JP2004147863A - X-ray bone density measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image which represents the relationship between a bone density and a body fat percentage in an easily understandable way by using an X-ray bone density measuring apparatus. <P>SOLUTION: A patient is scanned with high and low energy X-rays to obtain the attenuation of the X-rays at each pixel for each energy (S10 and S12). From the ratio of attenuations of each energy (attenuation ratio) (S14), whether each pixel represents a bone part or a soft tissue (S16) is discriminated. About a bone part pixel, the bone density is calculated by a DXA method (S18). About a soft tissue pixel, the body fat percentage is calculated by using a function for converting the attenuation ratio to the body fat percentage (S26). A bone part image expressing the bone density of each pixel of the bone part in a first color (S20) and a soft tissue image expressing each pixel of the soft tissue with a second color (S26) are combined according to the classification obtained at step S16. Thus, a synthetic image which displays bone density distribution and body fat ratio distribution as a list is prepared (S28). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus for measuring a bone density distribution of a subject using X-rays.
[0002]
[Prior art]
2. Description of the Related Art An X-ray bone density measuring apparatus that calculates bone density by transmitting X-rays through a subject has been conventionally used in many medical institutions for diagnosing and preventing bone diseases. As is well known, bones are composed of minerals (bone minerals) such as calcium that attenuate X-rays, and by calculating the amount of attenuation (attenuation rate) during X-ray transmission, the bone density per unit area is calculated. Is done. The bones are covered with soft tissues such as muscles and fats, and X-rays are attenuated in those areas as well. In order to eliminate such an influence due to soft tissue, a conventional bone density measuring apparatus uses X-rays of two types of energy. In this method, the simultaneous equations are solved based on the amounts of attenuation calculated for the respective energies, thereby specifying the amounts of attenuation of the bone portion and the soft tissue. This method is called a double X-ray absorption measurement method (DXA method). The principle of the bone density calculation by the DXA method will be described with reference to FIG. FIG. 5 shows the distribution of the attenuation when the X-rays of two kinds of high and low energies are transmitted through the subject 10 in which the soft tissue 14 covers the bone 12 as shown in FIG. 5B. (A). As can be seen from the figure, both the bone and the soft tissue attenuate more with low-energy X-rays than with high-energy X-rays, but the ratio of attenuation between the two energies is clearly different between bone and soft tissue. different. Therefore, in the DXA method, the ratio α of the attenuation of low-energy X-rays to the attenuation of high-energy X-rays in soft tissue is determined, and α is determined from the attenuation of low-energy X-rays to the attenuation of high-energy X-rays. By subtracting the product of the multiplication, the amount of attenuation of only the bone is obtained, and this is converted into bone density (in this case, the amount of bone mineral per unit area). Patent Documents 1 and 2 show examples of a bone density measuring device using such a method.
[0003]
In this type of bone density measuring device, for example, X-rays are irradiated from above to below a subject lying on a bed to detect the X-rays, thereby obtaining the bone density at each point when the subject is two-dimensionally projected. And the two-dimensional distribution can be displayed.
[0004]
Some conventional bone density measuring devices using the DXA method can display not only bones but also soft tissues for the purpose of easily grasping the external shape and the like of the subject. That is, in the general bone density calculation, the ratio α is used so that the value of the soft tissue becomes 0 as described above. However, if the value of α is set to a smaller value, the soft tissue also has a positive value. Therefore, if a display image is formed using such a small α, a display also showing a soft tissue can be obtained.
[0005]
[Patent Document 1]
Patent No. 2735507
[Patent Document 2]
Patent No. 3256667
[0006]
[Problems to be solved by the invention]
In recent years, an X-ray bone density measuring device has been used for confirming a drug effect using an animal such as a rat or a mouse. For example, there has been known an example in which a bone density distribution is measured by an X-ray bone density measuring device in order to examine the effect of changes in the amount of muscle and fat caused by a thinner drug on bone. In this application, it is very convenient to know the relationship between the distribution of the body fat percentage and the bone density distribution. However, there is no conventional bone density measurement device having a function of displaying such both distributions in association with each other.
