JPS61189763A - Reading method for radiation picture information - Google Patents

Abstract

PURPOSE:To compensate automatically the difference of sensitivity among plural photodetectors or the partial light guiding efficiency of a condenser by irradiating the reference light of even intensity to the condenser from an insident end face prior to reading the luminous emitted light to obtain a reference output signal from a photodetector and correcting the read signal. CONSTITUTION:A storage fluorescent sheet 30 underwent the full exposure is detected by photomultipliers P1-P4, and a high voltage power supply 62 which impresses the high voltage HV to these photomultipliers is controlled by a high voltage control circuit 63. This voltage HV is changed every (m) scans. The reference output signals DO delivered from photomultipliers P1-P4 are supplied to a correction value arithmetic circuit 64 after switching a switch 66. Then the difference between signals DO of the direction along an incident end face 58 is obtained every voltage HV and for each picture element. When the picture information is read, a correction circuit 61 obtains the voltage VH impressed based on the signal S1 supplied from a high voltage control circuit 63. Then the correction value of the voltage HV is read out of a memory 65, and read signals D of all picture elements are corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention is directed to irradiating excitation light to a stimulable phosphor sheet on which radiographic image information is accumulated and recorded, thereby excitation light emitted from the stimulable phosphor sheet. Regarding a radiation image information reading method in which stimulated emission light is photoelectrically detected to obtain an image signal indicating the radiation image information, in particular, compensation for partial characteristic differences in a stimulated waste light detection system is provided. The present invention relates to a radiation image information reading method that enables the following.

(Technical Background and Prior Art of the Invention) 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 emitted by 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.

(JP-A-55-12429, JP-A No. 56-11395,
No. 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 imaging conditions, the amount of stimulated luminescence light 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.

As mentioned above, a photomultiplier (Photomultiplier: Photomul) is widely used as one of the photodetectors that photoelectrically detects stimulated luminescence light emitted from a stimulable phosphor sheet. This photomultiplier tube is, for example,
As shown in Japanese Patent No. 11395 and Japanese Patent No. 56-11397, it is often used in connection with a light condenser so that light detection can be carried out efficiently. That is, one end of a light collector made of a light-guiding material is used as an incident end face for light, while the other end is used as an output end face, and a photomultiplier tube is connected to this output end face, so that the incident end face scans the light collector. By arranging them so as to extend along a line, the light emitted from each scanning point enters the light condensing body from the incident end face, is efficiently condensed, and guided to the photomultiplier tube.

Furthermore, for example, Japanese Patent Application Nos. 59-50024 and 59-5
As shown in the specification of No. 0025, in order to efficiently perform light detection even when the scanning line is relatively long, the incident end surface of the condenser is left as one, and the output end surface is divided into a plurality of sections. A photodetector device in which one photomultiplier tube is connected to each section has also been considered.

In a photodetection device consisting of a light condenser as described above and a plurality of photomultiplier tubes connected to the light condenser, it is naturally necessary to set the sensitivity of each photomultiplier tube to be equal to each other. Become. Therefore, before assembling the light condenser and photomultiplier tubes, adjustments are usually made to equalize the sensitivity of each photomultiplier tube. However, as is well known, the characteristics of photomultiplier tubes change over time, so the characteristics of each photomultiplier tube must be measured at any time even during the actual operation of the photodetector to maintain the sensitivity of these photomultiplier tubes at a constant level. Adjustments must be made to align them.

However, after the photomultiplier tubes have been connected to the light collector, each photomultiplier tube is removed from each section of the output end face of the light collector, the sensitivity is measured and adjusted, and the photomultiplier tubes are collected again. Connecting to the light body is extremely cumbersome.

Furthermore, depending on the shape of the light condenser described above, there may be parts with poor light guide efficiency (so-called shading), and when this phenomenon occurs, even if the light guide is Even if the characteristics of each photomultiplier tube are made the same, it becomes impossible to correctly detect stimulated luminescence light.

(Objective of the Invention) The present invention has been made in view of the above circumstances, and it is an object of the present invention to automatically compensate for differences in sensitivity of a plurality of photodetectors or differences in partial light guiding efficiency of a light condenser. The object of the present invention is to provide a radiation image information reading method that can correctly read stimulated luminescence light emitted from a stimulable phosphor sheet.

(Structure of the Invention) The radiation image information reading method of the present invention focuses the above-mentioned stimulated luminescent light using a light condenser having an incident end surface extending along a stimulable phosphor sheet, and A radiation image information reading method in which a reading signal indicating radiation image information is obtained by photoelectrically reading using a photodetector connected to an output end surface. A reference light of uniform intensity is made to enter the condenser from the incident end surface to obtain a reference output signal from the photodetector, and then when reading the stimulated luminescence light, the difference in the reference output signal between each pixel is calculated. The invention is characterized in that the read signal is corrected in accordance with the reference output signal for each pixel so as to solve the problem.

