JPH09129395A - X-ray automatic exposure control method, device, and x-ray photographing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make accurate automatic exposure control possible by correcting a reference value of automatic exposure control based on a detected signal in a suitably set virtual X-ray detecting region and a detected signal in the detecting region of an actual detector. SOLUTION: An X-ray irradiated from an X-ray tube 1 is passed through a subject 3, and photographed with a TV camera 9 through a split mask 4, a detector 5, an X-ray film 6, and an image intensifier 7. An X-ray control part 11 inputs a detected signal of the detector 5, corrects an exposure reference value with a correcting signal from an automatic photographic density correcting part 100 to perform automatic exposure control. The automatic photographic density correcting part 100 sets a virtual detecting region of a virtual detector based on a video signal inputted from the TV camera 9 and information from a main control part 200, arithmetically processes a corrected signal of an exposure control reference value, and outputs the processed value to the X-ray control part 11. Thereby, highly accurate automatic exposure control is made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray automatic exposure control method and apparatus and an X-ray imaging apparatus. More specifically, the present invention relates to an X-ray automatic exposure control method and apparatus and an X-ray imaging apparatus for optimizing the density of a captured image when the digestive tract such as the stomach or esophagus is X-rayed using a contrast agent.

[0002]

2. Description of the Related Art There is an X-ray TV (television) device as a device for X-raying an alimentary canal such as stomach and esophagus using a contrast medium. This device is a device that irradiates a subject with X-rays to display a fluoroscopic image on a display device, and captures an image on a photographic medium such as an X-ray film while observing the fluoroscopic image. The perspective image is an image intensifier (I.
I)) to increase the brightness and shoot with a TV camera.
It is displayed in athod-ray tube) etc.

Automatic exposure control is performed when photographing on a photographing medium. In the automatic exposure control, the dose of X-rays transmitted through the subject is detected by a detector, and the X-ray irradiation is stopped when the integrated dose amount reaches a predetermined reference value. The reference value is selected as a value that optimizes the density of the image of the region of interest in the captured image.

The detector is an I.D. A front photometric type disposed in front of the I.I. There is a rear surface photometric type arranged behind I. The front side photometric detector is adapted to directly detect transmitted X-rays using, for example, an ion chamber. The rear surface photometric detector is an I.D. Behind I, the light quantity of the optical image is detected by a photodetector.
Each of these detectors has a detection area of a predetermined size in the plane of the photographic screen, and detects the transmitted X-ray dose or light quantity in the detection area, respectively.

[0005]

When imaging (double contrast) the stomach, for example, with a contrast agent, the shadow of the contrast agent falls on the detection area of the detector, and the effective detection area decreases accordingly. To do. If automatic exposure control is performed in this reduced detection area, the time until the integrated value of the detected dose reaches the reference value becomes long, and the X-rays emitted during that time cause overexposure and excessively high density in the area of interest. .

In order to prevent this, it has been attempted to correct the reference value in accordance with the reduction of the effective detection area due to the shadow of the contrast agent to perform the proper exposure, but the exposure is still sufficiently accurate. There is a problem that control cannot be realized.

Further, for example, when imaging the esophagus, since X-rays (direct rays) that pass through the lung field and are less attenuated enter the detection region, the incident dose per unit time increases, so that On the contrary, the integrated value of the detected dose reaches the reference value in a short time, and the exposure is insufficient and the density becomes low in the region of interest.

If only for the imaging of the esophagus, the width of the detection area of the detector may be narrowed. However, since there is a compatibility with the imaging of the stomach, the shape and size of the detection area of the detector should be determined by compromise. I have no choice. However, this is not a sufficient countermeasure, and there is a problem that some degree of improper exposure must be tolerated.

The present invention has been made to solve the above problems, and an object of the present invention is to realize an X-ray automatic exposure control method and apparatus and an X-ray imaging apparatus for performing highly accurate automatic exposure control. is there.

[0010]

According to a first aspect of the present invention, a fluoroscopic image of a subject by X-rays is converted into an image signal and displayed on a display device, and the subject is photographed on a photographing medium. A virtual X-ray detection area in an X-ray automatic exposure control method for detecting the dose of transmitted X-rays with a detector and controlling the X-ray irradiation amount so that the integrated value of the detection signal matches a predetermined reference value. To obtain a detection signal in the virtual X-ray detection region from the image signal, obtain a detection signal in the detection region of the detector from the image signal,
The X-ray automatic exposure control method is characterized in that the reference value is corrected based on these two detection signals.

