JP2010154871A - Bone disease evaluating system, bone disease evaluating method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the accuracy of the quantification of the degree or change with the passage of time of a bone disease in an initial stage. <P>SOLUTION: A bone disease evaluating system has an X-ray source and the detector arranged in front of the irradiation direction of the X-ray source to detect the X rays emitted from the X-ray source to be transmitted through a subject including bones and is equipped with an X-ray photographing apparatus which enables phase contrast photographing executed under conditions that the distance R1 from the X-ray source to the subject is 0.1 m or above, the distance R2 from the subject to the detector is 0.3 m or above, the focal diameter D of the X-ray source is 0.2 mm or below and the average X-ray energy of the X-ray source is 23-45 keV. The bone disease evaluating system is equipped with a concerned region setting part for setting a concerned region from the image detected by the detector, a profile acquiring part for acquiring the X-ray signal intensity profile to the position within the concerned region, a frequency analyzing part applying the analysis of frequency to the X-ray signal intensity profile and an index calculating part for calculating an index showing the degree of the bone disease on the basis of the analytic result of frequency. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a bone disease evaluation system, a bone disease evaluation method, and a program.

At present, fractures caused by osteoporosis are a social problem, and early detection of osteoporosis is desired. For this reason, for example, an osteoporosis diagnostic apparatus that performs image processing for quantifying the number of trabecular structures and shows the quantification result has been developed (see, for example, Patent Document 1). In addition, wavelet analysis is performed in each direction of the X-ray image to obtain the maximum value of the wavelet analysis coefficient with a different reduction ratio for each pixel, and the bone density that relates the reduction ratio when the maximum value is calculated to the density of the trabecular bone Measurement methods and the like have also been developed (see, for example, Patent Document 2).
JP-A-9-248293 JP-A-6-269434

By the way, in the osteoporosis diagnostic apparatus and the bone density measuring method described above, the degree of osteoporosis and bone density is detected from an image of absorption contrast accompanying absorption / scattering when X-rays pass through an object. Absorption contrast images show that sharpness is insufficient for diagnosis of diseases related to bone and joints, and it is not suitable for early diagnosis before symptoms progress. For this reason, the level of disease detected on the basis of the absorption contrast image shows little difference between healthy subjects and initial patients, and further, subtle differences in symptoms cannot be detected, making it unsuitable for observation over time. It was.
Therefore, an object of the present invention is to improve the accuracy of quantification of the degree of disease in the initial stage and changes with time.

The bone disease evaluation system in the invention of claim 1 comprises:
An X-ray source that emits X-rays;
A detector that is disposed in front of the X-ray source in the irradiation direction and that detects X-rays irradiated from the X-ray source and transmitted through a subject including bone;
The distance R1 from the X-ray source to the subject is 0.1 m or more, the distance R2 from the subject to the detector is 0.3 m or more, the focal diameter D of the X-ray source is 0.2 mm or less, the X-ray An X-ray imaging apparatus capable of phase contrast imaging executed under the condition that the average X-ray energy of the source is 23 keV to 45 keV;
A region-of-interest setting unit that sets a region of interest from the image detected by the detector;
A profile acquisition unit that acquires an X-ray signal intensity profile for a position in the region of interest set by the region of interest setting unit;
A frequency analysis unit that performs frequency analysis on the X-ray signal intensity profile acquired by the profile acquisition unit;
And an index calculation unit that calculates an index representing the degree of the bone disease based on a result of frequency analysis by the frequency analysis unit.

The invention according to claim 2 is the bone disease evaluation system according to claim 1,
The frequency analysis unit performs either Fourier analysis or wavelet analysis on the X-ray signal intensity profile.

The invention according to claim 3 is the bone disease evaluation system according to claim 2,
When performing the Fourier analysis on the X-ray signal intensity profile, the frequency analysis unit multiplies the X-ray signal intensity profile by shifting a window function having a width of 10 mm or less by a predetermined length to perform a Fourier analysis. It is characterized by doing.

The invention according to claim 4 is the bone disease evaluation system according to claim 2 or 3,
The index calculation unit calculates the index based on the subtracted power spectrum after subtracting the influence of the background level from the power spectrum as the analysis result of the Fourier analysis by the frequency analysis unit. Yes.

The invention according to claim 5 is the bone disease evaluation system according to claim 2,
When the frequency analysis unit performs wavelet analysis on the X-ray signal intensity profile, the index calculation unit calculates the index using a statistical value of the wavelet coefficient obtained by the wavelet analysis. It is a feature.

The bone disease evaluation method in the invention of claim 6 comprises:
The distance R1 from the X-ray source to the subject is 0.1 m or more, the distance R2 from the subject to the detector is 0.3 m or more, the focal diameter D of the X-ray source is 0.2 mm or less, the average of the X-ray sources A region of interest is set from a phase contrast image obtained by detecting X-rays irradiated and transmitted from the X-ray source toward a subject including bone under the condition of X-ray energy of 23 keV to 45 keV. And a process of
Obtaining an X-ray signal intensity profile for a set position within the region of interest;
Performing a frequency analysis on the acquired X-ray signal intensity profile;
And a step of calculating an index representing the degree of the bone disease based on the result of the frequency analysis.

The program in the invention of claim 7 is:
The distance R1 from the X-ray source to the subject is 0.1 m or more, the distance R2 from the subject to the detector is 0.3 m or more, the focal diameter D of the X-ray source is 0.2 mm or less, the average of the X-ray sources Under the condition of X-ray energy of 23 keV to 45 keV, the X-ray source irradiates a subject including bone and is connected to a detector that detects a phase contrast image by transmitted X-ray, and based on the phase contrast image In the computer that performs arithmetic processing
The region of interest is set from the phase contrast image, the X-ray signal intensity profile for the set position in the region of interest is acquired, the frequency analysis is performed on the X-ray signal intensity profile, and the result of the frequency analysis Based on the above, an index indicating the degree of the bone disease is calculated.

  The inventor pays attention to the fact that the phase contrast image has higher sharpness than the absorption contrast image, and if frequency analysis is performed on the phase contrast image, the difference between the healthy person and the initial patient, It was found that an index that clearly shows the difference in symptoms can be obtained. For this reason, if the region of interest is set from the phase contrast image as in the present invention, and frequency analysis is performed on the X-ray signal intensity profile based on the X-ray signal intensity at each pixel position in the set region of interest, The degree of disease in the initial stage and the accuracy of quantification of changes over time can be improved.

  Hereinafter, an embodiment of a bone disease evaluation system 100 according to the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

  In FIG. 1, the structural example of the bone disease evaluation system 100 in this embodiment is shown. In this embodiment, the bone disease evaluation system 100 includes an X-ray imaging apparatus 1 that generates an image to be imaged by irradiating X-rays that are X-rays, and an image of an image generated by the X-ray imaging apparatus 1. An image processing device 30 that performs processing and the like, and an image output device 50 that displays an image or the like that has been subjected to image processing or the like by the image processing device 30 or outputs it to a film or the like. It is connected to a communication network (hereinafter simply referred to as “network”) N such as a LAN (Local Area Network) via a hub or the like.

