JP2003270742A - Radiograph read method and radiograph reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiograph read method and a radiograph reader which obtain an image of high γ and high contrast to accurately locate a radiotherapy object portion. <P>SOLUTION: In the radiograph read method, ≥100 kVp radiation energy is given to one surface of a support body through a subject, and exciting light is made to scan a radiograph conversion panel having a stimulable phosphor layer including a stimulable phosphor wherein a radiograph is stored, and stimulated phosphorescent light generated from the radiograph conversion panel is detected by the scanning to read the radiograph. The radiograph read method has an area recognition step, an image processing condition determination step, an individual difference extraction step, a correction condition determination step, and a step for subjecting the radiograph to image processing. <P>COPYRIGHT: (C)2003,JPO

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 a radiation image reading apparatus.

[0002]

2. Description of the Related Art Conventionally, X-ray photography has been used for a long time to obtain a radiation image. This method can easily obtain a fluoroscopic image in a subject, and has been widely used as an extremely effective method particularly in the field of diagnosis in medicine. However, this method has a small difference in the X-ray transmittance of each tissue in the human body, has a small contrast in the image obtained because the X-rays are scattered in the subject, and the X-rays are harmful to the human body. However, there were drawbacks such as narrow latitude and severe shooting conditions. To compensate for these drawbacks, an X-ray detector with high sensitivity and wide latitude is used to convert an X-ray image into an electric signal and perform image processing to reduce the influence on the human body and to provide a high image quality. Have been sought to get images of.

As an example of such a radiography method, the radiation transmitted through an object is absorbed and accumulated in a phosphor, and then the phosphor is excited by using a laser or the like to accumulate the phosphor. There is a method in which radiation energy is emitted as fluorescence and this fluorescence is detected and imaged.

As a concrete method, for example, in US Pat. No. 3,859,527 and JP-A-55-12144, a stimulable phosphor is used as a phosphor, and the excitation energy is selected from visible rays and infrared rays. A radiation image conversion method using electromagnetic radiation has been proposed.

This method uses a radiation image conversion panel in which a stimulable phosphor layer is formed on a support, and the stimulable phosphor layer of this radiation image conversion panel is made to absorb the radiation that has passed through an object, The radiation energy corresponding to the intensity of is accumulated, and then the stimulable phosphor layer is scanned with stimulating excitation light to extract the accumulated radiation energy as a light signal, and an image is formed according to the intensity of this light. I will get it.

This final image may be reproduced as a hard copy or may be reproduced on a picture tube such as a CRT.

The stimulable phosphor means radiation (X-ray, α
Radiation, β-rays, γ-rays, ultraviolet rays, etc.) and then excited by a certain energy such as light or heat, it exhibits stimulated emission depending on the radiation energy stored in this phosphor. Refers to a phosphor.

The radiation image conversion panel having a layer containing a stimulable phosphor is a plate (panel) having a surface of the stimulable phosphor, a drum or a flexible film. Various forms such as eggplants are collectively referred to (hereinafter simply referred to as a conversion panel).

The above method has the very practical advantage of being able to record an image over a very wide radiation exposure area as compared to a conventional radiographic system using silver salt photography. That is, it has been recognized that the exposure dose of radiation in the conversion panel and the intensity or amount of photostimulated luminescence emitted by photostimulation excitation light after the accumulation of radiation are proportional to each other over a very wide range. Even if the exposure amount changes significantly, the reading gain of the stimulated luminescence is set to an appropriate value and read by photoelectric conversion means to be converted into an electric signal, and a recording material such as a photographic light-sensitive material using this electric signal, By outputting a visible image on a display device such as a CRT, it is possible to obtain a radiation image that is not affected by variations in radiation exposure.

According to this method, the radiation image accumulated and recorded on the conversion panel is converted into an electric signal and then subjected to appropriate signal processing, and the electric signal is used to record a recording material such as a photographic light-sensitive material or a CRT. It is also possible to expect an extremely great effect that a radiation image excellent in diagnostic suitability can be obtained by outputting a visible image to a display device such as.

Incidentally, an example of the construction of a radiation element for the purpose of medical diagnosis is described in US Pat. No. 4,42,42 to Abbott et al.
5,425 and 4,425,426, Dic
Kerson U.S. Pat. No. 4,414,310, Ke
U.S. Pat. Nos. 4,803,150 and 4,900,652 to Lly et al., U.S. Pat.
252, 4423, and Research Disc
loss, Vol. 184, August 1979, It
em 18431 and the like.

