JPH03220548A - Radiation dose display method and radiation image photographing and reading device - Google Patents

Abstract

PURPOSE:To display accurate irradiation dose regardless of the elapsed time from photography time to read time by measuring the time from the photography time to the read time, correcting variation in the calculated value of the dose of radiation according to the time, and displaying the corrected dose. CONSTITUTION:An X-ray photographing and reading device irradiates a subject 13 with X rays 12 from an X-ray source 11 at its photography part 10 and transmitted X rays 12a irradiate an accumulable type phosphor sheet 14, so a transmitted-X-ray image of the subject 13 is accumulated and recorded on the sheet 14 and the time t1 of the photography is inputted to a computer system 40. In this case, fading characteristics of the sheet 14 vary with the kind of the phosphor, the structure of the sheet, etc., but once they are determined, attenuation characteristics of accumulated energy to the elapsed time from the photography time are nearly fixed. For the purpose, the elapsed time from the photography time to the read time is measured and the dose which is corrected corresponding to the time is found and displayed. Consequently, the exposure dose of the subject is accurately displayed.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention stores and records radiation images on a stimulable phosphor sheet, irradiates the stimulable phosphor sheet with excitation light, and collects the photosensitivity emitted by the stimulable phosphor sheet. A radiation dose display method for reading emitted light to obtain an image signal, and calculating and displaying lff1 of radiation irradiated to the stimulable phosphor sheet from this image signal, and a radiation image capturing and reading device for implementing this method. It is something.

(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 part of this radiation energy is accumulated in the phosphor, and this It is known that when a phosphor is irradiated with excitation light such as visible light, the phosphor exhibits stimulated luminescence depending on the accumulated energy. stimulable phosphor).

Using this stimulable phosphor, radiation image information of the human body, etc. is temporarily recorded on a stimulable phosphor sheet, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescence light. The resulting stimulated luminescent light is read photoelectrically to obtain an image signal, and based on this image signal, a radiation image is output as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT. An image recording and reproducing system has already been proposed by the applicant (Japanese Patent Laid-Open No. 12429/1983).

5B-11395, 55-163472, 5
B-104645.

No. 55-116340, etc.).

This system has the practical advantage of being able to record images over a much wider range of radiation exposures than conventional radiographic systems using silver halide photography. In other words, 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 imaging 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 electric signal and using this electric 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, a radiation image that is not affected by fluctuations in radiation exposure amount can be obtained. be able to.

(Problem to be Solved by the Invention) In a system using the above-mentioned stimulable phosphor sheet, in order to know the exposure dose of the subject, the image signal obtained by reading the stimulated luminescence light is used to determine the amount of radiation irradiated at the time of photography. The radiation dose was determined and displayed on a photosensitive material using a laser printer or on a CRT display.

However, the stimulable phosphor sheet has a so-called phase phenomenon in which even if the stimulable phosphor sheet is irradiated with radiation and the energy of the radiation is accumulated in the stimulable phosphor sheet, the amount of energy attenuates over time. Therefore, the dose calculated based on the image signal varies depending on the time between taking the image and reading the stimulated luminescence light to obtain the image signal, and therefore the dose to which the subject is exposed differs. There is a problem that it is not displayed accurately.

In view of the above circumstances, the present invention provides a radiation dose display method that can accurately display the dose of irradiated radiation regardless of the elapsed time from the time of imaging to the time of reading, and a radiation image capturing and reading device that implements this method. The purpose is to provide the following.

(Means for Solving the Problems) The radiation dose display method of the present invention includes irradiating a subject with radiation and irradiating the stimulable phosphor sheet with the radiation that has passed through the subject. Accumulating and recording a radiation image of a subject, irradiating excitation light to a stimulable phosphor sheet on which the radiation image has been accumulated, and reading stimulated luminescence light representing the radiation image emitted from the stimulable phosphor sheet. A radiation dose display method for obtaining an image signal and displaying the dose of radiation irradiated to the stimulable phosphor sheet calculated based on the image signal, comprising: accumulating and recording a radiation image of a subject on the stimulable phosphor sheet; 2. Measure the time from the time of photographing to the time of reading the stimulated luminescence light to obtain an image signal; It is characterized by correcting the variation in the D output value of the dose; displaying the dose corrected by -1.

