JPS5922719Y2 - mAs measurement circuit in 3-phase X-ray equipment - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an mAs measurement circuit that measures the product mAs of the X-ray tube current mA and the imaging time S in a three-phase X-ray apparatus.

Generally, in medical X-ray apparatuses, tube voltage, tube current, and imaging time are important requirements for X-ray generation.

Of these, the tube current and imaging time are generally displayed as a product of these two.

In other words, mAs as tube current (mA) x imaging time (S)
Displayed as a value.

The mAs measurement circuit for measuring the mAs value detects the tube current during energization of the X-ray tube, and stores it in a condenser as an electric charge.

The first example of this invention is a configuration of a conventional device of this type.
This will be explained using the block diagram shown in the figure.

Note that the part surrounded by the dashed line in Fig. 1 was newly added based on this invention.

In the figure, 1 is a tube current detection resistor whose both terminals a-1)
As is well known, is connected to the X-ray tube current circuit, that is, to the secondary winding neutral point of a high voltage transformer (not shown).

When the X-ray tube is energized, tube current mA flows through the tube current detection resistor 1, and a voltage proportional to it is induced across the resistor 1, which is connected in parallel to the tube voltage detection resistor 1. Integral capacitor 3 is charged.

The charge in this integrating capacitor 3 is transferred to an operational amplifier 4,
It is held in a hold capacitor 6 via a rectifier 5.

Therefore, since the charge charged in the integrating capacitor 3 is proportional to the product of the tube current mA and the time S during which it flows, that is, the amount of electricity mAs, an mAs indicator 7 is connected to both ends of the holding capacitor 6. By doing this, a charge proportional to the amount of electricity supplied to the integrating capacitor 3,
That is, the mAs value can be detected or measured.

In the figure, 2 is a charging resistor, and 8 is a reset switch for discharging the charge of the holding capacitor 7.

As is clear from the above configuration, the conventional mAs measurement circuit has an integrating capacitor 3 connected in parallel to the tube current detection resistor 1 connected to the tube current circuit. When a three-phase tube voltage with a waveform shown in is supplied, the tube voltage is applied and then cut off at t.

The integrating capacitor 3 is charged with the tube current for the entire energization time up to -13, and as a result, the tube current waveform t shown in FIG.

The amount of electricity supplied during the entire energization time up to -13 is stored as a charge.

However, in a three-phase X-ray device, the imaging time is t, during which tube voltage is applied to the X-ray tube.

For example, JISZ 470 rather than the total energization time of ~t3
2, the energization time t1 to t2 is 87% or more of the maximum value of the tube voltage (kVp), and t in FIG.

~t1. t2 to t3 are not included in the photographing time.

From this, the mAs measuring circuit of a three-phase X-ray device can detect or measure the amount of electricity, that is, mAs, during the energization time at a predetermined value (for example, 87%) or more of the maximum value of the tube voltage (kVp). It is necessary that the mAs set by the operator match the mAs set by the operator.

As mentioned above, in the conventional mAs measurement circuit of this type, a tube voltage is applied to the X-ray tube.

-Since the structure is such that the integrating capacitor is charged with the tube current flowing during the entire energization time of t3, the mAs measured by this circuit is specified by the three-phase X-ray device as described above. Unlike the shooting time, mA at this shooting time
s, and the error between the two becomes larger as the short-time imaging region becomes longer.

Furthermore, the mAs set by the operator at the time of imaging is the amount of electricity during the imaging time over a predetermined value (for example, 87%) of the maximum (peak) value of the tube voltage defined as above. An error occurs between the measured mAs and the mAs display value measured and displayed by the mAs measurement circuit, and this error becomes larger as the time range increases.

(As is clear from FIG. 2, the mAs measured by the mAs measuring circuit always indicates a larger value than the mAs set by the operator.

) Therefore, the mA measured and displayed by the mAs measuring circuit
s is the amount of electricity m for the imaging time specified for the three-phase X-ray device
It is necessary to correct As, and currently this correction is performed by the operator using the correction table shown in FIG.

In particular, recently, the demand for short-time imaging has increased, and methods have been adopted to cut off the primary side of high-voltage generators using control thyristors, so the above-mentioned errors can no longer be ignored in conventional mAs measurement circuits in the short-time range. It's coming.

In consideration of the above, this idea was developed to allow the tube current to flow through the integrating capacitor only for a specified imaging time, and by charging it, it was possible to measure the amount of electricity mAs during that time.
The present invention attempts to provide a mAs measurement circuit for a phase X-ray device.

In other words, this device installed a gate circuit in front of the integrating capacitor, and controlled this gate so that instead of integrating the entire amount of tube current, only the tube current flowing only for a set period was integrated as the mAs value. It is.

Next, this invention will be explained with reference to the embodiment shown in FIG.

In FIG. 1, since 1 to 8 have already been explained when explaining the configuration of the conventional mAs measurement circuit, the configuration of the part surrounded by the dashed-dotted line added according to this invention will be explained.