[0007]
Here, the soft tissue display shown in the above-mentioned prior art can display not only the bone density distribution but also the soft tissue surrounding the bone to some extent. The attenuation was converted to a bone density scale, and did not represent the body fat percentage. For example, the body fat percentage generally tends to be higher at the side of the body (such as the flank), but since the thickness of the side of the body is small, the attenuation of X-rays is small. Is a small value equivalent to that of the outside of the subject, and does not represent the state of the body fat percentage.
[0008]
The present invention has been made in view of such a problem, and an object of the present invention is to provide an X-ray bone density measurement device that can clearly show the relationship between bone density and body fat percentage.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an apparatus according to the present invention detects X-rays transmitted through a subject, and a measuring unit that obtains a two-dimensional distribution of X-ray attenuation based on the detection result, Discriminating means for discriminating between a bone part and soft tissue of a subject; a bone density calculating means for obtaining a bone density distribution of the bone part from the two-dimensional distribution; and a body fat percentage distribution of the soft tissue from the two-dimensional distribution. It includes a body fat percentage calculating means to be obtained and a synthesizing means for synthesizing the bone density distribution of the bone part and the body fat percentage distribution of the soft tissue into one image and outputting the image.
[0010]
In this configuration, from the two-dimensional distribution of attenuation, a bone density distribution is obtained for a bone, and a body fat percentage distribution is obtained for a soft tissue, and the two are combined to generate one image. Therefore, the user can view the bone density distribution and the body fat percentage distribution on the basis of the image, which facilitates the analysis of the relationship between the bone density and the body fat percentage.
[0011]
In a preferred aspect, the measurement means obtains a two-dimensional distribution of the attenuation amount for each of two different X-ray energies, and the bone density calculation means obtains a two-dimensional distribution from the two-dimensional distribution of each X-ray of each energy. A bone density distribution is obtained according to a heavy X-ray absorption measurement method, and the body fat percentage distribution calculating means has information on a correspondence relationship between a ratio between attenuation amounts of X-rays of respective energies and a body fat percentage, and the two-dimensional information. The distribution of the body fat percentage is obtained by obtaining the ratio between the attenuation amounts of the X-rays of each energy at each point from the distribution and obtaining the body fat percentage corresponding to the ratio from the information of the correspondence.
[0012]
In another preferred aspect, the synthesizing unit assigns different display form ranges to the bone density distribution and the body fat percentage distribution, and sets the bone density and the body fat percentage in the corresponding display form ranges respectively. Express in display form. According to this aspect, it is possible to generate an image in which the bone density and the body fat percentage are easily distinguishable from each other.
[0013]
In still another preferred aspect, the body fat percentage distribution calculating means calculates a ratio between attenuation amounts of X-rays of respective energies at respective points from the two-dimensional distribution. The value of the attenuation of the two-dimensional distribution with respect to the lower energy X-ray is corrected. According to this aspect, it is possible to perform appropriate attenuation correction appropriate for the characteristics of the soft tissue.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention (hereinafter, referred to as embodiments) will be described with reference to the drawings.
[0015]
The X-ray bone density measuring apparatus according to the present embodiment has a function of obtaining a bone density distribution and a body fat percentage distribution of a subject, synthesizing these into one image, and displaying them. This apparatus may have a hardware configuration substantially the same as a conventional bone density measuring apparatus using the DXA method, and the calculation of the body fat percentage distribution and the generation of a composite image are typically realized by software ( Of course, it is not impossible to implement a part or all of the calculation and image generation processing as a hardware circuit.)
[0016]
Therefore, first, a hardware configuration of an X-ray bone density measuring apparatus to which the simultaneous display method of the bone density and the body fat percentage according to the present invention is applied will be described with reference to FIG.
