JPH01274128A - Radiation image readout device - Google Patents

Abstract

PURPOSE:To utilize the dynamic range of a stimulable phosphorescence body sufficiently by allowing a 2nd photodetector to detect the constant permissible quantity of light of a 1st detector being exceeded when the accelerated phosphorescence body is irradiated with exciting light. CONSTITUTION:Part of light of stimulable phosphorescence light emission 33 which is incident on the 1st detector 31 is incident on the 2nd photodetector 32 and when the quantity of the light incident on the 1st photodetector 31 exceeds a constant value close to the maximum permissible quantity of incident light to the photodetector 31, the 2nd photodetector 32 detects the intensity of the stimulable phosphorescence light emission 33. When the output signal of the 2nd photodetector 32 is sent to and digitized by a signal converter 100, complement conversion is performed and the signal is sent to an arithmetic processor 100. The signal from the 1st photodetector 31 is not processed by the complement conversion. The arithmetic processor 100 stores the value obtained by multiplying the complement-converted signal by a constant coefficient as image signal. Consequently, the dynamic range that a stimulable phosphorescence body 12 has can be utilized sufficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a radiation image reading device, and in particular, stimulates luminescence (-degrees) corresponding to the amount of radiation absorbed up to that point by irradiation with excitation light. The present invention relates to a radiation image reading device for reading a radiation image recorded on a stimulable phosphor that emits light to return to its original state without absorption of radiation.

[Prior Art] For example, as a radiation image reading device that reads images accumulated by X-rays or other radiation, a stimulable fluorescence that emits light in response to the amount of radiation absorbed so far by irradiation with excitation light is used. A method using a light body has been proposed (see, for example, Japanese Patent Laid-Open No. 13230/1983).

This device exposes the photostimulable phosphor to radiation and then scans the photostimulable phosphor with excitation light, detecting the photostimulated light produced at each point one by one. , how much is it to read the radiation image recorded on the stimulable phosphor?

[Problems to be Solved by the Invention] Incidentally, in the above-described apparatus, a photomultiplier tube is generally used as a photodetector for detecting the stimulated luminescence light.

However, the dynamic range (ratio of minimum detection intensity to maximum detection intensity) of this photomultiplier tube is usually 103 to 1.
035, whereas the dynamic range of the photostimulable phosphor is 106.

For this reason, the conventional apparatus has a drawback in that the dynamic range of the photostimulable phosphor cannot be fully utilized.

An object of the present invention is to provide a radiation image reading device that eliminates the above-mentioned drawbacks.

[Means for Solving the Problems] The present invention makes full use of the dynamic range of the photostimulable phosphor by using two photodetectors as photodetecting means for detecting the intensity of stimulated luminescence. It has the following configuration.

A radiation image reading device that reads a radiation image recorded on an image recording means equipped with a photostimulable phosphor that emits photostimulable light according to the amount of radiation absorbed so far by irradiation with excitation light, An excitation light generation means for irradiating the excitation light onto the photostimulable phosphor; and a photodetection means for detecting the intensity of stimulated luminescence generated when the excitation light is irradiated onto the photostimulable phosphor. In the radiation image reading device, two photodetectors, a first and a second photodetector, are used as the photodetection means, and the second photodetector receives stimulated luminescence light incident on the first photodetector. When the amount of light incident on the first photodetector is below a certain value close to the maximum allowable amount of incident light of the photodetector, the first photodetector performs the photoexcitation. The intensity of the emitted light is detected, and when the amount of light incident on the first photodetector exceeds a certain value close to the maximum allowable amount of incident light of the photodetector, the second photodetector detects the stimulated luminescence. A radiation image reading device characterized by detecting the intensity of the radiation image.

[Operation 1 According to the above configuration, when the intensity of the stimulated luminescence is below a certain value close to the maximum allowable amount of incident light of the first photodetector, the stimulated luminescence is detected by the first photodetector. is detected, and when the amount of light incident on the first photodetector exceeds a certain value close to the maximum allowable incident light amount of the photodetector, the second photodetector detects the photoexcitation. The intensity of the emitted light is detected.

