JP2013202328A - X-ray diagnostic apparatus - Google Patents

Abstract

An object of the present invention is to reduce the exposure time of a subject by X-rays as much as possible and improve the throughput.
An X-ray generation unit that generates a fluoroscopic X-ray corresponding to each of a plurality of pulses, an X-ray detection unit that generates an output signal based on the fluoroscopic X-ray transmitted through a subject, and the X-ray generation The first output signal detected due to the first fluoroscopic X-ray in a first period in which the unit continuously generates the first fluoroscopic X-ray corresponding to the first pulse of the plurality of pulses. A comparison unit that compares one integral value with a predetermined threshold value, and a timing at which the first integral value reaches the threshold value or a timing that is determined based on the number of pulses per unit time of the plurality of pulses. An X-ray control unit that controls the X-ray generation unit so as to be the end of one period; an image generation unit that generates an X-ray image based on a first fluoroscopic X-ray corresponding to the first period; It comprises.
[Selection] Figure 1

Description

  Embodiments described herein relate generally to an X-ray diagnostic apparatus.

  There is a method of controlling the X-ray dose by automatic exposure control (hereinafter referred to as AEC) during X-ray exposure (mainly imaging) using an X-ray diagnostic apparatus. AEC is to automatically control the X-ray exposure time as a function of the X-ray diagnostic apparatus so that a desired amount of radiation can be obtained at a selected site. Hereinafter, AEC will be described in detail with reference to FIGS. 10 and 11. The X-ray detected by the AEC detector is converted into an electric signal proportional to the intensity of the X-ray and transmitted to the control device. The signal from the AEC detector is amplified by the amplifier circuit in the control device and output to the integrating circuit. The signal proportional to the X-ray intensity is converted into a signal proportional to the X-ray dose by the integrating circuit. When the output of the amplifier circuit is integrated by the integration circuit, the integrated output of the amplifier circuit is output to the comparison circuit. The comparison circuit triggers the next-stage X-ray cutoff signal generation circuit when the output from the integration circuit reaches a preset concentration reference value. The fact that the output of the integrating circuit has reached the concentration reference value means that the dose incident on the X-ray flat panel detector (FPD) has reached an appropriate amount. An X-ray cutoff signal is output to the X-ray control device by the triggered X-ray cutoff signal generation circuit. Finally, a signal for generating a high voltage is stopped by the X-ray control device, and X-ray exposure on the X-ray tube is stopped.

  In addition, there is a method of controlling the X-ray dose by automatic brightness adjustment (hereinafter referred to as ABC) during X-ray fluoroscopy using the X-ray diagnostic apparatus. Automatic brightness adjustment is to automatically adjust the brightness of a fluoroscopic image to be constant by changing the X-ray conditions. Hereinafter, ABC will be described with reference to FIGS. For the output video signal of the X-ray flat panel detector (FPD) converted into digital data by analog-digital conversion, the pixel average value in the region of interest is calculated by the pixel value calculation unit in the image processing apparatus. The image processing apparatus can take a plurality of forms, for example, when incorporated in an X-ray diagnostic apparatus, or when using a workstation or the like provided outside the X-ray diagnostic apparatus. Regarding the calculation of the pixel value, the average value of the pixel values in the region of interest (ROI) is usually calculated. The fluoroscopic (F) condition determining unit compares the pixel average value calculation result in the current frame with a predetermined reference value. When the pixel average value calculation result is lower than the reference value, the X-ray output is considered to be small. Therefore, the X-ray output condition is increased along a function as shown in FIG. Conversely, if the pixel value calculation result is higher than the reference value, the X-ray output is considered large, so the X-ray output condition is lowered along a function as shown in FIG. The F condition determination unit has a function that specifies the relationship between the fluoroscopic tube voltage (F_kV) and the fluoroscopic tube current-time product (F_mAs), and the F condition rises and falls along the function. This function is registered in advance and usually does not change. The amount that moves up and down along the function is calculated by normal feedback control such as PI control or PID control.

