JP5362444B2 - X-ray diagnostic imaging equipment - Google Patents

Description

  The present invention relates to an X-ray diagnostic imaging apparatus that generates an X-ray projection image by detecting X-rays irradiated from an X-ray generator and transmitted through a subject with an X-ray flat panel detector. The present invention relates to a technique for correcting a dark current of an X-ray flat panel detector included in a line projection image.

  The X-ray image diagnostic apparatus irradiates a subject with X-rays from an X-ray generator, detects X-rays transmitted through the subject with an X-ray flat panel detector, and generates an X-ray projection image. In general, an X-ray flat panel detector (hereinafter referred to as an X-ray FPD) is formed by two-dimensionally arranging a plurality of X-ray detection elements in a lattice pattern corresponding to the pixels of an X-ray projection image. As an X-ray detection element, one having a configuration in which an incident amount of X-rays is converted into a current by a photoelectric conversion element, the current is accumulated in a capacitor, and a charge accumulated in the capacitor is measured as a transmitted X-ray dose. That is, the X-ray projection image is generated by reading out the accumulated charges of the capacitors of a plurality of two-dimensionally arranged X-ray detection elements.

  By the way, it is known that an X-ray detection element of an X-ray FPD causes a current to flow through a photoelectric conversion element even when X-rays are not irradiated, and charges are accumulated in a capacitor. It is called. The accumulated charge due to the dark current becomes noise in the X-ray projection image, and there is a problem that the image quality is deteriorated.

  In order to solve the problem of dark current, it is conventionally known to initialize by discharging the accumulated charge for dark current stored in a capacitor when no X-rays are incident. However, according to this, if the time from the initialization of the capacitor to the actual photographing becomes long, the charge due to the dark current is accumulated in the capacitor and the image quality is deteriorated.

  On the other hand, before capturing an X-ray projection image, the amount of charge for dark current is read out, dark current correction data is created and stored, and detected by the X-ray FPD when generating the X-ray projection image It has been proposed to correct the X-ray projection image by subtracting the dark current correction data from the transmitted X-ray dose (Patent Document 1).

  By the way, since the dark current varies depending on the internal temperature of the X-ray FPD, dark current correction data is stored for each internal temperature of the X-ray FPD, and an X-ray projection image is obtained according to the temperature of the X-ray FPD at the time of imaging. Need to be corrected. Therefore, according to the method of Patent Document 1, there is a problem that the storage area of the dark current correction data becomes enormous.

  Therefore, in Patent Document 2, dark current correction data at at least two different temperatures of the X-ray FPD is stored for each detection element (pixel) of the X-ray FPD, and imaging is performed by interpolation using extrapolation or extrapolation. It has been proposed to calculate dark current correction data at the temperature of the X-ray FPD at the time. Further, the same document proposes that the necessity of dark current correction is determined based on the temperature of the X-ray FPD, thereby reducing the number of executions of dark current correction and avoiding the troublesomeness of X-ray imaging. Has been.

JP 2002-159482 A JP 2007-185375 A

  However, as described in Patent Document 2, two dark current correction data at different temperatures of the X-ray FPD are stored for each X-ray detection element, and the dark current at the temperature of the X-ray FPD at the time of imaging is obtained by interpolation. Even when the correction data is calculated, a storage area is required for each pixel, so that there is a problem that the storage device becomes large. For example, when the X-ray FPD is 9 million pixels, the storage capacity of dark current correction data at one temperature is about 18 MB, and when storing dark current correction data at two different temperatures, a storage capacity of about 36 MB is required. become.

  Further, in the prior art, since the characteristic change due to the aging of the X-ray detection element of the X-ray FPD is not considered, for example, when the temperature-dependent dark current correction data changes due to the characteristic change of the X-ray detection element May increase the error.

  The first problem to be solved by the present invention is to greatly reduce the storage capacity of temperature-dependent dark current correction data.

  A second problem to be solved by the present invention is to generate dark current correction data corresponding to a change in characteristics of the X-ray detection element of the X-ray FPD.

  The present invention includes an X-ray generator that irradiates a subject with X-rays, a planar X-ray detector that is disposed opposite to the X-ray generator and detects transmitted X-rays of the subject, and the X-ray detector A temperature detector for detecting a temperature of the X-ray detector; a first storage means for storing dark current data of the X-ray detector; and a first storage means for measuring a dark current of the X-ray detector. Dark current data updating means for updating the dark current data of the subject, and the transmitted X-ray data output from the X-ray detector is corrected based on the dark current data of the first storage means to correct the X of the subject. An X-ray diagnostic imaging apparatus including an image generation unit that generates a line projection image is an object.

