JP5355726B2 - Imaging apparatus, image processing apparatus, imaging system, radiation imaging apparatus, and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that it is difficult to calculate an incidence X-ray dosage because a gain value depending on the number of added pixels is not obtained due to non-linearity of analog calculation when adjacent pixel addition is performed on a FPD in an analog. <P>SOLUTION: A photographic device includes a detector including a plurality of detection elements that detect radiation intensity and performs analog addition of an analog electric signal according to distribution of the radiation intensity detected by the detector. The photographic device obtains correction information for correcting an electrical signal obtained by the analog addition indicating non-linear output for the number of added signals to be linear for the number of the added signals, and corrects the electrical signal obtained by the analog addition by the obtained correction information. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a technique for imaging a radiation intensity distribution, and more particularly to an imaging apparatus, an image processing apparatus, an imaging system, a radiation imaging apparatus, and an image processing method suitable for a medical radiographic apparatus.

The most common technique for non-invasively observing the inside of a human body and used for medical diagnosis is to directly image the transmittance distribution of X-rays transmitted through the human body. As an imaging method,
-The traditional method of imaging the fluorescence distribution caused by X-rays reaching the phosphor with a silver salt film,
A method of amplifying photoelectrons due to fluorescence with a photomultiplier tube and imaging with a TV camera,
A method of reading and visualizing latent image information produced by an X-ray intensity distribution on a photostimulable phosphor with a laser beam;
A method for imaging a spatial distribution of free electrons generated in a semiconductor layer or heavy metal by fluorescence or X-ray irradiation using a flat panel detector (hereinafter referred to as FPD) composed of a solid-state image sensor;
Etc.

  In particular, recently, due to advances in semiconductor technology, large-scale FPDs that can encompass the entire human body have also been developed, and acquisition of radiographic images using FPDs is also spreading in the medical field.

  In the FPD, a charge obtained by photoelectrically converting the fluorescence or a charge obtained by collecting the free electrons at a high potential is temporarily stored in capacitors corresponding to pixels distributed in a matrix on the image receiving surface. Thereafter, the switching transistors (TFTs) formed on the thin film are sequentially energized (scanned) to extract image information as a collection of one-dimensional data.

  FIG. 6 is a diagram for specifically explaining the operation of the FPD described above. In FIG. 6, the FPD 100 has pixel elements 101 distributed in an M × N matrix. More specifically, as shown in FIG. 7A, the pixel element 101 includes a capacitor 201 and a TFT 202 having a storage Cx capacity. Charges corresponding to the amount of light received from a photoelectric conversion element (not shown) are accumulated in the capacitor 201. A photoelectric conversion element is comprised with the photodiode which converts the fluorescence from the fluorescent substance resulting from a X-ray into an electrical signal, for example. Or the structure which accumulate | stores in the capacitor | condenser 201 the electric charge obtained by collecting the free electron which generate | occur | produces when the X-ray energetic particle which a semiconductor layer etc. flies at high potential is proposed.

  In FIG. 6, functional elements 103 are output holding units, and there are provided as many pixel elements 101 (M in FIG. 6) as one line of pixel elements 101 arranged in a matrix. Specifically, as shown in FIG. 7B, the functional element 103 is a unit having an output holding capacitor 204 having a Co capacitance and a signal resetting transistor 203.

In FIG. 6, a sub-scanning selection control circuit 102 sequentially selects and outputs selection control signals 1 to N for simultaneously selecting one line of pixel elements 101 arranged in a matrix. FIG. 9 is a diagram for explaining signal output timings of the selection control signals 1 to N by the sub-scanning selection control circuit 102. Only the selection control signal 1 is in the ON state at timings t _{1 to} t ₂ , and only the data in the first row (signals from the M pixel elements in the first row) in FIG. . Similarly, at the timing from t ₃ to t ₄ , only the selection control signal 2 is turned on, and only the data in the second row in FIG. 6 is transferred to the functional unit 103. By repeating such control N times, signals from M × N pixel elements are obtained.

In FIG. 9, at least the capacitor Cx and Co in FIGS. 7A and 7B are connected to the conduction resistance of the TFT 202 and the signal line during the time (for example, t ₂ −t ₁ ) during which the selection control signal is held in the ON state. This is the time required to achieve a substantially parallel connection through a resistor and achieve a sufficient equilibrium state.

となる。別の画素要素１０１の蓄積電荷をＱ₂とすると、出力される電圧Ｖ₂は、

となる。 Assuming that the charge accumulated in a certain pixel element 101 is Q ₁ , the output voltage V ₁ is

It becomes. When the accumulated charge of another pixel element 101 is Q ₂ , the output voltage V ₂ is

It becomes.

Here, in general, the capacitance of the capacitor on the pixel is very small, and Cx << Co. For this reason, said Formula (1) and Formula (2) are represented by the following formula | equation (3) and Formula (4), respectively.

  Returning to FIG. 6, the analog multiplexer circuit 104 outputs one line at a time and sequentially outputs M potential signals held by the M functional elements 103 for holding output as image output signals 106. Each input value from the functional element 103 is sequentially selected by the main scanning selection control circuit 105 and is output on the signal line 106. Therefore, a one-dimensional analog signal (video signal) is output from the signal line 106 as image information. When analog addition is performed in the main scanning direction, the signal 106 is input to the analog integrator 107, and the analog integrator 107 is reset by reset means (not shown) at an output timing for each number of pixels to be added. If the output of the analog integrator 107 immediately before the reset is used, an analog addition result in the main scanning direction can be obtained. However, hereinafter, description will be made using the output 106 that does not perform analog addition in the main scanning direction.

  Further, processing until the signal output from the analog multiplexer circuit 104 is stored in the memory as digital image data will be described with reference to FIG. The FPD 100 has the configuration as described with reference to FIG. The video signal output from the FPD 100 to the signal line 106 is converted into a digital value by an analog / digital conversion circuit 108 (A / D conversion), and is stored in the memory 109 as a digital image. As described above, the potential information of the pixels arranged in an M × N matrix is stored in the memory as a digital image.

