JP2561159B2 - Radiation image reader - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention two-dimensionally scans a stimulable phosphor sheet on which a radiation image is stored and recorded by a light beam, and irradiates the light beam. The present invention relates to a radiation image reading device for photoelectrically reading, by a photomultiplier tube, stimulated emission light representing the radiation image emitted from a phosphor sheet to obtain an image signal.

(Prior Art) When radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) is irradiated, a part of this radiation energy is accumulated, and then irradiation with excitation light such as visible light is accumulated. There is known a stimulable phosphor (stimulable phosphor) that exhibits stimulated emission of a light amount corresponding to the amount of energy. Using this stimulable phosphor, the radiation image information of a subject such as a human body is once recorded on a sheet-shaped stimulable phosphor, and the stimulable phosphor sheet is scanned with excitation light such as laser light to stimulate the irradiation. Generates emitted light, photoelectrically reads the obtained stimulated emission light to obtain an image signal, and based on this image signal, outputs a radiation image of the subject as a visible image on a recording material such as a photographic photosensitive material or a CRT. A radiation image recording / reproducing system for this has already been proposed by the present applicant (Japanese Patent Laid-Open Nos. 55-12429 and 56-11395).
No. 55-163472, No. 56-104645, No. 55-116340, etc.).

This system has the practical advantage of being able to record images over a very wide radiation exposure area compared to conventional radiographic systems using silver halide photography. In other words, it has been recognized that the stimulable phosphor has a light emission amount that is stimulated and emitted by excitation after storage is proportional to a radiation exposure amount over a very wide range. Therefore, the radiation exposure amount varies depending on various photographing conditions. Even if it fluctuates considerably, the amount of stimulated emission light emitted from the stimulable phosphor sheet is set to a proper reading gain, read by photoelectric conversion means, and converted into an electrical signal. By using the recording material such as a photographic light-sensitive material or a display device such as a CRT to output a radiation image as a visible image, a radiation image that is not affected by fluctuations in radiation exposure amount can be obtained.

In the above system, a light beam (excitation light) is usually passed over a stimulable phosphor sheet on which a radiation image is stored and recorded.
The main scanning in a predetermined direction by the sub-scanning in the direction substantially perpendicular to the main scanning direction, by detecting the stimulated emission light representing the radiation image obtained from each scanning point by the optical sensor, the image signal Is configured to obtain.

As the above-mentioned optical sensor, the light receiving surface (incident end surface) for receiving stimulated emission light extends along the main scanning and the emission end surface is formed into an annular shape, and the stimulated emission light emitted from the emission end surface of the light guide. Combination with a photomultiplier tube (photomultiplier) for receiving light, or a long length having a long light-receiving surface extending along the main scanning line and arranged in proximity to the stimulable phosphor sheet. Photomultiplier tube of
Abbreviated as "Long Photo Maru". ) (See JP-A-62-16666) and the like can be used.

After the radiation image is read as described above, the afterimage (residual energy) of the radiation image is usually left on the stimulable phosphor sheet, and after the reading, the afterimage erasing light is left on the stimulable phosphor sheet. The stimulable phosphor sheet from which the residual image has been erased by irradiating with is emitted the remaining radiation energy, and is used for accumulating and recording the radiation image again.

(Problems to be Solved by the Invention) In the radiation image reading apparatus configured as described above, there is a problem of how much light should be emitted to erase an afterimage. This is because if the residual image is not sufficiently erased, when the stimulable phosphor sheet is reused, an image signal representing an image obtained by superimposing the previously obtained radiation image on this radiation image is obtained. On the other hand, if the residual image is erased more than necessary, a light source that is larger than necessary and consumes a large amount of power is prepared, or it takes a long time to erase.

In determining the necessary and sufficient irradiation amount of the light for erasing the afterimage, by utilizing the fact that the light amount of stimulated emission light and the amount of remaining energy almost correspond to each other, the stimulated emission light is read. It is conceivable to find the irradiation amount of the afterimage erasing light by examining the level of the obtained image signal. However, the irradiation amount of the afterimage erasing light needs to correspond to the energy amount of the region in which the maximum radiation energy of the stimulable phosphor sheet remains, while the region where the maximum radiation energy remains is For example, the area where the radiation does not pass through the subject and is directly applied to the stimulable phosphor sheet,
In many cases, this is an area that can be ignored when obtaining a radiation image of a subject. Therefore, at the time of this reading, the reading gain and other settings are ignored while ignoring this area, and the image signal obtained from this area is saturated,
Therefore, the value of the image signal may not correspond to the amount of residual energy.

