JP2557213B2 - Radiation image information reader - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention provides image information recorded and accumulated by irradiating a radiation image conversion panel having a stimulable phosphor layer (hereinafter simply referred to as a conversion panel) with radiation. No image information of stimulable fluorescence that occurs after scanning the conversion panel surface by stimulating excitation light,
The present invention relates to an improvement of a radiation image information reading device that reads this by a detection system.

BACKGROUND OF THE INVENTION When a stimulable phosphor is irradiated with excitation light such as X-rays, electron beams, and ultraviolet rays, a part of the energy is temporarily metastable in the crystal of the stimulable phosphor depending on the irradiation dose. Accumulated in. When this is stimulated with stimulable excitation light such as visible light or infrared light, stimulable fluorescence emission that is proportional to the accumulated energy occurs. This phenomenon can be used for recording image information formed by various kinds of radiation. For example, in JP-A-55-12144, an image formed by radiation such as X-rays is formed on a conversion panel having a photostimulable phosphor layer. Information exposure is given to absorb radiation energy to form a kind of latent image, and then the conversion panel surface is scanned with a beam of stimulated excitation light, and the stimulated emission intensity of the phosphor is read by a detection system. A method of obtaining radiation image information is disclosed. In such a method, a laser beam or the like is usually used as the stimulated excitation light, and a photodetector such as a photomultiplier is used to read the stimulated emission, and the stimulated emission intensity is photoelectrically converted and extracted as an electric signal. Finally, it is used as a visible image in hard copy or reproduced on a CRT.

FIG. 4 is a configuration diagram of a digital radiography system using a stimulable phosphor, and FIG. 5 is a schematic diagram of an image information reading device. In these drawings, 1 is a radiation generating device such as an X-ray tube, 2 is a subject, and 3 is a radiation image conversion panel, and the image is mounted in the image information reading device 4 according to the conventional image capturing. The completed conversion panel 3 is conveyed by the conversion panel 3 in a direction perpendicular to the main scanning direction of the laser beam L passing through the vibration mirror (galvanometer mirror) 41 and the fθ lens 42 in the apparatus. Scan the entire surface. The light generated by scanning is collected in the photomultiplier tube 44 by the optical fiber assembly 43, converted into a time series electric signal, and then A / D converted.

Next, in the image processor 5, the digitized electric signal is subjected to processing such as gradation processing and edge enhancement processing by a computer according to the diagnostic purpose. The processed image is immediately displayed on the CRT monitor 6. Further, the processed image can be stored and stored in the memory device 7 such as a magnetic disk, a magnetic tape, an optical disk, a magneto-optical disk or the like.

The image recording device 8 is a part for performing D / A conversion on the processed signal, and again performing laser beam modulation by an optical modulator, and writing on the film F by this scanning. The written film is automatically developed to obtain a processed X-ray photograph as a final output image.

The radiation image information processing apparatus as described above has an extremely wide radiation exposure area that can be recorded, can freely perform signal processing on image information obtained as an electric signal, and can obtain an image most suitable for the purpose. Has features. In particular, there is an advantage that a clear image with a wide visible range can be constantly obtained, and low dose imaging can be performed according to the purpose.

In the image information reading device 4, the laser beam L of the stimulated excitation light is main-scanned by the galvanometer mirror 41 driven by the deflector, passes through the fθ lens 42, and is applied to the conversion panel 3. Laser beam L
Is irradiated, the radiation image recorded from the conversion panel 3 appears as stimulated emission. This stimulated excitation light emission is a light amount corresponding to the accumulated energy due to the initial irradiation amount of radiation.

[Problems to be Solved by the Invention] The sharpness of an image in the above-described radiation image information reading apparatus using the stimulable phosphor is determined depending on the spread of the stimulable excitation light in the conversion panel. On the image main scanning line of the conversion panel which is a sensitive detection system during reading scanning, stray light such as external light other than the laser beam or diffused reflection light, return scattered light from the scanning line, flare component light of the laser beam, light beam When scattered light at the time of shaping is incident, noise is generated in the stimulated excitation light, the sharpness (resolution) of the image of the obtained radiation image information is reduced, and noise image reproduction different from the original information that was recorded, This causes deterioration of image quality.

[Means for Solving the Problems] In view of the above-mentioned drawbacks, the present invention prevents the incidence of external light other than the laser beam on the main scanning line by the laser beam for reading the image accumulated on the conversion panel, It is an object of the present invention to provide a radiation image information reading device capable of obtaining a radiation image of good quality.

