to cover the incident surface side of the substrate 310. Further, the scintillator 905 is arranged so as to cover the back surface side of the substrate 310 opposite to the incident surface.

The conductive layers 318 form the lower electrodes of the conversion elements S, respectively. In addition, the conductive layer 322 and the electrode layer 325 form the upper electrode of each conversion element S. The conductive layer 318, the insulating layer 319, the semiconductor layer 320, the impurity semiconductor layer 321, and the conductive layer 322 configure a MIS type sensor as the conversion element S. For example, the impurity semiconductor layer 321 is formed using an n-type impurity semiconductor layer.

The

scintillators

904 and 905 can be configured using materials such as GOS (gadolinium oxysulfide) and CsI (cesium iodide). These materials can be formed by pasting, printing, vapor deposition, or the like. The scintillator 904 and the scintillator 905 may use the same material, or may use different materials depending on the energy of the radiation to be acquired.

In the present embodiment, the conversion element S shows an example in which a MIS type sensor is used, but the invention is not limited to this. The conversion element S may be, for example, a pn-type or PIN-type photodiode.

Next, the arrangement of the light shielding layer 903 arranged in the second conversion element 902 for blocking the light incident from the scintillator 904 or the scintillator 905 will be described. In the configuration shown in FIG. 3A, the second conversion element 902 of the pixel PIXB has a conductive layer 318 forming a lower electrode from the incident surface side of the substrate 310 toward the scintillator 904, a conductive layer forming a semiconductor layer 320, and an upper electrode. And layers 322 in that order. The conductive layer 322 forming the upper electrode functions as the light shielding layer 903. Specifically, the conductive layer 322 functions as the light-blocking layer 903 by forming the conductive layer 322 with a material that is opaque to light emitted from the scintillator 904, such as Al, Mo, Cr, or Cu. That is, the second conversion element 902 of the pixel PIXB has a light-shielding layer between the scintillator 904 and the second conversion element 902 so that the amount of light that can be received from the scintillator 904 is smaller than that of the first conversion element 901. 903 is arranged. The second conversion element 902 of the pixel PIXB is arranged so as to receive the light from the scintillator 905, similarly to the first conversion element 901 of the pixel PIXA. In the structure shown in FIG. 3B, the second conversion element 902 of the pixel PIXC forms a conductive layer 318, a semiconductor layer 320, and an upper electrode that form a lower electrode from the incident surface side of the substrate 310 toward the scintillator 904. The conductive layer 322 and the electrode layer 325 are included in this order. The conductive layer 318 forming the lower electrode functions as the light shielding layer 903. Specifically, by forming the conductive layer 318 with a material that is opaque to light emitted from the scintillator 905 such as Al, Mo, Cr, or Cu, the conductive layer 322 functions as the light-blocking layer 903. That is, the second conversion element 902 of the pixel PIXC has a light shielding layer between the scintillator 905 and the second conversion element 902 so that the amount of light that can be received from the scintillator 905 is smaller than that of the first conversion element 901. 903 is arranged. Further, the second conversion element 902 of the pixel PIXC is arranged so as to receive the light from the scintillator 904, similarly to the first conversion element 901 of the pixel PIXA.

On the other hand, in the first conversion element 901 of the pixel PIXA, the conductive layer 318 and the electrode layer 325 are made of a material transparent to light emitted from the scintillator 904, such as ITO (indium tin oxide). This makes it possible to obtain signals having different energy components between the adjacent pixel PIXA and pixel PIXB or pixel PIXC.

In addition, although an example in which the conductive layer 322 of the pixel PIXB and the conductive layer 318 of the pixel PIXC have a single-layer structure has been shown in the present embodiment, the present invention is not limited to this. For example, in the conductive layer 322 of the pixel PIXB and the conductive layer 318 of the pixel PIXC, a transparent material and an opaque material may be stacked, and in that case, the light shielding amount is determined by the area of the opaque material. Further, in the present embodiment, the conductive layer 322 of the pixel PIXB and the conductive layer 318 of the pixel PIXC are made to function as the light shielding layer 903, but the arrangement of the light shielding layer 903 is not limited to this. For example, in the pixel PIXB, a dedicated light-shielding layer 903 made of Al, Mo, Cr, Cu, or the like may be provided in the protective layer 323 for light incident from the scintillator 904. In this case, the potential of the light shielding layer 903 may be fixed to a constant potential before use.

Further, when the light from the scintillator 905 is blocked as in the pixel PIXC shown in FIG. 3B, the positions of the switch T and the column signal line Sig of the pixel PIXA that receives the light from the scintillator 905 are moved to the pixel PIXC side. You may distribute it. With such an arrangement, the aperture ratio of the first conversion element 901 to the scintillator 905 can be increased in the pixel PIXA.

