JPH03134651A - Radiograph reader - Google Patents

Abstract

PURPOSE:To calculate the exact quantity of light for the stimulated luminescence by storing data for correcting the fluctuation characteristic of a voltage in a main scanning direction for the bleeder resistance of photomultiplier and correcting the voltage to be applied to the bleeder resistance. CONSTITUTION:A stimulable phosphor sheet 1 accumulating a radiograph is set to the prescribed position of a radiograph reader and the radiograph is read. In such a case, a voltage V to be applied to the bleeder resistance of a long photomal 25 is monitored. Since the radiograph is accumulated and recorded to the stimulable phosphor sheet 11, the voltage V to be applied to the bleeder resistance is changed at every main scanning. After reading the radiograph, an envelop curve, where the voltage V is most lowered in each point of a main scanning direction, is found and further for the envelop curve, the fluctuation property is corrected. The irradiating quantity of light for erasing an after-image is found from the voltage at the point, where the voltage V is most lowered in the corrected envelop curve, and the quantity of light for a lamp 11 is controlled so as to obtained the found quantity of light for irradiation.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention involves two-dimensionally scanning a stimulable phosphor sheet on which a radiation image has been stored and recorded, and by irradiating the light beam with a stimulable phosphor sheet. The present invention relates to a radiation image reading device that photoelectrically continues stimulated luminescence light representing the radiation image emitted from a phosphor sheet using a photomultiplier tube to obtain an image signal.

(Conventional technology) Radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.)
When irradiated with , a part of this radiation energy is accumulated, and when excitation light such as visible light is irradiated, a stimulable phosphor (stimulable phosphor) that emits stimulated light with an amount of light corresponding to the amount of accumulated energy is produced. Are known. Using this stimulable phosphor, radiation image information of a subject such as a human body is partially recorded on a sheet of stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam to make it shine. The resulting stimulated luminescent light is generated and photoelectrically read to obtain an image signal, and based on this image signal, the radiation image of the subject is recorded as a visible image on a recording material such as a photographic light-sensitive material, a CRT, etc. A radiation image recording and reproducing system for outputting radiation images has already been proposed by the present applicant (Japanese Patent Laid-Open Nos. 55-12429 and 5B-11).
No. 395, No. 55-183472.

No. 56-104645, No. 55-116340, etc.)
.

This system has the practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, it is recognized that in stimulable phosphors, the amount of emitted light that is stimulated and emitted by excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range, and therefore the amount of radiation exposure varies depending on various imaging conditions. Even if the amount of stimulated luminescence light emitted from the stimulable phosphor sheet fluctuates considerably, the reading gain is set to an appropriate value and the photoelectric conversion means reads the amount of stimulated luminescence light and converts it into an electrical signal. By outputting a radiation image as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT, it is possible to obtain a radiation image that is not affected by fluctuations in the amount of radiation exposure.

In the above system, a stimulable phosphor sheet on which a radiation image is stored is usually scanned in a predetermined direction with a light beam (excitation light), and sub-scanned in a direction approximately perpendicular to the main scanning direction. , is configured to obtain an image signal by detecting stimulated luminescence light representing the radiation image obtained from each scanning point with an optical sensor.

The above optical sensor includes a light guide whose light receiving surface (incidence end surface) for receiving stimulated luminescence light extends along the main scanning direction and whose exit end surface is formed in an annular shape, and the stimulated luminescence emitted from the exit end surface of the light guide. A combination with a photomultiplier that receives light, or a long sheet having a long light-receiving surface extending along the main scanning line and placed close to the stimulable phosphor sheet. A photomultiplier tube (hereinafter abbreviated as "elongated photomultiplier tube") (see Japanese Patent Laid-Open No. 16668/1983), etc. can be used.

After the radiation image has been read as described above, the stimulable phosphor sheet usually retains an afterimage (residual energy) of the radiation image. The stimulable phosphor sheet is irradiated with the remaining radiation energy to emit the remaining radiation energy, and the stimulable phosphor sheet after which the afterimage has been erased is used again to store and record radiation images.