In this case, only a portion of the light that is incident on the first photodetector is incident on the second photodetector. Therefore, even if the intensity of the stimulated luminescence exceeds the maximum allowable incident light amount of the first photodetector, the intensity can be detected by the second photodetector.

This makes it possible to fully utilize the dynamic range of the photostimulable phosphor.

[Embodiment] FIG. 1 is a diagram showing the configuration of a radiation image reading apparatus according to an embodiment of the present invention.

In the figure, reference numeral 1 is an image recording means, reference numeral 2 is an excitation light generating means, and reference numeral 3 is a light detection means.

The image recording means 1 has a photostimulable phosphor layer 12 formed on the surface of a disc-shaped main body 11, and is held rotatably about the central axis of the disc-shaped main body 11 by a drive motor 13. has been done.

Further, the excitation light generating means 2 irradiates the phosphor layer 12 of the image recording means 1 with excitation light 21 through the dichroic mirror 4 and the lens 5, and in this embodiment,
A laser generator is used. In this case, the dichroic mirror 4 transmits the excitation light 21 emitted from the excitation light generation means 2, and also transmits the excitation light 21 emitted from the excitation light generation means 2, and also transmits the excitation light 21 emitted from the excitation light generation means 2, and also transmits the excitation light 21 emitted from the excitation light generation means 2. −
Of the light traveling from the lens 12 through the lens 5, only the wavelength component of the stimulated luminescence light 33 is selectively reflected.

Further, the photodetecting means 3 is constituted by two photodetectors 31 and 32, and the stimulated luminescence light 33 generated from the phosphor layer 12 by the irradiation of the excitation light 21 is transferred to the lens 5 and the dichroic mirror. 4. Semi-transparent 'MA6
and is detected through total reflection jA7. In this embodiment, these first and second photodetectors 31 and 32
Both are photomultiplier tubes (photomultipliers).
) is used.

The semi-transparent m 6 has an area approximately 11,500 times the beam cross-sectional area of the stimulated luminescent light 33 reflected by the dichroic mirror 4, and is a part of the stimulated luminescent light 33 (the stimulated luminescent light 33). Approximately 1/10 of the total amount of light
00) and sends this reflected light 34 to the total reflection mirror 7.
The light is made incident on the second photodetector 32 via the. In this case, most of the stimulated luminescence light 33 that is not reflected by the semi-transmissive mirror 6 enters the first photodetector 31. Although not shown, the optical system consisting of the excitation light generating means 2, the light detecting means 3, the dichroic mirror 4, the lens 5, the semi-transmissive mirror 6, and the total reflection 3A7 is integrally formed with respect to the image recording means. It is configured so that it can be moved relatively.

That is, by moving the optical system relative to the image recording means while rotating the disc-shaped main body 11 by the drive motor 13, the excitation light generating means 2
All points on the phosphor layer 12 are scanned by the excitation light 33 emitted from the phosphor layer 12, and stimulated luminescence light at each point can be detected. In this case, positional information at each scanning point is detected by a control device 101 (indicated by a dotted line in the figure) that drives and controls the optical system and the drive motor 13.

Now, driving power is supplied to the first photodetector 31 from a power source 38 via an applied voltage control means 37, and
The second photodetector 32 is directly supplied with driving power from the power source 38 . That is, the photodetectors 31 and 3
2 (photomultiplier tube) is provided with several to several stages of dynodes in order to multiply photoelectrons from the photocathode. And, between each of these dynodes, there are tens to hundreds of ■
A total of several hundred to several thousand hundreds of voltages are applied between the first-stage dynode and the last-stage dynode. The applied voltage controller 9237 turns ON/OFF the voltage applied between any of the dynodes based on a certain command.

Further, an output signal from the first photodetector is sent to one input terminal of the analog switch 8 and one input terminal of the comparator 9, and an output signal from the second photodetector 32 is sent to one input terminal of the analog switch 8. sent to the other input terminal.

The output signal of the analog switch 8 is sent through a signal converter 10 including an A-D converter, a complement converter, etc. to an arithmetic processing unit 100 including storage means, etc. Note that the output from the reference voltage generator 91 is sent to the other input terminal of the comparator 9, and the output signal of the comparator 9 is sent to the applied voltage control means 37, the analog switch 8, and the signal converter 10. . That is, this comparator 9 compares the output signal of the first photodetector 31 and the output of the reference voltage generator 91,
The applied voltage control means 37, analog switch 8 and signal converter 10 are controlled based on the comparison result.

