JPH05335094A - X-ray diagnostic device - Google Patents

Abstract

PURPOSE:To prevent an increase in the exposure dose of a subject and provide a stable fluoroscopic image. CONSTITUTION:A tube voltage control circuit 6 feeds back X-ray output transmitted through a subject, and applies control voltage Vv to a high voltage generation circuit, thereby controlling FKV. This control voltage Vv and another voltage corresponding to SID are inputted to a tube current control circuit 8, and tube current control voltage Va basically proportional to the voltage Vv but so limited as to correspond to SID is obtained. This voltage Va is, then, sent to a filament heating circuit 9 for controlling FmA.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a medical X-ray diagnostic apparatus, and more particularly to improvement of a fluoroscopic tube current control circuit for the apparatus.

[0002]

2. Description of the Related Art In an X-ray diagnostic apparatus, an X-ray fluoroscopic image is converted by an image intensifier, picked up by a TV camera and displayed on a TV monitor, and if necessary, taken on an X-ray film. The film is retracted at the time of see-through, and the film is conveyed to the front of the image intensifier at the time of photographing. Fluoroscopy is performed with a low X-ray dose, and a large dose of X-rays is exposed during imaging. for that reason,
The high voltage generator is controlled by the X-ray controller, and the conditions of the X-ray tube are changed between fluoroscopy and radiography.

Conventionally, the tube voltage setting range is 50 during fluoroscopy.
~ 125KV, tube current setting range is 0.5 ~ 3.0mA
Generally, the user changes the fluoroscope voltage (abbreviated as FKV) according to the subject thickness and the distance between the X-ray tube focus and the image intensifier input surface (abbreviated as SID). To obtain the necessary brightness of the perspective image.
In many cases, the brightness adjustment of the fluoroscopic image is performed by a photomultiplier provided separately for the X-ray output, or by an automatic brightness adjustment system which detects the X-ray output by the image brightness signal and feeds it back to the FKV. Also, S
Generally, the generated X-ray control according to the ID is not performed. And the tube current (abbreviated as FmA) at the time of see-through is FKV
The FKV usually varies within the above range depending on
Since the degree of dependence is small, the fluoroscopic image brightness is almost FK.
It can be said that the control is performed only by V.

[0004]

However, in a conventional image brightness automatic adjustment system at the time of fluoroscopy by feeding back the X-ray output to the FKV, a stable fluoroscopic image in which the exposure dose to the subject may increase can be obtained. There are problems such as not getting.

That is, since the generated X-ray dose control according to the SID is not performed, there is a problem that the subject radiation dose increases when the SID is short, and conversely, when the SID is long, the image is deteriorated due to insufficient X-ray dose. Either or both may occur. That is, the radiation dose of the subject changes depending on the SID, but since this is not taken into consideration, the radiation dose cannot be suppressed below a certain value set in the US FDA standard or the like. Also, FKV is 110K
When the value is higher than V, the contrast of the fluoroscopic image becomes poor and only an image of reduced clinical value can be obtained. Furthermore, since the amount of increase in FmA when FKV rises is small, FKV easily changes greatly with respect to changes in the subject,
Stable fluoroscopic images cannot be obtained.

In view of the above, the present invention has an improved fluoroscopic tube current control circuit that does not increase the exposure dose of the subject even if the SID becomes short and can obtain a stable fluoroscopic image. It is an object to provide a diagnostic device.

[0007]

In order to achieve the above object, according to the present invention, in an X-ray diagnostic apparatus, an SID corresponding signal obtained from a mechanical device supporting an X-ray tube and an image intensifier is provided. , A tube voltage control signal obtained by the tube voltage control circuit is used to obtain a tube current control signal proportional to the tube voltage control signal, and the tube current control signal is limited by the SID corresponding signal. It is characterized in that a tube current control signal is given to the power supply device to control the tube current during fluoroscopy.

[0008]

[Function] The tube current control signal is basically proportional to the tube voltage control signal. Therefore, by increasing the dependency of the tube current control signal on the tube voltage control signal, the tube voltage with respect to the change of the subject during the fluoroscopy. By decreasing the dependence and increasing the dependence on the tube current, it is possible to obtain a stable high-quality fluoroscopic image in which the tube voltage does not easily change during fluoroscopy.

