JP2000030046A - Radiation image detecting and processing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a radiation image suited to diagnosing, etc., by correcting influence by the variation, etc., of a photographing condition. SOLUTION: The plural two-dimensionally arrayed detecting elements of the radiation image detecting means picks up radiation image and an image processing circuit 26 gives image processing to data DT based on an electric signal obtained by the detecting elements. The circuit 26 executes normalizing processing and at least gradation processing. The radiation image detecting means is provided with a peculiar noise characteristic and obtains normalized image data DTreg by correcting the influence of the noise characteristic by referring to a normalizing processing look-up table to transform to a desired level. In addition, plural gradation transforming curves are stored in a gradation processing look-up table to decide a gradation transformation curve to use based on information on a photographing condition, a photographing part, etc. Through the use of the decided gradation transforming curve, normalized image data DTreg is converted in gradation to obtain output image data DTout. Based on data DTout, a radiation image suited to diagnosing, etc., can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image detection processing device capable of obtaining a radiation image suitable for diagnosis or the like.

[0002]

2. Description of the Related Art Conventionally, as a method of obtaining a radiation image such as a human body X-ray image for diagnosing a disease as an image signal, a method of reading a film image and a method of using a stimulable phosphor are known.

In this method of reading a film image, a radiographic film which has been subjected to a process such as chemical development and fixing is irradiated with laser light, and the transmitted light or reflected light is subjected to an electric signal by a photoelectric element such as a photomultiplier. Is converted to obtain image data of each pixel.

In the method using a stimulable phosphor, a part of radiation energy is accumulated, and then, when irradiated with excitation light such as visible light, the stimulable phosphor emits stimulable light in accordance with the accumulated energy. Utilizing a phosphor, a stimulable phosphor sheet in which the stimulable phosphor is formed into a sheet is used to record radiation image information of a subject, and then irradiated with a laser beam or the like, and the photostimulated light is emitted by a photoelectric element to generate an electric signal. By conversion, image data of each pixel is obtained.

As described above, in the method of reading a film image and the method using a stimulable phosphor, image data is obtained by condensing transmitted light, reflected light, or stimulated luminescence, and thus obtained. A radiographic image based on image data is an image with reduced sharpness. For this reason, image processing is performed to correct a decrease in sharpness.

[0006]

By the way, image data can be obtained without condensing transmitted light, reflected light or stimulable luminescence, such as a method of reading a film image or a method using a stimulable phosphor. Read a radiation image by arranging a plurality of detection elements in a two-dimensional manner.
A radiation image reading unit using a nel detector is known. In the apparatus using the FPD, image data is generated based on the radiation dose detected by each detection element, so that a radiation image with high sharpness can be obtained.

[0007] However, in such an FPD, when the radiation dose is reduced due to a change in imaging conditions or the like, S / N
The ratio may be deteriorated, or image data proportional to the radiation dose may not be obtained, so that a good radiation image suitable for diagnosis or the like may not be obtained.

In view of the above, the present invention provides a radiation image detection processing apparatus capable of obtaining a radiation image suitable for diagnosis or the like by correcting the influence of a change in imaging conditions and the like.

[0009]

A radiation image detection processing apparatus according to the present invention captures a radiation image with a plurality of two-dimensionally arrayed detection elements and uses a radiographic image based on electric signals obtained by the plurality of detection elements. A radiation image detection processing device having: a radiation image detection unit that generates and outputs an image signal; and an image processing unit that performs image processing on the image signal output from the radiation image detection unit. Normalization processing means for performing processing for converting a signal into a normalized image signal proportional to the radiation dose or the logarithm of the radiation dose applied to the radiation image detection means and including a predetermined signal value; And a tone processing means for performing at least a process of converting a tone on the normalized image signal obtained by the means.

The image processing apparatus further includes noise characteristic storage means for storing noise characteristic information specific to the radiation image detection means, and normalizes the image signal by the normalization processing means using the noise characteristic information stored in the noise characteristic storage means. A process for converting the image signal is performed.

[0011] Further, the image processing apparatus has a photographing information storage means for storing management information about photographing, and determines image processing conditions by the image processing means using the information about photographing stored in the photographing information storage means.

The image processing means includes a region of interest setting means for setting a desired region of interest by analyzing the image signal, and at least one representative signal value based on the image signal in the set region of interest. It has a representative signal value determining means for determining, and converts the representative signal value determined by the representative signal value determining means into a normalized image signal such that the representative signal value corresponds to a predetermined signal value.

Further, there are provided a gradation conversion curve storage means for storing a plurality of gradation conversion curves and a basic gradation curve storage means for storing a plurality of basic gradation curves, and are stored in the gradation conversion curve storage means. Select one of the plurality of gradation conversion curves from the plurality of gradation conversion curves, or select any one of the plurality of basic gradation conversion curves from the plurality of basic gradation conversion curves stored in the basic gradation conversion curve storage means. A desired gradation conversion curve is created by deforming the selected basic gradation conversion curve, and a normalized image signal is generated by the gradation processing means based on the selected gradation conversion curve and the created desired gradation conversion curve. Is to be converted.

The image processing means has frequency emphasis means for performing frequency emphasis processing and dynamic range compression processing means for performing dynamic range compression processing.

In the present invention, the image signal from the radiation image detecting means is normalized based on the noise characteristic information unique to the radiation image detecting means, and the image signal is converted into a normalized image signal. . Further, by using the management information relating to shooting, selecting a gradation conversion curve or selecting one of the basic gradation conversion curves from the basic gradation conversion curves, and modifying the selected basic gradation conversion curve, A gradation conversion curve is created, and gradation processing is performed on the normalized image signal based on the selected gradation conversion curve or a desired gradation conversion curve. Further, a frequency emphasis process and a dynamic range compression process are also performed.

