JPS6127099A - X-ray high voltage system - Google Patents

Abstract

PURPOSE:To keep proportional relation of actual X-ray dosage with the specified tube current to obtain desired X-ray dosage by measuring charge current to the capacitance of a high voltage cable, and correcting the specified tube current based on the measured value. CONSTITUTION:Filament heating current of an X-ray tube 4 is limited to small current so as not to supply current from an anode to a cathode. Only charging current to the cable capacitance is measured based on the measured value obtained in a tube current detector 11 with tube voltage changed. The charge current to each tube voltage is stored in a memory 14 of a micro computer 6. When tube voltage KV and tube current mAs are set by an X-ray condition setting unit 5 and X-ray is irradiated, charge current corresponding to the setting tube voltage is obtained by interpolation, and the tube current is controlled by adding the charge current to the setting tube voltage. Thereby, error of the tube current caused by the charge current to the high voltage cable capacitance is corrected.

Description

[Detailed description of the invention] (b) Industrial application fields This invention relates to improvements in X-ray high voltage equipment.

(b) In the conventional X-ray high-voltage apparatus, the high-voltage generator and the X-ray tube are connected by a high-voltage cable, but there is a capacitance between this high-voltage cable and the ground. Therefore, when applying high voltage from a high voltage generator to an X-ray tube via a high-voltage cable, in addition to the tube current flowing through the X-ray tube, the current required to charge the capacitance of this high-voltage cable is , it will be necessary to run it from a high voltage generator.

That is, in a normal X-ray high voltage device, the tube current is measured at the neutral point of the high voltage generator, but this measured current value also includes the charging current of the cable capacitance. This means that in a device that cuts off X-rays when the actually measured tube current amount (tube current x time) matches the set tube current amount, the shorter the exposure time, the more the actual tube current value The ratio of the cable capacity charging current to the cable capacity increases,
This means that the proportional relationship between the measured tube current amount, that is, the set tube current amount, and the X-ray dose deviates.

This will be explained in detail using FIG. FIG. 4A shows the tube voltage waveform, and FIG. 4B shows the tube current waveform. Generally, measurement of the X-ray exposure time is started from the time when the tube voltage reaches 87% of the set value. However, at this point, as shown by the shaded area in Figure 4B, there is still a charging current remaining for the capacitance of the high voltage cable, and the measured value of tube current will include this charging current. , extra current that does not contribute to X-ray exposure will also be measured as tube current. Therefore, if the X-rays are cut off when the actual amount of tube current matches the set value, the cutoff will occur before the desired amount of X-rays can be obtained.

Note that after the X-rays are cut off, the charge in the high-voltage cable becomes
Since the discharge occurs through the ray tube, the amount of tube current flowing through the X-ray tube can be obtained close to the set value, but after the X-rays are shut off, the tube voltage drops sharply, and even if the discharge current flows, there is no dose effect. However, the amount of X-rays is small and the desired X-ray dose cannot be obtained. This is because the dose effect of tube voltage is usually said to be the third to fourth power.

In this way, due to the charging current relative to the capacity of the high-voltage cable, errors are unavoidable in the measurement of the tube current when the tube voltage rises, so the proportional relationship between the X-ray dose and the tube current amount is greatly deviated, especially for a short period of time. The more the charge current amount accounts for the tube current amount, the more the inconvenience that the dose becomes less than the desired dose becomes significant.

(c) Purpose This invention aims to establish a proportional relationship between the actual X-ray dose and the set tube current amount, despite the inevitable error in the tube current measurement value caused by the charging current for the capacitance of the high-voltage cable. Improved X-rays to maintain the desired X-ray dose
The purpose is to provide line high voltage equipment.

(D) Structure In the X-ray high-voltage device according to the present invention, the amount of charging current for the capacitance of the high-voltage cable is measured in advance, this is memorized, and the above-mentioned amount of charging current is stored when the amount of tube current is set. By having a microcomputer or the like perform calculations based on the measured values of , the tube current is controlled by correcting errors caused by the cable charging current in the amount of tube current measured during X-ray irradiation.

