JPH1184552A - Method and device for picture read-out - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the response of a picture read out from being deteriorated even though the excitation energy of exciting light is large in the case of reading out a radiation picture from a stimulable phosphor sheet where the radiation picture is recorded. SOLUTION: The excitation energy of a laser beam 11 is set to be high or low by a read-out mode setting means 23. Beam expanders 21a and 21b changing a beam diameter are arranged in a swithcable state on the optical path of the laser beam 11 so that the response of the picture, obtained by making the beam diameter of the laser beam 11 radiated to a sheet 4 to be small when the excitation energy is set to be high, is made large and the response of the picture, obtained by making the beam diameter large when the excitation energy is set to be low, is reversely made small, in accordance with a read-out mode set. Thus, the picture whose response is not changed is read out regardless of the excitation energy of the laser beam 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading method and apparatus for irradiating a stimulable phosphor sheet on which a radiation image is accumulated and recorded with excitation light and obtaining an image signal representing the radiation image from the sheet. .

[0002]

2. Description of the Related Art A recorded radiographic image is read to obtain an image signal, and the image signal is subjected to appropriate image processing.
2. Description of the Related Art Reproduction and recording of images are performed in various fields.
For example, an X-ray image is recorded using a film having a low gamma value designed to be compatible with the subsequent image processing, and the X-ray image is read from the film on which the X-ray image is recorded and converted into an electric signal. By subjecting the electric signal (image signal) to image processing and reproducing it as a visible image on a copy photograph or the like, a system capable of obtaining a reproduced image having good image quality performance such as contrast, sharpness, and graininess can be obtained. It has been developed (see JP-B-61-5193).

[0003] Further, according to the present applicant, radiation (X-ray, α
Radiation, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a part of this radiation energy is accumulated, and then, when irradiated with excitation light such as visible light, the amount of stimulated emission light corresponding to the accumulated energy is increased. A radiation image of a subject such as a human body is once photographed and recorded on a sheet-shaped stimulable phosphor by using a stimulable phosphor (stimulable phosphor) which emits light, and the stimulable phosphor sheet is irradiated with laser light or the like. The excitation light is scanned to generate photostimulated light, and the obtained photostimulated light is photoelectrically read to obtain an image signal. Based on this image signal, a radiation image of the subject is recorded on a recording material such as a photographic photosensitive material. A radiation recording / reproducing system for outputting a visible image to a CRT or the like has already been proposed (Japanese Unexamined Patent Publication No.
55-12429, 56-11395, 55-0163472, 56-164
Nos. 645 and 55-116340).

As an image reading apparatus used in the above-described radiation image recording / reproducing system, there is an image reading apparatus that changes the excitation energy of excitation light in accordance with the dose of radiation applied to a stimulable phosphor sheet and reads the image. Are known. In such an apparatus, when the amount of radiation applied to the stimulable phosphor sheet is large, reading is performed using excitation light having a relatively low excitation energy, and when the amount of radiation is small, reading is performed using excitation light having a relatively high excitation energy. By performing reading, a predetermined amount of stimulating light is emitted from the stimulable phosphor sheet.

[0005]

On the other hand, according to the research conducted by the present applicant, even if the beam diameter of the excitation light and the frequency response of the image signal in the signal processing system are the same, the excitation light at the time of reading a radiation image is not affected. It has been found that as the excitation energy increases, the response (frequency response, MTF) of the read image decreases. For this reason, in a reading device that reads an image by changing the excitation energy of the excitation light described above, according to the change in the excitation energy of the excitation light,
The response of the obtained image changed.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an image reading method and apparatus which can prevent a change in response of an obtained image even when the excitation energy of excitation light changes. Things.

[0007]

A first image reading method according to the present invention provides a storage method in which a radiation image is stored and recorded by excitation light emitted from a light source capable of outputting excitation light having different excitation energies. An analog image signal representing the radiation image is obtained by scanning the phosphor sheet to convert the radiation image into stimulated emission light and photoelectrically reading the stimulated emission light obtained from the stimulable phosphor sheet. In the image reading method for obtaining an image signal representing the radiation image by converting the analog image signal into a digital image signal, the higher the excitation energy of the excitation light output from the light source, the more the stimulable phosphor sheet A beam diameter of the excitation light to be scanned is reduced.

In a second image reading method according to the present invention, instead of changing the beam diameter, the response of the image signal representing the radiation image increases as the excitation energy of the excitation light output from the light source increases. Is set to be higher.

