JPH04296843A - Radiation image information reading device - Google Patents

Abstract

PURPOSE:To prevent deterioration of sharpness in a read image caused by plural times of scanning in a radiation image information reading device wherein plural times scanning of stimulating light beams per picture element is conducted for a stimulable fluorescent sheet in which radiation image information is accumulatedly recorded, stimulable phosphorescent light beams emitted from this scanned part are photoelectrically read to obtain an image signal, and a plurality of image signals per picture element are added to each other to obtain an image signal relative to each picture element. CONSTITUTION:In main scanning which is conducted three times per picture element while a driving signal Sm is input to a driving control part 30 of a laser beam source 12 from a scanning control part 31, intensity of the laser beam is controlled so as to be relatively low in first and third main scanning and relatively high in second main scanning wherein a central portion of a picture element is scanned.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention irradiates excitation light onto a stimulable phosphor sheet on which radiographic image information is accumulated and recorded, thereby photoelectrically converting the stimulated luminescence light emitted from the stimulable phosphor sheet. The present invention relates to a radiation image information reading device that detects and reads the radiation image information.

0002

[Prior Art] Certain types of phosphors are exposed to radiation (X-rays, α-rays,
When irradiated with beta rays, gamma rays, electron beams, ultraviolet rays, etc., some of this radiation energy is accumulated in the phosphor, and when this phosphor is irradiated with excitation light such as visible light, the accumulated energy It is known that phosphors exhibit stimulated luminescence, and phosphors exhibiting this property are called stimulable phosphors (stimulable phosphors).

[0003] Using this stimulable phosphor, radiation image information of a subject such as a human body is temporarily recorded on a sheet having a layer of stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet),
This stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescent light, the resulting stimulated luminescent light is read photoelectrically to obtain an image signal, and based on this image signal, photosensitive The present applicant has already proposed a radiation image information recording and reproducing system that outputs a radiation image of a subject as a visible image to a recording material such as a recording material and a display device such as a CRT (Japanese Patent Laid-Open Nos. 55-12429 and 56). -11395 etc.).

In the above-mentioned radiation image information recording and reproducing system, generally, an excitation light beam deflected by an optical deflector is main-scanned over a stimulable phosphor sheet, and
The radiation image information is read using a reading device configured to perform sub-scanning by conveying the stimulable phosphor sheet in a direction substantially perpendicular to the main-scanning direction.

[0005] As the optical deflector, a rotating polygon mirror that rotates at high speed can be used. This rotating polygon mirror is superior in terms of scanning stability compared to other optical deflectors such as galvanometer mirrors, but for this purpose it is necessary to rotate it at high speed. On the other hand, in order to excite the above-mentioned stimulable phosphor, it is necessary to irradiate it with relatively high-energy excitation light. However, when the rotating polygon mirror is rotated at high speed as described above, the main scanning speed of the excitation light beam naturally increases, and the excitation energy received by the stimulable phosphor decreases. In this case, the level of stimulated luminescence light emitted from the stimulable phosphor sheet becomes low, and the S/N of the read image signal decreases.

[0006] In view of the above circumstances, the present applicant has developed a system for radiographic image information that can obtain a read image signal with a good S/N ratio even when an excitation light beam is scanned at high speed on a stimulable phosphor sheet. proposed a reading device (Japanese Patent Application Laid-Open No. 62-1612
Publication No. 65 and patent application No. 2-5421 filed by the applicant.
(see specification).

As described above, this radiation image information reading device scans an excitation light beam on a stimulable phosphor sheet, thereby photoelectrically detecting stimulated luminescence light emitted from the sheet. In the information reading device, one pixel is scanned multiple times with the excitation light beam, and a plurality of image signals for one pixel obtained through the multiple scans are added by an adding means to obtain one image signal. One read image signal is obtained for each pixel.

As described above, if one pixel is scanned several times with the excitation light beam (that is, if different parts of one pixel are scanned each time), the amount of stimulated luminescence light per pixel can be sufficiently increased. . Therefore, the read image signal obtained by adding a plurality of image signals for one pixel has a high S/N because it carries the total amount of stimulated luminescence light emitted from this one pixel.

[0009]

[Problems to be Solved by the Invention] However, according to subsequent research by the present inventors, although such radiation image information reading devices have the above-mentioned advantages, they also suffer from blurring of read images,
In other words, it was found that the sharpness tends to deteriorate.

Therefore, the present invention provides a method for reading radiographic image information that can obtain a read image signal with a good S/N even when an excitation light beam is scanned over a stimulable phosphor sheet at high speed, and that does not cause blurring of the read image. The purpose is to provide a device.