The analog switch 8 inputs the output signal of the first photodetector 31 and the output signal of the second photodetector 32, and selects one of these signals based on the output of the comparator 9. It performs high-speed switching for output.

Further, the signal converter 10 includes the analog switch 8
The analog signal sent from the comparator is converted into a digital signal, and this digital signal is subjected to complement conversion according to the output of the comparator and sent to the arithmetic processing unit 100.

This arithmetic processing device 100 performs certain arithmetic processing on the signal sent from the signal converter 10 as necessary, and at the time this signal is input, the position information signal detected by the control device 101 is processed. By inputting and matching these two signals, this is stored as information corresponding to the intensity of stimulated luminescence at each position on the phosphor layer 12, that is, as image information, and the stored image information is The information is sent to a display device or other device (not shown) so that it can be used.

Here, the control by the comparator 9 will be explained in more detail. As described above, this comparator 9 compares the output of the first photodetector 31 and the output of the reference voltage generator 91 and outputs an output signal according to the comparison result.

In this case, the output voltage of the reference voltage 91 is set to a constant voltage before the output of the first photodetector 31 is saturated. In other words, a constant voltage is sent out from the first photodetector 31 when the amount of light incident on the first photodetector 31 reaches a constant value close to the maximum allowable incident light amount of the photodetector. is set to Then, different voltages are sent out depending on whether the output voltage of the first photodetector 31 is below the predetermined voltage or exceeds the predetermined voltage. As a result, the applied voltage control means 37, analog switch 8, and signal converter 10 perform the following operations.

If the voltage is below a certain level, the applied voltage control means 37 is turned ON, that is, voltage is applied to all dynodes.

Analog switch 8 sends the output signal from the first photodetector 31 to the signal converter.

Signal converter 10 The data is sent to the arithmetic processing unit without complement conversion.

If the voltage exceeds a certain level, the applied voltage control means 37 is turned off, that is, the voltage applied to the first stage dynode is cut off.

Analog switch 8 sends the output signal from the second photodetector 31 to the signal converter.

Signal converter 10 Complement converted and sent to the arithmetic processing unit do.

In this way, when the amount of light incident on the first photodetector 31 is about to exceed the maximum allowable amount of incident light, the light detection by the first photodetector 31 is stopped and the amount of light incident on the first photodetector 31 is stopped. Photodetection is performed by the second photodetector 32, which allows only about 1/1000 of the amount of light incident on the first photodetector 31 to enter.

In this case, the reason why the first photodetector 31 stops detecting light when the second photodetector 32 detects light is as follows.

That is, if the first photodetector 31 is operated while the second photodetector 32 is detecting light, the first photodetector 31 will maintain the maximum allowable amount of incident light during that time. This means that more light will be detected.

For this reason, the interpacked photodetector 31 is in a saturated state during that time.

- Once the photodetector 31 has reached a saturated state, even if the amount of incident light subsequently becomes less than the maximum allowable amount of incident light, the photodetector 31 cannot immediately return to a normal detection state;
Therefore, in order to avoid such a saturated state, it is necessary to stop the process before the saturated state is reached.

Further, in order to stop the operation of the first photodetector 31, the voltage applied to the first stage dynode is turned off without turning off the total voltage applied to the photodetector 31. This is a new idea. That is,
When a photomultiplier tube is adopted as the photodetector 3 as in this embodiment, unless such a device is used, the 2
In practice, it is extremely difficult to switch the two photodetectors 31 and 32 alternately for detection. The reason is as follows.

The amount of light incident on the photodetectors 31 and 32 usually changes rapidly in a peak manner. For this reason, the first photodetector 31 stops at the point where the peak rises and the slope becomes steep, and restarts its operation at the point where it falls from the top of the peak and the slope becomes steep again. That is, the operation of the first photodetector 31 must be stopped and started very quickly, and when the operation is resumed, normal operation must be ensured immediately without any time delay. .

