JPH02207494A - Automatic exposure control device for mammography - Google Patents

Abstract

PURPOSE:To make it possible to correct change in film concentration which takes place when the thickness of a subject is changed by changing the level of a detecting means with time in response to a X-ray radiation starting signal. CONSTITUTION:A mirror integrating circuit 22 integrates photoelectric current which is the output of a X-ray detector 12. It is detected by a comparator 38 that the integrated value has come up to a specified one, and a relay 15 is actuated so that a X-ray radiation switch 4 is turned off. On the other hand, when a contact 26 which is closed by starting X-ray radiation, is closed, the mirror integration circuit 30 starts integrating voltage VA so as to output voltage VB which is changed with time. An addition circuit 37 adds voltage VB to voltage Vc in order to obtain output voltage VD which is changed with time. Voltage VD is the reference voltage of the comparator 38. When the integrated value of photoelectric current, that is, the integrated value of current in the circuit 22 comes up to the reference value, X-ray radiation is suspended with the relay 15 operated. Thus, change in film concentration which takes place when the thickness of a subject is changed, can thereby be corrected.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an X-ray automatic exposure control device for mammography, and in particular improves the radiation quality characteristics caused by low imaging tube voltage, and improves the subject thickness. The present invention relates to an X-ray automatic exposure control device that can obtain X-ray photographs with uniform density even if the density changes.

[Conventional technology]

The conventional X-ray automatic exposure control device for mammography equipment is
The X-rays that have passed through the subject, film, intensifying screen, etc. are converted into light using a light emitter such as an intensifying screen, the amount of light is detected using a photodetector such as a photomultitube, and the integral value of the amount of light is kept constant. The X-rays were compared using a comparator with a reference value, and when the integrated value of the amount of light reached a predetermined amount, the X-rays were blocked.

[Problem to be solved by the invention]

However, in the conventional xi automatic exposure control device for mammography X-ray imaging devices, the X-ray tube voltage used for breast x-mm imaging is as low as 25 to 35 KV (soft X-rays), so The quality of the remaining radiation changes, and the degree of this change also varies depending on the thickness of the object (such as the subject) through which it passes.

As a result, due to the radiation quality characteristics of the light emitter (such as an intensifying screen), the amount of light emitted is no longer proportional to the thickness of the subject, and when the integral value of the amount of light (Xg amount) reaches a predetermined value, the X-rays are blocked and the film is filmed. The function of the automatic X-ray exposure control device, which attempts to control the density at a constant level regardless of the thickness of the subject, is impaired, and as the body thickness of the subject changes, the density of the photograph changes, resulting in
There was a problem that the diagnostic value of line photographs decreased.

Note that the X-ray automatic exposure control device used in conventional mammography equipment generally has the characteristic that the density of the photograph decreases as the subject thickness increases, so the operator must It is necessary to perform an operation to correct it,
The current situation is that screening efficiency is declining.

The present invention was made to solve the above problems, and
The purpose is to provide a technique that can correct changes in film density that occur when the thickness of a subject changes in a mammography X-ray apparatus, and that can always obtain X-ray photographs with good density.

Another object of the present invention is to provide a technique by which X-ray photographs with good and uniform density can be obtained at all times.

Still another object of the present invention is to provide an X-ray apparatus for mammography with high screening efficiency.

[Means for solving problems]

In order to achieve the above object, the present invention integrates an output signal from an X-ray detector placed opposite to an X-ray tube device with a subject in between, and the integrated value reaches a predetermined value. It has a detection means for comparing and detecting.

In an automatic mammography exposure control device configured to stop X-ray irradiation when a signal is output from the detection means, means for generating a comparison reference voltage of the detection means by changing it over time. It is equipped with the following.

Further, the above object is achieved by using the comparison reference voltage as an output signal of the data generating means which is generated as a predetermined exponential value over time.

[Effect]

The automatic X-ray exposure control device consists of an X-ray detector (usually consisting of a combination of photomultiplier and fluorescent paper) that detects the X-rays that have passed through the subject, an integrator that integrates the output, and an integrator that integrates the output of the X-ray detector. It consists of a detection means (usually a comparator) that detects that the value has been reached.

The detection level (comparison reference voltage) of this detection means is changed as time elapses in response to the X-ray irradiation start signal (in this case, the film density decreases as the subject becomes thicker and the imaging time becomes longer). For example, if the thickness of the subject increases, the X-ray irradiation time is made even longer.

