JPS6297469A - Radiograph reader - Google Patents

Abstract

PURPOSE:To increase a reading speed, to heighten sensitivity for a radiation ray, and to obtain good sharpness by providing an image intensifying tube between a condensing and transmitting means for stimulated phosphorescene light emission and a photoelectric conversion means. CONSTITUTION:An image intensifying tube 102 is provided between a line type CCD101 which performs a photoelectric conversion, and an optical lens 105 which condenses the accelerated emitting light. Accelerated emitting light 107 at a position (A-A') is converged with the optical lens 105, and is added on the image intensifying tube 102 through a filter 106. The image intensifying tube 102 intensifies the accelerated light captured on an input surface 102b by at least, several thousands fold, and outputs it from an output surface 102a, and projects it on the line type CCD101. At such a time, it is permitted that a lens can be provided between the line type CCD101 and the output surface 102a, or, they can be adhered closely. By using the intensifying tube 102, con straint against the sensitivity is cancelled, and also, the reading speed can be increased remarkably.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application) The present invention relates to reading radiation image information using a radiation image conversion panel (hereinafter abbreviated as conversion panel) having a photostimulable phosphor layer. The present invention relates to the collection and transmission of stimulated luminescence and photoelectric conversion related to reading of the radiation image information.

(Background of the Invention) Radiographic images such as X-ray images are often used for disease diagnosis. In order to obtain this X-ray image, the X-rays that have passed through the subject are irradiated onto a phosphor layer (fluorescent screen), which generates visible light. So-called radiography is used in which a film using silver salt is irradiated and developed. However, in recent years, methods have been devised to directly extract images from the phosphor layer without using a film coated with silver salt.

This method involves making a phosphor absorb the radiation that has passed through the object, and then exciting the phosphor with, for example, light or thermal energy, so that the phosphor releases the radiation energy accumulated through the absorption. There is a method of emitting it as light, detecting this fluorescent light, and creating an image. Specifically, for example, U.S. Pat.
No. 5-12144 discloses a radiation image conversion method using a photostimulable phosphor and using visible light or infrared rays as photostimulation excitation light. This method uses a conversion panel in which a photostimulable phosphor layer is formed on a support, and the radiation transmitted through the object is applied to the photostimulable phosphor layer of this conversion panel, so that the radiation transmits through each part of the object. A latent image is formed by accumulating radiation energy corresponding to each part, and then by scanning this photostimulable phosphor layer with photostimulation excitation light, the accumulated radiation energy of each part is emitted and the image is illuminated. An image is obtained from an optical signal based on the intensity of this light.

This final image may be reproduced as a hard copy or on a CRT.

In the method described above, a conversion panel that stores radiation images as latent images is main-scanned with a spot light for photostimulation excitation, and the generated stimulated luminescence is photoelectrically converted to read radiation image information.

Main scanning using this spot light requires a considerable amount of time.

For example, if the reading area of the conversion panel is 400 x 360,
If the pixel size is 200μm＋×20011m, then 3
．． The number of pixels is 6 X l O', and each pixel is 2.
Assuming that the stimulated excitation spot light is irradiated for 011Sec, it will take 72 seconds just for the main scan. This is also a problem in terms of tolerance for waiting time.

The only way to shorten the time in a spot light scanning system is to shorten the irradiation time per pixel. However, if the irradiation time is shortened, the amount of stimulated luminescence decreases and the sensitivity decreases, making it impossible to obtain high-quality read images.

Furthermore, the response characteristics of the stimulable phosphor to the stimulable excitation light and the frequency response characteristics of the photoelectric converter, amplifier, etc. become more susceptible to the influence, and the sharpness of the image deteriorates.

On the other hand, the applicant has already applied for patent application No. 60-151521.
In this issue, a novel radiation image conversion method and device are proposed that improve the conventional drawbacks of radiation image reading devices using conversion panels as described above.

According to this, the conversion panel is irradiated with photostimulated excitation light in a linear manner,
Since the generated stimulated luminescence is photoelectrically converted using an image sensor, it is possible to read the radiation image at high speed without reducing the sharpness of the image.

However, in the radiation image reading method and apparatus, demands for higher reading speed and higher sensitivity to radiation are becoming more severe.

(Object of the Invention) The present invention provides the above-mentioned proposed radiation iu++ using a conversion panel.
The present invention relates to an image reading method and an apparatus for further improving the same, and an object of the present invention is to provide a radiation image reading apparatus (hereinafter abbreviated as a reading apparatus) having a high reading speed.

Another object of the present invention is to provide a reading device that is sensitive to radiation.

