JPH05219437A - X-ray picture system - Google Patents

Abstract

PURPOSE: To prevent an image effect which causes disturbances at switching by forming an image on a 3rd surface, whose size is between those of 1st and 2nd surfaces onto an output screen in the case of changing the 1st surface of an input screen into the 2nd surface. CONSTITUTION: An X-ray source 1 emits an X-ray beam 3 to irradiate an object 5. An input screen 7 detects an X-ray image of the object 5 and emits electrons. An adjustment means 33 forms an image of a 3rd surface of an input screen 7 and whose size is between those of 1st and 2nd surfaces onto an output screen 13, for the case that a setting of an image of the 1st surface of the input screen 7 is changed into a setting of an image of the 2nd surface. Thus, a gradual increase or decrease in the image format is obtained, while the image of the object 5 is well focused as is by forming the image of one or more surfaces with the intermediate size onto the output screen 13 in a focused state in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray image system using an X-ray image intensifier tube.

More particularly, the present invention is an X-ray imaging system as described above, which emits a -X-ray beam,
An X-ray source for irradiating an object placed in the X-ray beam with the beam to form a X-ray image; an input screen for detecting the X-ray image and emitting electrons, an output screen, An X-ray image intensifier tube having an electron optical system for forming the X-ray image detected on the input screen as an optical image on the output screen; and-a different-sized surface portion of the input screen (r1, adjusting means for adjusting the electron optics to image r2) onto the output screen.

The present invention also relates to an X-ray image intensifier and adjusting means suitable for use in the X-ray image system as described above.

[0004]

2. Description of the Prior Art An X-ray imaging system of the type described above is described in Phillips Technical Review, Vol. 41, 1983/84, Vol.
Issue, pages 137-148, by B. van der Eijk and W. Kuhl, "X-ray image intensifier with large image format".

The above document describes an X-ray imaging system which comprises an X-ray image intensifier which converts the X-rays formed on the CsI input screen into blue light which emits electrons at a photocathode. By using four electrodes, the electrons are accelerated and imaged on the output screen. The output screen, which has a relatively small diameter of the order of a few cm, has a fluorescent layer deposited on an optical fiber system in which the electrons generate light. The optical image formed on this output screen is taken out by, for example, a television camera or the like and displayed on a television monitor or displayed.
Recorded on 100mm photographic film. Depending on the size of the object to be imaged, different diameter portions of the input screen of the X-ray image intensifier tube are used. For example, imaging of both kidneys and stomach requires a large surface area of the input screen of an X-ray image intensifier tube, for example with a large diameter of about 38 cm, while imaging of a small object such as a single kidney. For example, 7 cm
Only surface areas of small diameter are needed. Even if the image format is adjusted, the entire output screen is still used, so the magnification will change.
If a small surface portion of the input screen of the x-ray image intensifier tube is used, the diaphragm preferably located between the patient and the x-ray source is adapted to this small image format. In this way, it is possible to avoid unnecessary irradiation of the non-imaged part of the patient. This is important not only to limit the adverse effects of irradiation on living tissue but also to reduce the scattering of X-rays in the patient, which lowers image contrast. To match the 38 cm image format to the 17 cm image format, the voltage on at least one of the electrodes needs to be varied by means of a regulation means, for example between 3 kV and 35 kV. In this case, the adjusting means is a variable high voltage power supply. In order to avoid seeing the focus shift due to the switching of the image format, such switching must be performed within the adaptation time of human eyes of about 0.2 s. This means that the output resistance of the high-voltage power supply connected in parallel with the capacitance of the electrode connected to the high-voltage power supply must be small. However, the small output resistance has the drawback of high losses, which makes miniaturization of the high-voltage power supply difficult and unfavorable for the long-term stability of the high-voltage power supply.

[0006]

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide an X-ray image system capable of preventing an image effect which may be a hindrance when switching image formats.

Another object of the present invention is that the service life of the X-ray image intensifier is not affected by the format switching, the loss in the high voltage power source is relatively small, and the high voltage power source is stable. It also provides a line imaging system.

In order to achieve the above object, X according to the present invention
In the line image system, when the adjusting means switches the setting of the image of the first surface portion of the input screen to the setting of the image of the second surface portion of the screen, the adjustment of the first surface portion and the second surface portion is performed. At least a third surface portion of the input screen having a dimension in between is configured to be imaged on the output screen.

