JPH029438B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic exposure compensation circuit in a panoramic X-ray imaging apparatus, particularly in a dental diagnostic X-ray imaging apparatus.

The quality of an X-ray photograph obtained with an X-ray photographing device is determined by the individual characteristics of the person to be photographed and the balance between the tube current and tube voltage of the X-ray tube, and the degree of darkening on the X-ray photograph side. (concentration ratio). In particular, with X-ray imaging equipment used for panoramic imaging in dental diagnosis, the amount of X-rays that reach the film varies depending on the differences between adults and children, gender, or even the front teeth and small/molar areas of the same subject. Changes occur;
Even if good contrast is obtained at one point on the film, the degree of blackening may deviate significantly from the optimum value at other parts, making it impossible to obtain good contrast.
To solve this problem, the automatic exposure mechanism usually detects the remaining amount of X-rays transmitted through the subject and the X-ray film, and feeds back this information to control the tube voltage or tube current of the X-ray tube. .

By the way, the sensor that detects the amount of transmitted X-rays during this X-ray photography scans the lower side of the eye of the person to be photographed.
This is because it is naturally expected that a metal crown as a prosthesis is attached to the tooth in the dental arch, and this is to prevent the sensor's detected value of transmitted X-rays from changing significantly due to the presence of the metal crown. It is. FIG. 1a shows a standard pattern of this sensor output signal waveform. However, some subjects may have a natural bone defect in the area corresponding to the sensor, or may have a prosthetic metal prosthesis as a result of treatment for a traffic accident, etc. When applied to a special part, the sensor output changes rapidly as shown in arrows A and B in Figure 1 b (state affected by bone defect) and Figure 1 c (state affected by metal attachment), respectively. Excessive feedback control is applied, and the image on the film becomes either extremely pale (bone defect) or extremely dark (metal attachment), and in either case cannot be used for diagnosis. Therefore, for patients with bone defects or metal attachments, it is necessary to switch to manual imaging.

Therefore, it is an object of the present invention to prevent excessive feedback control for people with bone defects or metal attachments, and even for people with special bone structures (for example, people with particularly large faces). An object of the present invention is to provide an automatic exposure compensation circuit capable of equally automatic photographing.

That is, the present invention detects the remaining amount of X-rays transmitted through the subject using a sensor, and returns this to the X-ray tube to automatically control exposure, in which the sensor output signal and this sensor detect the amount of X-rays remaining transmitted through the subject. An output circuit is provided to selectively feed back a compensation signal when the sensor enters the special part, and a circuit is also provided to detect the entry into the special part from the amount of change in the output signal of the sensor, and the detection signal of this detection circuit causes the output circuit to The present invention is characterized in that it is an automatic exposure compensation circuit in a panoramic X-ray imaging apparatus that sends out a compensation signal from a panoramic X-ray imaging device.

According to this invention, excessive feedback control can be avoided when the sensor enters a special site such as a bone defect, and the exposure of the special site can be kept constant using a compensation signal. It has now become possible to automatically take X-ray images of a person to be imaged that are clear enough to be used for diagnosis.

The details of this invention will be explained below using preferred embodiments.

Figure 2 shows the basic configuration of the feedback system of a panoramic dental X-ray imaging device. Block A is an X-ray tube drive circuit and feedback control circuit, to which a power source 9 and an X-ray tube 3 are connected, The X-ray remaining amount sensor 7 transmitted through the detector 17 and the X-ray film 4 is detected, and is fed back to the block A through the compensation circuit 18 and comparison means 13 and 14 according to the present invention. Further, a specific example of such a feedback system is explained with reference to FIG. 3, which includes a high voltage transformer 1, a filament transformer 2, and an X-ray tube 3.
High-voltage equipment is housed in the X-ray irradiation head. An X-ray film 4 is arranged to be automatically fed corresponding to this head, and a fluorescent plate 5 is installed behind the film 4, and a photoelectric conversion device outputs an electric signal corresponding to the luminance of the fluorescent plate 5. A device 6 is provided, which together constitute the sensor 7 described above.
8 is a circuit that amplifies the sensor output using amplifiers 8a and 8b. On the other hand, on the head side, the primary side of high voltage transformer 1 and filament transformer 2
Each primary side is connected to an AC power source 9 via a power on/off switch 10, and feedback control transistors 11 and 12 are connected to each primary side.
are provided, and these feedback control transistors 11,
Feedback control is applied to the high voltage transformer 1 and the filament transformer 2 by changing the base bias (conduction angle) of the transformer 12. Therefore, the output of the amplifier circuit 8 is sent to both the tube voltage control comparator 13 and the tube current control comparator 14, and these comparators 13 and 14 adjust the base bias. 15 and 16 are setters for the reference signal.

In this circuit, first, the optimum relationship ratio between the tube voltage value and the tube current value is determined. For example, tube voltage
We created a circuit by setting the tube voltage value and tube current value so that there was a certain correspondence so that 5 mA would flow as the tube current when the voltage was 60 KV, and 10 mA would flow when the voltage was 80 KV. Adjust the reference signal setters 15 and 17. This relationship ratio is based on clinical data.