Moreover, the light shielding layer 903 does not need to completely shield the light from the scintillator 904 or the scintillator 905 to the second conversion element 902 as described above. Energy subtraction is possible if the amount of light received from the scintillator 904 or scintillator 905 on the side where the light shielding layer 903 is arranged is different between the adjacent pixel PIXA and the pixel PIXB or pixel PIXC. In such a case, it is checked in advance what percentage of light with respect to the light received by the first conversion element 901 of the pixel PIXA is incident on the second conversion element 902 of the pixel PIXB or the pixel PIXC, This can be corrected by performing difference processing with the output of the first conversion element 901 as a reference.

As shown in FIGS. 3A and 3B, in the orthogonal projection onto the incident surface of the substrate 310, each of the column signal lines Sig is arranged so as to overlap a part of the pixel PIX. Such a configuration is advantageous in that the area of the conversion element S of each pixel PIX is increased, but is disadvantageous in that the capacitive coupling between the column signal line Sig and the conversion element S is increased. is there. When radiation enters the conversion element S, charges are accumulated in the conversion element S, and the potential of the conductive layer 318 as the lower electrode changes, the column signal line Sig is capacitively coupled between the column signal line Sig and the conversion element S. The crosstalk that changes the electric potential of occurs. 4a and 4b in FIG. 4 show a method of coping with this crosstalk. In the conversion elements S arranged in the row direction crossing the column direction among the plurality of conversion elements S, the number of pixels PIX having the second conversion element 902 in which the included light shielding layer 903 is arranged is the same for each row. To arrange. In the conversion elements S arranged in the column direction among the plurality of conversion elements S, the number of pixels PIX having the plurality of second conversion elements 902 included therein is arranged to be the same for each column. By arranging in this way, it is possible to suppress the occurrence of artifacts due to crosstalk in units of rows and columns.

Moreover, the radiation imaging apparatus 210 may have a function of automatically detecting the start of radiation irradiation. In this case, for example, the gate line Vg is operated so that the switch T is turned on/off, the signal from the conversion element S is read, and the presence or absence of radiation irradiation is determined from the output signal. When the number of pixels PIX including the second conversion element 902 including the light shielding layer 903 is different for each row, the amount of signals output for each row changes, and the detection accuracy varies. Therefore, as shown in 4a and 4b of FIG. 4, in the conversion elements S arranged in the row direction intersecting the column direction among the plurality of conversion elements S, the second conversion element 902 in which the included light shielding layer 903 is arranged is arranged. Are arranged so that the number of pixels PIX having the same is the same for each row. With such an arrangement, the detection accuracy of automatically detecting the start of radiation irradiation becomes stable.

In the arrangement example of the pixel PIX of 4b in FIG. 4, the density of the pixel PIX having the second conversion element 902 is reduced as compared with the arrangement example of the pixel PIX of 4a in FIG. Since the light from the scintillator 905 enters the conversion element S via the substrate 310, the light is diffused depending on the thickness of the substrate 310, and the MTF (Modulation Transfer Function) is reduced. Therefore, even if the density of the pixel PIX having the second conversion element 902 is reduced, the resolution does not substantially decrease. That is, when the second conversion element 902 receives the light emitted by the scintillator 905 which is opposed to the other scintillator via the substrate 310, the second conversion element 902 has a second number greater than the number of pixels PIX including the first conversion element 901. The number of pixels PIX including the conversion element 902 may be smaller.

The thickness of the substrate 310 may be reduced by mechanical polishing or chemical polishing in order to suppress the diffusion of light from the scintillator 905 through the substrate 310 and reduce the decrease in MTF. In order to reduce the decrease in MTF, as shown in FIGS. 3A and 3B, a louver layer, a microlens, or the like between the scintillator 905 and the substrate 310 that imparts directivity to the light emitted by the scintillator. The anti-scattering layer 326 may be provided. Further, in order to reduce the decrease in MTF, the image processing in the image processing unit 241 of the computer 240 may increase the resolution by sharpening processing. Further, as a method of matching the MTF of the low energy component due to the light from the scintillator 904 and the MTF of the high energy component due to the light from the scintillator 905, in addition to increasing the resolution, the MTF is decreased by matching the higher resolution to the lower one. Let After that, the energy subtraction process may be performed.

Next, operations of the radiation imaging apparatus 210 and the radiation imaging system 200 will be described with reference to FIG. Here, the operation of the radiation imaging apparatus 210 including the imaging panel 212 including the pixels PIX of 4 rows and 4 columns each including the conversion element S shown in FIG. 2 will be described as an example. The operation of the radiation imaging system 200 is controlled by the computer 240. The operation of the radiation imaging apparatus 210 is controlled by the control unit 214 under the control of the computer 240.