In the above arrangement, if one or more surface portions of intermediate size are imaged in focus on the output screen during image format switching, a gradual increase or decrease in image format will occur. The image of the object can be obtained with good focus. Therefore, it is possible to perform observation even while changing the image format. This is important in the medical field where the radiologist wants to see a stable image of the patient but does not want to be bothered by the effect of adjusting image flicker.

Gradual adjustment of the image format is used both for dose control to keep the average light output on the output screen of the X-ray image intensifier tube constant and for automatic gain control of the video signal of the television camera. It is attractive.
In this case, the amount of light generated on the output screen of the X-ray image intensifier is measured during the dose control, and the voltage of the X-ray source provides a constant average brightness on the output screen according to the thickness of the patient. To make adjustments. This arrangement is necessary both for correct exposure when recording the image on the output screen on photographic film and for the sufficient light output of the video camera. Since the x-ray source voltage cannot be increased excessively for relatively thick patients, the average brightness on the output screen of the x-ray image intensifier tube will be lower than for thin patients. In such cases, the average brightness of the video signal produced by the television camera is automatically gain controlled (AGC).
Is kept constant by. In the case of abrupt image format switching of the X-ray image intensifier tube, the brightness of the output screen of the X-ray image intensifier tube changes, and the dose control and the automatic gain control cause adjustment effects that disturb the image. there is a possibility. This phenomenon is counteracted by forming well-focused images of one or more intermediate image formats upon switching image formats.

Further, since the displacement of the electric charge during the gradual adjustment of one or more voltages of the electron optical system of the X-ray image intensifier tube is relatively small, flashing of the X-ray image intensifier tube is prevented. To be done. Such flushing occurs when electrons move from a high voltage electrode to a low voltage electrode through the insulating portion of the X-ray image intensifier tube during a rapid voltage change. In this case, ionization can occur in the residual gas of the X-ray image intensifier tube, which appears as flashing that disturbs the disturbing image on the output screen.

In one embodiment of the X-ray imaging system according to the present invention, the electron optical system has an electrode, and the voltage U of this electrode is
(r) determines the dimension r of the surface portion of the input screen imaged on the output screen, the adjusting means having a power supply circuit and an input circuit coupled to the electrodes, the output voltage of the power supply circuit being the above Embodiments that increase or decrease in response to an input signal to be formed by the input circuit include changing the size of the surface portion imaged on the output screen by the input circuit to change the dimension r. The signal is adjusted to exhibit a change r (t) that is continuous to the eye during the period dT. In this case, the adjustment is such that the output voltage is approximately equal to the voltage U (r (t)) at any point during the period dT.

When adjusting the image format, the output resistance of the power supply circuit is connected in parallel with the X-ray image intensifier tube, the power supply circuit and the capacity of the cable between the X-ray image intensifier tube and the power supply circuit. It will be. If the power supply circuit and the X-ray image intensifier tube were incorporated into a single housing, there would be no cable between the power supply circuit and the X-ray image intensifier tube. When the input signal for the power supply circuit to be formed by the input circuit changes stepwise because the output resistance is connected in parallel with the capacitance, the output voltage of the power supply circuit is determined by these output resistance and capacitance. It increases or decreases exponentially with RC time. The present invention allows a longer RC time by choosing a slower visible format adjustment, instead of aiming for a minimum RC time of the power supply circuit to obtain a fast invisible switching operation. Is based on the insight that high output resistance can be used resulting in advantages such as low loss in the power supply circuit and long term stability.

Instead of adjusting the image format, such as changing the image format with an exponential change in the output voltage of the power supply circuit in response to a step change in the input signal formed by the input circuit, for example, the image Often one wants to employ different temporal changes that increase or decrease linearly with time. However, since the output voltage U (r) of the power supply circuit has a predetermined inertial characteristic determined by its output resistance, an arbitrary image format change r (t) cannot be selected. The change r (t) in the image format is the exponential output signal of the power supply circuit due to the change in the output voltage U (r (t)) per unit time that should be output by the power supply circuit due to the stepwise change in the input signal. Must be slower than the change per unit time in. That is,