In recent years, at the time of radiological diagnosis, an image is formed using an X-ray tube of low energy (range of 20 kVp to 80 kVp), and further radiation for treatment (X-ray, α-ray,
High energy (for example, 100 kVp or more) to determine the irradiation area of β rays, γ rays, electron rays, neutron rays, etc.
The X-rays are generated and the treatment position is specified from the obtained image. In the art, such an image is called a linac image (also referred to as a linac image) or a portal radiographic image.

It is indispensable to obtain the radiation image in which the irradiation area is accurately specified by eliminating the influence of the variation of the photographing conditions, and the recording state of the radiation image accumulated and recorded in the conversion panel, the part of the subject, Alternatively, it is indispensable to perform appropriate signal processing for the radiation image based on the display of a visible image for observation and interpretation of image information such as an imaging method such as simple contrast enhancement.

However, in the conventionally known radiation image reading method, the body thickness (thickness of the imaged region) of the patient as the subject is different, and the irradiation energy at the time of image pickup is different on a case-by-case basis. Since image processing or image creation is always performed under constant conditions, it cannot be said that image analysis that is effective for accurate identification of the treatment site is always performed, and in addition to linacography and portal image generation. , It is necessary to irradiate high-energy radiation as described above, but in that case, the obtained image tends to have low γ and low contrast, and as a result, it is effective to perform accurate identification of the treatment site. The current situation is that high quality images have not been obtained.

[0015]

The object of the present invention is to achieve high γ
The present invention provides a radiographic image reading method and a radiographic image reading apparatus that can obtain a high-contrast image and that is effective for accurately identifying a radiation treatment site.

[0016]

The above objects of the present invention have been achieved by the following constitutions 1-14.

1. 100 kVp on one side of the support
The above irradiation energy is applied through a subject, and the radiation image is converted into a radiation image conversion panel having a stimulable phosphor layer containing a stimulable phosphor in which a radiation image is accumulated, and the radiation image is scanned by the scanning. A radiation image reading method for reading the radiation image by detecting stimulated emission light generated from the conversion panel, comprising the steps (a) to (e).

2. Irradiation energy is 1MVp ~ 30M
Vp is Vp, The radiographic image reading method of the said 1 characterized by the above-mentioned.

3. The image processing condition determining step detects a reference signal value corresponding to a predetermined structure of the subject based on the signal distribution of the image signal, and the correction condition determining step determines the correction condition based on the reference signal value. 3. The radiation image reading method according to 1 or 2 above.

4. 4. The radiographic image reading method according to any one of 1 to 3 above, wherein a difference between reference signal values is detected as an index.

5. The image processing is gradation processing for a radiation image, and the correction condition is density or contrast of the gradation processing.
The radiographic image reading method according to item.

6. The image processing is frequency processing for a radiation image, and the correction condition is a value of an enhancement coefficient used for the frequency processing.
The radiographic image reading method according to item.

7. 7. The radiation image reading method according to any one of 1 to 6 above, wherein the image processing is a dynamic range compression processing for the radiation image, and the correction condition is a correction coefficient used for the dynamic range compression processing.

8. 100 kVp on one side of the support
The above irradiation energy is applied through a subject, and the radiation image is converted into a radiation image conversion panel having a stimulable phosphor layer containing a stimulable phosphor in which a radiation image is accumulated, and the radiation image is scanned by the scanning. In the radiation image reading device for reading the radiation image by detecting the stimulated emission light generated from the conversion panel, the means (a) to
A radiation image reading apparatus having (e).

9. Irradiation energy is 1MVp ~ 30M
9. The radiation image reading device as described in 8 above, which is Vp.

10. The image processing condition determining means detects a reference signal value corresponding to a predetermined structure of the subject based on the signal distribution of the image signal, and the correction condition determining means determines the correction condition based on the reference signal value. The radiographic image reading device described in 8 or 9 above.

11. The radiation image reading device according to any one of items 8 to 10, wherein a difference between reference signal values is detected as an index.

12. 12. The radiation image reading device according to any one of 8 to 11 above, wherein the image processing is gradation processing for the radiation image, and the correction condition is density or contrast of the gradation processing.

13. 13. The radiation image reading device according to any one of 8 to 12 above, wherein the image processing is frequency processing on the radiation image, and the correction condition is a value of an enhancement coefficient used for the frequency processing.

14. 14. The radiation image reading apparatus according to any one of 8 to 13 above, wherein the image processing is a dynamic range compression processing for the radiation image, and the correction condition is a correction coefficient used for the dynamic range compression processing. .