  Note that the configuration of the bone disease evaluation system 100 is not limited to the one exemplified here. For example, the image processing device 30 and the image output device 50 are integrated and image processing and image processing are performed by one device. You may comprise so that the output (display or film output etc.) of an image may be performed.

First, the X-ray imaging apparatus 1 will be described with reference to FIGS.
2 and 3 show a configuration example of the X-ray image photographing apparatus 1. In the X-ray imaging apparatus 1, a support base 3 is provided so as to be movable up and down with respect to the support base 2. An imaging device main body 4 is supported on the support base 3 via a support shaft 5 so as to be rotatable in the CW direction and the CCW direction. The support base 3 is provided with a drive device 6 that drives its elevation and rotation of the support shaft 5. The drive device 6 includes a known drive motor (not shown). The support base 3 and the imaging device main body 4 are moved up and down according to the position of the subject H. The position of the subject H can be adjusted to a position at which the subject can take a posture in which his / her arm is placed on a subject table 14 (to be described later) and does not get tired.

  The imaging device main body 4 is provided with a holding member 7 along the vertical direction. An X-ray source 8 that emits X-rays to the subject H at a low tube voltage is attached to the upper portion of the holding member 7. A power supply unit 9 for applying a tube voltage and a tube current is connected to the X-ray source 8 via a support shaft 5, a support base 3, and an imaging apparatus main body unit 4. An aperture 10 for adjusting the X-ray irradiation field is provided at the X-ray emission port of the X-ray source 8 so as to be freely opened and closed. Further, the focal diameter of the X-ray source 8 is changed in accordance with an imaging method described later.

The X-ray source 8 is preferably a rotary anode X-ray tube. In this rotary anode X-ray tube, X-rays are generated when an electron beam emitted from the cathode collides with the anode. This is incoherent (incoherent) like natural light, and is not divergent X-rays but divergent light. If the electron beam continues to hit the place where the anode is fixed, the anode is damaged by the generation of heat. Therefore, in an X-ray tube that is usually used, the anode is rotated to prevent the anode from being shortened. An electron beam is made to collide with a surface of a certain size of the anode, and the generated X-rays are emitted toward the subject H from the plane of the certain size of the anode. The size of the plane viewed from the irradiation direction (subject direction) is called a focus. The focal diameter D (μm) is the length of one side when the focal point is a square, the long side or the short side when the focal point is a rectangle or a polygon, and the diameter when the focal point is a circle. Sure. In general, the larger the focal diameter D, the more X-rays can be irradiated.
In the present embodiment, the anode of the X-ray tube is a tungsten anode with a low low energy component that does not contribute to the formation of an X-ray image. This is usually used for general medical imaging, and enables X-ray imaging with a relatively low exposure dose.

In the X-ray imaging apparatus 1 of this embodiment, when obtaining an X-ray image of a finger, the tube voltage is adjusted and applied to the X-ray source 8 so that the average X-ray energy is within a range of 23 keV to 30 keV. To do. Here, the X-ray source 8 preferably has an intrinsic filtration of IEC 60522-1976 standard of 2.5 mm aluminum equivalent or more, and the use of a tungsten anode is used to calculate an index indicating the degree of bone joint disease. It is more preferable in obtaining a phase contrast X-ray image that can be endured. The tube voltage applied to the X-ray source 8 is preferably 25 kVp or more and 39 kVp or less. If the tube voltage is too low, the irradiated X-rays are all absorbed by the bone of the subject, and the transmitted X-ray dose necessary for measurement cannot be obtained. On the other hand, if the tube voltage is too high, the obtained object contrast becomes low, so that the measurement accuracy is deteriorated.
By setting the tube voltage in this way, it is possible to take an image with X-rays having an average X-ray energy of 23 keV to 30 keV.
The average X-ray energy is, for example, for a tungsten anode with an intrinsic filtration of 2.5 mm aluminum equivalent to IEC 60522-1976 standard, in the case of an average X-ray energy of 23 keV, the tube voltage is set to 30 kVp, and the average X-ray energy of 30 keV In this case, it can be obtained by setting 39 kVp.

  As described above, when obtaining an X-ray image of a finger, it is preferable to use an average X-ray energy within a range of 23 keV to 30 keV, but when applied to the lumbar spine or the like, a range of about 23 keV to 45 keV. Average X-ray energy is required.

Below the holding member 7 and on the lower surface of the detector holding unit 12, an X-ray dose detection unit 13 for detecting the irradiated X-ray dose by the detector 11 is provided.
The structure of the detector 11 will be described with reference to FIG. 4 by taking an FPD (flat panel detector) as an example. FIG. 4 is a perspective view of the detector 11. The detector 11 includes a housing 61 that protects the inside, and is configured to be portable as a cassette.
An imaging panel 62 that converts irradiated X-rays into electrical signals is formed in layers inside the casing 61. A light emitting layer (not shown) that emits light according to the intensity of incident X-rays is provided on the X-ray irradiation surface side of the imaging panel 62.

The light emitting layer is generally called a scintillator layer. For example, a phosphor is a main component, and based on incident X-rays, an electromagnetic wave having a wavelength of 300 nm to 800 nm, that is, an ultraviolet ray to an infrared ray centered on a visible ray. Outputs electromagnetic waves (light) over light.
An electromagnetic wave (light) output from the light emitting layer is converted into electric energy and accumulated on the surface opposite to the surface on which the X-ray is irradiated of the light emitting layer, and an image signal based on the accumulated electric energy. A signal detection unit 600 is formed in which photoelectric conversion units that perform the output are arranged in a matrix. Note that a signal output from one photoelectric conversion unit is a signal corresponding to one pixel as a minimum unit constituting the X-ray image data. The signal detection unit 600 takes out the stored electric energy as an electric signal by switching, amplifies the electric signal at a predetermined amplification rate (gain), and then converts the electric signal into digital data. In this way, X-ray image data is created by the imaging panel 62.
The detector 11 may be a detector composed of an intensifying screen, a film, a digitizer, CR, or the like other than the FPD described above.

  Between the X-ray source 8 and the detector holding unit 12, a plate-like subject table 14 that holds the subject's finger as the subject H from below is provided so that one end thereof is attached to the holding member 7. ing. The subject table 14 is connected to a position adjustment device 15 including a motor or the like that changes the position relative to the holding member 7 in order to adjust the shooting magnification (position adjustment in the height direction) during phase contrast shooting.