Incidentally, the category of the detector in the first invention for solving the problem includes at least the following. Of course, the following are examples and are not meant to be limiting. (1) I. Detecting X-rays in front of I (2) I. What detects the light quantity of the optical image on the rear surface of I (3) What is detected based on the video signal of the TV camera (4) What uses the ion chamber (5) What uses the photodetector In the first aspect of the invention, it is preferable that the virtual X-ray detection area is set according to the division of the photographing medium or the aperture of the X-ray in order to perform automatic exposure control suitable for the photographing target.

According to the first invention for solving the problem, the automatic exposure is performed based on the detection signal in the virtual X-ray detection area and the detection signal in the actual detection area of the detector which are appropriately set. Since the control reference value is corrected, an X-ray automatic exposure control method capable of performing highly accurate exposure control can be realized.

A second aspect of the present invention for solving the problem is to convert a fluoroscopic image of a subject by X-rays into an image signal, display the image on a display device, and photograph the image on a photographing medium. In the X-ray automatic exposure control device for controlling the X-ray irradiation amount so that the integrated value of the detection signal is detected by the detector and the integrated value of the detection signal matches a predetermined reference value. Setting means, first computing means for obtaining an X-ray detection signal in the virtual X-ray detection area from the image signal, and first obtaining means for obtaining an X-ray detection signal in the detection area of the detector from the image signal 2 calculation means,
An X-ray automatic exposure control device comprising: a correction unit that corrects the reference value based on these two X-ray detection signals.

The category of the detector in the second invention for solving the problem is as described above. In the second invention for solving the problem, the virtual X-ray detection area is set according to division of an image-capturing medium or aperture of an X-ray, and automatic exposure control suitable for an object to be imaged is performed. preferable.

According to the second invention for solving the problem, the automatic exposure is performed based on the detection signal in the virtual X-ray detection area and the detection signal in the actual detection area of the detector which are appropriately set. Since the control reference value is corrected, an X-ray automatic exposure control device capable of highly accurate exposure control can be realized.

A third invention for solving the problem is an X-ray irradiating means, a converting means for converting a perspective image of a subject by X-rays radiated from the X-ray irradiating means into an image signal, and the image signal. Display means for displaying an image based on the X-rays, photographing means for photographing a perspective image of a subject by the X-rays emitted from the X-ray irradiating means on a photographing medium, and X-rays transmitted through the subject.
X-ray imaging having a detection unit for detecting the dose of the radiation and a control unit for controlling the X-ray irradiation amount of the X-ray irradiation unit so that the integrated value of the detection signal of the detection unit matches a predetermined reference value. In the apparatus, virtual detection area setting means for setting a virtual X-ray detection area, first calculation means for obtaining an X-ray detection signal in the virtual X-ray detection area from the image signal, and the image signal. The X-ray imaging apparatus is provided with a second arithmetic means for obtaining an X-ray detection signal in the detection region of the detector from the above, and a correction means for correcting the reference value based on these two X-ray detection signals. Is.

The category of the detector in the third invention for solving the problem is as described above. Further, the category of the X-ray imaging apparatus in the third invention for solving the above-mentioned problems includes at least the following. Of course, the following are examples and are not meant to be limiting. (1) Over tube type X-ray imaging apparatus (2) Under tube type X-ray imaging apparatus In the third invention for solving the problem, the virtual X-ray detection area is provided. Is preferably set in accordance with the division of the photographing medium or the X-ray diaphragm in order to perform automatic exposure control suitable for the photographing target.

According to the third invention for solving the problem, the automatic exposure is performed based on the detection signal in the virtual X-ray detection area and the detection signal in the actual detection area of the detector which are appropriately set. Since the control reference value is corrected, an X-ray imaging apparatus capable of highly accurate exposure control can be realized.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a block diagram of the X-ray TV apparatus. This device is an example of an embodiment of the present invention. Note that an example of an embodiment relating to the device of the present invention is shown by the configuration of the present device. Further, an example of an embodiment relating to the method of the present invention is shown by the operation of the present apparatus.

In FIG. 1, X emitted from the X-ray tube 1
The line is squeezed by the variable iris 2 to illuminate the subject 3,
The X-rays that have passed through the subject 3 pass through the openings of the split mask 4, pass through the detector 5, and are irradiated onto the X-ray film 6 or the image intensifier 7. The subject 3 is placed on a table (not shown).

The X-ray tube 1 and the variable diaphragm 2 are X-rays in the present invention.
It is an example of embodiment of a line irradiation means. The detector 5 is an example of an embodiment of the detecting means in the present invention, and is a front photometric type that detects X-rays on the front surface of the image intensifier 7. As the detector 5, for example, an ion
A chamber is used. The detector 5 has a structure in which X-ray absorption is extremely small. The X-ray film 6 is an example of the embodiment of the photographing medium in the present invention. Split mask 4
The X-ray film 6 is an example of the embodiment of the photographing means in the present invention.