Further, in the second image reading method according to the present invention, the response of the image signal representing the radiation image may be changed by changing the response of the analog image signal. The response of the image signal representing the radiation image may be changed by changing the response of the image signal.

A first image reading apparatus according to the present invention provides a light source capable of outputting excitation light having different excitation energies, and a storage device in which a radiation image is stored and recorded by the excitation light emitted from the light source. By scanning the phosphor sheet to convert the radiation image into stimulated emission light and photoelectrically reading the stimulated emission light obtained from the stimulable phosphor sheet, an analog image signal representing the radiation image is obtained. An image reading apparatus comprising: a reading unit; and a signal processing unit that converts the analog image signal obtained by the reading unit into a digital image signal to obtain an image signal representing the radiation image. Beam diameter changing means for reducing the beam diameter of the excitation light for scanning the stimulable phosphor sheet as the excitation energy of the excitation light increases. It is an feature.

Further, in the second image reading apparatus according to the present invention, the signal processing means may be replaced with a beam diameter changing means.
A means for increasing the response of the image signal representing the radiation image as the excitation energy of the excitation light output from the light source is higher.

In the second image reading apparatus according to the present invention, the signal processing means may change the response of the analog image signal to change the response of the image representing the radiation image, Further, the response of the image representing the radiation image may be changed by changing the response of the digital image signal.

[0013]

According to the first image reading method and apparatus of the present invention, the higher the excitation energy of the excitation light output from the light source, the smaller the beam diameter of the excitation light for scanning the stimulable phosphor sheet. As a result, the response of an image obtained by increasing the excitation energy decreases, but the response of the image obtained increases by decreasing the beam diameter of the excitation light. In addition, although the response of an image obtained by reducing the excitation energy is improved, the response of the image obtained is increased by increasing the beam diameter of the excitation light. as a result,
The response of the obtained image can be made substantially the same even if the excitation energy of the excitation light changes, so that the frequency characteristic of the obtained image is substantially constant regardless of the excitation energy of the excitation light. can do.

According to the second image reading method and apparatus of the present invention, the higher the excitation energy of the excitation light output from the light source is, the higher the response of the image signal is. As a result, the response of an image obtained decreases, but the response of the image obtained increases as the response of the image signal increases. In addition, the response of an image obtained by reducing the excitation energy is improved, but the response of an image obtained is reduced by decreasing the response of the image signal. As a result, the response of the obtained image can be made substantially the same even when the excitation energy of the excitation light changes, so that the frequency characteristic of the obtained image is substantially constant regardless of the excitation energy of the excitation light. It can be.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a radiation image photographing apparatus. As shown in FIG. 1, the stimulable phosphor sheet 4 is arranged, the radiation source 3 is driven, and the radiation 2 is emitted, so that the radiation 2 transmitted through the subject 1 is irradiated on the stimulable phosphor sheet 4. Then, the radiation image information of the subject 1 is accumulated and recorded on the stimulable phosphor sheet 4.

Next, from the stimulable phosphor sheet 4, FIG.
The radiation image is read by the image reading device according to the first embodiment of the present invention as shown in FIG. 1, and an image signal representing the radiation image is obtained.

The stimulable phosphor sheet 4 is placed on an endless belt 9 rotated by a motor (not shown). Above the sheet 4, a laser light source 10 that emits a laser beam 11 as excitation light, a rotary polygon mirror 12 that reflects and deflects the laser beam 11 and performs a main scan on the sheet 4 are rotated by a motor 8. , Fθ lens 13 and a mirror 7 for reflecting the laser beam 11 transmitted through the fθ lens 13 toward the stimulable phosphor sheet 4. In addition, laser light 11
Above the position where is scanned, a condensing guide 14 that condenses stimulated emission light emitted by the scanning of the laser light 11 is arranged in close proximity. A photomultiplier (photomultiplier tube) 15 that photoelectrically detects stimulated emission light is connected to the condensing guide 14. This photo multiplier 15
Is connected to a logarithmic amplifier 16, and this logarithmic amplifier 16
Are connected to A / D converters 17, and each A / D converter 17 is connected to storage means 18.

The laser light source 10 is provided with a read mode setting means 23.
The excitation energy of the emitted laser beam 11 can be changed in two levels, high and low, according to the instruction from Laser light source
Two types of beam expanders 21a and 21b are interchangeably disposed on an optical path between the rotary polygon mirror 10 and the rotary polygon mirror 12. Each of the beam expanders 21a and 21b is provided with a read mode setting unit 23.
Beam expander position selection means in response to instructions from
22 is selected and arranged on the optical path. Here, the beam expander 21a is used to irradiate the sheet 4 with the laser light 11
The beam expander 21b adjusts the beam diameter so that the beam diameter of the laser beam 11 applied to the sheet 4 is relatively small. is there.