The subject table 14 is formed so as to protrude from the other end of the detector holding unit 12 toward the subject. Above the subject table 14, a compression plate 21 for compressing and fixing the subject H from above is provided so that one end thereof is attached to the holding member 7. The compression plate 21 is movable along the holding member 7. The movement of the compression plate 21 can be applied either automatically or manually. The end surface on the subject side of the compression plate 21 is disposed so as to slightly protrude toward the subject side from the X-ray source 8 and the detector 11 (effective image end surface) disposed in a substantially vertical direction. Therefore, it is preferable that the imaging target range (for example, the right hand) of the subject is arranged so as to be positioned closer to the holding member 7 than the compression plate 21 without causing image loss in the region of interest (imaging target range). In addition, it is preferable that the end surface of the subject table 14 has a curved shape so that an elderly subject having an average body shape can sit on the chair X and put the upper body on the subject table 14.
Further, in the present embodiment, a protector 25 is provided on the lower surface of the subject table 14 so as to extend in a substantially vertical direction so that the subject can take a shooting position without hitting his / her leg. . Thus, the subject can sit at the imaging position without sitting on the detector holding unit 12 while sitting on the chair X. Moreover, it is possible to prevent a part of the patient's body from entering the X-ray irradiation region and receiving unnecessary exposure. Note that the compression plate and the protector 25 are not essential components, and the compression plate and the protector 25 may not be used.

As shown in FIG. 5, the subject table 14 is provided with a hand holding unit 16 that holds the finger of the subject so as to cross the X-ray irradiation path. The size of the hand holding unit 16 is not particularly limited as long as the subject's fingers can be placed thereon. On the upper surface of the hand holding unit 16, a triangular magnet 17 is provided that is disposed between the thumb and the index finger while the subject puts his / her finger on the hand holding unit 16. The hand holding unit 16 is provided with photographing direction discriminating means 18 (see FIG. 6) for detecting the placement location of the triangular magnet 17 and discriminating the position of the subject's thumb as photographing direction information.
Here, the irradiation field P at the time of hand bone joint imaging is set in advance so that two phalanges sandwiching the joint can be accommodated (see FIG. 5). This is because, as will be described later, an X-ray image is acquired with high sharpness and low tube voltage phase contrast at the time of bone joint imaging, so that even a single joint image can sufficiently withstand follow-up observation This is because a value is obtained.

  As shown in FIG. 6, the photographing apparatus main body 4 includes a control device 22 including a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). An X-ray dose detection unit 13, a power supply unit 9, a drive unit 6, a position adjustment unit 15, an information supplement unit 26, an imaging direction determination unit 18, and a detector identification unit 29 are connected to the control device 22 via a bus 23. Yes. The control device 22 includes an input device 24a including a keyboard and a touch panel (not shown) for inputting photographing conditions and the like, a position adjustment switch for adjusting the position of the subject table 14, and a CRT display, a liquid crystal display, and the like. The operation device 24 having the display device 24b is connected. In addition, the imaging apparatus main body 4 may be provided with information acquisition means for acquiring patient information and the like by reading a barcode and the like.

  The ROM of the control device 22 stores a control program for controlling each part of the X-ray imaging apparatus 1 and various processing programs. It functions as an image data generation unit that performs overall control of operations of each unit of the imaging apparatus 1 to perform phase contrast imaging and generate image data of a phase contrast image.

  For example, the CPU controls the driving device 6 based on the determination result by the imaging direction determination means 18, the imaging conditions of the subject, and the like so that the imaging device body 4 matches the height of the subject. The support shaft 5 is rotated to adjust the X-ray irradiation angle. Then, the position of the subject table 14 is adjusted by the position adjusting device 15 to adjust the magnification of phase contrast imaging. Thereafter, the imaging apparatus main body unit 4 performs imaging processing, applies a tube voltage to the X-ray source 8 by the power supply unit 9 to irradiate the subject H with X-rays, and is input from the X-ray dose detection unit 13. When the X-ray dose reaches a preset X-ray dose, the power supply unit 9 stops the X-ray irradiation from the X-ray source 8. Alternatively, X-ray irradiation conditions may be set in advance, and X-rays may be irradiated under those conditions.

  As described above, the shooting direction information acquired by the shooting direction determination unit 18 and the left / right information input from the input device 24a are output to the information supplementary unit 26 via the control unit 22. In the present embodiment, patient information (photographed person information) regarding the subject H, information such as the date and time of photographing (information at the time of photographing), and the photographed subject H are obtained from the operation device 24 or information acquisition means (not shown). The part information related to the imaging part indicating which part of the patient is input is input, and the input information is output to the information supplement means 26 via the control device 22. In the case where the control device 22 has a timer function, the control device 22 automatically acquires the shooting time when shooting is performed without inputting the shooting time information again, and the shooting time is set. The information may be output to the information ancillary means 26 as shooting time information to be attached to the image data.

  The information supplementary means 26 associates these pieces of information (imaging direction information, left / right information, subject information, imaging information, part information, etc.) as supplementary information with the image data of the generated phase contrast image. ing. Note that the supplementary information attached to the image data by the information supplementary means 26 is not limited to this. For example, patient (photographed person) ID information and the like may be attached. Moreover, the information supplementary means 26 is not limited to supplementing all the information exemplified here, and any of these pieces of information may be supplemented.

  The detector identification unit 29 is built in the detector holding unit 12, and the detector 11 set in the detector holding unit 12 is for normal imaging, phase contrast imaging, or high magnification. It is used to identify whether it is for phase contrast photography. Specifically, the detector identifying unit 29 identifies by reading an identification mark (uneven portion) provided on the housing or the like of the detector 11, a conduction unit, an RFID, a barcode, and the like. Then, the detector identifying unit 29 determines, for example, whether or not it is suitable for X-ray imaging to be performed in the future as compared with the imaging conditions input from the operation device 24, and the identification result is transmitted to the control device. 22 for output. If the identification result is incompatible, the control device 22 controls the display device 24b to display a warning. That is, in this embodiment, the notification unit according to the present invention is the display device 24b. Note that the notification unit may be an audible notification instead of a visual notification.

  In addition, the control device 22 controls each unit so that normal imaging, phase contrast imaging, and high magnification phase contrast imaging are executed in response to an imaging switching instruction to the input device 24a.

Here, normal photographing is a photographing condition in which the subject H is brought into close contact with the detector 11, which is generally performed. In this case, the control device 22 sets the compatible detector to “normal imaging” so that the detector 11 for normal imaging is mounted.
In phase contrast imaging for imaging a wide range of hands, the focal diameter D of the X-ray source 8 is 0 so that phase contrast imaging is executed with an enlargement factor M described later corresponding to 1.5 to 3 times. 0.1 mm, the average X-ray energy is 26 keV. Further, in the phase contrast imaging, the ratio of the signal value output from the detector 11 to the X-ray dose (dose) irradiated to the detector 11 is set to be moderately higher than in the normal imaging. . This is because, for example, the distance between the X-ray tube and the detector is increased, and the average X-ray energy is decreased, so that the X-ray dose reaching the detector 11 is decreased.