Still another object of the present invention is to provide a reading device that provides a radiographic image with good sharpness.

(Structure of the Invention) The object of the present invention is to provide means for linearly irradiating at least photostimulable excitation light to a radiation image conversion panel having a photostimulable phosphor layer, and a means for linearly irradiating at least photostimulable excitation light to a radiation image conversion panel having a photostimulable phosphor layer; In a radiation image reading device having a means for condensing and transmitting stimulated luminescence and a means for photoelectrically converting the condensed and transmitted stimulated luminescence, a combination of the condensing and transmitting means and the photoelectric conversion means is provided. This is achieved by a radiation image reading device characterized by having an image intensifier tube provided between them.

In addition, in the present invention, the light collecting and transmitting means for stimulated luminescence is
It is preferable to use a light guiding member, and it is further preferable that the light condensing/light guiding member has an optical fiber bundle.

Next, the present invention will be explained in detail.

The present invention changes the conventional zero-dimensional irradiation unit of m-pixel irradiation in stimulated excitation, that is, spot irradiation, to a one-dimensional irradiation unit of linear irradiation, that is, pixel row unit irradiation, and utilizes an image intensifier tube. It is located where it was introduced.

Naturally, the collection of stimulated luminescence and transmission to the photoelectric converter also becomes a one-dimensional collection and transmission unit.

In the present invention, methods for linearly irradiating the conversion panel include, for example, = 6- (1) mask method in which the conversion panel is covered with a mask having linear slits and irradiated with stimulated excitation light, (2) line (3) Linear convergent light method where a cylindrical lens emits convergent light in a line, (4) Optical fibers are closely arranged in one dimension. Examples include an excitation light ray arrangement method in which an irradiation end face is made using a light-guiding sheet material, and stimulated excitation light is introduced from the other end.

In the case of narrow irradiation, the width of the stimulated excitation light on the conversion nosanel plane varies depending on the sharpness required for the image, but is less than 11, preferably 30 to 500 μm.

When using an irradiation light guide member in the linear arrangement method of the stimulated excitation light in (4) above, the width of the irradiation part, the numerical aperture (NA), and the distance from the conversion panel are taken into consideration when the stimulated excitation light is Adjust to match the width.

If stimulated excitation is performed by linear irradiation, stimulated luminescence will also emit light in a linear manner, and therefore it is necessary to collect the light in a linear form and transmit it to the photoelectric converter.

In addition, since the stimulated luminescence is emitted simultaneously in a linear manner, it is necessary to detect the stimulated luminescence intensity at each luminescent point (pixel) individually and simultaneously, so the photoelectric converter is connected to an imaging device (such as an OCD, an imaging device, etc.). pipe, etc.).

Furthermore, since the stimulated luminescence is weak light and the image sensor, which is the photoelectric converter, generally has low sensitivity, the stimulated luminescence is converted into an optical signal by an image intensifier tube before being photoelectrically converted by the image sensor. Well, it needs to be amplified.

For example, (1) a line-type photoelectric converter (for example, C0D) is used to collect the stimulated luminescence into a line, amplify it with an image intensifier tube, and then receive the light into a photoelectric converter. There is a one-dimensional image reception method that condenses and transmits the emitted light using an optical lens and receives the light as a comprehensive one-dimensional image. Furthermore, (2) the optical fibers are closely arranged one-dimensionally to form a one-dimensional optical fiber bundle with a condensing end face, and the other end is used as a transmission end face and brought into contact with the light-receiving surface of the image intensifier tube for amplification and then photoelectric conversion. There is a column light reception method, which can be further subdivided into (2) -a, the above transmission! 116, the original fiber is also one-dimensionally closely aligned with a vertical photoelectric converter (for example, C
aD) A one-dimensional light reception method in which light is received by a two-dimensional photoelectric converter (e.g. OO'D, image pickup tube, etc.) using the optical fiber at the transmission end surface as an original fiber bundle arranged in a two-dimensional plane. Examples include a two-dimensional light reception method in which light is received.

In the case of the dot array light reception method (2) using the optical fiber bundle, the sharpness of the image depends on the width of the original fiber bundle, the diameter of the optical fiber, the numerical aperture (NA), and the difference between the condensing end face and the conversion panel surface. It is determined by the interval etc.

The radiation image reading method according to the present invention comprises a combination of the method of linearly irradiating the stimulated excitation light described above and the method of collecting, transmitting and amplifying the linear stimulated luminescence and then receiving the light into a photoelectric converter. The reading device of the invention is therefore constructed based on a combination of the above methods. However, the embodiments of the irradiation light guide member and the light collecting light guide member are not limited to the above embodiments.