This corrects the characteristic that the film density decreases as the subject thickness increases, and it is possible to always obtain an X-ray photograph with a constant density, thereby improving the accuracy and efficiency of mammary X-ray diagnosis.

In addition, since the subject thickness-imaging time characteristic of soft X-rays used for mammography changes exponentially, the reference voltage for comparison is determined in advance as exponential function data that matches the characteristics, and the imaging start signal is sent from the data generating means. Data is generated sequentially over time in response to changes in the thickness of the subject.This makes it possible to make the photographic density finer and more uniform in accordance with changes in the thickness of the subject.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 is a circuit diagram showing the overall schematic configuration of an X-ray automatic exposure control device for mammography.

1 is a power supply terminal, 2 is a power supply switch, 3 is a single-turn transformer for setting the imaging tube voltage, and 4 is an X-ray irradiation switch, which are shown as contacts here. 5 is a main transformer of the X-ray high voltage generator, 6 is a high voltage rectifier, and 7 is a cathode-grounded X-ray tube normally used in mammography equipment. 8 is the subject (breast), 9 is the cassette in which the film and intensifying screen are stored, and 10 is the subject 8. An intensifying screen for mammography X-ray imaging (other fluorescent screens can also be used) is housed in a dark box to convert the X-rays transmitted through cassette 9 into light, and 11 is a photomultitube (optical semiconductor element). This is a photodetector that converts light into an electrical signal, and this 10.11 forms an X-ray detector 12. This X-ray detector 12 may be an X-ray detector such as a pin diode that directly converts X-rays into electrical signals.

Reference numeral 13 denotes an x and m irradiation start switch, and 14 an X-ray irradiation stop contact, which are excited by an excitation coil 15. Reference numeral 16 denotes an excitation coil for operating the X-ray irradiation switch 4, which is excited when the X-ray irradiation start switch 13 is closed.

Excitation is stopped when the X-ray irradiation stop contact 14 is opened.

17. 18 is an input resistor, 19 is an output resistor, 20 is an integrating capacitor, and 21 is an operational amplifier. Components 17 to 21 constitute a mirror integration circuit 22, which is the output of the photomultitube 11 of the X-ray detector 12. It integrates the photocurrent.

Normally, in an automatic X-ray exposure device, based on the idea that there is a proportional relationship between the integral value of photocurrent and the X-ray dose that gives the film an appropriate density, a comparator is used to detect when this integral value reaches a predetermined value. 38, the relay 15 is operated, and the X-ray irradiation switch 4 is turned off.

23 is a DC voltage Vcc, 24.25 is a resistor that obtains an appropriate voltage VA obtained by dividing the DC voltage Vcc, and 26 is a contact that operates simultaneously with the X-ray irradiation switch 4. By starting X-ray irradiation),
Resistance 27. Integrating capacitor 28. The Miller integration circuit 30 constituted by the operational amplifier 29 starts integrating the voltage {circle around (2)}, and outputs a voltage Va that changes with time.

31.32 is the voltage Vc obtained by appropriately dividing the DC voltage Vcc.
The resistors 33, 34, 35, and the operational amplifier 36 constitute an adder circuit 37. In this circuit, the voltages Va and V
c is added to obtain the output voltage vO. Voltage Vo is comparator 3
When the integrated value of the photocurrent, that is, the integrated value of the mirror integration circuit 22 reaches this reference voltage, the relay 15 is activated and the X-ray irradiation is stopped.

Figure 2 shows the VAT Va, Vc, V in Figure 1.
.

In the diagram showing the relationship, V^, Vc are always constant voltages, V
A is a voltage that is output at the same time as the start of X-ray irradiation and increases over time, and Vo is a voltage of VB+VC that also increases over time. That is, the reference voltage of comparator 38 increases with time.

Figure 3 shows the relationship between the thickness of the subject and the imaging time, which gives the film the proper density when X-ray photography is performed using an automatic X-ray exposure device.It shows that the thicker the subject, the longer the imaging time. ing.

In FIG. 3, (A) is a curve when the reference voltage of the comparator 38 is kept constant, and this curve has a characteristic that the film density becomes insufficient as the object thickness becomes thicker. In other words, there is not enough time to photograph a thick subject.

As shown in FIG. 2, the present invention increases the reference voltage Vo with the passage of time during imaging (the thickening of the subject can be indirectly detected by converting it into the imaging time). This is intended to correct the lack of photographing time at the thick part of the subject shown in FIG. 3 (curve (b)) to obtain an appropriate film density over the entire thickness of the subject.