Therefore, it has been considered to monitor the voltage applied to the bleeder resistance of the photomultiplier in order to know the amount of residual energy (see Japanese Patent Laid-Open No. 60-260035). This is because the voltage applied to the bleeder resistance is still changed even when a large amount of light that causes the current signal output from the photomultiplier to be saturated is incident on the photomultiplier.

However, the above-mentioned long photomultiplier or an optical sensor in which a light guide and a photomultiplier are combined has sensitivity unevenness in the main scanning direction, and from which position in the main scanning direction the stimulated emission light of the same amount of light enters. Therefore, the light receiving sensitivity differs, and the voltage applied to the bleeder resistance also changes. Therefore, even if the voltage applied to the bleeder resistance is monitored, the maximum residual energy is calculated depending on where in the main scanning direction of the stimulable phosphor sheet the region having the maximum residual energy exists, that is, the light intensity for erasing the afterimage. As a result, an error occurs in the calculation of the irradiation dose, which may result in an incomplete afterimage erasing or in a case where it takes more time than necessary for the afterimage erasing.

In addition to the problem of the amount of light irradiation for erasing afterimages,
When a large amount of stimulated emission light is emitted from a region that cannot be ignored as a radiation image and the image signal is saturated, it is also considered to use the voltage applied to the bleeder resistance as the image signal instead of this image signal. (Japanese Patent Laid-Open No. 60-2602
(See Publication No. 70). However, in the case of using an optical sensor or the like in which the above-mentioned long-length photomultiplier or an optical guide and a photomultiplier are combined, the voltage applied to the bleeder resistance changes depending on from which position on the light-receiving surface the stimulated emission light enters. Therefore, there is a problem that an error becomes large when the voltage applied to the bleeder resistance is used as an image signal.

In view of the above circumstances, the present invention provides a radiation image reading apparatus having a sensitivity distribution in the main scanning direction and an optical sensor such as a long photomultiplier or a combination of the light guide and the photomultiplier. It is an object of the present invention to provide a radiation image reading device capable of obtaining an accurate light amount of stimulated emission light from a value.

Further, the present invention provides the radiation image reading device, which is capable of more accurately obtaining the irradiation amount of light for erasing the afterimage and irradiating the necessary and sufficient amount of light for erasing the afterimage in the radiation image reading device. It is also intended to do.

(Means for Solving the Problems) In a radiation image reading apparatus according to the present invention, a stimulable phosphor sheet on which a radiation image is stored and recorded is scanned by a light beam in the main scanning direction a number of times, and the accumulation is performed. Means for two-dimensionally scanning the accumulative phosphor sheet with the light beam by moving the phosphor sheet and the light beam relatively in the sub-scanning direction substantially perpendicular to the main scanning direction. A photo-multiplier tube (photomultiplier) extending in the main scanning direction and receiving stimulated emission light representing the radiation image emitted from the stimulable phosphor sheet by the scanning. Photoelectric conversion means for obtaining an image signal, monitor means for monitoring the voltage applied to the bleeder resistance of the photomultiplier tube, and data for correcting the fluctuation characteristics of the voltage in the main scanning direction. To keep the storage means, and is characterized in that it comprises a correction means for correcting the voltage obtained by the monitoring unit based on the data stored in the storage means.

A second radiographic image reading device of the present invention is the radiographic image reading device of the first aspect, based on a light source that emits light for erasing an afterimage of the stimulable phosphor sheet, and the corrected voltage. A control means for controlling the irradiation amount of light for erasing the afterimage is provided.

Here, the "light-receiving surface extending in the main scanning direction" refers to a light-receiving surface of a long photomultiplier or an incident end surface of a light guide, and an incident surface of photostimulated luminescent light extending in the main scanning direction in a photoelectric conversion unit. .

Further, the "variation characteristic of the voltage in the main scanning direction" means that when the stimulated emission light of the same light amount sequentially enters the light receiving surface from different positions in the main scanning direction, the stimulated emission of the same light amount. It is the variation characteristic of the voltage applied to the bleeder resistance with respect to the incident position of light in the main scanning direction.

(Operation) In the present invention, the data for correcting the variation characteristic of the voltage applied to the bleeder resistance in the main scanning direction is stored in the storage means, and when the radiation image is read from the stimulable phosphor sheet, the monitor means is used. Since the voltage applied to the obtained bleeder resistance is corrected based on the data stored in the storage means, the exact amount of stimulated emission light can be obtained from the voltage value applied to the bleeder resistance. Further, in the second radiation image reading apparatus of the present invention, since the irradiation amount of the light for erasing the afterimage is controlled based on the corrected voltage, the amount of light necessary and sufficient for erasing the afterimage is controlled. It is possible to prevent the residual erasing from being insufficiently performed by irradiating the stimulable phosphor sheet with light and taking an unnecessarily long time for erasing the residual image.