The present invention will be described in detail below. The present inventors, as a result of detailed examination of the various problems described above,
As described in claim 1, on one surface of the support, 10
Irradiation energy of 0 kVp or more is applied through a subject, and a radiation image conversion panel having a stimulable phosphor layer containing a stimulable phosphor on which a radiation image is accumulated is scanned with excitation light, and the scanning causes the radiation. In the radiation image reading method for reading the radiation image by detecting the stimulated emission light generated from the image conversion panel, the step (a)
According to the radiation image reading method characterized by having (a) to (e), a high γ and high contrast image can be obtained even under irradiation of a high energy ray of 100 kVp or more, and the radiation treatment site can be accurately specified. It has been found that an image reading method and a radiation image reading device can be provided.

The radiation image reading method of the present invention will be described below. << Regarding Accumulation Step of Radiation Image on Photostimulable Phosphor >> The photostimulable phosphor according to the radiographic image reading method of the present invention may be a conventionally known photostimulable phosphor, but in the present invention, A feature of the present invention is that the treatment site is imaged using high-energy radiation of 100 kVp or higher in order to accurately specify the site to be irradiated with high energy rays.

As described above, the radiographing of the treatment site is performed using high energy radiation of 100 kVp or more.
In the present application, linacography (imaging for identifying a radiation treatment site) is significant in imaging a treatment site with high-energy radiation used for radiation treatment.

The radiation used in the present invention is not particularly limited as long as it propagates energy in the form of waves or particles in a space or a substance and can apply irradiation energy of 100 kVp or more to a subject. Specific examples of radiation include X-rays, γ-rays (gamma-rays), electron beams, proton beams, and heavy particle beams.

From the viewpoint of improving the accuracy of identifying the radiation-irradiated site and effective radiation irradiation to improve the therapeutic effect, the irradiation energy according to the present invention is 100 kV.
Irradiation with high-energy radiation of p or more is essential,
High energy irradiation in the range of 1 MVp to 20 MVp is preferred.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION A radiation image reading method of the present invention and a radiation image reading apparatus of the present invention embodying the method will be described below with reference to FIGS.

FIG. 1 is a schematic diagram showing an example of a radiation image reading method of the present invention and a radiation image reading apparatus of the present invention embodying the method, and FIG. 2 is an analog / digital (A) shown in FIG. 7 is a schematic diagram showing an example of a / D) conversion unit 7 and an image processing device 8. FIG. In the description of FIG. 1, X-rays will be taken as an example of radiation.

The X-ray irradiator 1, which is a radiation source, is controlled by an X-ray controller (not shown) and irradiates the subject 2 with X-rays. The image reading device 14 includes a radiation image conversion panel 3 facing the X-ray irradiation device 1 with the subject 2 interposed therebetween.
Is equipped with. The radiation image conversion panel 3 is provided with a stimulable phosphor layer, and the stimulable phosphor layer has a transmittance distribution of X-rays that pass through the subject 2 in accordance with the irradiation X-ray dose from the X-ray irradiation device 1. It accumulates the energy that follows and forms a latent image.
The radiation image conversion panel 3 is provided with the stimulable phosphor layer on a support, and the stimulable phosphor layer is shielded or covered by a protective member to prevent adverse effects and damages from the environment. There is. Examples of the stimulable phosphor material include those disclosed in JP-A-61-272091 and 59-75.
Conventionally known materials such as those disclosed in No. 00 can be used.

The stimulable excitation light source 4 generates a visible light ray or an infrared ray whose emission intensity is controlled, and scans the light ray by a scanning method through various optical systems.
To irradiate. This irradiation causes the radiation conversion panel 3 to generate stimulable fluorescence in proportion to the accumulated energy.
The filter 5 separates the light beam from the stimulated excitation light source 4 and the stimulated fluorescence and causes only the stimulated fluorescence to enter the photoelectric converter 6, and the photoelectric converter 6 analogizes a current signal proportional to the amount of the stimulated fluorescence. / Outputs to the digital (A / D) converter 7.

The A / D converter 7 converts the input current signal into digital image data and outputs it to the image processing device 8. As a specific hardware configuration of the A / D converter 7, as shown in FIG. 2, the output voltage of the current / voltage converter 7A for converting the output current of the photoelectric converter 6 into a voltage signal is passed through the amplifier 7B. Is input to the A / D converter 7C.

Here, the amplifier 7B may be a logarithmic amplifier. The A / D converter 7C converts the analog signal into a digital signal (digital image data) and outputs it to the control circuit 7D. The control circuit 7D performs the gain adjustment of the current / voltage converter 7A and the amplifier 7B and the input dynamic range adjustment of the A / D converter, and also comprehensively adjusts the read gain of the radiation image information at a predetermined timing. The image data is transferred to the image processing device 8.