In operation, as the X-ray tube 3 is activated, X-rays pass through the teeth of the person to be imaged 17 and expose the film 4, forming an image of the teeth on the film 4.
On the other hand, the remaining amount of X-rays transmitted through the film 4 causes the fluorescent plate 5 to
is emitted. Since this emission brightness is proportional to the X-ray intensity, the photoelectric conversion device 6 outputs an electrical signal corresponding to the X-ray intensity, which is sent as a sensor output to the comparators 13 and 14 via the amplifier circuit 8.
This value is compared with the values predetermined by the reference signal setters 15 and 16, and the base biases of the feedback control transistors 11 and 12 are changed so that they match, and the high voltage transformer 1 and filament transformer 2 are drive. However, X-ray tube 5
Both the tube voltage and tube current are feedback-controlled at the same time.

In such an automatic exposure circuit, the compensation circuit 18 according to the present invention includes an amplifier circuit 8, a comparator 13,
It will be equipped between 14 and 14. The details of the circuit in FIG. 4 are shown, and this will be explained using the time chart in FIG. , a circuit 20 for detecting that the sensor 7 enters a special part, and special signal generation circuits 26 and 28.The sensor output signal {Fig. 5a} is sent to the analog multiplexer 1.
In addition to being sent to the detection circuit 9, the signal is input to the detection circuit 20 in three branches. That is, the differentiating circuit 21 captures the amount of change over time in the sensor output signal a as shown in FIG.
When compared with Vref, only when the amount of change exceeds the voltage Vref, that is, when the amount of change is large, is extracted as shown in FIG. 5c. Further, the sensor output signal a enters the saturation voltage detection circuit (for example, composed of a window comparator) 23, and the saturation level of the signal a is
The signal at the time when Lmax and Lmin are reached is taken out {FIG. 5d}. In this case, the saturation level refers to the peak Lmax and minimum level Lmin of the sensor output. Then, the AND circuit 2 of the signal c and the signal d is
It is taken at 4. Therefore, of the signals C1 and C2 with a large amount of change extracted in FIG. Since the saturation voltage corresponding to Lmin is detected at this point, the AND circuit 24 outputs the signal shown in FIG. In the case of FIG. 5, the special site is caused by a metal attachment, but even if it is a special site due to a bone defect, it can be detected in the same way. This special part entry signal e is sent to a memory (for example, a bistable multivibrator) 25 and a sample hold circuit 26, and the memory 25 stores the special part entry point and sends the output of FIG. 5 f to an AND circuit 27. . A signal obtained by passing the sensor output signal a through an integrating circuit 28 and having an appropriate delay element is input to the sample hold circuit 26, and the circuit 26, which serves as a kind of analog signal memory, receives the special part entry signal e.
At this point, the signal at the level immediately before entering the special portion, that is, the compensation signal {FIG. 5h} is sent to the multiplexer 19. At the same time, the AND circuit 27 also sends a switching signal {FIG. 5g} to the multiplexer 19 based on the logical product of the signals d and f. In the case of the multiplexer 19, in the normal state, the sensor output signal a directly input thereto is selected and sent as is to the comparators 13 and 14, but when the switching signal g is input, the compensation signal h is selected. and convert this to comparator 13,1
4 and compensate the sensor output signal during the saturation range t ₁ as shown in FIG. 5i, thus suppressing excessive feedback control. This compensation value level is the level immediately before entering the special region. Please note that this explanation describes the case where a special part appears only once during imaging, but
This circuit is configured so that even if a special region appears multiple times during imaging, compensation is performed each time.

As described above, in the circuit of FIG. 4, the signal level immediately before entering the special portion is stored in the sample and hold circuit 26, and this is used as the compensation value level of the compensation signal h, but this compensation value level is set in advance. , this compensation signal may be outputted from the multiplexer 19 when the signal enters a special location. This circuit is shown in FIG. In this circuit, the memory 25
is to memorize that the sensor 7 has entered the special area and sends the inrush signal to the AND circuit 27. The multiplexer 19 is always given the compensation signal Vcom, and the AND circuit 27 due to the sensor 7 entering the special area This compensation signal Vcom is selectively output at the output of .

In addition, instead of constantly giving this compensation signal Vcom to the multiplexer 19, a second sensor for detecting a special part is provided separately from the sensor 7, and the compensation signal Vcom is generated by the special part detection operation by the sensor.
may be given and selected by the output signal of the AND circuit 27. FIG. 7 shows a circuit diagram for this purpose.

[Brief explanation of drawings]

FIGS. 1A, 1B, and 1C show each pattern of the sensor output signal, and are for explaining the technical problem of the present invention. FIG. 2 is a schematic diagram showing the basic configuration of the feedback system. FIG. 3 is a specific example of the circuit shown in FIG. FIG. 4 is a circuit diagram of one embodiment of the present invention. FIG. 5 is a time chart of the circuit of FIG. 4. FIGS. 6 and 7 are circuit diagrams showing modified examples of the present invention, respectively. (Explanation of symbols), 3...X-ray tube, 4...X-ray film, 7...sensor, 19...output circuit (multiplexer), 20...detection circuit.

Claims (1)

[Claims] 1 Detect the remaining amount of transmitted X-rays of the subject with a sensor,
This is returned to the X-ray tube to automatically control exposure, and an output circuit is provided for selectively returning the sensor output signal and a compensation signal when the sensor enters a special part of the person being photographed; An automatic exposure compensation circuit in a panoramic X-ray imaging apparatus, comprising: a circuit for detecting entry into the special region from the amount of change in the output signal of the sensor; and a compensation signal is sent from the output circuit based on the detection signal of the detection circuit.