KR20020086198A - Method for measurement of bone mineral density using X-ray image - Google Patents

Abstract

PURPOSE: A method for measuring bone density using an X-ray image is provided to improve the accuracy of bone density measurement by eliminating an X-ray absorbing effect by a soft part included in a bone region. CONSTITUTION: An input/output unit(11) inputs from and outputs to an external user data required to the measurement of bone density. Main/auxiliary memory units(12,13) store all sorts of data required to the process for measuring the bone density by using an X-ray image. A microprocessor(14) controls the main/auxiliary memory units(12,13) and the input/output unit(11) and performs all of calculation process for measuring the bone density by the X-ray image. The input/output unit(11) includes an X-ray film scanner for digitally imaging the X-ray image, a monitor, a printer, and an X-ray film.

Description

Method for measuring bone density using X-ray image {Method for measurement of bone mineral density using X-ray image}

The present invention relates to a method for measuring bone density for measuring bone density, which is an important indicator used for diagnosis of osteoporosis, and more particularly, to measure bone density using an X-ray image. The present invention relates to a bone density measuring method for measuring bone density by removing the X-ray absorption effect and a computer-readable recording medium recording a program for realizing the method.

Osteoporosis is a pathological condition with pain, fractures of the spine and thighs, bone deformation, etc. with abnormally reduced bone mass. In general, young people have a balance between bone production and absorption. However, osteoporosis is very frequent in the elderly after osteoporosis and in postmenopausal women whose estrogen secretion is decreased and bone resorption is improved. However, it is not easy to effectively recover the bone mass once reduced. Therefore, the prevention and early treatment of osteoporosis is important. For this purpose, it is very important to develop a method for measuring bone density that can be widely used on a daily basis.

Qualitative bone density measurement methods include the Saville index and the Singh index. The Saville index and the Singh index are methods for measuring bone mineral density using changes in bone litter patterns in the lumbar lateral X-ray and femoral X-ray images, respectively. However, since this method depends on the experience of the doctor, the error between readers is large and the reproducibility by the same reader is also low.

Quantitative bone density measurement methods include Quantitative Computed Tomography (QCT), Dual Energy X-ray Absorptiometry (DEXA), and Ultrasound BMD.

QCT can obtain a three-dimensional image of the bone, can be measured separately from the bone density of the cortical (cortical bone) and trabecular bone (trabecular bone), there is an advantage that can predict the structural stability of the bone. Despite these advantages, the cost of QCT equipment is very high and the radiation dose is several hundred times that of simple X-rays.

Compared to QCT, DEXA is cheaper in equipment price, has less radiation dose, and has high accuracy and reproducibility of bone density measurement. Therefore, DEXA has been widely used for the two-dimensional bone density measurement and the progress of osteoporosis treatment.

Ultrasound BMD is a device for measuring the bone density and structural strength of bone by using the change of the ultrasonic delivery speed or the change of elastic modulus according to the medium, there is a disadvantage that the reproducibility and accuracy is not high.

Although there are methods for measuring bone density such as QCT, DEXA, and ultrasonic bone mineral density measuring instrument, studies on the method of diagnosing osteoporosis and measuring bone density using X-ray images are continuously conducted from an academic standpoint. The reason is that most hospitals are equipped with X-ray imaging equipment, so there is no additional cost for purchasing bone density measurement equipment, and because of the high resolution of X-ray images, bone density measurement and spongy bone pattern analysis are possible. In particular, the cavernous bone pattern is believed to provide useful information about the possibility of fracture due to osteoporosis, and many researchers are studying the X-ray cavernous bone pattern.

However, although many methods for measuring bone density using X-ray images have been proposed, there are few examples of successful cases for clinical use. This is because the bone image shown in the X-ray image contains a considerable amount of X-ray absorption effect by the overlapped soft tissue, and only one sheet of X-ray image cannot remove the X-ray absorption effect by the overlapped soft tissue. Indeed, in some body parts, the amount of X-ray absorption by superimposed soft tissues is similar to the amount of X-ray absorption by bones to determine bone density. This can lead to significant bone density measurement errors.

Therefore, the present invention has been proposed to solve the above problems, when trying to measure the bone density using the X-ray image, to accurately measure the bone density by removing the X-ray absorption effect by the soft tissue contained in the bone region It is an object of the present invention to provide a method for measuring bone density and a computer-readable recording medium having recorded thereon a program for realizing the method.