Next, the operation in the pixel addition mode in the FPD 100 will be described. For example, when the pixel addition number is 2, the sub-scanning selection control circuit 102 is driven so as to simultaneously select two lines as shown in FIG. That is, the operation (FIG. 9) in which one selection control signal is turned on at one timing is switched to an operation in which the second selection control signal is turned on at one timing as shown in FIG. In this case, the two pixel elements 101 are electrically connected. Therefore, for example, when the charge of a certain pixel is Q ₁ and the charge of a connected pixel is Q ₂ , the output voltage V ₁₂ is expressed by Expression (5).

となり、式（３），式（４）と比較すると、電気的接続により出力電位が加算されていることがわかる。 Here, if there is a condition that Cx << Co,

Compared with the equations (3) and (4), it can be seen that the output potential is added by the electrical connection.

  Further, as the output holding circuit of FIG. 7B, an integration circuit having a sufficiently high input impedance using the operational amplifier 205 as shown in FIG. 11 is configured, so that equations (3), (4), (6 ) Can be used more accurately.

  In the above configuration, pixel signals in which 2 pixels and 3 pixels are added can be obtained by performing not only simultaneous selection of 2 lines but also simultaneous selection of 3 lines and 4 lines. Depending on the application used, it may be desired to obtain image data at high speed even at the expense of spatial resolution. In such a case, the above-described function of adding pixels in an analog manner (pixel addition mode) can be used.

  In the main scanning direction, the outputs of the multiplexers may be added in an analog fashion sequentially, or once taken into the memory, it is possible to add and average them by digital calculation. The shape can be kept square. A technique for adding adjacent pixel information in an analog manner is also described in Patent Document 1.

Japanese Patent Laid-Open No. 9-21879

  However, from the standpoint of an operator using the FPD, a constant X-ray dose is constant regardless of the number of added pixels when analog lines are added (referred to as line addition) or not. It is desirable to obtain value output information. However, it is difficult to accurately control the capacitance components and TFT characteristics of the FPD, which is a semiconductor product, and the voltage value when added in an analog manner is not necessarily a multiple of the added number. Dividing the value by the number of additions does not give a constant value. This can be said to be a phenomenon in which Cx in Expression (5) cannot be ignored by adding many lines.

  FIG. 12 is a graph of the pixel addition number and the pixel output value in two different FPDs, where the horizontal axis represents the line addition number (the number of pixels subjected to line addition), and the vertical axis represents the average output voltage. Show. In FIG. 12, a line indicated by A is a characteristic of an output voltage of a representative pixel of one FPD, and a line indicated by B is a characteristic of an output voltage of a representative pixel of another FPD. A straight line indicated by C shows an ideal characteristic proportional to the desired number of additions.

As is clear from FIG. 12, there are the following two features.
1) Go away from the desired straight line as the number of additions increases 2) The characteristics differ depending on the FPD.

  In view of the above, if a pixel value obtained by simply adding is used as in the conventional case, stable characteristics cannot be obtained due to variations in characteristics when line addition is performed. In other words, the user is not conscious of the pixel addition number and expects the output to be constant when a certain X-ray dose is irradiated, but in actuality line addition was performed with the pixel addition number. Even if the pixel value is divided, an accurate pixel value cannot be obtained. Therefore, there is a problem that it is very difficult to accurately calculate the incident X-ray dose from the image information obtained by line addition.

  As a method for solving such a problem, it is conceivable to digitally capture all pixel values without adding them and form an addition pixel by calculation. However, since the amount of digital transfer increases significantly, it cannot be said that the solution fully utilizes the merit of adding pixels to reduce the amount of data. That is, when analog adjacent pixels are added on the FPD, a gain value corresponding to the number of added pixels cannot be obtained due to the non-linearity of analog calculation, and it is not easy to calculate the incident X-ray dose.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to make it possible to accurately calculate the amount of incident radiation in a captured image obtained in the pixel addition mode.

In order to achieve the above object, a photographing apparatus according to the present invention has, for example, the following configuration. That is,
A plurality of radiation detection elements arranged two-dimensionally ;
An analog addition circuit for analog addition of analog electric signals obtained by the plurality of radiation detection elements every predetermined number ;
Acquisition of correction information corresponding to a difference between a value obtained by arithmetic addition of the values of the predetermined number of analog electrical signals and a value obtained by analog addition of the predetermined number of analog electrical signals by the analog addition circuit Means,
Dark current correction means for correcting an offset corresponding to a dark current component included in radiation image data obtained by the plurality of radiation detection elements;
And correction means for correcting the radiation image data corrected by the dark current correction means by the correction information acquired by the acquisition means .

  According to the present invention, it is possible to accurately calculate the amount of incident radiation in a captured image obtained in the pixel addition mode.

It is a block diagram which shows the structure of the radiography apparatus by 1st Embodiment. It is a flowchart which shows the calibration process by 1st Embodiment. It is a flowchart which shows the imaging | photography process by 1st Embodiment. It is a block diagram which shows the structure of the radiography apparatus by 2nd Embodiment. It is a flowchart which shows the calibration process by 3rd Embodiment. It is a block diagram explaining the structure of a general FPD. It is a block diagram explaining the structure in the pixel of FPD. It is a block diagram which digitally converts the FPD output and stores it in a memory. It is a timing chart when adjacent pixel addition is not performed. It is a timing chart when performing adjacent pixel addition. It is a block diagram when performing adjacent pixel addition with an operational amplifier. It is a figure explaining the relationship between an analog adjacent pixel addition number and an average value.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

<First Embodiment>
One of the corrections essential for X-ray imaging with FPD is gain correction for each pixel. Since FPD is a semiconductor product, accurate control of the capacitance component for each pixel is difficult in manufacturing, and generally the gain value for each pixel varies greatly. The gain correction is to correct such variation in gain value. Usually, an operation called calibration is performed to acquire image data (hereinafter referred to as a white image) obtained by capturing an X-ray distribution without a subject, and for each pixel of the captured image with the white image and an actual subject present. Gain variation is eliminated by calculating the ratio.