Further, although there is no limit to the number of irradiation light guide members and light collecting light guide members that constitute the present invention, it is possible to use a 1:1 combination, with two collective light guide members on both sides of one irradiation light guide member. A 1:2 combination or conversely a 2:1 combination arranged side by side is practical.

The optical fiber according to the present invention can be any type of original fiber used in optical communications, such as a step index type or a graded index type. Since stimulated luminescence of the optical fiber used in the light condensing light guide member is close to completely diffused light, it is preferable that the solid angle of reception is large, but the larger the solid angle of reception, the worse the sharpness of the image becomes.

In general, the acceptance solid angle of an optical fiber is given by the numerical aperture.
2, it is given by the following equation.

NA2fσ=Dingθ=23in'(NA)=23in'
(n) Therefore, it is preferable that the material and structure of the optical fiber 10- of the light collecting and guiding member according to the present invention are selected so as to satisfy the above-mentioned sharpness.

In addition, when the numerical aperture of the optical fiber used for the light condensing light guiding member is the same, the ratio of the outer diameter φ1 of the core material and the outer diameter φ2 of the sheath material (φ1/
As φ2) becomes larger, the light collection efficiency improves, but the sharpness of the N image tends to deteriorate. φ1/φ2 is φ1/φ2≧0.
If it is 5, there is no practical problem in terms of light collection efficiency.

Incidentally, the larger the diameter φ2 (equal to the outer diameter of the sheath material) of the optical fiber used in the light collecting light guide member, the more the light collecting efficiency improves, but the sharpness of the image deteriorates. It is generally selected from the range between 0.05 and 2, preferably between 0.05 and 1.

There are materials that provide optical fibers with a large numerical aperture and light-guiding plastics, such as polyacrylic resin, polystyrene resin, soft vinyl chloride resin, vinylidene chloride resin, transparent polyamide resin, polycarbonate resin, polyester resin, epoxy resin, Examples include fluororesin and polyethylene resin, which are used in combination as core and sheath resins based on nl and η2.

Plastic optical fibers also have the advantage of being inexpensive and easy to process.

In addition to the plastic optical fibers, examples of optical fibers with large aperture numbers include composite optical fibers made of the light-guiding plastic and quartz glass, and multicomponent quartz optical fibers made of multicomponent quartz glass.

LHiD is used as the light source for photostimulation excitation according to the present invention.

Examples include a halogen lamp, a tungsten lamp, a fluorescent lamp, a sodium lamp, a xenon lamp, an electrodeless discharge lamp using a seven-wave microphone, or a laser. Examples of lasers include He-Nθ laser, He-Od laser, Ar ion laser, Kr ion laser, N2 laser, YAG laser and its second harmonic, ruby laser, semiconductor laser, various dye lasers, copper vapor laser, etc. There are metal vapor lasers, etc.

When the light source light includes a portion that overlaps with the stimulated emission spectrum, it is preferable to use a filter that cuts off this spectral portion. Furthermore, it is preferable to use a filter that passes stimulated luminescence and cuts stimulated excitation light in the photoelectric converter.

As the photostimulable phosphor of the conversion panel according to the present invention, many photostimulable phosphors such as those exemplified in Japanese Patent Application No. 59-266912 can be used.

However, the phosphor is not limited to the above-mentioned phosphors, and may be any phosphor that exhibits stimulated luminescence when irradiated with radiation and then irradiated with stimulated excitation light.

Next, the present invention will be specifically explained using figures.

Figure 1 shows that an Lll:D array (linear light source method) is used for irradiation with stimulated excitation light, and an optical lens is used as a means for focusing and transmitting stimulated luminescence.
An example of an embodiment of a reading device of the present invention of a one-dimensional image reception type using a line type 00D as a photoelectric conversion means is shown. Figure (a) is a perspective view, and figure (b) is a cross-sectional view taken along a plane that includes the intersection line A-A' between the linearly irradiated stimulated excitation light and the conversion panel surface and the light collection direction. .

In Fig. 1, 101 is a line type 00D that performs photoelectric conversion;
Reference numeral 102 is an image intensifier tube to be described later, in which the stimulated luminescence captured by the input surface 102b is intensified at least several thousand times and sent to the output surface 102.
a to the line type C0D 101, where it is photoelectrically converted.

Reference numeral 103 is a linear LED light beam that linearly illuminates the conversion panel 104 at the A-A' position in the figure.

Note that the conversion panel 104 moves at a constant speed in the Y direction and is sub-scanned.

The stimulated luminescence 107 at the A-A' position is caused by optical lens 1.
05, passes through a filter 106, enters the image intensifier tube 102, becomes an intensified photoelectron 108, and becomes a line type 00D'
Project a one-dimensional image onto LO1.