1 is an exemplary view of a bone density measurement system to which the present invention is applied.

FIG. 2A is a flowchart illustrating an embodiment of a method for measuring bone density using X-ray images according to the present invention. FIG.

2b is a detailed flowchart illustrating an X-ray image acquisition process according to the present invention;

FIG. 2C is a detailed flowchart illustrating a background trend calculation process by soft tissue in the radial area in the ROI in accordance with the present invention. FIG.

3 is an exemplary view of an aluminum step-wedge used to calibrate an X-ray image in accordance with the present invention.

4 is an exemplary view of an X-ray image obtained by photographing a step wedge and a wrist according to the present invention.

5 is an exemplary view showing the relationship between the thickness of each step of the step wedge according to the present invention and the average gray level of each step of the step wedge shown in FIG.

6A is an exemplary view of a rectangular ROI selected for measuring x-ray images and radial bone density corrected using a step wedge according to the present invention.

6B is an illustration of a wrist cross section at one transverse line l of the region of interest in accordance with the present invention.

FIG. 7A is an exemplary view of a greylevel profile at transverse line l in FIG. 6A.

FIG. 7B is an exemplary view of a gray level profile with background trends removed by soft tissue in the radial area of FIG. 7A; FIG.

* Explanation of symbols for the main parts of the drawings

11: input / output device 12: main memory device

13: auxiliary memory 14: microprocessor

The method of the present invention for achieving the above object, in the bone density measurement method applied to the bone density measurement system for measuring bone density, the first step of obtaining an X-ray bone image; Setting a region of interest in the acquired X-ray bone image; Calculating a background trend due to soft tissue in the bone region within the set region of interest; And calculating a bone mineral density index by removing the background trend caused by the soft tissue in the bone region in the region of interest.

On the other hand, the present invention, the bone density measurement system having a processor, a first function for obtaining the X-ray bone image; A second function of setting a region of interest in the acquired X-ray bone image; A third function of calculating a background trend due to soft tissue in the bone region within the set region of interest; And a computer readable recording medium having recorded thereon a program for realizing a fourth function of calculating a bone mineral density index by removing a background trend caused by the soft tissue in a bone region in the region of interest.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is an exemplary view of a bone density measurement system to which the present invention is applied.

The bone density measurement system to which the present invention is applied includes an input / output device 11 for inputting / outputting data necessary for bone density measurement with an external user, and main data for storing various data necessary for measuring bone density using an X-ray image. Microcontroller for controlling the secondary / secondary storage devices 12 and 13 and the primary / secondary storage devices 12 and 13 and the input / output device 11 and performing arithmetic processing for measuring bone density using an X-ray image. And a processor 14.

The input / output device 11 includes a monitor, a printer, an X-ray film scanner for digitally imaging an X-ray film, and the like. In the case of using a digital image sensor (CCD or CMOS sensor) instead of the X-ray film, the digital image sensor is included in the input / output device 11.

Through the system as described above, a method for measuring bone density using an X-ray image is performed. An X-ray image is input / output device 11 in a state in which a program including the processing of FIG. When the program is executed by inputting), the program measures bone density using an X-ray image.

This operation will be described in detail with reference to FIGS. 2 to 7.

2A is a flowchart illustrating a method for measuring bone density using an X-ray image according to the present invention, FIG. 2B is a detailed flowchart illustrating an X-ray image acquisition process according to the present invention, and FIG. 2C is a flowchart illustrating an embodiment of the present invention. Detailed description of one embodiment of a process of calculating a background trend by soft tissue in a radial region in a region of interest.

3 is an exemplary view of an aluminum step-wedge used to calibrate an X-ray image according to the present invention. The characteristics of the X-ray generator, screen and film types, film development conditions, and An example of a radial aluminum step wedge used to correct an image characteristic change caused by X-ray image acquisition conditions such as an X-ray film digitizer characteristic (a characteristic of a solid-state image sensor or CMOS sensor in the case of a digital image sensor).

4 is an exemplary view of an X-ray image obtained by photographing a step wedge and a wrist according to the present invention, and FIG. 5 is an average of each step thickness of the step wedge and the step wedge shown in FIG. 4 according to the present invention. 6A is an exemplary view showing a relationship between gray levels, FIG. 6A is an exemplary view of a rectangular ROI selected for measuring X-ray images and radial bone density corrected using a step wedge according to the present invention, and FIG. a crossing according to the area of interest line l is one example of the wrist section is also on, Figure 7a is the soft tissue at the radial region of Figure is an example of a gray level profile of the cross-sectional of Figure 6a the line l, and Fig. 7b is Fig. 7a Figure 1 shows an example of a gray level profile from which background trends are eliminated.