In normalizing the image signal, a desired region of interest is set from the image signal, and at least one representative signal value is determined based on the image signal in the region of interest. Extract a signal region corresponding to the subject part based on the histogram of the image signal of
A signal value for which a substantially minimum value, a substantially maximum value in the signal area or a cumulative histogram value in the signal area becomes a predetermined value is set as a representative signal value, and converted so that the representative signal value corresponds to the predetermined signal value. Is performed.

[0017]

Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of the radiation image detection processing device. In FIG. 1, a radiation generator 30 is controlled by a control unit 10, and radiation emitted from the radiation generator 30 passes through a subject 5 and is connected to an imaging panel mounted on a front surface of a radiation image reader 40 serving as a detection unit. Is irradiated.

FIG. 2 shows the configuration of the image pickup panel. The imaging panel 41 has a substrate having a thickness enough to obtain a predetermined rigidity. On this substrate, a detection element 412- (1,1) that outputs an electric signal in accordance with the dose of irradiated radiation.
1) to 412- (m, n) are two-dimensionally arranged. Further, the scanning lines 415-1 to 415-m and the signal lines 416-1 to 416-n are arranged, for example, to be orthogonal.

The scanning lines 415-1 to 415 of the imaging panel 41
-m is connected to the scanning drive circuit 44. The read signal RS is sent from the scan drive circuit 44 to one of the scan lines 415-1 to 415 -m (p is any one of 1 to m).
Is supplied, the electric signal SV corresponding to the dose of the radiation emitted from the detection element connected to the scanning line 415-p.
-1 to SV-n are output and supplied to the image data generation circuit 46 via the signal lines 416-1 to 416-n.

The detection element 412 may be any element that outputs an electric signal corresponding to the dose of the irradiated radiation.
For example, when a detection element is formed using a photoconductive layer in which an electron-hole pair is generated when radiation is irradiated and the resistance value changes, the amount of radiation generated in the photoconductive layer depends on the amount of radiation generated in the photoconductive layer. An amount of charge is stored in the charge storage capacitor, and the charge stored in the charge storage capacitor is supplied to the image data generation circuit 46 as an electric signal. Japanese Patent Application Laid-Open No. 6-34209 discloses an imaging panel using such a configuration.
8 can be applied. It is preferable that the photoconductive layer has a high dark resistance value, such as amorphous selenium, lead oxide, cadmium sulfide, mercuric iodide, or a photoconductive organic material (a photoconductive layer to which an X-ray absorbing compound is added). And the like, and amorphous selenium is particularly desirable.

When the detecting element 412 is formed using, for example, a scintillator or the like that generates fluorescence when irradiated with radiation, a photodiode generates an electric signal based on the intensity of the fluorescence generated by the scintillator. It may be supplied to the image data generation circuit 46.
As disclosed in Japanese Patent Application Laid-Open No. 9-90048, an imaging panel 41 using such a configuration generates X-rays by absorbing X-rays into a phosphor layer such as an intensifying screen and generates the fluorescence. Is detected by a photodetector such as a photodiode provided for each pixel. As other means for detecting fluorescence,
There is also a method using a CCD or C-MOS sensor.

In particular, in the imaging panel (FPD) of the system disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 6-342098, since the X-ray dose is directly converted into the charge amount for each pixel, the sharpness of the FPD is hardly deteriorated and the sharpness is reduced. Therefore, the effect of the X-ray image recording system and the X-ray image recording method of the present invention is large and suitable.

Further, as the imaging panel 41, FIG.
And a configuration as shown in FIG. FIG. 15 is a front view of a radiation image detector that can be used as the imaging panel 41, and shows an example in which the radiation image detector is configured by a plurality of units. The dotted line in FIG.
Although they are the lines of the grid 50 of the radiation image detector, they are not actually seen from the front because they are hidden by the protective member and the X-ray scintillator. FIG. 15 shows a row of 6 × 6 = 36 units,
The number is not limited to this.

FIG. 16 is a schematic diagram of a longitudinal section of the radiation image detector. The radiation image detector is an X-ray scintillator 5
1, a lens array 52, and an area sensor 54 corresponding to each lens 53 of the lens array 52 are arranged in this order. The X-ray scintillator 51 is protected by a protection member 55. Each lens 53 of the lens array 52 is supported by a lens support member 58, and a transparent member 56 is disposed between the X-ray scintillator 51 and the lens array 52. The area sensor 54 is supported by an area sensor support member 57.

The shapes, thicknesses, ray paths, etc. of the components of the radiation image detector are not accurate. The grating 50 does not directly touch the X-ray scintillator 51, but abuts on the transparent member 56, thereby preventing the grating 50 from hitting the X-ray scintillator 51 and damaging it. Prevents missing parts.

FIG. 16 is a schematic diagram of a longitudinal section of the radiation image detector, and shows only an example. Essential elements of the present invention are an X-ray scintillator 51, a lens array 52, and an area sensor 54. Lens array 52 and each lens 53 of the lens array 52
Are arranged in this order,
It has high spatial resolution and optical image quality, is thin and small, and is lightweight.

The X-ray scintillator 51 emits visible light when exposed to X-rays such as gadolinium oxysulfide and cesium iodide, and the X-ray scintillator 51 emits visible light when exposed to X-rays, so that the spatial resolution is high. Optical image quality.