  According to a first aspect of the present invention, in order to solve the first problem, in the X-ray diagnostic imaging apparatus, a temperature correction coefficient for correcting the dark current data according to the temperature of the X-ray detector is stored. 2, the dark current data update means updates the dark current data of the first storage means with the temperature of the X-ray detector, and the image generation means includes the transmission X A difference between the temperature of the X-ray detector when the line data is output and the temperature of the X-ray detector attached to the dark current data stored in the first storage means; and the second Temperature-dependent dark current correction data calculating means for obtaining temperature-dependent dark current correction data based on the temperature correction coefficient stored in the storage means, and the first temperature-dependent dark current correction data obtained by the means. The dark current read from the storage means Temperature-dependent dark current data correcting means for correcting data, and correcting the transmitted X-ray data based on the dark current data corrected by the means to generate an X-ray projection image of the subject. It is characterized by.

That is, in the first aspect of the present invention, as will be described later, in view of the fact that the dark current I that changes with the temperature of the X-ray FPD increases in proportion to the temperature T of the X-ray FPD, the manufacture of the X-ray FPD is performed. At the time of shipment, the temperature characteristics of the dark current of the X-ray FPD are measured, and the gradient ΔI ₀ / ΔT ₀ of the temperature characteristics is stored in the second storage means as the initial value α ₀ of the temperature correction coefficient. Further, provided the temperature detector for detecting the temperature of the X-ray FPD, dark current data updating means in updating the dark current data by measuring the dark current, denoted by the temperature T _R of the X-ray FPD Refreshed The dark current data in the first storage means is updated. On the other hand, the image generation means detects the temperature T _C of the X-ray FPD during actual photographing, by multiplying the temperature correction coefficient alpha ₀ the difference in temperature at the time of update at the shooting (T C _{-T R),} can be determined temperature-dependent dark current correction data _{I TC} = alpha ₀ to _(T C -T _R). The temperature correction coefficient α ₀ is desirably set for each pixel of the X-ray FPD. However, since the temperature distribution of the X-ray FPD is practically small, the average of all the pixels of the X-ray FPD is used. A value can be used. In this case, the temperature-dependent dark current correction data _ITC is one data common to each pixel.

In this way, the dark current data in the first storage means is corrected to increase or decrease by the temperature-dependent dark current correction data _ITC , and the X-ray FPD at the time of actual imaging is used by using the corrected dark current data. By correcting the detection output of each pixel, an X-ray projection image with improved image quality can be obtained. As described above, according to the present invention, the temperature-dependent dark current correction data for each pixel of the X-ray FPD can be obtained by storing only one temperature correction coefficient α _0. The storage capacity required for current correction can be greatly reduced.

  Moreover, in order to solve the second problem, the second aspect of the present invention further includes dark current data updated by the dark current data updating means and dark current data before update in addition to the first aspect. And a temperature correction for updating the temperature correction coefficient of the second storage means by calculating the temperature correction coefficient based on the difference in temperature and the difference in temperature of the X-ray detector attached to the dark current data Coefficient updating means is provided.

  That is, in the X-ray FPD, a temperature-dependent dark current may change due to a change in characteristics of the X-ray detection element. Accordingly, the change ΔI in dark current, which is the difference between the updated dark current data and the dark current data before update, is divided by the temperature change ΔT of the X-ray FPD at the time of measurement of the dark current data to obtain the temperature The correction coefficient α = ΔI / ΔT is obtained, and the temperature correction coefficient of the second storage unit is updated. Thereby, since the dark current correction data can be generated in response to a change in characteristics of the X-ray detection element and a change in temperature dependency, the accuracy of dark current correction can be improved.

  Further, since the dark current of the X-ray FPD is caused by the accumulation of electric charges in the capacitor of the X-ray detection element in the non-imaging state (standby state), the dark current is measured and the dark current of the first storage unit is measured. The actual dark current data changes according to the elapsed time from the update of the data until the actual shooting is performed. That is, it is necessary to correct the dark current according to the elapsed time since the dark current data was updated.

  Therefore, in a third aspect of the present invention, in addition to the first or second aspect, the dark current data is stored in accordance with an elapsed time from when the dark current data in the first storage means is updated. A third storage unit storing an elapsed time correction coefficient to be corrected; and the dark current data update unit updates the dark current data of the first storage unit with an update time of the dark current data. The image generation means includes an elapsed time from an update time attached to the dark current data stored in the first storage means to a time when the transmission X-ray data is output, and the first The elapsed time dependent dark current correction data calculating means for obtaining elapsed time dependent dark current correction data based on the elapsed time correction coefficient stored in the storage means 3, and the elapsed time dependent dark current correction data obtained by the means Using said Elapsed time dependent dark current data correcting means for correcting the dark current data read from one storage means, and the elapsed time corrected dark current data correcting means and the temperature dependent dark current data correcting means. The transmission X-ray data is corrected based on the time-dependent dark current correction data and the temperature-dependent dark current correction data to generate an X-ray projection image of the subject.