  In the following embodiments, by applying this calibration operation, it is possible to perform correction so that the pixel value is constant when line addition is performed and when line addition is not performed. First, in all the pixel addition modes that can be set in the FPD that can select a mode in which adjacent pixels are added in an analog manner (in the following example, 2 × 2 pixel, 3 × 3 pixel, 4 × 4 pixel addition mode), the calibration operation All X-ray doses at are set the same. Then, the average value of all or a part of each white image data is stored. When performing gain correction in X-ray photography, after pixel-to-pixel ratio calculation with X-ray distribution image data taken in the absence of a subject, pixel addition was performed and pixel addition was performed. In this case, correction using the average value is performed so that the pixel value in this case becomes constant. Details will be described below.

  FIG. 1 is a block diagram showing the configuration of the X-ray imaging apparatus according to the first embodiment. In FIG. 1, an X-ray generation source 1 emits X-rays in the direction of broken arrows. The FPD 3 images the intensity distribution of X-rays emitted from the X-ray generation source 1 and transmitted through the subject 2. In this embodiment, it is possible to apply a human body as the subject 2, and the X-ray imaging apparatus of this embodiment can be used for medical image imaging. The imaging controller 4 controls the X-ray generation source 1 and the FPD 3 to synchronize the X-ray generation by the X-ray generation source 1 and the operation of the FPD 3.

  In this embodiment, the FPD has four pixel addition modes. Mode 1 is a mode in which pixel addition is not performed. Mode 2 is horizontal 2 pixels / vertical 2 pixels, that is, a mode in which a total of 4 pixels is analog-added, Mode 3 is horizontal 3 pixels / vertical 3 pixels, that is, a total of 9 pixels is analog-added, and mode 4 is horizontal 4 pixels / vertical In this mode, 4 pixels, that is, a total of 16 pixels are added in an analog manner. As described above, the main scanning direction may be added after digitization. The operation in these modes is controlled by the main controller 18. The main controller 18 includes a CPU and a ROM (not shown), and various controls are realized by the CPU executing a control program stored in the ROM.

  The A / D converter 5 sequentially converts the analog output from the FPD 3 into a digital value (analog-digital conversion). The frame memory 6 temporarily stores a digital image obtained by A / D conversion by the A / D conversion unit 5.

  The memory 8 is a memory for storing an image output value (hereinafter referred to as a dark image) in a state where X-rays are not emitted. A dark image is stored in the memory 8 by switching the changeover switch 7 to the B side and acquiring an image from the FPD 3 without X-ray emission. The FPD 3 has a unique offset output for each pixel, and the dark image represents a unique offset value for each pixel. Then, when the actual subject image is acquired, the offset correction is performed by subtracting the dark image acquired in advance and held in the memory 8. The subtraction for the offset correction is performed by the subtracter 9.

  A logarithmic reference table 10 (hereinafter referred to as a logarithmic lookup table or logarithmic LUT) performs logarithmic conversion on offset-corrected image data in order to perform subsequent gain correction. The selector 11 selects the output destination of the image data logarithmically converted by the logarithmic LUT 10. Selection of the output destination is controlled by the main controller 18. When a white image is obtained by performing X-ray photography without the subject 2 for calibration, the output destination by the selector 11 is set to one of the memories 12 to 15. The memories 12 to 15 are memories for holding logarithmically converted white image data. The white image shot in mode 1 is logarithmically converted and then stored in the memory 12 via the output D of the selector 11. Similarly, when a white image is taken in mode 2, the output E of the selector 11 is selected, and the logarithmically converted white image is stored in the memory 13. In mode 3, the output F of the selector 11 is selected, and the storage destination of the logarithmically converted white image is the memory 14. Further, in the case of the mode 4, the output G of the selector 11 is selected, and the storage destination of the logarithmically converted white image is the memory 15. When the subject 2 is photographed (in the case of normal photographing), the controller 18 sets the selection destination of the selector 11 to C.

  The multiplexer 17 selects which white image data is used among the white images in the memories 12 to 15. In the case of shooting in mode 1, the input H of the multiplexer 17 is selected to select a white image stored in the memory 12. Similarly, when shooting is performed in mode 2, input I of multiplexer 17 is selected, input J is selected when shooting is performed in mode 3, and input K is selected when shooting is performed in mode 4, and the corresponding memory is selected. Are output to the subtractor 16. The subtracter 16 subtracts a logarithmically converted image of a white image corresponding to the captured mode from an image obtained by logarithmically converting the image data of the subject 2 captured. Since subtraction is performed on the logarithmically converted value, the subtractor 16 substantially performs division.

  The memory 23 holds defective pixel position information indicating the position of the defective pixel existing in the FPD 3. The correction unit 24 corrects the output value of the defective pixel (defective pixel) existing in the FPD 3 by correcting the pixel value at the pixel position indicated by the defective pixel position information held in the memory 23. The defective pixel is corrected by, for example, estimating a pixel value from surrounding pixel values that are not defective, and an average value of the surrounding pixels is generally used for estimating the pixel value.

  The adder 25 adds a desired value to the image data obtained from the correction unit 24. However, since addition is performed on the logarithmically converted image data, multiplication is substantially performed. As will be described below, the adder 25 converts the pixel value into a value proportional to the X-ray dose incident on the corresponding pixel and the pixel addition number. The converted final image is stored in the data storage device 26 using a magnetic disk or the like, and thereafter used for image diagnosis such as display, transfer, and image printing.

  The memories 19 to 22 are memory for storing correction values for the captured images of mode 1, mode 2, mode 3, and mode 4, respectively. A correction value calculated by the controller 18 from each white image held in the memories 12 to 15 is stored. That is, under the control of the controller 18, a correction value corresponding to the set mode is selected by the multiplexer 27 and output to the adder 25. Thus, a correction value corresponding to the mode is added (substantially multiplied) by the adder 25 to the image captured in each mode, thereby converting the image to a pixel value proportional to the pixel addition number and the X-ray dose. The

  The correction values held in the memories 19 to 22 will be described below. In addition, since the X-ray imaging apparatus of this embodiment corrects with a white image, the output pixel value is a numerical value represented by a ratio from the white image.