The lens array 52 is composed of a lens group composed of a combination of two or more different lenses 53, and has a high spatial resolution, high image quality, and a small thickness. If the imaging magnification of the lens 53 is from 1 / 1.5 to 1/20, and if the imaging magnification is more than 1 / 1.5, the area sensor becomes too large and the arrangement becomes difficult.
If it is smaller than 20, the distance from the X-ray scintillator 51 to the lens becomes longer, and the thickness of the radiation image detector increases.

Further, as the area sensor 54, a CCD or C
-A clear image can be obtained by using a solid-state imaging device such as a MOS sensor.

In the image data generation circuit 46, the electric signals SV supplied based on an output control signal SC from a read control circuit 48, which will be described later, are sequentially selected and converted into digital image signals. The image data DT, which is a digital image signal, is supplied to the reading control circuit 48.

The reading control circuit 48 is connected to the control unit 10, and generates a scanning control signal RC and an output control signal SC based on the control signal CTD supplied from the control unit 10. The scan control signal RC is supplied to the scan drive circuit 44, and the readout signal RS is supplied to the scan lines 415-1 to 415-m based on the scan control signal RC. The output control signal SC is supplied to the image data generation circuit 46. In response to the scanning control signal RC and the output control signal SC from the reading control circuit 48, for example, the image pickup panel 41 causes the (m × n) detection elements 41 to operate as described above.
2, the detection element 412- (1, 1) to
Assuming that data based on the electric signal SV from 412- (m, n) is data DP (1,1) to DP (m, n), data DP (1,1),
DP (1,2), DP (1, n), DP (2,1), DP
In the order of (m, n), image data DT is generated and supplied from the image data generation circuit 46 to the reading control circuit 48. The reading control circuit 48 also performs a process of sending the image data DT to the control unit 10.

The image data DT obtained by the radiation image reader 40 is transmitted to a control unit 1 via a read control circuit 48.
0 is supplied. If the image data obtained by the radiation image reader 40 is supplied to the control unit 10 and the image data subjected to the logarithmic conversion processing is supplied, the processing of the image data in the control unit 10 can be simplified. .

Next, the configuration of the control unit 10 is shown in FIG. CP for controlling the operation of the control unit 10
A system bus 12 and an image bus 13 are connected to a U (Central Processing Unit) 11. The CPU 11 for controlling the operation of the control unit 10 includes a memory 1
The operation is controlled based on the control program stored in 4.

A display control circuit 15, a frame memory control circuit 16, an input interface 17, an output interface 18, a photographing control circuit 19, a disk control circuit 20, and the like are connected to the system bus 12 and the image bus 13.
The operation of each circuit is controlled by the CPU 11 using the system bus 12, and image data is transferred between the circuits via the image bus 13.

The frame memory control circuit 16 is connected to a frame memory 21 and a radiation image reader 40.
The image data obtained in step (1) is stored via the shooting control circuit 19 and the frame memory control circuit 16. The image data stored in the frame memory 21 is read and supplied to the display control circuit 15 and the disk control circuit 20. The frame memory 21 may store the image data supplied from the radiation image reader 40 after the CPU 11 processes the image data.

The display control circuit 15 includes an image display device 22
Is connected, and a radiographic image based on the image data supplied to the display control circuit 15 is displayed on the screen of the image display device 22. Here, when the number of display pixels of the image display device 22 is smaller than the number of pixels of the radiation image reader 40, the entire captured image can be displayed on the screen by thinning out and reading out the image data. In addition, if the image data of the area corresponding to the number of display pixels of the image display device 22 is read out, the captured image at the desired position can be displayed in detail.

When the image data is supplied from the frame memory 21 to the disk control circuit 20, for example, the image data is read continuously and the F
The data is written to the IFO memory, and then the disk device 2
3 recorded.

Further, the image data read from the frame memory 21 and the image data read from the disk device 23 are transmitted to the external device 1 via the output interface 18.
00 can also be supplied.

The image processing circuit 26 performs normalization processing, gradation processing, and irradiation field recognition processing of the image data DT supplied from the radiation image reader 40 via the imaging control circuit 19. Further, frequency emphasis processing, dynamic range compression processing, and the like may be performed. It should be noted that the image processing circuit 26 may be configured to also serve as the CPU 11 so as to perform image processing and the like.

An input device 27 such as a keyboard is connected to the input interface 17. By operating the input device 27, management information such as information for identifying the obtained image data and information on photographing is obtained. Input is performed.

As the external device 100 connected to the output interface 18, a scanning laser exposure device also called a laser imager is used. In this scanning laser exposure apparatus, the intensity of a laser beam is modulated by image data, exposed to a conventional silver halide photographic material or a thermal phenomenon silver halide photographic material, and then subjected to an appropriate development process to thereby obtain a radiation image. A hard copy is obtained.

Although the frame memory 21 stores the image data supplied from the radiation image reader 40, the frame data may be stored after the supplied image data is processed by the CPU 11. Further, the disk device 23 stores image data stored in the frame memory 21, that is, image data supplied from the radiation image reader 40 and image data obtained by processing the image data by the CPU 11 together with management information and the like. be able to.

Next, the operation will be described. When obtaining a radiation image of the subject 5, it is assumed that the subject 5 is located between the radiation generator 30 and the imaging panel 41 of the radiation image reader 40, and the radiation emitted from the radiation generator 30 is And the radiation transmitted through the subject 5 is incident on the imaging panel 41.

The control unit 10 is inputted with management information indicating the identification of the subject 5 to be photographed and information relating to the photographing using the input device 27. The input of the management information using the input device 27 is performed by operating a keyboard, using a magnetic card, a bar code, an HIS (In-Hospital Information System: information management by network), and the like. The management information includes, for example, an ID number, a name, a date of birth, a gender, an imaging date and time, an imaging site, and an imaging position (for example, which part of a human body is irradiated with radiation from which direction), an imaging method (simple imaging, imaging Photography, tomography, magnified photography, etc.),
It consists of information such as imaging conditions (tube voltage, tube current, irradiation time, use of scattered radiation removal grid, etc.).

