JP3185105B2 - Radiation image processing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a radiation image processing apparatus, and more particularly, to a radiation image processing apparatus suitable for performing gradation processing on a substantially line-symmetric radiation image captured by radiation such as X-rays. The present invention relates to a radiation image processing apparatus.

<Prior art> Radiation images such as X-ray images are widely used for diagnosing diseases and the like. In order to obtain such X-ray images, X-rays transmitted through a subject are applied to a phosphor layer (fluorescent screen). A so-called radiograph, which is obtained by irradiating a visible light to thereby generate a visible light and irradiating the visible light to a film using a silver salt in the same manner as a normal photograph and developing the film, has been conventionally used.

However, in recent years, a method has been devised for directly taking out an image from the phosphor layer without using a film coated with a silver salt.

As this method, the radiation transmitted through the subject is absorbed by the phosphor, and then the phosphor is excited by, for example, light or heat energy, so that the radiation energy accumulated by the absorption by the phosphor is converted into fluorescence. There is a method of emitting an image and photoelectrically converting the fluorescence to obtain an image signal.

Specifically, for example, U.S. Pat.
JP-A-5-12144 discloses a radiation image conversion method using a stimulable phosphor and using visible light or infrared light as stimulating excitation light. This method uses a radiation image conversion panel in which a stimulable phosphor layer is formed on a support, and irradiates the stimulable phosphor layer of the conversion panel with radiation transmitted through a subject.
A latent image is formed by accumulating radiation energy corresponding to the radiation transmittance of each part of the subject, and thereafter, the accumulated radiation energy is emitted by scanning the photostimulated layer with photostimulated excitation light, and this is irradiated with light. The optical signal is photoelectrically converted to obtain a radiation image signal.

The radiation image signal thus obtained may be used as it is or after being subjected to image processing, to a silver halide film, CRT
Etc. and visualized, but often digitized for computer image processing.

Further, the digitized radiation image signal is stored in an image storage device such as a semiconductor storage device, a magnetic storage device, an optical disk storage device, and a magneto-optical storage device. In some cases, it is output to a silver halide film, a CRT or the like and visualized.

Also, the silver halide film on which the radiation image is recorded is irradiated with light from a light source such as a laser or a fluorescent lamp to obtain the transmitted light of the silver halide film, and the transmitted light is photoelectrically converted to obtain a radiation image signal. There are also ways to digitize.

As described above, as a configuration of an apparatus for recording a radiation image and obtaining a digital radiation image signal from a silver halide film,
A structure in which a light beam is one-dimensionally scanned on a silver halide film, and at the same time, the silver halide film is conveyed in a direction perpendicular to the scanning direction, and transmitted light is detected by a photodetector provided on a side opposite to the light source. Or, a silver halide film on which a radiation image is recorded is attached to the side of a transparent drum containing a light source, and at the same time as the drum is rotated, an aperture for guiding transmitted light to a photodetector is rotated by the rotation axis of the drum. , And the like.

By the way, when the radiation image signal obtained as described above is reproduced, the density of the region of interest (the region including the image portion necessary for diagnosis for medical use) in the reproduced image is to be made constant and the human body In order to output shadows of structures and lesions more easily, they are subjected to image processing such as gradation processing and spatial frequency processing, and then output to a CRT or the like for visualization to be used for diagnosis.

The gradation processing is processing for determining a correspondence between an image signal level and an output density (or luminance) so that a desired gradation is obtained. The gradation processing is based on histogram information of an image signal. A device that determines gradation processing conditions (see Japanese Patent Application Laid-Open No. 63-31641) has been proposed.

In determining the gradation processing conditions disclosed in Japanese Patent Application Laid-Open No. 63-31641, a cumulative histogram, which is a cumulative frequency distribution representing the cumulative frequency (cumulative frequency) of signal values, is created as shown in FIG. For example, assuming that the image signal level when the cumulative frequency reaches 50% is the characteristic value Pc, a predetermined range + a ₁ , −a ₂ is set for both the large and small image signal levels, and this range (Pc + a
_{1 to} Pc−a ₂ ) is set as the reference image signal range.