(Examples) Examples of the present invention will be described below with reference to the accompanying drawings.

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

A subject is irradiated with radiation in an imaging device (not shown), and the radiation that has passed through the subject is applied to the stimulable phosphor sheet, whereby a radiation image of the subject is stored and recorded in the stimulable phosphor sheet.

The stimulable phosphor sheet 1 on which the radiation image is stored and recorded in this manner is set at a predetermined position of the radiation image reading device shown in FIG. 1, and is conveyed in the arrow Y direction by the sheet conveying means (not shown) (sub-scanning). ) Will be done. On the other hand, the excitation light beam 3 emitted from the laser light source 2 is reflected and deflected by the rotary polygon mirror 4 which rotates at a high speed in the direction of arrow Z, passes through the fθ lens 5, and then enters the sheet 1 with its optical path changed by the mirror 6. Main scanning is performed in an arrow X direction that is substantially perpendicular to the sub-scanning direction (arrow Y direction). Excitation light beam 3 on sheet 1
The stimulated emission light 7 having a light amount corresponding to the amount of accumulated radiation energy is emitted from the area irradiated with, and the stimulated emission light 7 is photoelectrically detected by the long photomultiplier 25. The light receiving surface 25a of the long photomultiplier 25 is the main scanning line 8
Extends along.

The analog image signal S _A obtained with this long-sized Photomaru 25
Is logarithmically amplified by a logarithmic amplifier 9, converted into a digital image signal S _D by an A / D converter 10, and input to a computer system 40. Further, the voltage V of the bleeder resistance of the long photomul 25 is monitored, converted into a digital signal by the A / D converter 10, and this signal is also converted into the computer system 40.
Is input to

The computer system 40 is responsible for overall control of the radiation image reading apparatus, various monitors, transmission of image signals _SD , etc., and a main body 41 having a CPU, internal memory, interface, etc. built-in, and an auxiliary storage medium. Floppy disk drive unit 4 with a floppy disk loaded and driven
2. It is composed of a keyboard 43 for inputting various instructions and a CRT 44 for displaying necessary information.

The image signal S _D input to the computer system 40 is
After that, the image is transmitted to an image processing device (not shown), subjected to appropriate image processing, and then sent to an image reproducing device (not shown) to reproduce and output a visible image based on the image signal S _D.

The stimulable phosphor sheet from which the radiation image has been read as described above is irradiated with the erasing light 12 emitted from the lamp 11 on the entire surface at the position 1'shown in the figure, whereby the stimulable phosphor sheet is irradiated. The radiation energy (afterimage) remaining on the sheet is released. The afterimage-erasable stimulable phosphor sheet is again used for radiographic reading.

FIG. 2A and FIG. 2B are partial cross-sectional perspective views showing an example of the structure of the elongated photomultiplier 25 of FIG. 1, respectively, and a cross-sectional view in the II direction shown in FIG. 2A.

The long photomultiplier 25 has an electrode structure generally called a Venetian blind type. In this long photomul 25, a main body 25A has a cylindrical shape, a photocathode 25b is provided along the main body 25A so as to face the light receiving surface 25a, and a plurality of dynodes 25c are provided below the photocathode 25b. Are stacked via the insulating member 25d and fixed by the pin 25e.
constitutes f. Each of the dynodes 25c is formed in a blind shape in which a large number of U-shaped cuts are made in one conductive plate. This multiplier 25
Below f, a shield electrode 25g is fixed by a pin 25e via an insulating member 25d, and an anode 25h is provided inside the shield electrode 25g. These electrodes are electrically connected to the terminals of the terminal group 25i provided at the end of the main body 25A in a one-to-one correspondence.

FIG. 3 shows an example of an electric circuit 50 for driving the long photomultiplier 25 and extracting a photoelectric output. Long Photomaru 25
The parts corresponding to the respective parts of are designated by the same reference numerals as in FIGS. 2A and 2B. A high negative voltage is applied to the photocathode 25b through the negative high voltage applying terminal 50a. Also, the negative high voltage application terminal
The high negative voltage applied to 50a is applied to each dynode 25c divided by the bleeder resistance group 50b.
The shield electrode 25g is grounded, and the anode 25h is grounded via the resistor 50c and is also input to one terminal of the amplifier 50d. The other terminal of the amplifier 50d is grounded, and the image data photoelectrically converted is taken out as an electric signal from the output terminal 50e. Further, the voltage V applied to the bleeder resistor 50b 'is monitored by the terminal 50f. The shield electrode 25g is not always necessary,
It may not be provided.