First, as shown in FIG. 2A, a wrist X-ray image of a person who is trying to measure bone density is obtained (21). When obtaining the X-ray image, the X-ray image acquisition condition is kept as constant as possible. In particular, the tube voltage (kVp) and the tube current (mA) of the X-ray generator are fixed to a specific value. For example, when obtaining the wrist X-ray image, the conditions of the X-ray generator use 50kVp and 50mA. An X-ray image is obtained by digitizing an X-ray film obtained through simple X-ray imaging with an X-ray film scanner. When using a digital image sensor, an X-ray image is directly obtained without using a film scanner. When the X-ray image is obtained, the spatial resolution is 200 pixels per inch (PPI) and each pixel is 256-color gray level of 8-bit depth.

4 illustrates an example of a wrist X-ray image digitized using an X-ray film scanner. Each pixel of the X-ray image is composed of gray levels related to the amount of X-rays absorbed by the human body. The amount of X-rays absorbed by the human body is determined by the density and thickness of bone and soft tissue. In general, X-ray bone image includes the effect of X-ray absorption by the overlapped soft tissue at the same time. Therefore, in order to measure the bone density using the gray level of the X-ray image, the X-ray absorption effect by the soft tissue included in the X-ray bone image should be removed.

Meanwhile, image characteristics such as brightness and contrast of the X-ray image are sensitive to changes in X-ray image acquisition conditions. That is, the brightness (gray level) of each pixel of the X-ray image may not be an absolute reference for the amount of X-ray absorption in the pixel. Therefore, when the bone density is to be measured using the X-ray image, first, the change of the image characteristic due to the X-ray image acquisition condition is corrected and the amount of X-ray absorption at each pixel is quantified.

In order to correct the change in X-ray image characteristics due to the X-ray image acquisition condition and to quantify the amount of X-ray absorption at each pixel, a metal step wedge having a plurality of steps is used as shown in FIG. 3. Aluminum, copper, etc. are used as a material of a metal step wedge. In general, the material and thickness of the metal step wedge are appropriately selected depending on the part of the body where the bone density is to be measured. In general, the material and thickness of the step wedge are selected so that the amount of X-ray absorption at the highest step of the step wedge is greater than the maximum amount of X-ray absorption of the body part to be measured for bone density. When the bone density is measured at the wrist, the maximum thickness of the aluminum step wedge should be 12 mm, and the step wedge containing heavy metal such as copper should be reduced in consideration of the large X-ray absorption coefficient. The step wedge illustrated in FIG. 3 is made by processing a square aluminum plate having a base of 40 mm x 40 mm and a thickness of 12 mm in a radial step of eight steps. In the aluminum step wedge, the height of each step is 1.5, 3.0, 4.5, 6.0, 7.5, 9.0, 10.5, 12.0 mm from the low.

As shown in FIG. 2B, an X-ray image photographing the radial step wedge and a wrist region to measure bone density to correct changes in X-ray image characteristics due to acquisition conditions of the X-ray image and to quantify X-ray absorption amount in each pixel. (211). 4 is an exemplary view illustrating an X-ray image of the step wedge and the wrist part. In FIG. 5, two-dimensional data consisting of the thickness of each step wedge and the average gray level of each step of the step wedge shown in the X-ray image are represented by a rectangle (■). In Fig. 5, the gray level when the thickness of the step wedge is 0 is the average of the background gray level values around the step wedge.