  However, since ABC is feedback control, a problem arises particularly in terms of responsiveness at the start of fluoroscopy. If the response of ABC is made sensitive, it does not converge to an appropriate dose, and hunting occurs between the overdose and underdose (FIG. 9). Therefore, the ABC response cannot be set sensitively. On the other hand, when the ABC response is not set sensitively, hunting does not occur, but the time until convergence to an appropriate dose becomes long. In low-rate pulse fluoroscopy with a small number of pulses per second, the pixel value calculation, the pixel value and the reference value are compared, and the cycle until the next fluoroscopic X-ray condition is determined becomes longer, and the convergence time is remarkable. It becomes long.

  In particular, since the thickness of the subject is unknown at the start of fluoroscopy, the fluoroscopy X-ray dose corresponding to the first pulse in the first frame is often not appropriate. For this reason, it often takes several frames after the start of fluoroscopy until an appropriate dose is reached, and fluoroscopic images corresponding to these several frames have insufficient diagnostic ability. Therefore, it is not possible to satisfy the need to reduce fluoroscopic time as much as possible while incurring unnecessary exposure.

  In view of the circumstances as described above, the object is to reduce the exposure time of the subject by X-ray as much as possible and to improve the throughput.

  An X-ray diagnostic apparatus according to an embodiment includes an X-ray generator that generates a fluoroscopic X-ray corresponding to each of a plurality of pulses, and an X-ray detection that generates an output signal based on the fluoroscopic X-ray transmitted through the subject. And a first period in which the X-ray generation unit continuously generates a first fluoroscopic X-ray corresponding to a first pulse of the plurality of pulses, and is detected due to the first fluoroscopic X-ray. A comparison unit that compares the first integrated value of the first output signal with a predetermined threshold value, and the timing at which the first integrated value reaches the threshold value or the number of pulses per unit time of the plurality of pulses as a reference. An X-ray image is generated based on the X-ray control unit that controls the X-ray generation unit and the first fluoroscopic X-ray corresponding to the first period so that the determined timing is the end of the first period. And an image generation unit to be generated.

It is a block diagram which shows the function of the X-ray diagnostic apparatus which concerns on 1st Embodiment. It is a schematic diagram showing the mode of the pulse during fluoroscopy. It is a flowchart for demonstrating the pulse fluoroscopic imaging process which concerns on 1st Embodiment. It is a flowchart for demonstrating the pulse fluoroscopic imaging process which concerns on 1st Embodiment. It is a function which shows the relationship between the tube voltage and tube current time product for determining the output of the X-ray which concerns on 1st Embodiment. It is a flowchart for demonstrating the pulse fluoroscopic imaging process which concerns on 2nd Embodiment. It is a flowchart for demonstrating the pulse fluoroscopic imaging process which concerns on 2nd Embodiment. It is a function which shows the relationship between the tube voltage for determining the output of the X-ray which concerns on 2nd Embodiment, and subject thickness. The hunting phenomenon regarding the X-ray dose by the conventional ABC is shown. It is a schematic diagram which shows the mode of the interruption | blocking of the pulse using the integration value by the conventional AEC, and a reference value. It is a block diagram which shows the structure of the control apparatus and X-ray high voltage apparatus using the conventional AEC. It is a block diagram for demonstrating the control method by the conventional ABC. In conventional ABC, it is a schematic diagram which shows the function for determining a tube voltage and a tube current time product by F condition determination part.

  The X-ray diagnostic apparatus according to this embodiment will be described below with reference to the drawings. In the following description, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description will be given only when necessary.

(First embodiment)
In the first embodiment, an X-ray diagnostic apparatus will be described in which fluoroscopic X-rays for the first pulse are controlled by AEC, and fluoroscopic X-rays corresponding to the pulse sequences after the second pulse are controlled by ABC.

  FIG. 1 is a block diagram of the X-ray diagnostic apparatus according to the first embodiment. As shown in FIG. 1, the X-ray diagnostic apparatus according to the first embodiment includes an X-ray source 1, an AEC detector 2, an FPD 3, an AEC control unit 4, an X-ray control unit 5, and a high voltage. A generation unit 6, an AD conversion unit 7, an image generation unit 8, an auto window processing unit 9, a display unit 10, an F condition determination unit 11, and a bed 12 are provided.