The X-ray film 6 is conveyed to the illustrated photographing position only when photographing. When the subject 3 is seen through, the X-ray film 6 is retracted to a place where it does not receive X-rays, and the transmitted X-rays are received by the image intensifier 7.

X-ray T of the over tube type
In the V apparatus, the X-rays are emitted from “above” (over) the table on which the subject 3 is placed, and the transmitted X-rays are the X-ray film 6 or the image intensifier arranged “below” the table. Light is received at 7.

Under-tube type X-ray T
In the V apparatus, X-rays are emitted from “below” (under) the table on which the subject 3 is placed, and transmitted by the X-ray film 6 or the image intensifier 7 placed “above” the subject 3. X-rays are received.

The output image of the image intensifier 7 is photographed by the TV camera 9 through the optical system 8 and converted into a composite video signal including a synchronizing signal and outputted. The image intensifier 7, the optical system 8 and the TV camera 9 are an example of an embodiment of the converting means in the present invention.

If the rear surface photometry is adopted and the amount of X-ray transmission is detected behind the image intensifier 7, the optical image is branched from the optical system 8 and the amount of light is detected by the photodetector. You can do it.

The composite video signal (video signal) of the TV camera 9 is input to the display unit 91 and displayed as an image on the display unit 91. For example, a CRT is used as the display unit 91. The display unit 91 is an example of an embodiment of the display means in the present invention.

The video signal of the TV camera 9 is also input to the automatic density correction unit 100. The automatic density correction unit 100 is an example of an embodiment of the virtual detection area setting unit, the first calculation unit, the second calculation unit, and the correction unit according to the present invention. The automatic density correction unit 100 will be described later in detail.

The X-ray controller 11 controls the X-ray irradiation of the X-ray tube 1. The X-ray control unit 11 applies a tube voltage and a tube current for generating a relatively weak X-ray during fluoroscopy.
The tube voltage and the tube current for supplying the X-ray to the X-ray tube 1 and generating a relatively strong X-ray at the time of photographing are supplied.

A detection signal from the detector 5 and a correction signal from the automatic density correction unit 100 are input to the X-ray control unit 11. X
The line control unit 11 has a calibration (calibrati
The standard value for proper exposure is set by (on). The X-ray control unit 11 performs time-integration of the detection signal input from the detector 5 at the start of imaging, and performs automatic exposure control for stopping X-ray irradiation when the integrated value reaches a reference value. . The X-ray controller 11 is an example of an embodiment of the control means in the present invention.

In this case, the reference value is the automatic density correction unit 100.
The exposure is corrected by a correction signal input from the device, and automatic exposure control is performed so that the density of the captured image is not changed even if the shadow of the contrast agent is applied to the detection area of the detector 5. The correction of the reference value will be described later in detail.

The main control unit 200 controls the operation of this device. The main control unit 200 is, for example, an MPU (micro pro
cessor). An operation unit 201 is connected to the main control unit 200. The operation unit 201 is operated by the user. The user operates the operation unit 201 to give various setting values and control signals for fluoroscopy and imaging to each unit of the apparatus through the main control unit 200.

As a result, a diaphragm control signal is given to the variable diaphragm 2, and the X-ray irradiation field suitable for the size of the imaging region is adjusted. Further, a division control signal is given to the division mask 4, and the opening of the division mask 4 corresponding to the screen division of the X-ray film 6 is adjusted. The screen can be divided into, for example, one frame (no division), vertical division into two, and four divisions.
Further, the X-ray control unit 11 is provided with set values of tube voltage and tube current for each of fluoroscopy and radiography, and is also provided with control signals for fluoroscopy and radiography.

A photographing button (not shown) is provided on the operation unit 201, and when the user presses the photographing button, X-rays are emitted and photographing is started. Main control unit 200
From the automatic density correction unit 100, the aperture information of the variable aperture 2,
The division information of the division mask 4 and the information about the tube voltage and tube current for photographing are given. The automatic density correction unit 100
Based on these pieces of information input from the main control unit 200 and the video signal input from the TV camera 9, a correction signal for automatic density correction is created as described below.

Next, the principle of density correction in the automatic density correction unit 100 will be described. In the present invention, the concept of virtual detector is introduced. Now, it is assumed that the virtual detection area A of the virtual detector is set as shown in FIG. 2, and the actual detection area B of the detector 5 is included in this virtual detection area A. The virtual detection area A is set independently of the actual detection area B of the detector 5.