[0017]
This bone density measuring device is a measuring device for measuring a bone density distribution of a body of a subject 10 such as a rat, for example, and the subject 10 is mounted on a fixedly arranged bed 16. Actually, a mechanism for fixing the small animal to the bed 16 exists, but is not shown in the figure to avoid complication. The subject 10 is a living body, and the bone 12 is covered with a soft tissue 14 composed of muscle, fat, and the like. In the present embodiment, an X-ray generator 18 is provided below the bed 16, and an X-ray detector 22 is arranged above the bed 16. The X-ray generation device 18 is a device that generates high-energy X-rays or low-energy X-rays as necessary, and the X-ray detection device is a device that detects the X-rays 100 transmitted through the subject 10. The X-ray generation device 18 and the X-ray detection device 22 are driven in a horizontal direction integrally by a scanning device 24. For example, the whole body of the subject is scanned by zigzag scanning, and transmitted X-rays are detected.
[0018]
The control unit 26 controls the operation of the present apparatus, and executes various calculations described later. Processing such as calculation of bone density and body fat percentage and generation of a composite display image are also realized by the arithmetic processing of the control unit 26. The storage unit 30 stores various programs and data for control and arithmetic processing of the control unit 26. The storage unit 30 is composed of, for example, an EEPROM. The display 32 displays the result of calculation in the control unit 26 and the like.
[0019]
As shown in FIG. 1, when measuring the subject 10, the subject 10 is first placed on the bed 16, and then the X-ray generation device 18 and the X-ray detection device 22 are horizontally moved by the scanning device 24. , High-energy X-rays and low-energy X-rays are alternately irradiated at a predetermined cycle of, for example, about several milliseconds. By detecting this with the X-ray detector 22, the count rate (Ih) of the high-energy X-rays and the count rate (Il) of the low-energy X-rays transmitted through the subject 10 are determined for each point in the horizontal plane. Each is required. The amount of attenuation at each point is represented by the natural logarithm of the actually measured count rates Ih and Il divided by the reference count rates Ioh and Iol, respectively. That is, the attenuation Rh of the high energy X-ray is obtained by ln (Ioh / Ih), and the attenuation Rl of the low energy X-ray is obtained by ln (Iol / Il). Note that the reference count rates Ioh and Iol are obtained by irradiating high-energy X-rays and low-energy X-rays from the X-ray generator 18 to a position on the bed 16 where there is no subject under the same conditions as when the subject is actually measured. The count rate obtained from the detection result of the X-ray detection device 22 can be used. The attenuation of each of the high-energy X-rays and the low-energy X-rays obtained in this manner becomes raw data measured by this apparatus. Hereinafter, based on the raw data, calculation of bone density and body fat percentage at each point is performed.
[0020]
Here, the calculation of the bone density may be performed in accordance with the well-known algorithm of the DXA method, and a description thereof will be omitted. The calculation method of the body fat percentage will be described with reference to FIG.
[0021]
In order to calculate the body fat percentage, calibration is performed using a phantom that simulates soft tissue with respect to X-ray transmission, and an attenuation ratio-body fat percentage function indicating the relationship between the attenuation ratio and the body fat percentage is obtained. . For this calibration, phantoms corresponding to two different body fat percentages are used. For example, two types of phantoms (called phantom Fat0) corresponding to a body fat percentage of 0% (ie, muscle 100%) and phantoms (called a phantom Fat100) corresponding to a body fat percentage of 100% (muscle 0%) are used. . Then, a phantom Fat0 having a body fat percentage of 0% is placed on the bed 16 and irradiated with high-energy X-rays and low-energy X-rays, the respective attenuation amounts Rh and Rl are calculated, and the ratio Rl / Rh between the two is calculated. I do. This ratio is called an attenuation ratio. The attenuation ratio obtained for the phantom Fat0 is indicated as RR0 in FIG. FIG. 2 shows the relationship between the body fat percentage on the vertical axis and the attenuation ratio on the horizontal axis, and the point corresponding to the body fat percentage of 0% is indicated by A. Similarly, the phantom Fat100 is measured, and the attenuation ratio RR100 corresponding to the body fat percentage of 100% is obtained. The corresponding point is shown as point B in FIG. The range excluding the two points of the body fat percentage of 0% and 100% is approximated by a function using these two points as parameters. This function is called a conversion function f. The example of FIG. 2 is an example of a case where the two points are approximated by a linear conversion function f. Of course, a more appropriate conversion function may be found and used by experiments or the like. In any case, the calibration process may be performed using phantoms having different body fat percentages, which are necessary to specify the conversion function to be used.