  The X-ray source 1 emits X-rays toward the subject mounted on the bed 12. X-rays are exposed to the subject intermittently at predetermined time intervals by the X-ray source 1 during fluoroscopy. In other words, in the present embodiment, the fluoroscopy is performed using pulse fluoroscopy in which pulses are generated intermittently at intervals of, for example, several milliseconds.

  The AEC detector 2 detects X-rays that have passed through the subject and converts them into an electrical signal corresponding to the intensity of the X-rays.

  The FPD 3 has a plurality of detection elements. Each detection element detects an X-ray and generates an electric charge according to the incident X-ray dose. The FPD 3 has a direct method and an indirect method. In the present embodiment, the FPD 3 adopting either method may be used. In the direct method, charges are generated by irradiating a photoconductor with incident X-rays, and the generated charges are accumulated in a pixel unit and read by an active matrix array element. In the indirect method, incident X-rays are converted into visible light by a phosphor, and the visible light is received by a photosensor such as a photodiode for each pixel to generate electric charge, which is read by an active matrix array element. These active matrix array elements are constituted by switching elements such as diodes or TFTs. The generated charge is accumulated and can be read out at a predetermined timing.

  The AEC control unit 4 includes an amplification circuit 401, an integration circuit 402, a concentration setting circuit 403, a comparison circuit 404, and an X-ray cutoff signal generation circuit 405.

  The amplifier circuit 401 amplifies the electrical signal from the AEC detector 2.

  The integration circuit 402 includes elements such as a capacitor and a coil, and integrates the amplified electric signal.

  The density setting circuit 403 sets a predetermined density reference value (threshold value).

  The comparison circuit 404 compares the density reference value with the integrated value as needed. When the integration value of the integration circuit 402 reaches the threshold value, the comparison circuit 404 transmits a trigger signal to the X-ray cutoff signal generation circuit 405 at the next stage.

  The X-ray cutoff signal generation circuit 405 transmits a signal for stopping X-ray generation to the X-ray control unit 5 based on the trigger signal from the comparison circuit 404.

  The X-ray control unit 5 controls the high voltage generation unit 6 and controls the tube current and tube voltage of the X-ray source 1 in order to control the power for applying the X-rays generated from the X-ray source 1. Determine for each pulse.

  The high voltage generator 6 generates a high voltage based on a control signal from the X-ray controller 5. The X-ray source 1 generates X-rays based on the generated high voltage and exposes the X-rays toward the subject.

The AD conversion unit 7 converts an analog signal based on the electric charge from the FPD 3 into a digital signal.

  The image generation unit 8 generates an X-ray image based on the digital signal. The image generation unit 8 includes a pixel value calculation unit 81. The pixel value calculation unit 81 calculates a pixel average value of a plurality of pixels in the region of interest in the X-ray image. The average pixel value in the region of interest is calculated by calculating and adding the pixel value in the region of interest for each pixel and dividing by the calculated number of pixels.

  For example, the auto window processing unit 9 automatically calculates a window width and a window level suitable for a site necessary for diagnosis. The window is a mechanism for converting the pixel value of the X-ray image into a density value (gray level) for display as a grayscale image. In the present embodiment, fluoroscopy is performed under substantially appropriate F conditions in each pulse. However, in a predetermined case such as when the subject is moved greatly, the F condition may not be met. At this time, the pixel values of the obtained X-ray image are distributed in numerical values that deviate from the pixel values of the appropriate F condition. The auto window processing unit 9 follows this shift, selects pixel value data in a range necessary for observation, and converts it into a density value. This selection range is called the window width and the center is called the window level.

  The image display unit 10 displays an X-ray image based on the calculated window width and window level.

  Based on the pixel value calculated by the pixel value calculation unit 81, the F condition determination unit 11 determines an F condition (that is, a tube voltage and a tube current time product) of X-rays generated immediately thereafter.

  The bed 12 is for mounting a subject.

FIG. 2 is a schematic diagram showing a state of a pulse during fluoroscopy. In the following description, it is assumed that n rectangular wave pulses for generating X-rays are generated during the fluoroscopic period, and k and k + 1 are natural numbers satisfying 1 ≦ k ≦ k + 1 ≦ n. The first pulse is a pulse that is first generated during the fluoroscopic period. It is assumed that the pulse is being seen through while the pulse is intermittently generated at a time interval of TI ₁ . The n pulses are generated, if the perspective period has expired, the next pulse sequence generated provided the period TI ₂ of X-rays is interrupted.