Here, according to the research by the present applicant, even if the beam diameter of the excitation light (laser light 11) and the frequency response in the signal processing system of the image signal are the same, the excitation light at the time of reading the radiation image is obtained. It has been found that the response (frequency response) of the read image decreases as the excitation energy increases. For this reason, in the above-described reading apparatus that reads an image by changing the excitation energy of the laser beam 11, the reading is performed by changing the excitation energy of the laser beam 11, as shown in FIG. The response of the image had changed. In FIG. 3, the response is shown as a relative value of MTF (sharpness) in both the main and sub directions. In the present embodiment, when the excitation energy of the laser light 11 emitted from the laser light source 10 is large, the beam expanders 21a and 21b are switched to reduce the beam diameter of the laser light 11 applied to the sheet 4. When the excitation energy of the laser beam 11 is small, the response of the obtained image is increased by increasing the beam diameter of the laser beam 11 applied to the sheet 4 when the excitation energy of the laser beam 11 is small. Is what you do.

Next, the operation of this embodiment will be described.

First, the reading mode is set by the reading mode setting means 23. This reading mode uses a laser light source.
This is to determine whether the laser light 11 emitted from 10 has high excitation energy or low excitation energy. Here, when the reading mode is set to the high excitation energy, the beam expander position selecting means 22 selects the beam expander 21b so that the beam diameter of the laser beam 11 applied to the sheet 4 becomes small, Conversely, when the reading mode is set to the low excitation energy, the beam expander position selecting means 22 selects the beam expander 21a so that the beam diameter of the laser beam 11 applied to the sheet 4 becomes large. is there.

After the reading mode is set as described above,
The stimulable phosphor sheet 4 on which the radiation image of the subject is stored is set on the endless belt 9. The stimulable phosphor sheet 4 set at this predetermined position is conveyed (sub-scan) in the direction of arrow Y by the endless belt 9. On the other hand, the laser light 11 emitted from the laser light source 10 is reflected and deflected by the rotating polygon mirror 12 driven by the motor 8 and rotated at high speed in the direction of the arrow, enters the sheet 4 via the fθ lens 13 and the mirror 7, and enters the sub-scanning direction. (Arrow Y direction)
The main scanning is performed in the direction of arrow X, which is substantially vertical. From the portion of the sheet 4 irradiated with the laser beam 11, the stimulated emission light 6 of a light amount corresponding to the radiation image information stored and recorded is emitted. The stimulated emission light 6 is guided by the condensing guide 14,
Photoelectrically detected by the photomultiplier 15.
Stimulated luminescence light 6 entering the condensing guide 14 from the incidence end face
Travels through the inside of the light-collecting guide 14 by repeating total reflection, exits from the exit end face, is received by the photomultiplier 15, and the amount of the photostimulated light 6 representing a radiation image is converted into an electric signal by the photomultiplier 15. Is converted.

The analog image signal S output from the photomultiplier 15 is logarithmically amplified by a logarithmic amplifier 16 and input to an A / D converter 17, where it is converted into a digital image signal S 'and stored in a storage means 18. Is input to Storage means 18
The digital image signal S 'input to the image processing unit 19 is input to the image processing unit 19, where the digital image signal S' is subjected to predetermined image processing, and the reproduction unit 20 supplies the radiation image for reproduction.

The reproducing means 20 may be a display means such as a CRT or a recording device for performing optical scanning recording on a photosensitive film.

As described above, in the first embodiment of the present invention, as the excitation energy of the laser light 11 output from the laser light source 10 increases, the beam diameter of the laser light 11 that scans the stimulable phosphor sheet 4 increases. Is reduced, the response of an image obtained by increasing the excitation energy is reduced, but the response of the image obtained is increased by the decrease in the beam diameter of the laser beam 11.
Further, the response of an image obtained by reducing the excitation energy increases, but the response of the image obtained decreases by increasing the beam diameter of the laser beam 11. As a result, the response of the image reproduced by the reproducing means 20 can be made substantially the same even if the excitation energy of the laser light 11 changes, and thus, the response can be obtained regardless of the excitation energy of the laser light 11. The frequency characteristics of the image can be made substantially constant.