When an image is taken using a contrast agent, the virtual detection area A and the detection area B are shaded. This state is schematically shown in FIG. In FIG. 3, the shaded area C is the shadow of the contrast agent.

In FIG. 3, the contrast agent is drawn from the virtual detection area A.
Area of the part excluding the shadow C of S₁, The area of the detection area B
S_2B, The area of the detection area B excluding the shadow C of the contrast agent
S _TwoAnd Area S₁The part of
This is the area of interest S₁To
U. Area S obtained by removing the shadow C of the contrast agent from the detection area B_TwoPart of
Is the effective detection area.
Minute effective detection area S _TwoThat.

The unit time of irradiation from the X-ray tube 1 and the dose per unit area are X ₀ (constant), and the imaging time is such that the region of interest S ₁ has an appropriate concentration when the subject has a uniform body thickness P _L. Is T ₀ , the dose to be incident on the region of interest S ₁ is given by the following equation.

[0039]

(Equation 1)

Here, the integral symbol represents the integral in the region of interest S ₁ . Hereinafter, the expression method according to this will be used for other areas. Note that μ is the X-ray absorption coefficient of the subject. Considering the calibration of the reference value of the automatic exposure control, the uniform subject thickness P _L in which the contrast agent is not injected is obtained.
Should be calibrated so that the image is taken at T ₀ time for, then the reference value is given by:

[0041]

(Equation 2)

In reality, the thickness of the subject is not uniform and varies depending on the pixel position in the region of interest S ₁ . Letting T ₁ be the time for photographing the region of interest S ₁ at an appropriate density for a subject having a non-uniform body thickness P ₁ , the following relationship is established.

[0043]

(Equation 3)

The automatic exposure control is performed based on the dose detected in the effective detection area S ₂ . The reference value in that case should be corrected to a value such that the photographing time becomes T ₁ . Therefore, when the correction amount is α, the following relationship is established.

[0045]

(Equation 4)

However, P ₂ is the thickness of the subject in the effective detection area S ₂ , and varies depending on the pixel position.
From the expressions (3) and (4), the following relationship is established,

[0047]

(Equation 5)

From the equation (5), the correction amount α is given as follows.

[0049]

(Equation 6)

In the equation (6), the numerator represents the dose of the transmitted X-ray incident on the effective detection area S ₂ as the area S of the detection area B.
It is divided by _2B and represents the average dose per unit area of the detection region B. Meanwhile, the denominator is obtained by dividing the dose of transmitted X-rays incident on the region of interest S ₁ in the area S ₁ region of interest represents the average dose per unit area of the region of interest S _1. Therefore, the correction amount α is given by the ratio of the average dose per unit area of the detection region B and the average dose per unit area of the region of interest S ₁ . That is, the detected dose of the actual detector and the detected dose of the virtual detector are both reflected in the correction amount α.

The following equation is obtained by rearranging the right side of equation (6).

[0052]

(Equation 7)

Further, ex is used as the numerator and denominator on the right side of the equation (7).
By multiplying by p (μP _L ), the correction amount α can be expressed by the following equation.

[0054]

(Equation 8)

Further, the correction amount can be expressed by the following equation by performing integration instead of integration.

[0056]

(Equation 9)

Expression (6) is an expression that faithfully represents the principle. Expression (7) is a refined expression by arranging it. Expressions (8) and (9) are modifications for convenience of actually calculating the correction amount α. Both formulas have substantially the same meaning.

That is, by correcting the reference value I _REF of the automatic exposure control with the correction amount α given by the equation (6), (7), (8) or (9), the region of interest S ₁ is always appropriate. It can be photographed in density.

The virtual detection area A is appropriately set according to the size and position of the region of interest. Therefore, the relationship between the virtual detection area A and the detection area B is not limited to the relationship shown in FIG. 2, and the virtual detection area A may deviate from the detection area B, and the virtual detection area A may be the detection area B. It may be smaller.

That is, the virtual detection area A and the detection area B can be set independently of each other without restriction from the other party. Therefore, when X-rays that pass through the lung field and have little attenuation may adversely affect automatic exposure control,
By setting the virtual detection area A so that such X-rays do not enter, adverse effects can be avoided.

FIG. 4 is a block diagram showing the function of the automatic density correction unit 100. In FIG. 4, the threshold generation function 10
1 generates a threshold value. The threshold value is set to a value that separates a portion (black level) corresponding to the shadow of the contrast agent from the video signal. As such a threshold value, for example, a fixed value, a variable value according to the irradiation X-ray dose, an analysis value from a fluoroscopic image, or the like is used.