First, the control unit 214 causes the drive circuit 114 and the reading circuit 113 to perform a blank reading until the radiation of the radiation from the radiation source 230, in other words, the irradiation of the radiation to the radiation imaging apparatus 210 is started. In the idle reading, the driving circuit 114 sequentially drives the gate signals supplied to the gate lines Vg1 to Vg4 of the respective rows of the pixel array 112 to the active level, and resets the dark charges accumulated in the conversion element S. is there. Here, at the time of idle reading, a reset pulse of the active level is supplied to the reset switch of the integrating amplifier 105, and the column signal line Sig is reset to the reference potential. The dark charges are charges that are generated even when no radiation is incident on the conversion element S.

The control unit 214 can recognize the start of radiation emission from the radiation source 230 based on a start notification supplied from the exposure control unit 220 via the computer 240, for example. Further, as shown in FIG. 1, the radiation imaging apparatus 210 may be provided with a detection circuit 216 that detects a current flowing through the bias line Bs or the column signal line Sig of the pixel array 112. The control unit 214 can recognize the start of irradiation of the radiation from the radiation source 230 based on the output of the detection circuit 216.

When irradiated with radiation, the control unit 214 controls the switch T to be in an open state (off state). As a result, the charges generated in the conversion element S due to the irradiation of radiation are accumulated. The control unit 214 waits in this state until the irradiation of radiation is completed.

Next, the control unit 214 causes the drive circuit 114 and the reading circuit 113 to execute the main reading. In this reading, the drive circuit 114 drives the gate signals supplied to the gate lines Vg1 to Vg4 of the respective rows of the pixel array 112 to the active level. Then, the readout circuit 113 reads out the electric charge accumulated in the conversion element S via the column signal line Sig and outputs it to the computer 240 as radiation image data through the multiplexer 108, the buffer 109 and the AD converter 110.

Next, the acquisition of offset image data will be described. The conversion element S continues to accumulate dark charges even when it is not irradiated with radiation. Therefore, the control unit 214 acquires the offset image data by performing the same operation as when acquiring the radiation image data without irradiating the radiation. By subtracting the offset image data from the radiation image data, the offset component due to the dark charge can be removed.

Next, driving for capturing a moving image will be described with reference to FIG. When capturing a moving image, a plurality of gate lines Vg are simultaneously driven to an active level for high-speed reading. At this time, if the signals of the pixel PIX including the first conversion element 901 and the pixel PIX including the second conversion element 902 are output to one column signal wiring Sig, the energy components cannot be separated. Therefore, as shown in FIG. 6, by simultaneously setting the gate signals supplied to the gate line Vg1 and the gate line Vg3 to the active level, the signals of the conversion elements S12 and S32, which are the first conversion elements 901, are converted. Is output to the column signal line Sig2. At the same time, the signals of the conversion elements S11 and S31 which are the second conversion elements 902 are output to the column signal line Sig1. Energy subtraction processing can be performed by outputting the signals of the first conversion element 901 and the second conversion element 902 to different column signal lines Sig.

Next, the image processing flow in this embodiment will be described with reference to FIGS. 7A and 7B. First, in step S701, after performing the above-mentioned blank reading, the control unit 214 controls to accumulate the charges generated by the conversion element S during the irradiation of the radiation in order to acquire the radiation image data. Next, in step S702, the control unit 214 causes the drive circuit 114 and the reading circuit 113 to perform the main reading, and reads the radiation image data. In step S702, the radiation image data is output to the computer 240. Next, the control unit 214 performs a storage operation for acquiring offset image data in step S703, and causes the drive circuit 114 and the reading circuit 113 to read the offset image data and outputs it to the computer 240 in step S704.

The image processing unit 241 executes the processes shown in and after step S705. The computer 240 including the image processing unit 241 is an example of an image processing apparatus that images a subject using a plurality of radiation images obtained by different radiation energies. First, in step S705, the image processing unit 241 of the computer 240 performs offset correction by subtracting the radiation image data acquired in step S702 by the offset image data acquired in step S704.

Next, in step S706, the image processing unit 241 outputs the radiation image data after the offset correction to the radiation image data output from the first conversion element 901 and the radiation image data output from the second conversion element 902. To separate. Here, in the configuration of FIG. 3A, the second conversion element 902 receives radiation from above in the drawing, shields light from the scintillator 904, and receives light generated by high-energy radiation from the scintillator 905. It will be described as a thing. Further, the radiation image data output from the first conversion element 901 is referred to as a double-sided incident image, and the radiation image data output from the second conversion element 902 is referred to as a single-sided incident image.

Next, in step S<b>707, the image processing unit 241 performs gain correction of the double-sided incident image using the gain correction image data obtained by performing radiation field irradiation in the absence of a subject. Further, in step S711, the image processing unit 241 uses the gain correction image data to perform gain correction on the single-sided incident image.