That is, in the third aspect of the present invention, the dark current increases in proportion to the elapsed time from when the dark current is measured and the dark current data in the first storage means is updated until the actual photographing is performed. In view of having the elapsed time dependency, the elapsed time characteristic of the dark current of the X-ray FPD is measured at the shipment stage at the time of manufacturing the X-ray FPD, and the gradient ΔI ₀ / ΔD ₀ of the temperature characteristic is calculated as the elapsed time correction coefficient. advance and stored in the initial value beta ₀ of the third storage means. On the other hand, the dark current data update means updates the dark current data in the first storage means with the update time of the dark current data. Then, the image generating means calculates the elapsed time D _C from the update time attached to the dark current data and the time at the time of photographing the transmitted X-ray data is output, the elapsed time correction coefficient β to the elapsed time D _C by multiplying the _0, it can be determined elapsed time dependent dark current correction data _{I DC} = _{β 0} D _C. Incidentally, the elapsed time-dependent dark current correction data I _DC, it is desirable to set for each pixel of inherent in the X-ray FPD, the difference between the dark current due to the elapsed time of the pixels is practically X-ray FPD is small Therefore, the average value of all pixels of the X-ray FPD can be used. In this case, the temperature-dependent dark current correction data _IDC is one data common to each pixel. According to the third aspect of the present invention, since the elapsed time-dependent dark current correction data can be obtained by storing only one elapsed time correction coefficient, it is necessary for the elapsed time-dependent dark current correction. The storage capacity can be greatly reduced.

  Furthermore, in the X-ray FPD, an elapsed time-dependent dark current may change due to a change in characteristics of the X-ray detection element. Therefore, in addition to the third aspect of the present invention, the difference between the dark current data updated by the dark current data update means and the dark current data before update, and the update time attached to the dark current data. And an elapsed time correction coefficient updating unit that calculates the elapsed time correction coefficient based on the difference between the two and updates the elapsed time correction coefficient of the third storage unit.

  According to this, the elapsed time correction coefficient β = ΔI / ΔD is obtained by appropriately dividing the change ΔI in dark current, which is the difference between the updated dark current data and the dark current data before update, by the elapsed time D. Thus, the elapsed time correction coefficient of the third storage means is updated. Thereby, since the dark current correction data can be generated in response to a change in the elapsed time-dependent dark current correction data due to a change in the characteristics of the X-ray detection element, the accuracy of the dark current correction can be improved.

  In any one of the above aspects, it is preferable that the dark current data update unit, the temperature correction coefficient update unit, and the elapsed time correction coefficient update unit perform update when the X-ray projection image is not imaged. Further, the dark current data update unit, the temperature correction coefficient update unit, and the temperature correction coefficient update unit execute update periodically (for example, at intervals of 1 minute) when the X-ray projection image is not captured.

  In any one of the above aspects, it is preferable that the temperature correction coefficient updating unit performs updating when a temperature change of the X-ray detector exceeds a set threshold value. Further, when the difference in temperature of the X-ray detector attached to the dark current data updated by the dark current data update means and the dark current data before the update exceeds a preset abnormal value, a temperature change abnormality is detected. Can be output.

  According to the present invention, the first effect that the storage capacity of the temperature-dependent dark current correction data can be significantly reduced is obtained.

  In addition, according to the present invention, the second effect that dark current correction data can be generated in response to a change in characteristics of the X-ray detection element of the X-ray FPD can be obtained.

1 is an overall configuration diagram of an X-ray image diagnostic apparatus according to Embodiment 1 of the present invention. It is a figure which shows an example of the temperature dependence characteristic of the dark current of X-ray FPD. It is a flowchart which shows the procedure of the dark current data update process of Embodiment 1 of this invention, and a temperature correction coefficient update process. It is a flowchart which shows the procedure of the image data process at the time of imaging | photography of Embodiment 1 of this invention. It is a whole block diagram of the X-ray image diagnostic apparatus of Embodiment 2 of this invention. It is a figure which shows an example of the elapsed time dependence characteristic of the dark current of X-ray FPD. It is a flowchart which shows the procedure of the dark current data update process of Embodiment 2 of this invention, a temperature correction coefficient update process, and elapsed time correction coefficient update process. It is a flowchart which shows the procedure of the image data process at the time of imaging | photography of Embodiment 2 of this invention.