(Problem to be Solved by the Invention) In the radiation image reading device configured as described above, the problem is how much light should be irradiated to erase the afterimage. This is because if the afterimage is insufficiently erased, when the stimulable phosphor sheet is reused, an image signal representing the superimposition of the previously obtained radiation image on the currently obtained radiation image will be obtained. On the other hand, if the afterimage is erased more than necessary, a light source that is unnecessarily large and consumes a large amount of power will be required, or it will take a long time to erase the afterimage.

In determining the necessary and sufficient amount of light to eliminate this afterimage, we take advantage of the fact that the amount of stimulated luminescence light almost corresponds to the amount of remaining energy, and read the stimulated luminescence light. It is conceivable to determine the amount of light irradiation for erasing the afterimage by checking the level of the image signal obtained. However, the amount of light irradiation for eliminating afterimages needs to correspond to the amount of energy in the area of the stimulable phosphor sheet where the maximum radiation energy remains; For example, areas where radiation is directly irradiated onto the stimulable phosphor sheet without passing through the subject, etc.
This is often an area that can be ignored when obtaining a radiographic image of a subject. Therefore, when reading this, the reading gain etc. are set ignoring this area, and the image signal obtained from this area becomes saturated.
Therefore, the value of the image signal and the amount of remaining energy may not correspond.

Therefore, in order to know the amount of remaining energy, it has been considered to monitor the voltage applied to the bleeder resistor of the photomultiplier (see Japanese Patent Laid-Open No. 60-260035).
. This is based on the fact that even if a large enough amount of light enters the photomultiplier to saturate the current signal output from the photomultiplier, the voltage applied to the bleeder resistor will still change. .

However, the above-mentioned long photomultipliers and optical sensors that combine a light guide and a photomultiplier have uneven sensitivity in the main scanning direction, and it is difficult to determine from which position in the main scanning direction the same amount of stimulated luminescence light is incident. The light-receiving sensitivity differs depending on the stimulable phosphor sheet, and the voltage applied to the bleeder resistor also changes. Therefore, even if the voltage applied to the bleeder resistor is monitored, there is a region with the maximum residual energy in the main scanning direction of the stimulable phosphor sheet. This may result in an error in the calculation of the maximum residual energy, that is, the amount of light irradiation for erasing the afterimage, and the afterimage may be incompletely erased or it takes more time than necessary to erase the afterimage. The result is that the case may occur.

In addition to the issue of the amount of light irradiation to eliminate afterimages, if a large amount of stimulated luminescence light is emitted from an area that cannot be ignored as a radiation image and the image signal becomes saturated, it is possible to replace this image signal with It is also considered to use the voltage applied to the bleeder resistor as an image signal (Japanese Patent Laid-Open No. 60-28
(See Publication No. 0270).

However, when using an optical sensor that combines the above-mentioned long photomultiplier or light guide with a photomultiplier, the voltage applied to the bleeder resistor changes depending on where on the light receiving surface the stimulated luminescence light enters. Therefore, when the voltage applied to the bleeder resistor is used as an image signal, there is a problem that an error becomes large.

In view of the above circumstances, the present invention provides a radiation image reading device equipped with an optical sensor having a sensitivity distribution in the main scanning direction, such as a long photomultiplier or a combination of the above-mentioned light guide and photomultiplier. It is an object of the present invention to provide a radiation image reading device that can accurately determine the amount of stimulated luminescence light from the value.

