WO2008044439A1

WO2008044439A1 - Apparatus for determining bone salt content

Info

Publication number: WO2008044439A1
Application number: PCT/JP2007/068148
Authority: WO
Inventors: Hiromu Ohara; Yuko Shinden
Original assignee: Konica Minolta Medical & Graphic, Inc.
Priority date: 2006-10-06
Filing date: 2007-09-19
Publication date: 2008-04-17
Also published as: JPWO2008044439A1

Abstract

It is intended to provide an apparatus for determining bone salt content which is widely applicable to medical examinations because of enabling convenient determination of bone mass content while imposing little burden even on aged subjects and which can establish such a high accuracy as being usable in the early detection of osteoporosis and follow-up for treating the same.

Description

Specification

Bone mineral content measuring device

Technical field

[0001] The present invention relates to a bone mineral content measuring apparatus, and more particularly, to a bone mineral content measuring apparatus that measures bone mineral content using single energy X-rays.

Background art

[0002] Conventionally, in the medical field, measurement of bone mineral content (bone mineral metering) has been performed in order to diagnose osteoporosis. Examples of bone mineral quantification methods used to measure this bone mineral content include the dual energy X-spring absorption method (Dual X-ray Absorptiometry: DXA method) and the quantitative ultrasonic bone density measurement method (Quantitative Ultrasound: QUS method). ), Quantitative X-ray CT (Quantitative Computed Tomography: QCT), single energy X-ray absorption (SXA method), etc. are currently known. The heavy energy X-ray absorption method has become the standard method for bone mineral content measurement!

[0003] Specifically, for example, in the case of using the dual energy X-ray absorption method, a difference signal is obtained by performing energy subtraction between a plurality of images obtained by irradiating radiations having different energy levels. Image signal, and subtracting between the correction image signal averaged in the main scanning direction and / or sub-scanning direction and the difference signal to obtain a correction difference signal, and this correction difference signal There is known a method of performing bone mineral quantitative analysis by the method (for example, see Patent Document 1).

[0004] In addition, as a method using quantitative X-ray CT examination, a CT tomographic image is obtained, and the bone density is calculated from the CT value for each pixel in a specific bone tissue that is discriminated and extracted from this CT tomographic image. An apparatus that performs this process has been proposed (see, for example, Patent Document 2).

[0005] As a means of measuring bone mineral density using the single energy X-ray absorption method, the subject is irradiated with a single energy X-ray and the X-ray absorption value of the subject is measured. In order to achieve this, by using a single type of filter made of only a single metal material to monochromatic continuous X-rays, the filter thickness, collimator diameter, tube voltage and current are optimized. A bone mineral content measuring device that makes X-rays monochromatic with a simple configuration has been proposed (for example, see Patent Document 3). [0006] Furthermore, it has been proposed that a finger placed in a water tank is photographed with a breast imaging apparatus as a subject and the bone mineral content of the subject is measured based on the obtained image data (for example, non-specialty). See Permissible Literature 1).

Patent Document 1: Japanese Patent Laid-Open No. 5-1111480

Patent Document 2: JP-A-2005-192657

Patent Document 3: Japanese Patent Laid-Open No. 2005-319236

Non-Patent Document 1: Toyofuku Inoue 7 "Bone salt quantitative measurement with phase contrast mammography (PCM) apparatus-Basic study with aluminum and water phantom" Jpn. J. Med. Phys., Vol. 26 supplement No. 3 , pp. 77—78, (2006)

Disclosure of the invention

Problems to be solved by the invention

[0007] By the way, osteoporosis increases with aging, and fractures of elderly people, particularly femoral neck fractures, are likely to be bedridden. In particular, it is said that in women over 40 years old, bone mineral content rapidly decreases, and fractures are more likely to occur when it is below 0.70 g / cm ² . Increasing the number of patients with osteoporosis is not only an obstacle to the lives of individual patients, but also a major problem in Japan, where the elderly population is increasing, which spurred an increase in medical expenses.

[0008] It is said that osteoporosis can be prevented by force by taking appropriate exercise and taking sufficient calcium from the diet. Therefore, it is important for individuals to accurately grasp their own bone mineral content at an early stage and strive to prevent osteoporosis. Therefore, today, bone mineral quantification is being examined.

[0009] However, the change in the amount of bone mineral is very small, and the measurement error of bone mineral content determination for osteoporosis prevention and early detection is required to be around 1%. Even if calcium is adequately consumed and appropriate exercise is continued, the increase in bone mineral density is considered to be about 0.5% per year, and appropriate prevention, early detection and treatment of osteoporosis are performed. In order to do this, it is preferable to regularly check the bone mineral content for a long period of at least several years and observe the progress. Therefore, bone mineral content can be easily measured for the prevention and early detection of osteoporosis. It is required to do so.

[0010] Further, as mentioned above, osteoporosis is a disease that affects a large number of elderly people. Therefore, it is preferable to measure the amount of bone mineral in such a way as to impose as little burden on the person undergoing the examination as possible.

[0011] However, the dual energy X-ray absorption method has excellent measurement accuracy but has a drawback that it takes time force S of several minutes or more for measurement. For this reason, it is not preferable as a method of screening regularly performed by elderly people. In addition, in the case of the dual energy X-ray absorption method, information cannot be obtained as a high-resolution image simultaneously with the measurement of bone mineral content.

[0012] Quantitative X-ray CT examination has the disadvantage that it has a large power exposure dose that can obtain information in three dimensions, and is not suitable for examinations (especially, examinations that are performed regularly over a long period of time).

Furthermore, the quantitative ultrasonic bone density measurement method using an ultrasonic device has problems such as measurement accuracy. Not suitable.