This way, the reference image signal range is set, the input signal level (Q _max ~Q _min) a predetermined electricity to the image reproducing means corresponding to the appropriate concentration range in the visible output image (D _max ~D _min) set as signal range, as the reference image signal range _{(Pc + a 1 ~Pc-a} 2) corresponds to the predetermined electric image signal range (Q _max to Q _min), i.e., Pc-a ₂ is Q _min
As, Pc + a ₁ is the gradation processing conditions are set so as to be outputted from the image processing unit as a Q _max. The tone processing pattern between Pc−a ₂ and Pc + a ₁ is generally determined in advance by defining in advance the basic form of the nonlinear tone processing condition having the most preferable pattern for each shooting condition. reference image signal range _{(Pc + a 1 ~Pc-a} 2) is to be gradation processing on the basis of the basic type.

<Problem to be Solved by the Invention> By the way, for example, in the front photographing of the human chest, if both lungs are normal, desired gradation processing can be performed by determining the above gradation processing conditions. For example, if there is a lesion in one lung that would reduce radiation transmittance, or a pacemaker with low radiation transmittance is implanted near the heart, the frequency (frequency) pattern of signal values (statistical data ) Changes so that a large frequency appears on the lower density side (lower radiation transmittance and lower signal level) as shown in FIG. 14, the cumulative frequency becomes a predetermined value (for example, 50%) under the influence of this. The reference image signal range centered on the image signal level at the time of reaching also shifts to the low density side.

For this reason, the gradation processing condition is determined so as to process the image as a whole on the dark side (the side with a higher signal level), which corresponds to a normal lung having a high radiation transmittance and a high density side. Signal level is the highest density D
_max (the input signal exceeding Pc + a ₁ is output as Q _max ), the normal lung part is blackened as a visible image, and the radiation is transmitted. There is a problem in that the density of the bone part having a low rate is excessively processed by the gradation processing so that the noise may not be noticeable.

That is, if the gradation processing conditions are determined based on the statistical properties of the image data of the entire image, the statistics of the image data can be reduced, for example, when there is a lesion in one lung or a pacemaker in front chest imaging. If the target characteristic is different from that in the normal state, the setting of the gradation processing condition is influenced by the characteristic, and the gradation processing is inappropriately performed.

The present invention has been made in view of the above problems, and focuses on the fact that when the subject is a human body, there are many radiation images that are substantially line-symmetric, such as front images of the chest and the head. Even if there is a factor in one side of the image area that changes the statistical properties of image data such as a lesion or a pacemaker compared to the normal, based on the statistical properties of the image data of the other image area without a lesion or a pacemaker, etc. It is an object of the present invention to provide a radiographic image processing apparatus capable of determining a gradation processing condition so that an appropriate gradation processing condition can be determined without being affected by an imaging site such as a lesion or a pacemaker.

<Means for Solving the Problems> Therefore, the radiation image processing apparatus according to the present invention has the first
It is configured as shown in the figure.

In FIG. 1, the symmetry axis recognizing means recognizes the symmetry axis of a substantially line-symmetric radiation image formed corresponding to the amount of radiation transmitted through the subject.

Then, the condition determining area selecting means, based on the image data of each of the two image areas bisected by the symmetry axis recognized by the symmetry axis recognizing means, determines the area of the two image areas which does not include the abnormal part. And select the selected area,
This is an area for determining gradation processing conditions.

Further, the characteristic amount detecting means obtains the characteristic amount of the image data in the one image area selected by the condition determining area selecting means, and the gradation processing condition determining means determines the gradation processing condition based on the characteristic amount. I do.

Here, the gradation processing means performs gradation processing on the radiation image based on the gradation processing conditions determined by the gradation processing condition determination means.

<Operation> According to this configuration, the gradation processing condition is set based on the feature amount of the image data in the image region of the example that does not include the abnormal part among the two image regions divided by the symmetry axis of the substantially linearly symmetric radiation image. Even if there is an imaged part such as a lesion or a pacemaker in one of the two image areas, the gradation processing condition is determined based on the feature amount of the image data of the other normal image area. Can be determined.

Therefore, even if one of the substantially line-symmetrical radiation images includes an imaging part such as a lesion or a pacemaker, the gradation processing condition is not determined by the influence of the image data of the imaging part. Also, since the gradation processing condition is determined based on the characteristic amount of the image data of one of the two image regions that are substantially line-symmetric, the gradation processing condition is determined based on the characteristic amount of the image data of the entire image. Can be determined in substantially the same manner as in the case of determining.