Furthermore, the radiographic image capturing and reading apparatus of the present invention irradiates a subject with radiation and irradiates the stimulable phosphor sheet with the radiation that has passed through the subject! : an imaging unit that stores a radiation image of the subject on the stimulable phosphor sheet;
a reading unit that obtains an image signal by irradiating the stimulable phosphor sheet on which the radiation image is stored and recorded with excitation light and reading the stimulated luminescent light representing the radiation image emitted from the stimulable phosphor sheet; a time measuring means for measuring the time from the time of photographing to accumulate and record the radiation image of the subject on the phosphor sheet to the time of reading to obtain the image signal by reading the stimulated luminescent light; Dose calculation means that calculates the dose of radiation irradiated to the stimulable phosphor sheet and corrects fluctuations in the dose calculation chain due to fading of the stimulable phosphor sheet based on the measured time; The present invention is characterized by comprising a display means for displaying the obtained line machine.

The above dose displayed here is, for example, x
It is not limited to those that directly display the radiation dose, such as displaying millimeters per antogen. The numerical value 17< may also be used to indirectly display the radiation dose by displaying a symbol or the like.

(Function) The blackout characteristics of a stimulable phosphor sheet vary depending on the type of stimulable phosphor carrying the stimulable phosphor sheet, the structure of the sheet, etc., but once these are determined, The attenuation characteristic of the accumulated energy with respect to the elapsed time from the time of photographing is approximately determined.

Therefore, in the present invention, the total elapsed time from the time of imaging to the time of reading is 7II11[2], and the dose corrected according to this time is calculated and displayed, so that the exposure dose of the subject is displayed accurately.

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

FIG. 1 shows the radiation display method of the present invention adopted in 1. 1 is a schematic configuration diagram of an X-ray image capturing and reading device.

In this X-ray photography/reading device, X-rays 12 are irradiated from an X-ray source 11 toward a subject 13 in the imaging section to, and the X-rays 12a transmitted through the subject 13 are transmitted to a stimulable phosphor sheet 1.
4, the transmitted X-ray image of the subject 13 becomes visible! -14, and the time tλ at which this photographing was performed is manually entered into the computer system 40.

This combination coater system 40 has a main body 41. The auxiliary memory is a drive section 42 into which two floppy disks are inserted and driven. It is comprised of a keyboard 43 for an operator to input necessary instructions to the combinator system 40, and a CRT display 44 for displaying necessary information.

After the above imaging is performed, the stimulable phosphor sheet 14 on which the X-ray image has been recorded is set at a predetermined position in the reading section 20. This reading section 20 performs pre-reading and main reading.

Here, pre-reading means that the stimulable phosphor sheet is read using an excitation light beam of low novelty in advance to obtain an image signal by reading it under optimal reading conditions according to the dose of radiation that has been irradiated on the anti-resistance phosphor sheet. Scanning the sheet (7 lever) This refers to reading the outline of the radiation image recorded on the sheet, and main reading is the analysis of the pre-read image signal obtained by this pre-reading.
After that, the sheet is irradiated with a high-level excitation light beam 24 and scanned, and the radiation image is read under optimal reading conditions to obtain an image signal. Here, reading conditions affect the relationship between the amount of stimulated luminescence light and the output of the reading device during reading! It is a general term for various conditions that can be achieved.
For example, the reading gain, which determines the relationship between human output, the
- High level/low level of the above-mentioned sheet; Novel refers to the high/low energy of the excitation light beam irradiated per unit area of the sheet, or the energy of the stimulated luminescence light emitted from the sheet is the same as the excitation light beam. If it depends on the wavelength of the beam (has a wavelength sensitivity distribution), it refers to the size of the weighted energy after weighting the energy of the excitation light beam irradiated per unit area of the sheet by the wavelength sensitivity. , as a method to change the level of the excitation light beam,
Methods of using excitation light beams of different wavelengths, methods of changing the intensity of the excitation light beam emitted from a laser light source, etc., inserting an ND filter etc. on the optical path of the excitation light beam,
A method of varying the intensity of an excitation light beam by removing,
Various known methods can be used, such as changing the beam diameter of the excitation light beam to change the scanning density, or changing the scanning speed.