The present invention also provides a radiation image reading device that can more accurately determine the amount of light irradiation for erasing afterimages and irradiate a necessary and sufficient amount of light for erasing afterimages. The purpose is also to

(Means for Solving the Problems) A first radiation image reading device of the present invention scans a stimulable phosphor sheet on which a radiation image is stored and recorded many times in the main scanning direction with a light beam, and scanning means for two-dimensionally scanning the stimulable phosphor sheet with the light beam by relatively moving the stimulable phosphor sheet and the light beam in a sub-scanning direction substantially perpendicular to the main scanning direction; , comprising a light receiving surface extending in the main scanning direction and a photomultiplier, for receiving stimulated luminescence light representing the radiation image emitted from the stimulable phosphor sheet during the scanning; photoelectric conversion means for obtaining an image signal; monitoring means for monitoring the voltage applied to the bleeder resistance of the photomultiplier tube; storage means for storing data for correcting the capsular motion characteristic of the voltage in the main scanning direction; and a correction means for correcting the voltage obtained by the monitor means based on the data stored in the storage means.

Further, a second radiation image reading device of the present invention is the first radiation image reading device, and further includes a light source that emits light for erasing an afterimage of the stimulable phosphor sheet, and a radiation image reading device based on the corrected voltage. The present invention is characterized by comprising a control means for controlling the amount of light irradiation for erasing the afterimage.

Here, "the light-receiving surface extending in the main scanning direction" refers to the incident surface of stimulated luminescence light extending in the main-scanning direction of the photoelectric conversion means, such as the light-receiving surface of a long photomultiple or the incident end surface of a light guide. .

Furthermore, "the fluctuation characteristics of the voltage in the main scanning direction" means
Fluctuation characteristics of the voltage applied to the bleeder resistance with respect to the incident position in the main scanning direction of the stimulated luminescence light of the same quantity of light when the same quantity of stimulated luminescence light sequentially enters the light receiving surface from different positions in the main scanning direction means.

(Function) The present invention stores data for correcting the fluctuation characteristics of the voltage applied to the bleeder resistor in the main scanning direction in the storage means, and when the radiation image is read from the stimulable phosphor sheet, the data is stored in the storage means. Since the obtained voltage applied to the bleeder resistance is corrected based on the data stored in the storage means, an accurate amount of stimulated luminescence light can be obtained from the voltage value applied to the bleeder resistance. Furthermore, in the second radiation image reading device of the present invention, the amount of light irradiation for erasing the afterimage is controlled based on the voltage after correction, so that the amount of light irradiation necessary and sufficient for erasing the afterimage is controlled. This prevents the stimulable phosphor sheet from being irradiated with light, resulting in insufficient erasure of the afterimage, or from taking more time than necessary to erase the afterimage.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

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

An imaging device (not shown) irradiates a subject with radiation, and the radiation that has passed through the subject is irradiated onto a stimulable phosphor sheet, whereby a radiation image of the subject is stored and recorded on the stimulable phosphor sheet.

The stimulable phosphor sheet 1 on which the radiation image has been stored and recorded in this way is set at a predetermined position in the radiation image reading device shown in FIG.
It is transported (sub-scanning) in the direction of arrow Y. On the other hand, the excitation light beam 3 emitted from the laser light source 2 is reflected and deflected by a rotating polygon mirror 4 that rotates at high speed in the direction of arrow Z, passes through an fθ lens 5, and then changes its optical path by a mirror 6 and is directed toward the sheet 1.
, and main scanning is performed in the direction of arrow X, which is substantially perpendicular to the sub-scanning direction (direction of arrow Y). From the part of the sheet 1 irradiated with the excitation light beam 3, stimulated luminescence light 7 is emitted with an amount of light corresponding to the amount of accumulated radiation energy. is detected in a charging manner by The light-receiving surface 25a of the elongated photomultiplex 25 extends along the main scanning line 8.

Analog image signal s obtained with this long photomultiple 25
A is logarithmically amplified by a logarithmic amplifier 9, converted into an upstream digital image signal SD by an A/D converter l, and inputted to a computer system 40.

Further, the voltage V of the bleeder resistor of the long photomultiplier 25 is monitored, converted into a digital signal by the A/D converter 10, and this signal is also input to the computer system 40.

