JPS5942959B2 - X-ray diagnostic equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an improved X-ray tube filament heating circuit.
The present invention relates to a radiation diagnostic device.

Computer tomography (C
computer 1zed tomography;
There is a computer-operated X-ray tomography apparatus called a CT apparatus (hereinafter abbreviated as CT apparatus).

This CT device moves an X-ray tube and an X-ray detector facing each other along the tomographic plane ζ of the subject in the same direction and at the same speed, and each time they move, the angle with respect to the tomographic plane changes. This is repeated again, and thereafter the angle is sequentially changed to collect X-ray absorption rate data for various angles of the tomographic plane of the subject.

After collecting sufficient data, this data is analyzed by a computer, the X-ray absorption rate of each position on the tomographic plane is calculated, and the tomographic plane is reconstructed at a gradation level corresponding to the absorption rate of 0. With this system, the composition of each part of the tomographic plane can be analyzed in as many as 2,000 gradations, making it possible to obtain clear tomographic images of everything from soft tissues to hard tissues.

In such a CT device, the detection of X-ray absorption rate is the basis of everything, so this detection must be performed with high precision, but a prerequisite for this is that X-rays with an extremely stable output dose must be irradiated. No.

By the way, in order to output a stable dose of X-rays, it is necessary to stabilize the tube current of the X-ray tube, which contributes to changes in the dose, but this X-ray tube current is a function of the tube voltage and filament current. It also depends on the temperature of the X-ray tube, and the X-ray tube current decreases as the temperature increases.

Figure 1 shows an example of the characteristics of the tube current when the tube voltage and filament current are constant.As the X-ray tube heats up over time, the tube current decreases over time. I'm going to go.

Figure 1a shows the case of continuous exposure, Figure 1b shows the case of palace
The case of radiation exposure is shown, and the decreasing tendency of the tube current is very similar in both cases.

As mentioned earlier, the x-ray tube current is a function of the tube voltage and filament current, and is dependent on the x-ray tube temperature.

That is, if the tube voltage is constant, the X-ray tube current will increase or decrease due to changes in the filament current, and if the tube voltage and filament current are constant, it will depend on the temperature, which increases over time. It is related to the anode heat capacity of the wire tube (Heat-Unit) (hereinafter abbreviated as H and U).

Here, H and C are a measure of the capacity of the X-ray tube, and since the anode temperature cannot be directly measured, the product of the respective conditions when X-ray irradiation is used to calculate the temperature ζ As a guide, the maximum allowable value of the product for each X-ray tube is H, U.
When using an X-ray tube, the H
, U should not be exceeded.

In other words, an X-ray tube emits X-rays by heating a filament to emit thermoelectrons, which collide with a point on the anode (this point is called the focal point). The collision generates heat, the temperature rises, and when X-rays are continuously emitted, the material eventually melts.

The allowable limit before this melting occurs is the capacity of the X-ray tube, which is determined by H and U.

Therefore, H and U are expressed as the product of the tube voltage, the X-ray tube current, and the time during which they are applied, and the integrated H and U are expressed by multiplying them by the exposure.

Therefore, it is possible to replace the tube voltage, tube current, time and number of applications applied to the X-ray tube with the integrated values H and U, and estimate the temperature of the X-ray tube from the integrated values H and U. By correcting the filament current by an amount that compensates for the corresponding decrease in the X-ray tube current, it becomes possible to maintain the X-ray dose constant.

The present invention has been made in view of the above circumstances, and calculates and integrates the loads H and U given to the X-ray tube, and corrects the amount of cooling of the X-ray tube during the period when X-ray exposure is stopped. By knowing the tube temperature and correcting the filament current by outputting a filament current correction signal that compensates for the decrease in the X-ray tube current at that temperature, it is possible to always maintain a constant X-ray dose.
An object of the present invention is to provide an X-ray diagnostic device capable of emitting radiation.

An embodiment of the present invention will be described below with reference to FIG.

FIG. 2 is a block diagram of the filament current correction device according to the present invention. In the figure, 1 is used to set the tube voltage and X-ray tube current to be applied to the X-ray tube, their application time, etc., and to give an X-ray exposure command. The X-ray controller 2 outputs the control output according to the set conditions for each time, and 2 is the above-mentioned 3 output from the X-ray controller 1.
3 is an exposure number command circuit that instructs the number of pulsed X-ray irradiations required to collect data per tomographic plane of the CT device; It outputs an exposure command and operates until a predetermined number of exposures is reached.

Reference numeral 4 denotes an integration circuit that integrates the calculated values of the calculation circuit 2 in response to the command signal from the exposure number command circuit 3. Reference numeral 5 denotes a timer circuit that measures the pause time of X-ray exposure and starts timing when the XM emission stops. When the exposure starts, it returns to zero.

Reference numeral 6 denotes a cooling equivalent correction circuit which performs correction by subtracting the temperature drop of the X-ray tube cooled during the downtime from the integrated value of the integration circuit 4 based on the downtime measured by the timer circuit 5; is intended to be used after receiving from the X-ray controller 1 controls regarding condition settings such as tube voltage, X-ray tube current, and application time; wholesale output signal and correction output signal from the cooling equivalent correction circuit 6. Determine the X-ray dose rate obtained by the X-ray setting conditions, and determine the X-ray dose rate required to maintain this dose rate.
8 is a filament current correction circuit that receives the output signal from the correction circuit 7 and outputs a filament current correction output signal in response to the output signal; be.