A fixed value is preferable because it is simple. The variable value according to the irradiation X-ray dose is preferable in that the change in X-ray dose is reflected in the threshold value. The analysis value from the fluoroscopic image is preferable in that the black level can be accurately divided, and thus the precise density correction can be performed.

The comparison function 102 compares the video signal input from the TV camera 9 with the threshold of the threshold generation function 101 to generate a binary comparison output signal. The comparison output signal is "1" when the level of the video signal is higher than the threshold value, and "0" when it is low.

[0064] index calculation function 103 and requests the _{exp {-μ (P-P L} )} based on the video signal. Here, P is P ₁ or P ₂ . Exponential operation function 103
The calculation of exp {-μ (P−P _L )} according to is performed as follows.

The tube voltage and tube current of the X-ray tube 1, the body thickness of the subject 3, and the video level of the video signal of the TV camera 9 have the relationship shown in FIG. FIG. 5 is a graph showing the relationship between the video level and the value D determined by the tube voltage kV and the tube current mA for each body thickness. It should be noted that D is given by the following equation and substantially corresponds to the intensity of X-rays. Hereinafter, D is tentatively called X-ray intensity.

[0066]

(Equation 10)

The video level curves for each body thickness are substantially parallel and are translated by a distance proportional to the difference in body thickness. Using such a relationship, the difference P between the unknown body thickness P and the preset constant body thickness P _L is obtained as follows.
Seek -P _L.

FIG. 6 is a diagram for explaining how to obtain P-P _L. In FIG. 6, the video level curves for the body thickness P _L (for example, 25 cm) and the body thickness 10 cm are known.

It is now assumed that an X-ray having a known intensity d ₁ which is determined by a certain tube voltage and tube current is irradiated, and this is transmitted through an unknown body thickness P to obtain a video level V. At this time, the video level V _L for the X-ray intensity d ₁ is obtained from the video level curve for the body thickness P _L. Also, body thickness 1
From the video level curve for 0 cm, X-ray intensity d and d _L corresponding to the video level V and V _L is obtained.

Video level curves are parallel to each other
From the premise, the triangle qrs and the triangle tuv are congruent. I
Therefore, the curve of the body thickness P and the body thickness P_LDistance to the curve of
x is the unit of X-ray intensity, d_LEqual to -d. Both curves
The distance x between is the body thickness difference PP _LNothing else, d_L−
Body thickness is calculated by multiplying d by a predetermined coefficient and converting it to distance.
Difference P-P_LIs found.

That is, when the input video signal of the video level V is given, the X-ray intensity d corresponding to the video level V is obtained from the video level curve of the body thickness 10 cm, and this is subtracted from the previously known d _L , The thickness difference P
-It can be converted to P _L. This makes it possible to determine the respective P-P _L based on the video level per unknown body thickness P take a variety of values.

Exp {-μ (P−P _L )} is obtained by subjecting the thus obtained body thickness difference P−P _L to the index conversion. It is preferable to use a look-up table to perform each of the above calculations in terms of speeding up.

Returning to FIG. 4, the address generation function 104 is for generating the pixel address of the video signal by utilizing the synchronizing signal included in the video signal. The area determination function 105 determines the area to which the pixel of the input video signal belongs based on the pixel address input from the address generation function 104, and generates a determination output signal.

A virtual detection area A and a detection area B are set in the area determination function 105, and a binary determination signal indicating whether or not each area belongs is output. That is, the determination signal D _B of the detection area B and the determination signal D _A of the virtual detection area A is outputted. These judgment signals indicate that "1" belongs to the area,
0 "indicates that it does not belong.

The virtual detection area A is set based on aperture information or division information input from the main control unit 200.
For example, when the stomach is imaged, the division information indicates "one shot", and the virtual detection area A as shown in FIG. 7 is set based on the division information. Further, when the esophagus is imaged, the division information indicates “vertical division into two”, and based on this, a virtual detection area A as shown in FIG. 8 is set, for example. 7 and 8 show the relationship between the respective detection areas on the perspective screen.

In addition to this, an appropriate virtual detection area A is set based on the division information or the aperture information. That is, a detector having a detection area of an optimum size is virtually provided according to the film division and the aperture of the diaphragm, and as a result, a large virtual detection is performed for an examination having a wide observation area such as the stomach and the large intestine. It is possible to use an elongated or small virtual detector for examinations such as spot imaging of the esophagus or stomach part using a gas detector, and the concentration stability of the double contrast part is good and the influence of harmful direct rays is also good. It is possible to realize shooting that is not affected.