[0014] On the other hand, the single energy X-ray absorption method can measure the amount of bone mineral by taking an image of the subject using an X-ray film, etc., and the bone mineral content can be determined most easily. It is a technique.

[0015] In order to measure bone mineral content using X-rays, for example, monochromatic X-rays obtained from a synchrotron radiation X-ray source or the like must be used. In this regard, as described in Non-Patent Document 1, it is used in mammography devices, etc.! /, Molybdenum anode X-ray tube has the power to irradiate X-rays with excellent monochromaticity S There is a problem that the influence of X-rays on the human body is large. Therefore, in conventional medical practice, braking X-rays are strong! / And tungsten anode X-ray tubes are widely used! /. However, the X-rays emitted from the tungsten anode X-ray tube are multi-colored X-rays, and the normal bone scan is set to a tube voltage of 50 kVp or higher, so the measurement accuracy is extremely low! For this reason, the single energy X-ray absorption method now plays an auxiliary role for other methods! /, But this method alone can be used for medical purposes such as early detection of osteoporosis and confirmation of progress. Is unbearable! /.

In addition, the mammography apparatus described in Non-Patent Document 1 uses refraction contrast enhancement caused by X-ray refraction in order to diagnose a shadow caused by microcalcification or disease in the breast. Yes, it uses a molybdenum anode X-ray tube as a radiation source. Meanwhile, bone mineral content In order to measure accurately, it is preferable to perform quantification based on the absorption contrast image of the bone, but it is taken using a molybdenum anode X-ray tube with an emission line spectrum, which tends to cause refraction contrast enhancement. In the image, an increase or decrease in X-ray dose due to refraction contrast appears near the edge of the bone. For example, when bone mineral content is measured by photographing a plurality of small bones such as fingers, there is a concern that some errors may occur in the measured value compared to bone mineral content measurement by other methods.

[0017] In order to appropriately carry out prevention, early detection and treatment of osteoporosis as described above, the ability to perform bone mineral quantification over a long period of time is not always performed in a single method. Absent. Therefore, the error in the measurement value caused by the measurement method becomes extremely complicated when there are a wide variety of force measurement methods that required correction such as matching with the measurement value in the existing measurement method. there is a possibility.

[0018] Therefore, the present invention has been made to solve the above-described problems, and enables simple bone mineral quantification that can be used for a wide range of examinations with less burden even for elderly people. It is another object of the present invention to provide a bone mineral content measuring apparatus capable of realizing measurement accuracy usable for follow-up for early detection and treatment of osteoporosis.

Means for solving the problem

[0019] In order to solve the above-mentioned problem, the bone mineral content measuring device according to claim 1 captures an X-ray image of a subject, and based on the obtained image data, the subject is measured. A bone mineral content measuring device for measuring the bone mineral content of a specimen,

An X-ray source for irradiating the subject with X-rays;

An X-ray detector for recording an X-ray image corresponding to an X-ray dose irradiated from the X-ray source and a liquid substance holding member for holding a liquid substance containing the subject at the time of imaging; The source is a tungsten anode X-ray tube with an intrinsic filtration of 2.5 mm thick aluminum or more,

The X-ray detector has a dynamic range of 3 digits or more and is arranged so that the distance from the subject is 15 cm or more! /.

[0020] The invention according to claim 2 is the bone mineral content measuring device according to claim 1. In

The X-ray source has a tube voltage set to 20 kVp or more and 49 kVp or less.

[0021] The invention described in claim 3 is the bone mineral content measuring device described in claim 1 or claim 2!

The X-ray source is characterized in that the tube voltage is set to 25 kVp or more and 39 kVp or less.

[0022] The invention according to claim 4 is the bone mineral content measuring device according to any one of claims 1 to 3, wherein

The dynamic range of the X-ray detector is 7 digits or less.

[0023] The invention according to claim 5 is the bone mineral content measuring device according to any one of claims 1 to 4, wherein

The X-ray detector is arranged so as to have a distance force im or less with respect to the subject.

[0024] The invention according to claim 6 is the bone mineral content measuring device according to any one of claims 1 to 5, wherein

It is a human finger or foot. The invention's effect

[0025] When measuring the amount of bone mineral by the single energy X-ray absorption method, it is necessary to irradiate the subject with monochromatic X-rays. According to the invention described in claim 1, Tungsten anode with an intrinsic filtration of 2.5 mm thick aluminum or more X-ray tube is used as an X-ray source, so unnecessary X-rays can be removed, X-rays can be monochromatic, and molybdenum anode Compared with X-ray tubes, refraction contrast enhancement is less likely to occur, so accurate bone mineral content can be measured.

[0026] Further, when X-rays pass through an object (subject), scattered X-rays having various energies are generated as secondary X-rays, and these scattered X-rays become noise in the X-ray image. In this regard, by separating the X-ray detector by 15 cm or more from the subject, the scattered X-rays can be reduced without reducing the primary X-ray dose due to the so-called Gradel effect, and the monochromaticity is further enhanced by the X-ray detector. X-ray transmitted X-ray dose can be captured.

[0027] In addition, because the dynamic range of the X-ray detector is as wide as 3 digits or more! / X-rays that greatly decrease at bones with high X-ray absorption when irradiated with low-energy X-rays are sufficient. In addition, an image contrast capable of measuring the bone mineral content can be obtained, and the measurement accuracy of the bone mineral content can be improved.

[0028] If the tube voltage of the X-ray source is too low, even if the subject is irradiated with X-rays, the X-rays are almost absorbed by the bone and the transmitted X-ray dose necessary for bone mineral content measurement cannot be obtained. Only adverse effects on the human body occur.