The shooting date and time can be obtained automatically from the CPU 11 by using the clock function built in the CPU 11. The management information to be input may be only information relating to the subject to be photographed at that time. A series of management information may be input in advance, and the subject may be photographed in the input order, or the management information may be input as needed. The information may be read and used.

When the power switch of the radiation image reader 40 is turned on, the reading control circuit 48 and the scanning drive circuit 44 of the radiation image reader 40 control the imaging panel 41 based on the control signal CTD from the control unit 10. Initialization is performed. This initialization is for obtaining a correct electric signal corresponding to the radiation dose emitted from the imaging panel 41.

Image pickup panel 41 in radiation image reader 40
Is completed, irradiation of radiation from the radiation generator 30 is enabled. Here, when a switch for irradiating radiation is provided in the radiation generator 30,
When this switch is operated, the radiation is emitted from the radiation generator 30 toward the subject 5 for a predetermined time, and a signal DFS indicating the start of irradiation and a signal DFE indicating the end of irradiation are supplied to the control unit 10. You.

At this time, the radiation dose of the radiation applied to the imaging panel 41 of the radiation image reader 40 is modulated by the subject 5 because the degree of radiation absorption by the subject 5 differs. Detection element 412- (1,1) of imaging panel 41
In 412- (m, n), an electric signal based on the radiation modulated by the subject 5 is generated.

Next, in the control unit 10, the signal DF
After a predetermined time from the supply of S, for example, when the irradiation time of the radiation is about 0.1 second, a time longer than the irradiation time (for example, about 1 second) or the signal DFE
Immediately after is supplied, the control signal CTD is supplied to the reading control circuit 48 of the radiation image reader 40 so that the radiation image reader 40 starts generating the image data DT.

On the other hand, when a switch for irradiating radiation is provided in the control unit 10, when this switch is operated, an irradiation start signal CST for starting irradiation of radiation is transmitted via the imaging control circuit 19. Is supplied to the radiation generator 30 and the subject 5
Is irradiated for a predetermined time. The irradiation time is set based on, for example, management information.

Next, the control section 10 outputs a control signal C for starting the generation of image data in the radiation image reader 40 after a predetermined time has elapsed after outputting the irradiation start signal CST.
The TD is supplied to the reading control circuit 48 of the radiation image reader 40. Note that the control unit 10 supplies the radiation image reader 40 with a control signal CTD for starting the generation of image data by the radiation image reader 40 after detecting the end of radiation irradiation by the radiation generator 30. It may be a thing. In this case, generation of image data during irradiation of radiation can be prevented.

The reading control circuit 48 of the radiation image reader 40
In, the scanning control signal RC and the output control signal SC are generated based on the control signal CTD for starting the generation of the image data supplied from the control unit 10. The scan control signal RC is supplied to the scan drive circuit 44 and the output control signal SC is supplied to the image data generation circuit 46, and the image data D obtained from the image data generation circuit 46 is output.
T is supplied to the reading control circuit 48. This image data D
T is sent to the control unit 10 by the reading control circuit 48.

The image data DT supplied to the control unit 10 is stored in the frame memory 21 via the photographing control circuit 19, the frame memory control circuit 16 and the like. Using the image data stored in the frame memory 21,
The radiation image can be displayed on the image display device 22. Further, the image data stored in the frame memory 21 is processed by the image processing circuit 26 and supplied to the display control circuit 15, and the image data on which the image processing has been performed is stored in the frame memory 21. Is supplied to the display control circuit 15, the brightness, contrast, sharpness, and the like are adjusted, so that a radiation image suitable for diagnosis or the like can be displayed. Further, the image data subjected to the image processing is transferred to the external device 1.
By supplying the radiographic image to 00, a hard copy of a radiation image suitable for diagnosis or the like can be obtained.

In the image processing circuit 26, as shown in FIG. 4, in order to always obtain a stable radiation image even when the distribution of the level of the image data output from the imaging panel 41 fluctuates due to different radiation doses. Is subjected to normalization processing of the image data DT. Further, even if the level distribution of the image data fluctuates, the gradation processing is performed on the normalized image data DTreg which is the image data after the normalization processing in order to obtain a radiation image having a density and contrast suitable for diagnosis and the like. Done. Although not shown, the image processing circuit 26 performs frequency emphasis processing for controlling the sharpness of the normalized radiation image on the normalized image data DTreg, and converts the entire radiation image having a wide dynamic range into a fine structure portion of the subject. A dynamic range compression process may be performed to reduce the contrast of the image to a range that is easy to see without lowering the contrast.

Here, in the image pickup panel 41, it is known that, for example, a signal having a level indicated by a characteristic curve CA in FIG. 5A is generated and noise having a level indicated by a characteristic curve CB is generated in accordance with the radiation dose. Have been. Here, the noise includes an electric noise component and a quantum noise component, and when the radiation dose is smaller than “RT”, the noise level is determined by the electric noise component, and the radiation dose becomes “R”.
When it is larger than "T", the noise level is determined by the quantum noise component. A signal generated according to the radiation dose and noise are added, and image data is generated based on the added signal and output from the imaging panel 41.

For this reason, the image data output from the image pickup panel 41 has a level corresponding to the radiation dose as shown by the characteristic curve CC in FIG. 5B. Here, when the radiation dose is “R
Since the noise characteristics are different when the value is larger than “T” and when the value is smaller than “T”, the radiation dose is “RT”
It has different characteristics depending on whether it is larger or smaller.

