JP6152894B2 - Radiation imaging device - Google Patents

Description

  The present invention relates to a radiation imaging apparatus for detecting a radiation image, which is used in the medical field, industrial field, nuclear power field, and the like, and more particularly to a technique for improving the image quality of a radiation image by offset correction.

  Conventionally, a radiation imaging apparatus is used as an imaging apparatus for medical X-ray images. The radiation imaging apparatus is equipped with a radiation source and a radiation detector, and in recent years, a flat panel detector (FPD) is used as the radiation detector. The FPD includes a large number of detection elements arranged in a two-dimensional matrix. Each detection element is irradiated from a radiation source, detects the radiation transmitted through the subject, and converts it into charge information. The converted charge information is sequentially read out and output as output data corresponding to radiation.

  The output to be read is composed of a number of components such as an output due to a noise component, an output due to a dark current of the detector, and the like in addition to an output depending on the detection element. Accordingly, the output of the detection element is not zero even when no radiation is incident and no input is made to the detection element, and the output varies among the detection elements. The output (offset value) read in this state is measured for each detection element, and the offset value (offset value profile) measured for each detection element is stored as correction data.

  When a radiation transmission image is captured using a radiation detector, offset correction is performed by subtracting correction data from output data read from the detection element. Since the offset value due to dark current or the like is removed by the offset correction, an artifact generated in the radiation transmission image can be reduced (for example, see Patent Document 1).

JP 2006-305228 A

However, the conventional example having such a configuration has the following problems.
That is, the offset value of the radiation detector according to the conventional example varies depending on the temperature of the radiation detector. Therefore, the offset value is high when the temperature of the radiation detector is high, and the offset value is low when the temperature is low. As described above, the offset value fluctuates depending on the temperature. Therefore, when the correction is performed by always using the correction data once acquired, the radiation image may be deteriorated due to excessive or insufficient offset correction. In particular, if offset correction is excessively performed, there is a concern that image information in the diagnosis area is lost and accurate diagnosis cannot be performed.

  As a method for avoiding such excessive or insufficient offset correction, it is possible to update the correction data every time the temperature of the radiation detector fluctuates to acquire appropriate correction data. However, it takes a certain time to update the correction data, and radiation imaging cannot be performed during the update. Therefore, the correction data cannot be updated when radiation imaging is urgently required. In such a case, it is difficult to obtain appropriate correction data. Further, when the temperature variation is severe, such as immediately after power-on, it is necessary to frequently update the correction data. If the correction data is frequently updated, the time required for radiographic image capture becomes long, and it is difficult to efficiently capture radiographic images.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a radiation imaging apparatus that can suitably avoid loss of radiation images and degradation of image quality due to temperature changes. To do.

In order to achieve such an object, the present invention has the following configuration.
That is, a radiation imaging apparatus according to the present invention includes a radiation source, a radiation detection unit in which detection elements that detect radiation emitted from the radiation source are arranged, and a temperature measurement unit that measures the temperature of the radiation detection unit, The offset value acquisition unit that acquires an offset value based on the output data of the detection element at the time of non-irradiation, the offset value acquired by the offset value acquisition unit, and the temperature measurement unit measured at the time of acquisition based on the temperature of the radiation detector, before Symbol offset correction data acquiring unit which temperature measuring unit calculates the offset correction data is an offset value at a temperature lower than the temperature of the radiation detector measured after the time the acquisition And an offset correction unit that performs offset correction using the offset correction data.

According to the radiation imaging apparatus according to the present invention, the offset correction data acquiring unit and the offset value offset value acquisition unit has acquired, based on the temperature of the radiation detection unit temperature measurement unit was measured at the time of the acquisition, temperature The measurement unit calculates an offset value at a temperature lower than the temperature of the radiation detection unit measured after the acquisition . The offset value varies depending on the temperature, and the offset value decreases as the temperature decreases. That is, when offset correction is performed using an offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit, the offset value is lower than that of the detection element, and thus offset correction is excessive for the output data of the detection element. Never done. Therefore, it is possible to reliably avoid the loss of image information due to excessive offset correction in the formed radiographic image.

  In addition, the radiation imaging apparatus according to the present invention preferably further includes an image processing unit that performs processing for compensating for image degradation on the output data of the detection element that has been offset-corrected by the offset correction unit. .