  In order to increase the ratio of the signal value output from the detector 11 to the irradiated X-ray dose, the highly sensitive detector 11 is selected and attached to the detector holding unit 12 or detected. A method of increasing the amplification ratio (gain) of the signal output from the device 11 or combining them can be considered. In order to increase the sensitivity of the detector 11, for example, the stimulable phosphor sheet accommodated in the detector 11 or the light emitting layer used for the imaging panel 62 emits light with high luminance even at a low X-ray dose. Make things. In order to increase the gain, for example, the amplification ratio of the electric signal in the signal detection unit 600 is increased, or the photostimulable phosphor sheet irradiated with X-rays is read to obtain the X-ray image data. In the output reading device, the amplification ratio of the electrical signal read from the photostimulable phosphor sheet is increased. Further, the ratio of amplifying the X-ray image data output from the detector 11 or the reading device may be increased. In the present embodiment, the control device 22 sets the suitable detector to “for phase contrast imaging” so that the detector 11 for phase contrast imaging having higher sensitivity and higher gain than the detector 11 for normal imaging is mounted. It is said. This phase contrast imaging is applied to quantitative diagnosis of osteoporosis. On the other hand, in high-magnification phase-contrast imaging applied in quantitative bone and joint deformation diagnosis for rheumatic diseases, phase-contrast imaging is performed with the magnification factor M corresponding to 3 to 10 times. The focal diameter D of the X-ray source 8 is 0.05 mm, and the average X-ray energy is 23 keV. Furthermore, in high magnification phase contrast imaging, both sensitivity and gain are higher than in phase contrast imaging. That is, the control device 22 sets the compatible detector to “for high magnification phase contrast imaging” so that the detector 11 for high magnification phase contrast imaging is mounted. This is because in high magnification phase contrast imaging, the subject H and the detector 11 are separated from each other than phase contrast imaging, and the average X-ray energy is low.

  Next, a phase contrast imaging method will be described. FIG. 7 is a diagram for explaining the outline of phase contrast imaging. As shown in FIG. 7, in the case of a normal photographing method, the subject H is disposed at a position where the detector 11 is in contact with the subject H (contact photographing position in FIG. 7). In this case, the X-ray image (latent image) recorded in the detector 11 is substantially the same size as the life size (which means the same size as the subject H).

  On the other hand, phase contrast imaging provides a distance between the subject H and the detector 11, and X-rays expanded with respect to the life size by X-rays emitted from the X-ray source 8 in a cone beam shape. A latent image of an image (hereinafter referred to as an enlarged image) is detected by the detector 11.

Here, the enlargement ratio M with respect to the life size of the enlarged image is determined such that the distance from the focal point a of the X-ray source 8 to the subject H is R1, the distance from the subject H to the detector 11 is R2, and from the focal point a of the X-ray source 8. If the distance to the detector 11 is L (L = R1 + R2), it can be obtained by the following equation (1).
M = L / R1 (1)

In the phase contrast enlarged image, as shown in FIG. 8, the X-ray refracted by passing through the edge of the subject H overlaps on the detector 11 with the X-ray that passes through the subject H without passing through the subject H. X-ray intensity increases. On the other hand, a phenomenon occurs in which the X-ray intensity is weakened in the portion inside the edge of the subject H by the amount of the refracted X-rays. Therefore, an edge emphasis action (also referred to as an edge effect) in which the X-ray intensity difference spreads at the border of the subject H works, and an X-ray image with high visibility in which the border portion is sharply depicted can be obtained. .
Specifically, the distances R1 and R2 are in the range of 0.1 (m) ≦ R1, 0.3 (m) ≦ R2, and the focal diameter D is in the range of D ≦ 0.2 (mm). desirable. Further, in consideration of the size of a general photographing room, the distances R1, R2, and L are set to 0.1 (m) ≦ R1 ≦ 2.0 (m) and 0.3 (m) ≦ R2 ≦ 2.0. (M), 0.8 (m) ≦ L ≦ 3.0 (m), the focal diameter D is in the range of 0.005 (mm) ≦ D ≦ 0.2 (mm), and the enlargement ratio M is The range of 1.5 ≦ M ≦ 10 is preferable.
As the enlargement ratio M is higher, finer image information can be obtained, and the accuracy of the quantitative result is also higher. On the other hand, an X-ray tube with a smaller focal diameter is required for high-magnification imaging, but because the output is low and the imaging time is long, blurring due to the movement of the subject tends to occur, and the sharpness of the image quality is impaired. Therefore, the above range is optimal in reality because highly accurate analysis cannot be performed.

  Next, the image processing apparatus 30 in the present embodiment will be described with reference to FIG.

  The image processing apparatus 30 according to the present invention performs image processing on the data of the X-ray image generated by the X-ray imaging apparatus 1 to generate an image suitable for diagnosis. As shown in FIG. 9, the image processing apparatus 30 includes a control unit 31, a storage unit 32, an input unit 33, a communication unit 34, an image processing unit 35, a region of interest setting unit 37, an index calculation unit 38, a direction determination unit 39, A profile acquisition unit 40, a frequency analysis unit 41, and the like are provided, and these units are connected to each other via a bus 36.

  The control unit 31 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and the like (none of which are shown). Alternatively, according to various programs stored in the storage unit 32, control operations are sent to the respective units to centrally control the overall operation of the image processing apparatus 30, and various processes such as an image extraction process to be described later are executed. Yes. Note that the image processing unit 35, the region of interest setting unit 37, and the direction determination unit 39 also operate in accordance with various programs in the same manner as the control unit 31.

  The storage unit 32 includes a magnetic or optical storage medium such as an HDD (Hard Disc Drive) or an optical disk, or a storage medium (not shown) such as a semiconductor memory, which is fixed or detachable, and includes an image processing program and the like. In addition to the various programs related to 30, various data used when executing these processing programs are stored.

  In the present embodiment, the storage unit 32 stores image data of an X-ray image captured by the X-ray image capturing apparatus 1 and sent to the image processing apparatus 30. In the present embodiment, as described above, the image data of the X-ray image is captured by the information supplementary means 26 of the X-ray image photographing apparatus 1 by the photographing direction information, left-right information, subject information, photographing information, and part information. And the like are sent to the image processing apparatus 30 as supplementary information, and the storage unit 32 stores these pieces of information attached to the image data.

The storage unit 32 stores the evaluation reference value of the index (calculated index) calculated by the index calculation unit 38, and the control unit 31 compares the calculated index with the evaluation reference value, thereby calculating the calculated index. Evaluation is to be made.
The storage unit 32 stores a shape list of each bone.
Further, the storage unit 32 stores the patient identification information in association with the calculated index.

