JPS636542A - Determining method for reading condition of radiation image information - Google Patents

Abstract

PURPOSE:To correctly read image information by detecting an instantaneous luminous afterglow by pre-read, correcting an excitation light by the instantaneous luminous afterglow, and executing regular read, in a device for obtaining an image by radiating the excitation light to a cumulative phosphor body sheet. CONSTITUTION:A laser light 3 is radiated to a cumulative phosphor sheet 1 in which radiation image information has been recorded, through a lens 10, etc. In such a case, as pre-read, an accelerated luminous light 14 is generated by moving the sheet 1 in the direction as indicated with an arrow A and radiating the laser light 3, and inputted to a photodetector 13. Its detecting signal is inputted to a controlling circuit 24, and a reproduced image processing condition. Subsequently, the sheet 1 is made to go backward by suspending the irradiation of the laser light 3, an instantaneous luminous afterglow at such a time is detected by the photodetector 13, and an afterglow level Sx is derived by an arithmetic circuit 25. Next, an excitation light quantity of an optimum reproduced image is derived by subtracting the afterglow level Sx from a reproduced image processing value of pre-read. Thereafter, an image is reproduced by regular read. Accordingly, since the influence of the instantaneous luminous afterglow is eliminated, an excellent reproduced radiation image can be obtained.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention irradiates excitation light onto a stimulable phosphor sheet on which radiographic image information is accumulated and recorded, thereby emitting light from the stimulable phosphor sheet. The present invention relates to a method for determining optimal reading conditions in a radiation image information reading method in which the radiation image information is read by photoelectrically detecting stimulated luminescence light.

(Prior art) When a certain type of phosphor is irradiated with radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a portion of this radiation energy is accumulated in the phosphor. It is known that when this phosphor is irradiated with excitation light such as visible light, the phosphor exhibits stimulated luminescence depending on the accumulated energy. It is called a stimulable fluorophore.

Using this stimulable phosphor, the subject 1 such as the human body can be photographed.
The radiation image information is once recorded on a stimulable phosphor sheet, and the stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescence light. The present application provides a radiation image information recording and reproducing system that photoelectrically reads the image signal to obtain an image signal, and outputs the radiation image of the subject as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT based on this image signal. Already suggested by someone.

(JP-A-55-12429, JP-A-56-11395, etc.) This system has practical advantages in that it can record images over an extremely wide radiation exposure range compared to conventional radiographic systems using silver halide photography. It has advantages. In other words, in a stimulable phosphor, the luminescent light that is stimulated to emit light due to excitation after being accumulated in response to the amount of radiation exposure.
It has been recognized that Set the reading gain to an appropriate value, read it with a photoelectric conversion means, convert it into an electrical signal, and use this electrical signal to output the 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. By doing so, it is possible to obtain a radiation image that is not affected by variations in radiation exposure amount.

In addition, according to this system, radiation image information stored and recorded on a stimulable phosphor sheet is converted into an electrical signal and subjected to very appropriate signal processing, and this electrical signal is used to produce recording materials such as photographic light-sensitive materials. By outputting a radiographic image as a visible image on a display device such as a CRT, it is possible to obtain a radiographic image with excellent suitability for observation and interpretation (diagnostic suitability).

In this way, in a radiation imaging system that uses a stimulable phosphor sheet, the reading gain can be set to an appropriate value to photoelectrically convert the stimulated luminescence light and output it as a visible image, so the radiation source fluctuations in the radiation exposure ω due to fluctuations in the tube voltage or MAS value, fluctuations in the sensitivity of the stimulable phosphor sheet, fluctuations in the sensitivity of the photodetector, changes in the exposure color due to subject conditions, or changes in radiation transmittance depending on the subject. Even if the energy stored in the stimulable phosphor differs due to various factors, or even if the amount of radiation exposure is reduced, it is possible to obtain radiographic images that are not affected by fluctuations in these factors. becomes.

However, in order to eliminate the effects of fluctuations in imaging conditions or to obtain radiographic images that are suitable for observation and interpretation, it is necessary to change the recording state of the radiographic image information accumulated and recorded on the stimulable phosphor sheet, or the chest, Recording patterns (hereinafter collectively referred to as 1, "accumulated record information") determined by the part of the subject such as the abdomen, the imaging method such as plain radiography or contrast radiography, etc., are used for observation and interpretation. The recording scale factor is determined prior to the output of a visible image, and the reading gain is adjusted to an appropriate value based on the acquired accumulated recording information, and the recording scale factor is adjusted to optimize the resolution according to the contrast of the recording pattern. When the read image signal is determined and further image processing such as gradation processing is performed on the read image signal, it is necessary to optimally set the image processing conditions.