  According to the radiation imaging apparatus according to the present invention, the image processing unit performs image processing on the output data of the detection element subjected to the offset correction. In many cases, only the offset correction by the offset correction unit is not enough to correct the output data of the detection element, and if the output data after the offset correction is used as it is for imaging, the image quality may be deteriorated. Therefore, in the radiation imaging apparatus according to the present invention, image processing for compensating for image degradation, such as contrast enhancement, is performed on the image after offset correction. Since image degradation is avoided by the processing by the image processing unit, a high-quality radiation transmission image can be formed.

  In the radiation imaging apparatus according to the present invention, a linear approximation curve for calculating a linear approximation curve indicating a correlation between the offset value acquired by the offset value acquisition unit and the temperature of the radiation detection unit measured by the temperature measurement unit. The offset correction data acquisition unit further includes an offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit based on the linear approximation curve calculated by the linear approximation curve calculation unit. Is preferably calculated.

  According to the radiation imaging apparatus according to the present invention, the linear approximation curve calculation unit acquires a linear approximation curve indicating a correlation between the offset value and the temperature of the radiation detection unit. The offset correction data acquisition unit calculates an offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit based on the linear approximation curve. The linear approximation curve is expressed by a linear function based on temperature. Therefore, the offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit can be easily calculated based on the temperature when the offset value is actually acquired. That is, it is not necessary to actually lower the temperature of the radiation detection unit. As a result, the time required to form the radiation transmission image is shortened, so that the radiation transmission image can be taken efficiently.

  Further, in the radiation imaging apparatus according to the present invention, the linear approximation curve calculation unit calculates a linear approximation curve for each of the detection elements, and the offset correction data acquisition unit performs the detection for each of the detection elements. It is preferable to calculate an offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit based on the linear approximate curve of the element.

  According to the radiation imaging apparatus of the present invention, an offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit is calculated using a linear approximation curve. In this case, a linear approximation curve is calculated for each detection element, and an offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit is calculated for each detection element based on the calculated linear approximation curve. Therefore, even if the offset value acquired by the offset value acquisition unit varies greatly for each detection element, the offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit for each detection element is more It can be calculated accurately. Accordingly, in the formed radiographic image, it is possible to more reliably avoid the loss of image information due to excessive offset correction.

  Further, in the radiation imaging apparatus according to the present invention, the linear approximate curve calculation unit may calculate an average of the offset values acquired by the offset value acquisition unit for two or more detection elements, and the radiation detection measured by the temperature measurement unit. An average linear approximation curve is calculated based on the temperature of the unit, and the offset correction data acquisition unit is configured to detect the radiation detected by the temperature measurement unit based on the average linear approximation curve calculated by the linear approximation curve calculation unit. It is preferable to calculate an offset value at a temperature lower than the temperature of the part.

  According to the radiation imaging apparatus of the present invention, the linear approximate curve calculation unit calculates the average of the offset values acquired by the offset value acquisition unit for two or more detection elements. Then, an average linear approximation curve is calculated based on the average of the offset values and the temperature of the radiation detection unit measured by the temperature measurement unit.

  The offset correction data acquisition unit calculates an offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit, for each detection element, using the calculated average linear approximation curve. That is, all offset values constituting the offset correction data are calculated based on the same linear approximation curve. Therefore, in order to calculate the offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit, it is not necessary to calculate a different linear approximation curve for each detection element and perform calculation using these. As a result, offset correction data at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit can be calculated more easily and quickly, so that radiography can be performed more efficiently.

  Further, an offset value at an arbitrary temperature lower than the temperature measured by the temperature measurement unit is calculated using the average linear approximation curve, and the value is obtained by subtracting the value from the pixel value of the pixel for which the average linear approximation curve is calculated. The offset difference value may be created by subtracting from each pixel of the offset correction image.

  Since the variation value of the pixel value per 1 ° C. of the temperature of each pixel can be calculated from the linear approximation curve, an offset correction image at an arbitrary temperature can be created from the offset correction image. For example, when creating an offset correction image that is 2 ° C. lower than the pixel value acquired by the offset value acquisition unit, a value that is twice the variation value of the pixel value per 1 ° C. may be subtracted from each pixel.

  The radiation imaging apparatus according to the present invention preferably further includes a calculation instruction unit that instructs calculation of the offset correction data by the offset correction data acquisition unit.