[0029] According to the invention described in claim 2 of this point, since the tube voltage is 20 kVp or more, there is an effect that a transmitted X-ray dose necessary for measuring the bone mineral content can be obtained. Play.

[0030] On the other hand, if the tube voltage exceeds 49kVp, the bremsstrahlung X-ray increases more than necessary and the measurement accuracy deteriorates. According to the present invention, the tube voltage is set to 49kVp or less, so the measurement accuracy It will not deteriorate.

[0031] According to the invention described in claim 3, since the tube voltage is set to 25 kVp or more and 39 kVp or less, the transmitted X-ray dose necessary for measuring the bone mineral content is obtained and the bremsstrahlung X There is an effect that it is possible to appropriately prevent deterioration in measurement accuracy due to an increase in the number of lines more than necessary.

[0032] According to the invention described in claim 4, since the dynamic range of the X-ray detector is 7 digits or less, the time spent on image data processing is short, and the apparatus cost can be suppressed at a low cost. ¾] Play the fruit that you can.

[0033] According to the invention described in claim 5, since the distance between the X-ray detector and the subject is 1 m or less, the X-ray dose to be detected by the X-ray detector is large. Without decreasing, the bone mineral content measurement accuracy is increased. In addition, since the distance between the X-ray detector and the subject is short, the apparatus can be downsized.

[0034] According to the invention described in claim 6, since the subject is a human finger or foot, it is not necessary to take a picture in a lying position, for example, while sitting on a chair or the like on a subject table. The amount of bone mineral can be measured by a simple method such as performing an examination while holding the hand. For this reason, the amount of bone mineral is low even when the burden on the subject is small, such as when the subject is an elderly person. The effect of the fact that the measurement and measurement of the above can be easily and conveniently performed can be achieved. .

Simple and simple explanation on the drawing

[[Fig. 11]] Side side view showing the configuration of the main part of the bone and bone salinity measuring instrument mounting device according to the present embodiment. It is a figure. .

[[FIG. 22]] Schematic diagram showing the internal / internal structure of the bone / salt salinity measuring / mounting apparatus in the present embodiment. It is. .

[[FIG. 33]] Front view showing the main components of the bone / salt salinity measuring / mounting device in the present embodiment. It is a figure. .

[[Fig. 44]] Addition of an additional filter element with no additional attachment Tatungsugutensten anode XX line tube and molyribbudeden anode anodic electrode XX line tube XX

5] This is a graph showing the X-ray spectrum of a tungsten anode X-ray tube with an additional filter attached.

6] It is a block diagram showing a control configuration of the bone mineral content measuring apparatus in the present embodiment. Explanation of symbols

1 Bone mineral content measuring device

3 Support base

4 Camera unit

5 Support shaft

7 Holding member

8 X-ray source

9 Power supply

11 X-ray detector

12 Detector holder

14 Subject table

15 Positioning device

21 Face guard

22 Control device

30 aquarium

31 Liquid

81 Additional filter

H Subject X chair

BEST MODE FOR CARRYING OUT THE INVENTION

[0037] Hereinafter, an embodiment of a bone mineral content measuring apparatus 1 according to the present invention will be described with reference to FIGS. However, the scope of the invention is not limited to the illustrated examples.

FIG. 1 to FIG. 3 show a configuration example of the bone mineral content measuring apparatus 1 in the present embodiment. The bone mineral content measuring device 1 is connected to a communication network (not shown; hereinafter simply referred to as “network”) such as a LAN (Local Area Network) via a switching hub (not shown), for example. Display the measurement result of the bone mineral content measured by the bone mineral content measuring device 1 on the monitor of a terminal device (not shown) connected to the network, or output the measurement result to the network. The film may be output from (not shown).

[0039] The configuration of the bone mineral content measuring device 1 is not limited to the one exemplified here. For example, the bone mineral content measuring device 1 outputs the measurement result (display or film output) of the bone mineral content. May also be configured.

As shown in FIG. 1, in the bone mineral content measuring apparatus 1 in the present embodiment, a support base 3 is provided on an imaging main body 4 serving as a base so as to be movable up and down with respect to the support 2. Yes. On the support base 3, an imaging body 4 having a substantially rectangular parallelepiped shape is rotatably supported via a support shaft 5 in the CW direction and the CCW direction (see FIG. 3 (a)).

[0041] By rotating the imaging main body 4 via the support shaft 5, the bone mineral content measuring apparatus 1 is inclined when imaging is performed with the apparatus angle perpendicular to the ground during imaging. It can be used when shooting at an angle of about 45 degrees (see Fig. 3 (b)).

[0042] 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) and the like, and the support base 3 and the imaging main body 4 are moved up and down according to the position of the subject H.

[0043] In the present embodiment, the bone mineral content measuring device 1 can perform imaging for performing bone mineral content measurement (bone mineral content determination) and general X-ray image imaging with a single device. The support base 3 and the imaging main body 4 can be moved according to the position of the subject H suitable for each imaging. [0044] For example, when taking a finger for bone mineral content measurement (quantity of bone mineral), the position of the subject H suitable for imaging is the vicinity of the chest of the subject sitting on the chair X or the chest. The position is adjusted so that it is less likely to get tired when the subject immerses his / her finger in a water tank 30 placed on the subject table 14 described later. It is possible.

[0045] When a general X-ray image is captured, the support base 3 and the imaging main body 4 are set in accordance with the position of the subject H so that the apparatus is in a state suitable for imaging the subject H. The height and position can be adjusted.

As shown in FIG. 2, the photographing 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 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 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.

In this embodiment, a tungsten anode X-ray tube is applied as the X-ray source 8. As the tungsten anode X-ray tube, for example, UH-6RC-307EY type X-ray tube (Hitachi Medical DHF-155HII high-pressure generator) manufactured by Hitachi Medical Corporation can be used.