[0011]

[Means for Solving the Problems] The radiation image information reading device of the present invention is configured to scan one pixel multiple times with the excitation light beam while shifting the scanning position each time, and has the following features: In addition to providing means for obtaining one image signal for each pixel by adding and/or subtracting a plurality of image signals for each pixel obtained in the multiple scans, The present invention is characterized in that a control means is provided for changing at least one of the intensity and the reading sensitivity of stimulated luminescence light for each scan.

0012

[Operation and Effects of the Invention] If the intensity or reading sensitivity of the excitation light beam is controlled by the above control means, the image signal obtained by addition and/or subtraction processing can be improved by increasing the intensity or reading sensitivity of the excitation light beam. It is responsible for more of the accumulated recorded information of the scanned part. In other words, this image signal is closer to the image signal obtained when scanning one pixel only once.

[0013] Therefore, according to this image signal, it is possible to suppress the degree of deterioration in sharpness due to multiple scans and reproduce a radiation image with less blur. In addition, in this device, the advantages of multiple scans mentioned above remain, so the S/N
A good read image signal can be obtained.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below based on embodiments shown in the drawings. FIG. 1 shows a radiation image information reading device according to a first embodiment of the present invention. In the stimulable phosphor sheet 10, transmitted radiation image information of a subject such as a human body is accumulated and recorded by irradiating radiation such as X-rays through the subject. This stimulable phosphor sheet 10 is transported by a sheet conveying means 1 such as an endless belt.
1, the paper is transported in the direction of arrow Y for sub-scanning. A laser beam 13 as excitation light emitted from a laser light source 12 is deflected by a rotating polygon mirror 14 that rotates at high speed, focused by a focusing lens 18 usually consisting of an f/theta lens, and reflected by a mirror 19 to generate stimulable fluorescence. body sheet 1
0 is main scanned in the direction of arrow X, which is substantially perpendicular to the sub-scanning direction Y.

[0015] From the portion of the sheet 10 irradiated with the laser beam 13 in this way, stimulated luminescence light 15 is emitted in an amount corresponding to the radiation image information stored and recorded, and this stimulated luminescence light 15 is transmitted to the light guide 16. The light is focused by a photomultiplier (photomultiplier tube) 1 as a photodetector.
7 is photoelectrically detected. The light guide 16 is made by molding a light-guiding material such as an acrylic plate, and the linear entrance end surface 16a is connected to the stimulable phosphor sheet 1.
The light receiving surface of the photomultiplier 17 is coupled to an annular output end surface 16b extending along the beam scanning line on the photomultiplier 17. Above entrance end surface 1
The stimulated luminescent light 15 entering the light guide 16 from 6a is
Stimulated luminescent light 1 travels through the light guide 16 by repeating total reflection, exits from the output end face 16b, is received by the photomultiplier 17, and carries the radiation image information.
This photomultiplier 17 detects a light amount of 5.

The analog output signal (image signal) S of the photomultiplier 17 is amplified by a logarithmic amplifier 20 and digitized by an A/D converter 21 at a predetermined recording scale factor. The digital image signal Sd obtained in this way is input to the adding section 22, and the adding section 2
2, addition processing is performed. This addition process will be explained in detail below.

As shown in FIG. 2, the laser beam 13 is focused on the stimulable phosphor sheet 10 so that the beam diameter is sufficiently smaller than the size of the pixel P. By appropriately setting the main scanning speed and sub-scanning speed of the laser beam 13, the beam 13 can be applied to one pixel P.
is divided into three main scans (that is, one pixel P is scanned in each main scan).
(approximately 1/3 of the area is scanned). Therefore, the above-mentioned digital image signal Sd includes, for example, (a1, b1, c1...n1) and (a
2, b2, c2...n2) and (a3, b3,
c3...n3) (see FIG. 3). The adder 22 adds signals for common pixels among these signals to (a1
+a2 +a3 ), (b1 +b2 +b3 ), (
c1 +c2 +c3 )…(n1 +n2 +n3
). Note that the addition by the adder 22 is performed using an X-clock Cx, which is synchronized with the main scanning and sub-scanning of the laser beam 13, respectively.
The address creation unit 24 receiving the Y-clock Cy creates pixel addresses, and for each address, each signal that is inputted later is made to correspond to each signal stored in the line memory 25 under the above address, This is done by adding corresponding signals together.