Arbitrary output pixel value is expressed as F, input A / D conversion value is expressed as G, and reference white image value is expressed as Ref.
F = K * ln (G / Ref) + P = K * ln (G) -K * ln (Ref) + P (7)
It can be expressed as Here, K and P are constants determined under the following two conditions, and ln represents a natural logarithmic function.
Condition 1) When the input A / D conversion value G is Lmin times the reference value Ref: F = Fmin
Condition 2) When the input A / D conversion value G is Lmax times the reference value Ref: F = Fmax

  Here, it can be said that Lmin and Lmax are latitudes from the reference value, and Fmin and Fmax respectively represent an effective minimum value and maximum value of the output pixel value. Usually, Fmin = 0 and Fmax = 4095 (in the case of 12-bit data). Further, the value of Ref is obtained from an average value of a part or the whole of the white image. When a part of the white image is used, when there is shading (decrease in the intensity of the peripheral part) in the X-ray irradiation intensity, the central part (part) of the image data without the intensity decrease is used.

From the above conditions 1), 2) and equation (7), K and P can be obtained as follows.
K = (Fmax−Fmin) / (ln (Lmax) −ln (Lmin)) (8)
P = (Fmax · ln (Lmin) −Fmin · ln (Lmax)) / (ln (Lmin) −ln (Lmax)) (9)

Next, a pixel output value when the same X-ray dose is irradiated in different modes will be considered. F ₁ pixel output values in Mode 1 when irradiated at the same X-ray dose, the pixel output value F ₂ in mode 2, the pixel output value F ₃ in Mode 3, the pixel output value of mode 4 F _{If it is 4} , these pixel output values must all be the same. Therefore, the following relationship is obtained.
F ₂ = F ₁ Formula (10)
F ₃ = F ₁ Formula (11)
F ₄ = F ₁ Formula (12)

Here, the reference value Ref is a value that does not change even if the mode is different. When a white image is taken by a calibration operation, a partial or overall average value of the white image is shown as A ₁ in mode ₁ , A ₂ in mode ₂ , A ₃ in mode ₃ , and mode. Case ₄ is A4. In the case of mode 1, when applied to the equation (7), the pixel output value F ₁ can be expressed by the following equation.
F ₁ = K · ln (A ₁ ) −K · ln (Ref) + P + C ₁ Formula (13)
Here, C ₁ is a correction value corresponding to mode 1.

It is necessary to maintain the relationship of Expression (10) to Expression (12) with respect to the pixel value F ₁ obtained by Expression (13). Therefore, correction values C ₂ , C ₃ , C for the conversion expression of Expression (7) using A / D conversion values G ₂ , G ₃ , G ₄ in each mode using Ref _{2 to} Ref ₄ respectively. By adding ₄ , the relationship of Expression (10) to Expression (12) is maintained.

F ₂ = K · ln (A ₂ ) −K · ln (Ref) + P + C ₂ Formula (14)
F ₃ = K · ln (A ₃ ) −K · ln (Ref) + P + C ₃ Formula (15)
F ₄ = K · ln (A ₄ ) −K · ln (Ref) + P + C ₄ Equation (16)

When correction values C _{2 to} C ₃ are obtained using Expressions (10) to (12) and Expressions (14) to (16), they can be expressed as follows.
C ₂ = K · ln (A ₁ ) −K · ln (A ₂ ) = K · ln (A ₁ / A ₂ ) Equation (17)
C ₃ = K · ln (A ₁ ) −K · ln (A ₃ ) = K · ln (A ₁ / A ₃ ) (18)
C ₄ = K · ln (A ₁ ) −K · ln (A ₄ ) = K · ln (A ₁ / A ₄ ) (19)
The correction values C _{1 to} C ₄ calculated as described above are held in the memories 19 to 22 as the correction values of mode 1 to mode 4.

Therefore, the flowchart for calculating the correction values C _{1 to} C ₄ to be held in the memories 19 to 22 can be represented by FIG. FIG. 2 is a flowchart showing processing in the controller 18 at the time of a calibration operation performed before the subject is actually photographed by this apparatus.

First, in step S1, the pixel addition mode of the FPD 3 is set to mode 1, and in step S2, a white image in mode 1 is obtained by photographing an X-ray image without placing a subject with a prescribed X-ray dose. Next, the white image in mode 1 is stored in the memory 12 by setting the output destination of the selector 11 to D in step S3. Then, in step S4, it reads the image data stored in the memory 12, calculates an average value of a portion or all of the white image, which is referred to as A _1. When calculating the average value, although not shown in the flowchart, the average value is calculated by excluding the pixel value at the defective position using the information on the defective pixel position held in the memory 23. May be.

  Further, when calculating the average value, since the values stored in the memories 12 to 15 are logarithmically converted values, the inverse logarithmic conversion is once performed to obtain a linear value. There is a need. However, when the numerical values to be averaged are similar, since the error is small even if the logarithmic values are averaged, it is usually possible to average the logarithm.

In steps S <b> 5 to S <b> 8, the same processing as in steps S <b> 1 to S <b> 4 is executed for the pixel addition mode 2, and the average value A ₂ of the white image in mode 2 is held in the memory 13. In step S9 to S12, the same processing as that in step S1~S4 the pixel addition mode 3 is performed, the average value A ₃ of the white image in the mode 3 is held in the memory 14. Further, in step S13 to S16, processing similar to step S1~S4 is performed for the pixel-addition mode 4, the average value A ₄ of the white image in the mode 4 is held in the memory 14. In this case, attention should be paid to the same X-ray dose when taking a white image in each pixel addition mode. Therefore, it is desirable to execute the processes of steps S1 to S16 continuously.

Next, in step S17 to S20, the correction values C ₁ -C ₄ calculated by equation (17) to (20), stored in the memory 19-22. In this embodiment, since the mode 1 is a reference, the correction value C ₁ is set to 0 and is stored in the memory 19. However, the reference mode is not limited to mode 1, and any mode of modes 1 to 4 may be used as a reference. That is, in equations (10) to (16), the correction value in the reference mode is set to 0, each correction value in the other mode is calculated, and the obtained correction value is used for calibration in each mode. Can do. Through the above processing, the correction values C ₁ to C 4 for the pixel addition modes 1 to ₄ are held in the memories 19 to 22.