Further, an additional filter 81 is attached to the X-ray source 8. As the attached calofilter 81, for example, molybdenum, rhodium, aluminum or the like can be used. The thickness of the additional filter 81 can be equal to or greater than 2.5 mm of aluminum. At this time, it is preferable to narrow the X-ray energy width using a diffraction grating or the like.

[0049] Fig. 4 shows an X-ray spectrum obtained from an X-ray tube with a molybdenum anode and X obtained from an X-ray tube with a tungsten anode without an additional filter 81 when the applied tube voltage is 30 kVp. The line spectrum W is shown. In any X-ray spectrum, the maximum X-ray intensity is 100, and the relative intensity is shown. The X-ray spectrum Mo has a large effect on the human body. 17. Extremely strong X-rays with a peak near 8keV are generated. When the X-ray detector 11 is taken away from the subject H, The X-rays that are absorbed and attenuated by and are refracted and superimposed near the edge of the bone.

[0050] On the other hand, in the X-ray spectrum W, an emission line spectrum is generated in the vicinity of lOkeV. From 15keV to 30keV, the characteristic X-rays are distributed gently. However, the X-ray dose is attenuated when the X-rays are transmitted through the bone by removing the emission line spectrum near lOkeV by the additional filter 81. Can be relaxed, and the accuracy of bone mineral content measurement is improved.

[0051] In the above, the force described to attach an additional filter As an actual tube configuration, an additional filter may be attached, or the X-ray tube itself has a filter effect in the form of intrinsic filtration. May be. As a result, the X-ray characteristics emitted from the X-ray tube need only be equivalent to aluminum 2.5 mm or more. Figure 5 shows the X-ray spectrum obtained when the filter is mounted on an x-ray tube with a 2.5 mm thick aluminum tungsten anode. The applied tube voltages were 25 kVp, 20 kVp, and 40 kVp, respectively. It's time.

By attaching the additional filter 81 to the X-ray tube of the tungsten anode, as shown in FIG. 5, X-rays in the low energy band V that adversely affect the human body are removed by the additional filter 81. As a result, the X-ray energy width of the X-rays emitted from the X-ray source 8 is reduced, and unnecessary portions of the multicolor X-rays emitted from the X-ray tube of the tungsten anode are removed to remove the X-rays. Can be monochromatic.

[0053] The X-ray source 8 is preferably a rotating anode X-ray tube! In this rotating 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 will be damaged by the generation of heat. Therefore, in a normal X-ray tube, the anode is rotated to prevent a decrease in the life of the anode! . The rotating anode X-ray tube causes an electron beam to collide with a surface of a certain size of the anode, and the generated X-ray is emitted toward the subject H from the plane of the certain size of the anode. The size of the plane viewed from this irradiation direction (subject direction) is called the focus.

[0054] The focus size D (11 m) is the length of one side when the focus is square, the length of the short side when the focus is rectangular or polygonal, and the diameter when the focus is circular. Point. The larger the focal spot size D, the more X-rays are emitted.

[0055] The focal spot size of the X-ray tube of the X-ray source 8 used in this embodiment is 1 μm force, preferably 500 μm force S. If it is less than 1 am, a sufficient amount of X-rays that pass through the subject H can be obtained within a few seconds. I can't. If it is longer than 500 m, the image will be blurred and the measurement accuracy will be reduced.

Further, the bone mineral content measuring apparatus 1 can adjust the set value of the tube voltage of the power supply unit 9 so that the tube voltage is adjusted and applied to the X-ray source 8. It is now possible to irradiate X-rays with the desired amount of energy!

In the present embodiment, the bone mineral content measuring apparatus 1 can measure the bone mineral content and take a general X-ray image as described above, and measures the bone mineral content. For this, it is preferable that the tube voltage applied to the X-ray source 8 is 20 kVp or more and set to 49 kVp or less. The more preferable setting tube voltage is 25 kVp or more and 39 kVp or less. If the tube voltage is too low, all of the irradiated X-rays are absorbed by the bone of subject H and the amount of transmitted X-rays required for measurement cannot be obtained! /. If the tube voltage is too high, the bremsstrahlung X-rays will increase more than necessary and the measurement accuracy will deteriorate.

[0058] By setting the tube voltage in this way, the bone mineral content measuring apparatus 1 can measure the bone mineral content in a low energy band (15 keV to 4) called so-called soft X-ray with a tube voltage of 50 kVp or less. OkeV) X-ray images can be taken.

[0059] Since conventional bone imaging was performed using a conventional silver halide photographic light-sensitive material with a dynamic range of about two digits, the tube voltage applied to the X-ray source 8 was set to 50 kVp or higher. Had gone. By setting the tube voltage as high as this, it is possible to obtain an image contrast that can withstand diagnosis and the like even when the dynamic range force is about three orders of magnitude. On the other hand, when the tube voltage applied to the X-ray source 8 is set lower than 50 kVp, the force that can provide an image contrast that can withstand diagnosis etc. for soft tissues such as skin S, the magnitude of X-ray absorption Sufficient contrast cannot be obtained at the bone. However, in this embodiment, a digital X-ray detector having a wide dynamic range is used as the X-ray detector 11 as will be described later, so that X-rays that greatly decrease in the bone can be sufficiently diagnosed. A tolerable contrast can be obtained and bone mineral content can be measured.

[0060] When a general X-ray image is taken, for example, the tube voltage applied to the X-ray source 8 is set to 50 kVp or more and 150 kVp or less. For general X-ray imaging, both low-energy imaging and high-energy imaging are performed. It is also possible to perform subtraction processing (energy subtraction processing). In this case, for example, a tube voltage of 60 kVp is applied in the case of shooting in the low energy band, and in the case of shooting in the high-engineering energy band. A tube voltage of 120 kVp is applied to the.

