JP2704382B2 - Radiation image information recording / reproduction method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording and reproducing radiation image information using a stimulable phosphor sheet, and more particularly to a method for recording and recording on a stimulable phosphor sheet. The present invention relates to a radiographic image information recording / reproducing method capable of reading the obtained radiographic image information without being affected by instantaneous light emission afterglow. [0002] Certain phosphors are exposed to radiation (X-ray, α-ray,
(β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a part of the energy of this radiation is accumulated in the phosphor, and then, when the phosphor is irradiated with excitation light such as visible light, it accumulates. The phosphor emits photostimulated luminescence in accordance with the applied energy. A phosphor exhibiting such properties is referred to as a stimulable phosphor. Utilizing this stimulable phosphor, radiation image information of a subject such as a human body is temporarily stored and recorded on a sheet having a layer made of a stimulable phosphor, and this is scanned with excitation light to excite. There has been proposed a radiation image information recording / reproducing method in which light is emitted, the stimulated emission is photoelectrically read, an image signal is obtained, and the image signal is processed to obtain a radiation image of a subject having good diagnostic suitability (for example, Japanese Patent Application Laid-Open Publication No. H11-163873). Kaikai 55-12429, 56-11395
Nos. 56-163472, 56-104645, and 55-116340). The sheet having the layer composed of the stimulable phosphor is hereinafter referred to as a "stimulable phosphor sheet" or simply as a "sheet". FIG. 1 shows a radiation image information reading apparatus used in the radiation image information recording / reproducing method proposed as described above, and the mechanism thereof will be described below. A laser beam 1a having a constant intensity from a laser light source 1 is made to enter a galvanometer mirror 2 as excitation light. The galvanometer mirror 2 causes the laser beam to main scan in the width direction of a sheet 3 placed below the galvanometer mirror 2. The laser beam is deflected so as to irradiate the sheet 3 (scan in the direction of arrow A). The sheet 3 is attracted to, for example, the endless belt device 9 and is conveyed in the direction of arrow B. Therefore, the main scanning is repeated at an angle substantially orthogonal to the sub-scanning, and the two-dimensional laser light 1b over the entire surface of the sheet 3 is used. Scanning is performed. The laser beam 1b is scanned according to the scanning by the laser beam 1b.
Is irradiated with light in accordance with the image information stored and recorded therein, and the emitted light is read by the photoelectric reading means including the condenser 4 and the photomultiplier 5. That is, the light collector 4 has a front end face 4a which is a light receiving surface extending in the main scanning direction, that is, in parallel with the main scanning line, in the vicinity of the sheet, and arranged so as to face substantially the entire width of the sheet in the main scanning direction. The emitted light enters the transparent light collector 4 from the front end face 4a. The light collector 4 has a front end 4b located in the vicinity of the sheet 3 formed in a planar shape, and is formed so as to gradually become cylindrical toward the rear end, and becomes substantially cylindrical at the rear end 4c. And the front end face 4a
The stimulated emission light entering from is collected at the rear end 4c and transmitted to the photomultiplier 5 via a filter (not shown) that selectively transmits the stimulated emission light. In the photomultiplier 5, the stimulated emission light is converted into an electric signal, and the obtained electric signal is sent to an image information processing circuit 6, subjected to various processes, and output to a CRT 7 as a visible image, for example. Or directly recorded as a hard copy on a photographic light-sensitive material or the like, or temporarily recorded on the magnetic tape 8 for them. [0007] As described above, the reading of image information is performed.
Since the front end face 4a, which is the light receiving surface, is parallel to the main scanning line and has a width that is almost the entire width of the sheet 3, all light from a position where the front end face 4a can be seen is read, and the laser light 1b Not only the stimulated emission light from the portion where the light is incident, but also all the light from the portion on the sheet 3 where the front end face 4a can be seen. As the light other than the stimulated emission light that is incident on and read from the front end face 4a, the afterglow emitted from the sheet 3 poses a problem. The afterglow includes instantaneous emission afterglow and stimulated emission afterglow. [0008] The instantaneous emission afterglow means that the instantaneous emission light of the sheet when the radiation is irradiated to record image information on the sheet is attenuated without erasing even after the irradiation of the radiation is stopped. Say what happens. The characteristics of this instantaneous luminescence afterglow vary depending on the type of stimulable phosphor used in the sheet, but are generally as shown in FIG.
