JPS6218536A - Reading method for radiation image information - Google Patents

Abstract

PURPOSE:To read extremely properly radiation image information which is built in and recorded on an accumulating phosphor sheet by approximating the stimulated luminescent afterglow characteristic on said sheet to the sum of more than three index functions and correcting electrically a picture signal according to the approximation. CONSTITUTION:After the picture signal S(x) as the radiation image information is corrected in a correcting device 30 in order to remove a signal component due to the stimulated luminescent afterglow, it is transmitted to a reading circuit 16. Namely a signal T(x) turns out to be a one whose signal component due to the stimulated luminescent afterglow is removed out of the radiation image information S(x) shown by the stimulated luminescent afterglow from the accumulating phosphor sheet 13. THe signal T(x) is transmitted to the reading circuit 16, sampled by a certain period and taken for a picture signal for each picture element. Then the radiation image reproduced on a CRT 17, etc., according to the picture signal becomes clearer, because the influence of the stimulated luminescent afterglow is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention involves irradiating excitation light onto a stimulable phosphor sheet on which radiographic image information is stored and recorded, thereby emitting radiation from the stimulable phosphor sheet. Regarding a radiation image information reading method for photoelectrically detecting stimulated luminescence light to obtain an image signal representing the radiation image information, in particular, the radiation image information is accurately read by removing the influence of stimulated luminescence afterglow. This article relates to a method for reading radiation image information that can be read easily.

(Technical Background and Prior Art of the Invention) When a type of phosphor is irradiated with radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), part of this radiation energy is released into fluorescent light. It is known that when this phosphor is accumulated in the body and is irradiated with excitation light such as visible light, the phosphor exhibits stimulated luminescence depending on the accumulated energy; The fluorophore is called a storage fluorophore.

Using this stimulable phosphor, radiation image information of a subject such as a human body is temporarily recorded on a stimulable phosphor sheet, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam. Generate stimulated luminescence light, photoelectrically read the resulting stimulated luminescence light to obtain an image signal, and based on this image signal, a radiation image of the subject is displayed on a recording material such as a photographic light-sensitive material or a display device such as a CRT. The applicant has already proposed a radiation image information recording and reproducing system that outputs a visible image.

(Unexamined Japanese Patent Publication No. 55-12429, No. 56-1 'l 39
No. 5, 56-11397@, 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. That is, in a stimulable phosphor, it is recognized that the amount of emitted light that is stimulated to emit light due to excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range.
Therefore, even if the amount of radiation exposure varies considerably due to various original conditions, the amount of stimulated luminescence emitted from the stimulable phosphor sheet can be read by the photoelectric conversion means by setting the reading gain to an appropriate value. By converting the radiation image into an electrical signal and using 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, it is possible to produce a radiation image that is not affected by fluctuations in radiation exposure. Obtainable.

Furthermore, according to this system, radiation image information accumulated and recorded on a stimulable phosphor sheet is converted into an electrical signal, then subjected to appropriate signal processing, and this electrical signal is used to produce recording materials such as photographic light-sensitive materials, CRTs, etc. By outputting a radiographic image as a visible image on a display device such as the above, it is possible to obtain a very large effect that a radiographic image with excellent observation and interpretation suitability (diagnosis suitability) can be obtained.

In the above-mentioned radiation image information recording and reproducing system, a specific method for reading radiation image information from a stimulable phosphor sheet is to scan the stimulable phosphor sheet two-dimensionally with a light beam such as a laser beam, At this time, the stimulated luminescence light emitted from the sheet is transmitted to a photodetector such as a photomultiplier through a light condenser having a light incident end surface extending along the main scanning line, and the stimulated luminescence light is transmitted to a photodetector such as a photomultiplier. There is a method of detecting emitted light in time series to obtain an image signal for each pixel.

By the way, as mentioned above, when irradiated with excitation light, a stimulable phosphor has the property of emitting the radiation energy stored in the phosphor as stimulated luminescence. The luminescence intensity rapidly reaches the maximum (in a few nanoseconds, for example) from the start point, and then the luminescence intensity slowly decreases, and even after the excitation light irradiation ends, the firefly remains as a so-called afterglow (stimulated luminescence afterglow). Light emission continues for the response time specific to the light object. Therefore, when a stimulable phosphor sheet is scanned with excitation light and the stimulated luminescent light is sent to a photodetector via the aforementioned light collector, the photodetector detects the emitted light from the pixel being irradiated with the excitation light. In addition to the components, afterglow components from pixels that have already been irradiated with excitation light are also detected as radiation image information components of pixels that are being irradiated with excitation light, so signals between pixels are not completely separated and are reproduced. Image sharpness decreases. The resolution of such detection of stimulated luminescence intensity between multiple pixels is
The higher the scanning speed of the excitation light and the response time of the phosphor, the lower the rate. Therefore, if a phosphor with a slow response to excitation (long stimulated emission afterglow) is used or if the scanning speed is increased, the sharpness of the reproduced image will decrease and the image quality will not be high enough for practical use. A problem arises in that a radiographic image cannot be obtained.