In the first embodiment, the excitation energy of the laser beam 11 emitted from the laser light source 10 is switched between high and low, and the two types of beam expanders 21a and 21b are correspondingly operated. The beam expander is used, but is not limited to this, so that the excitation energy can be switched in three or more steps and the beam diameter of the laser beam 11 can be changed in three or more steps correspondingly. May be provided.

Next, a second embodiment of the present invention will be described.

FIG. 4 is a diagram showing a configuration of an image reading apparatus according to a second embodiment of the present invention. In FIG. 4, the same components as those in FIG. 2 are denoted by the same reference numerals, and detailed description is omitted. In the second embodiment, instead of changing the beam diameter of the laser light 11 according to the excitation energy of the laser light 11, the response of the logarithmically converted analog image signal S is changed according to the excitation energy of the laser light 11. This is changed by two types of analog filters 31a and 31b.

Here, the logarithmic amplifier 16 and the analog filter
An analog switch 30 is provided between the analog filters 31a and 31b to switch which of the analog filters 31a and 31b receives the analog image signal S in accordance with the input from the reading mode setting unit 23. Here, the analog filter 31
a is for changing the response of the analog image signal S so that the response of the analog image signal S is high, and the analog filter 31b is for changing the response of the analog image signal S so that the response of the analog image signal S is low.

Next, the operation of this embodiment will be described.

First, the reading mode is set by the reading mode setting means 23. Here, when the reading mode is set to the high excitation energy, the analog switch 30 controls the logarithmic conversion of the analog image signal S so that the response of the analog image signal S becomes high.
If the read mode is set to low excitation energy, the analog switch 30
Is switched so that the logarithmically converted analog image signal S is input to the analog filter 31b so that the response of the analog image signal S is reduced.

Then, in this way, the analog filter
When the positions 31a and 31b are switched, a radiation image is read in the same manner as in the first embodiment.

As described above, according to the second embodiment, the higher the excitation energy of the laser beam 11 output from the laser light source 10 is, the higher the response of the analog image signal S is. As a result, the response of the obtained image decreases, but the response of the analog image signal S increases, and conversely, the response of the obtained image increases. Further, the response of an image obtained by lowering the excitation energy becomes higher, but the response of the image obtained by lowering the response of the analog image signal S becomes lower. As a result, the response of the obtained image can be made substantially the same even when the excitation energy of the laser light 11 changes, and thus the frequency characteristic of the obtained image can be changed regardless of the excitation energy of the laser light 11. It can be substantially constant.

In the second embodiment, the excitation energy of the laser light 11 emitted from the laser light source 10 is switched between high and low, and two types of analog filters 31a and 31b are used in response to the switching. However, the present invention is not limited to this. The excitation energy can be switched in three or more steps, and an analog filter is provided so that the response of the analog image signal S can be changed in three or more steps. You may do so.

Next, a third embodiment of the present invention will be described.

FIG. 5 is a diagram showing a configuration of an image reading apparatus according to a third embodiment of the present invention. In FIG. 5, the same components as those in FIG. 2 are denoted by the same reference numerals, and detailed description will be omitted. In the third embodiment, the laser light source 10
Instead of changing the beam diameter of the laser light 11 in accordance with the excitation energy of the laser light 11 emitted from the laser light 11, the response of the digital image signal S 'is changed in accordance with the excitation energy of the laser light 11 by a digital signal processor (Digital Signal
Processor, hereinafter referred to as DSP) 32.

Here, in response to the input from the read mode setting means 23, the DSP 32 increases the response of the digital image signal S 'when the read mode is set to the high excitation energy, and sets the read mode to the low excitation energy. When the energy is set, the response of the digital image signal S 'is changed by filtering or the like so as to lower the response of the digital image signal S'.

Next, the operation of this embodiment will be described.

First, the reading mode is set by the reading mode setting means 23. Here, when the reading mode is set to the high excitation energy, the DSP 32 changes the response of the digital image signal S 'so that the response of the digital image signal S' is high, and conversely, the reading mode is set to the low excitation energy. If set, the DSP 32 changes the response of the digital image signal S 'so that the response of the digital image signal S' becomes low.

When the DSP 32 is set in this way, a radiation image is read in the same manner as in the first embodiment.

As described above, according to the third embodiment, the higher the excitation energy of the laser beam 11 output from the laser light source 10, the higher the response of the digital image signal S 'is. The response of the obtained image decreases as the response increases, but the response of the image obtained increases as the response of the digital image signal S ′ increases. In addition, the response of an image obtained by decreasing the excitation energy increases, but the response of the image obtained decreases by decreasing the response of the digital image data S ′.
As a result, the response of the obtained image can be made substantially the same even when the excitation energy of the laser light 11 changes, and thus, regardless of the excitation energy of the laser light 11,
The frequency characteristics of the obtained image can be made substantially constant.