<Example> An example of the present invention will be described below.

FIG. 2 showing an embodiment is a radiation image information recording and reading apparatus including a radiation image processing apparatus according to the present invention,
An example is shown in which the present invention is applied to radiation imaging of the front of the chest of a human body for medical use.

Here, the radiation source 1 is controlled by the radiation control device 2 and irradiates a radiation (generally, an X-ray) toward a subject (a human chest or the like) M. The recording and reading device 3 includes a radiation image conversion panel 4 on a surface facing the radiation source 1 with the subject M interposed therebetween. The conversion panel 4 has an energy according to a radiation transmittance distribution of the subject M with respect to an irradiation radiation amount from the radiation source 1. Is accumulated in the stimulable phosphor layer, and a latent image of the subject M is formed thereon.

The conversion panel 4 includes a stimulable phosphor layer on a support,
It is provided by vapor deposition of a stimulable phosphor or application of a stimulable phosphor coating, and the stimulable phosphor layer is shielded or covered by a protective member to prevent adverse effects and damage due to the environment.

In addition, as the stimulable phosphor material, for example,
For example, materials disclosed in Japanese Patent Application Laid-Open No. 72091/1990 or Japanese Patent Application Laid-Open No. 59-75200 are used.

A light beam generator (gas laser, solid-state laser, semiconductor laser, etc.) 5 generates a light beam whose emission intensity is controlled, and the light beam reaches a scanner 6 via various optical systems, where it is deflected. Then, the optical path is further deflected by the reflecting mirror 7 and guided to the conversion panel 4 as stimulating excitation scanning light.

The light collector 8 has a light collecting end which is an optical fiber positioned close to the conversion panel 4 on which the stimulating excitation light is scanned, and is proportional to the latent image energy from the conversion panel 4 scanned by the light beam. The photostimulable light having the light emission intensity is received. Reference numeral 9 denotes a filter that passes only light in the stimulable fluorescence wavelength region from the light introduced from the light collector 8, and the light that has passed through the filter 9 enters the photomultiplier 10 and corresponds to the incident light. The current signal is photoelectrically converted into a current signal.

The output current from the photomultiplier 10 is a current / voltage converter 11
After being converted to a voltage signal by the amplifier and amplified by the amplifier 12, the A / D
Digital data (digital radiation image signal) by converter 13
Is converted to Then, the digital data is sequentially subjected to image processing in the image processing device 14, and the image data after the image processing is transmitted to the printer 17 via the interface 16.

15 is a CPU for controlling image processing in the image processing device 14
The digital radiation image data output from the A / D converter 13 is subjected to various image processing including gradation processing (for example, frequency processing, movement, rotation, and statistical processing) in the image processing apparatus 14. Then, the data is output to the printer 17 in a form suitable for diagnosis, so that the printer 17 can obtain a hard copy.

The connection via the interface 16 is a CRT
Or a storage device (filing system) such as a semiconductor storage device.

Reference numeral 18 denotes a reading gain adjustment circuit, which adjusts the light beam intensity of the light beam generator 5 and adjusts the power supply voltage of the high voltage power supply 19 for the photomultiplier.
The gain adjustment of 10, the gain adjustment of the current / voltage converter 11 and the amplifier 12, and the adjustment of the input dynamic range of the A / D converter 13 are performed, and the reading gain of the radiation image signal is adjusted comprehensively.

The part of the image processing device 14 relating to the gradation processing according to the present invention is specifically configured as shown in FIG.

That is, in the present embodiment, the subject M is assumed to be substantially line-symmetric left and right, such as the front of the human chest and the front of the head.
The symmetric axis recognizing unit 20 as the target axis recognizing means recognizes the symmetric axis of the substantially line-symmetric radiation image.

Then, the condition determining area selecting unit 21 as the next condition determining area selecting unit uses the condition determining area selecting unit 21 to determine the condition of the gradation processing among the two image areas divided by the symmetric axis obtained by the symmetric axis recognizing unit 20. An image region is selected, and a feature amount detection unit 22 as a feature amount detection unit detects a feature amount for determining a gradation processing condition from one of the image regions selected by the condition determination region selection unit 21.