[0022]
The conversion function f thus obtained is stored in the storage unit 30 and used. In the calculation of the body fat percentage, the attenuation ratio RRx is obtained by actually measuring the subject 100, and this RRx is substituted for the conversion function f to obtain the value F of the body fat percentage. The conversion function may be stored as a set of parameters defining the function form as described above, but may be implemented in a form such as a table in which values of the body fat percentage corresponding to each attenuation ratio are registered. Of course it is good.
[0023]
Next, with reference to FIG. 3, a procedure of processing performed by the apparatus according to the present invention will be described.
[0024]
First, the X-ray generator 18 and the X-ray detector 22 are scanned as described above to obtain attenuation amounts Rh and Rl of high-energy X-rays and low-energy X-rays at each point of the subject 100 (S10). Based on the measurement results, maps representing the two-dimensional distributions of Rh and Rl are created (S12). This map has the value of the amount of attenuation (Rh or Rl) for each pixel of the image. The set of these maps becomes the raw data of the measurement results. Thereafter, the processing of measuring the bone density and the processing of measuring the body fat percentage are executed based on the set of these maps.
[0025]
In both the bone density measurement and the body fat percentage measurement, the attenuation ratio RR = R1 / Rh is calculated for each pixel from the raw attenuation data (S14 and S20). However, the calculation of the attenuation amount ratio is not simply taking the ratio between the attenuation amounts of the high and low energies in the raw data, but in the case of the bone density measurement (S14) and in the case of the body fat percentage measurement (S20), respectively. Add an appropriate correction operation. This correction operation is performed to correct a deviation of a measurement result (bone density or body fat percentage) due to a difference in body thickness (also referred to as body thickness correction). Here, the body thickness is the length of the X-rays penetrating the subject, and ideally, even when the body thickness is different, when the same bone density (or body fat percentage) is measured, The same attenuation amount ratio RR should be obtained (that is, the relationship between the two is linearly proportional), but in reality this is not the case, and the relationship between the two becomes nonlinear. Therefore, after correcting the raw data of Rh and Rl so as to be as close to ideal as possible, the ratio between the two is determined. However, in the case of the bone density measuring device of the DXA method, the body thickness of each part of the subject cannot be measured due to the configuration of the device (a dedicated measuring mechanism may be provided for measuring the body thickness, but in view of cost, Therefore, a configuration is employed in which the attenuation of the raw data is simply converted to the attenuation corrected for the body thickness. That is, since the attenuations Rh and Rl are not proportional to the body thickness, but change monotonically, it can be assumed that the raw attenuation itself has a one-to-one correspondence with the body thickness. Such a conversion method is possible. For this conversion, a plurality of phantoms of the same material having different thicknesses are prepared, and they are measured with X-rays of high and low energies, so that the attenuation ratio Rl / Rh at that time is as uniform as possible irrespective of the body thickness. Next, a correction value of Rh or Rl is obtained.
[0026]
This body thickness correction is also performed by the conventional bone density measuring device of the DXA method. However, in the conventional device, by correcting the attenuation Rh for high-energy X-rays, good body thickness correction can be performed. Has been realized. However, this is a good correction of the body thickness for the measurement of bone density, and according to the experiments of the inventor, good results were not obtained even if the same correction was applied to the measurement of the body fat percentage. Therefore, when a body thickness correction method suitable for the body fat percentage was examined by an experiment, it was found that it is preferable to correct the attenuation Rl for low energy X-rays. Although a rigorous theoretical elucidation has not yet been made on this point, the rough mechanism is considered to be as follows. That is, since the attenuation of X-rays by bone is much greater than that of soft tissue, the high energy X-rays are sufficiently attenuated in the bone part (ie, the part where the bone is included in the X-ray transmission path). High energy X-ray attenuation is dominant in bone density. For this reason, it is considered that good body thickness correction can be performed by correcting the amount of attenuation of high-energy X-rays. On the other hand, since soft tissue has a small attenuation of X-rays, the difference in attenuation due to the difference in body thickness is small in the soft tissue portion (ie, the portion where bone is not included in the X-ray transmission path). Among them, since high energy X-rays have higher transparency, differences due to differences in body thickness are less likely to appear than low energy X-rays. Further, the difference between the attenuation of X-rays is small in fat and muscle of soft tissue, and the change in attenuation is extremely small even if the body fat percentage changes, especially for high-energy X-rays having high permeability. On the other hand, the attenuation of low-energy X-rays having a smaller penetrating power reflects the difference between attenuation of fat and muscle more greatly than that of high-energy X-rays. Therefore, in the body fat percentage calculation for the soft tissue portion, it is considered that a preferable body thickness correction becomes possible by correcting the attenuation amount of the low energy X-ray which is more sensitive to the ratio of fat and muscle. .