  The input unit 33 includes, for example, a keyboard having cursor keys, numeric input keys, and various function keys (not shown), and a pointing device such as a mouse, and can input image processing conditions and the like. . The input unit 33 outputs an instruction signal input by a key operation or a mouse operation on the keyboard to the control unit 31.

  The communication unit 34 includes a network interface and the like, and transmits and receives data to and from external devices such as the X-ray image capturing apparatus 1 and the image output apparatus 50 connected to the network N via a switching hub. That is, the communication unit 34 receives the image data of the X-ray image generated by the X-ray imaging apparatus 1 through the network N, and appropriately transmits the image processed image to an external device such as the image output device 50. Image data is transmitted.

  The direction determination unit 39 selects a bone to be evaluated from each bone in the phase contrast image detected by the detector 11, and determines the vertical and horizontal directions of the bone. As shown in FIG. 10, when the phase contrast image G1 of the hand is acquired, the direction determination unit 39 recognizes the shape of each bone in the image. As this recognition method, for example, there is a method of recognizing a shape by following a bone edge by discriminating a bone portion and a meat portion from an X-ray signal intensity profile. After the shape recognition, the recognized shape is compared with the shape list of each bone in the storage unit 32, and the type of each bone in the image is specified. When the specification of the shape is completed, the direction determination unit 39 selects a bone to be evaluated (a bone (such as the rib B1) in which an osteoporosis symptom is likely to appear). Thereafter, the direction determination unit 39 determines the vertical and horizontal directions of the rib B1 in the phase contrast image based on the rib shape list in the storage unit 32. Specifically, as shown in FIG. 11, the rib B2 in the shape list has a central axis along the longitudinal direction as the vertical direction T1, and a direction orthogonal to the vertical direction T1 as the horizontal direction T2. Then, the direction determination unit 39 detects the inclination of the rib B1 in the image and the rib B2 in the shape list, and corrects the vertical and horizontal directions of the rib B2 in the shape list based on the inclination. Thus, the vertical and horizontal directions of the rib B1 in the image are determined.

The region-of-interest setting unit 37 sets a region for calculating an index from the phase contrast image of the rib B1 whose vertical and horizontal directions are specified by the direction determination unit 39. There are various methods of setting the region of interest. For example, the region of interest can be set by specifying a rectangular frame using the input unit 33, or can be automatically set by performing image analysis on the X-ray image. In the case of automatic setting, for example, as shown in FIG. 12, a position (line L1) below a first predetermined distance (for example, 10 mm) from the apex P1 of the rib B1 in the phase contrast image is determined, and from the apex P1 A point on the inner side by a second predetermined distance (for example, 5 mm) from the point intersected with the line L2 drawn in the vertical direction is set as the center point P2 of the region of interest R. A square having a predetermined side length (for example, 1 cm) around the center point P2 is determined as the region of interest R. Here, the pair of opposite sides of the region of interest R are parallel to the vertical direction or the horizontal direction.
The first predetermined distance, the second predetermined distance, and the predetermined side length are values determined by various experiments, simulations, and the like.

  The profile acquisition unit 40 has an X-ray signal intensity profile based on the X-ray signal intensity at each pixel position in the vertical direction within the region of interest R set by the region of interest setting unit 37, and an X-ray signal at each pixel position in the horizontal direction. An X-ray signal intensity profile based on the intensity is acquired. Specifically, as shown in FIG. 13, the profile acquisition unit 40 acquires X-ray signal intensity profiles in the vertical and horizontal directions based on the X-ray signal intensity at each pixel position in the region of interest R in the phase contrast image. . A plurality of X-ray signal intensity profiles in the vertical direction and X-ray signal intensity profiles in the horizontal direction are acquired from the region of interest R at equal intervals K. For example, the graph shown in FIG. 14 is an X-ray signal intensity profile for a healthy person, and the graph shown in FIG. 15 is an X-ray signal intensity profile for a bone disease patient. The imaging conditions of the phase contrast image obtained to acquire the X-ray signal intensity profiles of FIGS. 14 and 15 are R1 = 0.65 m, R2 = 0.49 m, L = 1.14 m, and the enlargement ratio. M = 1.75 times, focal diameter D = 0.1 mm, average X-ray energy E = 25 keV.

  In the present embodiment, one line of the actually measured X-ray signal intensity profile is used as an X-ray signal intensity profile for one line when performing frequency analysis described later. An X-ray signal intensity profile for one line subjected to frequency analysis may be used for the average value of the X-ray signal intensity profiles. When averaged in this way, frequency analysis can be performed with an X-ray signal intensity profile with reduced noise, and calculation accuracy can be further improved. Even in this case, it is preferable to use a plurality of averaged X-ray signal intensity profiles.

The frequency analysis unit 41 performs Fourier analysis as frequency analysis on the X-ray signal intensity profile acquired by the profile acquisition unit 40. Specifically, when the frequency analysis unit 41 performs Fourier analysis on the X-ray signal intensity profile, for example, a window function having a width of, for example, 256 pixels (10 mm or less) is applied to the X-ray signal intensity profile. Multiply by shifting and perform Fourier analysis. The width of 256 pixels corresponds to 4 to 5 trabeculae. When the window function is about the width, a power spectrum of 0.5 to 2.0 cycle / mm corresponding to the trabecular bone is likely to appear in the analysis result. The X-ray signal intensity profile is plotted in units of pixels on the horizontal axis, so the window function must also be converted into units of pixels and Fourier transformed. At this time, although the pixel size differs depending on the device, it is desired to convert the pixel function so that the window function has a width of 10 mm or less at any pixel size.
For example, when the above-described Fourier analysis is performed on the X-ray signal intensity profiles of FIGS. 14 and 15, the analysis results as shown in FIGS. 16 and 17 with the power spectrum as the vertical axis and the spatial frequency as the horizontal axis. Is required. In the graph showing the analysis results, the vertical axis is the logarithmic axis.