Hereinafter, an X-ray diagnostic imaging apparatus according to the present invention will be described based on embodiments.
(Embodiment 1)
As shown in FIG. 1, an X-ray image diagnostic apparatus according to Embodiment 1 of the present invention includes an X-ray generator 1 that irradiates a subject 100 with X-rays, and a subject that is disposed facing the X-ray generator 1. A planar X-ray detector 2 that detects 100 transmitted X-rays, a temperature detector 3 that detects the temperature inside the X-ray detector 2, and an image display device 4 that displays information such as an X-ray projection image. It is configured with.

  Furthermore, the X-ray diagnostic imaging apparatus of Embodiment 1 is based on the detection output output from the X-ray detector 2 and the internal temperature of the X-ray detector 2 output from the temperature detector 3. Etc., and an arithmetic processing unit 10 that generates such information. The arithmetic processing unit 10 includes a dark current data update unit 11, a temperature correction coefficient update unit 12, and an image generation unit 13 that are realized by executing a program. Further, the image generation unit 13 includes a dark current correction data calculation unit 14 and a dark current data correction unit 15. Further, the dark current data is corrected in accordance with the dark current data storage means 16 which is the first storage means for storing the dark current data of the X-ray detector 2 measured as appropriate, and the internal temperature of the X-ray detector 2. A temperature correction coefficient storage unit 17, which is a second storage unit in which the temperature correction coefficient is stored, is connected to the arithmetic processing unit 10 through the data bus 18 so as to be able to transmit data to each other.

  The detailed configuration of each part of the X-ray image diagnostic apparatus of Embodiment 1 configured as described above will be described together with the operation. X-rays emitted from the X-ray generator 1 toward the subject 100 are incident on the X-ray detector 2 in accordance with the X-ray transmission amount of the subject 100. X-rays incident on the X-ray detector 2 are converted into electrical signals by the X-ray detection elements of the X-ray detector 2 and input to the arithmetic processing unit 10. The arithmetic processing unit 10 performs dark current correction, which will be described later, in the image generation unit 13, generates an X-ray projection image, and displays it on the image display device 4. Further, the generated X-ray projection image can be stored in a recording medium in the form of electronic data, or an X-ray projection image such as a film can be formed.

  Next, the detailed configuration of dark current correction, which is a feature of the first embodiment, will be described with reference to FIGS. The X-ray detector 2 used in the present embodiment is formed by two-dimensionally arranging a plurality of X-ray detection elements in a lattice shape corresponding to the pixels of the X-ray projection image. The X-ray detection element of this embodiment converts the incident amount of X-rays into a current by a photoelectric conversion element such as a photodiode, accumulates the current in a capacitor, discharges the accumulated charge of the capacitor, and discharges the current. The quantity is measured as a transmitted X-ray dose. That is, the X-ray projection image is generated by reading out the accumulated charges of the capacitors of a plurality of two-dimensionally arranged X-ray detection elements.

  By the way, the X-ray detection element of the X-ray detector 2 has a phenomenon in which a current (dark current) flows through the photoelectric conversion element even when X-rays are not irradiated. Since the accumulated charge due to the dark current becomes noise in the X-ray projection image, the charge accumulated in the capacitor of each pixel of the X-ray detector 2 in the non-imaging state is discharged, and the amount of discharge is read to correct darkness for correction. Current data is updated regularly or periodically. And the dark current noise of an X-ray projection image can be removed by removing the dark current updated immediately before from the output of each pixel of the X-ray detector 2 at the time of imaging | photography.

  However, even if the accumulated charge of the capacitor is discharged by updating the dark current data, the accumulated charge corresponding to the offset (hereinafter referred to as an offset component) remains in the capacitor. Further, a new charge is accumulated in the capacitor according to the elapsed time from discharging the accumulated charge of the capacitor to actual imaging (hereinafter referred to as an elapsed time component). Further, the dark current related to the accumulated charge of the capacitor varies according to the internal temperature of the X-ray detector 2 (hereinafter referred to as a temperature dependent component). Here, since the offset component is a constant value, it can be removed by updating the dark current data described above. Further, since the elapsed time component is smaller than the offset component as will be described later, there is no problem in a range where the elapsed time is short. On the other hand, the temperature-dependent component is relatively large and cannot be ignored.

  Therefore, dark current data update and temperature correction coefficient update processing are executed during non-photographing shown in FIG. 3 (steps S1 to S4 in FIG. 3). Note that S2 to S4 in FIG. 3 are processes to be executed as necessary, and will be described later.