FIG. 2 is a graph showing the light emission intensity on the vertical axis and the time (t) on the horizontal axis. After the irradiation is performed for Δt from time t ₁ to t ₂ , and the irradiation is stopped, the light emission intensity “A” is obtained. The intensity of the instantaneous emission light does not immediately become zero, but the instantaneous emission afterglow whose intensity decreases along an exponential function whose time constant gradually increases is shown. Specifically, the decay of the emission intensity of the instantaneous emission afterglow is, for example, about 180 seconds after irradiation (ie,
The emission intensity “B” of the instantaneous emission afterglow at the time “t ₃ ” at (t ₃ −t ₂ ) = 180 seconds) is about 10 ⁻ of the intensity of the stimulated emission light generated by the excitation light scanning. It will be about ⁴ times. For this reason, after irradiating the sheet with radiation through a subject and recording image information, if a predetermined time elapses before reading the image information, the intensity of the instantaneous afterglow is sufficiently reduced, and the afterglow is ignored. You can do it. However, when the radiation image information is read immediately after recording, the instantaneous emission afterglow is read before the emission intensity is sufficiently attenuated, and the influence of the instantaneous emission afterglow on the read image information increases. Also, the stimulated emission light is emitted from a very small area where the excitation light is incident, while the instantaneous emission afterglow is emitted from the entire surface irradiated with the radiation. From the front end face 4a of the light collector 4, stimulated emission light and instantaneous light emission afterglow from all places where the front end face 4a can be seen are simultaneously taken in and sent to the photomultiplier 5. In this case, the area of the portion where the front end face 4a of the light collector 4 can be seen is extremely large compared to the area of the portion of the sheet 3 where the laser beam is irradiated. Even after a lapse of time, even if the intensity of the instantaneous emission afterglow becomes negligibly small compared to the intensity of the stimulated emission light, the amount of the instantaneous emission afterglow cannot be ignored as the amount of light transmitted to the photomultiplier 5. . As described above, when image information is obtained by reading stimulated emission, there is a problem that instantaneous emission afterglow becomes a noise component of an image signal, and it becomes difficult to accurately read radiation image information. In particular, the problem of the noise due to the instantaneous emission afterglow becomes more serious as the time from the recording of the radiation image information to the reading is shorter. That is, the present applicant can continuously and efficiently record and read radiographic image information, and particularly, as an apparatus suitable for mass screening, puts a stimulable phosphor sheet in a predetermined circulation path. A circulating conveying means for conveying along the circulating passage, irradiating the sheet with radiation through the subject to irradiate the image with a radiation image information of the subject on the sheet; An excitation light source that emits excitation light for scanning a sheet on which radiation image information is stored and recorded in the image recording unit, and a photostimulated light emitted from the sheet scanned by the excitation light is read to obtain an image signal. An image reading unit comprising a photoelectric reading unit, and an image being recorded on a sheet in the circulation passage after the image reading is performed by the image reading unit. A so-called built-in type in which an erasing section for emitting radiation energy remaining on the sheet is incorporated in one apparatus in advance, and the stimulable phosphor sheet is circulated between the sections and used repeatedly. Has previously proposed a radiation image information recording / reproducing apparatus (Japanese Patent Application No. 58-66730). However, in this apparatus, since the stimulable phosphor sheet is recycled and used in general, the time from image recording to reading is generally short. It is extremely short, and the noise caused by the above-mentioned instantaneous emission afterglow is a particular problem. The present invention has been made in view of such a problem, and records and reproduces radiographic image information using a stimulable phosphor sheet by the above-described built-in type radiographic image information recording and reproducing apparatus. It is an object of the present invention to provide a radiation image information recording / reproducing method which can accurately read radiation image information without being affected by instantaneous light emission afterglow. In particular, the present inventors conducted various experiments on the effect of instantaneous emission afterglow on an image when reading out image information stored and recorded on a stimulable phosphor sheet by stimulating light emission with excitation light. As a result of the superposition, the level of the signal (instant emission afterglow signal) obtained by the photoelectric reading of the instantaneous emission afterglow is 10 times the level of the signal (stimulation emission signal) obtained by the photoelectric reading of the stimulated emission. If it is less than ^-3.5 times, we have found that the radiographic image obtained based on these signals is sufficiently accurate unless there is another noise signal, which indicates that the level of the instantaneous emission afterglow signal is constant. An object of the present invention is to provide a radiation image information recording / reproducing method capable of obtaining an accurate