JPH0648800Y2 - X-ray tube current correction circuit - Google Patents

Description

The present invention relates to an X-ray tube current correction circuit for obtaining a desired tube current by correcting a filament current supplied to an X-ray tube.

(Prior Art) Generally, an X-ray tube has an emission characteristic unique to each tube. When a tube voltage to be supplied and a tube current to be supplied are determined, a filament current required to maintain the condition is determined. If the tube voltage and the filament current are determined, the tube current that flows will be inevitably determined. FIG. 2 shows an example of emission characteristics. In the graph of the figure, the filament current is plotted on the horizontal axis and the tube current is plotted on the vertical axis, and the tube voltage is represented as a parameter. In the figure, for example, a tube voltage V _1, by setting the tube current in A _1, the filament current I _s is obtained. This is X
When the tube voltage V ₁ is applied to the wire tube and the filament current _{Is is} passed,
It shows that the tube current A ₁ can be obtained.

However, the curve of the tube voltage V ₁ may be as shown by aa ′ in FIG. 2 due to changes with time of the X-ray tube, changes in the control circuit, etc. In this case, an error occurs, Tube voltage
V _1, the filaments 'so becomes, tube current A point curve a-a _1' current I _s When operating at a tube current A ₁ does not flow through the filament current I _a at the point of intersection in the tube current A ₁ Can't get

For the conventional correction, a predetermined tube voltage as a parameter the tube current - the approximate equation or a table of filament current, based on the error between the measured value and the set value of the tube current, the correction of the filament current value I _s I try to get the value (I _s −I _a ).

(Problems to be solved by the invention) However, the correction value thus obtained is applicable only under the above conditions, that is, the tube voltage V ₁ and the tube current A ₁ , and other conditions such as the tube voltage and the tube current Not applicable for different settings. This is because, as can be seen from FIG. 2, the characteristic curve is not linear, has various functional systems, and is affected by space charges.

Therefore, in the conventional device, the correction is performed under the same condition as the previous correction, but under the other conditions, the correction value obtained last time is not utilized at all and is not corrected.

The present invention has been made in view of the above points, and an object thereof is to make it possible to perform correction in relation to a correction value in the corrected condition even in the case where the correction is not conventionally performed. It is to provide a correction circuit.

(Means for Solving the Problem) The present invention for solving the above-mentioned problems is directed to setting means for respectively setting the tube voltage and tube current of an X-ray tube, and a voltage corresponding to the set tube voltage for X-ray. A high voltage generating means for supplying to the tube, a filament current value necessary to obtain the set tube current under a set tube voltage, and a standard for obtaining a standard tube current with respect to a standard tube voltage. Read from the first storage means, which stores the data of the ratio to the filament current value of the second storage means, the second storage means which stores the standard filament current value, and the first storage means. Calculating means for obtaining a filament current value required to obtain the set tube current value by calculating the ratio data and the standard filament current value data read from the second storage means. Tafu An filament current supply means for supplying a filament current corresponding to the filament current value to the X-ray tube, and a tube current measuring means for measuring the tube current of the X-ray tube and sending the measured value to the calculation means. The calculating means compares the actually measured value of the tube current measured by the tube current measuring means with the set tube current value, and the second measured value is in a direction in which the actually measured value matches the set tube current value. The standard value of the filament current stored in the storage means is updated, while the updated standard value data of the filament current is read from the second storage means and read from the first storage means. It is characterized in that the filament current value is updated by calculating with the ratio data.

(Operation) When the tube voltage and the tube current are set, the calculation means reads the correction value for the standard filament current from the first storage means and the standard filament current value from the second storage means to perform the calculation. The filament current is supplied to the X-ray tube together with the set tube voltage. The tube current under the above conditions is measured and fed back to the calculating means, and if there is an error with the set value of the tube current, the contents of the second storage means are corrected, and the same procedure is repeated to set the tube current. A tube current having a current value is stably obtained.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of a circuit according to an embodiment of the present invention.
In the figure, 1 is a tube voltage setting device for setting a tube voltage applied to the X-ray tube 2, and 3 is a tube current setting device for setting a tube current to be passed through the X-ray tube 2. Reference numeral 4 is a high voltage generating circuit for generating a high voltage equal to the tube voltage set in the tube voltage setting device 1, and supplies an anode voltage to the X-ray tube 2. 5 is the standard filament current value for obtaining the tube current A ₁ at the tube voltage V ₁ which is the standard value, and the filament current value for obtaining each tube current at different tube voltages, V ₂ , V ₃ , ... Is stored in the first memory, and reference numeral 6 is a second memory in which a standard filament current value for obtaining the tube current A ₁ at the tube voltage V ₁ is recorded. When the tube voltage is set in the tube voltage setting device 1 and the tube current is set in the tube current setting device 7, the data 7 reads the data of the filament current ratio stored in the first memory 5, and the second memory 6 An arithmetic circuit that reads the standard filament current value from and outputs the corrected filament current value. The corrected filament current value data of the output is converted into an analog signal by the DA converter 8, It is input to the current control circuit 9. The filament current control circuit 9 supplies the filament current to the X-ray tube 2 based on the input data. Reference numeral 10 is a tube current measuring device for measuring the tube current flowing in the X-ray tube 2 and feeding it back to the arithmetic circuit 7. The output signal thereof is converted into a digital signal in the AD converter 11.