In the image processing device 8, as shown in FIG.
Area recognition means 9, image processing condition determination means 10, individual difference extraction means 11, correction condition determination means 12, correction processing means 13
And are provided. As a concrete hardware configuration of the image processing device 8, as shown in FIG. 2, a central processing unit (hereinafter, abbreviated as CPU) 21 is provided, and the CPU 21 has a confirmation monitor 22 and a display control unit 23 and an image. A configuration connected via the bus VB is used.

A frame memory 24 for storing image processing data and the like is connected to the CPU 21 via a frame memory controller 25 and an image bus VB. Also,
Enter the identification information of the subject (name, sex, date of birth, and also the information such as the thickness of the part to be imaged and the part to be imaged, and the irradiation energy of the X-rays used for imaging). A keyboard 26 and a display device 27 for displaying the input information are provided, and the keyboard 26 and the display device 27 are provided.
Are connected to the CPU 21 via an interface 28.

Further, a timing control section 29 for outputting a timing control signal is provided, and the timing control section 29 is provided.
Sends the timing control signal through the adapter 30 to the X
The radiation is output to the X-ray controller of the radiation irradiation apparatus 1 and also to the control circuit 7D. A magnetic memory 31 for recording image data is provided, and the magnetic memory 31 stores image processed image data and unprocessed image data.
It is stored by the signal from. Note that image data may be recorded using an external optical disk device or magnetic tape device as indicated by the broken line in FIG.

Reference numeral 34 is a memory for storing a control program and the like. Further, 33 is an external device (for example, the image output device 1
5, a host computer, etc.), which allows the image processing apparatus 8 to be connected to an external device. In the present invention, the CPU 21 includes at least area recognition means, image processing condition determination means, individual difference extraction means, correction condition determination means, and correction processing means as constituent elements.

<< Setting of Image Processing Conditions for Accumulated Radiation Images >> Image processing performed by the image processing means of the CPU 21 will be described below with reference to FIG. Figure 3
FIG. 4 is a schematic diagram illustrating a flow of image data processing in a central processing unit (CPU).

That is, the original radiation image data read from the stimulable phosphor layer of the radiation image conversion panel 3 by using the excitation light is shown in FIG. 2 according to the irradiation energy at the time of photographing the subject 2. Of the image processing (for example,
The region recognition of the radiation treatment site, the determination of the image processing condition of the region, the extraction of the individual difference of the photographed subject, the determination of the Hosoi condition of the determined image processing condition, and the correction process according to it) are performed.

Here, the processing program previously stored in the memory 34 is designed to include an optimized algorithm based on a huge image database in which a large number of radiation images are statistically processed in advance. Is.

Examples of such an algorithm include, for example, Japanese Patent Laid-Open Nos. 60-185944 and 61-2801.
No. 63, JP-A-2001-86409, etc. can be referred to, but in the present application, the algorithm is further improved so that an image with high γ and high contrast can be obtained.

<< Gradation Processing Method >> The gradation processing, which is one of the important parameters for image processing according to the present invention, will be described in more detail.

As described above, in the present invention, when the magnitude of the irradiation energy value to the subject 2 is determined, C
According to the processing program previously installed in the memory 34, the PU 21 performs the correction processing procedure 4 on the original image data through the area recognition procedure 44, the image processing condition determination procedure 45, the individual difference extraction procedure 46, and the correction condition determination procedure 47.
8, the image processing is performed. The gradation processing according to the present invention is also processed according to the above-described image processing flow.

The gradation processing is particularly effective for determining the optimum gradation processing condition for each image, performing the image processing, and outputting the image as an image having an appropriate gradation. In the radiation image reading method of the present invention and the radiation image reading apparatus of the present invention that embodies the method, it is preferable to perform the following automatic gradation processing, for example.

First, the obtained image data is analyzed according to the image analysis flow by the CPU shown in FIG. 3 to obtain a region of interest (ROI).
t) and the reference signal value are detected, and the gradation conversion table (L
UT) and the reference output density are set to determine gradation processing conditions, and gradation processing is performed.

The gradation processing will be described with reference to the conceptual diagram for explaining the detection of the region of interest in FIG. 4 and the histograms shown in FIGS. 5 (a) and 5 (b).

FIG. 4 is a conceptual diagram showing one mode of detection of a region of interest (simply referred to as a region) used for specifying a treatment site. In FIG. 4, first, the ROI is detected. ROI
At the time of detecting, the profile corresponding to the image data is acquired. A profile is a change in pixel value on an arbitrary line segment, which is represented by taking the position on the line segment on the horizontal axis and the pixel value on the vertical axis. Then, the horizontal profile P1 and the vertical profile P2 are scanned to obtain the minimum value, the maximum value, the inflection point, the intersection with the threshold value, etc., and based on these, R
The OI is calculated.