  According to the radiation imaging apparatus of the present invention, the calculation instruction unit instructs the offset correction data acquisition unit to calculate the offset correction data. By having this configuration, it is possible to calculate an offset value profile at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit at an arbitrary timing, and obtain this as offset correction data. Therefore, offset correction data can be calculated again even when the temperature of the radiation detector changes rapidly after preparation for X-ray imaging is completed and the offset value fluctuates greatly. Therefore, a more suitable X-ray transmission image can be formed even after the temperature of the radiation detection unit has changed rapidly.

  According to the radiation imaging apparatus of the present invention, the offset correction data acquisition unit is measured by the temperature measurement unit based on the offset value acquired by the offset value acquisition unit and the linear approximation curve calculated by the linear approximation curve calculation unit. An offset value at a temperature lower than the temperature of the radiation detection unit is calculated. The offset value varies depending on the temperature, and the offset value decreases as the temperature decreases. That is, when offset correction is performed using an offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit, the offset value is lower than that of the detection element, and thus offset correction is excessive for the output data of the detection element. Never done.

1 is a block diagram illustrating an overall configuration of a radiation imaging apparatus according to Embodiment 1. FIG. 1 is a plan view illustrating a schematic configuration of an FPD according to Embodiment 1. FIG. 3 is a flowchart for explaining the operation of the radiation imaging apparatus according to the first embodiment. In Example 1, it is a graph which shows the correlation with the offset value in detection element Agh, and the temperature of FPD7. In Example 1, it is a graph which shows the correlation with the offset value profile in measured temperature, and the offset value profile in minimum operating temperature.

  Embodiment 1 of the present invention will be described below with reference to the drawings. In addition, it demonstrates using an X-ray as an example of a radiation.

<Description of overall configuration>
As shown in FIG. 1, the radiation imaging apparatus 1 according to the first embodiment includes a top plate 3, an X-ray tube 5, an FPD 7, an X-ray irradiation control unit 9, an FPD control unit 11, and a signal processing unit 13. , A display unit 15, a temperature sensor 17, and a main control unit 19.

  The top 3 places a subject M in a horizontal posture. The X-ray tube 5 and the FPD 7 are disposed to face each other with the top plate 3 interposed therebetween. The X-ray tube 5 irradiates the subject M with X-rays. The FPD 7 detects X-rays transmitted through the subject M, and converts the detected X-rays into charge signals. The X-ray irradiation control unit 9 is connected to the X-ray tube 5 and controls the X-ray dose irradiated from the X-ray tube 5 and the timing for irradiating X-rays. The FPD control unit 11 is connected to the FPD 7 and controls an operation of reading out a charge signal converted in the FPD 7, that is, an X-ray detection signal.

  The signal processing unit 13 processes the X-ray detection signal read from the FPD 7 and outputs an image output signal. The display unit 15 is provided after the signal processing unit 13 and displays the image output signal output from the signal processing unit 13 as a radiation transmission image. The temperature sensor 17 is connected to the FPD 7 and measures the temperature of the FPD 7. The operations of the X-ray irradiation control unit 9, the FPD control unit 11, the signal processing unit 13, and the display unit 15 are comprehensively controlled by the main control unit 19. The X-ray tube 5 corresponds to the radiation source in the present invention, and the FPD 7 corresponds to the radiation detection unit in the present invention. The temperature sensor 17 corresponds to a temperature measurement unit in the present invention.

  As shown in FIG. 2, the FPD 7 further includes an active matrix substrate 21, a gate driver 23, an amplifier 25, and an AD converter 27. The active matrix substrate 21 is connected to the gate driver 23 and the amplifier 25. The active matrix substrate 21 has a plurality of detection elements A arranged in a two-dimensional matrix. In the first embodiment, the detection elements A are arranged in a two-dimensional matrix of about 4,096 × 4,096. However, FIG. 2 shows a simplified arrangement in which the detection elements A are arranged in a two-dimensional matrix of 3 × 3.

  The detection element A converts the irradiated X-rays into charges and accumulates them as charge information. The gate driver 23 is connected to the detection element A, and reads the charge information accumulated in the detection element A. The amplifier 25 is connected to the AD converter 27, amplifies the charge information read from the detection element A, and outputs the amplified charge information to the AD converter 27. The AD converter 27 converts the input charge information from an analog signal to a digital signal, and outputs it to the signal processing unit 13 as output data of the detection element A. The operations of the gate driver 23, the amplifier 25, and the AD converter 27 are comprehensively controlled by the FPD control unit 11.