Next, the operation of the circuit of the embodiment configured as described above will be described. As shown in the graph of FIG. 3, the contents stored in the first memory 5 are standard filament currents at standard tube voltage V ₁ and standard tube current A ₁ that are excluded from filament currents under different tube voltage and tube current conditions. It is the value of the ratio. Specifically, a ratio obtained by dividing the filament current value under other conditions by the filament current I ₁₁ corresponding to the tube voltage V _{1 and the} tube current A ₁ as shown in FIG. 4 is stored. In this table, tube voltage
The filament current at V _m and the tube current V _n is represented by I _mn . The second memory 6 stores the filament current I ₁₁ at the standard tube voltage V ₁ and the standard tube current A ₁ .

The operation when the tube voltage is set in the tube voltage setting device 1 and the tube current is set in the tube current setting device 3 will be described. Setting value is V ₁ ,
Assuming that it is A ₂ , the arithmetic circuit 7 outputs from the second memory 6 I
₁₁ is read out, the value of the first memory I ₁₂ / I ₁₁ is read out, both are multiplied to calculate I ₁₂ , and output to the filament current control circuit 9 via the DA converter 8. The filament current control circuit 9 controls the filament current circuit so that the filament current of the X-ray tube 2 becomes I ₁₂ . Under this condition, the tube current measuring device 10 measures the tube current of the X-ray tube 2, and the AD converter
It feeds back to the arithmetic circuit 7 via 11.

At this time, if the emission characteristic changes due to the aging of the X-ray tube 2 and the characteristic is V ₁ ′ shown by the broken line in FIG. 5, the tube current measured by the tube current measuring device 10 is A ₂ ′. Has changed to. Therefore, in order to obtain the desired tube current A ₂ , A ₂ and V ₁ ′
I ₁₂ ′ filament current at the intersection of must be applied. The arithmetic circuit 7 is the fourth memory stored in the first memory 5.
The standard filament current stored in the second memory 6 is corrected by calculating from the relationship in the figure and the tube current A ₂ ′. A ₂ ′>
In the case of A ₁₂ , I ₁₁ in the second memory 6 is reduced to A ₂ ′ <A ₁₂
In the case of, the contents of the second memory 6 are updated so as to increase the value of I ₁₁ . With this updated I ₁₁ ′, the arithmetic circuit 7
Newly calculates I ₁₂ ″, and the filament current control circuit 9
Output to. Next, the tube current measuring device 10 measures the tube current and feeds it back to the arithmetic circuit 7. By repeating this operation, the standard filament current set value stored in the second memory 6 is corrected so that the tube current does not change as the X-ray tube 2 changes over time. At this time, the tube voltage,
Even if the setting of the tube current changes, it can be corrected within the range of changes in the shape of the emission curve over time, etc. Therefore, set the tube voltage value and the tube current value that have not been used for a while, and Even if operated, no large error occurs.

As described above, according to the circuit of the present embodiment, the X-ray tube can be operated with the set tube voltage and tube current, and as described above, the tube voltage and tube current that have not been used for a while can be set. However, the set tube current can be obtained in a stable state.

The present invention is not limited to the above embodiment. The first memory is an example in which a table of the ratio of the filament current to the standard filament current at different tube voltages and tube currents is stored. However, an approximate expression of the emission characteristic or an expression as a function is stored. You may stay. In this case, the filament current value to be set next can be derived by calculation from the error between the setting of the tube current and the actual tube current.

(Effect of the Invention) As described in detail above, the present invention measures the tube current value of the X-ray tube and stores it in the second memory so that the measured value matches the set tube current value. The standard value of the filament current is increased / decreased, the filament current value is updated accordingly, and this operation is continued to correct the tube current value of the X-ray tube.

By adopting this new method, it becomes possible to always obtain a stable tube current even when X-rays are generated by a tube voltage and a tube current that have never been used up to now, and the practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of a circuit of an embodiment of the present invention, FIG. 2 is a diagram of emission characteristics of an X-ray tube, and FIG. 3 is an emission showing a relation between several tube voltages, tube currents and filament currents. FIG. 4 is a characteristic diagram, FIG. 4 is a diagram of data written in the first memory, and FIG. 5 is an explanatory diagram of influences due to changes with time of emission characteristics. 1 ... Tube voltage setting device, 2 ... X-ray tube 3 ... Tube current setting device, 4 ... High voltage generation circuit 5 ... First memory, 6 ... Second memory 7 ... Arithmetic circuit 9 ... Filament Current control circuit 10 ... Tube current measuring device

Claims (1)

[Scope of utility model registration request] 1. A setting means for respectively setting a tube voltage and a tube current of an X-ray tube, a high voltage generating means for supplying a voltage corresponding to the set tube voltage to the X-ray tube, and a set tube. The data of the ratio between the filament current value required to obtain the set tube current under a voltage and the standard filament current value to obtain the standard tube current with respect to the standard tube voltage is stored. First storage means, second storage means for storing the standard filament current value, the ratio data read from the first storage means, and read from the second storage means Calculating means for obtaining the filament current value necessary to obtain the set tube current value by the operation with the standard filament current value data thus obtained, and the filament current corresponding to the obtained filament current value. A filament current supply means for supplying the X-ray tube, and a tube current measuring means for measuring the tube current of the X-ray tube and sending the measured value to the calculating means, wherein the calculating means is the tube current measuring means. The filament current stored in the second storage means is compared with the actually measured value of the tube current measured by the above-mentioned set tube current value, and in the direction in which the actually measured value coincides with the set tube current value. The standard value of the current is updated, while the updated standard value data of the filament current is read from the second storage means, and is calculated with the ratio data read from the first storage means to calculate the filament. An X-ray tube current correction circuit characterized by updating the current value.