After the ROI is obtained, the reference signal value S is then determined by the image processing condition determining procedure 45 from the histograms obtained from the respective image data shown in FIGS. 5 (a) and 5 (b). The image processing condition determining procedure 45 statistically processes the image data of this ROI (chest region 512 in FIG. 4) to obtain a histogram H1 which is a frequency distribution of the image data.
Ask for. Then, the frequency distribution is analyzed to detect the reference signal value S (m, n). In FIG. 5, the reference signal value S
A plurality of reference signal values S (1,1) and S as (m, n)
An example in which (1, 2) is detected is shown. For the analysis of the frequency distribution, a method using a differential process, a method using an integration process, and other conventionally known methods can be applied.

In the following description, the reference signal value S (m,
Regarding the numerical value in parentheses in the notation of (n), m is an image for each shooting, that is, a section of the subject Km, and the signal value corresponding to the image F1 obtained by shooting the subject K1 is the reference signal value S.
(1, n), the signal value corresponding to the image F2 obtained by photographing the subject K2 is represented as a representative signal value S (2, n). Further, n is the division of the human body structure and is the human body structure A.
The signal value corresponding to (1) is the representative signal value S (m, 1), and the signal value corresponding to the human body structure A (2) is the representative signal value S.
It will be expressed as (m, 2).

ROI recognition and reference signal value S as described above
Is detected, the histogram is normalized based on this signal value, a gradation conversion table as shown in FIG. 5, which will be described later, is created, and gradation processing is performed based on the gradation conversion table.

<< Setting of Gradation Conversion Table >> Here, FIG.
Setting of the gradation conversion table will be described with reference to.

FIG. 6 is a schematic diagram showing an example of the setting method of the gradation conversion table. For example, as shown in FIG. 6, a pixel corresponding to the maximum signal value S2 in the treatment region specifying area and a pixel corresponding to the minimum signal value S3 in a region other than the treatment region specifying region are respectively densities D2, D3 ( For example, in the transmission density, the treatment site specific area is 2.0, and the non-treatment site specific area is 0.
The gradation conversion table is set so as to be 3).

In the image area recognition (also referred to as image area determination) for gradation processing, a predetermined minimum value as the frequency of the image data signal is set as a threshold value in advance in the algorithm of the processing program. , The identification code is given to each pixel. For example, an identification code 1 is assigned (also referred to as labeling) to pixels above the threshold, and an identification code 0 is assigned to pixels below the threshold to form a histogram.

Here, the image area recognized by the area recognition procedure 44 is a portion where the frequency of the image signal value is higher than the threshold value (specifically, a specific frequency value is set as the threshold value). On the other hand, a threshold value may be set for the maximum image signal value that can be processed in the image area. In that case, image data having an image signal value larger than the threshold value is unprocessed data.

Radiation energy irradiation with low energy (80 kVP or less) used for conventional image diagnosis forms a wide histogram as shown in FIG. 5 (a). Under the irradiation conditions of, the heavy metal sheet described below is arranged on the stimulable phosphor layer to convert the primary radiation into secondary radiation that is more easily absorbed by the stimulable phosphor layer, and Even if the apparatus is configured such that the scattered metal rays are absorbed by the heavy metal sheet, the original image data has a narrow histogram (low γ and low contrast) as shown in FIG. 5B. Only the image data shown can be obtained,
Even if such image data is processed using a conventionally known algorithm, only an image with extremely low accuracy in identifying the treatment site can be obtained, and accurate identification of the treatment site using high-energy radiation is difficult. is there.

In the present invention, image data showing a narrow histogram as shown in FIG. 5B is converted into wide data as shown in FIG. 5A, and finally high γ and high contrast are obtained. In order to obtain an image having the above, it becomes possible by the processing program according to the present invention in which a conventionally known gradation processing algorithm is incorporated with an algorithmic correction for increasing γ.

Specifically, for the original radiation image data of low γ and low contrast obtained at the time of high energy radiation irradiation, the treatment region specifying image region is determined by the region recognition procedure 44, and then the image is obtained. After performing the processing condition determining procedure 45 and the procedure 46 of extracting the individual difference of the subject (such as the thickness of the imaged region), the correction condition determining procedure 47 and the correction processing procedure 48 perform the image in the treatment region specifying image area. The data is statistically processed, and gradation processing is performed so as to have a gradient effective for specifying the treatment site even during irradiation with high energy radiation.