As a method for grasping the accumulated record information of radiographic images before outputting visible images, Japanese Patent Laid-Open No. 58-67240
The method disclosed in No. This method uses excitation light of a lower level than the excitation light that should be irradiated during the reading operation (hereinafter referred to as "main reading") to obtain a visible image for observation and interpretation. Perform reading operations (hereinafter referred to as "read ahead") to grasp the accumulated record information of radiographic images accumulated and recorded on the stimulable phosphor sheet, grasp the outline of accumulated records of radiographic images, and read the main reading. When performing this, the reading gain is appropriately adjusted, the recording scale factor is determined, or the image processing conditions are determined based on this pre-read information.

Note that the excitation light used for pre-reading is at a lower level than the excitation light used for main reading because the effective energy of the excitation light that the stimulable phosphor sheet receives per unit area during pre-reading is lower than the excitation light used for main reading. This means that it is smaller than the actual value.

Various methods have been considered for grasping the accumulated record information of a stimulable phosphor sheet from the pre-read image signal obtained by the above-mentioned pre-reading, and one such method is a method that uses a histogram of the pre-read image signal. It has been known. In other words, for example, the maximum and minimum values of the signal in this histogram,
Since it is possible to understand the accumulated recorded information from the signal value etc. at the maximum frequency point, if reading conditions such as reading gain and recording scale factor (latitude) and image processing conditions are determined based on these characteristic values, It becomes possible to reproduce radiographic images with excellent diagnostic suitability.

(Problems to be Solved by the Invention) However, the reading conditions and/or image processing conditions determined as described above are affected by the instantaneous afterglow from the stimulable phosphor sheet, and are The stored record information may become inappropriate. The above-mentioned instantaneous luminescence afterglow is the afterglow of instantaneous luminescence that is emitted when a stimulable phosphor sheet is irradiated with radiation. (for several tens of seconds) continues to emit light. Therefore, the pre-read image signal naturally also includes a signal component due to this instantaneous light emission afterglow, so that the pre-read image signal is raised as a whole compared to the signal component carrying actual image information. As a result, the histogram shifts to the side where the signal value is large (toward the high light emission side) and does not correctly reflect the actual accumulated recorded information. In other words, this histogram appears to have been created for an image with an overall higher density than the true recorded image.

Therefore, when radiation image information is read and the image is reproduced using reading conditions determined based on such a histogram, low-density portions of the reproduced image may be skipped.

SUMMARY OF THE INVENTION An object of the present invention is to provide a radiation image information reading condition determining method that can prevent the above-mentioned problems from occurring.

(Means for Solving the Problems) The radiation image information reading condition determination method of the present invention performs the above-mentioned pre-reading, and determines the reading conditions and/or in the main reading based on the histogram of the pre-read image signal obtained by this pre-reading. In a method for determining radiation image information reading conditions in which image processing conditions are determined, an instantaneous afterglow emission from a stimulable phosphor sheet is detected by a light detection means, a signal SX indicating the level thereof is obtained, and the above-mentioned histogram is obtained. The reading conditions and/or the image processing conditions are determined based on the value obtained by subtracting the value of the signal 3x from the characteristic value (maximum value, minimum value, etc.) of the pre-read image signal.

The signal SX indicating the level of the instantaneous light emission afterglow can be obtained, for example, by the method shown in JP-A No. 58-108238, or by providing a common reading system for pre-reading and main reading, when the pre-reading is completed. In a radiation image information reading device in which the stimulable phosphor sheet is returned to the reading system for actual reading, excitation light irradiation is stopped when the stimulable phosphor sheet is returned as described above. It can also be obtained by, for example, measuring the output of the photodetecting means above.

