阅读说明：本技术 一种基于dr系统的骨密度校正和测量的方法 (Bone density correction and measurement method based on DR system ) 是由 申果 金荣飞 于澜洋 于 2020-04-07 设计创作，主要内容包括：本发明涉及X射线数字图像处理技术领域,特别是涉及一种基于DR系统的骨密度校正和测量的方法。本发明包括以下步骤：1)建立模体,包括软组织模体和骨骼模体；2)通过DR设备设置不同的曝光条件以保证不同的曝光条件均可穿透模体并成像；3)采集软组织模体和骨骼模体在不同的曝光条件下的图像,并计算模体不同梯度对应的灰度均值；4)并得出不同曝光条件下,软组织模体衰减系数与软组织模体厚度的关系、以及骨骼模体衰减系数与骨骼模体厚度的关系；5)获取已知骨密度模体真实骨密度和计算得到的骨密度的校正关系及校正参数；6)得到待测对象真实骨密度值。本发明的有益之处在于精准性校正和准确性校正,最大限度保证计算骨密度值的精准性。(The invention relates to the technical field of X-ray digital image processing, in particular to a bone mineral density correction and measurement method based on a DR system. The invention comprises the following steps: 1) establishing a die body which comprises a soft tissue die body and a skeleton die body; 2) different exposure conditions are set through DR equipment to ensure that the different exposure conditions can penetrate through the die body and form images; 3) collecting images of a soft tissue die body and a skeleton die body under different exposure conditions, and calculating gray level mean values corresponding to different gradients of the die bodies; 4) obtaining the relation between the attenuation coefficient of the soft tissue mold body and the thickness of the soft tissue mold body and the relation between the attenuation coefficient of the skeleton mold body and the thickness of the skeleton mold body under different exposure conditions; 5) acquiring the real bone density of a known bone density die body and the correction relation and correction parameters of the bone density obtained by calculation; 6) and obtaining the real bone density value of the object to be detected. The method has the advantages of accurate correction and accuracy correction, and the accuracy of calculating the bone density value is guaranteed to the maximum extent.)

1. A method of bone density correction and measurement based on a DR system comprising the steps of:

1) establishing a die body which comprises a soft tissue die body and a skeleton die body; the soft tissue die body and the skeleton die body are both stepped die bodies;

2) different exposure conditions are set through DR equipment to ensure that the different exposure conditions can penetrate through the die body and form images;

3) collecting images of a soft tissue die body and a skeleton die body under different exposure conditions, and calculating gray level mean values corresponding to different gradients of the die bodies;

4) acquiring attenuation coefficients of the soft tissue die body and the skeleton die body under different exposure conditions through the acquired image, and acquiring the relation between the attenuation coefficient of the soft tissue die body and the thickness of the soft tissue die body and the relation between the attenuation coefficient of the skeleton die body and the thickness of the skeleton die body under different exposure conditions;

5) correcting the plurality of known bone density die bodies to obtain the correction relation and the correction parameters of the real bone density of the known bone density die bodies and the calculated bone density;

6) and obtaining the real bone density value of the object to be detected according to the correction parameters and the correction relation.

2. The method for bone density correction and measurement based on DR system of claim 1 wherein said different exposure conditions set in step 2) are low energy exposure conditions and high energy exposure conditions set according to different radiation energies.

3. A method of correcting and measuring bone density based on DR system as recited in claim 1 or 2 wherein said step 3) of acquiring images of soft tissue phantom and bone phantom under different exposure conditions comprises the following steps:

acquiring low-energy Image of soft tissue phantom under low-energy exposure condition_SL；

Collecting low-energy Image of skeleton phantom under low-energy exposure condition_BL；

Acquiring high-energy Image of soft tissue phantom under high-energy exposure condition_SH；

Collecting high-energy Image of skeleton die body under high-energy exposure condition_BH。

4. The method for correcting and measuring bone mineral density based on DR system as claimed in claims 1-3, wherein the calculating the gray level mean corresponding to different gradients of the phantom in step 3) comprises the following steps:

for images of different motifs acquired under different exposure conditions, calculating the mean value I of the grey scale of the motif region as follows:

m, N is the number of rows and columns of the pixel points in the area respectively; MN indicates the number of pixel points in the motif region, I_gray(x, y) represents a gray scale value with coordinates (x, y) in the area.