A stimulable phosphor sheet 1 set at a predetermined position in the reading section
4 is conveyed (sub-scanning) in the direction of arrow Y by a sheet conveying means 22 such as an entos belt driven by a motor 21. On the other hand, a weak excitation light beam 24 emitted from the laser beam aB23 is reflected and deflected by a rotating polygon mirror 26 that is driven by a motor 25 and rotates at high speed in the direction of the arrow, passes through a focusing lens 27 such as an fθ lens, and then is reflected by a mirror 28. After changing the optical path, the light enters the sheet 14 and performs main scanning in a direction (direction of arrow X) substantially perpendicular to the direction of sub-scanning (direction of arrow Y).

Stimulated luminescence light 29 is emitted from the location where the excitation light beam 24 of 14 is irradiated, and the amount of stimulated luminescence light 29 corresponds to the accumulated and recorded X-ray image information. The photomultiplier (photomultiplier tube) 31 detects photoelectrically. The light guide 30 is made by molding a light-guiding material such as an acrylic plate, and is arranged so that the linear entrance end surface 30a extends along the main scanning line on the stimulable phosphor sheet 14. The light receiving surface of the photomultiplier 31 is coupled to the annularly formed exit end surface 30b. Incidence end surface 30a
The stimulated luminescent light 29 that enters the light guide 30 travels through the light guide 30 through repeated total reflection, exits from the exit end face 30b, is received by the photomultiplier 31, and is emitted as a luminescent light representing an X-ray image. The exhausted light 29 is converted into an electrical signal by a photomultiplier 31.

The analog output signal SOp output from the photomultiplier 31 is logarithmically amplified by the logarithmic amplifier 32 and
The signal is digitized by a D converter 33, and a pre-read image signal Sp is obtained.

The obtained pre-read image signal Sp is sent to the computer system 4
0 is man-powered. The reading unit 20 also manually inputs the reading time t2. Strictly speaking, there is a time lag between the reading start time and the reading end time, but in this case, the stimulable phosphor sheet i4 has a time difference that is so sudden that the difference between the reading start time and the reading end time becomes a problem. It is assumed that there is no shading characteristic, and the average time between the reading start time and the reading end time is adopted as the reading time t2.

The stimulable phosphor sheet 14 on which the pre-reading has been completed is once returned in the direction opposite to the sub-scanning direction (arrow Y direction) for the next main reading.

On the other hand, the computer system 40 calculates an imaging sensitivity S representing information equivalent to the dose of X-rays irradiated to the stimulable phosphor sheet 14 during imaging based on the input pre-read image signal Sp.
e is required. Here, the imaging sensitivity is an index of the appropriate amount of X-ray exposure, similar to the ISO sensitivity of general color negative films, and the smaller this value is, the more the X-rays irradiated on the stimulable phosphor sheet 14 are This indicates that the dose is large.

However, the imaging sensitivity Se determined here is determined based on the pre-read image signal Sp, and the value of this pre-read image signal Sp is determined by the time difference t-t2- between the time of photographing t1 and the time of reading t2. It changes depending on t1. Therefore, in the computer system 40, the photographing sensitivity Se determined based on the pre-read image signal Sp is always displayed so that the photographing sensitivity Se determined as the standard when read 10 minutes after the photographing time t1 is displayed.
A correction value Am is added to .

FIG. 2 shows the photographing sensitivity Se, l! determined based on the pre-read image signal Sp with respect to the elapsed time t from the time of photographing t1 to the time of reading t2 when photographing is performed under the same conditions.
: is a diagram showing the standard and the correction value A+a for determining the photographic sensitivity Se determined in 17.

Since a part of the energy stored in the stimulable phosphor sheet 14 is released as time passes, the value of the photographic sensitivity Se determined based on the pre-read image signal Sp increases with the elapsed time t (i.e. (The X-ray dose during imaging is considered to be small.)

Therefore, in the computer system 40, a correction value AI1 as shown in FIG. A standard photographic sensitivity Se is required regardless of t. This final photographic sensitivity correction is displayed on the CRT display 44 of the combination coater system 40.