  As shown in FIG. 1, the signal processing unit 13 further includes an offset value acquisition unit 29, a linear approximate curve calculation unit 31, a correction data acquisition unit 33, an offset correction unit 35, and a recorrection unit 37. Yes. The offset value acquisition unit 29 is connected to the AD converter 27, and the output data of the detection element A when X-rays are not irradiated is input to the offset value acquisition unit 29. The offset value acquisition unit 29 acquires an offset value based on the output data of the detection element A when X-rays are not irradiated.

  The linear approximate curve calculation unit 31 is provided after the offset value acquisition unit 29 and is connected to the temperature sensor 17. The linear approximate curve calculation unit 31 calculates a linear approximate curve based on the offset value acquired by the offset value acquisition unit 29 and the temperature of the FPD 7 measured by the temperature sensor 17. The correction data acquisition unit 33 is provided after the linear approximate curve calculation unit 31. The correction data acquisition unit 33 calculates an offset value at an arbitrary temperature based on the calculated linear approximation curve, and stores it as offset correction data.

  The offset correction unit 35 is connected to the AD converter 27 and the correction data acquisition unit 33, and output data of the detection element A at the time of X-ray irradiation is input to the offset correction unit 35. The offset correction unit 35 performs offset correction on the output data of the detection element A using the offset correction data acquired by the correction data acquisition unit 33. The re-correction unit 37 is provided in the subsequent stage of the offset correction unit 35, and performs re-correction to compensate for image degradation on the output data of the detection element A subjected to the offset correction. The output data of the detection element A is output to the display unit 15 as an image output signal after being subjected to offset correction and recorrection. The recorrection unit 37 corresponds to the image processing unit in the present invention.

<Description of operation>
Next, the operation of the radiation imaging apparatus according to the first embodiment will be described. FIG. 3 is a flowchart for explaining the operation of the radiation imaging apparatus according to the first embodiment. In addition, when each detection element A is distinguished and called, the number of columns g and the number of rows h are given and described as detection elements Agh.

Step S1 (offset value acquisition)
First, after the radiation imaging apparatus is turned on, an offset value is acquired. That is, in a state where X-rays are not irradiated from the X-ray tube 5, the gate operation signal from the FPD control unit 11 to the gate driver 23, the amplifier operation signal to the amplifier 25, and the AD conversion signal to the AD converter 27. Is output.

  The gate driver 23 reads the charge information stored in each detection element A based on the gate operation signal. The charge information read at this time is charge information resulting from a noise component, a dark current of the detector, and the like. Then, the charge information read from each detection element A is transmitted to the amplifier 25. The amplifier 25 amplifies the transmitted charge information based on the amplifier operation signal and outputs the amplified charge information to the AD converter 27. The AD converter 27 converts the input charge information from an analog signal to a digital signal based on the AD conversion signal. The converted charge information is transmitted to the offset value acquisition unit 29 as output data of each detection element A.

  The offset value acquisition unit 29 acquires the transmitted output data as the offset value of the detection element A. The offset value acquisition unit 29 acquires an offset value for each detection element A, and stores a series of offset values (offset value profiles) acquired for each detection element A.

  Further, the temperature sensor 17 measures the temperature of the FPD 7 when the charge information is read from the detection element A. Then, the measured temperature data of the FPD 7 is transmitted from the temperature sensor 17 to the offset value acquisition unit 29. The offset value acquisition unit 29 acquires and stores the transmitted temperature data of the FPD 7 as temperature data of the FPD 7 corresponding to the acquired offset value. Note that the offset value acquired for the detection element Agh when the temperature (measured temperature) of the FPD 7 when the offset value is actually measured is t ° C. is hereinafter referred to as Ft (g, h).

  Then, the acquisition of the offset value and the temperature data of the FPD 7 is repeated. In the first embodiment, the number of acquisitions is four, but the number of acquisitions may be changed as appropriate. That is, in the first embodiment, four combinations of the FPD 7 temperature data and the offset value corresponding to the FPD 7 temperature are acquired. When the combination of the temperature data of the FPD 7 and the corresponding offset value profile is appropriately obtained, the process according to step S1 ends.