Further, the tube current control signal is basically proportional to the tube voltage control signal, but is limited by the SID corresponding signal. Therefore, an appropriate fluoroscopic X-ray dose according to the SID can be output, and an increase in the subject X-ray dose when the SID is short can be suppressed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an under-tube type C-arm type X-ray diagnostic apparatus to which the present invention is applied, which is held by a C-type arm type holding device 4 with an X-ray tube 1 and an image intensifier 2 facing each other. Has been done. A television camera 3 is connected to the image intensifier 2, and the image signal obtained there is sent to the monitor device 5.

X-ray tube 1 and image intensifier 2
Are held by a C-arm type holding device 4 so that they can be moved forward and backward with respect to each other so that the distance SID therebetween can be changed. This SID is 700 to 1 in this embodiment.
It is possible to change up to 150 mm and the voltage V proportional to this
s is obtained from this C-arm type holding device 4. This X
The subject 10 placed on the examination table 11 is inserted into the space between the line tube 1 and the image intensifier 2.

A high voltage generator 7 supplies a high voltage tube voltage to the X-ray tube 1, and a filament heating circuit 9 supplies a filament heating current to control the tube current. The high voltage generator 7 and the filament heating circuit 9 form a power supply device for the X-ray tube 1.

X-rays are emitted from the X-ray tube 1 and the subject 10
The X-ray fluoroscopic image signal is obtained from the television camera 3 and transmitted to the monitor device 5, and the X-ray fluoroscopic image is displayed on the screen. This image signal is sent to the tube voltage control circuit 6 as a signal representing the brightness of the display image, and the tube voltage control voltage Vv is supplied.
Is obtained. The high voltage generator 7 generates FKV corresponding to this voltage Vv. With such a feedback control system, automatic control of X-ray output is performed so that the brightness of the image is optimized according to the thickness of the subject 10 and the SID.

It should be noted that the output corresponding to the object transmitted X-ray dose input to the tube voltage control circuit 6 is provided so that the X-ray transmitted through the object 10 is separately incident instead of using the image signal as described above. It can also be obtained from a photomultiplier (not shown).

The tube voltage control voltage Vv is also applied to the tube current control circuit 8. This tube current control circuit has the above S
The ID corresponding voltage Vs is also input. The tube current control circuit 8 generates a tube current control voltage Va, which is proportional to Vv but limited by Vs, and supplies it to the filament heating circuit 9. The filament heating circuit 9 controls the tube current (FmA) by flowing a filament current corresponding to a voltage Va given from the outside into the X-ray tube 1.

The tube current control circuit 8 is mainly composed of eight operational amplifiers 81 to 88 as shown in FIG. Vv is input as Vv1, and this Vv1 is a voltage (5V / 100KV) proportional to FKV of 50 to 120 KV as shown in FIG. 3, for example. This V
v1 is input to the operational amplifier 81, and appears as Vv2 as shown in FIG. 4 at the output thereof. That is, the bias voltage is determined by adjusting the variable resistor 91, and the slope is determined by adjusting the variable resistor 92. Further, a bias voltage adjusted by the variable resistor 93 is applied, and the voltage Vv3 shown in FIG. 5 appears at the output of the operational amplifier 82.

On the other hand, the voltage Vs proportional to SID is Vs1.
However, since this is as shown in FIG. 6, the minimum value of SID (700 in this example) as shown in FIG.
mm) becomes zero volt, and is converted into a voltage Vs2 that increases in proportion to an increase in SID. The variable resistor 94 is for adjusting the bias voltage so that the minimum value of SID becomes zero volt.
Reference numeral 5 is for adjusting the inclination.

Further, the voltage determined by the variable resistor 96 is added in the operational amplifier 86, and the voltage Vs3 as shown in FIG. 8 is obtained at the output of the operational amplifier 87.

Operational amplifier 8 generating this voltage Vs3
The output of 7 is connected to the output side of the operational amplifier 83 via the operational amplifier 88 and the diode 89. Since the above-mentioned voltage Vv3 is applied to the input of this operational amplifier 83, when this voltage Vv3 is higher than Vs3, a current is drawn from the output of the operational amplifier 83 through the diode 89 and the operational amplifier 88, The voltage Vv3 is V
It is clamped to s3. Therefore, when Vv3 is lower than Vs3, it is output as Va as it is, but Vv3
Is higher than Vs3, Va is limited to the value of Vs3.

As a result, the control voltage Va output from the tube current control circuit 8 is basically FK as shown in FIG.
It is proportional to V, but limited by SID. The SID is the shortest (700 mm) to the longest (11
It continuously changes up to 50 mm) and is not discontinuous as in FIG. 9, but here representative five points are shown in discontinuous form.