Note that the tube voltage at the time of bone mineral content measurement and the tube voltage at the time of general X-ray imaging are not limited to the ranges exemplified here.

One end of a detector holding unit 12 that holds an X-ray detector 11 that detects X-rays that have passed through the subject H is attached to the lower part of the holding member 7.

Note that the X-ray detector 11 can be pulled out from the detector holding portion 12 in the horizontal direction (FIG. 3 (a)). It is preferable that the X-ray detector 11 can be pulled out in both the left and right directions. For example, the X-ray detector 11 is fixed in the detector holding portion 12 by a fixing means (not shown) so as not to drop during oblique imaging.

[0064] As the X-ray detector 11, for example, a digital X-ray detector such as CR (Computed Radiography) force set or FPD (Flat panel X-ray detector) containing a stimulable phosphor sheet is applied. The power to do S. As a CR force set, for example, a REGIUS force set for the REGIUS Vstage Model 190 can be used.

Note that the X-ray detector 11 is not limited to CR or FPD as long as it is a digital X-ray detector.

[0066] Silver halide photographic light-sensitive materials have been widely used for conventional X-ray imaging. However, when a silver halide photographic light-sensitive material is used, the amount of X-ray transmitted through the subject is measured. For this purpose, first, the image density of the film after development processing is measured and then calculated. Further, in the case of a silver halide photographic light-sensitive material, the dynamic range force is about an order of magnitude, and accurate measurement is impossible. On the other hand, if a digital X-ray detector is used, image data can be obtained directly as a digital image signal, which can be processed accurately and quickly.

[0067] In the present embodiment, the X-ray detector 11 has a dynamic range of three digits or more.

Here, the density range of the image detected by the bone mineral content measuring apparatus 1 in this embodiment is 3 Corresponds to X-ray absorption coefficient of more than digits. In other words, the X-rays irradiated to the subject H are attenuated (decreased) by several tenths by passing through the bone. In addition, the X-ray intensity distribution on the surface of the two-dimensional X-ray detector 11 usually has a difference (variation) of about twice the maximum value and the minimum value of the X-ray intensity. Therefore, in order to accurately measure the bone mineral content, it is necessary to perform X-ray intensity correction (shading correction described later) on the X-ray detector 11 surface. Considering such X-ray attenuation and the necessity for correction, the dynamic range of the X-ray detector 11 needs to be at least three digits or more in order to accurately measure bone mineral density. Since the dynamic range is 3 digits or more, it is possible to achieve higher sensitivity and higher resolution than when shooting with X-ray film, etc., and the tube voltage applied to the X-ray source 8 is low! /, Even when taking images in the low energy band, it is possible to detect images with good contrast.

[0069] It should be noted that the dynamic range is not particularly limited as long as it is 3 digits or more, and the dynamic range is as wide as possible in consideration of measurement errors. However, if the dynamic range exceeds 7 digits, it takes time to process the image data and the equipment becomes expensive, so the dynamic range is preferably 7 digits or less! /.

[0070] The relative position of the X-ray source 8 and the detector holding unit 12 is fixed, and the distance is R. In Fig. 2, the distance from X-ray source 8 to subject H is rl, and the distance between subject H and the X-ray detector is r2.

[0071] Note that, without making R constant, both the distance from the X-ray source 8 to the subject and the distance from the subject to the X-ray detector 11 may be appropriately variable.

[0072] The distance from the subject H to the X-ray detector 11 is 15 cm or more.

[0073] When X-rays pass through the subject H, the force that generates scattered X-rays with various energies from the subject H as secondary X-rays. Thus, the distance from the subject H to the X-ray detector 11 By separating them by 15 cm or more, the scattered X-rays can be reduced without reducing the primary X-ray dose by the so-called Gradel effect. By separating the distance between the subject H and the X-ray detector 11 in this way, it is possible to remove scattered X-rays and prevent the energy width of the X-rays detected by the X-ray detector 11 from widening. Therefore, it is preferable because X-rays with higher monochromaticity can be obtained.

[0074] However, when the distance force m to the subject H-force X-ray detector 11 is exceeded, the apparatus becomes very large. In addition, since the X-ray dose to be detected by the X-ray detector 11 is greatly reduced by the distance square law, if the distance is too far, the image is not sharp. For this reason, the distance from the subject H to the X-ray detector 11 is preferably lm or less.

[0075] As a method for removing scattered X-rays, it is generally known to use an X-ray grid. Even in this embodiment, it is possible to use an X-ray grid. If a force X-ray grid is used, it is preferable not to use it because primary X-rays are reduced.

[0076] An X-ray dose detector 13 for detecting the irradiated X-ray dose is provided below the holding member 7 and on the lower surface of the detector holder 12.

[0077] Between the X-ray source 8 and the detector holding unit 12, a flat object table 14 is provided so that one end thereof is attached to the holding member 7. The subject table 14 is provided with a motor or the like that changes the position relative to the holding member 7 in order to enable imaging magnification adjustment (position adjustment in the height direction) during phase contrast imaging in general X-ray imaging. Connected to device 15.

[0078] A water tank 30 for inserting the finger of the subject who is the subject H at the time of radiographing can be attached to and detached from the X-ray irradiation region irradiated from the X-ray source 8 on the subject table 14. It is placed. In this embodiment, the water tank 30 is a liquid material holding member that holds the liquid material 31 containing the subject H at the time of imaging, and the subject H is placed in the water tank 30 inside the water tank 30. At this time, the liquid material 31 is held in such an amount that the entire specimen H can be sufficiently immersed. In this embodiment, the subject H is submerged in the liquid material 31 having a certain depth, and X-ray imaging is performed with the subject H sufficiently immersed.