The detection area B is a fixed area known in advance. Since it does not matter what the detection area of the actual detector is, for example, X for general imaging using a cassette is used.
There is no problem even if a detector having a structure suitable for the line device is used. As a result, the X-ray TV device, which is originally a cassette, can also be used for cassette imaging, so that the application of the X-ray TV device can be expanded.

The output signals of the exponent calculation function 103 are input to the integration functions (or integration functions) 108 and 109 through the switch functions 106 and 107, respectively. The switch functions 106 and 107 are logical product functions 11 respectively.
It is switched by the output signals of 0 and 111.

The switch functions 106 and 107 are switched to the a side by the "1" output signals of the AND functions 110 and 111, respectively, and switched to the b side by the "0" output signal. The output signals of the exponential calculation function 103 are given to the a sides of the switch functions 106 and 107, and b
Signal 0 is applied to the side.

The logical product function 110 calculates the logical product of the output signal of the comparison function 102 and the output signal D _A of the area determination function 105. Therefore, when the pixel of the video signal belongs to the virtual detection area A and the video level thereof exceeds the threshold value, the output signal of the exponential calculation function 103 is integrated by the integration function 108.

The fact that the pixel of the video signal belongs to the virtual detection area A and the video level thereof exceeds the threshold value means that it is the video signal of the area of interest S ₁ . Therefore, when integration is performed for one frame of the video signal,

[0082]

[Equation 11]

Is obtained. AND function 111 is comparison function 1
The logical product of the output signal of 02 and the output signal D _B of the area determination function 105 is obtained. Therefore, when the pixel of the video signal belongs to the detection area B and the video level thereof exceeds the threshold value, the output signal of the exponential calculation function 103 is integrated by the integration function 109.

The fact that the pixel of the video signal belongs to the detection area B and the video level thereof exceeds the threshold value means that it is an effective video signal of the detection area S ₂ . Therefore, when the integration for one frame of the video signal is performed,

[0085]

(Equation 12)

Is obtained. The output signal of the AND function 110 is integrated by the integration function 112. AND function 110
The "1" output signal indicates that the pixel of the video signal belongs to the virtual detection area A and its video level exceeds the threshold value. Therefore, when this integration is performed for one frame of the video signal, The area S ₁ is obtained.

The output signal D _B of the area judging function 105 is integrated by the integrating function 113. Since "1" of the output signal D _B of the area determination function 105 indicates that the pixel of the video signal belongs to the detection area B, if this integration is performed for one frame of the video signal, the area of the detection area B S _2B Is required.

The multiplication / division function 114 has such an integration function 1
Using the output signals of 08, 109, 112 and 113, the multiplication / division by the equation (8) (or the equation (9)) is performed to obtain the correction amount α. This correction amount α is input to the X-ray controller 11.

Automatic density correction unit 1 having such a function
00 is actually configured using MPU. In Figure 9, MP
The block diagram of the automatic density correction | amendment part 100 comprised using U is shown. In FIG. 9, the MPU 301 exchanges signals with the X-ray controller 11 and the main controller 200 through the interfaces 302 and 303, respectively. The signal exchanged with the X-ray controller 11 includes the correction amount α. The signal exchanged with the main control unit 200 includes aperture information, division information, tube voltage information, and tube current information.

A frame memory 305, a program memory 306 and a data memory 307 are connected to the MPU 301 via a bus 304. As the frame memory 305, for example, VRAM (video random acce)
ss memory) is used. For example, a ROM (read-only memory) is used as the program memory 306. As the data memory 307, for example, SRAM (static rand)
om access memory) is used.

The composite video signal of the TV camera 9 is input to the video interface 308. The composite video signal is separated into an image signal and a synchronization signal by the video interface 308, and the image signal is AD (ana
A log digital) converter 309 and a synchronization signal are input to the sampling clock generator 310. The sampling clock generator 310 generates a sampling clock based on the synchronization signal included in the composite video signal and inputs the sampling clock to the AD converter 309.

The AD converter 309 converts the analog image signal into digital image data based on the sampling clock supplied from the sampling clock generator 310, and the frame memory 305 stores the SIO (serial input-).
output) Input through the port. As a result, the image data of the perspective image is stored in the frame memory 305.

Next, the operation of the automatic density correction unit 100 having such a configuration will be described. 11 to 15 show flow charts of the operation of the automatic density correction unit 100. These operations are performed by the program stored in the program memory 306.