(Function) The value obtained by subtracting the signal Sx from the characteristic value of the look-ahead image signal in the histogram becomes the characteristic value indicating the true accumulated recorded information excluding the influence of instantaneous light emission afterglow, so based on this value, Once the reading conditions and/or image processing conditions are determined, they will be appropriate for the actual stored record information.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows an example of a reading device that reads radiation image information by determining reading conditions and image processing conditions according to the method of the present invention. The first stimulable phosphor sheet 1 accumulates and records radiation image information regarding the subject by irradiating radiation such as X-rays through the subject.
The image is transferred to the reading device shown in the figure. In this reading device,
First, pre-reading is performed on the transported stimulable phosphor sheet 1. A laser beam 3 emitted from a laser light source 2 passes through a beam expander 4, and its beam diameter is precisely adjusted. Next, this laser beam 3 is passed through an ND filter 5, a prism 6, and a concave lens 7 to reduce its intensity and expand its beam diameter. Then, the laser beam 3 is deflected by an optical deflector 8 such as a galvanometer mirror, and passed through a flat reflector 9 to a stimulable phosphor sheet 1.
incident on the sheet and linearly scan the sheet. An fθ lens 10 is arranged between the optical deflector 8 and the plane reflecting mirror 9,
The beam diameter of the laser beam 3 scanning the phosphor sheet 1 is made uniform. Here, the laser light source 2 is selected so that the wavelength range of the laser light 3 does not overlap with the wavelength range of the stimulated luminescent light from the stimulable phosphor sheet 1. On the other hand, the stimulable phosphor sheet 1 is transported in the direction of arrow A by a sheet transport means 11 such as an endless belt, and is sub-scanned, so that the entire surface of the phosphor sheet 1 is irradiated with laser light 3. . The part of the stimulable phosphor sheet 1 irradiated with the laser beam 3 emits stimulated luminescent light 14 corresponding to the accumulated and recorded radiation energy, and this luminescent light 14 enters the light condenser 12. do. This light condenser 12 has an incident surface 12
a has a linear shape and is arranged to face the scanning line on the stimulable phosphor sheet 1, and the exit surface 12b has an annular shape and is in close contact with the light receiving surface of a photodetector 13 such as a photomultiplier. has been done. The light collector 12 is formed by processing a transparent thermoplastic resin sheet such as acrylic resin, and is configured so that the light incident from the incident surface 12a reaches the exit surface 12t while being totally reflected inside. Stimulated luminescent light 14 emitted from the stimulable phosphor sheet 1 is guided through the condenser 12, exits from the exit surface 12b, and is received by the photodetector 13. The preferable shape, material, etc. of the condenser 12 are described in Japanese Patent Application Laid-open Nos. 55-87970 and 56-1.
No. 1391, etc.

A filter (not shown) is attached to the light-receiving surface of the photodetector 13, which transmits only light in the wavelength range of the stimulated luminescence light 14 and cuts light in the wavelength range of the laser light 3 as excitation light. It is designed to detect only the stimulated luminescence light 14. The output of the photodetector 13 is input to a pre-read amplifier 21 via a switch 20, amplified by the pre-read amplifier 21, digitized by an A/D converter 22, and output as a pre-read image signal Sp via a switch 23. It is input to the main reading control circuit 24. This main reading control circuit 24 determines the reading gain setting value a, the recording scale factor setting value b, and the reproduction image processing condition setting value C by histogram analysis based on the accumulated recording information indicated by the preread image signal Sp (these conditions The decision will be discussed in detail later). Note that the read gain of the look-ahead amplifier 21 is a constant value a°.
The recording scale factor of the A/D converter 22 is also fixed to a constant value b'.

When the pre-reading is completed as described above, the sheet transport means 11 is reversed, the stimulable phosphor sheet 1 is returned to the reading start position 17, and reading of the sample is started. In this way, when the stimulable phosphor sheet 1 is returned, the laser light source 2
is deactivated, but the photodetector 12 remains activated. Therefore, in this case, the stimulated luminescent light 14 is not detected, but as mentioned above, the radiation is transferred to the stimulable phosphor sheet 1.
The photodetector 12 detects the instantaneous light emission afterglow that continues to emit light after being irradiated with the light. The output of the photodetector 12 indicating the level of the instantaneous emission afterglow is amplified by the amplifier 21, converted to a digital signal Sx' by the A/D converter 22, and inputted to the arithmetic circuit 25 via the switch 23. Ru. The arithmetic circuit 25 calculates the average value of this digital signal SX' and outputs an afterglow level signal Sx indicating the average afterglow level in one stimulable phosphor sheet 1.