Further, in the computer system 40, the pre-read image signal Sp
Based on this, the optimum reading conditions for main reading, that is, the voltage value of the high voltage to be applied to the photomultiplier 31, etc., are determined, and the reading unit 20 then uses a strong excitation light beam 24 to perform the same as in the case of pre-reading. An analog image signal SO0 carrying the X-ray image stored and recorded on the stimulable phosphor sheet 14 is output from the photomultiplier 31, and this analog image signal SOQ is logarithmically multiplied by the logarithmic amplifier 32. The A/D converter 33 obtains a digitized main reading image signal SQ. This main reading image signal S0 is subjected to appropriate image processing in the computer system 40, and then transferred to an image display device (not shown). The instantaneous image display device reproduces and displays a visible image that is highly suitable for observation (diagnosis) based on the image signal that has been transferred and subjected to image processing.

Although the above embodiment is an example of an apparatus that performs pre-reading, the present invention is not limited to an apparatus that performs pre-reading. For example, the present invention is not limited to an apparatus that performs pre-reading. Based on this, numerical values or symbols representing the radiation dose, such as imaging sensitivity, may be determined.

Further, in the embodiment described above, the imaging sensitivity (dose) is displayed on the CRT display 44, but for example, when a hard copy of an image is recorded, it may be displayed on the hard copy together with the image.

(Effects of the Invention) As explained in detail above, the present invention measures the time from the time of imaging to the time of reading, and based on this measured time, the amount of radiation caused by fading of the stimulable phosphor sheet is measured. Since fluctuations in the calculated value of the dose are corrected and the corrected dose is displayed, the accurate irradiation dose is displayed regardless of the elapsed time from the time of imaging to the time of reading.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of an X-ray image capturing and reading device that employs the radiation dose display method of the present invention, and Figure 2 shows the diagram from the time of imaging to the time of reading when imaging is performed under the same conditions. FIG. 7 is a diagram showing the photographing sensitivity determined based on the pre-read image signal and the correction value for determining the photographing sensitivity determined as a standard with respect to elapsed time. lO... Photographing section 11... X-ray source 14
...Stormable phosphor sheet 20...Reading section 24...
・Excitation light beam 26...Rotating polygon mirror 29...
- Stimulated luminescence light 31...Photo multiplier 40...Computer system 44...CRT display

Claims (2)

[Claims] (1) A radiation image of the subject is accumulated and recorded on the stimulable phosphor sheet by irradiating the subject with radiation and the radiation transmitted through the subject is irradiated onto the stimulable phosphor sheet, and the radiation image is accumulated and recorded. irradiate the stimulable phosphor sheet with excitation light and read the stimulated luminescent light representing the radiation image emitted from the stimulable phosphor sheet to obtain an image signal, and calculate based on the image signal. In the radiation dose display method for displaying the dose of radiation irradiated on the stimulable phosphor sheet, the stimulable luminescence light is read and an image signal is generated from the time of imaging when the radiation image of the subject is stored and recorded on the stimulable phosphor sheet. measuring the time until the reading is obtained, correcting fluctuations in the calculated value of the dose due to fading of the stimulable phosphor sheet based on the measured time, and displaying the corrected dose. A radiation dose display method characterized by: (2) an imaging unit that irradiates a subject with radiation and irradiates the stimulable phosphor sheet with the radiation that has passed through the subject, thereby accumulating and recording a radiation image of the subject on the stimulable phosphor sheet; and the radiographic image a reading unit for obtaining an image signal by irradiating excitation light onto a stimulable phosphor sheet on which the stimulable phosphor sheet has been stored and recorded and reading stimulated luminescence light representing the radiation image emitted from the stimulable phosphor sheet; a time measuring means for measuring the time from the time of photographing to accumulate and record the radiation image of the subject on a sheet to the time of reading to obtain an image signal by reading the stimulated luminescent light; a dose calculation means for calculating the dose of radiation irradiated to the body sheet and correcting a variation in the calculated value of the dose due to fading of the stimulable phosphor sheet based on the measured time; A radiation image capturing and reading device comprising: display means for displaying the dose.