Thereafter, as illustrated in FIG. 2B, the entire X-ray image is corrected using the thickness and gray level data of each step wedge (212). In order to correct the entire X-ray image using the step wedge, first, a gray level value at an arbitrary step wedge thickness must be calculated. To calculate the gray level at any step wedge thickness, the data of FIG. 5 is fitted using an appropriate function. In FIG. 5, as the thickness of the step wedge increases, the increase rate of the gray level gradually increases from 0 to 0, and later the gray level increase converges to 0 again. Since one of these features is the tangent hyperbolic function, we use a fitting function of the form f (t) = a + b * tanh (c * t + d). Where f (t) is a gray level, t is the thickness of the step wedge in mm, and a, b, c and d are fitting parameters, respectively. Here, the tanh function is fully symmetric about the point t = -d / c. By the way, as shown in Fig. 5, the gray level profile of the step wedge is generally not perfect symmetry. Therefore, fitting using one tanh function can cause a significant fitting error, so in the present invention, fitting is performed by dividing the data into two regions. The fitting function has four fitting parameters and requires four or more pieces of data in one fitting area. The first area consists of six data from the step of 0 mm to the step of 7.5 mm, and the second area consists of six data from the step of 4.5 mm to the step of 12.0 mm. Here, the two regions overlap each other to create a transition region for smoothly connecting the fitting results in the two regions. Thereafter, fitting is performed in each of the regions using the fitting function. The fitting uses the Levenberg-Marquardt fitting method.

The fitting result in the first region is referred to as f ₁ (t), and the fitting result in the second region is referred to as f ₂ (t). Now make two fitting functions into one final fitting function F (t) by First, t is in the <= 4.5, the interval _{F (t) = f 1 (} t) and a, t> = 7.5 interval _{F (t) = f 2 (} t). In section 4.5 <t <7.5, F (t) = x * f ₁ (t) + (1-x) f ₂ (t). Here, x = (7.5-t) / 3 is defined. Since the function F (t) is a simple incremental function, the inverse function F ^-1 (g) is uniquely determined. Where g is the gray level. Now, the gray level g of each pixel of the X-ray image is corrected as follows using the final fitting function F (t). If g> = F (12), the correction value is 255. If g <= F (0), the correction value is 0. Otherwise, the correction value is an integer part of 256 * F- ¹ (g) / 12.

6A is an exemplary view of FIG. 4 converted by the correction scheme. However, in the correction of the X-ray image using the above method, the fact that the change patterns of the X-ray absorption coefficients of aluminum and biological tissues according to the conditions (kVp, mA) of the X-ray generator showed a difference was neglected. Therefore, the correction effect is lowered for the change of severe X-ray imaging conditions (kVp, mA). However, since the stability of X-ray imaging equipment used in clinical practice is improving day by day, the possibility of serious change in X-ray imaging conditions is gradually decreasing.

Next, as shown in FIG. 6A, a rectangular ROI is set at the radial area to remove the X-ray absorption effect by the soft tissue included in the radial area of the X-ray image (22). The size of the ROI is 250x150 pixels, and the soft tissue area is included on the left and right of the radial area.

Thereafter, a background trend due to soft tissue is calculated in the radial area in the ROI (23).

To assist in understanding how to calculate the background trend by soft tissue, a wrist cross-section corresponding to one transverse line l of FIG. 6a is briefly shown in cross-section A of FIG. 6b. In FIG. 6B, the inner dark part is the radial area and the outer bright part is the soft tissue area. In general, the cross section of a long bone, such as a radial, is approximately close to a circle. Therefore, the cross section of the radial will be described in simplified form. As shown in Fig. 6B, (section A) = (section B in which the radial area of section A is replaced by soft tissue) + (section C in which only radial area of section A is extracted)-(section C by soft tissue) It can be considered as a relationship having cross section D). On the other hand, in FIG. 7A, the gray level profile in the horizontal line l of FIG. 6A is shown by the solid line. In FIG. 7A, horizontal is a coordinate of a pixel and vertical is a gray level. In Figure 7a a period _l ~ b _l, b _l ~ c _l, c _l ~ d _l is the soft tissue section between the respective transversal l soft tissue region in a radial section, the radius and ulna (ulna).