radiation image by performing reading in a state where the value is not more than the value. According to the present invention, there is provided a radiation image information recording / reproducing method for storing and recording radiation image information on a stimulable phosphor sheet, and then irradiating with excitation light. Radiation that causes stimulated emission according to the radiation image information stored and recorded, photoelectrically reads the stimulated emission to obtain an image signal, and reproduces a radiation image as a visible image based on the image signal. An image information recording / reproducing method, wherein circulating transport means for transporting the stimulable phosphor sheet along a predetermined circulating path, and irradiating the sheet with radiation through the subject in the circulating path. An image recording unit that accumulates and records radiation image information of a subject on a sheet; excitation light that scans the sheet on which radiation image information is accumulated and recorded in the image recording unit in the circulation path; An image reading unit having an excitation light source that emits light, and a photoelectric reading unit that obtains an image signal by reading a photostimulated emission light emitted from a sheet scanned by the excitation light; and Prior to image recording on a sheet after image reading has been performed in the section, by a radiation image information recording / reproducing apparatus having an erasing section for emitting residual radiation energy on the sheet, With respect to the level of the stimulating luminescence signal based on the stimulating luminescence from the portion where the light is radiated, even after irradiation with the radiation radiated to store and record the radiation image information on the stimulable phosphor sheet. The reading is performed in a state where the level of the instantaneous emission afterglow signal based on the instantaneous emission afterglow emitted from the stimulable phosphor sheet is 10 to ^3.5 times or less. Sign. According to another radiation image information recording / reproducing method of the present invention, in order to achieve the above object, radiation image information is accumulated and recorded on a stimulable phosphor sheet, and the stimulable phosphor sheet is excited with an excitation light. The main scanning is performed in a predetermined direction, and the sub-scanning is performed in a direction substantially orthogonal to the main scanning direction to cause stimulated emission according to the stored and recorded radiation image information. A radiographic image in which an image signal is obtained by photoelectrically reading by a photoelectric reading means having a light receiving surface opposed to substantially the entire width of the phosphor sheet in the main scanning direction, and the radiographic image is reproduced as a visible image based on the image signal. An information recording / reproducing method, comprising: circulating transport means for transporting the stimulable phosphor sheet along a predetermined circulating path; and irradiating the sheet with radiation through the subject in the circulating path. An image recording unit that accumulates and records the radiation image information of the subject on the sheet; in the circulation path, the sheet on which the radiation image information is accumulated and recorded in the image recording unit is main-scanned in a predetermined direction and substantially in the main scanning direction. An excitation light source that emits excitation light for sub-scanning in a direction perpendicular to the light source, and a light-receiving surface that extends in the main scanning direction and faces substantially the entire width of the stimulable phosphor sheet in the main scanning direction, and is scanned by the excitation light. An image reading unit having photoelectric reading means for obtaining an image signal by reading the stimulated emission light emitted from the printer, and recording an image on a sheet in the circulation path after the image reading is performed by the image reading unit Is carried out by a radiation image information recording / reproducing apparatus having an erasing unit for releasing the residual radiation energy on the sheet prior to the excitation light being emitted. For the level of the stimulating luminescence signal based on the stimulating luminescence emitted from the irradiated portion and read by the photoelectric reading unit, the stimulable phosphor sheet was irradiated to store radiation image information on the stimulable phosphor sheet. Even after irradiation with radiation, the level of the instantaneous emission afterglow signal based on the instantaneous emission afterglow emitted from the stimulable phosphor sheet and read by the photoelectric reading means is 10
^The reading is performed in a state where the reading is ^-3.5 times or less. In the above method, it is more preferable that the level of the instantaneous luminescence afterglow signal with respect to the level of the stimulus luminescence signal be ^10-4.0 times or less. Embodiments of the present invention will be described below. First, a method for quantitatively grasping the effect of instantaneous emission afterglow on an image will be described. In order to quantitatively grasp the instantaneous emission afterglow, the stimulable phosphor sheet is uniformly exposed to radiation (solid exposure). After a predetermined time after the irradiation of the radiation, the instantaneous light emission afterglow from the sheet surface is condensed by the light collector 4 shown in FIG. The signal (S ₁ ) is obtained. Then, after a sufficient time has passed, in a state where the instantaneous light emission afterglow has almost disappeared, the sheet surface is scanned with excitation light to cause stimulated emission, and the stimulated emission light is collected via the light collector 4 and photomultiplied. 5 and read the photoelectrically emitted light signal (S