  Next, a process for actually photographing a subject will be described with reference to a flowchart of FIG.

  In step S21, when a desired pixel addition mode is set and photographing is instructed, first, a dark image is captured by the processing in steps S22 and S23. That is, in step S22, the selector switch 7 is connected to the B side, and in step S23, the dark image is recorded in the memory 8 by driving the FPD 3 without exposing the X-rays and capturing the dark image.

  Next, the switch 7 is connected to the A side for normal shooting, and the output of the selector 11 is set to the output C. In steps S26 to S36, the multiplexers 17 and 27 are set according to the pixel addition mode set in step S21. For example, in the pixel addition mode 1, the input of the multiplexer 17 is set to H so as to use the white image for mode 1 held in the memory 12 (steps S26 and S27). Then, the input of the multiplexer 27 is set to L in order to use the correction value for mode 1 held in the memory 19 (step S28). Similarly, in the pixel addition mode 2, the input of the multiplexer 17 is set to I, and the input of the multiplexer 27 is set to M (steps S29, S30, S31). In the pixel addition mode 3, the input of the multiplexer 17 is set to J, and the input of the multiplexer 27 is set to N (steps S32, S33, S34). Similarly, in the pixel addition mode 4, the input of the multiplexer 17 is set to K, and the input of the multiplexer 27 is set to O (steps S32, S35, S36).

  After setting the multiplexers 17 and 27 in accordance with the pixel addition mode as described above, X-ray imaging of the subject 2 is performed in step S37. That is, when an X-ray image obtained by pixel addition according to the set pixel addition mode is output from the FPD 3, the X-ray image is converted into a digital image by the A / D converter 5 and held in the memory 6. The digital image held in the memory 6 is subjected to offset correction using the dark image held in the memory 8 by the subtracter 9 and further subjected to logarithmic conversion by the LUT 10. The logarithmically converted digital image is subjected to gain correction using a white image corresponding to the set pixel addition mode by the subtractor 16, and output value correction of a defective pixel (defective pixel) is performed by the correction unit 24. The Then, a correction value corresponding to the set pixel addition mode is added by the adder 25 and stored in the data storage device 26. Thus, a white image corresponding to the set pixel addition mode and an X-ray image (subject image) that has been calibrated using the correction value are obtained.

  Since the logarithmically transformed image is stored in the data storage device 26, it is necessary to perform inverse logarithmic transformation when making a visible image.

  Although not shown in the flowchart of FIG. 3, if the defective pixel position information becomes clear in advance during FPD manufacturing or by image analysis performed separately, the defective position information is stored in the memory 23.

  In this embodiment, the number of added pixels in modes 2 to 4 is set to 4, 9, and 16 pixels, but the present invention is not limited to this. The present embodiment can be applied to any form of addition of adjacent pixels in the pixel addition mode.

In this embodiment, adjacent pixels are added in an analog manner on the FPD. However, if the addition is performed in an analog manner, the same effect can be obtained not only on the FPD but also in the subsequent stage. Is obvious.
In the above-described embodiment, the non-linearity correction caused by the pixel addition mode is performed using the white image in the gain correction. However, the present invention is not limited to this. It is obvious that the correction values C ₁ , C ₂ , C ₃ , and C ₄ may be obtained using the image obtained by each pixel addition mode under the same irradiation condition and the same subject condition. .

  As described above, according to the first embodiment, it is possible to reduce the influence of deviation from the ideal value that occurs when performing pixel addition in an analog manner, and to obtain a good captured image in each pixel addition mode. . That is, according to the above-described embodiment, a correction value that eliminates non-linearity caused by analog addition of the FPD 100 is acquired based on a white image that is not analog-added and a white image that is analog-added, and is used in each pixel addition mode. It becomes possible to do. For this reason, it is possible to accurately calculate the incident X-ray dose in the captured image obtained in the pixel addition mode.

Second Embodiment
In the first embodiment, gain correction and correction according to the pixel addition mode are performed on an image subjected to logarithmic transformation. However, the present invention can also be applied to a system that does not use logarithmic transformation. In the second embodiment, correction processing corresponding to the pixel addition mode when logarithmic conversion is omitted will be described.

FIG. 4 is a block diagram showing the configuration of the X-ray imaging apparatus according to the second embodiment. In FIG. 4, the same components as those in FIG. 1 are denoted by the same reference numerals. In the configuration of FIG. 4, a divider 28 is provided instead of the subtracter 16, and a multiplier 29 is provided instead of the adder 25. That is, the same correction as in the first embodiment is performed by directly performing division and multiplication on the image data without using the logarithmic conversion LUT 10 of FIG. In this case, a logarithmic expression can be taken from the correction values C _{1 to} C ₄ and the calculation is performed as shown in the following expression.

C ₁ = 1 (20)
C ₂ = (A ₁ / A ₂ ) (21)
C ₃ = (A ₁ / A ₃ ) (22)
C ₄ = (A ₁ / A ₄ ) (23)

In steps S17 to S20 in FIG. 2, the correction values C _{1 to} C ₄ calculated by the above equations (20) to (23) are stored in the memories 19 to 22, respectively. In step S37 in FIG. 3, correction using the correction value is performed according to the set pixel addition mode, and the corrected image is stored in the data storage device 26. That is, when an X-ray image obtained by pixel addition according to the set pixel addition mode is output from the FPD 3, the X-ray image is converted into a digital image by the A / D converter 5 and held in the memory 6. The digital image held in the memory 6 is subjected to offset correction using the dark image held in the memory 8 by the subtracter 9. The offset-corrected digital image is subjected to gain correction using a white image corresponding to the set pixel addition mode by the divider 28, and the output value of the defective pixel (defective pixel) is corrected by the correction unit 24. The Then, the multiplier 29 multiplies the correction value corresponding to the set pixel addition mode and stores it in the data storage device 26. Thus, a white image corresponding to the set pixel addition mode and an X-ray image (subject image) that has been calibrated using the correction value are obtained.