FIG. 11 is a flow chart of a routine executed by a system communication interrupt. System information provided from the main control unit 200 through the interface 303 when the system communication interrupt occurs is stored in the data memory 307 ( Stage ST01).

The system communication interrupt is generated when the system information is changed. The system information includes at least aperture information, division information, tube voltage information, and tube current information. Therefore, the opening of the variable aperture 2 and the division mask 4
When any one of the opening, the tube voltage and the tube current is changed, a system interrupt occurs and the latest information is stored in the data memory 307. The diaphragm information, the division information, the tube voltage information, and the tube current information stored in the data memory 307 are used for the correction calculation described later.

FIG. 12 is a flow chart of a routine periodically executed by a timer interrupt. When the timer interrupt occurs, the capturing of the video signal is stopped (stage ST11), and it is determined whether the photographing button of the operation unit 201 is on (stage ST12). When the shooting button is on, the image in the frame memory 309 is stored in the data memory 307 as the final image (stage ST13).
The final image stored in the data memory 307 is used for the correction calculation described later.

After the final image is saved, the video signal acquisition is restarted (stage ST14). When the shooting button is off, the video signal is resumed by jumping from stage ST12 to stage ST14. Such a routine is repeatedly executed each time a timer interrupt occurs.

FIG. 13 is a flow chart of a routine executed by the shooting button interrupt. The user operates the operation unit 20.
This routine is started when the shooting button of 1 is pressed,
Correction calculation is executed (stage ST21).

The stage of the correction calculation is disassembled and shown in FIG. In FIG. 14, first, the threshold value for dividing the black level is determined (stage ST31), and then the correction amount is calculated (stage ST32). The calculation of the correction amount is performed by the method described above. The calculated correction amount is transferred to the system, that is, X through the interface 302.
It is transmitted to the line control unit 11 (stage ST33).

With this, each time the photographing button is pressed, the correction amount is calculated by the routine of FIG. 13, and the X-ray controller 11 performs automatic exposure control based on the reference value corrected by this correction amount.

FIG. 15 shows a flow chart of another form of the timer interrupt processing routine. This flow chart is one in which a correction calculation stage is incorporated in the routine of FIG. That is, in FIG. 15, stages ST41 to ST41
ST44 is the stage ST11 to ST of the routine of FIG.
It is the same as that of 14, and then the correction calculation stage S
T45 is added. According to this routine, the correction amount is calculated regularly regardless of whether the shooting button is on or off.

Next, details of the X-ray controller 11 will be described. FIG. 10 is a block diagram of the X-ray controller 11. In FIG. 10, a reference value generator 401 generates a reference value I _REF for automatic exposure control. The reference value I _REF is determined by calibration.

The multiplier 402 multiplies the reference value I _REF by the correction amount α given by the automatic density correction unit 100 to obtain α I _REF.
Is input to the comparator 403. The integrator 404 integrates the detection signal of the detector 5, and its output signal I _X is input to the comparator 403.

The comparator 403 outputs the output signal α of the multiplier 402.
I_REFAnd the output signal I of the integrator 404 _XCompare and compare
The force signal controls the switching of the switch 405.
By the output signal of the comparator 403, I_X<ΑI_REFWhen
The switch 405 is switched to the a side, and the control signal V_CCBut
A high voltage power supply 406 is provided. I_X≧ αI_REFWhen
Switch 405 is switched to the b side, and the control signal 0
A high voltage power supply 406 is provided.

The control signal V _CC is a control signal for continuing the X-ray irradiation, and the control signal 0 is a control signal for stopping the X-ray irradiation. Therefore, when the X-ray irradiation is performed by pressing the photographing button, the automatic exposure control with αI _REF as the reference value is performed by such a control signal.

[0106]

As described in detail above, according to the first invention for solving the problem, the detection signal in the virtual X-ray detection area and the detection area of the actual detector which are appropriately set are set. Since the reference value of the automatic exposure control is corrected based on the detection signal in step 1, it is possible to realize the X-ray automatic exposure control method capable of performing highly accurate exposure control.

Further, according to the second invention for solving the problem, based on the detection signal in the virtual X-ray detection area and the detection signal in the actual detection area of the detector which are appropriately set. Since the reference value of the automatic exposure control is corrected, it is possible to realize an X-ray automatic exposure control device capable of highly accurate exposure control.

According to the third invention for solving the problem, based on the detection signal in the virtual X-ray detection area and the detection signal in the actual detection area of the detector, which are set appropriately. Since the reference value of the automatic exposure control is corrected, it is possible to realize an X-ray imaging apparatus capable of highly accurate exposure control.