  The fluoroscopic X-ray corresponding to the first pulse is the fluoroscopic X-ray corresponding to the first pulse during the fluoroscopic period, the fluoroscopic X-ray corresponding to the second pulse is the fluoroscopic X-ray corresponding to the second pulse, k It is assumed that the fluoroscopic X-ray corresponding to the second generated pulse is a fluoroscopic X-ray corresponding to the k-th pulse, and the fluoroscopic X-ray corresponding to the (k + 1) th generated pulse is the fluoroscopic X-ray corresponding to the (k + 1) th pulse. .

  3 and 4 are flowcharts for explaining the pulse fluoroscopic imaging processing according to the first embodiment.

  First, fluoroscopic X-rays corresponding to the first pulse are generated from the X-ray source 1 (S11). At this time, a high tube voltage and a maximum tube current are set for the fluoroscopic X-ray corresponding to the first pulse during fluoroscopy. This is to prevent the dose from becoming insufficient.

  The AEC detector 2 detects a fluoroscopic X-ray corresponding to the first pulse, and generates an electric signal proportional to the intensity of the X-ray (S12).

  The X-ray detected by the AEC detector 2 is converted into an electric signal, and the electric signal is amplified by the amplifier circuit 401. Thereafter, the integrated value of the electric signal amplified by the integrating circuit 402 is sequentially calculated (S13).

  The integrated value calculated by the comparison circuit 404 is compared with a density reference value (threshold value) preset by the density setting circuit 403. Further, the X-ray control unit 5 monitors whether or not the pulse width of the first pulse has reached the longest width determined according to the fluoroscopic frame rate from the generation time of the fluoroscopic X-ray corresponding to the first pulse. (S14).

  If the integral value has not reached the threshold value in S14 and the pulse width of the first pulse has not reached the longest width, the processes in steps S11 to S13 are continued.

  On the other hand, when the integrated value reaches the threshold value in S14, or when the pulse width of the first pulse reaches the longest width, the reached timing is the end of the continuous generation period of the fluoroscopic X-ray corresponding to the first pulse. As described above, the X-ray cut-off signal generation circuit 405 generates a trigger signal in the X-ray control unit 5 and cuts off the fluoroscopic X-ray corresponding to the first pulse (S15). As a method for stopping the generated pulse, an X-ray control unit 5 includes a switch provided in at least one of the primary side coil and the secondary side coil for boosting the AC voltage of the high voltage generation unit 6. Is automatically turned off to stop the pulse. This coil is usually provided in the high voltage generator 6.

  As described above, for fluoroscopic X-rays corresponding to the first pulse at the start of fluoroscopy, the X-ray output is made appropriate by AEC control.

  After the fluoroscopic X-ray corresponding to the first pulse is interrupted, when the FPD 3 enters a reading period, the charge accumulated from the FPD 3 is read by the active matrix array element (S16).

  The electric signal based on the read charge is converted into a digital signal by the AD conversion unit 7. Based on the converted digital signal, the X-ray image of the fluoroscopic X-ray corresponding to the first pulse is generated by the image generation unit 8 and the pixel value of the X-ray image is an appropriate numerical value by the auto window processing unit 9. Even if it is deviated from, it is converted to an appropriate density value (gray level). The X-ray image is displayed with a density value having a gradation of, for example, 0 to 255 (S17).

  The pixel value calculation unit 81 adds the pixel values of each pixel in the region of interest based on the converted digital data, and calculates the average value of the pixel values in the region of interest by dividing by the calculated number of pixels. (S18). Note that the pixel value of the entire X-ray image may be calculated without being limited to the region of interest.

The F condition determination unit 11 calculates the pixel average value calculated in the region of interest, the tube voltage F ₁ and the tube current time product F ₂ used at the time of fluoroscopic X-ray exposure corresponding to the first pulse, and By substituting into (1), the object thickness (T = T ₁ ) is calculated and estimated (S19).

F ₁ ^d [kV] × F ₂ [mAs] × GLR = a × exp (b × T + c) (1)
Here, GLR is a value obtained by dividing a preset reference value by the pixel average value calculated in S18. F ₁ [kV] and F ₂ [mAs] are the fluoroscopic tube voltage and fluoroscopic tube current time product set in the X-ray generation of S11, respectively. a, b, c, d are coefficients.

