JPH05154140A - Radiation image information reader - Google Patents

Abstract

PURPOSE:To prevent uneven density from being generated in a read radiation image even when the semiconductor laser of a single mode is used as an excitation light source by providing a modulating means for modulating periodically the semiconductor laser so that a light quantity accumulated value in one picture element reading period becomes constant. CONSTITUTION:To a semiconductor laser driving circuit 34, a high frequency signal RF is inputted from modulating circuit 35, and a semiconductor laser 30 is modulated in such a period as the light quantity accumulates value of a laser beam 31 in one picture element reading period becomes constant by the high frequency signal RF. Accordingly, a mode hop state, that is, an excitation light wavelength fluctuation state in one picture element reading period becomes random, therefore, between each of one picture element reading periods, the wave-length fluctuation state is unified. Therefore, when one image signal is formed by an averaging processing circuit 18, based on prescribed pieces of digital image signals obtained in one picture element reading period, the obtained image signal of every picture element becomes that which is influenced roughly by mode hopping each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for irradiating a stimulable phosphor sheet, on which radiation image information is stored and recorded, with excitation light to read the radiation image information.
The present invention relates to a radiation image information reading device that uses a laser beam emitted from a single-mode semiconductor laser as excitation light.

[0002]

2. Description of the Related Art Radiation (X rays, α rays,
When β-rays, γ-rays, electron beams, ultraviolet rays, etc.) are irradiated, a part of this radiation energy is accumulated in the phosphor, and when this phosphor is irradiated with excitation light such as visible light, it is changed depending on the accumulated energy. It is known that phosphors exhibit stimulated emission, and phosphors exhibiting such properties are called stimulable phosphors (stimulable phosphors).

Using this stimulable phosphor, radiation image information of a human body or the like is once recorded on a sheet having a layer of the stimulable phosphor, and the stimulable phosphor sheet is two-dimensionally excited by excitation light such as laser light. Scanning produces stimulated emission light, and the obtained stimulated emission light is photoelectrically read to obtain an image signal. Based on the image signal, a radiation image is displayed on a recording material such as a photographic photosensitive material or a display device such as a CRT. A radiation image information recording / reproducing system for outputting a visible image has been already proposed by the present applicant (Japanese Patent Laid-Open Nos. 55-12492 and 56-11395). By the way, in the system described above, it is also considered to use a semiconductor laser as an excitation light source. This semiconductor laser is smaller and cheaper than a gas laser or the like and consumes less power, and is advantageous in forming a radiation image information reading apparatus compactly.

[0004]

By the way, it is known that in a single mode semiconductor laser, a phenomenon called mode hopping occurs due to a change in ambient temperature, a change in driving current and the like. When this mode hopping occurs, the amount of light changes or the oscillation wavelength changes.
By the way, when this mode hopping occurs in the semiconductor laser used as the excitation light source of the radiation image information reading apparatus, density unevenness may occur in the read radiation image. That is, the sensitivity of the stimulable phosphor sheet (which is defined by the amount of stimulated emission light with respect to a constant amount of excitation light) has wavelength dependency as shown in FIG. 2, so that if the wavelength of the excitation light changes, Even if the amount of excitation light is constant, the amount of stimulated emission light varies.

The present invention has been made in view of the above circumstances, and even when a single-mode semiconductor laser is used as an excitation light source, the read radiation image information does not cause density unevenness in the read radiation image. The purpose is to provide a device.

[0006]

As described above, the radiation image information reading apparatus according to the present invention uses the laser beam emitted from the single mode semiconductor laser as the excitation light for scanning the stimulable phosphor sheet. In the radiation image information reading device, the output signal of the photodetector for photoelectrically detecting the stimulated emission light is set to N within one pixel reading period.
A / D converter for sampling twice (2 ≦ N), signal processing means for forming one digital image signal based on N digital image signals obtained within one pixel reading period, and the semiconductor laser Is provided with a modulation means for periodically modulating the light quantity integrated value within one pixel reading period to be constant.

[0007]

If the semiconductor laser is modulated as described above, the mode hop state within one pixel reading period, that is, the excitation light wavelength variation state becomes random, and as a result, the wavelengths are changed between one pixel reading periods. The fluctuation state is made uniform. Therefore, if one image signal is formed based on the N digital image signals obtained within the one-pixel reading period, the obtained digital image signals of each pixel are substantially evenly affected by the mode hopping. It becomes a thing.
Therefore, if a radiation image is reproduced based on such an image signal, it is possible to prevent density unevenness due to mode hopping from occurring in the reproduced radiation image.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. FIG. 1 shows a radiation image information reading apparatus according to an embodiment of the present invention. As shown in the figure, in this apparatus, a single mode semiconductor laser 30 is provided as an excitation light source. A laser beam 31 as excitation light emitted in a divergent state from there is collimated by a collimator lens 36, and then enters an optical deflector 32 such as a galvanometer mirror. The semiconductor laser 30 is driven by the drive circuit 34.