₂ ) get. The ratio of the instantaneous emission afterglow signal (S ₁ ) to the stimulated emission signal (S ₂ ) is determined, and the relationship between the time after irradiation and the ratio is determined. Next, radiation is irradiated onto a sheet of the same material as the above-mentioned sheet through a subject, and image information of the radiation is stored and recorded. Then, after a predetermined time, the sheet surface is scanned with the excitation light to reproduce the stored and recorded radiation image, and the image quality of the reproduced image is examined to examine the influence of the instantaneous emission afterglow on the image quality. The following table shows the relationship between the ratio of the instantaneous emission afterglow signal (S ₁ ) to the stimulated emission signal (S ₂ ) and the image quality of the radiation image at the time when the ratio is reached. It became like. [Table 1] In Table 1, a mark "x" indicates that the effect of afterglow on the image quality in the obtained image is large enough to be visually recognized and has a practical problem. A mark "△" indicates that the effect of afterglow is slight. Seen, but practically no problem, "○"
The mark indicates that there is no effect of afterglow and that there is no practical problem at all. As described above, if the level of the instantaneous emission afterglow signal is ^10-3.5 times or less the level of the photostimulated emission signal, the quality of the radiation image read and reproduced by the excitation light scanning is practically sufficient. It turned out to be accurate. For this reason, in this embodiment, the above-mentioned built-in type radiation image information recording / reproducing apparatus, that is, a circulating conveying means for conveying the stimulable phosphor sheet along a predetermined circulating path, and the circulating means An image recording unit that irradiates the sheet with radiation through the subject in the passage to accumulate and record radiation image information of the subject on the sheet; and a radiation image information in the image recording unit that is in the circulation passage. An image reading unit comprising: an excitation light source that emits excitation light for scanning a sheet on which recording is recorded; and a photoelectric reading unit that obtains an image signal by reading stimulated emission light emitted from the sheet scanned by the excitation light. In the circulation passage, the image remains on the sheet before the image is recorded on the sheet after the image is read by the image reading unit. And a erasing section for emitting radiation energy into a single apparatus, and the stimulable phosphor sheet is circulated between the respective sections to be repeatedly used. When reading the image information by scanning the sheet on which the radiation image information is stored with the excitation light, the level of the instantaneous emission afterglow signal is higher than the level of the photostimulated emission signal.
It is performed in a state of ^10-3.5 times or less to obtain an accurate reproduced image. The time during which the level of the instantaneous luminescence afterglow signal becomes ^10-3.5 times or less the level of the photostimulated luminescence signal depends on the type of stimulable phosphor used in the sheet. For this reason, when the time from recording image information by irradiation to reading by excitation light is short as in the aforementioned built-in type radiation image information recording / reproducing apparatus, the intensity reduction rate of the instantaneous emission afterglow is reduced. Use a stimulable phosphor with large characteristics, delay reading until the level of the instantaneous luminescence afterglow signal is ^10-3.5 times or less the level of the stimulating luminescence signal, and obtain accurate images. I do. In the recording / reproducing method according to the present invention, the image reading section of the built-in type radiographic image information recording / reproducing apparatus may be arranged such that the sheet in which the radiographic image information is accumulated and recorded in the image recording section is mainly moved in a predetermined direction. An excitation light source that emits excitation light that scans and sub-scans in a direction substantially perpendicular to the main scanning direction; and a light receiving surface that extends in the main scanning direction and faces substantially the entire width of the stimulable phosphor sheet in the main scanning direction. The present invention can be particularly suitably applied to an image reading unit having a photoelectric reading unit that reads out stimulating light emitted from a sheet scanned by the excitation light to obtain an image signal. The image quality is affected by the level of the instantaneous emission afterglow signal used for image reproduction after the instantaneous emission afterglow is photoelectrically read. Also, this afterglow can be absorbed by a filter provided on the light collector, and the applicant's Japanese Patent Application No. 58-1536