Reference numeral 9 denotes a CT apparatus main body which provides command signals such as tube voltage, tube current, exposure time, and an X-ray exposure start signal to the X-ray controller 1.

Note that 10 is an X-ray tube, 11 is a filament transformer, and 12 is a high pressure generator.

Next, the operation of this apparatus having the above configuration will be explained.

The X-ray tube 10 emits X-rays under the conditions set in the X-ray controller 1.

Now, when the CT apparatus main body 9 generates an exposure start signal, the X-ray controller 1 outputs control output signals of the set tube voltage, X-ray tube current, and application time, and applies the voltage to the X-ray tube 10 according to the set conditions. ,
Apply current for a set time.

At that time, these control output signals are also sent to the calculation circuit 2 and the X-ray condition setting correction circuit 7, and the calculation circuit 2
H and U applied to the X-ray tube 10 are calculated by multiplying by the setting condition values.

These H and U calculated values are sent to the integration circuit 4.

The integrating circuit 4 receives the command signal from the irradiation circuit number command circuit 3 every time X-ray irradiation is performed, and calculates the H calculated by the calculation circuit 2.
, integrate the U value.

Therefore, the integrated value of the integrating circuit 4 represents the integrated values H and U from the start of the exposure applied to the X-ray tube 10 to the present.

On the other hand, the temperature of the X-ray tube 10 increases only while it is irradiating, and when irradiation is performed intermittently, such as with pulsed X-rays, the temperature increases due to the cooling effect during the pause period. Since the temperature decreases, it is necessary to correct the allowable range of the X-ray tube current due to this temperature decrease.

Therefore, the time value measured by the timer circuit 5 that measures the pause time of X-ray irradiation is given to the cooling equivalent correction circuit 6, which derives the value equivalent to the temperature cooled during the pause time. The integrated value of the integration circuit 4 is received and corrected by subtracting the amount equivalent to the temperature to be cooled from this integrated value.

Therefore, the output signal from the cooling equivalent correction circuit 6 indicates the integrated values H and U corresponding to the current temperature of the X-ray tube.

The output signal of the cooling equivalent correction circuit 6 is applied to the X-ray setting condition correction circuit 7.

On the other hand, the X-ray setting condition correction circuit 7 is supplied with a control output signal from the X-ray controller 1 that instructs each setting condition of tube voltage, X-ray tube current, and application time, and this X-ray setting condition correction circuit The circuit T maintains the target X-ray tube current value according to the setting conditions of the X-ray controller 1 based on the output signal from the cooling equivalent correction circuit 6, and guides the necessary decrease in the X-ray tube current value. Pull it out.

Then, the value derived by the X-ray setting condition correction circuit 7 is given to the filament current correction circuit 8.

Then, this filament current correction circuit 8
Based on the decrease in the X-ray tube current value from the line setting condition correction circuit 7, the filament current value required to compensate for this decrease is derived.

Therefore, if the filament current of the X-ray tube 10 is corrected by an amount corresponding to this derived value, the X-ray tube 1o will always be able to obtain X-rays at the set dose rate, allowing highly accurate reproduction. It becomes possible to obtain a configuration image.

In this way, according to the present invention, the integral H given to the X-ray tube,
In addition to calculating the U value, H and U corresponding to the temperature of the X-ray tube cooled during the X-ray exposure suspension period are subtracted from the integrated H and U values to correspond to the temperature of the X-ray tube at the current time ζ. H, U
By knowing the value and correcting the decrease in the X-ray tube current that is insufficient to obtain the target dose rate of the X-ray tube at these H and U values, the filament current is increased by that value. Since the insufficient dose weight is compensated for by filament current correction and the target dose rate is obtained, the dose rate is extremely stable. Therefore, data can be collected with high precision, making it possible to obtain accurate data. An excellent CT device that can obtain reconstructed images can be obtained.

[Brief explanation of the drawing]

FIGS. 1a and 1b are characteristic diagrams showing how the X-ray tube current decreases due to heating of the X-ray tube, and FIG. 2 is a block diagram showing an embodiment of the present invention. 1... X-ray controller, 2... Calculation circuit,
3... Exposure frequency command circuit, 4... Integration circuit, 5... Timing circuit, 6... Cooling equivalent correction circuit, 7... ...Correction circuit, 8...
- Filament current correction circuit, 9...CT device main body, 10...X-ray tube, 11...Filament transformer.

Claims (1)

[Claims] 1. A circuit for calculating a heat unit value of ζ applied to the X-ray tube, a circuit for integrating this heat unit value for each X-ray exposure, and a circuit for calculating the heat unit value ζ applied to the X-ray tube, a circuit that derives a heat unit value corresponding to a temperature drop in the X-ray tube and corrects the derived heat unit value by subtracting it from the integrated heat unit value; and the heat unit corrected by this circuit. A circuit for determining the amount of decrease in the X-ray tube current that is insufficient to obtain the target dose rate of the X-ray tube in the value, and a filament of the X-ray tube by the amount necessary to capture the decrease determined by this circuit. An X-ray diagnostic device comprising a circuit for correcting current.