First, in step S1 of FIG. 3, the dark current data update unit 11 of FIG. 1 measures the dark current of each pixel of the X-ray detector 2 at the time of non-imaging, and stores it in the dark current data storage unit 16. Here, the dark current has a temperature dependency that varies depending on the internal temperature of the X-ray detector 2, for example, as shown in FIG. 2. The horizontal axis in FIG. 2 indicates the internal temperature of the X-ray detector 2, and the vertical axis indicates the dark current amount [count] in units of pixels. Here, [count] is the number of luminance layers of the pixel. In general, the internal temperature of the X-ray detector 2 falls within the range of 20 ° C. to 50 ° C., but the illustrated example shows an example of 30 ° C. to 40 ° C. As apparent from FIG. 2, it was found that the temperature-dependent dark current _IT of the X-ray detector 2 increases in proportion to the internal temperature T of the X-ray detector 2.

Therefore, in this embodiment, at the stage during the production of the X-ray detector 2, for example at the shipping stage, measures the relationship between the dark current I _T and the internal temperature T of the X-ray detector 2, the slope [Delta] I _T / ΔT is obtained as the initial value (α ₀ ) of the temperature correction coefficient α and stored in the temperature correction coefficient storage means 17. Thereby, the dark current correction data calculation means 14 can obtain the dark current correction data I _TC at the time of imaging by the following equation (1).
[Equation 1]
_{I TC = α (T C -T} R) (1)

Here, T _C is the internal temperature of the X-ray detector 2 in the internal temperature of the X-ray detector 2 at the time of imaging (at the time of correction), T _R is the dark current update time (date). That is, Equation (1) is, dark current data to the dark current data stored in the storage unit 16, the temperature change ΔT = (T C _{-T R)} temperature dependence corresponding to the dark current correction data I _TC It is.

Therefore, as shown in step S1 of FIG. 3, the dark current data updating unit 11 discharges the charge accumulated in the capacitor of each pixel of the X-ray detector 2 at the time of non-imaging and uses the accumulated charge as the dark current. The dark current data in the dark current data storage means 16 is updated periodically or periodically. At this time, stores are denoted by the detected value of the internal temperature T _R of the update time of the X-ray detector 2. Even if the charge accumulated in the capacitor of each pixel of the X-ray detector 2 is read by the dark current data updating means 11, the capacitor is not completely discharged, and an offset portion remains. This offset is about 2,500 [count] in the example of FIG.

Dark current data correction means 15, by the following equation (2), can be obtained dark current data I _C at the time of imaging.
[Equation 2]
I _C = I _R + I _TC (2)
Here, I _R is the update data of the latest dark current data stored in the dark current data storage unit 16 is the sum of dark current offset component and the temperature-dependent component of the time of renewal.

Next, the processing of steps S2 to S4 in FIG. 3 will be described. In the above description, it is assumed that the dark current temperature characteristic of the X-ray detector 2 does not change over time, and the dark current correction data is obtained with the temperature correction coefficient α being the initial value (α ₀ ). However, since the temperature-dependent dark current of the X-ray detector 2 changes over time according to the use time and the use environment, it is necessary to update the temperature correction coefficient α appropriately. Therefore, in this embodiment, the temperature correction coefficient α is updated in steps S2 to S4 in FIG.

In step S2 of FIG. 3, a change ΔT between the temperature of the temperature detector 3 acquired this time in the dark current data update process of S1 and the temperature attached to the dark current data before the update is obtained, and that ΔT is abnormally large. In the case (for example, ΔT ≧ 10 ° C.), it is determined that imaging is impossible, the process proceeds to step S4, a warning is displayed on the image display device 4 (for example, “FPD abnormality”), and the process of FIG. .
On the other hand, in the judgment of step S2, if not ΔT is abnormal, the routine proceeds to step S3, the temperature correction coefficient updating means 12 is the temperature change ΔT of the dark current data before and after update, and the change [Delta] I _R of the dark current Based on the following equation (3), the temperature correction coefficient α is obtained, the storage of the temperature correction coefficient storage means 17 is updated, and the process of FIG. Note that the process of FIG. 3 can be executed periodically (for example, at an interval of 1 minute) during non-shooting. It can also be executed when necessary. In addition, it is desirable that the temperature correction coefficient α is originally set for each pixel of the X-ray detector 2. However, since the temperature distribution deviation of the X-ray detector 2 is practically small, the X-ray detection is performed. The average value of all the pixels of the device 2 can be used. In this case, the temperature-dependent dark current correction data _ITC is one data common to each pixel.
[Equation 3]
α = ΔI _R / ΔT (3)

Next, image data processing at the time of imaging according to the present embodiment will be described along the flowchart shown in FIG. The process of FIG. 4 is a process in the image generation unit 13. First, accepts the internal temperature T _C of the X-ray detector 2 from the temperature detector 3 (S11), the internal temperature of the X-ray detector 2 corresponding to the dark current data I _R stored in the dark current data storage means 16 T the difference between the _R [Delta] T ₌ seeking _(T C -T _R), determines whether within predetermined threshold value gamma (S12). If [Delta] T ≦ gamma, the process proceeds to step S19, the image data outputted from the X-ray detector 2, it is corrected by the dark current data I _R stored in the dark current data storage unit 16 X-ray projection image Is output to the image display device 4 and the process is terminated.