Next, I will explain the main reading. In the actual reading, the laser light 3 is emitted from the laser light source 2 in the same way as in the pre-reading, but in the case of the actual reading, the ND filter 5 and the prism 6 are emitted.
Since the concave lens 7 is moved in the direction of the arrow 18 so as to be out of the optical path, the energy level of the laser beam 3 (excitation light) becomes higher than the energy level of the excitation light at the time of pre-reading. Here, the energy of the excitation light refers to the effective energy of the excitation light that the stimulable phosphor sheet 1 receives per unit area. Note that the closer the ratio of the excitation light energy of the pre-reading to that of the main reading is to 1, the less the radiation energy base remaining and accumulated in the phosphor sheet 1 during the main reading, but if this ratio is less than 1, For example, it has been found that by appropriately adjusting the value of the reading gain, a radiographic image with 11 aptitude for interpretation can be obtained. However, in order to produce radiographic images with excellent observation and interpretation aptitude, it is desirable that the energy ratio of the excitation light for pre-reading and main reading be as small as possible, and should be 50% or less, preferably 10% or less, and more preferably 3% or less. is desirable. The lower limit of this ratio is determined by the accuracy of the pre-read stimulated luminescence light detection system.

This laser light 3 is irradiated onto the entire surface of the stimulable phosphor sheet 1 in the same manner as in the case of pre-reading. The portion of the stimulable phosphor sheet 1 that has been irradiated with the laser beam 3 emits stimulated luminescent light 14 at a level corresponding to the radiation image information that has been stored and recorded. This stimulated luminescent light 14 enters the condensing body 12 , transmits inside the condensing body 12 , and is detected by the photodetector 13 . The output of the photodetector 13 is input to the main reading amplifier 27 via the switched switch 20, and the main reading amplifier 2 has its sensitivity set based on the reading gain setting @a.
1, the electrical signal is amplified to an appropriate level. The amplified electrical signal is input to the A/D converter 28 and converted into a digital signal Sd with a scale factor (latitude) suitable for the signal fluctuation range based on the recording scale factor setting value S, and then sent to the signal processing circuit 29. is input. This signal processing circuit 29 performs signal processing on the digital signal @Sd based on the reproduced image processing condition setting value C so that a radiation image excellent in suitability for observation and interpretation is obtained.
This signal-processed digital signal So is transmitted to an image reproducing device 30 that outputs the radiation image as a visible image. The signal processing performed in the signal processing circuit 29 is disclosed in Japanese Patent Application Laid-Open No. 55-8797.
No. 0, No. 56-11038, No. 56-75137,
No. 56-75139, No. 56-75141, No. 56
Frequency processing disclosed in Japanese Patent Laid-open No. 104645, etc., and floor l! Examples include l processing.

The image reproducing device 30 reproduces the radiation image based on the image signal SO sent from the signal processing circuit 29. Reproduction methods include recording by scanning a photosensitive material with a laser beam, displaying it electronically on a CRT, etc., recording the radiation image displayed on a CRT, etc. on a video printer, etc., and using heat rays. Various recording methods can be used, such as recording on a heat-sensitive recording material.

In this device, as described above, the accumulated recording information of the stimulable phosphor sheet 1 is grasped in advance by pre-reading, and the optimum reading gain setting @a and recording scale adjustment are determined based on this information. The image is read according to the vector setting value,
Furthermore, since the image processing is performed based on the optimal reproduction image processing condition setting value C, the radiation image reproduced by the image reproduction device 30 has excellent observation and interpretation suitability (diagnosis performance).

Next, the characteristic part of the method of the present invention that eliminates the influence of the above-mentioned instantaneous light emission afterglow and makes it possible to appropriately set the reading gain setting value a, the recording scale factor setting value b1, and the reproduction image processing condition setting value C. I will explain about it. As shown in detail in FIG. 2, the main reading control circuit 24 includes a histogram creation section 4o, a histogram analysis section 41, a correction section 42, a reading section 43, and a storage section 44. The above-mentioned pre-read image signal Sp is input to the above-mentioned histogram creation section 40. The histogram creation section 40 creates a histogram for all of these pre-read image signals Sp. This histogram is, for example, as shown by the solid line in FIG.

However, since the pre-read image signal Sp also includes a signal component due to the above-mentioned instantaneous light emission afterglow, the histogram of the true accumulated recorded information should be as shown by the broken line in FIG. In other words, in the histogram, only the shaded portion in FIG. 3 is shifted to a large signal value (four high-light emission sides) due to the instantaneous light emission afterglow. Histogram analysis section 41
Information sh indicating this histogram is input to .