After performing the gain correction, in step S708, the image processing unit 241 compensates for the missing double-sided incident image of the pixel PIX that does not include the first conversion element 901, in other words, the pixel PIX that has the second conversion element 902. Pixel interpolation is performed. Similarly, in step S712, the image processing unit 241 performs pixel interpolation for compensating for the lack of the one-sided incident image of the pixel PIX not including the second conversion element 902, in other words, the pixel PIX having the first conversion element 901. .. Pixel interpolation in these steps S708 and S712 will be described using 8a and 8b in FIG. Here, as an example, an arrangement will be described in which the pixel PIX including the first conversion element 901 is larger in number than the pixel PIX including the second conversion element 902, which is illustrated in 4b of FIG.

First, the pixel interpolation of the double-sided incident image will be described with reference to 8a in FIG. The value in the double-sided incident image of the pixel E having the second conversion element 902 that outputs the single-sided incident image is adjacent to the pixel E, and the pixel A that has the first conversion element 901 that outputs the pixel value of the double-sided incident image, Interpolation is performed using pixel values of B, C, D, F, G, H, and I. For example, the image processing unit 241 may interpolate the value of the pixel E in the double-sided incident image by using the average value of 8 pixels adjacent to the pixel E in the double-sided incident image. Further, for example, the image processing unit 241 interpolates the value of the pixel E in the double-sided incident image by using the average value of a part of the pixels adjacent to each other in the double-sided incident image, such as the pixels B, D, F, and H. Good. In step S708, the radiation image data generated by the high energy component and the low energy component of the radiation of each pixel PIX is generated by performing pixel interpolation.

Next, pixel interpolation in a single-sided incident image will be described with reference to 8b in FIG. The pixel J having the first conversion element 901 that outputs the pixel value of the double-sided incident image is adjacent to the pixel J, and the pixels K, L, and M that have the second conversion element 902 that outputs the pixel value of the single-sided incident image. , N pixel values are used for interpolation. For example, the image processing unit 241 may interpolate the single-sided image data of the pixel J by using the average value of the single-sided image data of four pixels adjacent to the pixel J. In this case, for example, the distance from the position where the pixel J is arranged to the pixel K and the distance to the pixel N are different. Therefore, the pixel values of the single-sided incident images output from the pixels K, L, M, and N may be weighted and averaged according to the distance. By performing pixel interpolation in step S712, radiation image data (hereinafter, high energy image) generated by the high energy component of the radiation of each pixel PIX is generated.

Next, in step S709, the image processing unit 241 generates radiation image data (hereinafter, low energy image) based on low energy components of radiation. As described above, when the light-shielding layer 903 is provided on the side of the second conversion element 902 where the radiation enters, a high-energy image can be obtained by interpolating the single-sided incident image. The double-sided incident image generated by pixel interpolation in step S708 is a radiation image having both high energy and low energy components. Therefore, a low energy image can be generated by subtracting the high energy image acquired by pixel interpolation in step S712 from the radiation image pixel interpolated in step S708. In this way, the image processing unit 241 acquires a high energy image and a low energy image.

Although the light-shielding layer 903 is provided on the side of the second conversion element 902 where the radiation enters in the above description, it is also possible to provide the light-shielding layer 903 on the side of the second conversion element 902 opposite to the side where the radiation enters. .. In that case, the single-sided incident image becomes radiation image data with a low energy component, and the pixel-interpolated single-sided incident image is subtracted from the pixel-interpolated double-sided incident image to obtain high-energy component radiation image data (high-energy image). Can be generated. However, the radiation image of the high-energy component is a component of the radiation that cannot be completely absorbed by the scintillator 904 on the incident side of the radiation, and therefore the amount of light from the scintillator 905 is smaller than the amount of light from the scintillator 904. Therefore, when the high-energy image is generated by subtracting the single-side incident image from the double-side incident image, noise in the low-energy component radiation image is superimposed on the high-energy component radiation image. As a result, the S/N ratio of the radiation image of the high energy component becomes low. Therefore, as shown in the above-described embodiment, the side of the second conversion element 902 on which the radiation is incident is shielded, the double-sided image data is a high energy component+low energy component, and the single-sided image data is a high energy component image. Data. Then, the S/N ratio can be improved by subtracting the single-sided image data from the double-sided image data to generate the low energy image.

Next, in step S710, the image processing unit 241 corrects (MTF correction) the spatial frequency characteristic (MTF: Modulation Transfer Function) of the low energy image generated in step S709. Further, in step S713, the spatial frequency characteristic of the high energy image obtained in step S712 is corrected (MTF correction). The image processing unit 241 sets the high energy image and the low energy image so that the spatial frequency characteristic of the high energy image (first radiation image) and the spatial frequency characteristic of the low energy image (second radiation image) are close to each other. The spatial frequency characteristic of at least one of the above is changed. Therefore, both of the MTF correction in steps S710 and S713 do not necessarily have to be executed. The image processing unit 241 that performs the MTF correction as described above changes the spatial frequency of at least one of the plurality of radiation images so that the spatial frequency characteristics of the plurality of radiation images obtained by the plurality of different radiation energies come close to each other. It is an example of a changing unit.