[Equation 1] In the above equation, τ is the RC time of the power supply circuit coupled to the electrode and U (0) is the output voltage of the power supply circuit at the beginning of the image format change. For a linear format change such that r (t) = kt, the time derivative of U (r (t)) can be written as

[Equation 2] The function of the voltage U for the image format r can be known from measurements and calculations. Time t = 0 at voltage U (0) of 35kV
When the format is increased from 17 cm to 38 cm within the period of 1 second from d, and the maximum value of dU / dr occurs at t = 0 and is given by 4000 Vcm ^-1 , the above equations when t = 0 Gives τ = 0.4s. With this RC time, the output voltage of the power supply circuit can still follow the linear format change. For the electrode capacitance of about 150 pF, the output resistance R of the amplifier circuit of about several GΩ can be used. This is very advantageous in terms of power loss and stability of the power supply circuit.

An embodiment of the X-ray image system according to the present invention is characterized in that the input signal to be formed for the power supply circuit (63) by the input circuit (59, 61) is stepwise.

For RC time of about 0.4s, time t =
A linear change in format from 0 to 17 cm to 38 cm can be generated in N discrete steps with time Δt in 1 second, in this case from equation (1)

[Equation 3] Becomes In the above equation, U (0) = 35 kV, and ΔU (0) is the voltage step of the output voltage per time Δt at time t = 0. The voltage step per unit time is t = 0
Since it becomes the maximum with respect to the time, the time constant τ related to this value according to the equation (3) is
It is small enough to follow U (r (t)). For ΔU (0) =-377V, a value of Δt = 1/232 is found for Δt. The image format adjustment is done in 232 equally spaced steps.

In another embodiment of the X-ray imaging system according to the present invention, the electron optical system has several electrodes, which are respectively connected to power supply circuits, and input signals of these power supply circuits are input by the input circuit. The feature is that they are adjusted at the same time.

X-ray image intensifier tubes have, for example, five electrodes, and the voltages on these electrodes must be adjusted together to change the image format. The X-ray image intensifier is made of metal in particular, and one of the electrodes is always connected to the ground potential point. The voltages on the five electrodes are shown in Table 1 for five image formats. To adjust the image format in between these five image formats, the voltage on each electrode must be adjusted to the value on the curve plotted through the five points on that electrode. In Table 1, the electrode labeled "Anode 1" accelerates the electrons emitted by the cathode to high speed, the electrode labeled "Anode 2" mainly determines the image format, "focus electrode 1" and Each electrode labeled "focus electrode 2" has the effect of focusing.

[0019]

[Table 1]

Another embodiment of the X-ray imaging system according to the invention is a table in which the input circuit stores voltage values for at least one electrode and for the N dimension surface portions of the input screen to be imaged. Has a memory containing
Here, each dimension is represented by one address of the memory, further, the input circuit has means for sequentially supplying the voltage value to each of the power supply circuits of the respective electrodes, and the adjusting means is to be imaged. Entering a format value for a new dimension to set the surface portion and supplying to the memory an address associated with each dimension located between the current dimension of the surface portion and the new dimension to be set. It has a format adjustment circuit for

The user of the X-ray imaging system can supply the format adjustment circuit with the format value of the image format to be set. The difference signal to be supplied to the counter is obtained by comparing the format value of the image format with the counting position which is a measure of the image format used. Depending on the sign of this difference signal, the counting position is increased or decreased until the difference signal becomes zero. The counter then addresses a memory that stores, for example, electrode voltage values associated with, for example, 256 image formats. In response to each increment or decrement of the counter, a new voltage value for each electrode is transferred from the memory via the digital-to-analog converter to the power supply circuit. The speed of the counter is determined by the frequency of the clock connected to the counter. The power supply circuit has an operational amplifier with respect to each electrode excluding an electrode having a fixed potential, the output terminal of the operational amplifier is fed back to the inverting input terminal through the resistor, and the gain is, for example, 4000 times. After setting the desired image format, analog fine tuning signals can be provided to one or more of the electrodes if necessary to readjust the focus condition to the desired accuracy.

Yet another embodiment of the X-ray image intensifier tube according to the invention is characterized in that the adjusting means comprises calibration means for determining the voltage change as a function of the size of the surface portion with respect to at least one electrode, Calibrating means: a variable power supply providing a variable calibration signal to a power supply circuit of the at least one electrode to focus an image on the output screen for different image formats; Arithmetic means for inputting a calibration signal associated with the in-focus image of the image format and for determining from said voltage values adjusted by said calibration the voltage values associated with said N surface portions to be imaged. Is characterized by having.