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

FIG. 1 shows a radiation image information recording/reading apparatus for reading radiation image information according to an embodiment method of the present invention. .4.5.6.7.8.9.
10, guide rollers 11.12.13.14, and guide plates 15.16.17.18.19.20.21, which rotate following the endless belt 1.6.7.10, respectively.
A circulation path 26 for conveying the sheet is composed of nip rollers 22, 23, 24, 25, and a plurality of (five sheets in this example) stimulable phosphor sheets 30 are arranged in the circulation path 26. These stimulable phosphor sheets 30 are arranged at appropriate intervals from each other, and are connected to the endless belts 1 to 10 as sheet circulation conveyance means and the nip roller 22.
．． 23, 24, and 25, it is configured to be circulated and conveyed in the direction of the arrow in the figure.

The endless belts 2.3 are configured to vertically hold the stimulable phosphor sheet 30 between them, and a photographing table is provided on the side of the endless belts 2.3 (left side in the figure). 41 is provided, and a radiation source 42 such as an X-ray source is provided at a position facing the endless belt 2.3 with the imaging table 41 in between. A recording section 40 is configured. During radiographic imaging of a patient (subject) 43, the sheet 30 used for imaging is held between the endless belts 2.3 as shown in the figure, with the patient 43 positioned in front of the imaging table 41. Radiation source 42 is activated. As a result, the transmitted radiation image of the subject 43 is projected onto the sheet 30, and the radiation image information of the subject 43 is stored and recorded on the sheet 30.

An image reading unit 50 is located at the lower right end position in the figure of the circulation passage 26.
is provided. In this image reading section 50, a laser light source 51 is installed above the endless belt 8 that constitutes a part of the reading section 50, and its output laser beam 52 is directed onto the sheet 30 on the endless belt 8 in the width direction thereof. A mirror 53 and a galvanometer mirror 54 are provided for scanning. Note that after the radiation image is recorded in the image recording section 40, this sheet 30 is transferred to the image reading section 5 by driving the sheet circulating conveyance means.
It is transported to 0. FIGS. 2 and 3 show the main parts of this image reading section 50 in detail. Hereinafter, reading of radiographic image information will be explained with reference to FIGS. 2.3 as well. Photomultiplier tubes P1, P2, P as photodetectors
3. Four P4s are provided as an example, and each one is a condenser 57.
It is connected to the. The light condenser 57 is molded from, for example, acrylic resin, and has an incident end surface 58 extending along the entire width of the stimulable phosphor sheet 30, while an output end surface opposite to the incident end surface 58 has the same shape. The output end faces 59a, 59b,
59c, 59d are the photomultiplier tubes P1, P2,
P3 and P4 are each connected. Also, the light condenser 51
A prism 55 is attached to the upper surface of the edge along the entrance end surface 58 of the prism 55 via a dichroic surface 56 .

A stimulable phosphor sheet 3 on which radiation image information is stored and recorded
0 is main-scanned in the direction of the arrow X in FIG. The sub-scanning is performed by moving in the direction of arrow Y (six directions of arrows in FIG. 1), which is substantially perpendicular to the direction of arrow Y. As a result, this stimulable phosphor sheet 30 is activated by the laser beam 5 as excitation light.
As shown in FIG. 3, the sheet 30 is scanned two-dimensionally by the sheet 30, and as shown in FIG.

This stimulated luminescence light enters the light condenser 57 from the incident end face 58, and a part of it is reflected inside the light condenser 57 at the dichroic surface 56), causing total internal reflection inside the light condenser 51. Proceeding repeatedly, each of the emission end surfaces 59a to 59
d and is received by photomultiplier tubes P1, P2, P3, and P4. As shown in Figure 4, each photomultiplier tube P
The outputs of 1, P2, P3, and P4 are output from amplifiers A1 to A, respectively.
4, added by an adder 60, and output. The read signal output by the adder 60 carries the amount of stimulated luminescence for the entire surface of the stimulable phosphor sheet 30, so if this read signal is used, for example, a CRT, a scanning recording device, etc. , the radiation image stored and recorded on the stimulable phosphor sheet 30 can be reproduced.