[0027]
In order to obtain a specific conversion function (or conversion table) for correcting the body thickness, first, a plurality of phantoms having different thicknesses as described above are prepared for the bone density and the body fat percentage. Measurement is performed using X-rays of each energy, and the attenuation amounts Rl and Rh corresponding to each body thickness are obtained. Then, in the measurement results, the correction value Rh ′ of the attenuation Rh corresponding to each thickness of the high-energy X-ray is measured for the bone density measurement so that the attenuation ratio Rl / Rh is as uniform as possible irrespective of the thickness of the phantom. For the measurement of the body fat percentage, a correction value Rl 'of the attenuation Rl corresponding to each thickness of the low energy X-ray is obtained. For bone density measurement, a function approximating the correspondence between Rh and Rh 'for each thickness is determined as a conversion function, and for body fat percentage measurement, a function approximating the correspondence between Rl and Rl' for each thickness. Is determined as a conversion function. The conversion function for body thickness correction determined in this way is stored in the storage unit 30 in advance.
[0028]
Therefore, in S14, the body thickness correction is performed on the Rh of each pixel of the raw data using the conversion function for bone density, and in S22, the body thickness correction is performed on the Rl of each pixel of the raw data using the conversion function for the body fat percentage. , And the attenuation ratio Rl / Rh is calculated for each pixel using the correction result.
[0029]
When the map of the attenuation ratio corrected for the bone portion is created in S14, each pixel of this map is then converted to the bone portion (the portion including the bone in the X-ray transmission path) according to the value of the attenuation ratio of the pixel. ), Soft tissue (portion not including bone in the X-ray transmission path but including soft tissue), and air layer (portion where the X-ray transmission path includes only the air layer). Since the attenuation ratio Rl / Rh greatly differs between the bone, the soft tissue, and the air layer, the three types can be discriminated by threshold discrimination. As the discrimination threshold value at this time, the value of the attenuation ratio that separates the bone and the soft tissue and the value of the attenuation ratio that separates the soft tissue and the air layer may be determined in advance by experiments or the like. According to this discrimination, each pixel is always classified into one of a bone, a soft tissue, and an air layer.
[0030]
By this S16, in the attenuation amount map obtained in S12 and the attenuation amount ratio maps obtained in S14 and S22, a classification map showing which pixels correspond to bones and which pixels correspond to soft tissues is obtained. Can be
[0031]
In S18, only the pixels of the bone are extracted with reference to this classification map, and for each pixel of the bone, the value of the pixel in the attenuation ratio map obtained in S14 is extracted, and based on this value, The bone density of the pixel is calculated according to the well-known DXA method.
[0032]
When the bone density of each pixel of the bone portion is obtained in this way, the bone density of each pixel is converted into a gradation value of a predetermined first color for each pixel. Is formed (S20). A conversion function (or table) indicating the relationship between the bone density and the gradation value is registered in the storage unit 30 in advance.
[0033]
Thus, an image of the bone density distribution is completed. On the other hand, in the process of measuring the body fat percentage, after the process of S22, each pixel of the soft tissue is extracted with reference to the classification map obtained in S16, and the attenuation amount obtained in S22 is extracted for each pixel of the soft tissue. The value of the pixel in the ratio map is extracted, and based on the value, the body fat percentage of the pixel is calculated according to the above-described body fat percentage calculation method (S24).
