JPH0876301A - Radiation image reading method and device - Google Patents

Abstract

PURPOSE: To improve the resolution of the visible images obtd. without shortening the sampling period of a radiation image reader. CONSTITUTION: The timing signal Tf of a sampling period 1.2μsec to an A/D converter 37 which digitally converts the image signal S'f read from the front surface side of a stimulable phosphor sheet 1 and the timing signal Tb of a sampling period 1.27μsec to an A/D converter 38 which digitally converts the image signal S'b read from the rear surface side are outputted from a controller 42 by shifting these signals by 1/2 (i.e., 0.6μsec) of the period 1.2μsec. The image signals S'Df , S'Db obtd. from the respective surface sides are inputted to the controlled multiplexer 40 of the controller 42 and are time-serially obtd. as the image signal SD of one series.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image reading method and apparatus, and more particularly to a double-sided reading method and apparatus for reading image signals from both sides of a stimulable phosphor sheet.

[0002]

2. Description of the Related Art A part of this radiation energy is accumulated by irradiating with radiation, and then stimulated emission is emitted in accordance with the radiation energy accumulated by irradiation of excitation light such as visible light or laser light. Radiation image information of a subject such as a human body is temporarily stored and recorded on a sheet-shaped stimulable phosphor sheet in which a stimulable phosphor is laminated on a support using a stimulable phosphor (stimulable phosphor). An object is scanned with excitation light to generate stimulated emission light, and the obtained stimulated emission light is photoelectrically read at a predetermined sampling period to obtain an image signal. Meanwhile, accumulative fluorescence after reading the image signal Radiation image reading methods and devices for irradiating a body sheet with erasing light to release the radiation energy remaining on the sheet are already well known.

The image signal obtained by this method or the like is subsequently subjected to image processing such as gradation processing and frequency processing suitable for observation and interpretation, and the image signal after this processing is a visible image for diagnosis. Is recorded on a film or displayed on a CRT for diagnostic purposes. On the other hand, the stimulable phosphor sheet is irradiated with the erasing light so that the radiation energy remaining on the sheet is released and can be used repeatedly.

Further, the support of the stimulable phosphor sheet is formed of a transparent material through which stimulated emission light emitted from the stimulable phosphor layer is transmitted, and the stimulable luminescent light is emitted from both sides of the stimulable phosphor sheet. S / N is improved by reading light almost at the same time to improve the light collection efficiency of stimulated emission light, and by adding the image signals read from each surface on the front and back with a predetermined addition ratio for each corresponding pixel. There are known techniques for obtaining a visible image having a three-dimensional effect (Japanese Patent Laid-Open No. 55-87970, Japanese Patent No. 4280060, Japanese Patent Laid-Open No. 6-118525).

[0005]

By the way, it is desired that the diagnostic visible image finally recorded on the film or displayed on the CRT is reproduced with higher resolution in order to observe the fine structure. There is. In order to meet this demand, it is conceivable to shorten the sampling cycle for reading the stimulated emission light and increase the pixel density. However, if the sampling frequency is set high enough to control the entire sampling period by the response time of stimulated emission and the signal processing time for the obtained signal, even if the sampling period is simply shortened, It is difficult to shorten the sampling cycle unless the above is shortened. Further, if a device having a high signal processing speed is used, the cost will increase.

The present invention has been made in view of the above circumstances, and provides a radiation image reading method and apparatus capable of substantially improving the resolution of the obtained visible image without shortening the sampling cycle. It is intended to be provided.

[0007]

A radiation image reading method according to the present invention scans at least one surface of a stimulable phosphor sheet on which radiation image information is stored and recorded with excitation light, and accumulates by scanning this excitation light. The stimulated emission light emitted from both sides of the luminescent phosphor sheet is read at equal sampling periods to obtain two image signals so that the sampling timing does not match between one surface side and the other surface side, and one surface is read. The image signal read from the side is interpolated by the image signal read from the other surface side.

Here, the reason that the sampling timing on one surface side and the sampling timing on the other surface side do not coincide is that the read signals by both samplings interpolate with each other, and therefore preferably both samplings are performed. The timing is preferably shifted by 1/2 of the sampling period. in this case,
The sampling cycle of the interpolated image signal is a fixed cycle as a whole.

The image signal levels obtained from the one surface side and the other surface side do not necessarily have to match, but if they do not match, they are obtained from both surface sides with one signal level as a reference. The value of the ratio that makes the two signal levels coincident with each other is obtained for each signal level in advance, and the image signal obtained from the other surface side is multiplied by the value of this ratio, and then the interpolation process is performed. desirable. Also,
If the sampling periods are not the same on both sides, moire occurs in the reproduced image, making it difficult to observe.