The sheet 30 whose image has been read is conveyed along the guide plate 18 by the endless belt 9.10, and sent to the erasing section 70 through the nip roller 22, the guide plate 19, and the nip roller 23. The erasing unit 70 consists of a box 71 and a large number of erasing light sources 72 such as fluorescent tungsten lamps, sodium lamps, xenon lamps, and iodine lamps arranged inside the box 71. After the shutter 73 is opened, the nip roller 2
3 into the box 71. Sheet 30 is box 7
1, the shutter 73 is closed. The erasing light source 72 inside the box 71 mainly emits light in the excitation wavelength range of the stimulable phosphor of the sheet 30, and the radiation energy remaining in the sheet 30 after reading the image is transferred to the sheet 30. When such light is irradiated, it is emitted from the sheet 30. Note that since the shutter 13 is closed at this time, the erasing light does not leak and enter the image reading section 50 and generate noise in the read signal.

The sheet 30 in which the image (afterimage) has been erased to such an extent that radiation image information can be recorded again is transferred to the nip roller 2.
4 is rotated and discharged to the outside of the erasing section 70. The discharged sheet 30 is sent to the nip roller 25 through the guide plate 20, and then the nip roller 25 transfers the sheet 30 to the guide plate 2.
1 to the endless belt 1, and thereafter sent to the image recording section 40 in the same manner as described above and used for radiography.

Here, if the sensitivities of the photomultiplier tubes P1, P2, P3, and P4 are not uniform, the width direction of the stimulable phosphor sheet 30 ( A density difference occurs over the main scanning direction (X). That is, for example, if the relationship between the high voltage HV applied to each photomultiplier tube P1 to P4 and their sensitivity S is as shown in FIG. Even if stimulated luminescence light of various intensities is detected, the output signals d of the photomultiplier tubes P1 to P4 will differ as shown in FIG. 6.7. The difference in these output signals d is determined by the high voltage HV applied to the photomultiplier tubes P1 to P4, as shown in Fig. 6.7 above.
It changes depending on. Therefore, in this apparatus, the read signal is corrected by a correction circuit 61 shown in FIG. 4 to compensate for the sensitivity difference. This correction will be explained in detail below.

Before recording and reading radiation image information as described above, the stimulable phosphor sheet 30 is exposed to radiation 1 from an X-ray source, etc.
1i42 is used to irradiate radiation with uniform intensity. In this way, the stimulable phosphor sheet 3 has been subjected to so-called solid exposure.
0 is subjected to image reading in the image reading section 50 in the same manner as described above. The sheet 30 scanned by the laser beam 52 emits stimulated luminescence light with -lateral intensity,
This stimulated luminescence light is detected by photomultiplier tubes P1 to P4.

Further, a high voltage power supply 62 that applies a high voltage HV to the photomultiplier tubes P1 to P4 is controlled by a high voltage control circuit 63, and the high voltage HV is changed every m main scans. In this case, the variation range of the high voltage HV is set to cover the entire range of high voltage HV used in actual reading of radiographic image information. In this way, photomultiplier tubes P1 to P4 whose high voltage HV is changed as sub-scanning progresses.
Reference output signal output from is input to the correction value calculation circuit 64 by switching the switch 66. At the same time, this correction value calculation circuit 64 receives a signal S1 indicating the high voltage HV from the high voltage control circuit 63, and
For each reference output signal D in the direction along the incident end face 58
Find the difference between 0 pixel by pixel. That is, as shown in FIG. 8, along the main scanning direction X, Xl, Xz, Xl...
・If the pixels of the j column of Xj are lined up, then the m of the nth column
The average value of the reference output signals Do for the pixels is set as the representative signal value Rn of the nth column. And correction value calculation circuit 6
4 is the average value R8 of all representative signal values Rz, R2...Rj of columns 1 to j in each high voltage HV,
Find the difference Un - Rn Ro with each representative signal value Rn,
These values UI N Uz for each high voltage HV,...
. . . Uj is stored in the memory 65 as a correction value.

As described above, when reading the radiation image information of the subject 43 stored and recorded on the stimulable phosphor sheet 30, the read signal is outputted through the correction circuit 61.

Based on the signal S1 inputted from the high voltage control circuit 63, this correction circuit 61 selects the photomultiplier tubes P1 to P1 at that time.
Find the high voltage HV applied to 4, and calculate the correction value Lll, U2...at this high voltage 1-fV.
Uj is read out from the memory 65, and correction is performed on the read signals of all pixels by subtracting the correction value jln from the read signals of the pixels in the n-th column. If such a correction is made, the difference in sensitivity of each photomultiplier tube P1 to P4 will be compensated, and the stimulated luminescence light can be read correctly.
By using the corrected read signal @D', the radiation image of the subject 43 can be correctly reproduced.

Note that when reading radiation image information, photomultiplier tubes P1 to P
When the high voltage HV applied to 4 is changed steplessly or in very small steps, correction values U1 and L12 for several high voltages close to the set high voltage HV are set.
・・・・・・Read several ways of Uj from the memory 65,
The correction circuit 61 may interpolate these correction values to obtain a correction value corresponding to the set high voltage HV.