At this time, a lens may be provided between the line type C0D 101 and the output surface 102a, and the image output to the output surface 102a may be formed on the image detection section 101, or
A may be brought into close contact with a.

In addition, if a fiber plate in which a large number of original fibers are bundled is used as the window material of the output fluorescent surface that constitutes the output surface 102a, blurring of the output image due to the thickness of the window material can be prevented, and the sharpness of the obtained image will be improved. do.

Next, another embodiment of the present invention is shown in FIG. That is, this is an example of a combination of the excitation beam array method and the two-dimensional light receiving method of the dot array light receiving method. In this example, since one-dimensional images are stored two-dimensionally, it is necessary to rearrange them as one-dimensional image signals without disturbing the information.

FIG. 2(a) is a perspective view of the reading device, and FIG. 2(b) is a straight line A-A" formed by the linear stimulated excitation light on the surface of the conversion panel 104.
FIG.

In FIGS. 2(a) and (b), 104 is a conversion panel;
206 is a stimulated excitation light source, 204 is an irradiation light guide member using an optical fiber or a light guide sheet, 204b is an irradiation end face,
203 is a condensing light guide member, 203b is a condensing end face, 202 is an image intensifier tube, and 201 is a two-dimensional CCD. The rest of the mechanism is the same as that of the above-mentioned reading device &.

In the illustrated example, the irradiation light guiding member and the condensing light guiding member have a combination of l:], but as described above, there is no limit to the combination.

This combination, its irradiation end face 204b, and its condensing end face 203b
The morphology of the vicinity is shown in FIGS. 3(a), (b), and (c). The figure (a) shows the irradiation light guide member 304 and the light condensing light guide member 3.
03 is kept parallel by the holding plate and converts the panel ]-0
In the example shown in FIG. 3(b), they are held adjacent to each other at an angle suitable for irradiation of stimulated excitation light and condensation of stimulated luminescence. Further, (Q) in the same figure is an example in which irradiation with stimulated excitation light is performed from two directions to increase the excitation effect and concentrate stimulated luminescence to one direction.

Further, FIG. 4 shows a light guiding member 401 made of an optical fiber bundle used for irradiation or focusing. In the irradiation light guide member, 401a and 401b serve as an introduction end face and an irradiation end face for stimulated excitation light, respectively, and in the condensing light guide member, they serve as a transmitting end face and a light collecting end face for stimulated luminescence, respectively.

The light guiding member may be provided with a cover or a single layer of cover for blocking light or protecting it from damage.

Next, the light collecting end face of the light collecting light guiding member will be explained.

In FIG. 2(c), 203p, 203q, and 203r are optical fiber wires constituting the light collecting and guiding member 203,
On the condensing end surface 203b side, they are arranged densely in one dimension. On the transmission end surface 203a side, they are two-dimensionally arranged densely.

The range in which the optical fiber wire 203p can focus stimulated luminescence on the conversion panel 104 is determined by the numerical aperture (NA) and diameter (φ2) of the optical fiber wire 203p, the outer diameter φ1 of the core material and the outer diameter φ2 of the sheath material. It is determined by the ratio (φl/φ,) and the distance (h) between the condensing end surface 203b and the conversion panel 104, which is 104p in the figure. Similarly, for 203q, 104q,
It is 104r compared to 203r. Here 104p, 10
4q, 104r, etc. correspond to pixels of a radiation image.

As can be seen from the figure, the numerical aperture (N
A), the diameter (φ2), the distance from the conversion panel (h), etc. are appropriately selected to determine the pixel size.

The pixel size is generally 50 to 400 μm. Also, each pixel 104p, lO4q, 104
It is preferable that r be independent, and if they overlap, the sharpness of the image will deteriorate.

In FIG. 2(c), for example, stimulated luminescence from 104p enters optical fiber strand 203p and is transmitted to transmission end surface 203a. Stimulated luminescence emitted from 203a is amplified by an image intensifier tube and converted into an electrical signal by an image sensor. The electrical signals are reconstructed in the order of arrangement of each pixel of the conversion panel.

Next, the image intensifier tube will be explained.

FIG. 5(a) is a sectional view of an example of an image intensifier tube.

501 is an image intensifier tube, 502 is a light entrance window, and 503 is a photocathode that converts incident light into electrons.

Reference numeral 504 denotes an electron lens that controls the flight direction of the generated electrons, for example, divergence or convergence. 505 is a microchannel brake that multiplies electrons controlled by an electron lens) (
(denoted as MOP).

