JPH0449700B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a radiation image information reading method that scans a stimulable phosphor plate with excitation light to read radiation image information recorded on the phosphor plate. Regarding equipment.

(Prior art) So-called radiography using silver salt has traditionally been used to obtain radiographic images, but in recent years, due to problems such as decreasing silver resources, radiographic image processing systems that do not use silver salt have been put into practical use. It is becoming more and more popular. One such system is a system using a stimulable phosphor plate as a recording medium. The radiation image information reading device reads the information recorded on this stimulable phosphor plate, and as shown in FIG.
The transmitted radiation (generally The radiation energy is emitted as fluorescent light, and a radiographic image is obtained by detecting this fluorescent light.

FIG. 2 is a diagram showing only the main parts of a conventional configuration example of this radiation image information reading device. In this device, a laser beam emitted from a laser oscillator 1 is directed by a deflector 2 at a fixed angle θ to a phosphor plate SP.
scanned above. As a result, the phosphor plate SP is stimulated to emit light, and the emitted light is guided by the fiber-shaped photoconductor 3 to a photodetector 4 such as a photomultiplier tube and converted into an electrical signal. . After this electrical signal is amplified by an amplifier 5, it is sent to an image processing device 6 to obtain a radiation image.

With this conventional device, the imaging conditions during radiography,
For example, since the radiation dose, radiation quality, subject, etc. are not constant, the amount of light emitted from the phosphor plate will fluctuate even when excited with excitation light of a constant intensity, resulting in the problem of not being able to obtain an appropriate image signal. It was hot. On the other hand, in order to solve this problem, methods such as changing the power supply voltage of the laser oscillator 1 or the gain of the amplifier 5 depending on the imaging conditions may be adopted. but,
This method has the disadvantage that an appropriate dynamic range cannot be obtained because the noise fluctuates.

(Object of the Invention) The present invention has been made in view of the above points, and its purpose is to provide a radiographic image that can prevent image distortion and always obtain an optimal image even if the imaging conditions change. The objective is to realize an information reading device.

(Structure of the Invention) The structure of the present invention that achieves this object includes a first means for outputting a reference signal according to the radiographing conditions when radiographing is performed, and an intensity of the excitation light based on the output of the second means. The invention is characterized by comprising a second means for controlling.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 3 is a configuration diagram showing an embodiment of the present invention. In this figure, the same reference numerals as in FIG. 2 are used. In this embodiment, a laser beam emitted from a laser oscillator 1 is first beam-shaped by an appropriate optical system (not shown), and then enters an optical modulation element 10. As the laser oscillator 1, for example, a gas laser, a solid-state laser, or a semiconductor laser is used, and as the optical modulation element 10, for example, an acousto-optic modulation element (AOM), KDP, ADP, etc. using electro-optic effect are used. An electro-optical element is used. The laser beam incident on the optical modulation element 10 is modulated in intensity by a control signal from the drive circuit 11, then beam-shaped again by an appropriate optical system (not shown), and then incident on the deflector 2. do. This incident beam is deflected by a deflector 2,
The phosphor plate SP is main-scanned by the deflected beam. The phosphor plate SP is designed to be main-scanned in the direction shown in the figure and sub-scanned in a direction substantially perpendicular thereto. With this scanning beam (excitation light), the phosphor plate SP is stimulated to emit light, and this light is transmitted to the photoconductor 3.
The light is focused and guided to the photodetector 4. As this photoconductor 3, for example, a bundle of optical fibers is used. The photodetector 4 generates an electrical signal of a magnitude corresponding to the intensity of the received light, and the signal is amplified by the subsequent amplifier 5 and then input to the image processing device 6.

On the other hand, the reference signal generation circuit 12 outputs a reference signal corresponding to variations in the influencing conditions during radiography. As a method of generating the reference signal, for example, there is a method of detecting the instantaneous amount of light emitted during radiography with a photodetector and generating a signal according to the photoelectric conversion output. The reference signal (voltage) generated by the reference signal generation circuit 12 is compared with the electric signal (voltage) generated by photoelectrically converting the excitation light described above in the subsequent comparison circuit 13. This comparison circuit generates a signal according to the difference between the two signals, and its output is input to the drive circuit 11. The drive circuit 11 sends a control signal according to the output of the comparison circuit 13 to the optical modulation element 10.
and adjust the intensity of the output light. This adjustment is performed so that the photoelectric conversion output of the laser beam that has passed through the optical modulation element 10 becomes equal to the reference signal generated by the reference signal generation circuit 12. As mentioned above, the reference signal is a signal that corresponds to the influence conditions during radiography, so the excitation light whose photoelectrically converted electrical signal matches this reference signal has an intensity that depends on the fluctuations in the radiography conditions. With phosphor plate SP
This results in luminescence. Therefore, the phosphor plate
SP provides stimulated luminescence that has been corrected for fluctuations in imaging conditions. Furthermore, the emission intensity characteristics of the phosphor plate SP are as follows:
This is shown in FIG. In the figure, the horizontal axis is excitation light intensity and the vertical axis is emission intensity.

The image signal obtained by the image processing device 6 is displayed on, for example, a CRT, and can be made into a hard copy if necessary. For the reasons mentioned above, this image is accurate and is not subject to variations in imaging conditions.