Next, the F condition determination unit 11 determines the tube voltage and tube current time product of the fluoroscopic X-ray corresponding to the second pulse based on the subject thickness calculated in S19 (S20). The output of the fluoroscopic X-ray corresponding to the second pulse is determined as follows. That is, the subject thickness (T = T ₁ ) calculated in S19 is substituted into the equation (1), and GLR = 1 (that is, when the pixel value is equal to the reference value) is substituted into the equation (1). . An expression in which the object thickness and GLR = 1 are substituted is shown in (2).

F ₁ ^d [kV] × F ₂ [mAs] = a × exp (b × T ₁ + c) (2)
FIG. 5 is a diagram showing an example of a function that defines the relationship between the tube voltage and the tube current time product. The F condition determination unit 11 obtains a point satisfying the expression (2) on the function of FIG. That is, when the expression (2) having two variables F ₁ and F ₂ is represented on the graph of FIG. 5, the intersection of the linear function of FIG. 5 and the expression (2) is obtained. The F condition (output condition of the X-ray tube voltage and the X-ray tube current time product) determined from this intersection is the output of the fluoroscopic X-ray corresponding to the second pulse. The linear function shown in FIG. 5 is set in advance and is not normally changed.

  Using the determined tube voltage and tube current time product, the fluoroscopic X-ray corresponding to the second pulse is emitted from the X-ray source 1 toward the subject (S21).

  In response to the generation of fluoroscopic X-rays corresponding to the second pulse, the fluoroscopic X-rays corresponding to the second pulse transmitted through the subject by the FPD 3 are converted into electric charges, and the electric charges are accumulated. The accumulated charge is read at a predetermined timing (S22).

  The analog signal based on the electric charge is converted into a digital signal by the AD converter 7. Based on the output of the electrical signal converted into digital, the image generation unit 8 generates an X-ray image of a fluoroscopic X-ray corresponding to the second pulse, and the auto window processing unit 9 generates pixels of the X-ray image. Even if the value deviates from an appropriate numerical value, it is converted to an appropriate density scale of 0 to 255, and an image is displayed on the image display unit 10 (S23).

  The pixel value calculation unit 81 calculates the pixel average value in the region of interest (S24).

The pixel average value of the region of interest of the X-ray image based on the calculated fluoroscopic X-ray output corresponding to the second pulse and the F condition of the fluoroscopic X-ray corresponding to the second pulse (the fluoroscopic X-ray corresponding to the second pulse By substituting the tube voltage and tube current time product for application into equation (1), the F condition determining unit 11 calculates and estimates the object thickness (T = T ₁ ) (S25). When the object thickness is calculated, the calculated object thickness (T = T ₁ ) is substituted into the equation (1), and GLR = 1 (that is, when the pixel value is equal to the reference value) is (1). (2) is obtained by substituting it into (). A point satisfying the expression (2) is obtained on the function of FIG. That is, the F condition determination unit 11 represents the linear function of FIG. 5 and the formula (2) when the formula (2) having two variables F ₁ and F ₂ is represented on the graph of FIG. An intersection is obtained, and an output condition of the tube voltage and tube current time product of the fluoroscopic X-ray corresponding to the third pulse is determined from the intersection (S26).

  Using the determined tube voltage and tube current, fluoroscopic X-rays corresponding to the third pulse are generated (S27). Thereafter, regarding the generation of fluoroscopic X-rays corresponding to the k-th pulse (3 ≦ k ≦ n), the tube voltage of the X-ray tube and the tube current time product are obtained by repeating each process of S22 to S27. The output is optimized in accordance with (S28). When the fluoroscopy is started again by changing the position of the subject, the final X-ray output conditions obtained by the processing of S11 to S28 may be taken over, or initialized and again steps S11 to S28. You can also step on.