This computer system 40 is responsible for controlling the entire radiation image reading apparatus, various monitors, transmitting image signals So, etc., and includes a CPU and an internal memory.

Main body part 41 with built-in interface etc. A floppy disk drive section 42 in which a floppy disk as an auxiliary storage medium is loaded and driven, a keyboard 43 for inputting various instructions, and a CR for displaying necessary information.
It is composed of T44.

The image signal So input to the computer system 40 is then transmitted to an image processing device (not shown) to undergo appropriate image processing, and then sent to an image reproduction device (not shown) to reproduce a visible image based on the image signal SD. Output.

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

2A and 2B are a partially sectional perspective view and a partially sectional perspective view showing an example of the structure of the long photomultiplier 25 shown in FIG.
It is a sectional view taken in the I-1 direction shown in the figure.

This long photomultiplier 25 has an electrode structure generally referred to as a Venetian blind type. This long photomultiple 25 has a cylindrical main body 25A, a photocathode 25b is provided along the main body 25A facing the light receiving surface 25a, and a plurality of dynodes 25c are provided below the photocathode 25b. are stacked on top of each other with an insulating member 25d interposed therebetween.
The dynodes 25c constitute a multiplier section 25'' fixed at 5e. Each of the dynodes 25c is formed into a bent blind shape by making a number of U-shaped cuts in a single conductive plate. A shield electrode 25g is fixed with a pin 25e through an insulating member 25d below the multiplier 25f, and an anode 25h is provided within the shield electrode 25g.

These electrodes are electrically connected to each terminal of the terminal group 251 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 photoelectric output. Portions corresponding to each portion of the long photomultiplex 25 are shown in FIG. 2A.

The same reference numerals as in FIG. 2B are given. A negative high voltage is applied to the photocathode 125b via the negative high voltage application terminal 50a. Further, the negative high voltage applied to the negative high voltage application terminal 50a is applied to each of the dynodes 25c divided by the bleeder resistor group 50b. Further, the shield electrode 25g is grounded, and the anode 25h is grounded via a resistor 50c and is input to one terminal of the amplifier 50d. The other terminal of the amplifier 50d is grounded, and the charge-converted image data is taken out as an electrical signal from the output terminal 50C. Further, the voltage V applied to the bleeder resistor 50b' is monitored by the terminal 501'. Note that the shield electrode 25g is not necessarily required and may not be provided.

Next, a method of determining the irradiation amount of the light 12 for eliminating afterimages will be explained.

The entire surface of the stimulable phosphor sheet is uniformly irradiated with radiation (
This is called "solid exposure." ), uniform radiation energy is accumulated and recorded over the entire surface of the sheet. This solidly exposed stimulable phosphor sheet 1 is set in the radiation image reading device shown in FIG. 1, and is read in the same manner as in the case of reading the radiation image described above. (see Figure 3) is monitored.

FIG. 4 shows the bleeder when the stimulated luminescence light 7 emitted from the stimulable phosphor sheet 1 that has been exposed all over with various doses of radiation is read by the long photomultiplier 25 to which various voltages are applied. The voltage V applied to the resistor in the main scanning direction (X
FIG. 3 is a diagram showing the variation characteristics of

This voltage V represents the absolute value of the voltage monitored by the terminal "i'50r" shown in Fig. 3.Excluding changes due to fluctuation characteristics, the lower the voltage V, the more the radiation from the cauldron is irradiated, or the longer the High voltage (negative high voltage)
is being applied. That is, when the voltage applied to the long photomultiplier is constant, excluding changes due to fluctuation characteristics, the lower the voltage V, the greater the energy remaining in the stimulable phosphor sheet 1 after reading.

The voltage V applied to the bleeder resistor has fairly large fluctuation characteristics as shown in this figure, so even if you find the minimum value of the voltage ■ obtained when reading a radiographic image,
The amount of energy remaining in the stimulable phosphor sheet 1 cannot be accurately determined.