This addition is performed by first adding signals (a2, b2, b2...n) by the next main scanning to the signals (a1, b1, c1...n1) stored in the line memory 25.
2) is added to obtain the addition signals (a1 + a2 ), (b1
+b2 ), (c1 +c2 )...(n1 +n2 )
These addition signals may be stored in the line memory 25 again, and the signals (a3, b3, c3...n3) from the next main scan may be added to these addition signals, or the main Signals for 3 scans (a1,
b1, c1...n1), (a2, b2, c2
...n2), (a3, b3, c3...n3) may be temporarily stored in the line memory 25, and then added at once after these three main scans are completed. Note that instead of the line memory 25, the stimulable phosphor sheet 1
A frame memory that can store image signals for the entire area of 0 may be used, but if each signal is added each time main scanning is performed as described above, the image signal for one or two lines can be stored. A line memory with a relatively small capacity can be used.

Addition signal (a1 +a2 +a3), (
b1 +b2 +b3 ), (c1 +c2 +c3
)...(n1 +n2 +n3) are read image signals Sp for the pixels Pa, Pb, Pc...Pn based on the above address, for example, on an optical disc,
It is stored in a large capacity memory 26 such as a magnetic disk. Similarly, the addition signals of the pixel rows following the pixel rows Pa, Pb, Pc...Pn are also stored one after another in the memory 26, and the read image signal Sp for the entire surface of the stimulable phosphor sheet 10 is stored in the memory 26. That will happen.

When reproducing the radiation image recorded on the stimulable phosphor sheet 10, the large-capacity memory 26
The read image signal Sp read from the image processing device 27
The radiation image is then input to an image reproducing device 28 such as a CRT display device or an optical scanning recording device, and the radiation image stored and recorded on the stimulable phosphor sheet 10 is reproduced in the image reproducing device 28 .

As described above, in this radiation image information reading device, the beam diameter of the laser beam 13 as excitation light is made sufficiently smaller than the size of the pixel P, so the energy density of this laser beam 13 is The height is sufficiently high, and since different parts of each pixel P are scanned multiple times with such a laser beam 13,
The amount of stimulated luminescence light per pixel is sufficiently high. Therefore, the read image signal Sp obtained by performing the above-described addition has a high level corresponding to the total amount of stimulated luminescence light from one pixel. By using such a high-level read image signal Sp, it is possible to reproduce a high-quality image with a good S/N ratio in the image reproduction device 28.

Further, as a characteristic part of the present invention, as shown in FIG. A drive control signal Sm that takes a unique value in each of the three main scans for pixels is input, and the output of the laser light source 12 is changed for each main scan based on the signal Sm. In this embodiment, as shown in FIG. 6, the intensity of the laser beam 13 in the three main scans is relatively low in the first and third main scans, and the intensity of the laser beam 13 is relatively low in the first and third main scans. The output of the laser light source 12 is controlled so that it is relatively high during the main scanning.

By doing this, the image signals (a2, b2, c2...n2) obtained in the second main scan
is the image signal (
a1 , b1 , c1 ... n1 ) and (a3 , b
3, c3...n3), it carries more accumulated recording information in the central portion of each pixel. Therefore, the read image signal Sp obtained by adding these signals is
This is closer to the image signal obtained when each pixel is main-scanned once. Therefore, this read image signal Sp
The radiation image reproduced by the image reproducing device 28 based on the above can be prevented from deteriorating in sharpness as described above, and can have less blur.

Note that the number of times the excitation light beam is scanned per pixel is not limited to three times as in the above embodiment, but may be two times, or four or more times, depending on the number of scans and the pixel size. The diameter of the excitation light beam may be appropriately set. Further, the shape of the excitation light beam (laser beam) 13 is not limited to that shown in FIG. 2, but may be flat in the main scanning direction, for example, as shown in FIG. Further, the diameter of this excitation light beam may be set to such a size that some of the same locations are overlapped and scanned in adjacent main scans, as shown in FIG. Furthermore, the diameter of this excitation light beam may be set larger than the pixel size, as shown in the specification of Japanese Patent Application No. 2-5421.

Furthermore, in the present invention, one image signal for each pixel may be obtained by subtracting a plurality of image signals for each pixel obtained through multiple scans, or by combining addition and subtraction.

In other words, if we explain based on the above-mentioned embodiment,
Signal (-a1 +a2 -a3), (-b1 +b2
-b3 ), (-c1 +c2 -c3 )...(-n
1 +n2 -n3) respectively, as pixels Pa and Pb
, Pc . . . Pn may be read image signals. Furthermore, when scanning one pixel P with the laser beam 13 five times as shown in FIG. 9 and setting the beam intensity at that time as shown in FIG.
a2 + a3 - a4 + a5 ), (b1 - b2
+b3 -b4+b5 ), (c1 -c2 +c3
−c4 +c5 )…(n1 −n2 +n3 −n4
+n5) respectively for pixels Pa, Pb, Pc
...Pn may be used as a read image signal.