Step S2 (calculation of linear approximation curve)
After the process related to step S1 is completed, a linear approximate curve is calculated. That is, each offset value acquired by the offset value acquisition unit 29 and the temperature data of the FPD 7 are transmitted to the linear approximate curve calculation unit 31. The linear approximate curve calculation unit 31 calculates a linear approximate curve indicating the correlation between the temperature and the offset value for each of the detection elements A based on a combination of a plurality of acquired offset values and temperature data of the FPD 7 corresponding thereto. In the linear approximation curve, the temperature x and the offset value y are represented by a linear function represented by the following (1).
y = ax + b (a and b are constants) (1)
The linear approximate curve calculation unit 31 calculates a linear approximate curve indicating the correlation between the offset value and the temperature for each detection element A.

Step S3 (acquisition of offset correction data)
After the linear approximation curve is calculated for each detection element A, the offset correction data is calculated. That is, each linear approximation curve calculated by the linear approximation curve calculation unit 31 is transmitted to the correction data acquisition unit 33. The correction data acquisition unit 33 calculates an offset value at a temperature t _{low that} is lower than the temperature of the FPD 7 (hereinafter referred to as an actually measured temperature) when the offset value is acquired based on each transmitted linear approximation curve.

t _low is an arbitrary temperature lower than the actually measured temperature, but is preferably the lowest temperature at which the FPD 7 can operate (hereinafter referred to as the minimum operating temperature). In the first embodiment, the correction data acquisition unit 33 calculates an offset value at the minimum operating temperature. In Example 1, the minimum operating temperature is 10 ° C., but the minimum operating temperature may be changed as appropriate. That is, the offset value F ₁₀ (g, h) at the minimum operating temperature is calculated based on the offset value Ft (g, h) at the actually measured temperature t and the linear approximation curve calculated for the detection element Agh.

Here, an example of calculating the offset value F ₁₀ (g, h) at the minimum operating temperature will be described with reference to FIG. FIG. 4 is a graph showing the correlation between the offset value in the detection element Agh and the temperature of the FPD 7.

First, the offset value acquisition unit 29 acquires an offset value profile four times. Then, the linear approximate curve calculation unit 31 calculates a linear approximate curve for each of the detection elements A based on the offset value profile acquired by the offset value acquisition unit 29 and the temperature data of the FPD 7. In the example shown in FIG. 4, for the detection element Agh, the linear approximate curve L indicating the correlation with the temperature x ° C. of the FPD 7 and the offset value y is expressed by a linear function y = 166.56x + 2479.3. That is, the offset value F ₁₀ (g, h) at the minimum operating temperature is 4144.9, which is the value of y when x = 10 is substituted.

  The correction data acquisition unit 33 calculates the offset value at the minimum operating temperature for all the detection elements A by the same calculation method. As a result, an offset value profile at the minimum operating temperature is acquired. The correction data acquisition unit 33 acquires and stores the offset value profile at the minimum operating temperature as offset correction data.

The offset value varies depending on the temperature of the FPD 7. That is, the offset value increases as the temperature of the FPD 7 increases, and the offset value decreases as the temperature decreases. Therefore, the offset value F ₁₀ (g, h) constituting the offset correction data is the lowest offset value that can be taken by the detection element Agh. That is, the offset value profile at the minimum operating temperature is calculated (indicated by symbol PB in FIG. 5) based on the offset value profile at t ° C. (indicated by symbol PA in FIG. 5) and the linear approximation curve, which are actually measured temperatures. The offset value profile at the minimum operating temperature is lower than the offset value profile acquired at the actually measured temperature t.

  When the correction data acquisition unit 33 acquires and stores the offset correction data, the process according to step S3 ends. Note that the processes related to Step S1 to Step S3 are performed after the radiation imaging apparatus is powered on until the preparation for X-ray imaging is completed and X-ray irradiation becomes possible.

Step S4 (X-ray irradiation, reading of charge information)
After offset correction data is acquired and preparation for X-ray imaging is completed in the radiation imaging apparatus, X-rays are emitted. X-rays irradiated to the subject M from the X-ray tube 5 pass through the subject M and enter each detection element A constituting the FPD 7. Each detection element A converts incident X-rays into electric charges and accumulates them as electric charge information.