[0079] The depth (amount) of the liquid material 31 held in the water tank 30 varies depending on the subject H. For example, about 3 cm to 10 cm for fingers and about 5 cm to 15 cm for feet.

[0080] As the liquid substance 31, water is most convenient, inexpensive and safe because it is preferable. You may use the thing which added the fragrance | flavor, disinfectant, the pigment | dye, etc. to water, and gave the device which makes a patient feel safe. In addition, it is preferable to use a liquid 31 that is closer to human flesh and body fluid than water. For example, a hyaluronic acid solution, a gelatin solution, a glycerin solution, a mannose solution, a rice juice, a starch solution, etc., alone or in a solution with water can be used. [0081] Further, the liquid material 31 may be held in the water tank 30 after being placed in a plastic bag or the like so that the subject H does not directly touch the liquid material 31. In this case, place the finger, which is the subject H, on the subject table 14 and then place the liquid 31 in a plastic bag on the finger during imaging, for example, using a compression plate. Then press liquid 31 from above. As a result, the thickness of the finger and the liquid material 31 can be made constant. In this case, the subject table 14 that does not require the water tank 30 functions as a liquid material holding member that holds the liquid material 31 placed in a plastic bag or the like.

[0082] Further, the liquid 31 or the liquid 31 in a bag or the like may be heated to about body temperature.

[0083] In addition, a fixing tool (not shown) for fixing the subject's fingers can be attached to and removed from the subject table 14 by itself.

[0084] In the present embodiment, the bone mineral content measuring apparatus 1 is capable of taking a general X-ray image in addition to measuring the bone mineral content (bone mineral content) as described above. When taking general X-ray images, remove the aquarium 30 from the subject table 14, place a finger on the subject table 14 as the subject H, and fix the finger with a fixture. And then shoot.

It should be noted that the subject table 14 may be provided with a sensor or the like that detects the orientation of the fingers or the left and right.

Yes

[0086] An example of the bone mineral content measuring apparatus 1 in the present embodiment is as follows. For example, the entire apparatus height HI force S2200mm, the distance H2 between the X-ray tube 8 and the subject table 14 is manually in the range of 430mm to 650mm. The distance H3 from the subject table 14 to the X-ray detector 11 can be manually adjusted within the range of 490 mm to 750 mm. Further, for example, the apparatus width W is 780 mm and the apparatus depth Dl is 1160 mm, and the limit of the distance A shown in FIG. 1 is preferably about 440 mm, and the limit of the distance B is preferably about 470 mm. The height of the subject table 14 (distance from the subject table 14 to the ground) H4 is preferably 900 mm or less (see FIG. 2).

[0087] In the present embodiment, X-rays are irradiated on the end of the imaging apparatus main body 4 above the subject table 14 so that X-rays emitted from the X-ray source 8 do not reach the subject. A shielding face guard 21 is provided extending substantially in the vertical direction.

[0088] In addition, the subject should be at the shooting position on the lower surface of the subject table 14 without hitting the leg. The protector 25 is provided so as to extend substantially in the vertical direction. As a result, the subject can reach the imaging position without hitting his / her leg on the detector holding unit 12.

Note that the fixing tool, the face guard 21 and the protector 25 are not essential components, and the fixing tool, the compression plate 21 and the protector 25 may not be used.

[0090] As shown in FIG. 6, the imaging main unit 4 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like (all not shown). A control device 22 is provided. An X-ray dose detection unit 13, a power supply unit 9, a drive device 6, and a position adjustment device 15 are connected to the control device 22 via a bus 23. The control device 22 includes a keyboard touch panel (not shown) for inputting photographing conditions and the like, an input device 24a having a position adjusting switch for adjusting the position of the object table 14, and the CRT. An operation device 24 having a display device 24b such as a display or a liquid crystal display is connected.

[0091] The ROM of the control device 22 stores a control program and various processing programs for controlling each part of the bone mineral content measuring device 1. The CPU cooperates with the control program and the various processing programs. The bone mineral content measuring device 1 controls the operation of each part in an integrated manner, performs X-ray imaging, and generates X-ray image data.

[0092] For example, the CPU controls the driving device 6 on the basis of the imaging conditions of the subject, measurement of bone mineral content or general X-ray imaging! /, The type of imaging, and the like. Raise and lower 4 to a height that matches the height of the subject, and rotate support shaft 5 to adjust the X-ray irradiation angle. Then, the position adjustment device 15 adjusts the position of the subject table 14 and adjusts the magnification of phase contrast imaging in the case of general X-ray imaging. Thereafter, the imaging unit 4 performs imaging processing, and the power supply unit 9 applies a tube voltage and a tube current to the X-ray source 8 to irradiate the subject H with X-rays. When the X-ray dose input from 13 reaches the preset X-ray dose, the X-ray irradiation from the X-ray source 8 is stopped by controlling the power supply unit 9.

In the present embodiment, the ROM of the control device 22 includes various programs related to image processing and bone mineral quantification, such as an image processing program and bone mineral quantification program, as well as these processes. Stores various data used when executing physical programs. The CPU of the control device 22 cooperates with these control programs and various processing programs to measure the bone mineral content based on the image processing of the acquired image data and the data subjected to the image processing. I do.

Specifically, the control device 22 performs the following processing.

[0095] First, the control device 22 performs X-rays using an aluminum step in order to correct the device characteristics when the bone mineral content measuring device 1 is shipped from the factory or when it is installed at the installation location. Take a picture and based on the obtained image data, find the shading correction value for the deviation of the X-ray dose on the 14th subject table. Then, shading correction is performed on the image data based on the obtained correction value.