On the other hand, if ΔT> γ is determined in step S2, the process proceeds to step S13, where it is determined whether ΔT is abnormal. If it is abnormal, a warning is displayed as in steps S2 and S3 of FIG. The process ends (S13, S17). If ΔT is not abnormal in the determination in step S13, the processes in steps S14 to S16 are executed. That is, if the temperature change is not abnormal, the dark current correction data I _TC at the time of imaging is calculated by the equation (1) (S14). Then, according to the equation (2), the dark current data I _R stored in the dark current data storage means 16 is corrected by the dark current correction data I _TC, obtaining the dark current data I _C at the time of imaging (S15) . Then, the image data output from the X-ray detector 2, and generates and outputs an X-ray projection image by correcting the image display device 4 by the corrected dark current data I _C, the process ends.

In this way, the dark by the current correction data I _TC, corrected increase or decrease the dark current data I _R, using the corrected dark current data I _C was, the X-ray detector 2 at the time of actual shooting of each pixel Since the detection output is corrected, it is possible to obtain an X-ray projection image with improved image quality from which temperature dependency is removed. In particular, according to the present embodiment, the temperature-dependent dark current correction data for each pixel of the X-ray detector 2 can be obtained by storing only one temperature correction coefficient α ₀ (or α). The storage capacity required for dark current correction can be greatly reduced.

  Further, according to the present embodiment, even if the temperature-dependent dark current changes due to the characteristic change of the X-ray detection element of the X-ray detector 2, the temperature correction coefficient α is appropriately updated. Even when the temperature dependency of the X-ray detection element changes due to a characteristic change, the accuracy of dark current correction can be improved.

(Embodiment 2)
FIG. 5 shows an overall configuration diagram of Embodiment 2 of the X-ray image diagnostic apparatus of the present invention. The present embodiment is different from the first embodiment of FIG. 1 in that an elapsed time correction coefficient update unit 19 is provided in the arithmetic processing apparatus 10 and an elapsed time correction coefficient storage unit 20 is provided. Since other configurations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

  In the present embodiment, it is considered that the actual dark current changes from the dark current data stored in the dark current data storage unit 16 depending on the elapsed time from the update of the dark current data to the shooting. Is. That is, when the charge accumulated in the capacitor of the X-ray detection element in the non-imaging state (standby state) increases with time, the dark current data when the imaging is actually performed after the dark current data is updated differs. Therefore, the present embodiment is characterized in that the dark current data is corrected according to the elapsed time.

Here, the dark current depending on the elapsed time has characteristics as shown in FIG. 6, for example. The horizontal axis in FIG. 6 represents the elapsed time [s] from the previous update, and the vertical axis represents the dark current amount [count] in pixel units. In the example of illustration, the example of 0-300 [s] is shown. As can be seen from the figure, the elapsed time dependent dark current _ID of the X-ray detector 2 increases in proportion to the elapsed time D [s].

Therefore, in the present embodiment, the relationship between the dark current _ID of the X-ray detector 2 and the elapsed time D is measured at the time of manufacture of the X-ray detector 2, for example, at the shipping stage, and the slope ΔI _D / ΔD is obtained as an initial value (β ₀ ) of the elapsed time correction coefficient β and stored in the elapsed time correction coefficient storage means 20. Thus, the dark current correction data calculation means 14, the following equation (4) can be obtained dark current correction data I _DC of the elapsed time-dependent.
[Equation 4]
I _DC = β · D _C (4)

Here, D _C is the time elapsed from the update time of the most recent dark current data until the time of imaging (at the time correction).

Therefore, as shown in step S21 of FIG. 7, the dark current data update unit 11 measures the dark current of each pixel of the X-ray detector 2 at the time of non-imaging and stores it in the dark current data storage unit 16. Update the dark current data. In this case, the point storing denoted by the internal temperature T _R of the update time of the X-ray detector 2 is similar to that of Embodiment 1. Further, an elapsed time ΔD from the previous update time to the current update time is added and stored. Thus, dark current data correction means 15, by the equation (4) and following equation (5), can be obtained dark current data I _C dependent elapsed time at the time of imaging.
[Equation 5]
I _C = I _R + I _DC (5)
Here, I _R is the update data of the latest dark current data stored in the dark current data storage unit 16.