The stimulable phosphor sheet 1 on which the radiation image information of the subject is accumulated and recorded by irradiating the radiation transmitted through the subject is a sub-scanning means such as an endless belt.
It is moved in the Y direction by arrow 11. At the same time, the laser beam 31 is deflected by the optical deflector 32, and normally f
The sheet 1 is passed through the scanning lens 33, which is a θ lens, and the sheet 1 is main-scanned in the X direction. From the portion of the stimulable phosphor sheet 1 that has been scanned with this excitation light, stimulated emission light 13 having a light amount corresponding to the radiation image information stored and recorded is diverged. The stimulated emission light 13 enters the inside of the light guide 14 from one end face 14a of the light guide 14 formed by molding a transparent acrylic plate, and travels through the light guide 14 while repeating total reflection to form a circular shape. The light is emitted from the end face 14 b rounded into the light and is received by the photomultiplier (photomultiplier tube) 15. The photomultiplier 15 outputs an analog image signal S corresponding to the amount of stimulated emission light 13, that is, the analog image signal S indicating the radiation image information.

The image signal S is logarithmically amplified by a logarithmic amplifier 16 and then passed through an A / D converter 17 to be converted into a digital image signal Do. This digital image signal Do is then sent to the averaging processing circuit 18, subjected to averaging processing described later, and converted into a digital image signal D. The digital image signal D is then subjected to image processing such as gradation processing in the image processing circuit 20, and then sent to the image reproducing device 21,
It is used for reproducing radiographic images. This image playback device 21
May be a display means such as a CRT or a recording device for performing optical scanning recording on a photosensitive film.

Next, description will be given of how to prevent density unevenness in a read image due to mode hopping of the semiconductor laser 30. The semiconductor laser driving circuit 34 receives the high frequency signal RF from the modulation circuit 35,
30 is periodically modulated directly on the basis of this radio frequency signal RF. The change in the optical output of the laser beam 31 thus modulated is shown in (1) of FIG. As shown, the laser beam 31 is modulated according to a predetermined sine function so that the maximum output is 20 mW and the minimum output is 18 mW.

On the other hand, the above-mentioned A / D converter 17 is (2) in FIG.
As shown in, the time t1, t within the one-pixel reading period To
The analog image signal S is sampled at 2, t3, and t4, respectively. Therefore, the digital image signal Do output from the A / D converter 17 consists of four digital signals per pixel. The averaging circuit 18 performs an averaging process on the digital image signal Do to convert the four digital signals per pixel into one digital signal. As shown in (1) of FIG. 3, the semiconductor laser 30 has a laser beam 31 within one pixel reading period To.
Are modulated in a cycle so that the integrated value of the light amount of is constant. In order to do so, in the present embodiment, the cycle of the one-pixel reading period To and the modulation cycle are made to coincide with each other, but generally, the former cycle may be an integral multiple of the latter cycle. ..

If the radiation image is reproduced by the image reproducing device 21 based on the digital image signal D that has been subjected to the averaging process described above, it is possible to prevent density unevenness due to mode hopping of the semiconductor laser 30 in the radiation image. Can be done.
The reason is as described in detail above.

In the embodiment described above, the analog image signal S is sampled four times during the one-pixel reading period To, but the number of samplings within this period To is not limited to four, but a plurality of times. Any number of times will do. However, in order to suppress the occurrence of image density unevenness due to mode hopping of the semiconductor laser 30, it is advantageous to increase the number of times of sampling.

Further, in order to form one digital image signal D from N (2.ltoreq.N) digital image signals Do per pixel obtained as described above, averaging is performed as in the above embodiment. In addition to processing, N digital image signals Do
May be added.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing a radiation image information reading apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of spectral sensitivity characteristics of a stimulable phosphor sheet.

3 is a graph showing the relationship between the modulation state of the semiconductor laser and the sampling period of the photodetector output signal in the radiation image information reading apparatus of FIG.

[Explanation of symbols]

 1 Storage phosphor sheet 11 Sub-scanning means 13 Photostimulated emission light 14 Optical guide 15 Photomultiplier 17 A / D converter 18 Averaging circuit 30 Semiconductor laser 31 Laser beam 32 Optical deflector 34 Semiconductor laser drive circuit 35 Modulation circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H04N 1/04 E 7251-5C

Claims (1)

[Claims] 1. A radiographic image in which a stimulable phosphor sheet on which radiographic image information is stored and recorded is two-dimensionally scanned by excitation light, and photostimulated luminescent light emitted from the sheet is detected by a photodetector. In a radiation image information reading device for reading information, a single mode semiconductor laser is used as a light source for emitting the excitation light, and an output signal of the photodetector is output N times (2 ≦ N) within one pixel reading period. ) A / D converter for sampling, signal processing means for forming one digital image signal based on N digital image signals obtained within one pixel reading period, and the semiconductor laser for reading one pixel A radiation image information reading device, comprising: a modulation unit that periodically modulates the light amount integrated value within a period to be constant.