JP2002281274A - Radiation image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation image reader which can read the radiation image of higher image quality while cost is suppressed to be low. SOLUTION: When the average value, the cumulative histogram and the median value of pixel values in first image data obtained by reading the radiation image form a photostimulable fluorescent plate 4 are not more than prescribed values, a personal computer main body 25 judges that the image on the basis of the values becomes indistinct, adds second image data and obtains the image of higher image quality.

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 apparatus, and more particularly to a radiation image reading apparatus for reading a radiation image imprinted on a stimulable phosphor plate.

[0002]

2. Description of the Related Art By irradiating a stimulable phosphor plate, on which an X-ray image has been captured, with an X-ray image, which is a kind of radiation, with a laser beam, which is an excitation light, the stimulable phosphor emits light corresponding to the excitation light. And the photostimulated light is received by the photodetector,
2. Description of the Related Art There is known a radiation image reading apparatus that converts image data corresponding to an X-ray image.

[0003]

When a stimulable phosphor plate is irradiated with a laser beam of higher intensity, the amount of stimulable luminescence is increased accordingly, and image data with less noise is obtained. Tend to be However, since general-purpose lasers generally have low light intensity, when irradiation is performed using such laser light, depending on the image, S / N
Image data with a poor ratio may be obtained. However, if a laser capable of irradiating a high-intensity laser beam is used to obtain image data with a good S / N ratio, there is a problem that the cost of the radiation image reading apparatus is greatly increased.
There is also a problem that there are few types of lasers that can irradiate high-intensity laser light, and depending on the specifications, they cannot always be used.

On the other hand, irradiating the stimulable phosphor plate only once with laser light releases all the energy stored in the stimulable phosphor plate forming a latent image of an X-ray image. is not. Usually, the stimulable phosphor plate from which the image has been read is irradiated with, for example, ultraviolet light so that the stimulable phosphor plate is not affected by the next photographing. A process of releasing all stored energy is performed. Here, using the energy of the latent image that has been conventionally emitted,
There is a possibility that a higher quality image can be formed. However, even if the stimulable phosphor plate from which the image has been read once is irradiated with the excitation light again, the intensity of the stimulable light emitted in response to the excitation light is weak, and generally a clear radiation image cannot be read. There's a problem. Therefore, the image based on the composite image data obtained by adding the image data based on such weak stimulating light and the image data obtained first is better than the image based on only the image data obtained first. May also have poor image quality.

[0005] The present invention has been made in view of the above problems, and has as its object to provide a radiation image reading apparatus capable of reading a higher quality radiation image while keeping costs low.

[0006]

(1) The radiation image reading apparatus according to the first aspect of the present invention irradiates a stimulable phosphor plate on which a radiation image is recorded with excitation light to thereby emit the stimulable phosphor. In a radiation image reading apparatus that reads an image by receiving stimulating light emitted from a plate and converts it into image data, first image data obtained by first reading an image from the stimulable phosphor plate On the other hand, the second image data obtained by reading an image from the stimulable phosphor plate for the second or subsequent times is converted into a pixel value of a predetermined area of the second image data, and / or Image data corresponding to a radiation image is obtained by performing weighting in accordance with the magnitude of the pixel value of a predetermined area of one image data and performing a synthesis process. Here, as the pixel value, a pixel value in a predetermined area of the first image data may be used alone, a pixel value in a predetermined area of the second image data may be used alone, or both are combined. You may use it.

[0007] Here, 2 from the stimulable phosphor plate.
Since the second image data obtained by reading the image after the first time has a poor S / N ratio when compared with the first image data, it is difficult to simply add the first image data to the second image data. However, noise increases and the image quality of the image based on the combined image data is degraded. Therefore, when adding the second image data, it is considered that weighting of, for example, 1 or less is necessary. However, the second image data depends on the energy of the radiation received by the stimulable phosphor plate.
Various pixel values can be taken. Therefore, if uniform weighting is applied to the second image data, the image quality may be degraded.