Next, the processes in steps S22 to S24 in FIG. 7 are the same as the processes in steps S2 to S4 in FIG. Further, in the process of step S25, as with the update of the temperature correction coefficient α, the elapsed time correction coefficient β is also considered to change over time according to the usage time of the X-ray detector 2 and according to the usage environment. It is a provided step. That is, the elapsed time correction coefficient updating unit 19 determines the elapsed time ΔD from the previous update to the current update, and the change ΔI _D = (I _R −) between the previous update (R−1) and the current update (R). Based on I _R-1 ), the elapsed time correction coefficient β is obtained by the following equation (6), the storage of the elapsed time correction coefficient storage means 20 is updated, and the processing of FIG.
[Equation 6]
_{β = ΔI D / ΔD (6} )

Note that the processing in FIG. 7 can be executed periodically (for example, at an interval of 1 minute) during non-shooting. It can also be executed when necessary. In addition, the elapsed time correction coefficient β is desirably set for each pixel of the X-ray detector 2 in nature, but practically, variation of each pixel due to the elapsed time of the X-ray detector 2 is small. The average value of all the pixels of the X-ray detector 2 can be used. In this case, the dark current correction data I _DC of the elapsed time-dependent will each pixel one common data.

Next, image data processing at the time of imaging according to the present embodiment will be described with reference to the flowchart shown in FIG. The process of FIG. 8 is a process in the image generation unit 13. First, to calculate the elapsed time D _C until the time of shooting from the last update of the dark current data stored in the dark current data storage unit 16 (S31). Calculating elapsed time D _C that determines whether predetermined within the threshold [delta] (S32). If D _C ≦ [delta], the routine proceeds to step S36, the image data outputted from the X-ray detector 2, correcting the X-ray projection by the dark current data I _R stored in the dark current data storage means 16 An image is generated and output to the image display device 4, and the process ends.

On the other hand, if D _C > δ is determined in step S32, the process proceeds to step S33, and dark current correction data I _DC at the time of imaging is calculated by the above equation (4). Then, from the equation (5), the dark current data I _R stored in the dark current data storage means 16 is corrected by the dark current correction data I _DC, obtaining the dark current data I _C at the time of imaging (S34) . Then, the image data output from the X-ray detector 2, and generates and outputs an X-ray projection image by correcting the image display device 4 by the corrected dark current data I _C, the process ends.

Thus, according to the present embodiment, the dark current data update unit 11 updates the dark current data in the dark current data storage unit 16 with the update time of the dark current data, and the image generation unit 13 calculating the elapsed time D _C from the update time that is attached to the current data until the time of the transmissive X-ray imaging data is output, multiplying the elapsed time correction coefficient beta _{0 (or} beta) to the elapsed time D _C Thus, the elapsed time-dependent dark current correction data I _DC = βD _C is obtained. Therefore, the elapsed time-dependent dark current correction data can be obtained by storing only one elapsed time correction coefficient β. The storage capacity required for the elapsed time dependent dark current correction can be greatly reduced.

  Further, the elapsed time-dependent dark current may change due to the characteristic change of the X-ray detection element. According to this embodiment, the dark current data updated by the dark current data update unit 11 and the pre-update dark current data are updated. Since the elapsed time correction coefficient β is calculated and updated based on the difference from the dark current data and the update time difference attached to the dark current data, the dependence on the elapsed time of the X-ray detection element Since dark current correction data can be generated in response to a change in the dark current correction data, the accuracy of dark current correction can be improved.

FIG. 8 does not describe the dark current data correction step based on the temperature-dependent dark current correction data I _TC of S14 and S15 in FIG. 4, but both the image data processing at the time of shooting in FIGS. By performing the above, temperature-dependent dark current correction and elapsed time-dependent dark current correction can be performed, so that the accuracy of dark current correction can be further improved.

The update of the elapsed time correction coefficient β according to the present embodiment uses the difference (ΔI _D ) in dark current between the previous update and the current update as shown in Equation (6). The updated value includes a temperature-dependent dark current component as an error. However, as can be seen by comparing FIG. 2 and FIG. 6, the elapsed time component has less influence on the dark current data than the temperature-dependent component. Therefore, when the temperature change ΔT is within the threshold value in the determination of step S12 in the flowchart of FIG. 4, correction using the elapsed time component of FIG. 8 is executed. Then, when the temperature change ΔT exceeds the threshold in the determination of step S12 in the flowchart of FIG. 4, the correction by the temperature dependent component is executed in steps S14 to S15 in the same figure, and the correction by the elapsed time component may be omitted. desirable.