In this way, the number of correction values stored in the memory 65 can be reduced. In addition, in order to reduce the number of correction values stored in the memory 65, correction values for discrete pixel columns (for example, odd-numbered pixel columns, etc.) among the j-column pixel columns from 1 to j are stored. Alternatively, the correction values for the pixel columns between them may be calculated by interpolating the correction values read from the memory 65 in the correction circuit 61 in the same manner as described above. .

The mechanism for compensating for the sensitivity difference between the plurality of photomultiplier tubes P1 to P4 has been described above, but in the method of the present invention, the correction value is determined based on the stimulated luminescence light that has passed through the light condenser 57. Therefore, even if the above-mentioned shading occurs in the condenser 57, for example, this shading is compensated for along with the sensitivity difference between the photomultiplier tubes P1 to P4, and the stimulated luminescence is correct. can be detected.

Furthermore, in the embodiment described above, the reference light that is incident on the condenser 57 to determine the correction value is the stimulated luminescence light emitted from the stimulable phosphor sheet 30 that has been solidly exposed to radiation such as X-rays. However, the reference light for determining the correction value is not limited to this. For example, a stimulable phosphor sheet formed to the same size as the stimulable phosphor sheet 30 and capable of storing visible light energy is uniformly irradiated with visible light from the erasing light source 72, and then the image reading unit 50
It is also possible to irradiate this stimulable phosphor sheet with a laser beam 52 and then utilize the stimulated luminescent light emitted from the stimulable phosphor sheet. In this case, the erase light source 72 built into the device can be used to find the correction value, which is convenient.

(Effects of the Invention) As explained in detail above, according to the radiation image information reading method of the present invention, partial characteristic differences in a photodetection system, such as characteristic differences between multiple photodetectors and shading of a condenser, are automatically detected. It becomes possible to correctly read the stimulated luminescence light by compensating for the above, and it becomes possible to accurately reproduce the radiation image information stored and recorded on the stimulable phosphor sheet. Furthermore, according to the method of the present invention, it is possible to obtain the correction value at any time even during the actual operation of the stimulated luminescence light detection system, so that the sensitivity difference can be adjusted appropriately in response to changes in the stimulated luminescence detection system over time. can be compensated for.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a radiation image information recording/reading device that performs image reading according to an embodiment method of the present invention, and FIGS. 2 and 3 each show a main part of the image reading section of the recording/reading device. A perspective view and a side view, FIG. 4 is a circuit diagram showing the electric circuit of the image reading section, FIG. 5 is a graph showing the relationship between high voltage and sensitivity of the photomultiplier tube according to the present invention, FIG. FIG. 7 is a graph showing a change in a read signal due to a sensitivity difference between photomultiplier tubes according to the present invention, and FIG. 8 is an explanatory diagram for explaining read signal correction according to the method of the present invention. 30... Accumulative phosphor sheet 50... Image reading section 52... Laser beam 54... Galvanometer mirror 57... Condenser 58... Incident end surface 59a, 59b of condenser, 59c, 59d-
・・Emission end face 61 of the condenser ・・Correction circuit 6
4...Correction value calculation circuit 65...Memory

Claims (3)

[Claims] (1) By irradiating a stimulable phosphor sheet on which radiographic image information is accumulated and recorded with excitation light, the radiographic image information accumulated and recorded on the sheet is converted into stimulated luminescent light, and the The emitted light is collected by a light collector having an entrance end face extending along the stimulable phosphor sheet, and photoelectrically read using a photodetector connected to the output end face of the light collector, In the radiation image information reading method for obtaining a read signal indicative of the radiation image information, prior to reading the stimulated luminescence light, a reference light having a uniform intensity is incident on the condenser from the incident end face, and the light is detected. A reference output signal is obtained from the device, and then, when reading the stimulated luminescence light, the reading is performed according to the reference output signal for each pixel so as to eliminate the difference in the reference output signal between each pixel. A radiation image information reading method characterized by correcting a signal. (2) As the light collector, use one having one incident end face and a plurality of divisions of the output end face, and as the photodetector, use a plurality of photomultiplier tubes connected to each division of the output end face. A radiation image information reading method according to claim 1, wherein the radiation image information reading method is used. (3) The stimulable phosphor sheet is irradiated with radiation of uniform intensity to accumulate its energy, and then the sheet is irradiated with the excitation light, thereby emitting a luminescence of uniform intensity from the sheet. The radiation image information reading method according to claim 1 or 2, characterized in that exhaustion light is used as the reference light.