As described above, since the level of image data is different between when the radiation dose is larger than "RT" and when it is smaller, the radiation dose is higher than "RT" as shown by the broken line in FIG. 5B. In order to be able to obtain image data according to the radiation dose with the same characteristics regardless of whether it is large or small,
The image data is corrected based on the noise characteristics, and the corrected image data is normalized to a desired level.

Here, if the signal VA output from the image pickup panel according to the radiation dose E is assumed to have the characteristic shown in the equation (1) in consideration of the noise characteristic, the normalized signal VB is obtained by the equation It is obtained based on equation (2) using the inverse function of (1). “A” and “b” are constants.

VA = f (logE) (1) VB = af-1 (VA) + b (2) In the image processing circuit 26, as shown in FIG. And a normalization process lookup table corresponding to the above operation are provided. As described above, the normalization lookup table corresponding to the operation of the inverse function is provided, and the image data DT is converted by referring to the normalization lookup table based on the image data DT from the radiation image reader 40. It is possible to obtain the image data in which the influence of the noise characteristic has been corrected simply and promptly without using any calculation.

In this embodiment, the normalization lookup table also serves as the noise characteristic storage means. However, a noise characteristic storage means for storing the noise characteristic is provided, and the noise characteristic is normalized by equation (2). May go.

Therefore, for example, when the distribution of the radiation dose is in the range of “Ra” to “Rb” including “RT” as shown in FIG. 6, the levels of the image data are “VAa” to “VAb”.
Is corrected and the levels “VACa” to “VACb (≒ VA
b) ".

When the influence of the noise characteristic is corrected as described above, next, a process of converting the level distribution obtained by the correction into a desired level distribution is performed.

By the way, when taking a radiographic image,
For example, to prevent radiation from being irradiated to a part not required for diagnosis, or to irradiate radiation to a part not required for diagnosis, radiation scattered in this part is incident on a part required for diagnosis. To prevent the resolution from deteriorating, a part of the subject 5 and the radiation generator 3
A radiation non-transmissive substance such as a lead plate is placed at 0, and an irradiation field stop for limiting an irradiation field of the radiation to the subject 5 is performed.

When this irradiation field aperture is performed, it is assumed that level conversion processing and subsequent gradation processing are performed using image data of the irradiation field inside area and the irradiation field outside area. Image processing of a portion required for diagnosis in the irradiation field is not properly performed.
Therefore, irradiation field recognition for discriminating the irradiation field inside area and the irradiation field outside area is performed.

In the irradiation field recognition, for example, Japanese Patent Application Laid-Open No. 63-25 / 1988
For example, as shown in FIG. 7A, a differentiation process is performed using image data on a line segment from a predetermined position P on the imaging surface toward the end of the imaging surface, using a method described in No. 9538. The differential signal Sd obtained by this differential processing is
As shown in FIG. 7B, since the signal level increases at the irradiation field edge, one signal field edge candidate point EP1 is obtained by determining the signal level of the differential signal Sd. A plurality of irradiation field edge candidate points EP1 to EPk are obtained by radially performing the process of obtaining the irradiation field edge candidate points around a predetermined position on the imaging surface. The irradiation field edge portion is obtained by connecting the edge candidate points adjacent to the plurality of irradiation field edge candidate points EP1 to EPk thus obtained by a straight line or a curve.

Further, a method disclosed in JP-A-5-7579 can be used. According to this method, when the imaging surface is divided into a plurality of small regions, in a small region outside the irradiation field where the irradiation of the radiation is blocked by the irradiation field diaphragm, the radiation dose of the radiation becomes substantially uniform, and the variance of the image data is reduced. Becomes smaller. Also, in a small area inside the irradiation field, the radiation amount is modulated by the subject, so that the variance value is higher than in the outside of the irradiation field. Further, in a small region including the irradiation field edge portion, the portion having the smallest radiation dose and the portion of the radiation dose modulated by the subject are mixed, so that the variance value is the highest.
From this, the small area including the irradiation field edge is determined based on the variance value.

Further, a method disclosed in JP-A-7-181609 can be used. In this method, the image data is rotated and moved with respect to a predetermined center of rotation, and rotated by the parallel state detection means until the boundary line of the irradiation field is parallel to the coordinate axis of the rectangular coordinates set on the image. When the state is detected, the straight-line equation calculating means calculates the straight-line equation of the boundary before rotation based on the rotation angle and the distance from the rotation center to the boundary. After that, the area of the irradiation field can be determined by determining the area surrounded by the plurality of boundary lines from the linear equation. If the irradiation field edge is a curve, the boundary point extracting means extracts, for example, one boundary point based on the image data, and extracts the next boundary point from a group of boundary candidate points around the boundary point. Similarly, by sequentially extracting the boundary points from the boundary candidate point group around the boundary point, it is possible to determine even if the irradiation field edge portion is a curve.

The irradiation field can be recognized using image data before the effect of the noise characteristic is corrected. Further, if the image data corrected for the influence of the noise characteristic is used, it is possible to accurately recognize the irradiation field since the image data is corrected.

When the irradiation field recognition is performed as described above,
The area in the recognized irradiation field is an area for determining the level distribution of the corrected image data when converting the distribution of the image data in which the influence of the noise characteristic has been corrected into the distribution of the desired level (hereinafter referred to as “the area of the irradiation field”). Region of interest ").
Determining a representative value from image data in which the influence of the noise characteristic in the region of interest has been corrected or image data in which the effect of the noise characteristic in the signal region described later has been corrected, and converting the representative value to a desired level. Thus, image data of a desired level can be obtained.