On the other hand, if the pixel value of the second image data is large to some extent, it can be distinguished from background noise and the S / N ratio is considered to be relatively high. Therefore, in the radiation image reading apparatus of the present invention, if the pixel value of the second image data (or the pixel value of the first image data is high), it is naturally determined that the pixel value of the second image data is also high. The pixel value of the first image data may be used. If the pixel value is relatively high, a high weight is assigned to the second image data. If the pixel value is relatively low, a low weight ( Including zero) and the first
By performing the synthesizing process with the image data, the image based on the synthesized image data can be made to have high image quality.

(2) Preferably, the second image data is synthesized with the first image data by processing a spatial frequency component. For example, a sharper image can be obtained by performing edge enhancement or noise removal, which is a type of spatial frequency component processing.

(3) In the radiation image reading apparatus according to the second aspect of the present invention, the stimulable phosphor plate on which the radiation image is recorded is irradiated with excitation light to emit light from the stimulable phosphor plate. In a radiation image reading apparatus that reads an image by receiving light and converting it into image data, a pixel value of a predetermined area in first image data obtained by first reading an image from the stimulable phosphor plate When it is determined that the statistic value satisfies the predetermined condition, the image is read again from the stimulable phosphor plate, and the first and second image data are read out of the stimulable phosphor plate for the second and subsequent times. The image data corresponding to the radiographic image is obtained by synthesizing the second image data obtained by reading.

Here, if the image based on the first image data is clear, it can be said that it is not necessary to add the second image data having a poor S / N ratio. In such a case,
A method of displaying an image based on the first image data on a display or printing, judging whether the image is clear by human eyes, and adding an image based on the image data to the second image data if the image is unclear is also considered. But it takes time and effort. Therefore, in the radiation image reading apparatus of the present invention, when the statistical value (for example, the average value, the cumulative histogram, the median value) of the pixel value of the predetermined area in the first image data satisfies the predetermined condition (for example, the threshold value or the predetermined value). (When the value is equal to or less than the value), it is determined that the image based on it is unclear, and the second image data is added to obtain a higher quality image. If it is determined that the statistic of the pixel value of the predetermined area in the first image data does not satisfy the predetermined condition before obtaining the second image data, it is not necessary to obtain the second image data. Therefore, the reading time can be shortened, but not limited thereto.

(4) Further, the second image data has a size of a pixel value of a predetermined area of the second image data, and / or
Alternatively, the image data corresponding to the radiation image is obtained by performing weighting processing according to the magnitude of the pixel value of the predetermined area of the first image data and then synthesizing the first image data. Then, an image based on the composite image data has higher image quality, which is preferable.

(5) When the second image data is synthesized with the first image data by processing a spatial frequency component, an image based on the synthesized image data has higher image quality. Is preferred.

(6) The statistical value is a value obtained from an average value, a median value, or a cumulative histogram of pixel values of the predetermined area, and the predetermined condition is that the statistical value is a predetermined value. In the following case, it is possible to determine with a simple calculation, and it is possible to determine whether or not to read the image again with little time lag.

(7) When the predetermined area is an area corresponding to a radiation irradiation area of the stimulable phosphor plate,
Since the area that affects image quality is the radiation irradiation area,
When it is determined that the image based on the first image data is unclear based on the pixel value corresponding to the radiation irradiation area,
By adding the second image data, a high-quality image can be obtained.

[0016]

Embodiments of the present invention will be described below in detail. FIG. 1 is a diagram showing a schematic configuration of a radiation image reading apparatus according to the present embodiment. As shown in FIG. 1, the radiation image reading device 50 includes a reading device 3 and a controller 2.