  As described above, according to the first and second embodiments, when analog adjacent pixels are added on the FPD 3, a constant pixel value that does not depend on the number of pixels to be added is obtained, and the obtained image information Therefore, it is possible to easily calculate the incident X-ray dose.

<Third Embodiment>
In the first and second embodiments, correction is performed so that a constant output value is obtained regardless of the number of pixels added in the pixel addition mode. However, in the pixel addition mode, there is a case where it is expected that the output value is obtained at a magnification of the number of additions from the consciousness that the pixel outputs are simply added. Therefore, in the third embodiment, an X-ray imaging apparatus that obtains an output value with a magnification according to the number of added pixels will be described. However, since the configuration of the apparatus is substantially the same as that of the first embodiment (FIG. 1), detailed description is omitted.

Now, consider pixel output values when the same X-ray dose is irradiated in different pixel addition modes. F ₁ pixel output values in Mode 1 when irradiated at the same X-ray dose, the pixel output value F ₂ in mode 2, the pixel output value F ₃ in Mode 3, the pixel output value of mode 4 F _{If it is 4} , these pixel output values must be multiplied by a multiplier corresponding to the number of added pixels. Therefore, in the third embodiment, the following relationship is used instead of the equations (10) to (12) of the first embodiment.

F ₂ = F ₁ + K · ln (4) Equation (10 ′)
F ₃ = F ₁ + K · ln (9) ... Formula (11 ')
F ₄ = F ₁ + K · ln (16) Equation (12 ′)

Like the first embodiment, a correction value corresponding to the mode 1 in case of the C _1,
F ₁ = K · ln (A ₁ ) −K · ln (Ref) + P + C ₁ (13)
It is necessary to maintain the relationship of Expression (10 ′) to Expression (12 ′) with respect to the pixel value F ₁ obtained in step ( ₁ ). Therefore, as in the first embodiment, the correction value C _{2 is applied} to the conversion equation (7) using the A / D conversion values G _{2 to} G ₄ in each mode using Ref _{2 to} Ref ₄ respectively. , C ₃ , C ₄
F ₂ = K · ln (A ₂ ) −K · ln (Ref) + P + C ₂ Formula (14)
F ₃ = K · ln (A ₃ ) −K · ln (Ref) + P + C ₃ Formula (15)
F ₄ = K · ln (A ₄ ) −K · ln (Ref) + P + C ₄ Equation (16)
By maintaining the relationship, the relationship of Expression (10 ′) to Expression (12 ′) is maintained.

When correction values C _{2 to} C ₃ are obtained using Expression (10 ′) to Expression (12 ′) and Expression (14) to Expression (16), they can be expressed as follows.
C ₂ = K · ln (A ₁ ) −K · ln (A ₂ ) + K · ln (4) = K · ln (4 · A ₁ / A ₂ ) (17 ′)
_{C 3 = K · ln (A} 1) -K · ln (A 3) + K · ln (9) = K · ln (9 · A 1 / A 3) ... (18 ')
_{C 4 = K · ln (A} 1) -K · ln (A 4) + K · ln (16) = K · ln (16 · A 1 / A 4) ... (19 ')

In the third embodiment, the correction value C ₁ = 0 and the correction values C _{2 to} C ₄ obtained by the above formulas (17 ′) to (19 ′) are held in the memories 19 to 22 with the mode 1 as a reference. . Then, calibration is performed using a correction value corresponding to the pixel addition mode, thereby obtaining an output value multiplied by a multiplier corresponding to the number of added pixels (an output value corresponding to a value obtained by multiplying the number of added pixels). be able to.

FIG. 5 is a flowchart for explaining calibration processing according to the third embodiment. Steps S1 to S16 are the same as in the first embodiment. In steps S17 ′ to S20 ′, the correction values C ₁ = 0 and the correction values C _{2 to} C ₄ obtained by the equations (17 ′) to (19 ′) are held in the memories 19 to 22. Then, by performing the calibration using the correction value corresponding to the pixel addition mode by the process described with reference to the flowchart of FIG. 3, an output value that is a multiplier multiple corresponding to the number of added pixels can be obtained.

  As described above, according to the third embodiment, the influence of deviation from an ideal value that occurs when pixel addition is performed in an analog manner is reduced, and more accurately according to the number of added pixels in each pixel addition mode. Thus, an output value multiplied by a multiplier can be obtained.

<Fourth embodiment>
In the third embodiment, gain correction and correction according to the pixel addition mode are performed on an image subjected to logarithmic transformation, but the present invention can also be applied to a system that does not use logarithmic transformation. In the fourth embodiment, correction processing corresponding to the pixel addition mode when logarithmic conversion is omitted will be described. The configuration of the X-ray imaging apparatus of the fourth embodiment is the same as that of the second embodiment (FIG. 4). That is, the same correction as in the first embodiment is performed by directly performing division and multiplication on the image data without using the logarithmic conversion LUT 10 of FIG. In this case, a logarithmic expression can be taken from the correction values C _{1 to} C ₄ and the calculation is performed as shown in the following expression.

C ₁ = 1 ... (20 ')
C ₂ = (4 · A ₁ / A ₂ ) (21 ')
C ₃ = (9 · A ₁ / A ₃ ) (22 ')
C ₄ = (16 · A ₁ / A ₄ ) (23 ')

In steps S17 ′ to S20 ′ of FIG. 5, correction values C _{1 to} C ₄ calculated by the above equations (20 ′) to (23 ′) are stored in the memories 19 to 22, respectively. In step S37 in FIG. 3, correction using the correction value is performed according to the set pixel addition mode, and the corrected image is stored in the data storage device 26.

  As described above, according to the third and fourth embodiments, when analog adjacent pixel addition is performed on the FPD 3, it is possible to more accurately obtain a pixel value multiplied by a multiplier according to the number of pixels to be added. The incident X-ray dose can be easily calculated from the obtained image information.