9 is a switching transistor (gate) for transmitting the detection voltage detected by the tube current detection resistor 1 to the integrating capacitor 3; the collector is connected to one end a of the resistor 1, and the emitter is connected to the charging resistor 2. .

10.11 is 0N-OF of switching transistor 9
The base of the transistor 9 is connected to the anode of the thyristor 10 and the collector of the OFF transistor 11.

In the mAs measurement circuit having the above configuration, when the X-ray tube (not shown) is energized and the tube voltage shown in FIG. 2a is applied, the tube current with the waveform shown in FIG. flows through A]).

Therefore, a voltage proportional to the tube current is induced across the resistor 1.

At this time, the switching transistor 9 is the thyristor 10
Since it is non-conductive, it is in an OFF state, and therefore, the integrating capacitor 3 is not charged by the tube current flowing through the resistor 1.

On the other hand, in a three-phase X-ray device, in order to prevent the generation of surge voltage when the power is turned on and to ensure the safety of the device, a single-phase voltage is initially applied to the X-ray tube when the power is turned on, and a predetermined period of time is applied. A so-called two-stage closing method is used in which a predetermined three-phase voltage is then applied.

Therefore, the time t in FIG. 2 is determined by the X-ray exposure start signal.

The first stage is turned on at time t1, a single-phase voltage is applied to the X-ray tube, and a little later (60 degrees in electrical angle) is reached at time t1.
Then, the second stage is turned on and a predetermined three-phase voltage is applied.

At this time, the time point t1 when the second stage of power supply is turned on is exactly as shown in Fig. 2a.
This coincides with the point t1 at which the tube voltage reaches 87% of the peak value e shown in FIG.

Therefore, if the second stage closing signal or an electric signal synchronized therewith is applied as the gate signal to the thyristor 10, the thyristor 10
%, the ONL and then the switching transistor 2 turn ON, and the integrating capacitor 3 starts to integrate (charge) in proportion to the voltage across the tube current detection resistor 1. At the same time, the operational amplifier 4 and the rectifier 5 The holding capacitor 6 is also charged with electric charge via the holding capacitor 6.

The signal indicating the end of the imaging time is generated by the timer when timer imaging is used, or by the automatic exposure control section when using the automatic exposure mechanism, and interrupts the high voltage circuit of the X-ray apparatus.

(Time t2 in FIG. 2). If the configuration is such that this photographing end signal is applied to the base of the transistor 11, at the time t2 when the photographing ends, the transistor 11 or ONj
As a result, the switching transistor 2 is turned off, and the integration of the integrating capacitor 3 immediately stops, and the tube current after t2 is no longer integrated.

In this way, the integrating capacitor is charged only in the shaded area (between 11 and t2) of the tube current waveform in FIG. 2, and the other portions (to-tl) and (t2-t3) are not charged.

Further, this period almost coincides with a region of 87% or more of the peak of the tube voltage waveform.

Therefore, the operator of the X-ray apparatus can read the mAs value that almost matches the set mA and time on the display 7, and
There is no need to perform correction using a correction table as shown in the figure.

Furthermore, it is expected that the relationship between the mAs of the display and the degree of blackening of the photographed photograph will become clearer.

Furthermore, accurate measurement or display of mAs is possible even in an X-ray device that controls X-ray exposure on the primary side of a high-voltage transformer, as is usually done in three-phase X-ray devices.

In the above embodiment, a signal at a certain time delay from the start signal for high voltage application is applied to the gate of the thyristor 10 as the start signal for integration, but the region of 87% or more of the tube voltage peak value is It is also possible to detect this and use the detected signal as the gate signal for the thyristor 10.

As detailed above, mA in the three-phase X-ray apparatus of this invention
The s measurement circuit can measure mAs values that match the set mA and rubbing time, so there is no need for correction when reading, and it is useful for extremely short-time shooting, automatic exposure mechanisms, primary side cutoff of high voltage equipment, etc. Regardless of the imaging time, the correct mAs for the imaging time specified in the three-phase X-ray apparatus can be measured and displayed, and the mAs display value matches the mAs set by the operator.

Therefore, labor savings can be expected for the operator as well.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing the configuration of an embodiment of this invention;
Figures a and l) are waveform diagrams of the tube voltage and tube current of the three-phase X-ray device, respectively, and Figure 3 shows the correction coefficient of the mAs meter. 1: Tube current detection resistor, 2: Charging resistor, 3: Integrating capacitor, 4: Operational amplifier, 5: Rectifier, 6: Holding capacitor, 8: mA3 display, 9 Niswitching transistor (gate), 10 A thyristor for turning ON the Niswitching transistor 9, and a transistor for turning OFF the Niswitching transistor 9.

Claims (1)

[Scope of utility model registration request] A tube current detection resistor is connected to the tube current circuit of a three-phase X-ray device, and an integrating capacitor is connected in parallel with this resistor, and the electrical connection between the resistor and the integrating capacitor is controlled. 1. An mAs measurement circuit for a three-phase X-ray apparatus, characterized in that it is provided with a gate for detecting mAs.