The index calculation unit 38 calculates an index representing the degree of bone disease based on the result of frequency analysis by the frequency analysis unit 41. Specifically, the index calculation unit 38 subtracts the influence of the background level as a logarithm from the power spectrum as the analysis result of the Fourier analysis by the frequency analysis unit 41, and then based on the subtracted power spectrum, Calculate the indicator. For example, when the analysis results shown in FIGS. 16 and 17 are obtained, the index calculation unit 38 converts the power spectrum of the analysis results into a logarithm, and creates a known approximate curve such as exponential approximation for the logarithm. An approximate curve is obtained by applying the method to the analysis result. This approximate curve becomes the background level. FIGS. 18 and 19 are graphs in which approximate curves (background levels C1 and C2) are overlaid on FIGS. 16 and 17, respectively.
The index calculation unit 38 subtracts the background levels C1 and C2 from the power spectrum, and uses the maximum value as an index indicating the degree of bone disease. For example, FIGS. 20 and 21 are graphs showing values obtained by subtracting the background levels C1 and C2 from the power spectra of FIGS. The index of the healthy person is 0.73 (maximum value) as shown in FIG. On the other hand, the patient index is 0.55 (maximum value) as shown in FIG. Based on this, in the present embodiment, a case where 0.6 is stored in the storage unit 32 as the evaluation reference value of the index is illustrated.
In this embodiment, the power spectrum is logarithmically converted, and then an approximate curve is obtained and subtracted as a background level. However, the approximate curve is obtained at a stage before logarithmically converting the power spectrum, May be subtracted as the background level to subtract the effect of the background level.

Then, the control unit 31 compares the calculated index calculated by the index calculation unit 38 with the evaluation reference value stored in the storage unit 32 to determine the degree of the disease of the rib B1 that falls within the region of interest R. To do.
For example, when determining the degree of disease for a subject whose past calculation index is stored in the storage unit 32, the control unit 31 reads the past calculation index from the storage unit 32, and calculates the calculation index. And the calculated index obtained this time are compared and displayed.
On the other hand, when determining the degree of disease for a subject whose past calculation index is not stored in the storage unit 32, the control unit 31 reads the evaluation reference value (in this embodiment, the evaluation reference) from the storage unit 32. Value 0.6) is read out, and it is determined that the evaluation reference value is compared with the calculated index obtained this time.
Note that the evaluation reference value is obtained from experiments, simulations, analysis of past data, and the like so that the presence or absence of a disease can be determined.

  And based on the above-mentioned determination result, the control part 31 makes the display part of the image output device 50 mentioned later display according to the determination result, or make the film output according to the determination result. It has become.

  The image processing unit 35 performs image processing such as gradation processing for adjusting the contrast of the image, processing for adjusting the density, frequency processing for adjusting the sharpness, and the like on the image data of the X-ray image. Thereby, it is possible to perform image processing suitable for conditions such as an imaging region.

  Note that image processing parameters that define image processing conditions corresponding to conditions such as an imaging region, an imaging condition, and an imaging direction are stored in advance in the storage unit 32 and the like. In accordance with information attached to the image data, such as which part is imaged, the part that was imaged, the imaging direction, and the like, the image processing unit 35 reads out the corresponding image processing parameters from the storage unit 32. The image processing conditions are preferably determined based on the read parameters. Note that when the image data does not include information such as the imaged part and the imaging direction, necessary conditions may be input from the input unit 33 or the like, and image processing may be performed based on this.

  Next, the image output device 50 prints (film outputs) image data on a monitor (display unit) such as a CRT (Cathode Ray Tube) or LCD (Liquid Crystal Display), or on a medium such as a film or paper. An image display device, a printer, and the like configured to include an output unit such as a print unit, a communication unit for connecting to an external device, a power supply unit that supplies power (not shown), and the like. When the control unit 31 (determination unit) determines whether or not there is a change in each part between the target image and the past image, and the presence or absence of a changing part (change area), the image output device 50 It functions as an output means for outputting the determination result. The communication unit is configured by a network interface or the like, and transmits / receives data to / from external devices such as the X-ray image capturing apparatus 1 and the image output apparatus 50 connected to the network N via a switching hub.

  When the communication unit 34 receives image data of an X-ray image subjected to image processing by the image processing device 30 via the network N, the image output device 50 appropriately outputs the image by the output unit (display unit or print unit). It is supposed to let you.

  Further, as described above, when the display content is determined by the image processing apparatus 30, for example, the fact is displayed on the display unit of the image output apparatus 50, or the fact is displayed on the film output. It has become explicit.

  In the case where the image output device 50 is an image display device including a monitor (display unit), a medical image for diagnosis is displayed and used for diagnosis of a doctor or the like. Therefore, a general PC (Personal Computer) is used. It is preferable to provide a higher-definition monitor (display unit) than the above.

Next, a bone disease evaluation method by the bone disease evaluation system 100 of the present embodiment will be described with reference to FIG.
First, when imaging order information is registered, for example, when an imaging subject (patient) performs examination registration (imaging order registration) by receiving an examination (not shown), the imaging subject is moved either left or right based on the imaging order information. The arm portion is placed on the subject table 14, and the triangular magnet 17 is placed between the thumb and the index finger (step S1).

Thereafter, the drive device 6 and the position adjustment device 15 adjust the position of the subject table 14 and the angle of the imaging device main body 4 in accordance with imaging conditions such as the X-ray irradiation angle, irradiation distance, and imaging magnification. In the present embodiment, the position of the subject table 14 is adjusted so as to achieve phase contrast imaging (step S2).
In step S3, the control device 22 shifts to step S4 when the detector 11 identified by the detector identifying unit 29 does not match the conformity detector set in step S2, that is, incompatibility. If it is identified that it is for contrast photography, the process proceeds to step S5.

  In step S4, the control device 22 controls the display device 24b to display that the set detector 11 is incompatible with the main photographing, and the process is terminated.

  In step S5, after adjusting the position and angle of the subject table 14, the power supply unit 9 applies a tube voltage to the X-ray source 8 so that the average radiant energy is 26 keV, and the X-ray source 8 is applied to the subject H. By irradiating with X-rays, phase contrast imaging is performed.

  When the image data of the phase contrast image is generated, shooting direction information, left / right information, subject information, shooting time information, part information, and the like are attached to the generated image data as additional information (step S6). Then, the X-ray image capturing apparatus 1 transmits the generated image data of the X-ray image together with the accompanying information to the image processing apparatus 30 (Step S7).

  When the image processing apparatus 30 receives the image data and its accompanying information from the X-ray imaging apparatus 1 (step S8), it stores (stores) the received image data and its accompanying information in the storage unit 32 (step S9).

  Thereafter, the control unit 31 controls the direction determination unit 39 to recognize the shape of each bone in the image data (step S10).

  Then, the control unit 31 specifies the rib B1 from each bone in the image data from the recognized shape of each bone and the shape list in the storage unit 32, and determines the vertical and horizontal directions of the rib B1 (step S11). .

  When the vertical and horizontal directions are determined, the control unit 31 controls the region of interest setting unit 37 to set the region of interest R based on the vertical and horizontal directions (step S12).

  When the setting of the region of interest R is completed, the control unit 31 controls the profile acquisition unit 40 to acquire a plurality of X-ray signal intensity profiles at predetermined pixel positions in the vertical direction and the horizontal direction in the region of interest R. (Step S13).

  When acquiring a plurality of vertical and horizontal X-ray signal intensity profiles, the control unit 31 controls the frequency analysis unit 41 to perform frequency analysis on the X-ray signal intensity profile (step S14).