In the radial section b _| ~ c _| of FIG. 7a, it is impossible to accurately calculate the background trend by soft tissue. Therefore, we use an approximate method for calculating background trends. The method used in the present invention is to interpolate the gray level profiles of the soft tissue sections a _| ~ b _| and c _| ~ d _| to the radial section b _| ~ c _| to set the background trend. For interpolation, as shown in FIG. 2C, first, a differential fitting function for calculating a background trend of the radial area is selected (231). In general, a polynomial is appropriate as a fitting function, but with more restrictions, we fit a polynomial P ( x ) = C ₀ + C ₁ x + C ₂ x ² + C ₃ x ³ + C ₄ x ^4, which is less than or equal to 4th order. Used as. Where C ₀ , C ₁ , C ₂ , C ₃ , C ₄ are fitting parameters. Interpolation is achieved by fitting data from soft tissue sections a _l ~ b _l and c _l ~ d _l to the fitting function using the Levenberg-Marquardt fitting method, and softening the interpolation results in the radial section. Set as background trend by organization. In other words, the gray level profile of the soft tissue region adjacent to the radial region is interpolated into the radial region using the fitting function and set as a background trend (232). The above-described description of the process will be described in more detail. A process of obtaining a gray level profile on a horizontal line of the region of interest, dividing a bone region and a soft tissue region from the gray level profile, and Interpolating a gray level profile into the bone region with the fitting function and setting the interpolation result as a background trend by soft tissue. L 1 in FIG. 7A is a background trend set by interpolation with the polynomial described above. This background trend corresponds to the gray level profile by B in FIG. 6B. Now, the background line is calculated by moving the above-mentioned transverse line l to every row in the ROI.

If the background trend is set in the above, the bone density index of the radius is calculated by removing the background trend due to soft tissue from the gray level of the radial area (24). In more detail, the process 24 removes the set background trend from the gray level of each pixel of the valley area, and calculates an average value <G> of gray levels in the valley area from which the background trend is removed. Calculating a mean thickness (2 R ) of the bones in the region of interest, and multiplying a half ( R ) of the average thickness (2 R ) of the bones by a specific constant (c ₀ ) and the average value of the gray levels. ( <G> ) plus the value set to the bone mineral density index.

The gray level profile the background removal of the trend is shown in Figure 7b only in radial section b ~ c _{l l.} The gray level profile of FIG. 7B is approximately equal to the removal of the gray level profile by D from the gray level profile by C of FIG. 6B. The bone density of the radial is determined by the gray level profile by C of FIG. 6B. Therefore, in the interval b _l c ~ _l, the average of the gray level profile of the C _<l G _C> can be obtained by adding the gray level profile by D in Figure 6b to a gray level profile of Figure 7b.

In Equation 1, G _| (n) is the gray level profile of FIG. 7B, G _{| D} (n) is a gray level profile by D, and n is an index of a pixel. Equation (1) is expressed by an approximate integral formula as shown in Equation (2) below.

In Equation (2), x = ( n -b _| ) / (c _| -b _| ), And Is the transform function of G _| (n) and G _{| D} (n) according to the variable conversion. here, In order to calculate, we need to know the exact shape of section D. However, it is impossible to know the exact shape of D using X-ray images. Therefore, on the basis of the fact that the cross-section D of the radial anatomy is close to the circle, it is approximated as a circle and the radius is defined as r _| = (c _| -b _| ) / 2. Then, <G _{| C} > of Equation 2 is described by Equation 3 below.

In Equation 3, c ₀ is a constant.

Now, Equation 3 is calculated for every transverse line l in the region of interest, and then the average <G _C > is calculated as Equation 4 below.

In Equation 4, N is the number of possible crossing lines in the ROI.

Now, <G _C > in Equation 4 becomes the radial bone density index. In order to use Equation 4 for the measurement of radial bone density, the constant c ₀ must first be determined. To determine the constant c ₀ , wrist x-ray images obtained from a sufficient number of subjects are used. In each wrist X-ray image, the first term of Equation 4 And second protest Calculate Where R corresponds to half of the radial mean thickness of the radial within the region of interest. And each subject measures the BMD (g / cm <2> unit) of the bone density value using DEXA in the same site of a radial bone. Now, the constant c ₀ is set to the value at which the least-squares fit error between BMD and <G> + c ₀ R is minimum. C ₀ , set to the least square fit for 200 adult female subjects, is about 0.23.

Now, since the necessary constant c ₀ has been determined, the subject's radial bone mineral density index is calculated by <G> + c ₀ R. In general, the <G> value is more than twice the value of c ₀ R and the standard deviation of R values between subjects is about 4%. On the other hand, the standard deviation of <G> values between subjects is 40%. Therefore, the bone density index may be set to <G> only.

Looking at another preferred embodiment for calculating the bone mineral density index of the radial in the present invention (24) is as follows.

If the background trend is set in the above, the bone density index of the radius is calculated by removing the background trend due to soft tissue from the gray level of the radial area (24). In more detail, the process 24 removes the set background trend from the gray level of each pixel of the valley area, and calculates an average value <G> of gray levels in the valley area from which the background trend is removed. And calculating a weighted average P of bone cross section lengths within the region of interest, and a specific constant for the weighted average P And adding the value multiplied by) and the average value of the gray levels ( <G> ) to set the BMD.