Among the many curves 15a to 151 representing the fluctuation characteristics shown in FIG. 4, FIG.
The fluctuation characteristics are corrected so that e becomes a straight line, and other curves 15a to 15d are calculated based on the correction.

15'' to 151 is also a diagram showing a corrected graph.

Curves (straight lines) 15a' to 151' shown in this figure correspond to curves 15a to 151 shown in FIG. 4, respectively.

Curves other than curve 15e'! 5a' to 15d',
15f" to 151' are also corrected almost linearly, except for the end of the light receiving surface of the long photomultiple 25. This end is not used when reading the radiographic image, so it can be ignored. Data for correcting the fluctuation characteristics of the voltage V applied to the bleeder resistance of the long photomultiplier 25 as described above is stored in the computer system 40. This correction data of the computer system 40 is stored in the computer system 40. The storing function is considered as an example of the storage means of the present invention.

Next, an example of how to determine the amount of afterimage erasing light to be applied to the stimulable phosphor sheet 1 on which a radiation image has been stored and recorded will be explained.

The stimulable phosphor sheet 1 on which the radiation image has been stored and recorded is set in a predetermined position of the radiation image reading device shown in FIG. 1, and the radiation image is read as described above. Voltage applied to bleeder resistor■
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 during this reading, an envelope curve 17 of the large number of curves IB, and an envelope curve 18 after correction. be.

Since radiation images are stored and recorded on the stimulable phosphor sheet 1, the voltage V applied to the bleeder resistance changes for each main scan (curve 1B). Therefore, after reading the radiation image stored and recorded on the stimulable phosphor sheet 1, the points at which the voltage V, which has changed in each main scan, has decreased the most at each point in the main scanning direction (X direction) are determined. Connected envelope curve 1
7 is obtained, and this envelope curve 17 is further corrected based on the data for correcting the fluctuation characteristics, and a corrected envelope curve 18 is obtained. The amount of light irradiation for erasing the afterimage is determined from the voltage vo at the point where the voltage V is lowest in the corrected envelope curve 18, and the lamp 11 (
The amount of light (see FIG. 1) or the lighting time of the lamp 11 is controlled. In this embodiment, the function of the computer system 40 to obtain the corrected envelope curve 18 and the voltage v obtained from the corrected envelope curve 18.

The function of controlling the amount of light or the lighting time of the lamp 11 according to the above is considered to be an example of the correcting means and the controlling means of the present invention, respectively.

By erasing the afterimage as described above, it is possible to prevent insufficient afterimage erasure, and also to prevent unnecessary power and time from being spent on erasing the afterimage.

FIG. 7 is a perspective view showing another embodiment of the radiation image reading device of the present invention. Components that are the same as those in the radiation image reading device shown in FIG. 1 are given the same numbers as in FIG. 1, and their explanations will be omitted.

The stimulated luminescent light-7 enters the light guide 13. This light guide 13 is made by molding a light-guiding material such as an acrylic plate, and is arranged in such a way that a linear entrance end surface 13a extends along the main scanning line, and is formed in an annular shape. A light receiving surface of a photomultiplier 25' is coupled to the exit end surface Hb. The stimulated luminescent light 7 entering the light guide 13 from the entrance end face 13a travels through the light guide 13 through repeated total reflection, exits from the exit end face 13b, and is received by the photomultiplier 25', resulting in a radiation image. An image signal S^ representing . The voltage V applied to the bleeder resistor of the photomultiplier 25' is also monitored.

Here, depending on the position of the incident end surface 13a of the light guide 13 from which the stimulated emitted light enters, the photomultiplier 25
The value of the signal S^ output from ' is different, and the voltage V applied to the bleeder resistor is also different. The fluctuation characteristics of this voltage V are also corrected in the same manner as in the embodiment described above.