[Brief description of the drawings]

FIG. 1 is a block diagram of an apparatus according to an example of an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a virtual detection area and a detection area in the apparatus according to the exemplary embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a virtual detection area and a detection area in the apparatus according to the example of the embodiment of the present invention.

FIG. 4 is a block diagram showing a function of an automatic density correction unit in the apparatus according to the exemplary embodiment of the present invention.

FIG. 5 is a graph showing a video level of a perspective image.

FIG. 6 is a diagram for explaining a method of obtaining a body thickness of a subject from a video level of a perspective image.

FIG. 7 is a diagram showing a relationship between virtual detection areas and detection areas in the apparatus according to the exemplary embodiment of the present invention.

FIG. 8 is a diagram showing a relationship between a virtual detection area and a detection area in the apparatus according to the example of the embodiment of the present invention.

FIG. 9 is a block diagram showing a configuration of an automatic density correction unit in the apparatus according to the exemplary embodiment of the present invention.

FIG. 10 shows X in the apparatus according to the embodiment of the present invention.
It is a figure which shows the structure of a line control part.

FIG. 11 is a flowchart of the operation of the automatic density correction unit in the apparatus according to the example of the embodiment of the present invention.

FIG. 12 is a flowchart of the operation of the automatic density correction unit in the apparatus according to the example of the embodiment of the present invention.

FIG. 13 is a flowchart of the operation of the automatic density correction unit in the apparatus according to the example of the embodiment of the present invention.

FIG. 14 is a flowchart of the operation of the automatic density correction unit in the apparatus according to the example of the embodiment of the present invention.

FIG. 15 is a flowchart of the operation of the automatic density correction unit in the apparatus according to the example of the embodiment of the present invention.

[Explanation of symbols]

 1 X-ray tube 2 Variable aperture 3 Subject 4 Divided mask 5 Detector 6 X-ray film 7 Image intensifier 8 Optical system 9 TV camera 11 X-ray control unit 100 Automatic density correction unit 200 Main control unit 201 Operation unit 101 Threshold Generation function 102 Comparison function 103 Exponential operation function 104 Address generation function 105 Area determination function 106,107 Switch function 108,109,112,113 Integration function 110,111 AND function 114 Multiplication / division function 301 Microprocessor 302,303 Interface 304 Bus 305 Frame Memory 306 Program Memory 307 Data Memory 308 Video Interface 309 AD Converter 310 Sampling Clock Generator 401 Reference Value Generator 402 Multiplier 403 Comparator 404 Integrator 4 05 Switch 406 High-voltage power supply

Claims (3)

[Claims] 1. When converting a fluoroscopic image of a subject by X-rays into an image signal for display on a display device and photographing on a photographing medium, the dose of X-rays transmitted through the subject is detected by a detector and the detected signal In an X-ray automatic exposure control method for controlling an X-ray irradiation amount so that an integrated value matches a predetermined reference value, a virtual X-ray detection area is set and the virtual X-ray detection area is set from the image signal. To obtain a detection signal in the detection region of the detector from the image signal,
An X-ray automatic exposure control method, characterized in that the reference value is corrected based on these two detection signals. 2. When converting a fluoroscopic image of a subject by X-rays into an image signal for display on a display device and photographing on a photographing medium, a dose of X-rays transmitted through the subject is detected by a detector and the detected signal In an X-ray automatic exposure control device that controls an X-ray irradiation amount so that an integrated value matches a predetermined reference value, a virtual detection region setting unit that sets a virtual X-ray detection region, and the virtual signal from the image signal. Based on these two detection signals, first calculation means for obtaining a detection signal in a typical X-ray detection area, second calculation means for obtaining a detection signal in the detection area of the detector from the image signal, An X-ray automatic exposure control device, comprising: a correction unit that corrects the reference value. 3. An X-ray irradiating means, a converting means for converting a perspective image of a subject by the X-rays radiated from the X-ray irradiating means into an image signal, and a display means for displaying an image based on the image signal. A photographing means for photographing a perspective image of a subject by the X-rays emitted from the X-ray irradiating means on a photographing medium;
Detection means for detecting the dose of X-rays transmitted through the subject; and control means for controlling the X-ray irradiation dose of the X-ray irradiation means so that the integrated value of the detection signal of the detection means matches a predetermined reference value. An X-ray imaging apparatus having: a virtual detection area setting means for setting a virtual X-ray detection area; and a first calculation means for obtaining a detection signal in the virtual X-ray detection area from the image signal, Second calculating means for obtaining a detection signal in the detection area of the detector from the image signal;
An X-ray imaging apparatus comprising: a correction unit that corrects the reference value based on one detection signal.