In the medical field, etc., there is a desire for a reading device that can process a large amount of stimulable phosphor sheets in a short time, that is, a reading device that can increase the excitation light scanning speed and perform high-speed reading. In the current situation, there is a practical limit to improving the stimulated luminescence afterglow properties by improving the body itself.
There is a desire for a reading method that can eliminate the above-mentioned reduction in sharpness of radiographic images.

Therefore, the present applicant has already proposed a method of electrically correcting the interference between pixels of image signals due to the response characteristics of the stimulable phosphor sheet, that is, the stimulated luminescence afterglow characteristics (Japanese Patent Application Laid-Open No.
No. 9-105759). This method is effective in removing the component due to stimulated luminescence afterglow from the image signal of each pixel. However, the intensity of the stimulated luminescence afterglow rapidly decreases after excitation ends, and the intensity of the stimulated luminescence afterglow decreases rapidly after excitation ends. It has a characteristic that it continues to occur for a long time, and the above methods have not been able to sufficiently eliminate the influence of stimulated luminescence afterglow that continues to occur at this weak level.

(Objective of the Invention) Therefore, the present invention aims to completely eliminate the influence of the stimulated luminescence afterglow that continues to occur at a weak level, and to greatly improve the radiation image information stored and recorded on the stimulable phosphor sheet. The purpose of this invention is to provide a method for reading radiation image information that can be read accurately.

(Structure of the Invention) As described above, the radiation image information reading method of the present invention irradiates excitation light onto a stimulable phosphor sheet on which radiation image information of a subject is accumulated and recorded, and the excitation light irradiation causes the sheet to In a method for reading radiation image information, in which the stimulated luminescence light emitted from the stimulable luminescent material is photoelectrically read by a photodetector to obtain a time-series image signal in pixel units carrying the radiation image information, It is characterized in that the stimulated luminescence afterglow characteristic of the sheet is approximated to the sum of two or more exponential functions, and the image signal is electrically corrected based on this approximation.

The above-mentioned electrical correction can necessarily be performed analogously or digitally using, for example, a circuit as described below. Further, the timing of this correction may be before or after the read image signal is stored in the memory, for example, immediately before inputting it to the image reproducing device. Further, the correction may be performed immediately before performing other image processing, or as part of the image processing by combining the correction device with a circuit that performs such image processing.

Since the method of the present invention electrically corrects signal interference in pixel units due to stimulated luminescence afterglow, the device implementing the method of the present invention may be It is possible to change the method of electrical correction depending on the scanning speed.

Further, the stimulable phosphor sheet used in the present invention does not necessarily have to be in the form of a sheet. The scanning of excitation light is not limited to simple linear one-dimensional scanning.
Rust scanning or curved scanning may be used, and the excitation light may be irradiated not only continuously but also in a pulsed manner.

Hereinafter, the point that the influence of stimulated luminescence afterglow is eliminated by the correction based on the above-mentioned approximation will be explained in detail.

The radiographic image accumulated and recorded on one main scanning line on the stimulable phosphor sheet is defined as T(X) (X is the distance from the main scanning start point), and this radiographic image T(x) is exposed to excitation light. If the radiation image information obtained by scanning and extracting the stimulated luminescence light in time series and photoelectrically detecting the stimulated luminescence light is 5(X), then the radiation image T(X) and the radiation image information It is thought that the following relationship exists between S (X).

That is, when a stimulable phosphor sheet is scanned with excitation light as described above, if the excitation light irradiation time at one point on the sheet is sufficiently short compared to the time during which stimulated luminescence afterglow exists. When the scanning excitation light is at the scanning point (pixel) Xo, the scanning point X-1# x-
21x-3-...

The stimulated luminescence afterglow emitted from X-n is simultaneously detected as the light emission at the scanning point xO, and the radiation image T(Xo) reproduced based on the read image signal is the radiation image information of a plurality of adjacent pixels. 5 (Xo).

S (X-1>, S (X-2>, S (X-3>)
, ++++e+s(X-r+), resulting in a blurred image with low sharpness (see FIG. 3).

