JPS61230562A - Radiographic image information reader - Google Patents

Abstract

PURPOSE:To process the output signal of a photodetector extending over a wide dynamic range and to improve the S/N of a read signal by providing a gain switching means that switches the gain of an amplifier to plural stages and a control circuit. CONSTITUTION:The output signal S of a photomultiplier 20 is sent to a logarithmic amplifier 23 that consists of an amplifier 21 and a logarithmic computing element 22 and an amplification and a logarithmic conversion are performed on it. At such a case, at the feedback line of the amplifier 21, feedback resistors 26 and 27 and a switch 28 are provided constituting the gain switching means that switches the gain of the amplifier 21. Namely, the gain of the amplifier 21, through a comparison circuit 29, is switched comparatively to be low when the level of the signal S is comparatively high and is switched comparatively to be high when that of the signal S is comparatively low. Thus, by providing the gain switching means which consists of resistors 26 and 27 and the switch 28, it is possible to process the output signal of the photodetector extending over the wide dynamic range and to improve the S/N of the read signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention is directed to irradiating excitation light to a stimulable phosphor sheet on which radiographic image information is accumulated and recorded, thereby excitation light emitted from the stimulable phosphor sheet. This invention relates to a radiation image information reading device that photoelectrically detects stimulated luminescence light and reads the radiation image information, and particularly to a radiation image information reading device that can detect stimulated luminescence light emitted over a wide intensity range. It is.

(Technical Background and Prior Art of the Invention) When a certain type of phosphor is irradiated with radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a portion of this radiation energy is emitted by fluorescent light. It is known that when this phosphor is accumulated in the body and is irradiated with excitation light such as visible light, the phosphor exhibits stimulated luminescence depending on the accumulated energy; The fluorophore is called a storage fluorophore.

Using this stimulable phosphor, radiation image information of a subject such as a human body is temporarily recorded on a stimulable phosphor sheet, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam. Generate stimulated luminescence light, photoelectrically read the resulting stimulated luminescence light to obtain an image signal, and based on this image signal, a radiation image of the subject is displayed on a recording material such as a photographic light-sensitive material or a display device such as a CRT. The applicant has already proposed a radiation image information recording and reproducing system that outputs a visible image.

(JP-A-55'-12429, JP-A No. 56-11395, etc.) This system has practical advantages in that it can record images over an extremely wide radiation exposure range compared to conventional radiographic systems that use silver halide photography. It has many advantages. That is, in a stimulable phosphor, it is recognized that the amount of emitted light that is stimulated to emit light due to excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range.
Therefore, even if the amount of radiation exposure varies considerably due to various imaging conditions, the amount of stimulated luminescence light emitted from the stimulable phosphor sheet can be read by the photoelectric conversion means by setting the reading gain to an appropriate value. By converting the radiation image into an electrical signal and using this electrical signal to output the radiation image as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT, it is possible to produce a radiation image that is not affected by fluctuations in radiation exposure. Obtainable.

Furthermore, according to this system, radiation image information accumulated and recorded on a stimulable phosphor sheet is converted into an electrical signal, then subjected to appropriate signal processing, and this electrical signal is used to produce recording materials such as photographic light-sensitive materials, CRTs, etc. By outputting a radiographic image as a visible image on a display device such as the above, it is possible to obtain a very large effect that a radiographic image with excellent observation and interpretation suitability (diagnosis suitability) can be obtained.

In this way, in a radiation imaging system that uses a stimulable phosphor sheet, the reading gain can be set to an appropriate value to photoelectrically convert the stimulated luminescence light and output it as a visible image, so the radiation source fluctuations in the amount of radiation exposure due to fluctuations in the tube voltage or MAS value, fluctuations in the sensitivity of the stimulable phosphor sheet, fluctuations in the sensitivity of the photodetector, changes in the amount of exposure due to subject conditions, or differences in radiation transmittance depending on the subject. Even if the energy accumulated in the stimulable phosphor differs due to factors such as these, and even if the amount of radiation exposure is reduced, it is possible to obtain radiographic images that are not affected by fluctuations in these factors. Become.