  After the frequency analysis, the control unit 31 controls the index calculation unit 38 to calculate an index representing the degree of bone disease based on the result of the frequency analysis (step S15).

  The control unit 31 controls the storage unit 32 to store the calculated index (step S16).

  Then, the control unit 31 determines whether or not the past calculation index of the subject is stored in the storage unit 32 based on the subject information attached to the image data (step S17). When the past calculation index of the subject is stored (step S17; YES), the control unit 31 proceeds to step S18, and when not stored (step S17; NO), the control unit 31 proceeds to step S19. .

  In step S18, the control unit 31 reads a past calculated index of the subject to be inspected from the storage unit 32, determines that the calculated index and the calculated index calculated this time are compared and displayed, and step S20. Migrate to

  In step S19, the control unit 31 reads the evaluation reference value from the storage unit 32, determines that the evaluation reference value is compared with the calculated index obtained this time, and proceeds to step S20.

  In step S20, the control unit 31 displays the image data transmitted from the X-ray imaging apparatus 1, the accompanying information, the current calculation index, the evaluation reference value, the determination result, and the past calculation index, if any, the communication unit. 34 to the image output device 50.

When receiving data from the image processing device 30 (step S21), the image output device 50 causes the output unit to output the received content (step S22). As described above, the output method may be either viewer display on a monitor (display unit) or film output (hard copy) on a print unit. As a result, the image output device 50 can browse image data, supplementary information, current calculation index, evaluation reference value, comparative display based on the determination result, and past calculation index. Here, in the image output device 50, the current calculated index and the past calculated index can be compared and displayed, or the current calculated index and the evaluation reference value can be compared and displayed.
In the present embodiment, when the past calculated index of the subject is stored in step S17, only the process of step S18 is performed. However, the process of step S19 may be performed together. .

  As described above, according to the bone disease evaluation system 100 in the present embodiment, the region of interest R is set from the phase contrast image, and the X-ray signal intensity based on the X-ray signal intensity at each pixel position in the set region of interest R Since the frequency analysis is performed on the profile, the degree of disease in the initial stage and the accuracy of quantification of changes over time can be improved.

  In the present embodiment, the case where the image processing device 30 and the image output device 50 are provided as separate devices has been described as an example. However, the image processing unit, the storage unit, the determination unit, and the display unit as the output unit are described. Alternatively, the printing unit or the like may be provided in one apparatus, and the image processing apparatus 30 and the image output apparatus 50 may be combined into one apparatus.

  In the above-described embodiment, the frequency analysis for the X-ray signal intensity profile has been described by way of example where Fourier analysis is performed. However, wavelet analysis may be performed. In this case, the frequency analysis unit 41 performs wavelet analysis as frequency analysis on the X-ray signal intensity profile acquired by the profile acquisition unit 40. For example, when wavelet analysis is performed on the X-ray signal intensity profiles of FIGS. 14 and 15, analysis results as shown in FIGS. 23 and 24 are obtained with the wavelet coefficient as the vertical axis and the pixel position as the horizontal axis.

  The index calculation unit 38 calculates an index representing the degree of bone disease based on the result of wavelet analysis by the frequency analysis unit 41. Specifically, the index calculation unit 38 calculates the statistical value of the wavelet coefficient as a calculation index from the analysis result of the wavelet analysis by the frequency analysis unit 41. Here, the statistical value is, for example, at least one of the maximum value, minimum value, variance, standard deviation, or count value of a certain threshold value or more of the wavelet coefficients. For example, in the case of a healthy person in FIG. 23, the maximum value of the wavelet coefficient is 0.15, the minimum value is −0.22, the variance is 0.0097, and the standard deviation is 0.0991. On the other hand, in the case of the patient in FIG. 24, the maximum value of the wavelet coefficient is 0.08, the minimum value is −0.08, the variance is 0.0012, and the standard deviation is 0.0348. Based on these values, the evaluation reference value of the index is determined and stored in the storage unit 32. Examples of the evaluation standard values based on the above values are 0.1 for the maximum value, -0.15 for the minimum value, 0.005 for the variance, and 0.06 for the standard deviation. The evaluation reference value is obtained from experiments, simulations, analysis of past data, and the like so that the presence or absence of a disease can be determined.

  In this embodiment, the X-ray signal intensity profile is obtained based on the phase contrast image. This is because the difference in X-ray signal intensity is clearer in the phase contrast image than in the X-ray image obtained by normal imaging. This is because the detection accuracy can be increased. For example, the same portion of the subject from which the X-ray signal intensity profiles of FIGS. 14 and 15 described above were acquired was captured by absorption contrast imaging, and the X-ray signal intensity profile was acquired by the same method. The imaging conditions for the absorption contrast imaging were R1 = 1 m, R2 = 0 m, focal diameter D = 1.2 mm, and average X-ray energy E = 33 keV. FIG. 25 is an X-ray signal intensity profile of a healthy person acquired from an absorption contrast image, and FIG. 26 is an X-ray signal intensity profile of a patient acquired from an absorption contrast image. 27 and 28 show analysis results obtained by performing Fourier analysis on the X-ray signal intensity profiles of FIGS. Even if the analysis results of FIG. 27 and FIG. 28 are compared, it is clear that the difference between the healthy person and the patient is not clear even when compared with the comparison of the analysis results of FIG. 16 and FIG.

On the other hand, FIGS. 29 and 30 show analysis results obtained by performing wavelet analysis on the X-ray signal intensity profiles of FIGS. When the above calculation index is calculated from the analysis result, in a healthy person (FIG. 29), the maximum value of the wavelet coefficient is 0.06, the minimum value is −0.04, the variance is 0.0003, and the standard deviation is 0.0169. In the patient (FIG. 30), the maximum value of the wavelet coefficient is 0.03, the minimum value is −0.03, the variance is 0.0001, and the standard deviation is 0.0119. As described above, even in the case of an absorption contrast image, although there is a difference in calculation index between a healthy person and a patient, the difference is small compared with the difference in the above-described phase contrast image.
As described above, by performing frequency analysis on the phase contrast image, it is possible to detect a subtle difference in symptom and change over time as compared with the absorption contrast image.

  As frequency analysis, both Fourier analysis and wavelet analysis can be performed on the X-ray signal intensity profile, and the degree of disease can be determined based on the index calculated by each.