Next, in step S714, the image processing unit 241 generates an energy subtraction image and/or a spectral imaging image using the high energy image and the low energy image after MFT correction. Well-known methods can be used to generate the energy subtraction image and the spectral imaging image. The image processing unit 241 that performs the process of step S714 is an example of a processing unit that generates an image of a subject using a plurality of radiographic images after the change by the changing unit described above. The image processing unit 241 may generate a normal radiation image based on the double-sided image data output from the first conversion element 901 in step S715. The first conversion element 901 receives light from the scintillator 904 on the side where the radiation enters and light from the scintillator 905 on the side opposite to the side where the radiation enters. As a result, a higher S/N ratio can be obtained in a normal radiation image than in the case where only one of the scintillators emits light.

Next, an example of the process of changing the spatial frequency characteristic of the radiation image in steps S710 and S713 will be described. First, the spatial frequency characteristics of each of the high-energy image and the low-energy image are measured before the subject is imaged. Although a slit method, a chart method, an edge method, etc. have been proposed as a method for calculating the spatial frequency characteristic, any method may be used in this proposal.

FIG. 9 is a graph showing the tendency of the spatial frequency characteristic of the high energy image and the spatial frequency characteristic of the low energy image. The spatial frequency characteristic 501 of the low energy image tends to maintain the signal value even when the frequency becomes high, but the spatial frequency characteristic 502 of the high energy image tends to maintain no high frequency component. This is because, for example, fluorescence is scattered in the layer provided between the scintillator 904 and the scintillator 905. In the present embodiment, the image processing unit 241 functioning as the changing unit measures the spatial frequency characteristic measured for one radiation energy of the plurality of radiation energies and measures the other radiation energy of the plurality of radiation energies. A process preset to bring the spatial frequency characteristics closer to each other is applied to a radiation image obtained with another radiation energy. Hereinafter, the process of the changing unit will be described more specifically.

The image processing unit 241 of the first embodiment approximates the spatial frequency characteristics of the radiation image obtained by the other radiation energy to the spatial frequency characteristics of the radiation image obtained by the lowest radiation energy of the plurality of radiation energies. .. That is, the image processing unit 241 performs the process set so that the first spatial frequency characteristic previously measured for the lowest radiation energy is approximated to the spatial frequency characteristic previously measured for another radiation energy. It is applied to a radiation image obtained by radiation energy.

For example, the image processing unit 241 approximates the high spatial frequency characteristic 501 of the low energy image to the low spatial frequency characteristic 502 of the high energy image. In this case, step S710 is skipped. An appropriate filter is designed based on the spatial frequency characteristics of the low energy image and the high energy image obtained in advance. Alternatively, the filter may be designed using an existing function such as Gaussian distribution. In step S713, the image processing unit 241 performs a convolution operation on the high energy image using the created filter to change the spatial frequency characteristic of the high energy image. Step S710 is skipped.

High-energy images are expected to have almost no high-frequency components remaining as compared to low-energy images, and high-frequency noise is expected to increase as high-frequency components increase, so appropriate filter design that takes this into account is necessary. Is. In addition, since the contrast of the image differs between the low energy image and the high energy image due to the difference in radiation energy, it is difficult to correct the same spatial frequency characteristic. Therefore, the image processing unit 241 causes the spatial frequency characteristic of the radiation image obtained with other radiation energy to fall within the margin range set with respect to the spatial frequency characteristic of the radiation image obtained with one radiation energy, The radiation image obtained with other radiation energy is processed. For example, as shown in FIG. 10, when changing the spatial frequency characteristic 502 of the high energy image, a tolerance is set for the spatial frequency characteristic 501 of the target low energy image, and a margin 503 is provided at each spatial frequency. Further, in order to suppress the emphasis of noise particularly on the high frequency side, the margin 503 may be switched to the margin 504 with a predetermined spatial frequency as a boundary so as to be wide on the low value side. For example, the margin 503 is set to ±0.05 or less, and on the high frequency side, the margin 504 is set to −0.1 or less on the low value side.

Thus, in the process of changing the spatial frequency characteristic of the high energy image, the difference between the spatial frequency characteristic measured for high radiation energy and the spatial frequency characteristic measured for low radiation energy is within ±0.05 at each frequency. Is set as follows. Also, this process is set so that the difference between the spatial frequency characteristic measured for high radiation energy and the spatial frequency characteristic measured for low radiation energy is within -0.2 in a region higher than a predetermined spatial frequency. To be done. By this method, the spatial frequencies of the high energy image and the low energy image can be made equal. Although the margin 503 and the margin 504 are switched in FIG. 10, the margin may continuously increase as the spatial frequency decreases.