A radiation image reading apparatus of the present invention comprises an excitation light source for emitting excitation light, and a scanning optical system for scanning the excitation light on at least one surface of a stimulable phosphor sheet on which radiation image information is stored and recorded. Two image reading systems that read stimulated emission light emitted from both sides of the stimulable phosphor sheet by scanning excitation light at equal sampling periods so that sampling timings do not match on one surface side and the other surface side And a signal that performs signal processing so as to interpolate the image signal read from one surface side of the two image signals read separately by the two image reading systems with the image signal read from the other surface side. It is characterized by comprising processing means.

Here, it is preferable that the sampling timing on the one surface side and the sampling timing on the other surface side of the image reading system are set to be shifted by 1/2 of the sampling cycle as described above. In this case, The sampling cycle of the interpolated image signal is a constant cycle as a whole.

In the radiation image reading method and apparatus of the present invention, when the excitation light for scanning the stimulable phosphor sheet is separately scanned from both sides of the sheet, the scanning positions of the excitation light are synchronized on both sides. It is necessary to respond after doing it.

Further, since the radiation image reading method and apparatus of the present invention reads optical information from both sides of the stimulable phosphor sheet, the stimulable phosphor sheet used in this method and apparatus is stimulated to emit light to both sides. Is assumed to be emitted, and the support layer supporting the stimulable phosphor layer is formed of a transparent material so as to transmit the stimulated emission light.

[0014]

According to the radiation image reading method and apparatus of the present invention, stimulated emission light emitted from both sides of the stimulable phosphor sheet by scanning with excitation light is emitted from one surface side and the other surface side. By reading at the same sampling period so that the sampling timing does not match with,
The obtained image signals of the two systems can be signals interpolating the other in time series and spatially. That is, the image signals of these two systems are time-sequentially arranged in the order of the front surface signal, the back surface signal, the front surface signal, the back surface signal, and so on, and are sampled at a higher frequency than the image signal obtained from only one surface as a whole. The obtained image is obtained. This makes it possible to obtain an image signal for reproducing an image having a higher resolution than the image read from only one surface. In particular, if the shift amount of the sampling timing is set to 1/2 of the sampling period, it becomes equal to that the sampling is performed at about twice the frequency as a whole, and the sampling period can be made constant as a whole, which is easier to observe. A visible image can be obtained.

[0015]

Embodiments of the radiation image reading apparatus of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a main part of the radiation image reading apparatus of the present embodiment, and FIG. 2 is a timing chart of signals output from the control unit and showing sampling timing. The stimulable phosphor sheet used in the illustrated radiation image reading apparatus has a stimulable phosphor layer capable of accumulating and recording predetermined radiation image information on the front surface side, and stimulating emitted light on the back surface side. Each of the stimulable phosphor layers and the support layer is formed by a support layer made of a transparent material, and radiation image information is stored and recorded. Further, the illustrated radiation image reading apparatus includes a laser light source 11 for emitting a laser beam L and a rotary polygon mirror 12 for scanning the emitted laser beam L on the surface of the stimulable phosphor sheet 1 on which radiation image information is stored and recorded. , Fθ lens 14, a reflecting mirror 15, and a scanning optical system including a motor 13 for driving the rotary polygon mirror 12, and stimulated emission light M _f emitted from both surfaces of the stimulable phosphor sheet 1 by scanning with the laser light L. , M _b for reading the front side and the back side separately, optical guides 31 and 32, PMT (photomultiplier) 33 and 34, logarithmic converters 35 and 36, electric signals converted by the logarithmic converters 35 and 36, respectively. A / D converter that digitally converts the data with an equal sampling period of 1.2 μsec 37.
38, Level adjuster 39 for adjusting the levels of the digital signals respectively obtained from the front and back sides of the stimulable phosphor sheet 1.
40, a multiplexer 41 that outputs a level-adjusted digital signal in time series, and sampling timings of the A / D converter 37 and the A / D converter 38
The image reading system is composed of a control device 42 which controls the output of the multiplexer 41 and shifts by 1/2 of 1.2 μsec, that is, 0.6 μsec, and the conveying means 21 and 22.

Next, the operation of the radiation image reading apparatus of this embodiment will be described. The laser beam L emitted from the laser light source 11 is incident on the rotary polygon mirror 12 rotating in the direction of arrow Z, is deflected, is condensed by the fθ lens 14, and is reflected by the reflecting mirror 15.
The main scanning of the surface of the stimulable phosphor sheet 1 which is reflected by and carries radiation image information is carried out in the direction of arrow X. On the other hand, the stimulable phosphor sheet is conveyed (sub-scanning) in the direction of arrow Y by the conveying means 21 and 22.

From the phosphor layer of the stimulable phosphor sheet 1 irradiated with the laser beam L, stimulated emission light M _f is emitted to the surface side according to the radiation image information carried by this phosphor layer, while , Stimulated emission light M _b transmitted through the support layer to the back side
Is emitted. The stimulated emission light M _f emitted to the surface side is
The light is collected by the light guide 31 provided on the front side, and the PMT
The image signal S _f is photoelectrically converted by 33. On the other hand, the stimulated emission light M _b emitted to the back surface side is condensed by the light guide 32 provided on the back surface side, and photoelectrically converted into the image signal S _b by the PMT 34.