  As described above, according to the first embodiment, the fluoroscopic X-ray corresponding to the first pulse is controlled by the AEC, and the output of the X-ray source 1 is stopped when the desired X-ray dose is reached. The output of fluoroscopic X-rays is optimal. Therefore, it is possible to provide an X-ray diagnostic apparatus that can suppress the hunting phenomenon (FIG. 9) or response delay, which has been a problem in the prior art, and has improved throughput. For fluoroscopic X-rays corresponding to the pulse sequence after the second pulse, the control method is switched from AEC to ABC. In ABC after the second pulse, the subject thickness is calculated based on the pixel value of the X-ray image based on the generated X-ray dose, the output of the X-ray generated immediately after is determined, and the immediately following X-ray is generated The cycle to do is repeated. Thereby, as the fluoroscopic period elapses, the X-ray dose exposed to the subject can be optimized according to the subject thickness, and a medical image with high image contrast can be displayed according to the subject thickness. it can. Since the second pulse condition is optimally set as described above, the ABC after the second pulse is sufficiently stable even when the conventional feedback control is used. Furthermore, even if the determined X-ray output is slightly deviated from the optimum condition, it can be displayed with appropriate correction by an auto window.

  As described above, according to the first embodiment, it is possible to provide an X-ray diagnostic apparatus that can improve throughput and reduce exposure by X-rays.

(Second Embodiment)
In the description of the first embodiment, the method is described in which the fluoroscopic X-ray corresponding to the first pulse is controlled by AEC, and the fluoroscopic X-ray corresponding to the pulse sequence after the second pulse is controlled by ABC. In the second embodiment, an X-ray diagnostic apparatus controlled by AEC throughout the fluoroscopic period will be described.

  The block diagram which comprises 2nd Embodiment is FIG. 1 similarly to 1st Embodiment.

  6 and 7 are flowcharts for explaining the processing of the second embodiment.

  A fluoroscopic X-ray corresponding to the first pulse is generated from the X-ray source 1 (S31).

  The AEC detector 2 detects a fluoroscopic X-ray corresponding to the first pulse, and generates an electrical signal corresponding to the intensity of the X-ray (S32).

  The X-ray detected by the AEC detector 2 is converted into an electric signal, and the electric signal is amplified by the amplifier circuit 401. Thereafter, the integrated value of the electric signal amplified by the integrating circuit 402 is sequentially calculated (S33).

  The calculated integration value is compared with the density reference value (threshold value) preset in the density setting circuit 403 by the comparison circuit 404 (S34).

  If the integrated value has not reached the threshold value in S34 and the pulse width of the first pulse has not reached the longest width, the processing in steps S31 to S33 is continued.

  On the other hand, when the integrated value reaches the threshold value in S14, or when the pulse width of the first pulse reaches the longest width, the reached timing is the end of the continuous generation period of the fluoroscopic X-ray corresponding to the first pulse. As described above, the X-ray cut-off signal generation circuit 405 generates a trigger signal in the X-ray control unit 5 and cuts off the fluoroscopic X-ray corresponding to the first pulse (S35). As a method for stopping the generated pulse, an X-ray control unit 5 includes a switch provided in at least one of the primary side coil and the secondary side coil for boosting the AC voltage of the high voltage generation unit 6. Is automatically turned off to stop the pulse. This coil is usually provided in the high voltage generator 6.

  After the fluoroscopic X-ray corresponding to the first pulse is cut off in S35, when the FPD 3 enters a reading period, the charges accumulated from the FPD 3 are read (S36).

  The electric signal based on the read charge is converted into a digital signal by the AD conversion unit 7. An X-ray image is generated by the image generation unit 8 based on the converted digital signal, and an appropriate density value is obtained even if the pixel value of the X-ray image is deviated from an appropriate numerical value by the auto window processing unit 9. Converted to (gray level). The X-ray image is displayed with a density value having a gradation of, for example, 0 to 255 (S37).

  The pixel value calculation unit 81 adds the pixel values of each pixel in the region of interest based on the converted digital data, and calculates the average value of the pixel values in the region of interest by dividing by the calculated number of pixels. (S38). Note that the pixel value of the entire X-ray image may be calculated without being limited to the region of interest.

The F condition determination unit 11 calculates the calculated pixel average value in the region of interest and the tube voltage F ₁ and tube current time product F ₂ used during fluoroscopic X-ray exposure corresponding to the first pulse. By substituting into Equation (1), the object thickness (T = T ₁ ) is calculated and estimated (S39).