When radiation is emitted from a radiation (eg, X-ray) irradiator 31 driven by a drive source 32, the reader 3 accumulates a part of this radiation energy, and thereafter, emits visible light, laser light, or the like. A plate-like stimulable phosphor consisting of a stimulable phosphor laminated on a support using a stimulable phosphor that emits stimulable light in response to the radiation energy accumulated when irradiated with excitation light The plate 4 temporarily stores radiation image information of a subject such as a human body by X-rays emitted from the X-ray irradiator 30 and sequentially scans with laser light to emit stimulating light. Photoelectric reading unit 20
The image signal is obtained by photoelectrically reading the image signal sequentially. Then, the reading device 3 irradiates the stimulable phosphor plate 4 with the erasing light after reading the image signal to release the radiation energy remaining on the plate and prepares for the next photographing.

The reading device 3 is a laser light source comprising a stimulable phosphor plate 4 for transmitting radiation image information of the subject M and a laser diode for generating a laser beam as excitation light for the stimulable phosphor plate 4. Unit 6, a laser driving circuit 5 for driving the laser light source unit 6, an optical system 7 for scanning the laser light from the laser light source unit 6 on the stimulable phosphor plate 4, and an excitation laser light. And a photoelectric reading unit 20 that collects the excited photostimulated light, performs photoelectric conversion, and obtains an image signal. The photoelectric reading unit 20 includes a condenser 8 that collects stimulated emission excited by the excitation laser light, a photomultiplier (photomultiplier tube) 10 that photoelectrically converts the light collected by the condenser 8, and , A high-voltage power supply 10a for applying a voltage to the photomultiplier 10, and a converter for converting a current signal from the photomultiplier (photomultiplier tube) 10 into a digital signal by current-voltage conversion, voltage amplification, A / D conversion, etc. 11, a correcting unit 12 for correcting the digital signal converted by the converting unit 11, and an image transmitting unit 13 for transmitting the digital signal corrected by the correcting unit 12. A signal is transmitted to the controller 3. Note that the correction unit 12
It is composed of a RISC processor and corrects response delays and unevenness of digital signals.

The reading device 3 further includes a halogen lamp 14 for irradiating erasing light to emit radiation energy remaining on the stimulable phosphor plate 4 after reading the image signal.
And a driver 15 for driving the halogen lamp 14. The reading device 3 includes a laser driving circuit 5, a high-voltage power supply 10a, a conversion unit 11, a correction unit 12, and an image transmission unit 1.
3 and a control unit 17 for controlling the driver 15 respectively
Having. Further, the laser light source unit 6, the optical system 7, the light collector 8, the photomultiplier 10, and the halogen lamp 14 of the reading device 3 are integrated as a sub-scanning unit (not shown) by a ball screw mechanism (not shown). Move in the sub-scanning direction perpendicular to the direction. This sub-scanning unit
At the time of image reading, the sub-scanning is performed by moving, and during the backward movement, the halogen lamp 14 emits light to erase the image.

The controller 2 includes a personal computer main body 25
, A keyboard 26, and a monitor display unit 27. The digital signal of the radiation image information received from the reading device 3 is temporarily stored in a memory, image-processed, and
In response to an operation input from, the control unit controls display on the monitor display unit 27 and image processing, and outputs radiation-processed radiation image information. The processing program of the radiation image reading apparatus described with reference to FIG.
5 (computer) to store in a storage medium readable,
Read the above processing program from this storage medium,
The processing program of the radiation image reading apparatus described with reference to FIG. 2 can be run. Further, the processing program may be transmitted as it is or in a compressed and converted form via a network, installed, and run.

Next, the operation of this embodiment will be described. FIG. 2 is a flowchart illustrating the process of the radiation image reading apparatus according to the present embodiment, and FIG. 3 is a diagram illustrating a state in which the stimulable phosphor plate is scanned with an excitation laser beam.

In step S101 of FIG. 2, X-ray photography is performed. In step S102, the stimulable phosphor plate 4 is irradiated with a laser beam as shown in FIG. Is condensed by a condenser 8, photoelectrically converted by a photomultiplier 10, digitally converted by a conversion unit 11, and further subjected to predetermined correction by a correction unit 12,
A digital signal (first image data) is obtained. The first
Is transmitted to the controller 2.