In the third embodiment, the excitation energy of the laser light 11 emitted from the laser light source 10 is switched between high and low, and the DSP 32 responds to this by responding to the digital image signal S '. Although the switching is performed in two stages, the present invention is not limited to this. The excitation energy can be switched in three or more stages, and the response of the digital image signal S 'can be changed in three or more stages in accordance with this. The DSP 32 may be set as described above.

[Brief description of the drawings]

FIG. 1 is a diagram showing a radiographic image capturing apparatus;

FIG. 2 is a view showing an image reading apparatus according to the first embodiment of the present invention;

FIG. 3 is a graph showing a relationship between excitation energy and image response.

FIG. 4 is a diagram showing an image reading apparatus according to a second embodiment of the present invention.

FIG. 5 is a diagram showing an image reading device according to a third embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 subject 2 radiation 3 radiation source 4 stimulable phosphor sheet 5 sensor 6 stimulated emission light 7 mirror 8 motor 9 endless belt 10 laser light source 11 laser light 12 rotating polygon mirror 13 fθ lens 14 light condensing guide 15 photomultiplier 16 logarithm Amplifier 17 A / D converter 18 Storage means 19 Image processing means 20 Reproduction means 21a, 21b Beam expander 22 Beam expander position selection means 23 Reading mode setting means 30 Analog switch 31a, 31b Analog filter 32 DSP

Claims (8)

[Claims] An excitation light emitted from a light source capable of outputting excitation light having different excitation energies scans a stimulable phosphor sheet on which a radiation image is stored and stimulates the radiation image to emit light. The analog image signal representing the radiation image is obtained by photoelectrically reading the stimulated emission light obtained from the stimulable phosphor sheet, and the analog image signal is converted into a digital image signal. An image reading method for obtaining an image signal representing a radiation image, wherein the higher the excitation energy of the excitation light output from the light source, the smaller the beam diameter of the excitation light that scans the stimulable phosphor sheet. Image reading method. 2. A stimulable phosphor sheet on which a radiation image is accumulated and recorded is scanned by the excitation light emitted from a light source capable of outputting excitation light having different excitation energies to stimulate the radiation image to emit stimulating light. The analog image signal representing the radiation image is obtained by photoelectrically reading the stimulated emission light obtained from the stimulable phosphor sheet, and the analog image signal is converted into a digital image signal. An image reading method for obtaining an image signal representing a radiation image, wherein the higher the excitation energy of the excitation light output from the light source, the higher the response of the image signal representing the radiation image. 3. The image reading method according to claim 2, wherein a response of the image signal representing the radiation image is changed by changing a response of the analog image signal. 4. The image reading method according to claim 2, wherein a response of the image signal representing the radiation image is changed by changing a response of the digital image signal. 5. A light source capable of outputting excitation light having different excitation energies, and the excitation light emitted from the light source scans a stimulable phosphor sheet on which a radiation image is stored and records the radiation image. Reading means for converting the stimulable luminescent light into light and photoelectrically reading the stimulable luminescent light obtained from the stimulable phosphor sheet to obtain an analog image signal representing the radiation image; A signal processing unit that obtains an image signal representing the radiation image by converting the analog image signal into a digital image signal, wherein the higher the excitation energy of the excitation light output from the light source, An image reading apparatus further comprising a beam diameter changing means for reducing a beam diameter of the excitation light for scanning the stimulable phosphor sheet. 6. A light source capable of outputting excitation light having different excitation energies, and the excitation light emitted from the light source scans a stimulable phosphor sheet on which a radiation image is stored and records the radiation image. Reading means for converting the stimulable luminescent light into light and photoelectrically reading the stimulable luminescent light obtained from the stimulable phosphor sheet to obtain an analog image signal representing the radiation image; A signal processing unit for converting the analog image signal into a digital image signal to obtain an image signal representing the radiation image, wherein the signal processing unit excites excitation light output from the light source. An image reading apparatus characterized in that the higher the energy, the higher the response of the image signal representing the radiation image. 7. The image reading apparatus according to claim 6, wherein the signal processing unit changes a response of the analog image signal to change a response of an image representing the radiation image. 8. The image reading apparatus according to claim 6, wherein the signal processing unit changes a response of the image representing the radiation image by changing a response of the digital image signal.