In step S713, the image processing unit 241 processes the high-energy image acquired in step S712 by using the filter generated as described above, thereby changing the spatial frequency characteristic of the high-energy image to the space of the low-energy image. Close to the frequency characteristics. In step S714, the energy subtraction image and/or the spectral imaging image are generated using the high-energy image and the low-energy image whose spatial frequencies are close to each other, so that the image quality of these images is improved.

<Second Embodiment>
In the first embodiment, the spatial frequency characteristics of the high energy image and the low energy image are approximated by performing the MTF correction on the high energy image. That is, the configuration has been described in which the radiation image obtained with another radiation energy is processed so as to approach the spatial frequency characteristic of the radiation image obtained with the lowest radiation energy of the plurality of radiation energies. In the second embodiment, an example of performing MTF correction on a low energy image will be described. That is, in the second embodiment, a radiation image obtained with another radiation energy is processed so as to approach the spatial frequency characteristic of the radiation image obtained with the highest radiation energy among the plurality of radiation energies. The configurations and operations of the radiation imaging system and the radiation imaging apparatus according to the second embodiment are similar to those of the first embodiment (FIGS. 1 to 8). However, in the second embodiment, the MTF correction of the low energy image in step S710 is executed, and the MTF correction of the high energy image in step S713 is skipped.

In step S710, the image processing unit 241 approximates the spatial frequency characteristic 502 of the low energy image to the spatial frequency characteristic 502 of the high energy image. An appropriate filter is designed in advance based on the spatial frequency characteristics of the low energy image and the high energy image obtained in advance. Alternatively, the filter may be designed in advance using an existing function such as Gaussian distribution. In step S710, the image processing unit 241 changes the spatial frequency characteristic 501 of the low energy image by performing a convolution operation on the low energy image using a filter created in advance.

With this change, it is predicted that the high-energy image has almost no high-frequency components remaining compared to the low-energy image, and most of the high-frequency components of the low-energy image will be lost due to this calculation. However, high-frequency noise is suppressed, and stable output can be expected in subsequent processing. In addition, since the contrast of the image differs between the low energy image and the high energy image due to the difference in radiation energy, it is difficult to correct the same spatial frequency characteristic. Therefore, as shown in FIG. 11, when the spatial frequency characteristic 501 of the low energy image is changed, a tolerance is set on the curve of the spatial frequency characteristic 502 of the target high energy image, and a margin 503 is provided at each spatial frequency. The margin is, for example, ±0.05 or less.

In step S710, the image processing unit 241 processes the low-energy image generated in step S709 by using the filter generated as described above, thereby changing the spatial frequency characteristic of the low-energy image to the space of the high-energy image. Close to the frequency characteristics. In step S714, the energy subtraction image and/or the spectral imaging image are generated using the high-energy image and the low-energy image whose spatial frequencies are close to each other, so that the image quality of these images is improved.

<Third Embodiment>
In the first and second embodiments, one of the spatial frequency characteristic of the high energy image and the frequency characteristic of the low energy image is approximated to the other. In the third embodiment, the plurality of radiation images are processed so that the respective spatial frequency characteristics of the plurality of radiation images obtained by the plurality of radiation energies approach the preset spatial frequency characteristics. As an example, in the third embodiment, a spatial frequency characteristic that is a model of a spatial frequency characteristic necessary for diagnosing a target organ is set, and the spatial frequency characteristic of a high energy image and the spatial frequency characteristic of a low energy image are set to the characteristic. To approximate. The configurations and operations of the radiation imaging system and the radiation imaging apparatus of the third embodiment are the same as those of the first embodiment (FIGS. 1 to 8). However, in the third embodiment, the MTF correction of the low energy image in step S710 and the MTF correction of the high energy image in step S713 are executed.

The modification of the spatial frequency characteristic according to the third embodiment is performed by setting a process of approximating the spatial frequency characteristic measured in advance for each of a plurality of radiation energies to a preset spatial frequency characteristic, and performing the set process in a plurality of radiations. Apply to images. Hereinafter, a more specific example will be described. In the third embodiment, a filter for converting the spatial frequency characteristic from the spatial frequency characteristic of each of the high energy image and the low energy image is designed. The filter may be designed using an existing function such as Gaussian distribution. In the present embodiment, as shown in FIG. 12, the first filter that brings the spatial frequency characteristic 501 of the low energy image closer to the arbitrary spatial frequency characteristic 505 and the spatial frequency characteristic 502 of the high energy image are set to the spatial frequency characteristic 505. A second filter to approach is designed. The spatial frequency characteristic 505 is, for example, a spatial frequency characteristic that models the spatial frequency characteristic necessary for diagnosing the target organ. By performing the convolution operation on the low energy image using the first filter and the convolution operation on the high energy image using the second filter, the spatial frequency characteristic 501 of the low energy image and the spatial frequency characteristic of the high energy image are obtained. 502 is modified to approach the spatial frequency characteristic 505.