The calibration means allows the user of the X-ray imaging system to adjust a large number of working voltages in order to obtain a well-focused image. Each voltage associated with the intermediate image format is calculated by the calculation of the voltage curve as a function of the image format using said computing means. In this way, for each X-ray image intensifier tube, an optimum voltage change as a function of the image format for a particular user is obtained.

[0024]

Embodiments of the X-ray imaging system according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an X-ray imaging system in which an X-ray beam 3 emitted by an X-ray source 1 illuminates an object 5 such as a patient. Since the X-ray beam 3 is attenuated in the object 5 depending on the local density of the object, the image-bearing X-ray beam 3'is emitted from the object and the X-ray image intensifier tube is emitted. It is incident on the input screen 7 of the multiplier through the titanium diaphragm of the (image intensifier) 9. This input screen 7
Has a scintillation layer such as CsI, in which light is emitted in accordance with the intensity of X-rays, and the X-ray image formed by the X-ray beam 3 ′ bearing the above image is detected. In order to improve the brightness of the detected X-ray image, the light emitted in the scintillation layer is incident on the photocathode, which causes electrons to be emitted. These electrons are accelerated and focused on the output screen 13 via an electron optical system 11 having a large number of electrodes. An optical image with increased brightness is formed on the output screen 13 including the fluorescent layer, and the image is formed on the photosensitive input screen of the television camera 17 via the optical system 15. This television camera 17 has a solid-state sensor such as a CCD image sensor or a television image pickup tube having a PbO input screen. The video signal formed by the television camera 17 is supplied to the television monitor 21 via the video amplifier 19 having an automatic gain control function. A part of the light beam from the output screen 13 is transmitted through the semitransparent separating mirror 23.
It is recorded on the film of the 0 mm camera 25. In order to achieve the correct exposure of the film in the camera 25 and the correct exposure of the input screen of the television camera 17 for different thicknesses of the patient 5, said output screen 13
The average brightness of is kept constant. For this purpose, part of the light beam between each lens 15 is deflected by means of a prism 27 and imaged on a photodiode (not shown). The electrical signal produced by this photodiode is supplied to a control unit 29 which, as long as the high voltage and current of the X-ray tube (source) deviates from the desired value for optimum exposure of the output screen 13. Readjust.

When irradiating objects 5 of different sizes,
It is desirable to block a portion of the X-ray beam that is not used for image formation by using the diaphragm 31. This shield is
This is done in view of the fact that patient exposure must be minimized due to the adverse effects of X-rays and the view of scattered radiation that occurs within the patient. If the aperture 31 is set too small, a dark edge may appear on the output screen 13 of the X-ray image intensifier tube 9, or
Or it is not desirable to see extraneous details in the X-ray image without a diaphragm. For this reason, the image format of the input screen of the X-ray image intensifier tube 9 is reduced by imaging the surface portion of the diameter r2 on the output screen 13. The voltage of the electrode of the electron optical system 11 is set by the adjusting means 33 to a value corresponding to five image formats such as the maximum image format diameter r1 of 38 cm or the minimum image format diameter r2 of 17 cm. be able to. The user of the X-ray imaging system can set the image format to be set in the adjusting means 33 by a method such as a push button, a monitor and a keyboard or a mouse. In this case, the adjusting means 33 adjusts the position of the diaphragm 31 to the set image format, and the electrodes of the electron optical system 11 change the image format continuously and linearly with respect to the eye, and the image format on the output screen is changed. Input a voltage that changes with time so that the image can be observed without interruption.

FIG. 2 is a vertical sectional view of the X-ray image intensifier tube 9. This X-ray image intensifier tube 9 has 5 electrodes, namely -300V.
A cathode 35 having a voltage of about 0V, a first focus electrode 37 having a constant voltage of 0V, a second focus electrode 39 having a voltage of about 2kV, a format adjusting electrode 41 of a voltage varying between 3kV and 35kV, and a constant voltage of 35kV. Of the anode 43. Each voltage U of the cathode 35, the second focus electrode 39 and the format adjustment electrode 41 is shown in FIG. 3 as a function of the image format r.