The multiplied electrons enter the fluorescent surface 506 and are converted into light again. Incidentally, the portion from the photocathode 503 to the fluorescent surface jQ6 is a vacuum tube.

In addition, the entrance window 502 can be made of flat glass or an optical fiber plate to provide a low-distortion type, and furthermore, if an original fiber is used as the window material for the fluorescent surface 506, coupling with other image elements can be made more efficient. Become.

FIG. 5(b) shows the operating principle of an image intensifier.

When an image is formed on the photocathode 503 through the lens L, photoelectrons e fly out depending on the brightness of the image, and this photoelectron image is enlarged or reduced by the electron lens 504 and then converted to the MOP.
It is imaged in the entrance direction of 5Q5, passes through the channel of the MOP while being intensified and accelerated at least several thousand times while colliding with the channel wall, enters the fluorescent surface 5Q6, and is observed again as an optical image. The brightness of the final observed image can be increased approximately 40,000 times compared to the brightness of the initial image.

FIG. 6(a) is an enlarged view of the MOP, and FIG. 6(b) shows the enhancement mechanism with one channel taken out.

The illustrated MOP is a thin glass plate with a diameter of 25 mm and a thickness of 0.48 mm, but it has 15 thin holes of 12 μmφ.
It has a honey structure with about 10,000 photoelectrons, and when a photoelectron θ enters the channel, the photoelectron e starts colliding with the inner wall due to the potential gradient, and the collision generates secondary electrons. Since secondary electrons are generated, the output electrons are at least several thousand times stronger than the input photoelectrons.

Furthermore, each of the approximately 1.5 million channels can be made to correspond to each pixel of an image, so each pixel is simultaneously enhanced according to its brightness.

In the image intensifier tube according to the present invention, in addition to the embodiment in which an image element such as a CCD is brought into contact with the fluorescent surface 506 shown in FIG. Alternatively, a mode may be adopted in which a semiconductor device detection element is placed and the image is directly converted into an image.

Further, in the present invention, an image intensifier tube that does not use the MCP may be used. An example is shown in FIG. 5(c).

In this example, the brightness of the fluorescent image is enhanced by reducing the electron image using an electron lens and accelerating the electrons.

(Effect of the invention) In reading radiation images using a photostimulable phosphor, sensitivity,
Graininess and sharpness are mutually contradictory characteristics, and it was extremely difficult to improve all of these characteristics at the same time. However, by using an image intensifier, restrictions on sensitivity were largely removed, and image quality and sharpness were improved. The aspect of tone reproduction or control has been greatly liberalized.

Furthermore, by using an image intensifier tube, it has become possible to significantly improve the reading speed of radiographic images.

[Brief explanation of drawings]

FIG. 1 is a perspective view and a sectional view showing an example of a reading device having a combination of a linear light source method and a one-dimensional image reception method. FIG. 2 is a perspective view and a sectional view showing an example of a reading device having a combination of an excitation beam array method and a two-dimensional light reception method using a dot array light reception method. FIG. 3 is a diagram showing an example of the arrangement of the irradiation end face and the condensing end face. Further, FIG. 4 is a perspective view of an example of a light guide member made of a fiber bundle used for irradiation and focusing. FIG. 5 is a cross-sectional view of an example of an image intensifier tube and a diagram explaining the operating principle;
FIG. 6 is an enlarged perspective view of the MOP and an explanatory diagram of the reinforcement mechanism. 101...Line type 00D. 102.202... Image intensifier tube, 103... LED array, 104... Conversion panel, 105... Optical lens, 106... Filter, 201... Two-dimensional COD. 203... Light collecting light guide member, 204... Irradiation light guide member, 206... Stimulating excitation light source, 501... Image intensifier tube, 503... Photocathode, 504... Electron lens, 505 ...MOP. 506... Fluorescent surface, 601... Channel applicant Konishi Roku Photo Industry Co., Ltd. Figure 2 Figure 3 ('a> Hiroshi) 01b Figure 5 <a> g, 3. Figure 5 (α) (4 粂 in(,1)/

Claims (2)

[Claims] (1) means for irradiating at least photostimulable excitation light onto a radiation image conversion panel having a photostimulable phosphor layer; and means for collecting and transmitting stimulated luminescence generated by the irradiation with the photostimulable excitation light; A radiation image reading device having a means for photoelectrically converting the focused and transmitted stimulated luminescence is characterized in that an image intensifier tube is provided between the light collecting and transmitting means and the photoelectric converting means. Radiographic image reading device. (2) The radiation image reading device according to claim 1, wherein the light collecting/transmitting means is a light collecting/light guiding member having an optical fiber bundle.