Also, it is difficult to correct the same spatial frequency characteristics between the low-energy image and the high-energy image because the image contrast differs due to the difference in radiation energy. Therefore, as shown in FIG. 12, a tolerance is set for the target spatial frequency characteristic 505, and a margin 503 is provided at each spatial frequency. The margin is, for example, ±0.05 or less.

In step S710, the image processing unit 241 processes the low-energy image generated in step S709 by using the first filter generated as described above to spatially measure the spatial frequency characteristic 501 of the low-energy image. It approaches the frequency characteristic 505. In step S713, the image processing unit 241 processes the high-energy image acquired in step S712 by using the second filter generated as described above, thereby spatially processing the spatial frequency characteristic 502 of the high-energy image. It approaches the frequency characteristic 505. In this way, the spatial frequency characteristics of the low energy image and the high energy image are approximated to each other. In step S714, the energy subtraction image and/or the spectral imaging image are generated using the high energy image and the low energy image whose spatial frequencies are approximated, so that the image quality of these images is improved.

In the above, the spatial frequency characteristic 305 is set by modeling the spatial frequency required for diagnosing the target organ, but the present invention is not limited to this. For example, the spatial frequency characteristic may be set as follows. That is, the spatial frequency characteristic measured for the lowest radiation energy (or the highest radiation energy) of the plurality of radiation energies becomes 0 at the spatial frequency at which the spatial frequency becomes equal to or less than the threshold value, and the spatial frequency becomes lower in the frequency region lower than the spatial frequency. The spatial frequency characteristic may be set so that the characteristic gently changes from 0 to 1.

For example, as shown in FIG. 13, a threshold value 510 is set to the spatial frequency characteristic 502 of the high energy image. Then, the value of the spatial frequency characteristic 502 becomes 0 at the spatial frequency where the threshold value 510 is set, and the spatial frequency characteristic 507 that is smoothly connected from 0 to 1 in the spatial frequency region lower than the spatial frequency is set as the target spatial frequency characteristic. Good. Similarly, a threshold value 510 is set to the spatial frequency characteristic 501 of the low energy image, and the value of the spatial frequency characteristic 501 becomes 0 at the spatial frequency at which the threshold value 510 becomes, and the value gradually decreases from 0 to 1 in the spatial frequency region lower than the spatial frequency. The connected spatial frequency characteristic 506 may be set as a target spatial frequency characteristic. Although 0.1 is used as the threshold value 510, the threshold value 510 is not limited to this. However, the threshold value 510 is preferably 0.2 or less.

<Modification>
In addition, in each of the above-described embodiments, a specific example of the configuration using two radiation images having different radiation energies is described, but it is also applicable to a configuration that generates an image using three or more radiation images. As described above. In that case, in the first embodiment, for example, the spatial frequency characteristic of the radiation image captured by the other radiation energy is approximated to the spatial frequency characteristic of the radiation image captured by the lowest radiation energy among the plurality of radiation energies. become. In addition, in the second embodiment, for example, the spatial frequency characteristic of a radiation image captured with the highest radiation energy of a plurality of radiation energies is approximated to the spatial frequency characteristic of a radiation image captured with another radiation energy. Become. It should be noted that the approximate target spatial frequency characteristic is not limited to the image of the highest or lowest radiation energy. You may make it approximate the spatial frequency characteristic of the radiation image imaged by other radiation energy to the spatial frequency characteristic of the radiation image imaged by one of several radiation energy.

In addition, in the third embodiment, a plurality of spatial frequency characteristics of a radiation image captured by a plurality of radiation energies are approximated to a preset target spatial frequency characteristic. Alternatively, for one of a plurality of spatial frequency characteristics of a radiation image captured by a plurality of radiation energies, the spatial frequency characteristic becomes 0 at a spatial frequency that is a threshold value, and the spatial frequency characteristic becomes 0 from a spatial frequency lower than the spatial frequency. The spatial frequency characteristic smoothly connecting to 1 may be set to the target spatial frequency.

<Other Embodiments>
The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program. It can also be realized by the processing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

The invention is not limited to the above embodiment, and various modifications and variations can be made without departing from the spirit and scope of the invention. Therefore, the following claims are attached to open the scope of the invention.

The present application claims priority based on Japanese Patent Application No. 2019-002140 filed on January 9, 2019, and the entire contents thereof are incorporated herein.