No. 91, Japanese Patent Application No. 59-171227, Japanese Patent Application No. 59-185179, Japanese Patent Application No. 59-201171 and Japanese Patent Application No. 59-201172, etc. Thus, the level of the instantaneous emission afterglow may be set to a predetermined value or less ( ^10-3.5 times or less). As described above, according to the method of the present invention, the radiation stored in the stimulable phosphor sheet in the built-in type radiation image information recording / reproducing apparatus as described above. When image information is read by stimulated emission with excitation light, the level of the stimulated emission signal obtained by photoelectrically reading the stimulated emission is compared with the level of the instantaneous emission remaining obtained by photoelectrically reading the instantaneous emission afterglow. Since reading is performed in a state where the level of the optical signal is ^10-3.5 times or less, an accurate radiation image can be obtained with almost no influence on the image quality due to the instantaneous emission afterglow.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a conventional radiation image information reading apparatus. FIG. 2 is a graph showing the relationship between the intensity of instantaneous emission afterglow and time. Light source 2 Galvanometer mirror 3 Sheet 4 Condenser 5 Photomultiplier

Claims (1)

(57) [Claims] The radiation image information is stored and recorded on the stimulable phosphor sheet, and then the excitation light is emitted to cause stimulated emission according to the accumulated and recorded radiation image information, and the stimulated emission is photoelectrically read to obtain an image. A radiation image information recording / reproducing method for obtaining a signal and reproducing a radiation image as a visible image based on the image signal, comprising: a circulating transport means for transporting the stimulable phosphor sheet along a predetermined circulating path; An image recording unit that irradiates the sheet with radiation through the subject in the circulation path, thereby accumulating and recording radiation image information of the subject on the sheet; An excitation light source that emits excitation light for scanning a sheet on which information is stored and recorded, and a photostimulated emission light emitted from the sheet scanned by the excitation light are read to obtain an image signal. An image reading unit having a photoelectric reading unit, and residual radiation energy on the sheet in the circulation passage prior to image recording on the sheet after the image reading is performed by the image reading unit. A radiation image information recording / reproducing apparatus having an erasing unit for emitting light, wherein the level of a stimulating luminescence signal based on the stimulating luminescence from a portion irradiated with the excitation light is compared with the level of the stimulable fluorescence. The level of the instantaneous luminescence afterglow signal based on the instantaneous luminescence afterglow radiated from the stimulable phosphor sheet after irradiation with the radiation radiated for storing and recording the radiation image information on the optical body sheet is ^10-3.5 times. A method for recording and reproducing radiation image information, wherein the reading is performed in the following condition. 2. 2. The radiation image information recording / reproducing method according to claim 1, wherein the reading is performed in a state where the level of the instantaneous emission afterglow signal is 10 ^-4.0 times or less of the level of the stimulated emission signal. 3. Radiation image information is accumulated and recorded on the stimulable phosphor sheet, and the stimulable phosphor sheet is main-scanned in a predetermined direction with excitation light and sub-scanned in a direction substantially orthogonal to the main scanning direction. Photostimulated light is emitted according to the radiation image information, and the photostimulated light is extended by the photoelectric reading means extending in the main scanning direction and having a light receiving surface facing substantially the entire width of the stimulable phosphor sheet in the main scanning direction. A radiation image information recording / reproducing method for reproducing a radiation image as a visible image based on the image signal, and conveying the stimulable phosphor sheet along a predetermined circulation path. Circulating conveyance means, in the circulating passage, by irradiating the sheet with radiation through a subject, an image recording unit that accumulates and records radiation image information of the subject on the sheet; An excitation light source that emits excitation light that performs main scanning in a predetermined direction and sub-scans in a direction substantially orthogonal to the main scanning direction on a sheet on which radiation image information is stored and recorded in the image recording unit; An image reading means having a light receiving surface facing substantially the entire width of the phosphor sheet in the main scanning direction and having photoelectric reading means for obtaining an image signal by reading stimulated emission light emitted from the sheet scanned by the excitation light; And an erasing unit in the circulation passage, which emits residual radiation energy on the sheet before the image is recorded on the sheet after the image is read by the image reading unit. An image information recording / reproducing apparatus, wherein the excitation light is emitted from a portion irradiated with the excitation light and is based on the stimulated emission read by the photoelectric reading unit. In response to the level of the emission signal, the radiation is emitted from the stimulable phosphor sheet and read by the photoelectric reading means even after the irradiation with the radiation radiated to store and record the radiation image information on the stimulable phosphor sheet. Wherein the reading is performed in a state where the level of the instantaneous emission afterglow signal based on the instantaneous emission afterglow obtained is ^10-3.5 times or less. 4. 4. The radiation image information recording / reproducing method according to claim 3, wherein the reading is performed in a state where the level of the instantaneous emission afterglow signal is 10 ^-4.0 times or less of the level of the stimulated emission signal.