Gradation processing condition determination unit 23 as gradation processing condition determination means
Then, the gradation processing condition is determined based on the characteristic amount of one image area detected by the characteristic amount detection unit 22, and the gradation processing unit 24 as the gradation processing unit is operated in accordance with the determination. By applying gradation processing, the density of the region of interest (the region including the image part necessary for medical diagnosis) in the reproduced image of the radiation image can be made constant, and the structure of the human body and the shadow of the lesion can be output more easily. To be visualized.

Actually, the line memory for storing the original digital radiation image signal until the gradation processing condition is determined, and the line memory after the gradation processing until output to the printer 17 after the gradation processing. The image processing device 14 is provided with a line memory for storing digital radiation image signals.

The digital radiation image signal that has been subjected to gradation processing by the above configuration is sent to a printer 17 via an interface 16.
The data is output to a hard copy and the printer 17 is configured as shown in FIG. 4, for example.

In the printer 17 shown in FIG.
The digital radiation image signal read out via the buffer memory 30 is first subjected to various signal correction processes by the signal correction circuit 31 via the buffer memory 30, and then converted into an analog signal by the D / A converter 32. Then, in order to modulate the laser light according to the analog signal, the output of the D / A converter 32 is input to a modulator driving circuit 33, and the modulator driving circuit 33 adjusts the output level of the D / A converter 32. The corresponding driving voltage is output to the optical modulator.

The light modulator 34 modulates the laser light emitted from the laser light source 35 in accordance with the image signal level based on the drive voltage, and the modulated laser light is rotated by a motor (not shown). The light is reflected by the 36 polygonal reflecting surfaces and is distributed in the main scanning direction. Note that a galvanometer mirror may be used as the deflection mirror.

The reflected light from the deflecting mirror 36 passes through the fθ lens 37 and is adjusted to a constant scanning speed, and the scanning light is received by a recording medium (photosensitive material) 38 conveyed in the sub-scanning direction, so that recording is performed. Recording a two-dimensional radiographic image on the medium 38,
Thereafter, by developing the recording medium 38, a hard copy of the digital radiation image can be obtained.

Next, an image processing apparatus whose detailed configuration is shown in FIG.
The state of the gradation processing according to the present invention performed in 14 will be described.

First, the symmetry axis recognizing unit 20 obtains a symmetry axis of a digital radiographic image which is a frontal radiographic image of the chest or head of a human body and is substantially line symmetric.

Here, the term “substantially line-symmetric” means that a pattern in which a skeleton of a human body is projected is substantially line-symmetric, and the distribution of image signal values is not always exactly line-symmetric.

Specifically, as shown in FIG. 5, when the front of the human chest, which is substantially line-symmetric to the left and right, is the subject, there is a lung field with a relatively large transmitted dose on the left and right, and the vertical between the lungs. Since the radiation transmission amount (signal level) drops at the interval, the projection (or profile, averaging profile) in the horizontal direction of the image that intersects with the axis of symmetry is reduced, for example, in the vertical direction of the image that is predicted to include the lungs. A pixel row having a minimum density (signal level) in a range of 1/3 of the central part obtained by dividing the horizontal projection into three parts, for example, is set as a symmetric axis C, based on data in an area near the center. The horizontal projection is obtained based on the data of the uppermost region of the image which is predicted to include the cervical vertebra and not the lung, and the pixel row having the minimum density (signal value) may be set as the symmetry axis C. . Or, in the case of shooting the front of the human chest,
Since the image is taken such that the symmetry axis (the spine portion) is located substantially at the center of the normal image in the left-right direction, the axis that divides the image into two equal parts may be simply set as the symmetry axis C.

When the symmetry axis C is recognized by the symmetry axis recognition unit 20 in this manner, the image is divided into two right and left by the symmetry axis C. Which of the image areas to determine the gradation processing condition in the gradation processing unit 24 is selected as follows.

That is, for example, as shown in FIG. 5, a horizontal projection of the image intersecting with the symmetry axis C is obtained and the symmetry axis C is obtained.
The maximum value of the signal level on each side (excluding the snake part of radiation) max _L and max _R on both sides sandwiching. Then, an image area in which a larger signal value (larger radiation transmittance) is obtained among the respective maximum values is selected as an area for determining a gradation processing condition.