By the way, in the radiation image information recording and reproducing system as described above, radiation exposure is sometimes set to be particularly large or, conversely, radiographed by setting it to be particularly small, so that the intensity range of the stimulated luminescence light is It fluctuates greatly. Taking this into consideration, it is desirable that an amplifier that amplifies the output signal of a photodetector such as a photomultiplier (photomultiplier tube) be able to amplify a signal over a dynamic range of about four orders of magnitude. Therefore, in the past, amplifiers that can amplify signals with a particularly wide dynamic range have been selected and used, but when such amplifiers are used, the amplified signal extends to an extremely weak region, resulting in a low S/N ratio. This causes a problem in that the image quality of the reproduced radiation image deteriorates.

(Objective of the Invention) The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to obtain a read signal that can process the output signal of a photodetector over a particularly wide dynamic range and has a high S/N ratio. The object of the present invention is to provide a radiation image information reading device that can perform the following functions.

(Structure of the Invention) The radiation image information reading device of the present invention is, for example, disclosed in Japanese Unexamined Patent Publication No. 58
Similar to the conventional radiation image information reading device shown in No. 67241, No. 58-67242, etc., a stimulable phosphor sheet on which radiation image information of a subject is stored and recorded has two
An excitation light irradiation means that irradiates the excitation light dimensionally, a photodetector that photoelectrically reads the stimulated luminescence light that carries radiation image information emitted from the stimulable phosphor sheet by the excitation light irradiation, and this light. an amplifier for amplifying the output signal of the detector; and gain switching means for switching the gain of the amplifier into multiple stages; and a gain switching means for detecting the output signal of the photodetector and adjusting the gain according to its level. The present invention is characterized in that it is provided with a control circuit that operates a switching means to switch the gain of the amplifier.

(Embodiments) Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

The figure shows radiation 'i! according to an IM embodiment of the present invention. ItI!
This shows an information reading device. When radiation such as X-rays is irradiated through a subject such as a human body, the stimulable phosphor sheet 10, which has accumulated and recorded radiation image information regarding the subject, is transferred to the reading device by a transfer means (not shown). come. The laser light 12 emitted from the laser light source 11 passes through a filter 13 that cuts light in the wavelength range of stimulated luminescence light emitted from the stimulable phosphor sheet 10 by excitation of the laser light 12, and then passes through a galvanometer mirror or the like. The light beam is one-dimensionally deflected by a light deflector 14 and scanned on the stimulable phosphor sheet 10 in the direction of arrow X via a plane reflecting mirror 15 (main scanning). Here the laser beam 8111
is selected so that the wavelength range of the laser light 12 as excitation light does not overlap with the wavelength range of the stimulated luminescent light emitted by the stimulable phosphor sheet 10. Furthermore, a scanning lens 1 consisting of an fθ lens is provided between the optical deflector 14 and the plane reflection mis.
The laser beam 12 scans the stimulable phosphor sheet 10 while keeping the beam diameter constant.
Focus on 0. On the other hand, the stimulable phosphor sheet 10 is transported in the direction of the arrow Y by a sheet transport means 17 such as a transport roller to perform sub-scanning, and as a result, the entire surface of the stimulable phosphor sheet 10 is irradiated with laser light 12. Ru.

When irradiated with the laser beam 12 in this manner, the stimulable phosphor sheet 10 emits stimulated luminescence light 18 in an amount proportional to the radiation energy stored and recorded.

This stimulated luminescence light 18 enters the light condenser 19 and the light condensing body 1
9, exits from its exit surface, and is received by a photomultiplier (photomultiplier tube) 20 as a photodetector. On the light receiving surface of this photomultiplier 20,
A filter is attached that transmits only light in the wavelength region of the stimulated luminescence light 18 and cuts light in the wavelength region of the laser beam 12 as excitation light, so that only the stimulated luminescence light 18 is detected. It has become.

The photomultiplier 20 outputs a signal S carrying the stimulated luminescent light 18 (ie carrying the radiation image information).

The output signal S of this photomultiplier 20 is sent to a logarithmic amplifier 23 consisting of an amplifier 21 and a logarithm operator 22, where it is amplified and logarithmically converted. The read signal S' output from the logarithmic amplifier 23 is sent to an image processing circuit 24, where it undergoes processing such as gradation processing and frequency processing, and then is sent to an image reproduction device 25 such as a CRT.

The image reproducing device 25 reproduces the radiation image information stored and recorded on the stimulable phosphor sheet 10 based on the read signal S'. In addition to the above-mentioned CRT, an optical scanning recording device or the like can also be used as the image reproducing device 25. Alternatively, the radiation image information may not be immediately reproduced using the read signal S', but the read signal S' may be immediately recorded on a recording medium such as a magnetic disk, an optical disk, or a magnetic tape.