The radiation image information reading device of the present invention to achieve the above object, the radiation image conversion panel having a stimulable phosphor layer in which the radiation image information is stored and recorded is exposed by scanning with a semiconductor laser beam which is excitation light, and image information is obtained. According to, in a radiation image information reading device for photoelectrically converting the stimulated emission light by a photodetector to read image information, before the semiconductor laser beam that is the excitation light is incident on the panel, and the radiation image conversion panel A diaphragm plate having a slit is provided outside the optical path between the photodetector, and the width of the slit in the direction perpendicular to the scanning direction of the semiconductor laser beam as the excitation light is larger than the beam diameter at the diaphragm position. It is characterized by that.

[Examples] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic perspective view of a radiation image information reading apparatus according to the present invention. Regarding the reference numerals used in the drawings, the same functional portions as those in FIGS. 4 and 5 are given the same reference numerals.

Radiation image information conversion panel 3 having stimulable phosphor layer
Is installed at a predetermined position in the image information reading device.
The main scanning system and the reading system of the reading device are integrally formed so as to be movable in the linear direction, and the sub scanning (b) is performed by moving relative to the conversion panel 3. Reference numeral 50 denotes a semiconductor laser device for generating stimulated excitation light, which is driven by a laser driver 51. The laser beam L generated by the semiconductor laser device 50 is collimator lens 52, monochromatic light filter 53, beam shaping optical system (prism pair) 5
4. After reaching the deflector 56 through the mirror 55. The deflector 56 includes a galvanometer mirror (vibration mirror) 41 driven by a deflector driver 57, and vibrates and deflects the laser beam L in a scanning region at a constant angular velocity. The deflected laser beam L is adjusted by the fθ lens 42 so as to have a constant speed on the main scanning line, and is main-scanned on the conversion panel 3 in the arrow (a) direction via the mirror 58. At the same time, the conversion panel 3 relatively moves in the direction of the arrow (b) (sub-scanning), and the entire surface of the conversion panel 3 is raster scan-scanned.

The photostimulable light generated by the conversion panel 3 after being scanned by the laser beam L is condensed by the optical fiber assembly 43 and passes through the filter 45 that allows only the wavelength region of the photostimulable light to pass therethrough. It reaches the light-receiving portion provided with and is converted into an analog electric signal. The image signal output as a current from the photomultiplier tube 44 is voltage-amplified through the current-voltage conversion amplifier 61, and further a Log converter 62 for converting the emission intensity signal into an image density signal, in synchronization with the image clock signal. After passing through the sample hold circuit 63 that maintains the signal for a certain period,
After being converted to a digital signal by the A / D converter 64,
Stored in memory 65. The memory 65 is connected to a CPU 66 that performs digital calculation and the like. The CPU 66 can be connected to an external device such as a computer for storing and processing data, a CRT display device or a printer for outputting an image through the interface 67, and can calculate and transfer the data stored in the memory. And

A diaphragm plate 59 is fixedly provided between the mirror 58 and the main scanning line of the conversion panel 3. The diaphragm plate 59 is provided in the vicinity of the main scanning line of the conversion panel 3, and has a slit 59A through which the main scanning light of the laser beam L passes.

FIG. 2 is a side sectional view schematically showing an optical system of the reading device according to the present invention. FIG. 3 is an enlarged explanatory view of the luminous flux of the laser beam L. In these figures, the diaphragm plate 59 is at a position that does not prevent the light receiving end surface of the optical fiber assembly 43 from approaching the main scanning line on the conversion panel 3, that is, the optical path through which stimulated emission enters the light receiving end surface of the optical fiber assembly 43. The slit 59A having a width W is fixed at a position a distance l before the main scanning line of the outer conversion panel 3 and has a width W at substantially the center. The laser beam L is on the main scanning line and has a spot diameter d (about 120
μm), and a curved surface having an asymptote of the spread angle θ. Here, the spread angle θ is represented by the following equation.

θ = tan ⁻¹ (2λ / πdn) (1) When θ is a minute angle, the equation (1) is expressed by θ≈2λ / πdn (2). In the formula, λ ... Emission wavelength of semiconductor laser device (λ = 780 μm in case of GaAlAs semiconductor laser) n ... Refractive index (n = 1 in case of air) π ... Circular ratio Beam diameter D at a position 1 from the main scanning line Is n
When = 1, it is expressed by the following equation.