This is because, in the case of a chest radiographic image, if there is a lesion (or a foreign substance such as a pacemaker) in the lung, the amount of such a lesion decreases in the amount of radiation transmitted as compared with a normal lung, and the signal level decreases. As described above, the level of the signal maximum value (the maximum value of the amount of radiation transmission) is compared between the two image regions (the two lung fields on the left and right). It is estimated that the signal level of the projection has decreased due to the presence of a lesion or a pacemaker in the lower level lung.

If the gradation processing conditions are determined including the image data corresponding to the lesion and the pacemaker, the overall image level will be affected by the image level corresponding to the lesion and the pacemaker, and will be shifted to the low density (low radiation transmission) side. Recognition and gradation processing conditions are determined, and the high-density side (normal lung) is blackened out, and the low-density side (bone) is darkly processed and noise becomes noticeable. The gradation processing condition should not be determined based on the image area on the side where the level of the transmitted dose is low and the lesion or the pacemaker is estimated to exist among the two image areas divided by the symmetry axis C as described above. The gradation processing condition is determined based on the feature amount of the image area on the relatively high transmission amount side where it is estimated that there is no lesion or pacemaker.

In other words, it is estimated that at least one of the two image regions divided by the symmetry axis C is normal lung and has no pacemaker, and the gradation processing condition is determined based on the feature amount of the image region where the lesion exists. The determination is avoided, and the entire gradation processing condition is determined based on the feature amount of one image region that is a normal lung.

As a result, since the radiographic image is substantially line-symmetric, it is possible to perform appropriate gradation processing even on the image area on the side where a lesion or a pacemaker is predicted to exist, and the lesion or the pacemaker exists. Even if it is, the abnormal processing (low-density part; low-transmittance part) is affected and the gradation processing condition is improperly set to the high-density side, and the normal lung, which is the high-density part, is blackened by the gradation processing. In addition, a low density bone part or the like is processed at a high density so that noise is not noticeable, and visualization suitable for diagnosis can be performed by performing appropriate gradation processing.

By the way, in order to select an image area without a lesion or a pacemaker for determining the gradation processing condition from the two image areas divided by the symmetry axis C, as described above, the maximum signal in each of the two image areas is used. In addition to the method of comparing levels, as shown in FIG. 5, a threshold value of a signal for detecting a normal lung is set in advance, and a signal level exceeding the threshold value is set for each region divided by the axis of symmetry C. Counting a certain number of pixel columns (in a range indicated by a bold line in FIG. 5), and discriminating that the larger the counted number is a region including a normal lung where the signal level is higher than that of a lung including a lesion. Can also.

Further, when a histogram is obtained for each of the two regions divided by the symmetry axis C, as shown in FIG. 6, the histogram of the region including the affected lung is smaller than the histogram of the region including the normal lung. Is closer to the level of the mediastinum, the variance of the histogram is reduced, and the maximum level of the signal is also reduced, except for the level of the snake where radiation does not pass through the human body.

Therefore, a histogram is created for each of the two regions divided by the symmetry axis C as described above, and a comparison of the degree of dispersion of the two histograms or a comparison of the maximum signal level excluding the snake portion also allows the two image regions to be obtained. The region containing the normal lung can be selected.

Further, the user can select the higher signal average value (higher average transmittance) for each of the two image areas divided by the symmetry axis C as the one including the normal lung, or select the two images divided by the symmetry axis C A higher median value (median of the transmittance range) for each region may be selected as an image region including a normal lung.

Further, the comparison of the image data between the two image regions divided by the symmetry axis C according to the above-described method is performed by using a limited region including the lung field in each image region as shown in FIG. May be performed.

In order to determine a limited area including the lung field as shown in FIG. 7, for example, a projection in a lateral direction of an image orthogonal to the axis of symmetry C is obtained, and each of the projections is in a range of 1/3 from the left and right outside of the projection. The points with the minimum density are the left and right ends of the lung field. Further, a vertical projection of the image in a range sandwiched between the left and right ends of the lung field is obtained, and a point having a minimum signal level in each of an upper half and a lower half of the vertical projection is defined as an upper end and a lower end of the lung field. Set as

Note that the vertical projection may be obtained for each of two regions divided by the symmetry axis C, and the upper and lower ends of the lung fields may be set independently for each of the left and right sides.