The image signals S _f and S _b thus detected from both sides of the stimulable phosphor sheet 1 are logarithmically converted into image signals S _f ′ and S _b ′ by the logarithmic converters 35 and 36, respectively. The analog signals S _f ′ · S _b ′ after logarithmic conversion are sampled by the A / D converters 37 and 38 and converted into digital signals S _Df · S _Db . Here, each analog signal S
_When sampling _f ′ · S _b ′, the control device 42
The signal T _f · T _b indicating the sampling timing is A
It is output to the / D converters 37 and 38.

A signal T indicating this sampling timing
_f · T _b is based on a clock signal Ti having a constant period of 0.6 μsec, which is generated from a clock incorporated in the control device 42 (see FIG. 2), and is used as a timing signal T _f for the front side A / D converter 37. Among the signals Ti, signals T1, T3, T5, ... Corresponding to i = 2N-1 (N; natural number of 1 or more) are output in time series, and the A / D on the back surface side is output.
Of the time-series manner i = 2N clock signal Ti as a timing signal T _b for converter 38 (N; 1 or greater natural number) signal T2, T4, T6 corresponding to, ... are output.

The digital signals S _Df and S _Db after being digitally converted by the A / D converters 37 and 38 based on the timing signals T _f and T _b are input to the level adjusters 39 and 40, respectively. The stimulated emission lights M _f and M _b emitted from the front surface side and the back surface side of the stimulable phosphor sheet 1 are different due to the difference between the incident surface of the radiation image information and the incident surface of the laser light L that is excitation light. Generally, the levels of emitted light amount are different. Also, the signal level obtained may differ due to individual differences in the light guides 31 and 32 and the PMTs 33 and 34. Level adjuster
39 and 40 are for adjusting the level of the image signal obtained from the front side and the image signal obtained from the back side, and are defined in the stimulable phosphor sheet in which predetermined image information is recorded in advance. It is adjusted so that the input signal is converted by the conversion table and output so that the level of the image signal obtained from the front side by irradiating the laser beam and the level of the image signal obtained from the back side are substantially equal. .

The two image signals S _Df ′ · S _Db ′ whose levels have been adjusted in this way are input to the multiplexer 40 and are output in time series under the control of the control device 42 to output one image signal S. _D. Since the clock signal Ti is a signal emitted in time series, two image signals S _Df ′ ·
It can be said that S _Db ′ is an image signal read alternately along the main scanning direction of the laser beam L, and the finally obtained image signal S _D is the image signal obtained from the front side and the image signal obtained from the back side. The obtained image signal becomes an image signal in which the other is interpolated. Therefore, it is possible to obtain an image signal train having substantially double the resolution without shortening the sampling cycle on any surface of the sheet 1, and it is possible to substantially improve the resolution of the obtained visible image. it can.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a main part of an embodiment of a radiation image reading apparatus of the present invention.

FIG. 2 is a timing chart of signals indicating sampling timing output from the control device.

[Explanation of symbols]

1 Storage phosphor sheet 11 Laser light source 12 Rotating polygon mirror 13 Motor 14 fθ lens 15 Reflecting mirror 21,22 Conveying means 31,32 Optical guide 33,34 Photomultiplier 35,36 Log converter 37,38 A / D conversion 39, 40 Level adjuster 41 Multiplexer 42 Control device L Laser beam M _f , M _b Photostimulated emission light

Claims (4)

[Claims] 1. An excitation light is scanned on at least one surface of a stimulable phosphor sheet on which radiation image information is stored and recorded,
The stimulated emission light emitted from both surfaces of the stimulable phosphor sheet by the scanning is read at the same sampling cycle so that the sampling timings do not match on one surface side and the other surface side, and two image signals are read. A radiation image reading method, characterized in that an image signal read from one surface side is interpolated with an image signal read from the other surface side. 2. The radiation image reading method according to claim 1, wherein the sampling timing on the one surface side and the sampling timing on the other surface side are shifted by ½ of the sampling cycle. 3. An excitation light source for emitting excitation light, a scanning optical system for scanning the excitation light on at least one surface of a stimulable phosphor sheet on which radiation image information is stored and recorded, and a scanning optical system for scanning the excitation light. Two image reading systems that read stimulated emission light emitted from both sides of the stimulable phosphor sheet at equal sampling periods so that sampling timings do not match on one surface side and the other surface side; Signal processing means for performing signal processing so that two image signals read separately by one image reading system are interpolated with image signals read from one surface side by image signals read from the other surface side. A radiographic image reading device comprising: 4. The radiation image reading apparatus according to claim 3, wherein the sampling timing on the one surface side and the sampling timing on the other surface side are shifted by ½ of the sampling cycle.