The region of interest is not limited to the case where the region of interest is equal to the region within the irradiation field. For example, since it is common to perform imaging with the most important part in performing a diagnosis as the center of the irradiation field, a region such as a circle or rectangle is set at the center of the irradiation field region and the region of interest is set as You may do it. Here, in the area such as a circle or a rectangle, the diameter of the circle or the length of one side of the rectangle is set as, for example, “１ ／ to“ １ ／ ”of the long side or the short side of the irradiation field or the diagonal line.

Further, a region of interest corresponding to a predetermined human body structure may be set in the region within the irradiation field. For example, Japanese Unexamined Patent Publication
As described in Japanese Patent No. 218578, projections in the vertical direction and the horizontal direction (cumulative values in one direction of image data) are obtained, and an anatomical region determining unit determines an area of a lung field portion from the data. The determined area is set as a region of interest. As disclosed in JP-A-5-7578, the image data of each pixel is compared with a threshold, and an identification code is added to each pixel based on the comparison result. A region is determined by performing labeling for each group of consecutive pixels, and the determined region is set as a region of interest. Next, representative values D1 and D2 are set from the image data in which the influence of the noise characteristics in the set region of interest has been corrected, and a process of converting the representative values into desired levels S1 and S2 is performed. Also,
A region for setting a representative value (hereinafter, referred to as a “signal region”) is extracted from the region of interest, and a representative value D is obtained from the image data in which the influence of the noise characteristic in the extracted signal region is corrected.
1, D2 are set.

As a method of extracting a signal region from the region of interest, a histogram of image data is created, and the signal region is extracted based on the histogram. For example, FIG. 8A shows a radiation image of a human hip joint, and a region PA is a region where irradiation field aperture is performed and radiation is not irradiated. FIG. 8B is a diagram in which irradiation field recognition is performed and a region in the recognized irradiation field is set as a region of interest. FIG. 8C shows a histogram of the image of the region of interest. The direct irradiation area PB in the area of interest shown in FIG. 8B
Is a region where the radiation is directly irradiated without transmitting through the subject, and the radiation dose is large. Therefore, the direct irradiation area PB corresponds to the area Pb having a high level of image data as shown in FIG. 8C. The radiation shielding area PC (the area where the radiation is shielded by the radiation protective equipment or the like) in the region of interest has a small radiation dose because the radiation is shielded. Therefore, the radiation shielding area PC corresponds to the area Pc where the level of the image data is low. Further, in the subject area PD in the region of interest, radiation is modulated by the subject, and the subject area PD corresponds to an area Pd between a high-level area Pb and a low-level area Pc of image data. Thus, by the histogram of the image data,
Since the subject area can be determined, the high-level area Pb and the low-level area Pc of the image data shown in FIG. 8C are removed, and the area Pd is set as the signal area.

The extraction of the signal area is described in
262141 can also be used.
In this method, a histogram of image data is divided into a plurality of small areas by an automatic threshold selection method using a discrimination criterion method or the like, and a desired image portion among the divided small areas is extracted as a signal area.

In setting the representative values D 1 and D 2, for example, a substantially minimum value and a substantially maximum value in a region of interest or an extracted signal region are used as representative values. Also, a signal value such that the cumulative histogram in the signal area becomes a predetermined value, for example, 20% and 80% is used as a representative signal value. In addition, a signal value in which the cumulative histogram in the signal area is 60% with one representative value used, for example, is used as the representative signal value. Representative value D
In the setting of 1 and D2, the use of the image data in the signal area enables the normalization process more suitable for the subject to be performed than in the case of using the image data in the area of interest.

When the representative values D1 and D2 are set as described above, the representative values D1 and D2 are set to the desired reference value S as shown in FIG.
The calculation is performed by setting the constants “a” and “b” of the equation (2) so as to be 1, S2.

As described above, the influence of the noise characteristic is corrected using the normalization lookup table, and thereafter, the setting of the region of interest and the extraction of the signal region are performed, and the representative value is set. The conversion of the image data subjected to the correction of the influence of the noise characteristic is performed so that the representative value becomes a predetermined level, and the normalization processing ends. As a result of this normalization processing, as shown in FIG.
Even if the radiation doses Ra and Rb are lower than the doses R1 and R2 at which the image data of S2 through S2 can be obtained, the desired reference value S
Since the image data of 1 to S2 can be obtained, the exposure of the subject can be reduced.

Next, as shown in FIG. 4, gradation processing is performed using the normalized image data DTreg obtained after the normalization processing is completed. In the gradation processing, for example, a gradation conversion curve as shown in FIG.
The normalized image data DTreg is converted into output image data DTout with the reference values S1, S2 of g as levels S1 ', S2'. The levels S1 'and S2' correspond to predetermined luminance or photographic density in the output image.

The gradation conversion curve is represented by the normalized image data DTre.
It is preferably a continuous function over the entire signal region of g, and its differential function is also preferably continuous.
Further, it is preferable that the sign of the differential coefficient is constant over the entire signal region.

Further, since the preferred shape of the gradation conversion curve and the levels S1 'and S2' differ depending on the photographing part, photographing position, photographing conditions, photographing method, etc., the gradation transformation curve is created for each image. Also, for example, Japanese Patent Publication 5-261
As shown in No. 38, a plurality of basic tone conversion curves are stored in advance, and one of the basic tone conversion curves is read out and rotated and translated to obtain a desired tone conversion curve. Can be easily obtained. As shown in FIG. 4, in the image processing circuit 26, a gradation processing lookup table corresponding to a plurality of basic gradation curves is provided, and the gradation processing lookup table is stored based on the normalized image data DTreg. Output image data DTou that has undergone gradation conversion by correcting the image data obtained by reference in accordance with the rotation and translation of the basic gradation conversion curve.
You can get t. In the gradation conversion processing, not only two reference values S1 and S2 but also one reference value or three or more reference values may be used.