By the way, 2 divided by the symmetry axis C as described above
As a result of comparing the image data levels of two image areas, 2
If a remarkable difference appears in one image region, the presence of a lesion or a pacemaker in one image region can be estimated, and one of the image regions, which is a normal lung, is used to determine the gradation processing condition. If both lungs are normal and there is no significant difference in signal level between the two image regions, either image region may be selected.

In order to determine the gradation processing condition, of the two image regions divided by the symmetry axis of the radiation image which is substantially line-symmetric as described above, the image region on the side which is predicted not to contain a lesion, a pacemaker, etc. When the region is selected as the region, the feature amount of the image data in the selected image region is detected in order to determine the gradation processing condition.

The feature amount of the image data is preferably a statistical amount of the image data in the selected image area. For example, the gradation processing condition is determined by using a cumulative histogram as disclosed in JP-A-63-31641. can do.

That is, based on image data in one selected image area of the two image areas divided by the symmetry axis C,
A histogram and a cumulative histogram are created as shown in FIG. 13, and the cumulative histogram is a predetermined value (for example, 50
%) As a characteristic value Pc, and a predetermined range + a ₁ , −a ₂ is taken for both the magnitude of the image signal level,
Setting this range _{(Pc + a 1 ~Pc-a} 2) as a reference image signal range. Then, this reference image signal range is made to correspond to the input signal level (Q _{max to} Q _min ) to image reproducing means such as a printer, or a predetermined value (for example, 95%) of a predetermined value (for example, 5%) of the cumulative histogram. ) Can be set as the reference image signal range.

Further, a non-linear basic gradation processing table having the most preferable gradation for each photographing condition is prepared in advance, and the reference image signal level Qdef on the table is set so that the cumulative histogram has a predetermined value (for example, 50%). Signal value Pc
By moving the table in parallel in the level direction of the input signal value so as to correspond to the above, a new table for determining the gradation processing condition can be obtained.

As a method of determining the gradation processing condition, in addition to the above-described method using the cumulative histogram, the gradation processing condition may be determined using the maximum value, the minimum value, and the average value of the image data in the selected image area. it can.

As the image data used for determining the gradation processing conditions, thinned data (for example, data for every 32 pixels) may be used from the viewpoint of shortening the calculation time and saving the memory capacity. The maximum value, the minimum value, the average value, and the cumulative frequency distribution hardly differ from those of the original image data.

The preferred density range or luminance range of the reproduced image that has been subjected to the gradation processing is different depending on the part of the image and the shooting conditions,
For example, in hard copy, the minimum density is preferably in the range of fog density of the film to (fog density + 0.3), and the maximum density is preferably in the range of 2.0 to 3.5. Also,
Particularly in a chest image, the lung field is the most important area for diagnosis, and the maximum density of the lung field is preferably in the range of 1.3 to 2.4, and particularly preferably in the range of 1.6 to 2.2. That is, it is preferable to use a smooth non-linear gradation processing table created so as to satisfy, for example, the above three conditions of the highest density, the lowest density, and the highest density in the lung field as the gradation processing conditions of the chest image.

Here, in detecting the above-described feature amount, one entire image region divided into two by the symmetry axis C as shown in FIG. 8 may be set as the target region. The feature quantity may be extracted only for a limited area (see FIG. 9) including the lung field to be obtained, or the contour of the lung field in the selected image area may be recognized as shown in FIG. Then, the feature amount may be detected only for the lung field part.

The contour recognition of the lung field can be performed as follows, for example, as disclosed in JP-A-63-240832. That is, the left and right lung field contours are, as shown in FIG.
And inner contour lines BR, BL and diaphragm contour lines CR, CL, respectively.

When recognizing the contour lines AR, AL, BR, and BL, first, profiles for one row of image data in the horizontal direction are obtained as shown in FIG. Ask for.

Next, in the image data having a value within the range of the threshold value, when the relation between a point and the preceding and following points satisfies a specific condition described later, the position of the point is determined by the contour of the lung field in the row. Record as column position.

As the specific conditions, a minimum point (for example, point a in FIG. 12; a point for obtaining the outer contour lines AR and AL) and a point with a minimum inclination (for example, point c in FIG. 12; a minimum point) are obtained. If there are no points, the outer contours AR and AL are determined), the point where the inclination is the maximum (for example, point b in FIG. 12; the point where the inner contours BR and BL are determined)
And find points that satisfy these conditions.