FIG. 4 conceptually shows a power supply circuit forming a part of the adjusting means 33, in which each electrode has a power supply circuit. The load on the electrodes of the X-ray image intensifier tube can be represented as a current source Ii, which is connected in parallel with the capacitance Ci. The input signal Vref appears at the output terminal of the power supply circuit after being amplified 4000 times. In practice, the high output resistance R and high voltage gain are achieved using a transformer and a rectifier circuit, so that the power supply circuit will be more accurately represented by a in FIG. In FIG. 5a, Ro is the output resistance of the rectifier D, which is much smaller than 4000R. It can be seen that in order to switch from a large image format to a small image format, the output voltage of the power supply circuit must be increased for the format adjustment electrode 41. An equivalent circuit of the power supply circuit for switching from a large image format to a small image format is shown in Fig. 5b, where the RC time τ is approximated by τ = RoCi. For switching from a small image format to a large image format, the output voltage of the power supply circuit is reduced and the equivalent circuit of the power supply circuit is shown in Figure 5c. In this case, the RC time τ is equal to 4000RCi. The broken line in FIG. 6 shows the time-dependent change of the output voltage of the power supply circuit of the format adjustment electrode 41 regarding the stepwise change of the input voltage from 0.75V to 8.75V. In response to a step change in the input signal of the power supply circuit, the output voltage of the power supply circuit exponentially increases or decreases. When the output voltage increases, the RC time is the RC when the output voltage decreases.
Being smaller than time, the increase and decrease of the image format as a function of time will occur differently for step changes in the input voltage. According to known image format changing methods, this change is generated in an invisible manner. For this purpose, Ro
Since the RC time of Ci and 4000RCi must be significantly smaller than the eye adaptation time of about 0.2 seconds, the time intervals dT for switching between the times t1 and t2 and the times t3 and t4 in FIG. Was less than 0.2s. However,
The low output resistance of the power supply circuit requiring such a small RC time is disadvantageous from the viewpoint of power supply circuit loss and long-term stability.

According to the present invention, the input voltage of the power supply circuit is changed so that the output voltage of the power supply circuit changes as shown by the solid line in FIG. In this case, the switching time interval dT located between the times t1 and t2 and between the times t3 and t4 is, for example, 1 second. From FIG. 3, when r = kt, that is, when the image format r (t) changes linearly as a function of time, the output voltage U (r (t)) of the power supply circuit is equal to the voltage U ( It turns out that it changes like r). The visible image format change r (t) that occurs and is visible during the time interval dT may also be non-linear depending on the nature of the object to be observed. FIG. 6 shows that, regarding the change r (t) of the image format during the period dT, the output voltage U (r (t)) of the power supply circuit controlled by adjusting the input signal of the power supply circuit is (1) ) Must satisfy the requirements given by This is because the maximum change in the output voltage of the power supply circuit is given by the exponential change in time based on the stepwise adjustment of the input signal of the power supply circuit.

FIG. 7 shows that for a linear decrease of the image format r from 38 cm to 17 cm within a one second period dT, the output voltage of the power supply circuit exhibits a change U (kt) indicated by the solid line. There is. This change U (kt) can be approximated by adjusting Δt at a step of 255, which is 1/255 seconds of the input signal of the power supply circuit. Since the time derivative of U (kt) is the maximum at t = 0, the equation (1) becomes the equation (3) at the time t = 0. U (0) = 35kV, ΔU (0) =-377
The minimum RC time τ for V, Δt = 1/255 is 364 ms. The maximum value of the output resistance of 4000R that can be used for the capacitance Ci of about 150 pF of the X-ray image intensifier tube, the capacitance of the power supply circuit itself, and the power supply cable between the power supply circuit and the electrodes. Is equal to a few GΩ.