Here, the selection of the basic gradation curve and the rotation and translation of the basic gradation curve are performed based on the photographing part, photographing position, photographing conditions, photographing method and the like. When such information is input as management information using the input device 27, by using this management information, the basic gradation curve can be easily selected and the rotation direction of the basic gradation curve can be selected. And the amount of translation can be determined. Further, the levels of the reference values S1 and S2 may be changed based on an imaging part, an imaging position, an imaging condition, and an imaging method.

Further, the selection of the basic gradation curve and the rotation or translation of the basic gradation curve may be performed based on the information on the type of the image display device and the type of the external device for outputting the image. This is because the preferable gradation may differ depending on the image output method.

Next, the frequency emphasis processing and the dynamic range compression processing will be described. In the frequency emphasizing process, for example, in order to control the sharpness by the non-sharp mask process shown in Expression (3), the function F is calculated by
3 and JP-B-62-62376.

Soua = Sorg + F (Sorg−Sus) (3) where Soua is image data after processing, Sorg is image data before frequency enhancement processing, and Sus is image data before frequency enhancement processing. This is the unsharp data obtained by the above method.

In this frequency emphasis processing, for example, F (Sor
g−Sus) is set to β × (Sorg−Sus), and β (emphasis coefficient) is changed almost linearly between the reference values S1 and S2 as shown in FIG. As shown by the solid line in FIG. 13, when low luminance is emphasized, β from the reference value S1 to the value “A” is maximized, and is minimized from the value “B” to the reference value S2.
From the value “A” to the value “B”, β changes almost linearly. When the high luminance is emphasized, β from the reference value S1 to the value “A” is minimized and the value “B”
To the reference value S2. From the value “A” to the value “B”, β changes almost linearly. It should be noted that although not shown, β of the value “A” to the value “B” is maximized when the medium luminance is emphasized. Thus, in the frequency emphasis processing, the sharpness of an arbitrary luminance portion can be controlled by the function F.

Here, the reference values S1, S2 and the values A, B
Are the reference values S1,
It is obtained by a method similar to the method of determining S2. Also,
The method of the frequency emphasis processing is not limited to the above-described unsharp mask processing, and a technique such as a multi-resolution method disclosed in JP-A-9-44645 may be used.

In the frequency emphasizing process, the frequency band to be emphasized and the degree of emphasis are determined on the basis of the photographing site, photographing position, photographing conditions, photographing method, etc., similarly to the selection of the basic gradation curve in the gradation processing. Is set.

In the dynamic range compression processing, a function G is determined by the method disclosed in Japanese Patent Publication No. 266318 in order to perform control so that the density is within a legible range by the compression processing shown in equation (4).

Stb = Sorg + G (Sus) (4) where Stb is image data after processing, Sorg is image data before dynamic range compression processing, and Su is image data before dynamic range compression processing. This is the unsharp data obtained by the above method.

Here, as shown in FIG. 14A, when the non-sharp data Sus has such a characteristic that G (Sus) increases when the level of the non-sharp data Sus becomes smaller than the level “La”, the low-density region Is high, and the image data Sorg shown in FIG. 14B is image data Stb in which the dynamic range on the low density side is compressed as shown in FIG. 14C. Further, as shown in FIG. 14D, when the non-sharp data Sus becomes smaller than the level “Lb”, as shown in FIG.
If (Sus) decreases, the density of the high-density area is determined to be high, and the image data Sorg shown in FIG. 14B has a high-density-side dynamic range compressed as shown in FIG. 12E. You. Here, the level “La”,
“Lb” is obtained by the same method as the method of determining the reference values S1 and S2 in the setting of the gradation processing conditions described above.

In the dynamic range compression processing as well, the correction frequency band and the degree of correction are set based on the imaging region, imaging position, imaging conditions, imaging method, and the like.

The image pickup panel 41 often has different characteristics such as noise characteristics. Therefore, the noise characteristic of each imaging panel 41 is stored in the noise characteristic recording unit, and the noise characteristic is read from the noise characteristic storage unit based on the information for identifying the imaging panel 41 attached to the imaging panel 41, and the noise characteristic is read out. It is preferable to perform a normalization process using the characteristic. Thereby, an optimal image can be obtained for each imaging panel 41. Of course, a normalization lookup table may be provided for each imaging panel 41.

As described above, according to the above-described embodiment,
Even if the radiation dose is different, the effect of the noise characteristics of the imaging panel is corrected to obtain image data of a desired level, and the obtained image data is subjected to gradation processing, so that it is useful for diagnosis and the like. A radiographic image with a suitable density and contrast can always be obtained stably. In addition, a radiographic image with good sharpness can be obtained by performing the frequency emphasizing process, and a radiographic image within a concentration range that is easy to view without reducing the contrast of a fine structure portion of the subject can be obtained by the dynamic range compression process. be able to.

[0093]

According to the present invention, the normalization processing is performed on the image signal from the radiation image detecting means and the gradation processing is performed on the normalized image signal obtained by the normalization processing. Thus, a radiation image having a density and contrast suitable for diagnosis or the like can always be obtained stably.
Further, since the normalization processing is performed using the noise characteristic information unique to the radiation image detecting means, a good radiation image can be obtained even if the radiation dose is different. Furthermore, since the image processing conditions are determined using the management information regarding the shooting,
Image processing according to the taken radiation image can be easily performed.