Further, the position on the image to be analyzed, the position of the obtained point, the signal level (density value) of the obtained point,
The slope of the value at the obtained point, the range of the used threshold value, and the like are comprehensively determined to determine which contour point or noise.

For example, if the point constitutes the outer contour line AR of the right lung field,
A point that is in the range of 1/3 to the left of the image and that satisfies such conditions as "a point that has a value equal to or less than the average value of all density data and the relationship with the preceding and following points is minimal or the slope is zero" Search for. In this way, the positions of the points constituting the respective contours of each row of the image data are obtained, and the necessary portions are combined to obtain the respective contour lines. The outline of the diaphragm is obtained by performing the same method as described above in the vertical direction (row direction) of the image, and thereby the outline of the entire lung field is obtained.

In this example, a system for obtaining a digital radiation image using a stimulable phosphor was used. However, a system for obtaining a digital radiation image signal by photoelectrically converting light transmitted through a silver halide film on which a radiation image was recorded was used. There is no limitation on the configuration for obtaining the digital radiation image signal.

Further, the radiation image signal that has been subjected to the gradation processing according to the present invention may be immediately copied into a hard copy by the printer 17 as described above, but may be reproduced on a CRT or temporarily stored in a filing system. Then, when necessary, the data may be read out and hard-copied or displayed on a CRT.

When storing the image in the filing system, the processed radiation image signal that has been subjected to the gradation processing according to the present invention may be stored, but it is determined based on the pre-processing radiation image signal and the present invention. The gradation processing conditions may be stored in pairs, and gradation processing may be performed at the time of reading.

Further, in the present embodiment, the radiographic image obtained by imaging the front of the human chest is mainly described, but a radiographic image obtained by imaging the front of the human head may be used. It is assumed that.

<Effects of the Invention> As described above, according to the present invention, for example, in a radiographic image of the front of the human chest, even if there is a lesion in one lung or a pacemaker is present, the lesion is affected by these lesions and the signal level of the pacemaker. It is possible to prevent the gradation processing condition from being inappropriately determined, and to determine the appropriate gradation processing condition so that the gradation processing can be performed. Since it can be prevented from being crushed black by the processing, there is an effect that the diagnostic performance based on the reproduced visible image can be improved for medical use.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a system block diagram showing one embodiment of the present invention, and FIG.
FIG. 4 is a system block diagram showing a detailed configuration example of the printer shown in FIG. 2, and FIG. 5 is a system block diagram showing a configuration example of a printer shown in FIG. FIG. 6 is a diagram illustrating the difference between histograms according to the presence or absence of a lesion, FIG. 7 is a diagram illustrating a method for obtaining a limited area including a lung field, FIG. FIG. 10 to FIG. 10 are diagrams each showing a region for extracting a feature amount for determining a gradation processing condition from a selected region, and FIG. 11 and FIG. 12 are diagrams for explaining how to obtain a contour of a lung field, respectively. 13 and FIG. 14 are diagrams showing how the gradation processing conditions are determined using the cumulative histogram. 14 image processing apparatus, 20 symmetry axis recognition unit 21 condition determination area selection unit 22, feature amount detection unit 23 gradation processing condition determination unit 24 gradation processing unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-42286 (JP, A) JP-A-61-231476 (JP, A) JP-A-62-44224 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G06T 1/00 290 G06T 5/00 100 H04N 5/325

Claims (1)

(57) [Claims] 1. A radiation image processing apparatus for performing gradation processing on a radiation image that is substantially symmetrical with a line formed in accordance with the amount of radiation transmitted through a subject, wherein a symmetry axis for recognizing a symmetry axis of the radiation image is provided. An axis recognizing unit, and selecting an area on the side that does not include an abnormal part from the two image areas based on image data of each of two image areas bisected by the symmetry axis recognized by the symmetry axis recognizing means. ,
Condition determining area selecting means for setting the selected area as an area for determining a gradation processing condition; and feature amount detecting means for obtaining a feature amount of image data in one of the image areas selected by the condition determining area selecting means. Means, a tone processing condition determining means for determining a tone processing condition based on the feature value obtained by the feature value detecting means, and a tone processing condition determined by the tone processing condition determining means. A radiation image processing apparatus comprising: a gradation processing unit configured to perform gradation processing on the radiation image.