In step S103, the personal computer body 25 of the controller 2 determines whether or not the pixel value (signal value) of the predetermined area of the first image data is sufficiently large. Specifically, as shown in the cumulative histogram shown in FIG. 4, when the pixel value is indicated on the horizontal axis and the frequency is indicated on the vertical axis, the average value (or median value) AV, which is a statistical value, satisfies a predetermined condition. Is determined, specifically, whether it is smaller than a threshold value (predetermined value).

If it is determined that the average value AV is larger than the threshold value, the personal computer body 25 determines that the S / N ratio of the first image data is good, and performs the first image reading without performing the second reading. The data is output as image data corresponding to the radiation image (step S107).

On the other hand, if it is determined that the average value AV is equal to or less than the threshold value, the personal computer 25 determines that an image of good quality cannot be obtained because the S / N ratio of the first image data is poor. By deciding to perform the second reading, and by transmitting a driving signal to the reading device 3 in step S104,
The stimulable phosphor plate 4 is irradiated with laser light again, and the generated stimulable luminescence light is condensed by the condensing body 8, photoelectrically converted by the photomultiplier 10, and digitally converted by the conversion unit 11. Then, the correction unit 12 performs a predetermined correction, and
A digital signal (second image data) is obtained. The second
Is also transmitted to the controller 2.

In step S105, the personal computer 25 of the controller 2 performs a large weighting according to the pixel value of a predetermined area of the first or second image data, for example, if the average value of the pixel values is large, and averages the pixel values. If the value is small, a small weighting is performed, and after performing the weighting process, the combining process is performed with the first image data in step S106. The second image data can be subjected to edge enhancement and noise removal as processing of a spatial frequency component. Therefore, an image based on the composite image data has higher image quality than an image based on the first image data. The synthesized image data obtained in this way is
The data is output as image data corresponding to the radiation image (step S107).

By the way, it can generally be said that a radiation image is not formed on the entire stimulable phosphor plate 4. This is because, in order to irradiate only the portion of the subject M to be imaged with X-rays, a part of the radiation irradiation unit 31 is covered with a diaphragm (not shown) that does not transmit X-rays during imaging. However, as shown in FIG. 5, in the stimulable phosphor plate 4, a region 4a irradiated with X-rays (referred to as a radiation irradiation region or an X-ray bombardment region) is not irradiated with X-rays by a diaphragm. In the region of, the corresponding pixel value becomes extremely small (peak value R shown in FIG. 4). Therefore,
When the area of the region other than the X-ray irradiation region 4a increases, the peak value R increases, and there is a problem that the average value AV is depressed even though the pixel value corresponding to the X-ray irradiation region 4a is high. .

Therefore, as a second embodiment, the first embodiment
When reading the image data of
If the histogram shown in FIG. 6 is formed by extracting only the pixel values of the area corresponding to the X-ray irradiation area 4a shown in FIG. 5, the peak values in the areas other than the X-ray irradiation area 4a (FIG. 2), the average value is stabilized, and a more accurate determination can be made by comparison with the threshold value performed in step S103 of FIG.

The X-ray irradiation area 4a can be obtained by performing image processing on the first image data, but can also be obtained by another method. FIG. 7 is a diagram illustrating a schematic configuration of a radiation image reading apparatus according to another embodiment. In the embodiment of FIG. 7, a shutter (aperture) 60 made of a member that is opaque to X-rays and having a variable opening range, and a driving device 61 for driving the shutter are provided. Information such as the position of the shutter (aperture) 60, the opening amount, the angle and the position of the X-ray irradiator 31, and the like are input to the means 62. Since the distance between the X-ray irradiator 31 and the stimulable phosphor plate 4 is input in advance to the irradiation field determination means 62, the irradiation field determination means 62 is specified by a shutter (aperture) 60 based on these. The X-ray irradiation area 4 a (FIG. 5), which is the X-ray irradiation range, is determined and transmitted to the controller 2 via the control unit 17. Based on the determined X-ray irradiation area 4a, the personal computer body 25
Can perform the above-described processing.