  Although the embodiment has been described in detail above, the present invention can take an embodiment as a system, apparatus, method, program, storage medium, or the like. Specifically, the present invention may be applied to a system composed of a plurality of devices, or may be applied to an apparatus composed of a single device.

  In the present invention, the functions of the above-described embodiments are achieved by supplying a software program directly or remotely to a system or apparatus, and the computer of the system or apparatus reads and executes the supplied program code. Including the case. In this case, the supplied program is a program corresponding to the flowchart shown in the drawing in the embodiment.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, or the like.

  Examples of the recording medium for supplying the program include the following. For example, floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD- R).

  As another program supply method, a client computer browser is used to connect to a homepage on the Internet, and the computer program of the present invention is downloaded from the homepage to a recording medium such as a hard disk. In this case, the downloaded program may be a compressed file including an automatic installation function. It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  Further, the program of the present invention may be encrypted, stored in a storage medium such as a CD-ROM, and distributed to users. In this case, a user who has cleared a predetermined condition is allowed to download key information for decryption from a homepage via the Internet, execute an encrypted program using the key information, and install the program on the computer. You can also.

  In addition to the functions of the above-described embodiment being realized by the computer executing the read program, the embodiment of the embodiment is implemented in cooperation with an OS or the like running on the computer based on an instruction of the program. A function may be realized. In this case, the OS or the like performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  Furthermore, the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, so that part or all of the functions of the above-described embodiments are realized. May be. In this case, after a program is written in the function expansion board or function expansion unit, the CPU or the like provided in the function expansion board or function expansion unit performs part or all of the actual processing based on the instructions of the program.

Claims (30)