The gray level profile the background removal of the trend is shown in Figure 7b only in radial section b ~ c _{l l.} The gray level profile of FIG. 7B is approximately equal to the removal of the gray level profile by D from the gray level profile by C of FIG. 6B. Within the region of interest, the bone mass of the radius is determined by the sum of the gray level profiles by C in FIG. 6B. Therefore, the interval from b ~ c _{l l,} the sum of the gray level profile of the C ( ) Can be obtained by adding the sum of the gray level profiles by D in FIG. 6B to the sum of the gray level profiles in FIG. 7B.

In Equation 5 above Is the gray level profile of Figure 7b, Is the gray level profile by D, and n is the index of the pixel. In Equation 5, In order to calculate, the gray level profile by cross section D must be known, and the exact shape of cross section D must be known to know this gray level profile. However, it is impossible to know the exact shape of D using X-ray images. Therefore, on the basis of the fact that the cross section D of the radial anatomy is close to the circle, I think. Then the expression (5) Can be approximated by the following equation (6).

In Equation 6 above Is a constant.

Now, Equation 6 is calculated for all the transversal lines l in the ROI, and the sum is calculated as Equation 7 below.

The left side of Equation (7) is the radial bone mass index in the region of interest.

Now, the left and right sides of Equation (7) represent the area of the bone region in the region of interest ( ) Divided by the radius BMD Becomes

In order to use the above Equation 8 for the measurement of radial bone density, Must be determined. a constant In order to determine, a wrist X-ray image obtained from a sufficient number of subjects is used. In each wrist X-ray image, a region of interest is set at a predetermined radial region, and the first term of Equation 8 ) And the second term constant Except for ( Calculate Where P in the second term It can be rewritten in form and shows the weighted average of the above-described bone region transverse lengths. In general, weighted averages do not differ significantly from simple averages, so P It can also be set to the average value of, i.e., the average transverse length of the valley area within the region of interest. And each subject measures the BMD (g / cm <2> unit) of the bone density value using DEXA in the same site of a radial bone. Now, the constant With the BMD Set the least-squares fit error to the minimum value. Set to a least squares fit for 200 adult female subjects Is about 0.10.

Now, the constants needed Was determined, the radial bone mineral density index of the subject Calculate by In general, the <G> value should be More than twice the value, the standard deviation of the P value between the subjects is about 4%. On the other hand, the standard deviation of <G> values between subjects is 40%. Therefore, the bone density index may be set to <G> only.

As described above, specific examples of the present invention have been shown. The numerical values or images used herein may be changed to improve the performance of the method of the present invention. The core of the present invention is to measure the bone density by removing the X-ray absorption effect by the soft tissue contained in the bone area when trying to measure the bone density using the X-ray image. In the measurement of bone density using conventional X-ray images, many error factors exist because the X-ray absorption effect of soft tissues included in bone images was not removed. In the present invention, after interpolating the gray level profile of the soft tissue around the bone into the bone region, the interleaved soft tissue gray level profile was removed from the gray level profile of the bone region. In addition, a method of modeling a cross section of the bone in a circular shape was introduced in order to correct an error due to the size and shape of the bone.

As described above, the method of the present invention may be implemented as a program and stored in a recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.) in a computer-readable form.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible in the art without departing from the technical spirit of the present invention. It will be apparent to those of ordinary knowledge.

The present invention as described above, when trying to measure the bone density using the X-ray image, there is an effect that can accurately measure the density of the bone by removing the X-ray absorption effect by the soft tissue included in the bone area.