Claims

Changing means for changing the spatial frequency characteristics of at least one of the plurality of radiation images so that the spatial frequency characteristics of the plurality of radiation images obtained by different plurality of radiation energies approach each other;
Processing means for generating an image of a subject using the plurality of changed radiation images,
The changing unit preliminarily brings the spatial frequency characteristic measured for one radiation energy of the plurality of radiation energies close to the spatial frequency characteristic measured for another radiation energy of the plurality of radiation energies. An image processing apparatus, wherein the set process is applied to a radiation image obtained with the other radiation energy.
The changing means is configured so that the spatial frequency characteristic of the radiation image obtained by the other radiation energy falls within a margin range set with respect to the spatial frequency characteristic of the radiation image obtained by the one radiation energy. The image processing apparatus according to claim 1, wherein a radiation image obtained with other radiation energy is processed.
The image processing apparatus according to claim 1, wherein the one radiation energy is the lowest radiation energy among the plurality of radiation energies.
The changing unit performs a process set to approximate a spatial frequency characteristic previously measured for the other radiation energy to a first spatial frequency characteristic previously measured for the lowest radiation energy. The image processing apparatus according to claim 3, wherein the image processing apparatus is applied to a radiation image obtained by energy.
The processing in the changing means is set so that the difference between the spatial frequency characteristic measured for the other radiation energy and the first spatial frequency characteristic is within ±0.05 at each frequency. The image processing apparatus according to claim 4, which is characterized in that.
In the processing in the changing means, the difference between the spatial frequency characteristic measured for the other radiation energy and the first spatial frequency characteristic is within −0.2 in a region higher than a predetermined spatial frequency. The image processing apparatus according to claim 5, wherein the image processing apparatus is set.
The image processing apparatus according to claim 1, wherein the one radiation energy is the highest radiation energy among the plurality of radiation energies.
The changing means performs a process set to approximate a spatial frequency characteristic previously measured for the other radiation energy to a first spatial frequency characteristic previously measured for the highest radiation energy. The image processing apparatus according to claim 7, wherein the image processing apparatus is applied to a radiation image obtained by radiation energy.
The processing in the changing unit is set such that the difference between the spatial frequency characteristic of the image obtained by the other radiation energy and the first spatial frequency characteristic is within ±0.05 at each frequency. The image processing device according to claim 8, wherein
Changing means for changing the spatial frequency characteristics of at least one of the plurality of radiation images so that the spatial frequency characteristics of the plurality of radiation images obtained by different plurality of radiation energies approach each other;
Processing means for generating an image of a subject using the plurality of changed radiation images,
The changing means processes the plurality of radiation images such that the respective spatial frequency characteristics of the plurality of radiation images obtained by the plurality of radiation energies approach a preset spatial frequency characteristic. Image processing device.
The changing unit sets a process of approximating a spatial frequency characteristic measured in advance for each of the plurality of radiation energies to the preset spatial frequency characteristic, and applying the set process to the plurality of radiation images. The image processing apparatus according to claim 10, wherein:
The preset spatial frequency characteristic is 0 at a spatial frequency at which the spatial frequency characteristic measured for the lowest radiation energy of the plurality of radiation energies is equal to or less than a threshold value, and in a region of a frequency lower than the spatial frequency, The image processing apparatus according to claim 11, wherein the spatial frequency characteristic is set so as to gently change from 0 to 1.
The preset spatial frequency characteristic is 0 at a spatial frequency at which the spatial frequency characteristic measured for the highest radiation energy among the plurality of radiation energies is equal to or less than a threshold value, and in a region of a frequency lower than the spatial frequency, The image processing apparatus according to claim 11, wherein the spatial frequency characteristic is set so as to gently change from 0 to 1.
The image processing device according to any one of claims 1 to 13, wherein the changing unit changes the spatial frequency characteristic by a process of applying a filter to the radiation image.
A changing step of changing the spatial frequency characteristics of at least one of the plurality of radiographic images so that the spatial frequency characteristics of the plurality of radiographic images obtained by the plurality of different radiation energies approach each other;
A processing step of generating an image of a subject using the plurality of changed radiographic images,
In the changing step, a spatial frequency characteristic measured for one radiation energy of the plurality of radiation energies is approximated to a spatial frequency characteristic measured for another radiation energy of the plurality of radiation energies in advance. An image processing method, wherein the set process is applied to a radiation image obtained with the other radiation energy.
A changing step of changing the spatial frequency characteristics of at least one of the plurality of radiographic images so that the spatial frequency characteristics of the plurality of radiographic images obtained by the plurality of different radiation energies approach each other;
A processing step of generating an image of a subject using the plurality of changed radiographic images,
In the changing step, the plurality of radiation images are processed so that each of the spatial frequency characteristics of the plurality of radiation images obtained by the plurality of radiation energies approaches a preset spatial frequency characteristic. Image processing method.
A program for causing a computer to function as each unit of the image processing apparatus according to any one of claims 1 to 14.