  Then, signals are output from the FPD control unit 11 to the gate driver 23, the amplifier 25, and the AD converter 27. The gate driver 23, the amplifier 25, and the AD converter 27 read out the charge information accumulated in each detection element A based on the output signal. The read charge information is transmitted to the offset correction unit 35 as output data of each detection element A. Note that the output data of the detection element Agh read at the time of X-ray irradiation is E (g, h).

Step S5 (offset correction)
After the charge information is read, the correction data acquisition unit 33 transmits the offset value profile at the minimum operating temperature, that is, the offset correction data to the offset correction unit 35. The offset correction unit 35 performs offset correction on the transmitted output data of each detection element A, and calculates an offset correction value. That is, the offset correction value G (g, h) in the detection element Agh is obtained by the calculation formula shown in the following (2).
G (g, h) = E (g, h) −F ₁₀ (g, h) (2)
The offset correction unit 35 calculates an offset correction value for each detection element A according to the calculation formula shown in (2). The calculated offset correction value is transmitted to the re-correction unit 37.

As described in step S3, the offset value F ₁₀ (g, h) constituting the offset correction data is the lowest value that the offset value Ft (g, h) can take. That is, the offset value actually included in the output data of the detection element Agh is necessarily higher than the offset value F ₁₀ (g, h) used for offset correction. Therefore, the omission of image components due to overcorrection is reliably avoided by the offset correction according to the first embodiment.

Step S6 (re-correction)
The recorrector 37 forms an image based on the transmitted offset correction value. Since the offset value F ₁₀ (g, h) subtracted in step S5 is a low value, only the offset correction according to step S5 completely removes components caused by dark current or the like from the output data of the detection element A. Can not. For this reason, image deterioration often occurs in an image formed using an offset correction value.

  Therefore, the recorrection unit 37 performs image processing such as enhancing the contrast on the image formed based on the offset correction value. By image processing, the image after offset correction becomes a high-quality image with enhanced contrast. The image that has been subjected to image processing and compensated for image degradation is transmitted to the display unit 19 by the recorrection unit 37. The display unit 19 displays the transmitted image as an X-ray transmission image.

  Thus, according to the radiation imaging apparatus according to the first embodiment, the linear approximate curve calculation unit 31 calculates the linear approximate curve for each detection element A, and the correction data acquisition unit 33 calculates each linear approximate curve. Using this, an offset value profile at a temperature lower than the actually measured temperature is calculated. The calculated offset value profile at the minimum operating temperature is stored as offset correction data.

  The offset correction unit 35 performs offset correction on the output data of the detection element during X-ray irradiation using the offset correction data. After the offset correction, the re-correction unit 37 performs image processing for enhancing the contrast. By using an offset value at a temperature lower than the actually measured temperature, the loss of image information due to excessive offset correction is reliably avoided. The reduction in contrast due to insufficient offset correction is eliminated by image processing by the re-correction unit 37, and a high-quality image is acquired. Therefore, the radiation imaging apparatus according to the first embodiment can acquire a high-quality X-ray transmission image without missing image information.

  The offset correction data is calculated from when the radiation imaging apparatus is turned on until the preparation for X-ray imaging is completed. Therefore, X-ray imaging is not hindered by the calculation of offset correction data. The temperature of the FPD 7 fluctuates from when the radiation imaging apparatus is turned on until the preparation for X-ray imaging is completed. That is, the offset value acquisition unit 29 acquires corresponding offset values for a plurality of temperatures over a wide range. As a result, since the linear approximate curve calculation unit 31 can calculate an accurate linear approximate curve, the numerical value calculated as the offset value at a temperature lower than the actually measured temperature is closer to the actually measured value.

  In the radiation imaging apparatus according to the first embodiment, an offset value at a temperature lower than the actually measured temperature is always used as offset correction data regardless of the temperature of the FPD 7. Therefore, there is no need to update the offset correction data in accordance with the temperature variation of the FPD 7 as in the prior art. As a result, the time required to form an X-ray transmission image can be shortened, so that the radiation imaging apparatus according to Embodiment 1 can perform more efficient X-ray imaging.