Claims (18)

In the bone density measuring method applied to the bone density measuring system for measuring bone density, A first step of obtaining an X-ray bone image; Setting a region of interest in the acquired X-ray bone image; Calculating a background trend due to soft tissue in the bone region within the set region of interest; And A fourth step of calculating a bone mineral density index by removing a background trend caused by the soft tissue in the bone region in the region of interest Bone density measurement method using an x-ray image comprising a. The method of claim 1, The first step is, A fifth step of acquiring an X-ray image of a radial step wedge and a bone (bone) to measure bone density in order to correct changes in X-ray image characteristics due to acquisition conditions of the X-ray image and to quantify the amount of X-ray absorption at each pixel. ; And A sixth step of correcting the entire X-ray image using the thickness of each step of the radial step wedge and gray level data; Bone density measurement method using an x-ray image comprising a. The method of claim 1, The second step, The bone density measurement method using the X-ray image, characterized in that the region of interest is set to include the soft tissue region on the left and right of the bone region of the obtained X-ray bone image. The method according to any one of claims 1 to 3, The third step, A seventh step of selecting a fitting function for calculating a background trend of the valley area; And An eighth step of interpolating the gray level profile of the soft tissue region adjacent to the bone region into the bone region with the selected fitting function and setting it as a background trend; Bone density measurement method using an x-ray image comprising a. The method of claim 4, wherein The eighth step, A ninth step of obtaining a gray level profile in the region of interest; Dividing a bone region and a soft tissue region in the gray level profile; And An eleventh step of interpolating the gray level profile of the divided soft tissue region into the bone region by the fitting function and setting the interpolation result as a background trend by the soft tissue; Bone density measurement method using an x-ray image comprising a. The method of claim 4, wherein The fitting function is Bone density measurement method using an X-ray image, characterized in that the polynomial of the fourth order or less. The method of claim 6, The polynomial fitting, Bone density measurement method using an X-ray image, characterized in that the fitting by Levenberg-Marquardt fitting method. The method of claim 4, wherein The fourth step, A ninth step of removing the set background trend from the gray level of each pixel of the valley area; A tenth step of calculating an average value <G> of gray levels in the valley area from which the background trend is removed; An eleventh step of calculating an average thickness of the bones 2 R in the region of interest; And Step 12 In addition to the specific constants (c ₀₎ the value obtained by multiplying the mean value (<G>) of the gray levels in half (R) of the average thickness (R 2) of the goal set to the bone mineral density factor Bone density measurement method using an x-ray image comprising a. The method of claim 8, And a specific constant c ₀ of the twelfth step is set to zero. The method of claim 8, The specific constant c ₀ of the twelfth step is A method for measuring bone density using an X-ray image, characterized in that the minimum square fitting error between the bone density measured by the bone density measuring device and the bone density index ( <G> + c ₀ R ) is set to a minimum value. The method of claim 4, wherein The fourth step, A ninth step of removing the set background trend from the gray level of each pixel of the valley area; A tenth step of calculating an average value <G> of gray levels in the valley area from which the background trend is removed; An eleventh step of calculating a weighted average P of bone cross sections in the region of interest; And A twelfth step of setting the bone density index by adding the weighted average P multiplied by a specific constant c ₀ and an average value <G> of the gray levels; Bone density measurement method using an x-ray image comprising a. The method of claim 11, The bone density measurement method using the X-ray image, characterized in that the weighted average ( P ) of the bone cross-section length in the region of interest of the eleventh step is set to the average cross-sectional length of the bone region in the region of interest. The method of claim 11, In the eleventh step of the region of interest, the weighted average P of bone cross sections is set to (sum of squares of cross sections of bone regions in the region of interest) / (sum of cross lengths of bone regions in the region of interest). Bone density measurement method using an x-ray image, characterized in that. The method of claim 11, And a specific constant c ₀ of the twelfth step is set to zero. The method of claim 11, The specific constant c ₀ of the twelfth step is A method for measuring bone density using an X-ray image, characterized in that the minimum square fitting error between the bone density measured by a bone density measuring device and the bone density index ( <G> + c ₀ P ) is set to a minimum value. The method of claim 15, The bone density measuring equipment, BEX measurement method using an X-ray image, characterized in that DEXA (dual energy x-ray absorptiometry). In a bone density measurement system equipped with a processor, A first function of acquiring X-ray bone images; A second function of setting a region of interest in the acquired X-ray bone image; A third function of calculating a background trend due to soft tissue in the bone region within the set region of interest; And A fourth function of calculating a bone mineral density index by removing a background trend caused by the soft tissue in the bone region in the region of interest A computer-readable recording medium having recorded thereon a program for realizing this. The method of claim 17, The third function, A fifth function of selecting a fitting function for calculating a background trend of the valley area; And A sixth function of interpolating the gray level profile of the soft tissue area adjacent to the bone area into the bone area with the selected fitting function as a background trend A computer-readable recording medium having recorded thereon a program for realizing this.