D = lθ = 2λl / πd (3) The slit width W of the diaphragm plate 59 needs to be larger than the size of D. When the slit width W becomes D or less,
The laser beam is narrowed down and the s / n ratio of the read image signal decreases. Also, the sharpness of the image read by the laser beam diffracts is reduced. In the actual device, due to various problems in the work,
It is desirable to set at least twice as much as. That is, the minimum slit width Wmin is Wmin ≧ 2D. By substituting the equation (3) into this, Wmin ≧ 4λl / πd (4) is obtained.

Next, according to the experimental results, when the slit width W becomes 8 times or more the laser beam diameter D at the position of the diaphragm plate 59, the unnecessary light enters the conversion panel surface, and the effect of the slit becomes thin. I will end up. That is, the maximum slit width Wmax is expressed by the following equation.

Wmax ≦ 16λl / πd (5) It is desirable that the diaphragm plate 59 including the slit 59A is as close as possible to the main scanning line, but the optical fiber assembly 43 is arranged very close to the main scanning line. It is fixed at an appropriate position so that it does not interfere.

Here, when the position of the diaphragm plate 59 is set to 1 = 60 mm and the spot diameter d of the laser beam is set to 120 μm using a GaAlAs laser (wavelength λ = 780 nm), the maximum and minimum dimensions of the slit width are Wmin≈0.5. mm Wmax ≈ 2.0 mm.

Therefore, if a parallel slit having a slit width W within the range of 0.5 to 2.0 mm is created, the unnecessary light is cut and the image deterioration is prevented. The required slit width Wmin, Wmax
Since both are proportional to the distance l, when the diaphragm plate 59 is brought close to the conversion panel 3, the slit width W is set to be narrow in proportion to the distance l.

[Advantages of the Invention] As described above, according to the radiation image information reading apparatus of the present invention, unnecessary light other than the scanning laser beam enters the main scanning line of the image information conversion panel forming a sensitive detection system during reading scanning. This is prevented, and the reproduced image of the radiation image information is a high quality image having excellent resolution, sharpness and gradation without noise.

[Brief description of drawings]

1 is a schematic perspective view of a radiation image information reading device according to the present invention, FIG. 2 is a partial schematic view of an optical system of the reading device, and FIG.
The figure is an enlarged explanatory diagram of the luminous flux of the laser beam. FIG. 4 is a block diagram of digital radiography using a stimulable phosphor, and FIG. 5 is a schematic diagram of a conventional image reading apparatus. 3: Radiation image conversion panel 4: Image information reader 41: Galvanometer mirror (vibration mirror) 42: fθ lens, 43: Optical fiber assembly 44: Photomultiplier tube 50: Semiconductor laser device, 58: Mirror 59: Aperture plate , 59A: Slit a: Main scan, b: Sub-scan D, d: Beam diameter, l: Interval L: Laser beam, W: Slit width

Claims (3)

(57) [Claims] 1. A radiation image conversion panel having a stimulable phosphor layer on which radiation image information is stored and recorded is exposed by scanning with a semiconductor laser beam as excitation light, and photostimulated emission light according to image information is detected. In a radiation image information reading device for photoelectrically converting image information by a device, before the semiconductor laser beam that is the excitation light enters the panel, and outside the optical path between the radiation image conversion panel and the photodetector. In the radiation image information reading device, a diaphragm plate having a slit is provided, and a width of a semiconductor laser beam, which is excitation light of the slit, in a direction perpendicular to a scanning direction is larger than a beam diameter at the diaphragm position. . 2. The radiation image information reading apparatus according to claim 1, wherein the width W of the semiconductor laser beam as the excitation light of the slit in the direction perpendicular to the scanning direction satisfies the following expression. . 4λl / πd ≦ W ≦ 16λl / πd, where λ is the wavelength of the semiconductor laser beam that is the excitation light, and
Is the distance between the diaphragm plate and the panel, π is the circular constant, and d is the spot diameter of the semiconductor laser beam, which is the excitation light, on the scanning line of the panel. 3. The distance l between the diaphragm plate and the panel is 5 mm or more 2
The radiation image information reading apparatus according to claim 2, wherein the radiation image information reading apparatus has a length of 00 mm or less.