[0034]
When the body fat percentage of each pixel of the soft tissue is determined in this manner, the body fat percentage of the pixel is then determined for each pixel by a predetermined number different from the first color assigned to the bone density display. By converting the image into a gradation value of the second color, an image having a body fat percentage distribution is formed (S26). Here, the conversion function (or table) indicating the relationship between the body fat percentage and the gradation value is registered in the storage unit 30 in advance.
[0035]
Then, in S28, the image of the bone density distribution generated in S20 and the image of the body fat percentage distribution generated in S26 are combined to generate one output image. In this synthesis, the classification table created in S16 is referred to, the value of the corresponding pixel in the bone density distribution is adopted for the pixel corresponding to the bone, and the value of the corresponding pixel in the body fat percentage distribution is used for the pixel corresponding to the soft tissue. Adopt the value.
[0036]
Note that the first color assigned to the bone density and the second color assigned to the body fat percentage may be selected from, for example, the primary colors of the display output mechanism. For example, in the case of a display device of RGB display, G (green) is selected as the first color and R (red) is selected as the second color. In addition, a method of expressing the bone density in a black and white gray scale in which the correspondence with the bone is intuitive and easy to understand, and expressing the body fat percentage in a chromatic (for example, red) gradation can be considered. Of course, these are only examples, and any combination of colors can be used for the first color and the second color as long as they can be distinguished from each other even if the gradation is changed. Can be.
[0037]
Then, the synthesized image generated in this manner is displayed on, for example, the display 32 or printed out from a printer (not shown) (S30).
[0038]
FIG. 4 schematically shows an example of a composite image of the bone density distribution and the body fat percentage distribution, which is output from the device of the present embodiment. Since colors cannot be represented in the figure, the first color is indicated by hatching and the second color is indicated by cross hatching, and the magnitude of bone density and body fat percentage is indicated by hatching density. As shown in this figure, a scale 210a representing the correspondence between the gradation of each color and the value (or magnitude) of the bone density or the body fat percentage is provided near the composite image 200 of the bone density distribution and the body fat percentage distribution. , 210b are shown. Although the number of gradations is reduced in this figure to avoid complexity, the gradation can be further reduced in an actual output image.
[0039]
As described above, according to the apparatus of the present embodiment, a composite image 200 is created that shows the bone density in the portion corresponding to the bone of the subject and the body fat percentage in the portion corresponding to the soft tissue. , Can be output. Since the user can view the distribution of the bone density and the distribution of the body fat percentage from the composite image 200, the user can easily grasp the relationship between the body fat percentage and the bone density. Further, in the present embodiment, since the calculation method and the body thickness correction method suitable for the body fat percentage are used, unlike the soft tissue display described in the related art, highly reliable information on the body fat percentage is provided. be able to.
[0040]
Further, in the present embodiment, since the bone density and the body fat percentage are respectively expressed by gradations of the first color and the second color which are different from each other, on the composite image 200, each pixel has a bone density (bone portion). Or the body fat percentage (soft tissue).
[0041]
It should be noted that the image expression method of expressing the bone density and the body fat percentage by the gradations of the first color and the second color different from each other is merely an example. In principle, a display form range that does not overlap each other may be assigned to the bone density and the body fat percentage. This display form range includes the gradation range of one color as in the example described above. In this case, for example, “first color” is one display form range, and a color of a certain gradation within the first color range becomes one display form within the display form range. A range on the hue circle such as a cool color or a warm color is also a kind of display form range. That is, for example, a method of assigning a gradation of hues in a cool color range to bone density and assigning a gradation of hues in a warm color range to body fat percentage is possible. Also, the distinction of hatching shown in FIG. 4 is a kind of display form range, and in this case, each type of hatching (falling hatched hatch or cross hatching) corresponds to one display form range. Hatching of a certain density in the hatching type corresponds to one display form within the display form range. In any case, the display form range assigned to each of the bone density and the body fat percentage is such that the bone density and the body fat percentage can be easily distinguished on the composite image 200 regardless of the value from the upper limit to the lower limit. Desirably.