Further, the representative signal value is set based on the image signal in the region of interest or the signal region, and normalization is performed so that the representative signal value becomes a predetermined signal value. Can be improved.

Further, using the management information relating to photographing, selecting a gradation conversion curve or selecting one of the basic gradation conversion curves from the basic gradation conversion curves, and transforming the selected basic gradation conversion curve. Creates a desired gradation conversion curve, and performs gradation processing using the obtained gradation conversion curve. Therefore, gradation processing according to a captured radiographic image can be easily performed. .

Further, by performing the frequency emphasizing process and the dynamic range compressing process, it is possible to obtain a radiographic image with good sharpness and within a visible density range.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a radiation image detection processing device.

FIG. 2 is a diagram illustrating a configuration of an imaging panel.

FIG. 3 is a diagram illustrating a configuration of a control unit.

FIG. 4 is a diagram illustrating a configuration of an image processing circuit.

FIG. 5 is a diagram illustrating characteristics of the imaging panel.

FIG. 6 is a diagram for explaining correction of the influence of noise characteristics.

FIG. 7 is a diagram for explaining irradiation field recognition processing.

FIG. 8 is a diagram illustrating a method for extracting a signal region.

FIG. 9 is a diagram for explaining level conversion.

FIG. 10 is a diagram showing a normalization process.

FIG. 11 is a diagram showing gradation conversion characteristics.

FIG. 12 is a diagram illustrating a relationship between an enhancement coefficient and image data.

FIG. 13 is a diagram illustrating a relationship between an enhancement coefficient and image data.

FIG. 14 is a diagram illustrating a dynamic range compression process.

FIG. 15 is a diagram illustrating a configuration of an imaging panel.

FIG. 16 is a diagram illustrating a configuration of an imaging panel.

[Description of Signs] 10 Control unit 11 CPU 21 Frame memory 26 Image processing circuit 30 Radiation generator 40 Radiation image reader 41 Imaging panel

Claims (12)

[Claims] 1. A radiation image detecting unit that captures a radiation image with a plurality of two-dimensionally arranged detection elements, generates and outputs an image signal based on an electric signal obtained by the plurality of detection elements, An image processing unit that performs image processing on the image signal output from the radiation image detection unit, wherein the image processing unit emits the image signal to the radiation image detection unit. Normalization processing means for performing a process of converting to a normalized image signal that is proportional to the logarithm of the dose or the radiation dose, and includes a predetermined signal value, and the normalized image signal obtained by the normalization processing means On the other hand, a radiation image detection processing device having a gradation processing means for performing at least a process of converting a gradation. 2. A noise processing apparatus comprising: a noise characteristic storage unit configured to store noise characteristic information specific to a radiation image detection unit; and the normalization processing unit uses the noise characteristic information stored in the noise characteristic storage unit to generate the image. The radiation image detection processing device according to claim 1, wherein a process of converting a signal into the normalized image signal is performed. 3. An image processing apparatus according to claim 1, further comprising: a photographing information storage unit configured to store management information related to photographing, wherein the image processing unit determines an image processing condition using information related to photographing stored in the photographing information storage unit. The radiation image detection processing device according to claim 1 or 2, wherein 4. The image processing unit includes: a region of interest setting unit that sets a desired region of interest by analyzing the image signal; and at least one representative based on the image signal in the set region of interest. It has representative signal value determining means for determining a signal value, and performs conversion to a normalized image signal such that the representative signal value determined by the representative signal value determining means corresponds to the predetermined signal value. The radiation image detection processing device according to any one of claims 1 to 3. 5. The representative signal value determining means creates a histogram of an image signal in the region of interest, extracts a signal region corresponding to a subject portion from the region of interest based on the histogram, and 5. The radiation image detection processing apparatus according to claim 4, wherein one or both of the substantially minimum value and the substantially maximum value in the area are set as the representative signal value. 6. The representative signal value determination means creates a histogram of an image signal in the region of interest, extracts a signal region corresponding to a subject portion from the region of interest based on the histogram, and 5. The radiation image detection processing apparatus according to claim 4, wherein a signal value at which a cumulative histogram value within the region becomes a predetermined value is set as a representative signal value. 7. A gradation conversion curve storage means for storing a plurality of gradation conversion curves, wherein the gradation processing means selects one of the plurality of gradation conversion curves stored in the gradation conversion curve storage means. The radiation image detection processing device according to claim 1, wherein the gradation conversion curve is selected, and a process of converting the gradation based on the selected gradation conversion curve is performed. . 8. The gradation processing unit selects a gradation conversion curve from a plurality of gradation conversion curves stored in the gradation conversion curve storage unit based on management information relating to the photographing. A radiation image detection processing device according to claim 7. 9. A basic tone curve storage means for storing a plurality of basic tone curves, wherein said tone processing means includes a plurality of basic tone conversion curves stored in said basic tone conversion curve storage means. To create a desired tone conversion curve by transforming the selected basic tone conversion curve, and convert the tone based on the created tone conversion curve. The radiation image detection processing apparatus according to claim 1, wherein the apparatus performs processing. 10. The image processing apparatus according to claim 1, wherein the gradation processing unit selects a basic gradation conversion curve from a plurality of basic gradation conversion curves stored in the basic gradation conversion curve storage unit based on management information regarding the photographing. The radiation image detection processing device according to claim 9, wherein: 11. The radiographic image detection processing apparatus according to claim 1, wherein said image processing means has frequency emphasis means for performing frequency emphasis processing. 12. The radiation image detection processing apparatus according to claim 1, wherein said image processing means includes a dynamic range compression processing means for performing said dynamic range compression processing.