F ₁ ^d [kV] × F ₂ [mAs] × GLR = a × exp (b × T + c) (1)
Next, the tube condition and the tube current of the fluoroscopic X-ray corresponding to the second pulse are determined by the F condition determination unit 11 based on the subject thickness calculated in S39 (S40). That is, the F condition determining section 11 using the function defining the relationship between the tube voltage and the specimen thickness Metropolitan shown in FIG. 8, the (T = T ₁₎ tube voltage that satisfies (V = V ₁₎ obtained . Among the obtained tube voltages (V = V ₁ ), the maximum possible tube current is obtained. The obtained tube voltage and tube current are the tube voltage and tube current of the fluoroscopic X-ray corresponding to the second pulse.

  The fluoroscopic X-ray output corresponding to the second pulse is determined, and the fluoroscopic X-ray corresponding to the second pulse is generated from the X-ray source 1 (S41).

  The AEC detector 2 detects the fluoroscopic X-ray corresponding to the second pulse, and generates an electrical signal proportional to the intensity of the X-ray (S42).

  The X-ray detected by the AEC detector 2 is converted into an electric signal, and the electric signal is amplified by the amplifier circuit 401. Thereafter, the integrated value of the electric signal amplified by the integrating circuit 402 is sequentially calculated (S43).

  A density reference value (threshold value) is set by the density setting circuit 403. The calculated integration value is compared with the threshold value by the comparison circuit 404 (S44).

  When the integrated value reaches the threshold value, the X-ray cutoff signal generation circuit 405 generates a trigger signal to the X-ray control unit 5 to cut off the second pulse (S45).

  After the fluoroscopic X-ray corresponding to the second pulse is interrupted, when the FPD 3 enters a reading period, the charge accumulated from the FPD 3 is read by the active matrix array element (S46).

  An analog signal based on the read charge is converted into a digital signal by the AD conversion unit 7. An X-ray image is generated by the image generation unit 8 based on the converted digital signal, and an appropriate density value is obtained even if the pixel value of the X-ray image is deviated from an appropriate numerical value by the auto window processing unit 9. The X-ray image is displayed with a density value having a gradation of, for example, 0 to 255 (S47).

  The pixel value calculation unit 81 adds the pixel values of each pixel in the region of interest based on the converted digital data, and calculates the average value of the pixel values in the region of interest by dividing by the calculated number of pixels. (S48). Note that the pixel value of the entire X-ray image may be calculated without being limited to the region of interest.

The F condition determination unit 11 calculates the calculated pixel average value in the region of interest, the tube voltage F ₁ used at the time of fluoroscopic X-ray exposure corresponding to the second pulse, and the tube current time product F ₂ as described above. By substituting into Equation (1), the object thickness (T = T ₁ ) is calculated and estimated (S49).

F ₁ ^d [kV] × F ₂ [mAs] × GLR = a × exp (b × T + c) (1)
Next, the F condition determination unit 11 determines the tube voltage and tube current of the fluoroscopic X-ray corresponding to the third pulse, based on the subject thickness calculated in S49 (S50). A fluoroscopic X-ray corresponding to the third pulse is generated using the determined tube voltage and tube current (S51).

  Thereafter, regarding the generation of fluoroscopic X-rays corresponding to the k-th pulse (3 ≦ k ≦ n), the tube voltage and tube current of the X-ray tube depend on the subject thickness by repeating the processes of S42 to S51. Is output so as to be optimal (S52). When the fluoroscopic X-ray corresponding to the last n-th pulse is stopped and the fluoroscopy is started again by changing the position of the subject or the like, the final obtained by the processing of S42 to S51 is performed. The X-ray output conditions may be taken over, or may be initialized and steps S42 to S51 may be performed again.