FIG. 5 is a diagram showing a configuration example of a laser beam intensity control circuit when an AOM (acousto-optic modulator) is used as the optical modulator 10.
The same parts as in FIG. 3 are indicated with the same reference numerals.
In this embodiment, a portion of the laser beam directed toward the deflector 2 is reflected by the beam splitter 20, enters the photodetector 21, and is converted into an electrical signal. The output of the photodetector 21 is amplified by an amplifier 22 and then input to the comparison circuit 13. This comparison circuit 13 compares the reference signal output from the reference signal generation circuit 12 and the output of the amplifier 22, and sends a signal corresponding to the difference between the two signals to the drive circuit 11. The drive circuit 11 applies a control signal (AC) according to the output of the comparison circuit 13 to the AOM 10. Incidentally, the diffracted light intensity characteristics of the AOM are shown in FIG. In the figure,
The horizontal axis shows the applied power, and the vertical axis shows the diffracted light intensity.
AOM10 receives the output light of laser oscillator 1,
A laser beam with an intensity corresponding to a control signal (applied power) from the drive circuit 11 is output. As a result,
The excitation light of the laser beam output from the AOM 10 has an intensity that corresponds to the imaging conditions during radiography.

FIG. 7 is a configuration diagram showing another embodiment of the laser beam intensity control circuit. Compared to the embodiment shown in FIG. 5, there is no optical modulation element 10, and instead a laser drive circuit 30 directly drives the laser oscillator 1. That is, the output of the comparison circuit 13 enters the laser drive circuit 30, which directly drives the laser oscillator 1. When a semiconductor laser is used as the laser oscillator 1, by directly driving the laser oscillator 1 itself in this way, its oscillation output can be controlled.

FIG. 8 is a timing chart showing operating waveforms of various parts when an AOM is used as the optical modulation element 10. a indicates a reference signal output according to fluctuations in photographing conditions, b indicates the output of the drive circuit 11, c indicates the excitation light intensity of the laser beam, and d indicates the image signal obtained as a result. . _t0 , _t3
indicates the shooting start time, t ₁ and t ₄ indicate the image signal reading start time, and t ₂ and t ₅ indicate the reading end time, respectively. When the level of the reference signal a fluctuates in response to fluctuations in the photographing conditions, the output b of the drive circuit 11 also changes accordingly, and the excitation light intensity c changes, resulting in an image signal d that is not affected by the photographing conditions. You can see what you can get. FIG. 9 shows an image signal obtained by the conventional method. In this figure, a indicates the excitation light intensity, and b indicates the image signal. Since the excitation light intensity a is constant regardless of variations in the photographing conditions, it can be seen that the amplitude of the resulting image signal b varies greatly due to the influence of the photographing conditions.

(Effects of the Invention) As described above, in the present invention, a means for generating a reference signal according to radiation imaging conditions is provided, and the intensity of excitation light is controlled based on this reference signal. It is possible to prevent image distortion even if the image quality fluctuates, and it is possible to always obtain the optimum image.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing recording of a radiation image on a phosphor, FIG. 2 is a configuration diagram showing a conventional example of a radiation image information reading device, and FIG. 3 is a configuration diagram showing an embodiment of the present invention. FIG. 4 is a characteristic diagram showing the emission intensity characteristics of the phosphor plate, FIG. 5 is a configuration diagram showing an example of a laser beam intensity control circuit, and FIG. 6 is a characteristic diagram showing the diffracted light intensity characteristics of the AOM. FIG. 7 is a configuration diagram showing another embodiment, FIG. 8 is a timing chart showing operating waveforms of each part, and FIG. 9 is a timing chart showing operating waveforms of each part of a conventional device. DESCRIPTION OF SYMBOLS 1... Laser oscillator, 2... Deflector, 3... Light condensing conductor, 4, 21... Photodetector, 5, 22...
... Amplifier, 6 ... Image processing device, 10 ... Optical modulation element, 11 ... Drive circuit, 12 ... Reference signal generation circuit, 13 ... Comparison circuit, 20 ... Beam splitter, 30 ... Laser drive circuit , S...radiation source, OBJ...subject, SP...storage phosphor.

Claims (1)

[Scope of Claims] 1. Imaging conditions when imaging with radiation in a radiation image information reading device that scans a stimulable phosphor plate with excitation light and reads radiation image information recorded on the phosphor plate. The first one outputs a reference signal according to the
A radiation image information reading device comprising: means; and second means for controlling the intensity of the excitation light based on the output of the first means. 2. The second means includes a photodetector that receives the excitation light and generates an electrical signal according to the intensity of the excitation light;
2. The radiation image information reading device according to claim 1, further comprising means for changing the intensity of the excitation light by comparing the output of the photodetector with the reference signal. 3. A laser beam is used as the excitation light, and the means for changing the intensity of the excitation light is an acousto-optic modulator that receives the laser beam and a drive circuit that drives the acousto-optic modulator. A radiation image information reading device according to claim 2. 4. The radiation image information reading device according to claim 2, wherein a laser beam is used as the excitation light, and a laser drive circuit that directly drives a semiconductor laser is used as means for changing the intensity of the excitation light. .