[0096] Next, X-ray imaging is performed using a bone mineral quantification phantom containing calcium carbonate. Then, the control device 22 transmits the bone mineral quantitative phantom from the X-ray amount detected by the X-ray detector 11 and transmitted through the bone mineral quantitative phantom and the calcium carbonate content in the bone mineral quantitative phantom. Determine the relationship between X-ray dose and calcium carbonate content.

[0097] When the relationship between the X-ray dose detected by the X-ray detector 11 and the calcium carbonate content is obtained in this way, the control device 22 calculates the relationship for each tube voltage of the X-ray source 8. Store in a storage unit (not shown) such as ROM. Then, when an image is taken to measure the bone mineral content of the subject H, it is stored in association with the tube voltage of the X spring source 8 at the time of imaging! /, X dose and carbonate content The bone mineral content is quantified based on the relationship. Note that the relationship between the X-ray dose stored in the storage unit of the control device 22 and the calcium carbonate content is not limited to this if the bone mineral content can be quantified. And the calcium carbonate content, or the X-ray dose detected by the X-ray detector 11 and the calcium equivalent amount.

In addition, when performing general X-ray image capturing, the control device 22 performs gradation processing and density adjustment for adjusting the image contrast to the image data of the X-ray image acquired by the X-ray detector 11. Image processing such as adjustment processing and frequency processing for adjusting sharpness is performed. As a result, it is possible to perform image processing suitable for conditions such as an imaging region.

Next, the operation of the bone mineral content measuring apparatus 1 in the present embodiment will be described. [0100] First, the aluminum step was used to determine the shearing correction value for the X-ray irradiation bias on the 14th surface of the subject table, and the X-ray image was taken using the bone mineral quantification phantom. Find the relationship between absorbed and attenuated X-ray dose and calcium carbonate content.

[0101] Thereafter, the height of the subject table 14 is adjusted to the position of the subject H of the subject, and the X-ray detector 11 and the subject H are separated by a distance of 15 cm or more and lm or less. Adjust as follows. Further, a water tank 30 holding an appropriate amount of liquid substance 31 is placed at a predetermined position on the subject table 14, and the subject H is immersed in the water tank 30. For example, when the subject H is a finger, the finger is sufficiently immersed in the liquid 31 in the water tank 30. Then, a predetermined amount of X-rays are irradiated from the X-ray source 8 with the fingers immersed in the liquid material 31 of the water tank 30, and X-ray images are taken.

[0102] The X-ray dose detected by the X-ray detector 11 is sent to the control device 22 as image data. The control device 22 first determines the bone mineral content measurement target in the image data. The bone mineral content is determined based on the relationship between the X-ray dose obtained and the calcium carbonate content.

[0103] In this embodiment, X-ray images are shot by irradiating soft X-rays with low energy, so in the case of an original image that is not processed, the entire image is captured. It becomes ugly and the finger image cannot be clearly identified. On the other hand, in the case of a quantitative image obtained by performing processing based on the correction coefficient, the finger image can be clearly identified, and the bone mineral content is accurately measured based on this quantitative image. It becomes possible.

[0104] When the bone mineral content is measured by the aluminum thickness equivalent (mmAl), the control device 22 executes the following processing.

[0105] X-ray imaging using aluminum step-edge A1 detects X-ray dose that passes through aluminum step wedge A1 with different thickness and X-ray dose that passes through acrylic Ac. Obtain the attenuation coefficient of aluminum.

A1

[0106] For example, a material with X-ray absorption coefficients of μ and μ and thicknesses of X and X, respectively.

1 2 1 2 When there are superimposed objects, the thickness “L” of the entire object is x + x = L. So

1 2

Then, let the X-ray dose incident on this object be "I", and the X-ray when it passes through the object of thickness "L"

0

When the dose is “I”, the following equation (1) is established.

[0107] 1 = 1 exp (-μ χ-μ χ) · · · Equation (1) When this equation (1) is transformed, the following equation (2) is obtained.

[0108] μ + μ = ln (I / I) .. Formula (2)

1 1 2 2 0

At this time, the following equation (3) is derived.

[0109] χ = {1η (Ι /!)-/ (U-μ) ··· Equation (3)

1 0 2 1 2

As a result, In (I / 1) can be obtained by X-ray imaging. At this time I and L and force S already

0 2

If you know, you can get the value of X if you get II force S.

[0110] When measuring the amount of bone mineral, μ is a liquid such as water as described above.

2

1 is used, and μ is the bone of the finger that is the subject's heel. L can be made constant by immersing your finger in the water tank 30 containing the liquid material 31 such as water and adjusting the amount of the liquid material 31.

[0111] In addition, in order to accurately determine this μ, it is necessary to use monochromatic X-rays obtained from, for example, synchrotron radiation X-ray sources. When the tungsten anode X-ray tube is used, it is possible to obtain X-rays with excellent monochromaticity by removing unnecessary X-rays, so that μ can be accurately obtained.

[0112] Therefore, when calculating the attenuation coefficient of aluminum, the thickness of the object is set to “L”.

A1

The X-ray dose incident on the object is “I”, and the X-ray dose attenuated by the object is “I”.

0 1 When the X-ray dose when passing through an object of “L” is “I”, first, Equation (5) is obtained from Equation (4).

[0113] I = 1 θχρ (-X) Equation (4)

1 0 u u

μ = ln (I / I) / X Equation (5)

u 0 1 u

The energy (Eeff) corresponding to Lu is obtained based on the absorption coefficient database.

[0114] Further, based on the absorption coefficient database, an attenuation coefficient of aluminum (A1) corresponding to Eeff is obtained.