Here, the feedback line of the amplifier 21 is provided with two feedback resistors 26, 21 having different resistance values, and one of these feedback resistors 26, 27 is selectively inserted into the feedback line by a switch 28. It has become. When the feedback resistance value of the amplifier 21 is changed in this way, the gain of the amplifier 21 is changed.

In other words, the resistance values of feedback resistors 26 and 27 are rl and r, respectively.
z (rt < rz ), the ratio of the gain of the amplifier 21 when the feedback resistor 26 is inserted in the feedback line and the gain when the feedback resistor 21 is inserted is rl
: rz. As is clear from the above, the feedback resistor 26
．． 27 and switch 28 act as gain switching means for switching the gain of amplifier 21. The output signal S of the photomultiplier 20 is also input to a comparison circuit 29 as a control circuit. This comparison circuit 29 compares the output signal S with the reference signal Sr, and sends a switching signal Sv to the switch 28 when the output signal S exceeds the reference signal. When this switching signal Sv is input, the switch 28 connects the feedback resistor 2 to the feedback line.
6 is inserted, and on the other hand, this switching signal Sv is not input, that is, the output signal S
When is less than the reference signal Sr, the feedback resistor 27 is held in the position where it is inserted into the feedback line. In other words, the gain of the amplifier 21 is switched relatively low when the level of the output signal S of the photomultiplier 20 is relatively high, and relatively high when the level of the output signal S is relatively low. . In this way, the amplifier 21 can handle the photomultiplier output signal S having a wide dynamic range, and the read signal S' does not extend into a weak region, resulting in a high S/N ratio. In other words, the gain ratio of the switched amplifier 21 is 2
If it is on the order of magnitude, even if a general amplifier 21 that can amplify a signal with a dynamic range of about two orders of magnitude is used, it will be able to handle the photomultiplier output signal S with a dynamic range of about four orders of magnitude. . The switching signal SV output from the comparison circuit 29 is also input to the image processing circuit 24 described above, and the image processing circuit 24 uses this switching signal S when performing gradation processing on the read signal S', for example.
Processing is performed to compensate for the gain difference based on the presence or absence of V input.

In the embodiment described above, the gain of the amplifier 21 is switched between two stages, but the level of the output signal S of the photomultiplier 20 is divided into three or more stages, and the amplifier is switched according to the level. The gain of 21 may be switched in three or more stages.

Furthermore, in the embodiment described above, the gain of the amplifier 21 is switched during so-called "book reading" in which the image reproducing device [25 obtains the read signal S' for reproducing radiation image information. Showa 58-6724
As shown in No. 1, etc., when performing so-called "pre-reading" to grasp the accumulated record information of the stimulable phosphor sheet 10 prior to the above-mentioned "actual reading", depending on the output level of the photodetector, Alternatively, the gain of the amplifier may be switched by

(Effects of the Invention) As explained in detail above, the radiation image information reading device of the present invention is capable of processing output signals from a photodetector with a particularly wide dynamic range. Radiation image information can be read even from a phosphor sheet, or a particularly small stimulable phosphor sheet, and the scope of use of a radiation image information recording and reproducing system using the stimulable phosphor sheet is greatly expanded. It becomes like this.

According to the radiation image information reading device of the present invention, S/
Since a read signal with a high N value can be obtained, a high-quality radiographic image with less noise can be reproduced.

[Brief explanation of the drawing]

The figure is a schematic diagram showing one embodiment of the present invention. 10...Storage phosphor sheet 11...Laser light source 12...Laser light 14...Light deflector 1
6... Scanning lens 17... Sheet transport means 18... Stimulated luminescent light 20... Photomultiplier 21... Amplifier 22... Logarithm operator 26.27... Feedback resistor 28 ...Switch 29...Comparison circuit S...Output signal S' of photomultiplier...
Read signal

Claims (1)

[Claims] Excitation light irradiation means for two-dimensionally irradiating excitation light onto a stimulable phosphor sheet on which radiographic image information of a subject is accumulated and recorded; a photodetector for photoelectrically reading the stimulated luminescence light; an amplifier for amplifying the output signal of the photodetector; gain switching means for switching the gain of the amplifier into multiple stages; and a photodetector for detecting the output signal of the photodetector. , a radiation image information reading device comprising a control circuit that operates the gain switching means to switch the gain of the amplifier according to the level.