Each of the above embodiments is an example of determining the amount of light irradiation for erasing an afterimage. For example, if the image signal So (see Fig. 1) is
is saturated, the voltage V applied to the bleeder resistor at the time when the image signal So is saturated is corrected based on the correction data stored in the computer system 40, and this corrected voltage V is applied to the saturated voltage V as described above. It may be used as an image signal instead of the image signal So.

(Effects of the Invention) As described above in detail, the radiation image reading device of the present invention stores data for correcting the fluctuation characteristics of the voltage of the bleeder resistor in the main scanning direction, and Since the voltage applied to the bleeder resistor obtained when reading the radiation image is corrected based on the voltage value applied to the bleeder resistor, the accurate amount of stimulated luminescence light can be determined from the voltage value applied to the bleeder resistor. In addition, by controlling the amount of light irradiation for erasing afterimages based on the voltage after correction, necessary and sufficient afterimage erasure is performed, and insufficient erasure is not performed, which is unnecessary due to the afterimage erasure. It does not require a lot of electricity or time.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the radiation image reading device of the present invention, FIG. 2A is a partially cross-sectional perspective view showing the structure of a long photomultiply, and FIG. 2B is FIG. 2A. 3 is a diagram showing an example of an electric circuit attached to a long photomultiply, and FIG. 4 is a cross-sectional view of the voltage applied to the bleeder resistor of the long photomultiplier in the main scanning direction. FIG. 5 is a diagram showing the fluctuation characteristics after correction; FIG. 6 is a diagram showing the voltage applied to the bleeder resistance for each main scan when reading a radiation image; A diagram showing the envelope curves of these many curves and the corrected engineering-Sivelobe curves,
FIG. 7 is a perspective view showing another embodiment of the radiation image reading device of the present invention. 1... Stimulable phosphor sheet 3... Excitation light beam 7... Stimulated luminescence light 11.
... Afterimage erasing lamp 12 ... Light emitted from lamp 11 ... Light guide 25 ... Long photomultiplier tube (long photomultiplier) 25
'...Photomultiplier tube 40...Computer system 1999 patent application 2. Name of the invention No. 272,951, November 1999 Relationship with the case of person who corrects radiographic IaWa acquisition device Appointment of patent applicant Location 210ii Nakanuma, Minamiashigara City, Kanagawa Prefecture Place name Title
(520) Fuji Photo Film Co., Ltd. 2nd, 6th, "Detailed Description of the Invention" column 7 of the specification subject to amendment, Contents of the amendment (1) After "will be done" on page 22, line 16 of the specification. ``However, in this embodiment, the fluctuation characteristics of the voltage applied to the bleeder resistor are smaller than in the case of a long photomultiplier.'' is inserted. 4. Agent address: 5-2-1 Roppongi, Minato-ku, Tokyo Hauraiya Pill 71! ! 5 5. Voluntary amendment of date of amendment order

Claims (2)

[Claims] (1) A light beam is scanned multiple times in the main scanning direction over the stimulable phosphor sheet on which a radiation image has been stored and recorded, and the stimulable phosphor sheet and the light beam are moved relative to each other in the main scanning direction. scanning means for two-dimensionally scanning the stimulable phosphor sheet with the light beam by moving in a substantially perpendicular sub-scanning direction; comprising a light-receiving surface extending in the main-scanning direction and a photomultiplier tube; , a photoelectric conversion means for obtaining an image signal by receiving stimulated luminescence light representing the radiation image emitted from the stimulable phosphor sheet by the scanning, and a monitor for monitoring the voltage applied to the bleeder resistor of the photomultiplier tube. means, storage means for storing data for correcting fluctuation characteristics of the voltage in the main scanning direction, and correcting the voltage obtained by the monitoring means based on the data stored in the storage means. What is claimed is: 1. A radiation image reading device characterized by comprising a correction means for: (2) The radiation image reading device according to claim 1, further comprising a light source that emits light for erasing an afterimage of the stimulable phosphor sheet, and an irradiation amount of light for erasing the afterimage based on the corrected voltage. A radiation image reading device characterized by comprising a control means for controlling.