FIG. 8 shows the adjusting means 33, which has a format adjusting circuit 50. The adjustment circuit 50 includes a clock circuit 51, an input unit 53, a comparison circuit 55, a counter 57, a memory 59, four digital-analog converters 61, and four power supply circuits 63. ing. The memory 59 has, for example, an EPROM,
The voltage curves for electrodes 35, 39 and 41 shown in FIG.
It is stored in each of 256 addresses in one table. In this case, each table corresponds to one image format. The voltage of the electrode 43 is constant. The clock circuit 51 supplies clock pulses to the counter 57 at a frequency of 256 Hz, and the counter counts up or counts down these pulses to form an 8-bit address for each clock pulse. This address is supplied to the address input terminal of the memory 59. Memory 5
When 9 is addressed, the four voltage values stored in the storage space of that address are supplied as input signals to the power supply circuit 63 via the digital-analog converter 61.
These input signals are amplified by 4000 times, 200 times and -50 times, and then, through these power supply circuits, the related electrodes 4
3, 41, 39 and 35. On the other hand, the user can select five image formats by supplying five format codes to the input section 53. In the input section 53, the format code is stored in the memory 59 as described above.
It is converted to a format value corresponding to one of 256 addresses. In the comparison circuit 55, the format value is compared with the counting position of the counter 57, and thus the difference between the image format currently used and the new image format to be set is determined. Since the counter 57 is driven to count up or count down depending on whether the new image format to be set is larger or smaller, the address of the memory 59 is increased or decreased in a stepwise manner. To be done. When the count position of the counter 57 becomes equal to the format value set via the input unit 53, the counter is stopped and the image format is in a static state. In order to fine-tune the focus of the image formed on the output screen 13 of the X-ray image intensifier tube 9, the cathode 35 is connected to the fine adjustment voltage via the multiplexer 65 after the format change is completed. This multiplexer 6
The format code is supplied to 5 to select the fine adjustment voltage corresponding to the image format to be set.

FIG. 9 shows another embodiment of the adjusting means 33,
The adjusting means is provided with a calibrating means for supplying five variable voltage values to the cathode 35. In this case, regarding a predetermined image format, a variable power source, which is the variable resistor 71 in this example, is supplied to the power supply circuit 63 of the cathode 35 via the multiplexer 75 and the analog / digital converter 77, and further via the data bus 79. Supplied.
The user adjusts the variable resistor 71 so that a focused and stable image can be seen on the output screen 13 of the X-ray image intensifier tube 9. Each voltage value adjusted in this way is stored in the arithmetic means having the microprocessor 73. In this microprocessor these voltage values are fitted to a curve. Therefore, the voltage change of the cathode 35 shown in FIG. 3 is obtained for, for example, 256 image formats. Then, these voltage values are stored in the memory 59 via the data bus 79. When the image format is changed, the addresses of the memory 59 are generated in the microprocessor 73, and these addresses are supplied to the memory via the address bus 85. The microprocessor determines the voltage change as a function of the image format r from five voltage values to be fine tuned by the user, at least for the cathode 35, so that for each X-ray image intensifier tube an individual optimum Image format adjustment can be obtained.

Also, an external data bus can be connected via the circuit 81, eg for service purposes,
See the contents of the memory 59 or the microprocessor 73
You can check.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an X-ray imaging system,

FIG. 2 is a longitudinal sectional view of an X-ray image intensifier tube,

FIG. 3 is a graph showing the voltage on each electrode of an X-ray image intensifier as a function of image format,

FIG. 4 is a circuit diagram of a power supply circuit,

FIG. 5 is an equivalent circuit diagram of the same power supply circuit, where a is a constant image format, b is a decrease in image format, and c is a case in which the image format is increased.

FIG. 6 is a time chart showing a time-dependent voltage change of a format adjustment electrode according to a change of an image format,

FIG. 7 is a time chart showing a normalized voltage change of a format adjustment electrode according to a linear format change and a voltage change of a format adjustment electrode according to a stepwise adjustment of an input signal of a power supply circuit,

FIG. 8 is a block diagram showing an embodiment of adjusting means in the present invention,

FIG. 9 is a block diagram showing another embodiment of the adjusting means in the present invention.

[Explanation of symbols]

1 ... X-ray source, 3 ... X-ray beam, 5
… Object, 7… Input screen,
9 ... X-ray image intensifier, 11 ... Electron optical system, 13
... Output screen, 33 ... Adjusting means, 35 ... Cathode, 37, 39 ... Focus electrode, 41 ...
Format adjustment electrode, 43 ... Anode, 50 ... Format adjustment circuit, 51 ... Clock circuit, 53 ... Input section,
55 ... Comparison circuit, 57 ... Counter,
59 ... Memory, 63 ... Power supply circuit,
65 ... Multiplexer, 71 ... Variable resistance,
73 ... Microprocessor.