It is a figure which shows the principal part structure of the bone disease evaluation system in this embodiment. It is a side view which shows the principal part structure of the X-ray imaging apparatus in this embodiment. It is a schematic diagram which shows the internal structure of the X-ray image imaging device in this embodiment. It is a perspective view of the detector with which the X-ray imaging device in this embodiment is equipped. It is a top view at the time of the subject putting the back of the left hand on the hand holding part in this embodiment toward the upper part. It is a block diagram which shows the control structure of the X-ray imaging apparatus in this embodiment. It is a figure explaining the outline of phase contrast photography in this embodiment. It is a figure explaining a phase contrast effect. It is a block diagram showing the control structure of the image processing apparatus in this embodiment. It is a figure which shows an example of the phase contrast image obtained by the X-ray imaging device in this embodiment. It is explanatory drawing which shows the vertical and horizontal direction of the rib in the shape list memorize | stored in the memory | storage part of the image processing apparatus in this embodiment. It is explanatory drawing showing the region of interest set with the phase contrast image of FIG. It is explanatory drawing which shows the profile direction in the region of interest of FIG. FIG. 13 is an example of an X-ray signal intensity profile for one line in a vertical direction or a horizontal direction in the region of interest in FIG. 12, and is a diagram showing an X-ray signal intensity profile for a healthy person. FIG. 13 is an example of an X-ray signal intensity profile for one line in a vertical direction or a horizontal direction in the region of interest in FIG. 12, and is a diagram showing an X-ray signal intensity profile for a patient. It is a diagram which shows the analysis result at the time of performing a Fourier analysis with respect to the X-ray signal intensity profile of the healthy person of FIG. It is a diagram which shows the analysis result at the time of performing a Fourier analysis with respect to the X-ray signal intensity profile of the patient of FIG. FIG. 17 is a diagram in which a background level is superimposed on the analysis result of FIG. 16. FIG. 18 is a diagram in which a background level is superimposed on the analysis result of FIG. 17. It is the diagram which deducted the background level from the analysis result shown in FIG. FIG. 20 is a diagram obtained by subtracting a background level from the analysis result shown in FIG. 19. It is a flowchart showing the bone disease evaluation method in this embodiment. It is a diagram which shows the analysis result at the time of performing a wavelet analysis with respect to the X-ray signal intensity profile of the healthy person of FIG. It is a diagram which shows the analysis result at the time of performing a wavelet analysis with respect to the X-ray signal intensity profile of the patient of FIG. It is a diagram which shows an example of the X-ray signal intensity profile for 1 line in the absorption contrast image of a healthy person. It is a diagram which shows an example of the X-ray signal intensity profile for 1 line in a patient's absorption contrast image. It is a diagram which shows the analysis result at the time of performing a Fourier analysis with respect to the healthy person's X-ray signal intensity profile of FIG. It is a diagram which shows the analysis result at the time of performing a Fourier analysis with respect to the X-ray signal intensity profile of the patient of FIG. It is a diagram which shows the analysis result at the time of performing a wavelet analysis with respect to the X-ray signal intensity profile of the healthy person of FIG. It is a diagram which shows the analysis result at the time of performing a wavelet analysis with respect to the X-ray signal intensity profile of the patient of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray imaging device 2 Support stand 3 Support base 4 Imaging device main-body part 5 Support shaft 6 Drive device 7 Holding member 8 X-ray source 9 Power supply part 11 Detector 12 Detector holding part 13 X-ray dose detection part 14 Subject stand DESCRIPTION OF SYMBOLS 22 Control apparatus 24 Operation apparatus 29 Detector identification part 30 Image processing apparatus 31 Control part 32 Storage part 33 Input part 34 Communication part 35 Image processing part 37 Area of interest setting part 38 Index calculation part 39 Direction determination part 40 Profile acquisition part 50 Image Output device 100 Bone disease evaluation system R Area of interest

Claims (7)

An X-ray source that emits X-rays;
A detector that is disposed in front of the X-ray source in the irradiation direction and that detects X-rays irradiated from the X-ray source and transmitted through a subject including bone;
The distance R1 from the X-ray source to the subject is 0.1 m or more, the distance R2 from the subject to the detector is 0.3 m or more, the focal diameter D of the X-ray source is 0.2 mm or less, the X-ray An X-ray imaging apparatus capable of phase contrast imaging executed under the condition that the average X-ray energy of the source is 23 keV to 45 keV;
A region-of-interest setting unit that sets a region of interest from the image detected by the detector;
A profile acquisition unit that acquires an X-ray signal intensity profile for a position in the region of interest set by the region of interest setting unit;
A frequency analysis unit that performs frequency analysis on the X-ray signal intensity profile acquired by the profile acquisition unit;
A bone disease evaluation system comprising: an index calculation unit that calculates an index representing a degree of the bone disease based on a result of frequency analysis by the frequency analysis unit. In the bone disease evaluation system according to claim 1,
The bone disease evaluation system, wherein the frequency analysis unit performs either Fourier analysis or wavelet analysis on the X-ray signal intensity profile. The bone disease evaluation system according to claim 2,
When performing the Fourier analysis on the X-ray signal intensity profile, the frequency analysis unit multiplies the X-ray signal intensity profile by shifting a window function having a width of 10 mm or less by a predetermined length to perform a Fourier analysis. A bone disease evaluation system characterized by: In the bone disease evaluation system according to claim 2 or 3,
The index calculation unit calculates the index based on the subtracted power spectrum after subtracting the influence of the background level from the power spectrum as the analysis result of the Fourier analysis by the frequency analysis unit. Bone disease evaluation system. The bone disease evaluation system according to claim 2,
When the frequency analysis unit performs wavelet analysis on the X-ray signal intensity profile, the index calculation unit calculates the index using a statistical value of the wavelet coefficient obtained by the wavelet analysis. Characteristic bone disease evaluation system. The distance R1 from the X-ray source to the subject is 0.1 m or more, the distance R2 from the subject to the detector is 0.3 m or more, the focal diameter D of the X-ray source is 0.2 mm or less, the average of the X-ray sources A region of interest is set from a phase contrast image obtained by detecting X-rays irradiated and transmitted from the X-ray source toward a subject including bone under the condition of X-ray energy of 23 keV to 45 keV. And a process of
Obtaining an X-ray signal intensity profile for a set position within the region of interest;
Performing a frequency analysis on the acquired X-ray signal intensity profile;
And a step of calculating an index representing the degree of the bone disease based on the result of the frequency analysis. The distance R1 from the X-ray source to the subject is 0.1 m or more, the distance R2 from the subject to the detector is 0.3 m or more, the focal diameter D of the X-ray source is 0.2 mm or less, the average of the X-ray sources Under the condition of X-ray energy of 23 keV to 45 keV, the X-ray source irradiates a subject including bone and is connected to a detector that detects a phase contrast image by transmitted X-ray, and based on the phase contrast image In the computer that performs arithmetic processing
The region of interest is set from the phase contrast image, the X-ray signal intensity profile for the set position in the region of interest is acquired, the frequency analysis is performed on the X-ray signal intensity profile, and the result of the frequency analysis Based on the program, an index representing the degree of the bone disease is calculated.