Although the present invention has been described with reference to the embodiments, the present invention should not be construed as being limited to the above-described embodiments, and it is needless to say that modifications and improvements can be made as appropriate. is there. For example, the image reading may be performed not three times but three or more times, and some or all of the obtained image data may be combined.

[0031]

According to the present invention, it is possible to provide a radiation image reading apparatus capable of reading a higher quality radiation image while keeping costs low.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of a radiation image reading apparatus according to an embodiment.

FIG. 2 is a flowchart illustrating a process performed by the radiation image reading apparatus according to the exemplary embodiment;

FIG. 3 is a diagram showing a state in which an excitation laser beam is scanned on a stimulable phosphor plate.

FIG. 4 is a histogram of pixel values of first image data.

FIG. 5 is a diagram showing a state in which an excitation laser beam is scanned on a stimulable phosphor plate.

FIG. 6 is a histogram of pixel values of first image data corresponding to an X-ray irradiation area.

FIG. 7 is a diagram illustrating a schematic configuration of a radiation image reading apparatus according to another embodiment.

[Explanation of symbols]

 2 Controller 3 Reading device 4 Stimulable phosphor plate 20 Photoelectric reading unit 25 Personal computer main body 31 Radiation irradiating unit

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H04N 1/04 H04N 1/04 EF term (reference) 2G083 AA03 BB04 BB05 CC10 EE03 EE10 2H013 AC04 AC06 5B047 AA17 BA02 CB05 CB09 CB12 DC20 5C072 AA01 BA10 BA11 BA15 RA06 VA01 WA03 5C076 AA11 AA12 AA31 BA01 BA06 CA10

Claims (7)

[Claims] An image is obtained by irradiating a stimulable phosphor plate on which a radiation image is recorded with excitation light to receive stimulable light emitted from the stimulable phosphor plate and converting it into image data. In the radiation image reading apparatus for reading the first image data obtained by first reading the image from the stimulable phosphor plate, by reading the image from the stimulable phosphor plate for the second and subsequent times The obtained second image data is weighted according to the magnitude of the pixel value of the predetermined area of the second image data and / or the magnitude of the pixel value of the predetermined area of the first image data. A radiation image reading apparatus that obtains image data corresponding to a radiation image by performing synthesis processing after performing the synthesis processing. 2. The radiation image reading apparatus according to claim 1, wherein the second image data is synthesized with the first image data by processing a spatial frequency component. 3. A stimulable phosphor plate on which a radiation image is recorded is irradiated with excitation light to receive stimulable light emitted from the stimulable phosphor plate and convert the image into image data. In the radiation image reading apparatus that reads the image, when it is determined that the statistical value of the pixel value of the predetermined area in the first image data obtained by first reading the image from the stimulable phosphor plate satisfies the predetermined condition An image is read again from the stimulable phosphor plate, and second image data obtained by reading an image from the stimulable phosphor plate for the second and subsequent times is combined with the first image data. A radiation image reading apparatus that acquires image data corresponding to a radiation image by performing processing. 4. The second image data according to a size of a pixel value of a predetermined area of the second image data and / or a size of a pixel value of a predetermined area of the first image data. The radiation image reading apparatus according to claim 3, wherein the weighted image data is combined with the first image data to obtain image data corresponding to the radiation image. 5. The radiation image reading apparatus according to claim 3, wherein the second image data is synthesized with the first image data by processing a spatial frequency component. apparatus. 6. The statistical value is a value obtained from an average value, a median value, or a cumulative histogram of pixel values of the predetermined area, and the predetermined condition is that the statistical value is equal to or less than a predetermined value. The radiation image reading device according to any one of claims 3 to 5, wherein 7. The radiation image reading apparatus according to claim 1, wherein the predetermined area is an area corresponding to a radiation irradiation area of the stimulable phosphor plate.