Claims (11)

[Claims] 1. An X-ray source (1) which emits an X-ray beam (3) and irradiates an object (5) located in the X-ray beam with the beam to form an X-ray image, Input screen for detecting the X-ray image and emitting electrons
(7), an output screen (13), and an electron optical system (11) for forming the X-ray image detected on the input screen as an optical image on the output screen (11)
A line image intensifier tube (9), and an adjusting means (33) for adjusting the electron optical system so as to form different-sized surface portions (r1, r2) of the input screen on the output screen. In the X-ray imaging system, the adjusting means may be arranged between the first and second surface portions when the image setting of the first surface portion of the input screen is changed to the image setting of the second surface portion. An X-ray imaging system configured to image at least one third surface portion having a dimension on the output screen. 2. X-ray imaging system according to claim 1, wherein the electron optics comprises an electrode (41), the voltage U (r) of which is imaged on the output screen. The size r of the surface portion of the input screen is determined, and the adjusting means controls the power circuit (63) connected to the electrode (41) and the input circuit (5).
9, 61) and the output voltage of the power supply circuit should be imaged on the output screen in an X-ray imaging system in which the output voltage is increased or decreased in response to an input signal formed by the input circuit. Dimension r of the surface portion of the input screen
The input signal is adjusted by the input circuit to exhibit a change r (t) such that the input signal is continuous to the eye within the time period dT, which adjustment involves adjusting the output voltage to the time period dT.
An X-ray imaging system characterized in that it is substantially equal to the voltage U (r (t)) at any point in time. 3. The X-ray imaging system according to claim 2, wherein the input signal formed by the input circuit (59, 61) for the power supply circuit (63) is a step-shaped signal. X-ray imaging system. 4. X-ray imaging system according to claim 3, characterized in that the time interval between two successive steps of the input signal is constant. 5. The X-ray imaging system according to claim 2, claim 3 or claim 4, wherein the electron optical system (11) has a plurality of electrodes (35-43). Power circuit (6
An X-ray imaging system, which is connected to each of 3), and each input signal of these power supply circuits can be adjusted simultaneously by the input circuits (59, 61). 6. The X-ray imaging system according to claim 2, wherein the input circuit (59, 6).
1) has a memory (59), said memory having at least one electrode (41) a voltage value for a surface portion of N dimensions of said input screen (7) each represented by an address of the memory. The input circuit further comprises means for sequentially supplying the voltage values to the power supply circuits (63) of the electrodes, and the adjusting means sets the surface portion to be imaged. A formatter circuit for inputting a format value for a new dimension to be supplied and for supplying to the memory (59) each an address associated with each dimension of the surface portion of the input screen between the current dimension and the new dimension. An X-ray imaging system having (50). 7. The X-ray imaging system according to claim 6, wherein the format setting circuit (50) has a clock circuit (51) for supplying a clock pulse to a counter (57), and the output terminal of the counter is It is coupled to the memory for supplying an address value to the memory and is also coupled to an input terminal of a comparison circuit (55) for comparing the signal of the counter with the new format value to be set. The output terminal is coupled to the counter for setting the counting direction of the counter and for stopping the counter when the signal of the counter becomes equal to the new format value to be set. X-ray imaging system. 8. An X-ray imaging system according to claim 6 or 7, for providing a fine tuning signal to at least one of said electrodes when the dimensions of said surface portion are stable after setting. And the former value is a multiplexer circuit
X, characterized in that it is adapted to be supplied to (65)
Line imaging system. 9. An X-ray imaging system according to claim 6, 7 or 8 wherein said adjusting means (33) is of a size of said surface portion with respect to at least one of said electrodes. A calibration means (71, 73, 75) for determining the voltage change of said electrode as a function, said calibration means supplying a variable calibration signal to said at least one electrode power supply circuit (63), Variable power supply (71) to focus the image on the output screen for different image formats
And inputting said calibration signal relating to focused images in different image formats on said output screen and corresponding voltage values corresponding to N dimensions of said surface portion to be imaged to said calibration signal. An X-ray imaging system, comprising: an arithmetic unit that determines the voltage value to be applied. 10. A combination of an X-ray image intensifier tube and an adjusting means used in the X-ray image system according to claim 1. 11. The adjusting means in the X-ray imaging system according to claim 1.