[0042]
In the embodiment shown in FIG. 1, the X-ray generator 18 and the X-ray detector 22 are driven in the horizontal direction. The simultaneous display does not depend on such a configuration of the detection system. For example, the X-ray generator 18 and the X-ray detector 22 may be fixedly arranged, and the bed 16 may be driven in the horizontal direction. In this case, the bed 16 is driven by the scanning device 24, thereby scanning the subject 10 itself. As a detection system, a pencil beam for focusing on one point may be output from the X-ray generator 18 and detected by the X-ray detector 22 including one detector. A fan beam spreading in a fan shape may be output from 18, and the fan beam may be detected by the X-ray detector 22 having an array in which a plurality of detectors are arranged in a line. Further, a configuration using a cone beam that spreads conically from the X-ray generator 18 may be used. In the above-described example, high-energy X-rays and low-energy X-rays are alternately irradiated at short intervals. Instead, a wide-band X-ray is irradiated. The discrimination may be performed, and the detection signal corresponding to the high energy X-ray and the detection signal corresponding to the low energy X-ray may be discriminated and individually counted.
[0043]
【The invention's effect】
As described above, according to the present invention, the bone density distribution of the subject's bone and the body fat percentage distribution of the subject's soft tissue can be combined into a single image and displayed. It becomes easy to grasp the relationship between the body fat percentage and the bone density.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a schematic configuration of an X-ray bone density measuring device according to an embodiment.
FIG. 2 is a diagram for explaining the principle of measuring body fat percentage according to the embodiment.
FIG. 3 is a diagram for explaining a processing flow of the apparatus of the embodiment.
FIG. 4 is a diagram schematically illustrating an example of an output image of the apparatus according to the embodiment.
FIG. 5 is a diagram for explaining the principle of bone density measurement by the DXA method.
[Explanation of symbols]
DESCRIPTION OF REFERENCE NUMERALS 10 subjects, 12 bones, 14 soft tissues, 16 beds, 18 X-ray generators, 22 X-ray detectors, 24 scanners, 26 controllers, 30 storage units, 32 displays.

Claims (4)

Measuring means for detecting X-rays transmitted through the subject and obtaining a two-dimensional distribution of X-ray attenuation based on the detection result;
Discriminating means for discriminating a bone portion and a soft tissue of the subject from the two-dimensional distribution,
Bone density calculation means for obtaining a bone density distribution of the bone from the two-dimensional distribution,
Body fat percentage calculating means for obtaining a body fat percentage distribution of the soft tissue from the two-dimensional distribution,
A synthesizing unit that synthesizes and outputs a bone density distribution of the bone part and a body fat percentage distribution of the soft tissue into one image,
An X-ray bone density measurement device comprising: The measuring means obtains a two-dimensional distribution of the attenuation amount for each of two different energy X-rays,
The bone density calculation means obtains a bone density distribution from the two-dimensional distribution for the X-rays of each energy according to a double X-ray absorption measurement method,
The body fat percentage distribution calculating means has information on a correspondence relationship between a ratio between attenuation amounts of X-rays of each energy and a body fat percentage, and attenuates X-rays of each energy at each point from the two-dimensional distribution. Determine the ratio between the amounts, determine the body fat percentage distribution by determining the body fat percentage corresponding to the ratio from the information of the correspondence relationship,
The X-ray bone density measuring device according to claim 1, wherein: The synthesizing unit assigns different display form ranges to the bone density distribution and the body fat percentage distribution, and expresses the bone density and the body fat percentage in display forms within the corresponding display form ranges. The X-ray bone density measuring device according to claim 1 or 2, wherein The body fat percentage distribution calculating means calculates the ratio between the amounts of X-ray attenuation of each energy at each point from the two-dimensional distribution. The X-ray bone density measuring apparatus according to any one of claims 1 to 3, wherein a value of an attenuation amount of the two-dimensional distribution with respect to a line is corrected.

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