Here, the reference voltage VD is input to the Miller integrator 30 shown in FIG.
We explained the method of linearly changing the film density, but the shooting time to give the film an appropriate density needs to be changed exponentially as shown in Figure 3. It is also possible to make the reference voltage VD a broken line (Vo').

FIG. 4 shows a second embodiment of the present invention, which is the embodiment of FIG. 1 that can accommodate the exponential relationship between object thickness and imaging time shown in FIG. A modification of the correction unit in FIG. In FIG. 4, circuits 1 to 23 and 38 are the same as those in FIG. 1, so a description thereof will be omitted.

41 is a relay contact that opens and closes in conjunction with the contact of the X-ray irradiation switch 4; 42 is an oscillator that starts oscillating at the same time as imaging; 4
3 is a counter that counts the output signal of the oscillator 25 and indicates the elapsed shooting time; 44 is a memory (p-
ROM, etc.), and 45 is a D/A converter that converts the digital data from the memory 44 into an analog value, the output of which becomes a comparison value that is compared with the output of the Miller integration circuit 22 in the comparator 38. Before shooting, counter 4
3 is a count O state, and the D/A converter 45 outputs a voltage corresponding to Vc in FIG. 2 based on the output of the memory 44. When photographing is started and relay contact 41 is closed, oscillator 42 oscillates, and counter 43 counts this oscillation signal, so that the count value increases as the photographing time elapses. This count value is connected to the address input of the memory 44, and as this count value increases, the exponential digital data stored in the memory 44 is sequentially transferred to the D/A converter 45.
The D/A converter 45 outputs a signal obtained by converting the data into an analog signal as a comparison reference value of the comparator 38.

According to this embodiment, since the output (comparison value) of the D/A converter 45 increases exponentially in accordance with the characteristics of the phototimer programmed in the memory 44, film density correction can be made more finely and accurately. I can do it.

FIG. 5 shows a third embodiment in which film density is corrected using a microcomputer.

In this embodiment, 1 to 23, 38 and 41 are circuits similar to those shown in FIG. 4, 50 is a microcomputer, and 5
1 is a latch IC, and 52 is a D/A converter. Before starting shooting, the V as shown in FIG.
A value such that the voltage of c is output is sent to the latch IC 51,
It is set from the microcomputer 50. At the same time as the photographing signal is input, the microcomputer 50 sequentially sets exponential function data to be corrected to the latch IC 51 according to the phototimer characteristics as the photographing time elapses, thereby adjusting the output from the D/A converter 52. The film density is corrected by increasing exponentially with time. In this embodiment as well, the same effects as in the second embodiment described above can be obtained.

〔Effect of the invention〕

According to the present invention, when the breast thickness increases (or
Since the auto-exposure characteristic of decreasing film density (when the breast is dense and has large linear absorption) is automatically corrected, good mammograms can be obtained and the efficiency of examination is significantly improved. Furthermore, according to the present invention, since the comparison reference voltage can be changed to match the subject thickness-imaging time characteristic curve, even if the subject thickness changes, the quality of the photograph will always be good and uniform. be able to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between the comparison reference voltage of the comparator, and FIG. 3 is a diagram showing the relationship between subject thickness and imaging time. FIG. 4 is a block diagram showing another embodiment of the present invention, and FIG. 5 is a block diagram showing an embodiment in which a microcomputer is used in the present invention. 12... X-ray detector, 22... Integrating circuit, 26.4
1... Contacts interlocking with the X-ray irradiation switch, 30... Integrating circuit, 37... Adding circuit, 39... Comparator, 44...
...Memory, 45...D/A converter, 5o...
microcomputer. 1st ri: J outside - Kisho rumor is thick (! Shi paper *h 9v#i1 (
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Claims (1)

[Claims] 1.
It has an integrator that integrates the output signal from the radiation detector, and a detection means that compares and detects that the integrated value has reached a predetermined value, and when a signal is output from the detection means, X-ray irradiation is started. An automatic X-ray exposure control device for mammography configured to stop, characterized in that the automatic exposure control device for mammography comprises means for changing and generating a comparison reference voltage of the detection means over time. . 2. It has a means for outputting a signal that starts changing in response to the X-ray irradiation start signal and changes at a predetermined exponential function value over time, and the signal outputted by this means is transmitted to the detection means. The automatic exposure control device for mammography according to claim 1, characterized in that the comparison reference voltage is used as a comparison reference voltage.