Next, a second embodiment of the present invention will be described with reference to FIG. Note that in FIG. 7, elements equivalent to those in FIG. 1 are given the same numbers, and explanations thereof will be omitted unless particularly necessary (the same applies hereinafter).

In this embodiment, the high voltage control circuit 32 controls the high voltage Hv of the photomultiplier 17.
is adjustable. The high voltage control circuit 32 receives the aforementioned drive control signal Sm from the scan control section 31.
is input, and the high voltage Hv is changed for each main scan based on the signal Sm. In this example, 3 pixels related to one pixel are used.
In the second main scan, the high voltage Hv is controlled to be relatively low in the first and third main scans, and relatively high in the second main scan that scans the central portion of the pixel.

In this case, unlike the first embodiment, the reading sensitivity is changed for each main scan by adjusting the high voltage Hv.
Even in this case, the same effect as in the first embodiment can be obtained.

Note that the high voltage control circuit 32 that adjusts the high voltage Hv as described above operates, for example, to adjust the high voltage Hv.
An analog switch is interposed between the line supplying V and the line supplying relatively low high voltage Hv and the photomultiplier 17, and this analog switch is switched according to the value of the drive control signal Sm. It is possible to use one in which one of the two lines is selectively connected to the photomultiplier 17. Furthermore,
It is also possible to use a system in which a multiplication type DA is interposed in one line that supplies the high voltage Hv to the photomultiplier 17, and the multiplication coefficient is switched according to the value of the drive control signal Sm.

Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, the amplification factor of the logarithmic amplifier 20 is adjustable. The above-described drive control signal Sm is inputted to the logarithmic amplifier 20 from the scan control section 31, and the amplification factor is changed for each main scan based on the signal Sm. In this example, 3 pixels related to one pixel are used.
In the second main scan, the amplification factor is controlled so that it is relatively low in the first and third main scans, and relatively high in the second main scan that scans the central portion of the pixel.

In this case as well, unlike the first embodiment, the amplification factor is adjusted to change the reading sensitivity for each main scan, but even in this case, the same effect as in the first embodiment can be obtained. . Note that the logarithmic amplifier 20 whose amplification factor can be adjusted may be constructed from, for example, an analog switch or a multiplication type DA as described above.

As described above, the intensity of the excitation light beam 13 and the high voltage H of the photomultiplier 17 are changed for each main scan.
v, the amplification factor of the logarithmic amplifier 20 is changed 3
Although two embodiments have been described, two or even all three of these three conditions may be changed for each main scan.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a device according to a first embodiment of the present invention.

[Figure 2]
Schematic diagram showing the shape of the excitation light beam in the first embodiment device

FIG. 3 is an explanatory diagram illustrating signal addition in the first embodiment device.

FIG. 4 is a schematic diagram showing another example of the excitation light beam shape in the device of the present invention.

FIG. 5 is a schematic diagram showing still another example of the excitation light beam shape in the device of the present invention.

FIG. 6 is a graph showing the intensity of the excitation light beam for each main scan in the first embodiment device.

FIG. 7 is a schematic diagram showing a device according to a second embodiment of the present invention.

[Figure 8]
Schematic diagram showing a device according to a third embodiment of the present invention

FIG. 9 is a schematic diagram showing still another example of the excitation light beam shape in the device of the present invention.

FIG. 10 is a graph showing another example of the excitation light beam intensity for each main scan in the present invention.

[Explanation of symbols]

10 stimulable phosphor sheet 11 Sheet conveyance means 12 Laser light source 13 Laser beam 14 Rotating polygon mirror 17 Photo multiplier 18 Focusing lens 20 Logarithmic amplifier 22 Addition section 24 Address creation section 25 Line memory 30 Drive control section 31 Scanning control section 32 High voltage control circuit P Pixel

Claims (1)

[Claims] Claim 1: An excitation light beam is scanned over a stimulable phosphor sheet on which radiographic image information is stored and recorded, and stimulated luminescence light emitted from a portion of the sheet scanned by the excitation light beam is detected by a photodetector. A radiation image information reading device that photoelectrically reads an image signal and obtains an image signal is configured to scan one pixel multiple times with the excitation light beam while shifting the scanning position each time, and the plurality of scans means for adding and/or subtracting a plurality of image signals for each pixel obtained in the above to obtain one image signal for each pixel; 1. A radiation image information reading device comprising means for changing at least one of light reading sensitivities for each scan.