As the image processing according to the present invention, in addition to the gradation processing described above, an individual difference extraction procedure 46 in the case where frequency processing and dynamic range compression are applied, and a correction condition determination procedure 48 for image processing conditions Etc. are preferably performed.

<< Frequency Processing >> An example of application to frequency processing when a body trunk is imaged will be described. FIG. 7 is an example of a histogram according to the subject Km.
(A) is a histogram H corresponding to a thin subject K2
2, FIG. 7B shows an example of the histogram H3 corresponding to the fat subject K3.

With respect to the image signal, the reference signal value S (m, 1) in the low signal region showing the bone and the reference signal value in the high signal region showing the soft part are obtained by the signal value analysis such as the histogram analysis as described above. Find S (m, 2).

Next, the reference amount Sa representing the feature of the subject (patient), which is an example of the index of the present invention, is determined in the individual difference extraction procedure 46 from the plurality of reference signal values Sa as follows. First, two reference signal values S (m, 1), S
From (m, 2), using the function z = f (x, y), x = S
Assuming that (m, 1) and y = S (m, 2), the reference amount Sa representing the characteristics of the patient is calculated as in the equation (2).

Formula (2): Sa = f (S (m, 1), S (m, 2)) This function z = f (x, y) can be expressed by, for example, Formula (3) to obtain the signal distribution Indicates the histogram width. This is because a fat patient has a smaller Sa because the difference between the signal values of the bone and the soft part is smaller.

Formula (3): f (x, y) = (x-y) Therefore, this Sa serves as a guideline for representing the characteristics of the patient's physique as to whether he is fat or thin. Sa makes it possible to represent a difference in body thickness and individual differences among patients, such as the presence or absence of a fitting such as a cast. In FIGS. 7A and 7B, reference amounts Sa2 and Sa3 are shown in a histogram H2 in which a thin patient is a subject and in a histogram H3 in which a fat patient is a subject, respectively.

Next, based on the obtained reference amount Sa, the emphasis count of the frequency processing is corrected. Since the sharper the patient becomes, the sharper the image becomes due to the influence of scattered rays and the enlargement of geometrical images. Therefore, β2, which is obtained by correcting the frequency processing enhancement coefficient β1 according to Sa, is expressed as in equation (4). Ask for. This β2
The larger is, the stronger the frequency emphasis is.

Formula (4): β2 = β1 × k / Sa where k is a constant, and the calculation of Formula (4) is the setting of the correction condition of the image processing condition of the present invention, and this calculation is the correction condition determining procedure. At 47.

According to the equation (4), the emphasis coefficient β2 becomes larger as Sa representing the histogram width becomes smaller, and it becomes possible to compensate for the lowered sharpness. Therefore, sharpness can be compensated for in a fat patient whose Sa tends to be small. Moreover, since Sa becomes smaller as the patient gets fater, the degree of correction is changed according to the degree of physique, and the output becomes stable.

<< Dynamic Range Compression Processing >> In addition to frequency processing, an example of application to dynamic range compression processing in which the entire image having a wide dynamic range is contained in a density range that is easy to see without lowering the contrast of the fine structure of the subject Will be explained.

Similar to the application example to the frequency processing, the reference signal value S (m, 1) in the low signal region and the reference signal value S (m, 2) in the high signal region are obtained, and further the reference amount Sa is obtained. .

Based on the reference amount Sa thus obtained, the correction coefficient for the dynamic range compression processing is corrected.

For example, the bones near the side of the body of a thin patient such as the pelvis and the side of the lumbar spine are sharply changed by X in comparison with a patient with thick meat.
Since the amount of linear transmission changes, the bone signal distribution extends over a wide concentration range.

Therefore, β4, which is obtained by correcting the correction coefficient β3 for dynamic range compression according to the reference amount Sa, is obtained as in equation (5). The larger β is, the stronger the correction by the dynamic range compression becomes.

Equation (5): β4 = β3 × k × Sa However, k is a constant, and the calculation of Formula (5) is the setting of the correction condition of the image processing condition of the present invention, and this calculation is the correction condition determining procedure. At 47.

According to the equation (5), the correction coefficient β4 becomes larger as Sa representing the histogram width becomes larger, and it becomes possible to compress the dynamic range with a higher intensity for a wide signal distribution. Therefore, the dynamic range compression processing can be performed with a stronger intensity for a lean patient whose Sa tends to increase. Moreover, since Sa becomes large enough to make the patient thin, the degree of correction changes in accordance with the degree of physique, and the output becomes stable.

In addition, an example of application to gradation processing in chest radiography and the like will be described. Similar to the application example to frequency processing,
The reference signal value S (m, 1) in the low signal area and the reference signal value S (m, 2) in the high signal area are obtained, and further the reference amount Sa is obtained.