Generally, the above-mentioned stimulated emission afterglow decays exponentially with time, and the rise of the stimulated emission destination is extremely rapid compared to the decay of this afterglow, so as mentioned above, the scanning point xO The afterglow from the previous scanning point is the scanning point
Being detected as light emitted from o is considered to be equivalent to observing a radiation image T(X) with a slit f (x) having the following spatial distribution, for example.

......(1) Here, α is the scanning speed of the excitation light, and τ and τ' are both the luminescence lifetime (the intensity of the stimulated luminescence light decreases by 1/2 after the excitation light irradiation ends).
e), τ is the luminescence lifetime that decays over a short period of time, τ' is the luminescence lifetime that decays over a long period of time, and a is a constant.

That is, according to the research conducted by the present inventors, the stimulated luminescence afterglow characteristic of a stimulable phosphor sheet can be approximated to the sum of two exponential functions, as shown in FIG. (X) and the radiation image information 5(x) are related by the following integral transformation formula.

5(X)=f(Xo X)T(Xo)dXo...(
2) T (x)=a (x'-x)S (x')dx
'-(3) Here, CI (X) is a kernel function of inverse transformation, and is a correction function for obtaining the radiographic image T(x) from the radiographic image information 5(X).

Solving the above equations (2) and (3), C1(X) In the above equation (1), if -(1-a)=A and 1a=8, τbe C1(X) Usually, B/AI Therefore, considering the integral operator δ(X), g(x), therefore...(4), and finally, from the radiation image information 5(x) obtained by reading In order to obtain the radiographic image T(X), it is sufficient to add the differential value at that point to the image information at that point, and then subtract from it the integral value weighted by the second component of the afterglow. Become.

(Embodiments) Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIGS. 1 and 2 show a radiation image information reading apparatus that implements the method of the present invention. As shown in FIG. 1, a laser beam 11a of a constant intensity is emitted from a laser light source 1o, and this laser beam 11a is deflected by an optical deflector 12 such as a galvanometer mirror. Then, the deflected laser beam 11b is irradiated as excitation light onto the stimulable phosphor sheet 13, which has been irradiated with the radiation that has passed through the object and has accumulated and recorded the radiation image of the object. At this time, the stimulable phosphor sheet 13 is arranged so as to be main-scanned in the sheet width direction (direction of arrow Transport it in the Y direction. Therefore, the main scan is repeated at an angle substantially perpendicular to the sub-scan, and the stimulable phosphor sheet 13 is two-dimensionally scanned by the laser beam 11b over its entire surface.

The portion of the stimulable phosphor sheet 13 irradiated with the laser beam 11b emits stimulated light with an intensity corresponding to the radiographic image stored there, and this stimulated emitted light 2° is transmitted to the sheet 13.
The light enters into the transparent light condenser 14 from the incident end face 14a of the transparent light condenser 14 arranged nearby. This light condenser 14 has a front end 14b located near the stimulable phosphor sheet 13 formed into a flat shape, and the above-mentioned incident end face 14 which is located at the end face of the front end 14b.
A is arranged so that it is parallel to the main scanning line. The condenser 14 is formed so as to gradually become cylindrical toward the rear end, and has a substantially cylindrical shape at the rear end 14C, so that light from a photomultiplier or the like disposed on the exit end surface 14d is formed. It is coupled to a detector 15. Therefore, the stimulated luminescent light 20 entering the light collector 14 from the incident end face 14a is photoelectrically detected by the photodetector 15. Note that a filter (not shown) that transmits only light in the wavelength range of the stimulated luminescent light 20 is arranged between the light collector 14 and the photodetector 15, so that only the stimulated luminescent light 20 is transmitted to the photodetector. 15.

The time-series electrical image signal 5(x) outputted from the photodetector 15 is information that carries the radiation image stored and recorded on the stimulable phosphor sheet 13. The image signal 5(x) as this radiation image information is sent to the correction device 30.
After being corrected to remove the signal component due to stimulated luminescence afterglow (this correction will be explained in detail later), the signal is sent to the reading circuit 16, where it is made into a signal for each pixel, and then sent to, for example, a CRT 17. It is used to output a radiation image as a visible image, or it is used to reproduce a radiation image as a hard copy on a photographic material, etc.
Generally, the information is simply recorded on a recording medium 18 such as a magnetic tape, a magnetic disk, or an optical disk.

FIG. 2 shows the correction device 30 in detail. The correction of the image signal 5(X) will be explained below with reference to FIG. As shown in the figure, this correction device 30 includes a differentiating section 31, a differential weighting section 32 connected in series to the differentiating section 31, and an integrating section 3 connected in parallel to the differentiating section 31.
3, and an adding section 34 that adds the outputs of the integrating section 33 and the differential weighting section 32.