  Next, the operation of the radiation imaging apparatus according to the second embodiment of the present invention will be described with reference to the drawings. The overall configuration of the radiation imaging apparatus according to the second embodiment is the same as that of the radiation imaging apparatus according to the first embodiment. Further, detailed description of the parts common to the operation of the radiation imaging apparatus according to the first embodiment is omitted. Further, the flowchart according to the second embodiment is as shown in FIG.

Step S1 (offset value acquisition)
First, after the radiation imaging apparatus is turned on, an offset value is acquired. That is, in a state where X-rays are not irradiated from the X-ray tube 5, the offset value acquisition unit 29 acquires four combinations of the measured temperature t and the offset value profile at the measured temperature t as in the first embodiment.

Step S2 (calculation of linear approximation curve)
The linear approximate curve calculation unit 31 calculates the average value of the acquired offset values for two or more representative detection elements A in the acquired offset value profile at each of the four actually measured temperatures t. The average value of the offset values calculated at the actually measured temperature t is defined as Ft (Ave). The linear approximate curve calculation unit 31 then uses the linear approximate curve f (t) indicating a correlation between Ft (Ave) and the actually measured temperature t based on the combination of the four calculated average values Ft (Ave) and the actually measured temperature t. Is calculated. It is represented by a linear function represented by (3) below the linear approximation curve f (t).
f (t) = ct + d (c and d are constants) (3)
Note that the linear approximate curve f (t) calculated in Example 2 corresponds to the average linear approximate curve in the present invention.

Step S3 (acquisition of offset correction data)
The linear approximate curve calculation unit 31 transmits the calculated linear approximate curve f (t) to the correction data acquisition unit 33. The correction data acquisition unit 33 calculates the assumed pixel value P at the minimum operating temperature for the transmitted linear approximate curve f (t). In the second embodiment, since the minimum operating temperature is 10 ° C. as in the first embodiment, the following formula (4) is established for the assumed pixel value P.
P = 10c + d (4)

Next, the correction data acquisition unit 33 calculates the difference pixel value Q by taking the difference between the average offset value Ft (Ave) and the assumed pixel value P. That is, for the difference pixel value Q, the calculation formula shown in the following (5) is established.
Q = Ft (Ave) −P = Ft (Ave) − (10c + d) (5)

  Then, the correction data acquisition unit 33 calculates a value obtained by subtracting the difference pixel value Q from the offset value of the detection element A acquired at the actually measured temperature t. Further, the correction data acquisition unit 33 performs a calculation for subtracting the difference pixel value Q from the offset value for all of the detection elements A, and acquires and stores each calculated value as an offset value profile at the minimum operating temperature.

Step S4 (X-ray irradiation, reading of charge information)
After offset correction data is acquired and preparation for X-ray imaging is completed in the radiation imaging apparatus, X-rays are emitted. The charge information accumulated in each detection element A is read out and transmitted to the offset correction unit 35 as output data of each detection element A.

Step S5 (offset correction)
The offset value profile at the minimum operating temperature stored in the correction data acquisition unit 33 is transmitted to the offset correction unit 35 as offset correction data. The offset correction unit 35 calculates an offset correction value for each detection element A using the transmitted offset value profile. The calculated offset correction value is transmitted to the re-correction unit 37.

Step S6 (re-correction)
After the offset correction value is transmitted to the re-correction unit 37, the re-correction unit 37 performs image processing for enhancing contrast on the image formed based on the offset correction value, as in the first embodiment. The image subjected to the image processing is transmitted to the display unit 19 by the recorrection unit 37. The display unit 19 displays the transmitted image as an X-ray transmission image.

  By having such a configuration, in the radiation imaging apparatus according to the second embodiment, all offset values constituting the offset correction data are calculated based on the same linear approximation curve. Therefore, in order to calculate the offset value at the minimum operating temperature, it is not necessary to calculate a different linear approximation curve for each detection element and perform calculation using these. As a result, offset correction data at the minimum operating temperature can be acquired with a simpler configuration. That is, since the offset correction data can be calculated more easily and quickly, radiation imaging can be performed more efficiently.

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

  (A) In each of the above-described embodiments, the processes according to step S1 to step S3 are performed from when the radiation imaging apparatus is turned on until the preparation for X-ray imaging is completed, but is not limited thereto. That is, part or all of the acquisition of the offset value, the calculation of the linear approximation curve, and the acquisition of the offset correction data may be performed in advance at the stage of shipment of the radiation imaging apparatus. By calculating a linear approximation curve and offset correction data in advance, the time required for X-ray imaging can be further shortened. In addition, even in a situation where X-ray imaging is urgently required, it is possible to form a suitable X-ray transmission image using a linear approximation curve calculated in advance.