The gradation processing parameters are corrected based on the reference amount Sa thus obtained. Reference signal value S (m, 1) in the low signal area, reference signal value S in the high signal area
When gradation processing is performed with (m, 2) as a reference so that the density of this portion is constant, this layer is used for patients with a wide histogram such as a fat patient (small reference amount Sa). The contrast adjustment makes the contrast too high. Therefore, when Sa becomes equal to or less than the constant value k, the contrast is limited as in Expressions (6-1) and (6-2).

Expression (6-1): When k> Sa S (m, 1) ′ = S (m, 1) + (k
−Sa) × (1-a) Formula (6-2): S (m, 2) ′ = S (m, 2) − (k−Sa) × a where 0 <a <1 and Formula (6− 1) The operation of (6-2) is
This is the setting of the correction condition of the image processing condition, and this calculation is executed in the correction condition determining procedure 47.

According to the equations (6-1) and (6-2), Sa becomes smaller as the patient gets fater, so the degree of correction changes according to the degree of the physique, and the body type of the patient is changed. Depending on the situation, the output will be stable without avoiding too much contrast.

As described above, according to the image processing apparatus of the present embodiment, for example, when gradation processing is executed as image processing, it is possible to prevent excessive contrast, and when frequency processing is executed, The sharpness can be prevented from decreasing, and when performing dynamic range compression processing, it is possible to stabilize the density, for example, to stabilize the image to be output according to the image processing executed on the image data. It will be possible.

(Histogram) Here, the histogram used in the present invention will be described.

The histogram can be obtained by those skilled in the art using an algorithm described in a conventionally known document as described below.

Regarding the method for obtaining the reading condition based on this histogram, if this is subdivided, both the maximum value and the minimum value of the range required as image information are obtained from the histogram of the image signal, and the maximum value and the minimum value are obtained. A method for obtaining reading conditions so that image information within a sandwiched range can be read accurately in, for example, actual reading (Japanese Patent Laid-Open No. 60-1560).
55), only the maximum value is obtained from the above histogram, the value obtained by subtracting a predetermined value from the maximum value is set as the minimum value, and the range sandwiched between the maximum value and the minimum value is defined as the necessary image information range. Method (see Japanese Patent Laid-Open No. Sho 60-185944), only the minimum value is obtained from the histogram, and the value obtained by adding a predetermined value to the minimum value is set as the maximum value, and a range sandwiched between the minimum value and the maximum value is required. A method of setting a range of various image information (see JP-A-61-280163), a method of using a difference histogram (see JP-A-63-233658), and a method of using a cumulative histogram (JP-A-61-1).
No. 70730), a method of dividing a histogram into a plurality of small areas according to a discrimination criterion (Japanese Patent Laid-Open No. 63-262141).
No.) etc. are used to determine the range of necessary image information and the reading conditions are determined by this method.

<< Heavy Metal Sheet >> The heavy metal sheet used in the present invention will be described.

In the radiation image conversion panel according to the present invention, on the stimulable phosphor layer at the time of irradiation with high energy rays,
A heavy metal sheet may be provided on the surface opposite to one surface of the support having the stimulable phosphor layer. For example, 1
When irradiated with high-energy radiation of 00 kVp or more (also referred to as primary radiation), the heavy metal sheet absorbs the primary radiation and converts it into lower-energy secondary radiation. The stimulable phosphor layer may be designed so that the secondary radiation is absorbed by the stimulable phosphor layer.

Further, the heavy metal sheet may have a function of absorbing scattered rays generated after the primary radiation passes through the subject, and may contribute to improving the image contrast.

[0093]

According to the present invention, it is possible to provide a radiographic image reading method and a radiographic image reading apparatus that can obtain a high γ and high contrast image and that is effective for accurately specifying a radiation treatment site. It was

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a radiation image reading method of the present invention and a radiation image reading apparatus of the present invention embodying the method.

FIG. 2 is a schematic diagram showing an example of an analog / digital (A / D) converter 7 and an image processing device 8 used in the radiation image reading device of the present invention.

FIG. 3 is a schematic diagram illustrating a flow of processing of image data in a central processing unit (CPU).

FIG. 4 is a conceptual diagram showing an aspect of detection of a region of interest (also simply referred to as a region) used for specifying a treatment site.

5A and 5B are schematic diagrams showing an example of a histogram of image data in an image area.

FIG. 6 is a schematic diagram showing an example of a setting method of a gradation conversion table.

FIG. 7 shows an example of a histogram according to a subject Km.