(E) Example In FIG. 1, a high voltage is applied to the X-ray tube 4 from the secondary winding of the three-phase high voltage transformer 1 via the rectifier 2.2 and the tetrode tube 3.3, and tube current is supplied. Ru. This tetrode tube 3.3 and the X-ray tube 4 are connected by a high voltage cable. The tube voltage KV and tube current amount mA are set in the X-ray condition setting device 5.
When s (tube current tetrode tube 3.3 is turned on or off. In this way, the X-ray radiation from the X-ray tube 4 is turned off. Tube voltage is resistance 9.9
The tube current is also detected by the tube current detector 11, digitized via the A/D converter 12, and sent to the microcomputer 6. It is sent to computer 6. The microcomputer 6 is equipped with a CPU 13 and a memory 14, and performs calculation and storage functions.

First, prior to actual X-ray exposure, the amount of charging current with respect to the capacitance in the high voltage cable is measured. The amount of charging current depends only on the applied voltage. Therefore, X-ray tube 4
The filament heating current in the X-ray tube 4 is a current with little carburization (for example,
(approximately 2 A), and only the amount of charging current of the cable capacity is measured based on the measurement value obtained from the tube current detector 11 while varying the tube voltage. For example, while outputting an X-ray exposure signal intermittently at certain intervals as shown in Figure 2A, the voltage is varied such that the peak value of the tube voltage increases by, say, 10 KV (Figure 2B). let At this time, the tube current detector II detects the tube current (m A
) waveform can be measured, so from now on, the amount of tube current (tube current x
time), that is, the amount of charging current for each tube voltage is determined.

In this way, as shown in FIG. 3, a plot of the amount of charging current against the tube voltage is obtained, and by drawing a line connecting these plots, a supplementary booklet between the plots can be created. The measured value of the amount of charging current for each tube voltage is stored in the memory 14 of the microcomputer 6, and the above interpolation calculation is performed by the CPU 13.

After that, the tube voltage KV and tube current amount mA are set using the X-ray condition setting device 5.
When actually performing X-ray exposure with s set, the charging current amount corresponding to the set tube voltage is determined by interpolation, and the tube current is calculated by adding this charging current amount to the set tube current amount. Amount control is performed. That is, X-ray exposure is performed until the integral value of the tube current measured by the tube current detector 11 after the start of X-ray exposure reaches the tube current amount corrected by adding the charging current amount to the set tube current amount. The X-rays are blocked when they arrive. Therefore, the error factors caused by the cable capacitance charging current are corrected and the tube current amount is controlled.
The correspondence relationship between the set tube current amount and the actually irradiated X-ray dose is maintained, and the desired X-ray dose can be obtained.

Although a tetrode tube is used in the above embodiment, it goes without saying that the present invention can also be applied to an X-ray high-voltage device that uses an inverter system and is capable of short-time irradiation.

(F) Effect This invention can control the amount of tube current by correcting the error in the tube current measurement value that is unavoidable due to the charging current for the capacitance of the high-voltage cable. The correspondence relationship with the actually irradiated X-ray dose is maintained, and the desired X-ray dose can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a time chart for explaining the operation, Fig. 3 is a graph showing the relationship between the amount of charging current and the tube voltage, and Fig. 4 is X-ray exposure. 3 is a time chart showing a tube voltage waveform and a measured tube current waveform at the time of the test. 1... Three-phase high voltage transformer 2... Rectifier 3... Tetrode tube 4... X-ray tube 5... X-ray condition setting device 6... Microcomputer 7... Grid controller 8 ... Grid voltage generator 9 ... Tube voltage detection resistor 10.12 ... A/D converter 11 ... Tube current detector 13 ... CPU 14 ...
·memory

Claims (1)

[Claims] (1) In an X-ray high-voltage device that supplies tube current from a high-voltage generator to an X-ray tube via a high-voltage cable, the charging current for the capacitance of the high-voltage cable is measured in advance, and based on this measured value, An X-ray high voltage apparatus characterized in that the tube current is controlled by correcting a set amount of tube current.