DESCRIPTION OF SYMBOLS 1 X-ray generator 2 X-ray detector 3 Temperature detector 4 Image display apparatus 10 Arithmetic processor 11 Dark current data update means 12 Temperature correction coefficient update means 13 Image generation means 14 Dark current correction data calculation means 15 Dark current data correction Means 16 Dark current data storage means 17 Temperature correction coefficient storage means 18 Data bus 19 Elapsed time correction coefficient update means 20 Elapsed time correction coefficient storage means

Claims (7)

An X-ray generator for irradiating the subject with X-rays, a flat-type X-ray detector disposed opposite to the X-ray generator for detecting transmitted X-rays of the subject, and the X-ray detector A temperature detector for detecting temperature; first storage means for storing dark current data of the X-ray detector; and dark current data of the first storage means by measuring dark current of the X-ray detector. And an X-ray projection image of the subject by correcting the transmitted X-ray data output from the X-ray detector based on the dark current data of the first storage means. In an X-ray diagnostic imaging apparatus comprising an image generating means for generating,
A second storage means for storing a temperature correction coefficient for correcting the dark current data according to the temperature of the X-ray detector;
The dark current data update means updates the dark current data of the first storage means with the temperature of the X-ray detector,
The image generation means includes the temperature of the X-ray detector when the transmission X-ray data is output and the X-ray detector attached to the dark current data stored in the first storage means. Temperature-dependent dark current correction data calculating means for obtaining temperature-dependent dark current correction data based on the difference from the temperature and the temperature correction coefficient stored in the second storage means, and the temperature-dependent darkness obtained by the means Temperature-dependent dark current data correction means for correcting the dark current data read from the first storage means using current correction data, and the transmitted X-rays based on the dark current data corrected by the means Correcting the data to generate an X-ray projection image of the subject ;
The temperature correction coefficient based on the difference between the dark current data updated by the dark current data updating means and the dark current data before the update, and the temperature difference of the X-ray detector attached to the dark current data An X-ray image diagnostic apparatus comprising temperature correction coefficient updating means for calculating the temperature correction coefficient of the second storage means and calculating the temperature correction coefficient . The X-ray diagnostic imaging apparatus according to claim 1 , further comprising:
A third storage means for storing an elapsed time correction coefficient for correcting the dark current data according to an elapsed time from when the dark current data of the first storage means is updated;
The dark current data update means updates the dark current data of the first storage means with an update time of the dark current data,
The image generation means includes an elapsed time from an update time attached to the dark current data stored in the first storage means to a time when the transmission X-ray data is output, and the third Using elapsed time dependent dark current correction data calculating means for obtaining elapsed time dependent dark current correction data based on the elapsed time correction coefficient stored in the storage means, and using elapsed time dependent dark current correction data obtained by the means And an elapsed time dependent dark current data correcting unit that corrects the dark current data read from the first storage unit, and is corrected by the elapsed time dependent dark current data correcting unit and the temperature dependent dark current data correcting unit. The transmitted X-ray data is corrected based on the elapsed time-dependent dark current correction data and the temperature-dependent dark current correction data to generate an X-ray projection image of the subject. X-ray image diagnostic apparatus according to. The X-ray diagnostic imaging apparatus according to claim 2 ,
The elapsed time correction coefficient is calculated based on the difference between the dark current data updated by the dark current data update means and the dark current data before update, and the difference in the update time attached to the dark current data. An X-ray diagnostic imaging apparatus comprising: elapsed time correction coefficient updating means for updating the elapsed time correction coefficient of the third storage means. The X-ray diagnostic imaging apparatus according to claim 3 ,
The X-ray diagnostic imaging apparatus, wherein the dark current data updating unit, the temperature correction coefficient updating unit, and the elapsed time correction coefficient updating unit execute updating when the X-ray projection image is not imaged. The X-ray diagnostic imaging apparatus according to claim 3 ,
The X-ray diagnostic imaging apparatus according to claim 1, wherein the temperature correction coefficient updating unit executes updating when a temperature change of the X-ray detector exceeds a set threshold value. The X-ray diagnostic imaging apparatus according to claim 3 ,
The X-ray diagnostic imaging apparatus characterized in that the dark current data updating unit, the temperature correction coefficient updating unit, and the temperature correction coefficient updating unit periodically update when the X-ray projection image is not imaged. The X-ray diagnostic imaging apparatus according to claim 1 or 2 ,
The temperature correction coefficient updating means has a temperature difference between the dark current data updated by the dark current data updating means and the dark current data before update exceeding the preset abnormal value. An X-ray diagnostic imaging apparatus characterized by outputting a warning of abnormal temperature change.

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