Next, how to obtain the irradiation amount of the afterimage erasing light 12 will be described.

Radiation is uniformly applied to the entire surface of the stimulable phosphor sheet (this is referred to as "solid exposure"), and uniform radiation energy is accumulated and recorded on the front surface of the sheet. This solid-exposure stimulable phosphor sheet 1 is set in the radiation image reading apparatus shown in FIG. 1, and is read in the same manner as in the case of reading the radiation image described above, and the voltage V of the bleeder resistance at the time of reading is also set. (See FIG. 3) is monitored.

FIG. 4 shows stimulated emission light 7 emitted from the stimulable phosphor sheet 1 which was solidly exposed by various doses of radiation,
The main scanning direction (X) of the voltage V applied to the bleeder resistance when read by the long photomultiplier 25 to which various voltages are applied.
It is a figure showing the fluctuation characteristic of the (direction).

This voltage V represents the absolute value of the voltage monitored by the terminal 50f shown in FIG. 3. Except for changes due to fluctuation characteristics, the lower the voltage V, the greater the dose of radiation that is irradiated or the long photomultiplier. It means that a high voltage (negative high voltage) is applied to. That is, when the applied voltage of the long photomul is constant, it means that the energy remaining in the stimulable phosphor sheet 1 after reading is larger as the voltage V is lower, except for the change due to the fluctuation characteristic.

The voltage V applied to the bleeder resistance has a considerably large variation characteristic as shown in this figure. Therefore, even if the minimum value of the voltage V obtained when reading a radiation image is obtained, the stimulable phosphor sheet 1 It is not possible to accurately grasp the amount of energy remaining in the.

In FIG. 5, among the many curves 15a to 15i showing the variation characteristics shown in FIG. 4, the curve 15e corresponding to the radiation dose at the level which is the most problematic when performing afterimage elimination is a straight line. FIG. 11 is a diagram showing a graph in which the fluctuation characteristics are corrected as described above, and the other curves 15a to 15d and 15f to 15i are also corrected based on the correction. The curves shown in this figure (the straight lines 15a 'to 15i' correspond to the curves 15a to 15i shown in FIG. 4 respectively).

The curves 15a 'to 15d' and 15f 'to 15i' other than the curve 15e 'are also corrected substantially linearly except for the end portion of the light receiving surface of the long photomultiplier 25. Note that the end portion is a region that is not used when reading a radiation image and can therefore be ignored. Data for correcting the variation characteristic of the voltage V applied to the bleeder resistance of the long photomul 25 as described above is stored in the computer system 40. The function of the computer system 40 for storing the correction data is regarded as an example of the storage means of the present invention.

Next, an example of how to determine the irradiation amount of the afterimage erasing light with which the stimulable phosphor sheet 1 on which the radiation image is stored and recorded will be described.

The stimulable phosphor sheet 1 on which the radiation image is accumulated and recorded is set at a predetermined position of the radiation image reading device shown in FIG. 1, and the radiation image is read as described above.
At this time, the voltage V applied to the bleeder resistance of the long Photomaru 25
Is monitored.

FIG. 6 is a diagram showing a large number of curves 16 representing the voltage V applied to the bleeder resistance for each main scan at the time of reading, an envelope curve 17 of the large number of curves 16, and an envelope curve 18 after correction. is there.

Since the radiation image is accumulated and recorded on the stimulable phosphor sheet 1, the voltage V applied to the bleeder resistance changes for each main scan (curve 16). Therefore, after reading the radiation image accumulated and recorded on the stimulable phosphor sheet 1, the point at which the voltage V changed for each main scanning is the lowest at each point in the main scanning direction (X direction). Tie envelope curve 17
Then, the envelope curve 17 is corrected based on the data for correcting the variation characteristic, and the corrected envelope curve 18 is calculated. The voltage at the point where the voltage V is the lowest in the corrected envelope curve 18
The irradiation amount of the light for erasing the afterimage is calculated by V _0, and the lamp 11 (see FIG. 1) is adjusted so that the calculated irradiation amount is obtained.
The amount of light or the lighting time of the lamp 11 is controlled. still,
In the present embodiment, the function of obtaining the correction envelope curve 18 of the computer system 40, and the function of controlling the light amount or the lighting time of the lamp 11 according to the voltage V ₀ obtained from the correction envelope curve 18, It is considered as an example of the correction means and the control means of the invention, respectively.

By performing the afterimage erasing as described above, it is possible to prevent insufficient afterimage erasing, and it is also possible to prevent extra power and time from being consumed for the afterimage erasing.