  (B) Moreover, in each Example mentioned above, it is good also as a structure which performs the process which concerns on step S1 to step S3 at arbitrary timings. In other words, a calculation instruction unit configured by switches, buttons, and the like may be further provided, and the process related to steps S1 to S3 may be performed by operating the calculation instruction unit in an ON state. By having this configuration, it is possible to calculate an offset value profile at the minimum operating temperature at an arbitrary timing and acquire offset correction data. Therefore, even when the temperature of the FPD 7 changes rapidly after the preparation for X-ray imaging is completed and the offset value fluctuates greatly, the offset correction data can be calculated again. Therefore, a more suitable X-ray transmission image can be formed even after the temperature of the FPD 7 has changed rapidly.

  (C) In each of the above-described embodiments, a direct conversion type FPD that directly converts radiation into electric charge is used. However, the present invention is not limited to this. That is, it is also possible to apply an indirect conversion type FPD that converts radiation into light and further converts the converted light into electric charges.

  (D) In each of the above-described embodiments, a medical device is used. However, the present invention can also be applied to industrial and nuclear devices.

1 ... Radiation imaging device
5 ... X-ray tube (radiation source)
7 ... FPD (radiation detector)
DESCRIPTION OF SYMBOLS 9 ... X-ray irradiation control part 11 ... FPD control part 13 ... Signal processing part 17 ... Temperature sensor (temperature measurement part)
DESCRIPTION OF SYMBOLS 19 ... Main control part 29 ... Offset value acquisition part 31 ... Linear approximation curve calculation part 33 ... Data acquisition part for correction | amendment (Data acquisition part for offset correction | amendment)
35 ... Offset correction unit 37 ... Re-correction unit

Claims (6)

A radiation source;
A radiation detection unit in which detection elements for detecting radiation emitted from the radiation source are arranged;
A temperature measurement unit for measuring the temperature of the radiation detection unit;
An offset value acquisition unit that acquires an offset value based on output data of the detection element at the time of non-irradiation;
And an offset value wherein the offset value acquisition unit has acquired, based on the temperature of said radiation detector where the temperature measuring portion is measured at the time of the acquisition, prior Symbol the radiation detection temperature measuring portion is measured after the time of the acquisition An offset correction data acquisition unit that calculates offset correction data that is an offset value at a temperature lower than the temperature of the unit;
A radiation imaging apparatus, comprising: an offset correction unit that performs offset correction using the offset correction data. The radiation imaging apparatus according to claim 1,
A radiation imaging apparatus, further comprising: an image processing unit that performs processing for compensating for image degradation on output data of the detection element that has been offset-corrected by the offset correction unit. The radiation imaging apparatus according to claim 1 or 2,
A linear approximation curve calculation unit that calculates a linear approximation curve indicating a correlation between the offset value acquired by the offset value acquisition unit and the temperature of the radiation detection unit measured by the temperature measurement unit;
The offset correction data acquisition unit calculates an offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit based on the linear approximation curve calculated by the linear approximation curve calculation unit. apparatus. The radiation imaging apparatus according to claim 3.
The linear approximate curve calculation unit calculates a linear approximate curve for each of the detection elements,
The offset correction data acquisition unit calculates, for each of the detection elements, an offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit, based on the linear approximation curve of each detection element. A radiation imaging apparatus. The radiation imaging apparatus according to claim 3.
The linear approximation curve calculation unit calculates an average linear approximation curve based on an average of offset values acquired by the offset value acquisition unit for two or more detection elements and a temperature of the radiation detection unit measured by the temperature measurement unit. Calculate
The offset correction data acquisition unit calculates an offset value at a temperature lower than the temperature of the radiation detection unit measured by the temperature measurement unit based on the average linear approximation curve calculated by the linear approximation curve calculation unit. Imaging device. The radiation imaging apparatus according to any one of claims 1 to 5,
A radiation imaging apparatus, further comprising a calculation instruction unit that instructs calculation of the offset correction data by the offset correction data acquisition unit.

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