  As described above, in the second embodiment, the fluoroscopic X-ray corresponding to the first pulse is controlled by the AEC, and the output of the X-ray source 1 is stopped when the desired X-ray dose is reached. The output of fluoroscopic X-rays is optimal. Therefore, it is possible to provide an X-ray diagnostic apparatus that can suppress the hunting phenomenon (FIG. 9) or response delay, which has been a problem in the prior art, and has improved throughput. Further, the fluoroscopic X-ray corresponding to the pulse sequence after the second pulse is also controlled by AEC. After the second pulse, the X-ray output is sequentially optimized in accordance with the subject thickness by combining the subject thickness estimation cycle with the AEC control. Thereby, as the fluoroscopic period elapses, the X-ray dose exposed to the subject can be optimized according to the subject thickness, and a medical image with high image contrast can be displayed according to the subject thickness. it can. Furthermore, even when X-ray cutoff by AEC control is not performed by the time when the longest possible pulse width is possible depending on the fluoroscopic frame rate, it is possible to display the image with appropriate correction by the auto window.

  As described above, according to the second embodiment, it is possible to provide an X-ray diagnostic apparatus that can improve throughput and reduce exposure by X-rays.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... X-ray source, 2 ... AEC detector, 3 ... Flat panel detector (FPD), 4 ... AEC control part, 401 ... Amplifier circuit, 402 ... Integration circuit, 403 ... Density setting circuit, 404 ... Comparison circuit, 405 DESCRIPTION OF SYMBOLS ... X-ray interruption | blocking signal generation circuit, 5 ... X-ray control part, 6 ... High voltage generation part, 7 ... AD conversion part, 8 ... Image generation part, 81 ... Pixel value calculation part, 9 ... Auto window processing part, 10 ... Display unit, 11 ... F condition determination unit, 12 ... Bed

Claims (5)

An X-ray generator that generates fluoroscopic X-rays corresponding to each of the plurality of pulses;
An X-ray detector that generates an output signal based on the fluoroscopic X-ray;
In the first period in which the X-ray generator continuously generates the first fluoroscopic X-ray corresponding to the first pulse of the plurality of pulses, the first detected due to the first fluoroscopic X-ray A comparison unit that compares the first integral value of the output signal with a predetermined threshold;
The X-ray generator is controlled so that the timing at which the first integrated value reaches the threshold value or the timing determined based on the number of pulses per unit time of the plurality of pulses is the end of the first period. An X-ray control unit,
An image generating unit that generates an X-ray image based on a first fluoroscopic X-ray corresponding to the first period;
An X-ray diagnostic apparatus comprising: X-rays generated based on the k-th fluoroscopic X-ray corresponding to the k-th of the plurality of pulses (where k is a natural number satisfying 1 ≦ k ≦ n and n is a natural number satisfying n ≧ 2). A determination unit for determining a fluoroscopic tube voltage and a tube current time product for generating a fluoroscopic X-ray corresponding to the (k + 1) th of the plurality of pulses based on a pixel value of the image;
The X-ray control unit controls the X-ray generation unit based on the determined fluoroscopic tube voltage and tube current time product;
The X-ray diagnostic apparatus according to claim 1. The comparison unit continues the k-th fluoroscopic X-ray corresponding to the k-th of the plurality of pulses (where k is a natural number satisfying 1 ≦ k ≦ n and n is a natural number satisfying n ≧ 2). The k-th integrated value of the k-th output signal detected due to the k-th fluoroscopic X-ray in the k-th period generated by
Based on a pixel value of an X-ray image generated based on the k-th fluoroscopic X-ray, a fluoroscopic tube voltage and a tube current for generating a fluoroscopic X-ray corresponding to the (k + 1) th of the plurality of pulses, Further comprising a determination unit for determining
The X-ray control unit is configured such that the timing at which the k-th integral value reaches the threshold value or the timing determined based on the number of pulses per unit time of the plurality of pulses is the end of the k-th period. Controlling the X-ray generation unit and controlling the X-ray generation unit based on the determined fluoroscopic tube voltage and tube current when generating the (X + 1) th fluoroscopic X-ray. ,
The X-ray diagnostic apparatus according to claim 1. The determination unit
Calculating the body thickness of the subject based on the pixel value of the X-ray image generated based on the k-th fluoroscopic X-ray;
Determining the fluoroscopic tube voltage and tube current or the fluoroscopic tube voltage and tube current time product based on the calculated body thickness;
The X-ray diagnostic apparatus according to claim 2, wherein: 5. An auto window processing unit that executes auto window processing for each X-ray image generated based on fluoroscopic X-rays corresponding to each of the plurality of pulses.
The X-ray diagnostic apparatus as described in any one of these.

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