FIG. 7 is a perspective view showing another embodiment of the radiation image reading apparatus of the present invention. The same components as those of the radiation image reading apparatus shown in FIG. 1 are designated by the same numbers as in FIG.
Description is omitted.

The bright emission light 7 is incident on the light guide 13. The light guide 13 is formed by molding a light guide material such as an acrylic plate, and the linear incident end face 13a is arranged so as to extend along the main scanning line, and is formed in an annular shape. Exit face 13
The light receiving surface of the photomultiplier 25 'is coupled to b. The photostimulated luminescent light 7 that has entered the light guide 13 from the incident end face 13a proceeds by repeating total reflection inside the light guide 13 and then emerges from the exit end face 13b.
An image signal S _A representing the radiation image is obtained by being received by 5 ′. The voltage V applied to the bleeder resistance of the photomultiplier 25 'is also monitored.

Here, the value of the signal S _A output from the photomultiplier 25 'differs depending on from which position of the incident end surface 13a of the light guide 13 the stimulated emission light enters, and the voltage V applied to the bleeder resistance also differs. The fluctuation characteristic of the voltage V is also corrected in the same manner as in the above-described embodiment. However, in this embodiment, the variation characteristic of the voltage applied to the bleeder resistance is smaller than that in the case of the long photomul.

Although each of the above-described embodiments is an example of obtaining the irradiation amount of light for erasing the afterimage, for example, when the image signal S _D (see FIG. 1) is saturated, the bleeder at the time when the image signal S _D is saturated is obtained. The voltage V applied to the resistor may be corrected based on the correction data stored in the computer system 40, and the corrected voltage V may be used as an image signal instead of the saturated image signal S _D.

(Effects of the Invention) As described in detail above, the radiation image reading apparatus of the present invention stores data for correcting the variation characteristic of the voltage of the bleeder resistance in the main scanning direction, and the stored data. Since the voltage applied to the bleeder resistance obtained when reading the radiation image is corrected based on
The exact amount of stimulated emission light can be obtained from the voltage value applied to the bleeder resistance. Further, by controlling the irradiation amount of light for erasing the afterimage based on the corrected voltage,
Necessary and sufficient afterimage erasure is performed, insufficient erasure is not performed, and unnecessary power and time are not required for the afterimage erasure.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a radiographic image reading apparatus of the present invention, FIG. 2A is a partial cross-sectional perspective view showing the structure of a long photomal, and FIG. 2B is a view shown in FIG. 2A. 3 is a cross-sectional view in the I-I direction of FIG. 3, FIG. 3 is a diagram showing an example of an electric circuit attached to the long photomul, and FIG. 4 is a main scanning direction of a voltage applied to a bleeder resistance of the long photomul. FIG. 5 is a diagram showing the variation characteristic, FIG. 5 is a diagram showing the variation characteristic after correction, and FIG. 6 is a number of curves showing the voltage applied to the bleeder resistance for each main scan when reading the radiation image. FIG. 7 is a perspective view showing another embodiment of the radiation image reading apparatus of the present invention, showing the envelope curves of these many curves and the envelope curve after correction. 1 ... stimulable phosphor sheet 3 ... excitation light beam, 7 ... stimulated emission light 11 ... afterimage erasing lamp 12 ... light emitted from lamp 13 13 ... optical guide 25 ... long length Photomultiplier tube (long photomultiplier) 25 '…… Photomultiplier tube 40 …… Computer system

Claims (2)

(57) [Claims] 1. A stimulable phosphor sheet on which a radiation image is stored and recorded is main-scanned in the main scanning direction by a light beam a number of times, and the stimulable phosphor sheet and the light beam are relatively scanned by the main scanning. Scanning means for two-dimensionally scanning the stimulable phosphor sheet by the light beam by moving in the sub-scanning direction substantially perpendicular to the direction, a light receiving surface extending in the main scanning direction, and a photomultiplier tube. Photoelectric conversion means provided for receiving photostimulated emission light representing the radiation image emitted from the stimulable phosphor sheet by the scanning to obtain an image signal, and monitoring a voltage applied to a bleeder resistance of the photomultiplier tube. Monitoring means, storage means for storing data for correcting the variation characteristic of the voltage in the main scanning direction, and the monitor based on the data stored in the storage means. A radiation image reading apparatus comprising a correction unit that corrects the voltage obtained by the input unit. 2. The radiation image reading apparatus according to claim 1, wherein a light source that emits light for erasing an afterimage of the stimulable phosphor sheet, and a light for erasing the afterimage based on the corrected voltage. A radiation image reading apparatus comprising a control means for controlling an irradiation amount.