A plurality of radiation detection elements arranged two-dimensionally ;
An analog addition circuit for analog addition of analog electric signals obtained by the plurality of radiation detection elements every predetermined number ;
Acquisition of correction information corresponding to a difference between a value obtained by arithmetic addition of the values of the predetermined number of analog electrical signals and a value obtained by analog addition of the predetermined number of analog electrical signals by the analog addition circuit Means,
Dark current correction means for correcting an offset corresponding to a dark current component included in radiation image data obtained by the plurality of radiation detection elements;
An imaging apparatus comprising: correction means for correcting the radiation image data corrected by the dark current correction means with correction information acquired by the acquisition means . Wherein the correction information, corrects the pixel value of the resultant white image by performing X-ray imaging in the absence of an object state, the pixel value is directly proportional to the predetermined number is the number of times obtained by adding the arithmetic addition and the analog adder The imaging apparatus according to claim 1, wherein:
An A / D converter for converting the analog added analog electric signal into a digital value;
3. The photographing according to claim 1, wherein the correction unit corrects the image data obtained by the analog addition and then converted into a digital value by the A / D converter using the correction information. apparatus. A digital addition circuit for digitally adding digital values;
The analog addition circuit performs analog addition of analog electric signals from detection elements arranged adjacent to each other in the first direction,
The digital adder circuit digitally adds a digital value based on an analog electric signal obtained from detection elements arranged adjacent to each other in a second direction orthogonal to the first direction. 4. The photographing apparatus according to any one of items 3 . Further comprising a first images based on the electrical signals are not analog addition by the analog adder circuit, the resulting Ru images forming means and a second image based on electrical signals analog addition by the analog adder circuit The imaging device according to any one of claims 1 to 4 . The obtaining means comprises: a first charge storage capacity of the radiation detection element, rear of and disposed upstream of the analog summing circuit second of retaining charges read out from the radiation detection elements of the radiation detection element imaging device according to any one of claims 1 to 5, characterized in that to obtain the based rather correction information to the image obtained via the charge storage capacitor. Said acquisition means, and characterized in that when performing the same shooting at the same radiation dose, obtains correction information to equalize the mean value of all or part of the pixels of the first and second images The imaging device according to claim 5 . It said acquisition means, performing and imaging in the absence of an object at the same radiation dose to form first and second white image information, a pixel in the whole or a part of said first and second white image information The photographing apparatus according to claim 7 , wherein the correction information is determined so that average values are equal. The acquisition unit, when performing the same shooting at the same radiation dose, the ratio of the average value of the first and all or part of the pixel values of the second images, the second images imaging apparatus according to claim 5, characterized in that to obtain the correction information to match the number of Oite summed pixel values. It said acquisition means, performing and imaging in the absence of an object at the same radiation dose to form first and second white image information, a pixel in the whole or a part of said first and second white image information imaging apparatus according to claim 9, characterized in that the ratio of the mean value of the values to determine the correction information so as to match the number of pixels Oite added to the second image. A memory for holding the first and second white images;
Imaging apparatus according to claim 8 or 10, further comprising a second correcting means for performing gain correction of the first or second images by using the first or second white image. Further comprising a conversion means for logarithmically converting the first or second images,
The second correcting unit performs the gain correction by subtraction between the corresponding pixel values of the white image information of the log-transformed image information,
The imaging apparatus according to claim 11 , wherein the correction unit adds the correction information to a pixel value of the image information subjected to the gain correction. The second correcting unit performs the gain correction by dividing the pixel value of the first or second images in the corresponding pixel value of the white image information,
The photographing apparatus according to claim 11 , wherein the correction unit multiplies the pixel value of the image information subjected to the gain correction by the correction information. Before Kiga image forming means is capable of switching the addition number of neighboring pixels,
The acquisition unit acquires the correction information corresponding to the number of summing, imaging apparatus according to any one of claims 7 to 13, characterized in that stored in the memory.   The imaging apparatus according to claim 1, wherein the analog adder circuit includes a capacitive element connected to the radiation detection element via a switch element. Imaging device according to any one of claims 1 to 15, wherein the radiation is X-ray. And two-dimensionally arranged plurality of radiation detection element, the image obtained luer analog electric signals obtained by the plurality of radiation detecting elements from the imaging device and an addition circuit for analog addition every predetermined number of processing An image processing apparatus that
Preparative you get the correction information corresponding to the difference between the value obtained values as analog electrical signal of the predetermined number of obtained values of the predetermined number of analog electrical signals by arithmetic addition and analog addition by said adder circuit Obtaining means;
Dark current correction means for correcting an offset corresponding to a dark current component included in radiation image data obtained by the plurality of radiation detection elements;
An image processing apparatus comprising: correction means for correcting the radiation image data corrected by the dark current correction means by correction information acquired by the acquisition means . A detector having a plurality of radiation detection elements arranged two-dimensionally ;
An analog addition circuit for analog addition and the resulting luer analog electrical signal by the plurality of radiation detection elements,
Acquisition means for acquiring correction information corresponding to a difference between a value obtained by arithmetic addition of values of a predetermined number of analog electric signals and a value obtained by analog addition of the predetermined number of analog electric signals by the analog addition circuit When,
Dark current correction means for correcting an offset corresponding to a dark current component included in radiation image data obtained by the plurality of radiation detection elements;
An imaging system comprising: correction means for correcting the radiation image data corrected by the dark current correction means by correction information acquired by the acquisition means . And two-dimensionally arranged plurality of radiation detection element, the image obtained luer analog electric signals obtained by the plurality of radiation detecting elements from the imaging device having an analog addition circuit for analog addition every predetermined number An image processing method comprising:
Obtaining correction information corresponding to a difference between a value obtained by arithmetic addition of the values of the predetermined number of analog electrical signals and a value obtained by analog addition of the predetermined number of analog electrical signals by the analog addition circuit; When,
Correcting an offset corresponding to a dark current component included in radiation image data obtained by the plurality of radiation detection elements;
And correcting the radiation image data corrected in the correcting step with the correction information acquired in the acquiring step . An image processing apparatus that processes a radiation image obtained by a radiation detector that includes a plurality of detection elements that detect radiation and obtain an analog signal and an addition circuit that analog-adds the analog signal,
An acquisition means for acquiring a first radiation image based on the analog signal and a second radiation image based on the analog added signal;
Storage means for storing coefficients for aligning pixel values of corresponding regions in the first radiographic image and the second radiographic image obtained by imaging the same subject;
An image processing apparatus comprising: a correcting unit that corrects at least one of the first radiographic image and the second radiographic image using the coefficient.   21. The image processing apparatus according to claim 20, wherein the acquisition unit acquires a radiological image based on an analog signal not subjected to the analog addition as the first radiographic image.   An image processing apparatus that processes a radiation image obtained by a radiation detector that includes a plurality of detection elements that detect radiation and obtain an analog signal,
  Two radiographic image data obtained by radiographing the same subject with the same dose, a first radiographic image obtained by reading out the analog signal from the detector via a first storage capacity; An acquisition means for acquiring a second radiation image obtained by reading the analog signal through a second storage capacity larger than the first storage capacity;
  Storage means for storing a coefficient for aligning pixel values of corresponding regions in the first radiographic image and the second radiographic image;
  An image processing apparatus comprising: a correcting unit that corrects at least one of the first radiographic image and the second radiographic image using the coefficient.   A first white image obtained by reading out the analog signal from the radiation detector through a first storage capacitor, which is two pieces of radiation image data obtained by irradiating the same dose of radiation without passing through a subject. From the image and a second white image obtained by reading the analog signal through a second accumulated dose greater than the first accumulated capacity, the coefficients for aligning the pixel values of the corresponding regions are The image processing apparatus according to any one of claims 20 to 22, further comprising a determining unit for determining. A plurality of detection elements for detecting radiation and obtaining analog signals;
An addition circuit for analog addition of the analog signals;
Image forming means for forming a first radiation image based on the analog signal and a second radiation image based on the analog added signal;
Storage means for storing a coefficient for aligning pixel values of corresponding regions in the first radiographic image and the second radiographic image obtained by imaging the same subject;
A radiation imaging apparatus comprising: a correcting unit that corrects at least one of the first radiation image and the second radiation image using the coefficient. 25. The radiographic apparatus according to claim 24, wherein the image forming unit forms a radiographic image based on an analog signal not subjected to the analog addition as the first radiographic image. A detector having a plurality of detection elements for detecting radiation and obtaining an analog signal;
Two radiographic image data obtained by radiographing the same subject with the same dose, a first radiographic image obtained by reading out the analog signal from the detector via a first storage capacity; An acquisition means for acquiring a second radiation image obtained by reading the analog signal through a second storage capacity larger than the first storage capacity;
Storage means for storing a coefficient for aligning pixel values of corresponding regions in the first radiographic image and the second radiographic image;
A radiation imaging apparatus comprising: a correcting unit that corrects at least one of the first radiation image and the second radiation image using the coefficient. Two radiographic image data obtained by irradiating the same dose of radiation without passing through the subject, and a first white image obtained by reading the analog signal from the detection element through a first storage capacitor And a second white image obtained by reading out the analog signal from the detection element via a second accumulation dose larger than the first accumulation capacity, to align the pixel values of the corresponding region 27. The radiation imaging apparatus according to claim 24, further comprising a determining unit that determines the coefficient.   An image processing method for processing a radiation image obtained by a radiation detector comprising a plurality of detection elements for detecting radiation and obtaining an analog signal and an addition circuit for analog addition of the analog signal,
  Obtaining a first radiation image based on the analog signal and a second radiation image based on the analog summed signal;
  Storing coefficients for aligning pixel values of corresponding regions in the first radiographic image and the second radiographic image obtained by imaging the same subject;
  And a step of correcting at least one of the first radiographic image and the second radiographic image using the coefficient.   An image processing method for processing a radiation image obtained by a radiation detector comprising a plurality of detection elements for detecting radiation and obtaining an analog signal,
  Two radiographic image data obtained by radiographing the same subject with the same dose, a first radiographic image obtained by reading out the analog signal from the detector via a first storage capacity; Obtaining a second radiation image obtained by reading the analog signal through a second storage capacity larger than the first storage capacity;
  Storing coefficients for aligning pixel values of corresponding regions in the first radiographic image and the second radiographic image;
  And a step of correcting at least one of the first radiographic image and the second radiographic image using the coefficient.   A program for causing a computer to execute each step of the image processing method according to any one of claims 19, 28, and 29.

Images