However, if the total voltage applied to the first photodetector 31 is turned off to stop its operation, then when the voltage is applied to make it operate again, it will take a certain amount of time before it can operate normally. Therefore, a high-speed recovery that satisfies the above conditions was not possible. For this reason, there are disadvantages such as what is originally one peak is apparently detected as two peaks, and the detection intensity becomes inaccurate.

As a result of various experiments conducted by the present inventor, the above-mentioned method can be achieved by turning ON/OFF the voltage applied to the first stage of the dynode without turning ON/OFF the total voltage applied to the first photodetector 31. It was found that the inconvenience of the above was almost completely eliminated (note that the voltage applied to the first stage may not necessarily be applied to the other stages, but the voltage applied to the first stage was most effective).

Furthermore, the light detected by the second photodetector 32 is approximately 1/2 of the light detected by the first photodetector 31.
/1000. Therefore, it is necessary to make this detected value correspond accurately to the detected value by the first photodetector 31. This correspondence arrangement is performed as follows.

When the output signal of the second photodetector 32 is sent to the signal converter 10 for digital conversion, this digital signal is simultaneously subjected to complement conversion and sent to the arithmetic processing unit 100. Conversely, the signal from the second photodetector 31 is not complemented. Therefore, in the arithmetic processing device 10,
First, it is determined whether the input signal has been complement-converted. Next, if this input signal has not undergone complement conversion, use the value as is, or if it has undergone complement conversion, use the value obtained by multiplying that signal by a certain coefficient as image information. Remember.

As a result, even if the scene incident on the first photodetector 31 exceeds the first permissible amount of incident light,
This can be detected.

As described above, according to this embodiment, the image recording means 1
By making full use of the dynamic range of the stimulable phosphor layer 12, it is possible to read a wide range of image information recorded on the phosphor layer 12 without omitting it.

In the above embodiment, the semi-transmissive mirror 6 was used as a means for making the light incident on the second photodetector part of the light incident on the first photodetector. for example,
A glass plate with approximately the same area as the beam cross-sectional area of stimulated luminescence light and a surface reflectance of about 71,000 m (partially transmitted m )
Alternatively, a total reflection mirror whose reflecting surface area is about 1/1000 of the beam cross-sectional area of the stimulated luminescence light may be used.
Further, the amount of light incident on the second photodetector does not necessarily have to be 1/1000 of the amount of light incident on the first photodetector; in short, this ratio is determined by the dynamic Any value that can cover the range is sufficient.

[Effects of the Invention] As described in detail above, the present invention uses two photodetectors as photodetecting means for detecting the intensity of stimulated luminescence, thereby fully utilizing the dynamic range of the photostimulable phosphor. This made it possible to make use of it.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a radiation image reading apparatus according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Image recording means, 12... Stimulable phosphor layer, 2... Excitation light generation means, 3... Light detection means, 31... First photodetector, 32. ... Second photodetector, 37... Applied voltage control means, 38... Power source, 4... Dichroic mirror, 5... Lens, 6... Semi-transmissive mirror, 7... - Total reflection mirror, 8... Analog switch 9... Comparator, 10... Signal converter, 100... Arithmetic processing unit. Applicant Mac Science Co., Ltd.

Claims (1)

[Scope of Claims] A radiation image that reads a radiation image recorded on an image recording means equipped with a photostimulable phosphor that emits photostimulable light in response to the amount of radiation absorbed so far by irradiation with excitation light. A reading device, comprising: an excitation light generating means for irradiating the excitation light to the photostimulable phosphor; and detecting the intensity of stimulated luminescence generated when the excitation light is irradiated to the photostimulable phosphor. A radiation dual image reading device having a photodetecting means, wherein two photodetectors, a first and a second photodetector, are used as the photodetecting means, and the second photodetector has a radiation beam incident on the first photodetector. Only a part of the stimulated luminescence light is incident on the first photodetector, and when the amount of light incident on the first photodetector is below a certain value close to the maximum allowable incident light amount of the photodetector, the first The intensity of the stimulated luminescence is detected by a photodetector, and when the amount of light incident on the first photodetector exceeds a certain value close to the maximum allowable amount of incident light of the photodetector, the intensity of the stimulated luminescence is detected by the second photodetector. A radiation image reading device characterized in that the intensity of the stimulated luminescence is detected by a detector.