[Explanation of symbols]

1 X-ray irradiation device 2 subject 3 Radiation image conversion panel 8 Image processing device 14 Image reader

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G06T 7/00 250 G21K 4/00 L 5L096 G21K 4/00 H04N 1/04 E H04N 1/04 A61B 6 / 00 303K F term (reference) 2G083 AA03 BB05 CC10 DD11 EE02 2H013 AC06 4C093 AA28 CA04 EB05 FF28 5B057 AA08 BA03 CA08 CA12 CB08 CB12 CE11 CH01 CH11 DC16 5C072 A01 BA07 CA02 DA09 EA00 LUA06 UA00 UA01 UA00 UA00 UA00 UA00 UA00 UA00 UA00 UA00 UA00

Claims (14)

[Claims] 1. A radiation image having a stimulable phosphor layer containing a stimulable phosphor on which radiation energy of 100 kVp or more is applied via a subject on one surface of a support. In the radiation image reading method for reading the radiation image by scanning the conversion panel with excitation light and detecting the stimulated emission light generated from the radiation image conversion panel by the scanning, the following steps (a) to (e): And a radiation image reading method. (A) an area recognition step of recognizing a specific area corresponding to a predetermined structure of the subject; (b) a signal value obtained by analyzing an image signal of the specific area has a predetermined constant density or contrast. An image processing condition determining step of determining an image processing condition so as to be reproduced, (c) an individual difference extracting step of extracting an index of individual difference of the subject based on a signal distribution of the image signal in the specific region, d) a correction condition determining step of determining a correction condition of the image processing condition determined in the image processing condition determining step based on the index, and (e) the radiation based on the image processing condition corrected by the correction condition. The process of applying image processing to an image. 2. The irradiation energy is 1 MVp to 30 MV.
The radiation image reading method according to claim 1, wherein p is p. 3. The image processing condition determining step detects a reference signal value corresponding to a predetermined structure of the subject based on the signal distribution of the image signal, and the correction condition determining step determines the correction condition based on the reference signal value. The radiation image reading method according to claim 1, wherein the radiation image reading method is determined. 4. The radiographic image reading method according to claim 1, wherein a difference between reference signal values is detected as an index. 5. The image processing is gradation processing for a radiation image, and the correction condition is density or contrast of the gradation processing.
The radiographic image reading method according to item. 6. The image processing is frequency processing for a radiation image, and the correction condition is a value of an emphasis coefficient used for the frequency processing.
The radiographic image reading method according to item. 7. The image processing is a dynamic range compression processing for a radiation image, and the correction condition is a correction coefficient used in the dynamic range compression processing. Radiographic image reading method. 8. A radiation image having a stimulable phosphor layer containing a stimulable phosphor on which radiation energy of 100 kVp or more is applied through a subject on one surface of a support. In the radiation image reading device for reading the radiation image by scanning the conversion panel with excitation light and detecting the stimulated emission light generated from the radiation image conversion panel by the scanning, the following means (a) to (e) are used. )
A radiation image reading apparatus comprising: (A) area recognition means for recognizing a specific area corresponding to a predetermined structure of the subject, (b) a signal value obtained by analyzing an image signal of the specific area has a predetermined constant density or contrast. Image processing condition determining means for determining image processing conditions so as to be reproduced, (c) individual difference extracting means for extracting an index of individual difference of the subject based on the signal distribution of the image signal in the specific region, d) correction condition determining means for determining a correction condition of the image processing condition determined by the image processing condition determining means based on the index, and (e) the radiation based on the image processing condition corrected by the correction condition. A means of performing image processing on images. 9. The irradiation energy is 1 MVp to 30 MV.
The radiation image reading apparatus according to claim 8, wherein the radiation image reading apparatus is p. 10. The image processing condition determining means detects a reference signal value corresponding to a predetermined structure of the subject based on the signal distribution of the image signal, and the correction condition determining means determines the correction condition based on the reference signal value. The radiation image reading apparatus according to claim 8 or 9, wherein the radiation image reading apparatus determines. 11. The radiographic image reading device according to claim 8, wherein a difference between reference signal values is detected as an index. 12. The radiation according to claim 8, wherein the image processing is gradation processing for the radiation image, and the correction condition is density or contrast of the gradation processing. Image reading device. 13. The radiation according to claim 8, wherein the image processing is frequency processing on the radiation image, and the correction condition is a value of an enhancement coefficient used for the frequency processing. Image reading device. 14. The image processing is a dynamic range compression processing for a radiation image, and the correction condition is a correction coefficient used for the dynamic range compression processing, according to any one of claims 8 to 13. The radiographic image reading device described.