The differentiator 31 includes resistors R1, R2 and an operational amplifier OP1.
and a differentiating circuit including a capacitor C1, a resistor R2, and an operational amplifier OP1.

Here, if each element is selected so that 01・R1=τ, the image signal S(×) output from the photodetector 15 will be 5(X)+τα−LS(X) of the equation (4) above. It is converted to correspond to the X term.

Further, the differential weighting section 32 is composed of resistors R3, R4 and operational amplifier OP2, where R4/R3=
If each element is selected so that (1+a>), the output from the differentiator 31 is converted to correspond to the term in the equation (4).

The integrating section 33 includes a resistor R5, a capacitor C2, an operational amplifier OP3,
and an analog switch SW connected in parallel with the capacitor C2. The analog switch SW has a trigger signal 1 synchronized with a drive signal for the optical deflector 12, for example.
'-r automatically opens and closes, e.g. laser beam 11
The capacitor C2 is closed before the start of main scanning of one line by the capacitor C2.

Then, when main scanning for one line is started, analog switch SW is opened, and this state is maintained until main scanning for one line is completed. Note that in this embodiment, correction is performed by integrating one line, but this may be performed for multiple lines depending on the reading method. Therefore, during this period, the image signal S(x) output from the photodetector 15 is integrated. Here, τ'O(Z') such that 1/C2・R5 becomes -<1--L> If each element is selected, the above radiation image information S(x) is
It is converted to correspond to the term in equation (4) above. Therefore, by adding the output of the integrating section 33 and the output of the differential weighting section 32 in the adding section 34, the signal T(x) expressed by the above equation (4) is obtained. As mentioned above, this signal T
(X) is the stimulated luminescence light 2 from the stimulable phosphor sheet 13
The signal component due to stimulated luminescence afterglow is removed from the radiation image information S (X) indicated by 0. Therefore, if this signal T(X) is sent to the reading circuit 16 and sampled at regular intervals to produce an image signal for each pixel, the radiation image reproduced on, for example, the CRT 17 based on this image signal will be The effect of luminescence afterglow has been removed and the sharpness has been improved.

In the embodiment described above, the analog image signal 5(x) emitted from the photodetector 15 is corrected by an electric circuit, but the image signal from the photodetector 15 is A/D converted, The digital image data obtained thereby may be subjected to correction similar to the above.

(Effects of the Invention) As explained in detail above, according to the radiation image information reading method of the present invention, it is possible to strictly prevent the sharpness of reproduced radiation images from decreasing due to the stimulated luminescence afterglow of the stimulable phosphor sheet, and to diagnose It becomes possible to obtain reconstructed radiographic images with significantly superior performance. Further, according to the method of the present invention, since the influence of stimulated luminescence afterglow can be eliminated as described above, it is possible to obtain a radiation image information reading device capable of increasing the scanning speed of excitation light and performing high-speed reading.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing a radiation image information reading device that implements the method of the present invention, FIG. 2 is a circuit diagram showing a signal correction device of the radiation image information reading device, and FIGS. FIG. 3 is an explanatory diagram illustrating the influence of stimulated luminescence afterglow according to the invention on a read image signal. 10...Laser light source 11a111b...Laser light 12...Light deflector 13...Storage phosphor sheet 14...Concentrator 15...
Photodetector 16...reading circuit 2o...stimulated luminescence light 30...correction circuit 31...differentiation section 32...differential weighting section 33...integration section 34.
...Additional Department (Autopsy procedure amendment to the Commissioner of the Patent Office, November 18, 1985, Patent Application No. 158858/1988 2, Title of the invention: Radiographic image information reading method 3, Person making the amendment. Relationship with the case. Patent applicant. Address: 210 Nakanuma, Minamiashigara City, Kanagawa Prefecture Name:
Fuji Photo Film Co., Ltd. 4, Agent 5-2-1-6 Roppongi, Minato-ku, Tokyo Number of inventions to be increased by the amendment None 7 Subject of the amendment ``Detailed description of the invention'' column 8 of the specification;
Contents of correction

Claims (1)

[Claims] irradiating a stimulable phosphor sheet on which radiation image information of a subject is stored and recorded with excitation light; and photoelectrically reading the stimulated luminescent light emitted from the sheet by the irradiation of the excitation light with a photodetector; In the radiation image information reading method for obtaining time-series image signals in pixel units carrying radiation image information, the stimulated luminescence afterglow characteristic of the stimulable phosphor sheet is calculated as the sum of two or more exponential functions. A radiation image information reading method characterized in that the image signal is approximated and the image signal is electrically corrected based on this approximation.