A1

[0115] Based on these calculated values, Equation (8) is obtained from Equation (6) and Equation (7).

'Calculate the theoretical thickness (X).

[0116] X + = = ln (I / I) X + X • Formula ½)

Al Al Lu Lu u

X + X = L 'Expression (7)

Al Lu X = {ln (I /!)-/ (U-) · · · · Equation (8)

Al 0 Lu Al Lu

The control device 22 then calculates the calculation result X and the actual aluminum step edge.

A1

Using the measured value X of the thickness, the correction coefficient in the bone mineral content measuring device 1 is obtained.

[0117] Furthermore, the control device 22 performs quantitative measurement of aluminum using this correction coefficient.

[0118] Since the image density correlates with the X-ray dose detected by the X-ray detector 11, by measuring the image density in the image density profile (b), the X-ray dose and the X-ray attenuation rate are measured. And the theoretical thickness X of the aluminum step edge A1 as described above.

A1 can be calculated. Then, by correcting using the correction coefficient, the thickness X of the aluminum can be quantified.

[0119] That is, in the CXD (Computed X-ray Densitometry) method, an X-ray photograph of a finger is taken together with an aluminum step edge A1, and for example, the aluminum corresponding to the density of C1 near the midpoint of the second metacarpal bone is taken. By quantifying the thickness X, the amount of bone mineral can be expressed by the thickness equivalent of aluminum (mmAl).

[0120] As described above, according to the bone mineral content measuring device 1 in the present embodiment, the bone mineral content is simply and accurately measured using an apparatus that can be used for general X-ray imaging. That power S. As a result, bone mineral content can be measured at the time of regular medical examinations, etc., and measurement can be repeated over time. For this reason, prevention and early detection of osteoporosis that often occurs in the elderly can be performed with as little burden as possible on the elderly.

[0121] In addition, since a tungsten anode X-ray tube is used as the X-ray source 8 with a low tube voltage setting, X-rays with excellent monochromaticity can be obtained, and accurate bone mineral content can be measured. Can do. The tungsten anode X-ray tube is extremely strong in the specified energy band like the molybdenum anode X-ray tube! /, And there is no characteristic X-ray that generates the emission line spectrum! /, So it is gentle over a certain energy band. Distributing characteristics X-rays can be used, and the attenuation of X-ray dose when X-rays pass through the bone is mitigated, and the accuracy of bone mineral content measurement is improved. Since it does not have an emission line spectrum, even if the X-ray detector 11 is taken away from the subject H, X-rays refracted near the edge of the bone are superimposed on the absorbed and attenuated X-rays. This is suitable for bone mineral quantification over a long period of time when errors in the detected X-ray dose are unlikely to occur.

[0122] The tube voltage of the X-ray source 8 is 20 kVp or more, 49 kVp or less, more preferably 25 kVp or more, Therefore, the transmission X-ray dose necessary for bone mineral content measurement can be obtained, and the bremsstrahlung X-ray does not increase more than necessary, so the measurement accuracy is not deteriorated. .

[0123] Further, by separating the X-ray detector 11 by 15 cm or more from the subject H, the scattered X-rays can be reduced without reducing the primary X-ray dose due to the so-called Gradel effect. Can capture the transmitted X-ray dose from X-rays with better monochromaticity. In addition, since the distance force between the X-ray detector 11 and the subject H is less than Sim, the measurement accuracy of the bone mineral amount is increased so that the X-ray dose to be detected by the X-ray detector 11 does not greatly decrease. . In addition, since the distance between the X-ray detector and the subject is short, the size of the apparatus can be reduced.

[0124] Furthermore, since the dynamic range of the X-ray detector 11 is as wide as 3 digits or more, X-rays that greatly decrease in the bone can be measured sufficiently, and the measurement accuracy of bone mineral content can be improved. . In addition, since the dynamic range is 7 digits or less, the time spent on image data processing is short, and the device cost can be kept low.

[0125] Since subject H is a human finger or the like, the subject sat in chair X and dipped his hand into aquarium 30 placed on subject table 14 in front of the apparatus. The bone mineral content can be measured by a simple method of photographing in a state.

[0126] In this embodiment, the force S and the bone mineral content measuring device 1 configured so that the bone mineral content measuring device 1 can also serve as a general X-ray imaging apparatus are: It may be a dedicated machine for measuring bone mineral content.

[0127] In this embodiment, the force subject H is not limited to the force H as an example of the human hand as the subject H, and the bone mineral content is measured using the foot or other body part as the subject H. May be.

Claims

The scope of the claims

[1] A bone mineral content measuring apparatus for taking an X-ray image of a subject and measuring the bone mineral content of the subject based on the obtained image data,

An X-ray source for irradiating the subject with X-rays;

The X-ray detector has a dynamic range of 3 digits or more and a distance from the subject.

A bone mineral content measuring device, which is arranged so as to be separated by 15 cm or more.

[2] The bone mineral content measuring device according to claim 1, wherein the X-ray source has a tube voltage set to 20 kVp or more and 49 kVp or less!

[3] The bone mineral content measuring device according to claim 1 or 2, wherein the X-ray source has a tube voltage set to 25 kVp or more and 39 kVp or less.

[4] The bone mineral content measuring device according to any one of claims 1 to 3, wherein the dynamic range of the X-ray detector is 7 digits or less. .

[5] The X-ray detector according to any one of claims 1 to 4, wherein the X-ray detector is arranged so as to be less than or equal to a distance force Sim with respect to the subject. The bone mineral content measuring device described.

[6] The bone mineral content measuring device according to any one of claims 1 to 5, wherein the subject is a human finger or foot.