To determine the voltage Vs3 in FIG. 8, a dosimeter is actually placed between the X-ray tube 1 and the image intensifier 2, and the FKV is set as the maximum allowable value (for example, 110 KV). And measure the dose.
Place the dosimeter at the actual subject position (for example, 30 cm in front of the input surface of the image intensifier 2),
The dose rate at that position is 10 R / min (2.58 ×
FmA such that 10 ³ c / kg) is obtained for each SID. The characteristic of the voltage Vs3 shown in FIG. 8 is determined so as to correspond to the FmA characteristic with respect to the SID thus obtained. In other words, this will define the maximum allowed FmA for each SID.

From FIG. 9, when SID is large, FKV
It can be seen that FmA continues to increase in proportion to the increase in F.sub.A, and when the FmA is greater than or equal to the FmA allowed by the SID, FmA saturates even if FKV increases and does not increase and levels off. This Fm
Dependence of A on FKV (proportionality coefficient) is 2 mA / 10
It should be relatively large, about KV.

Therefore, when the subject 10 changes, a stable and good perspective image can be obtained. That is,
When the subject 10 is thick, FKV is increased due to the feedback control by the tube voltage control circuit 6, but
Since FmA also increases in proportion to this, the FKV acts in the direction of being lowered, the rise of FKV is suppressed, and the disadvantage that FKV rises too much and the contrast of the image deteriorates can be avoided. Maximum Fm depending on SID
Since A is automatically limited and the dose rate does not exceed the above value for any SID, excessive X-ray exposure to the subject 10 can be prevented.

On the contrary, for a thin subject 10 such as a human hand or foot, FKV is lowered by the feedback control by the tube voltage control circuit 6, but FKV is proportionally increased.
Since the mA also decreases, the FKV acts in the direction of being increased, and the FKV is prevented from falling too much.

In this way, FK for changes in the subject 10
Since the dependency of V is lowered and the dependency of FmA is relatively increased, FKV does not easily change, and the fluoroscopic image becomes stable.

It is needless to say that the present invention can be applied to various X-ray diagnostic apparatuses other than the C-arm X-ray diagnostic apparatus of the undertube type shown in the figure.

[0027]

As described above, according to the X-ray diagnostic apparatus of the present invention, the tube current during fluoroscopy is basically proportional to the tube voltage and is limited according to the SID. Therefore, it is possible to suppress the increase in the X-ray dose to the subject when the SID is short, and to reduce the tube voltage dependency on the change of the subject during fluoroscopy to increase the tube current dependency, which facilitates the tube voltage during fluoroscopy. It is possible to obtain a stable high-quality transparent image.

[Brief description of drawings]

FIG. 1 is a schematic view of an embodiment of the present invention.

FIG. 2 is a circuit diagram of a tube current control circuit of the same embodiment.

FIG. 3 is a diagram showing a characteristic of a voltage Vv1 in the tube current control circuit.

FIG. 4 is a diagram showing characteristics of voltage Vv2 in the tube current control circuit.

FIG. 5 is a diagram showing characteristics of voltage Vv3 in the tube current control circuit.

FIG. 6 is a diagram showing characteristics of voltage Vs1 in the tube current control circuit.

FIG. 7 is a diagram showing characteristics of voltage Vs2 in the tube current control circuit.

FIG. 8 is a diagram showing characteristics of voltage Vs3 in the tube current control circuit.

FIG. 9 is a diagram showing characteristics of voltage Va in the tube current control circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 X-ray tube 2 Image intensifier 3 Television camera 4 C type arm type holding device 5 Monitor device 6 Tube voltage control circuit 7 High voltage generator 8 Tube current control circuit 9 Filament heating circuit 10 Subject 11 Examination table 81-88 Calculation Amplifier 89 Diode 91-96 Variable resistor

Claims (1)

[Claims] 1. An X-ray tube for irradiating X-rays, an image intensifier into which X-rays transmitted through an object are incident, and a television camera coupled to the image intensifier, and an image signal from the television camera is input to the X-ray tube. A monitor device that displays a fluoroscopic image, a power supply device that applies a high-voltage tube voltage to the X-ray tube and a filament heating current, and a signal that corresponds to the object X-ray transmission output is fed back to the power supply device. A tube voltage control circuit for providing a voltage control signal, a distance signal corresponding to the distance between the X-ray tube focus and the image intensifier input surface, and the tube voltage control signal are input, and are proportional to the tube voltage control signal and An X-ray diagnostic apparatus comprising: a tube current control circuit that generates a tube current control signal limited in accordance with a distance signal and supplies the tube current control signal to the power supply device.