The histogram analysis unit 41 analyzes the histogram indicated by this histogram information sh, and for example, the maximum value 3
Characteristic values such as max, minimum value 3m1n, and maximum frequency value Sy are determined. The storage unit 44 stores these characteristic values Swax,
Optimum reading gain setting values a1 corresponding to 31n, SV, etc., recording scale factor setting values, and image processing condition setting values C are stored, and the reading unit 43 reads setting values a, b, c is read from the storage section 44 and sent to the amplifier 21, A/D converter 28 and signal processing circuit 29, respectively, as described above. However, here, the characteristic value Smax, 5 determined by the histogram analysis unit 41
atin, SV, etc. are not directly sent to the reading unit 43, but are first stored in a storage means (not shown) of the correction unit 42, and after the above-mentioned afterglow level signal Sx is input, the signals Sx After subtracting the value of , it is sent to the reading unit 43. As mentioned earlier, this afterglow level signal Sx carries the average level of the instantaneous afterglow from the stimulable phosphor sheet 1, so the correction characteristic value after this subtraction is Smax', 5ain', S'/'
represents the true accumulated recorded information excluding the influence of instantaneous light emission afterglow. Therefore, these correction characteristic values 3ma
The reading gain setting value a1 recording scale factor setting value and image processing condition setting value C determined based on The reproduced image reproduced by the image reproduction device 30 has high image quality without the low-density parts being skipped as described above.

Note that the minimum value of the pre-read image signal Sp is 5sin and the maximum value is 1i1.
Since there is usually a difference of about two orders of magnitude or more from S max, the effect of the characteristic value correction by the above subtraction is the minimum signal value 3 wi
It is most noticeable at n (in FIG. 3, 2 is a logarithm of the horizontal axis indicating the signal value).

In the embodiment described above, when returning the stimulable phosphor sheet 1 to the reading start position after the end of pre-reading, the sheet 1
At this time, the instantaneous emission afterglow level is detected by utilizing the passage of the emitted light through the emitted light detection system, but this instantaneous emission afterglow level detection may be performed by other methods. That is, for example, as shown in the above-mentioned Japanese Patent Application Laid-Open No. 58-108238, when the laser beam 3 has finished one line of main scanning and is at a position away from the stimulable phosphor sheet 1, the photodetector 13 is It is also possible to obtain the instantaneous light emission afterglow level by sampling the output.

(Effects of the Invention) As explained above in detail, according to the radiation image information reading condition determination method of the present invention, the influence of instantaneous light emission afterglow can be eliminated,
Since the optimal reading conditions and image processing conditions can be determined for the true accumulated recorded information, it becomes possible to obtain reproduced radiation images with excellent diagnostic performance.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a radiation image information reading device that implements the method of the present invention, FIG. 2 is a block diagram showing a part of the device in FIG. 1 in detail, and FIG. 3 is a pre-read image according to the present invention. FIG. 3 is an explanatory diagram illustrating correction of a signal histogram and characteristic values. 1...Storage phosphor sheet 2...Laser light source 3.
...Laser light 4...Beam expander-5
...ND filter 6...prism 7...
Concave lens 8... Light deflector 11... Sheet transport means 13... Photodetector 21.27...
Amplifier 22.28...A/D converter 24.
...Reading control circuit 25...Arithmetic circuit 29...
・Signal processing circuit 30...Image reproduction device Sp・
...Pre-reading image signal SO...Actual reading image signal SX
...Afterglow level signal 3 wax...Maximum value of pre-read image signal 5IIlin
... Minimum value Sy of pre-read image signal ... Maximum frequency value of pre-read image signal Fig. 2 sy sy' Fig. 3

Claims (1)

[Claims] A stimulable phosphor sheet on which radiographic image information is stored and recorded is irradiated with excitation light, and the stimulated luminescent light emitted from the sheet by the irradiation with the excitation light is photoelectrically detected by a photodetector. A radiographic image is read to obtain an image signal for visible image reproduction, and prior to this main reading, pre-reading is performed to read an outline of the stored information recorded on the stimulable phosphor sheet. In the information reading method, a histogram of the pre-read image signal obtained in the pre-reading is obtained, and an instantaneous light emission afterglow from the stimulable phosphor sheet is detected by a light detection means to obtain a signal Sx indicating its level; A radiation image information reading condition determining method, characterized in that reading conditions and/or image processing conditions in the main reading are determined based on a value obtained by subtracting the value of the signal Sx from the characteristic value of the pre-read image signal in the histogram.