5. A method of bone density correction and measurement based on DR system according to claims 1-4 wherein said step 4) comprises the following steps:

A. calculating attenuation coefficient mu of soft tissue under certain gradient corresponding thickness under low-energy exposure condition_SL：

Wherein the function ln (#) represents a natural logarithm; i is_SLImage representing Image_SLThe gray average value of the thickness corresponding to a certain gradient; i is_0SLImage representing Image_SLThe mean value of the gray levels of the middle air region;

according to a certain gradient thickness T of soft tissue under the condition of low-energy exposure_SLLower corresponding attenuation coefficient mu_SLFitting of mu_SLAnd thickness T_SLThe relationship function of (1) is as follows: namely the relation function f of the attenuation coefficient and the thickness of the stepped soft tissue phantom under the condition of low exposure_SLThe following were used:

μ_SL＝f_SL(T_SL)

B. calculating the thickness T corresponding to a certain gradient of the skeleton phantom under the condition of low-energy exposure_BLLower attenuation coefficient mu_BL：

Wherein, I_BLRepresents an Image_BLMean gray level of a certain gradient thickness of the middle skeleton model, I_0BLRepresents an Image_BLThe mean value of the gray levels of the middle air region;

according to a certain gradient thickness T of the skeleton under the condition of low-energy exposure_BLLower corresponding attenuation coefficient mu_BLFitting of mu_BLAnd thickness T_BLA relation function f_BLThe following were used:

μ_BL＝f_BL(T_BL)

C. calculating attenuation coefficient mu of soft tissue die body under the condition of high-energy exposure under the condition of certain gradient corresponding thickness_SH：

Wherein, I_SHRepresents an Image_SHGradient of medium soft tissue phantomGray scale mean of thickness, I_0SHRepresents an Image_SHGrey scale mean of the mid-air region.

According to the thickness T corresponding to a certain gradient of the skeleton under the high-energy exposure condition_SHLower corresponding attenuation coefficient mu_SHFitting of mu_SHAnd thickness T_SHA relation function f_SHThe following were used:

μ_SH＝f_SH(T_SH)

D. calculating the attenuation coefficient mu of the skeleton phantom under the condition of high-energy exposure under the thickness corresponding to a certain gradient_BH：

Wherein, I_BHRepresents an Image_BHMean gray level of a certain gradient thickness of the middle skeleton model, I_0BHRepresents an Image_BHThe mean value of the gray levels of the middle air region;

according to a certain gradient thickness T of the skeleton under the condition of high-energy exposure_BHCorresponding attenuation coefficient mu_BHFitting of mu_BHAnd thickness T_BHA relation function f_BHThe following were used:

μ_BH＝f_BH(T_BH)。

6. the method for bone density correction and measurement based on DR system as recited in claim 1, wherein said step 5) comprises the following steps:

step 1.1: selecting a plurality of die bodies with known bone density and containing soft tissues and bones as objects;

step 1.2: adopting the set high-energy exposure condition and low-energy exposure condition for each die body, and acquiring corresponding low-energy images and high-energy images to form a group of images;

step 1.3: respectively obtaining gray level mean values corresponding to a soft tissue region and a bone region for the low-energy image and the high-energy image in each group of images, and calculating the soft tissue thickness of a uniform object for each measured bone density object according to the relation between the attenuation coefficient of the soft tissue phantom and the thickness of the soft tissue phantom and the relation between the attenuation coefficient of the bone phantom and the thickness of the bone phantom under different exposure conditions;

step 1.4: calculating bone thickness from the soft tissue thickness of the uniform object;

step 1.5: obtaining a bone density value of the subject according to the bone thickness;

step 1.6: and obtaining correction parameters by linear fitting according to the known real bone density value and the calculated bone density value.

7. A method of bone density correction and measurement based on DR system according to claim 6 wherein said step 1.3 is specifically:

selecting a soft tissue region and an air region in the image, and calculating the soft tissue thickness of the soft tissue region as follows:

setting a soft tissue effective thickness range [ T 'for the bone density model body'_Smin,T'_Smax]Taken from T'_Smin≤T'_Si≤T'_SmaxCalculating thickness T 'when the following expression is satisfied'_SiI.e. thickness value T 'of soft tissue of low energy image'_SL；

min{abs[f_SL(T'_Si)·T'_Si+ln(I'_SL)-ln(I'_0L)]}

Wherein, I'_SLRepresenting a grayscale mean, I 'of a selected soft tissue region in a low energy image'_0LMean gray level representing selected air regions in the low energy image, min {. represents the minimum value calculation, abs [. multidot. ]]Represents an absolute value calculation;

setting soft tissue effective thickness range [ T'_Smin,T'_Smax]Taken from T'_Smin≤T'_Si≤T'_SmaxCalculating thickness T 'when the following expression is satisfied'_SiI.e. thickness value T 'of the soft tissue of the high-energy image'_SH；

Calculating soft tissue thickness value T 'of corresponding region of high-energy image'_SHThe expression is as follows:

min{abs[f_SH(T'_Si)·T'_Si+ln(I'_SH)-ln(I'_0H)]}

wherein, I'_SHRepresenting a grayscale mean, I 'of a selected soft tissue region in a high energy image'_0HA mean value of the gray levels representing selected air regions in the high-energy image;

calculating to obtain the soft tissue thickness T 'of the uniform object'_SThe following were used:

8. a method of bone density correction and measurement based on DR system according to claim 6 wherein said step 1.4 is specifically:

bone regions were selected and bone thickness was calculated as follows:

setting a bone effective thickness range [ T'_Bmin,T'_Bmax]Taken from T'_Bmin≤T'_Bj≤T'_BmaxCalculating a bone thickness value T 'obtained when the following expression is satisfied'_BjNamely the real bone density thickness value T'_B：

min{abs[f_SL(T'_Si)·T'_Si+f_BL(T'_Bj)·T'_Bj+ln(I'_BL)-ln(I'_0L)]+abs[f_SH(T'_Si)·T'_Si+f_BH(T'_Bj)·T'_Bj+ln(I'_BH)-ln(I'_0H)]+abs[T'_Si+T'_Bj-T'_S]}

Wherein, I'_BLGray scale mean, I 'representing selected bone regions under a low energy image'_BHRepresenting the mean of the gray levels of selected bone regions under the high-energy image.

9. A method of bone density correction and measurement based on DR system according to claim 6 wherein said step 1.5 specifically is:

repeating the step 1.2 to the step 1.4 to obtain real bone density thickness values T 'of a plurality of objects'_BFrom a plurality of known bone objectsObtaining a plurality of groups of calculated BMD values; BMD ═ T'_B*β_B；

Wherein BMD is bone density value, beta_BThe density value of the skeleton model body is obtained;

the step 1.6 specifically comprises the following steps:

according to a plurality of groups of calculated BMD values and pre-acquired real BMD values, obtaining a linear relation between the BMD values and the real BMD values by using the step model correction through linear fitting:

y＝kx+b

wherein x represents the calculated BMD value, y represents the real BMD value acquired in advance, and k and b represent the slope and intercept of the linear relation, namely the correction parameter of the bone density.

10. The method for bone density calibration and measurement based on DR system as claimed in claim 1 or 6, wherein the step 6) of calculating the true bone density value of the subject comprises the following steps:

step 2.1: acquiring a low-energy image and a high-energy image of an object to be detected under a low-energy exposure condition and a high-energy exposure condition;

step 2.2: selecting an object to be detected, a peripheral soft tissue area and a peripheral air area;

step 2.3: calculating the gray average value of the region according to the selected peripheral soft tissue parts, and obtaining the uniform soft tissue thickness of the object to be measured according to the step 1.3;

step 2.4: according to the step 1.4, obtaining the thickness of the object to be measured, namely the bone density thickness value;

step 2.5: according to the step 1.5, obtaining a calculated BMD value;

step 2.6: and (3) obtaining the calculated BMD value by substituting the BMD value obtained in the step (2.5) according to the linear relation between the BMD value calculated in the step (1.6) and the real BMD value, so as to obtain the real bone density value, namely the bone density value of the object to be detected.

Technical Field

The invention relates to the technical field of X-ray digital image processing, in particular to a bone mineral density correction and measurement method based on a DR system.

Background

The existing bone density detection methods are classified into Single-Photon Absorption measurement (SPA), Dual-Energy X-Ray Absorption measurement (DEXA), Quantitative CT (QCT), and other methods. These methods require special devices or settings to perform bone density measurements and are costly. Dual energy X-ray absorptiometry methods are not calibrated to the same degree, and it is preferable to use the same equipment, otherwise, there may be situations where the image results may not be comparable. The dual-energy X-ray absorption measurement method and the quantitative CT detection have higher cost, and the bone mineral density detection can be completed only by multiple detections; secondly, the existing bone density detection method has low image resolution, low image definition and poor fineness, and meanwhile, the existing bone density detection method cannot display digital images in real time in a perspective state.

Disclosure of Invention

The invention can complete the functions of collecting, storing, managing, processing and transmitting the image information on a DR system (a digital X-ray photography system), so that the image data can be effectively managed and fully utilized. Through reasonable correction, the bone density value can be calculated in a DR system without depending on special bone density equipment, and the image can be detected in real time; by selecting different exposure conditions twice, the obtained image has high resolution and is clear, and a Bone Density value (BMD for short) can be obtained well under the condition of reducing the measurement cost, so that the defects are overcome.

The technical scheme adopted by the invention for realizing the purpose is as follows: a method of bone density correction and measurement based on a DR system, comprising the steps of:

1) establishing a die body which comprises a soft tissue die body and a skeleton die body; the soft tissue die body and the skeleton die body are both stepped die bodies;

2) different exposure conditions are set through DR equipment to ensure that the different exposure conditions can penetrate through the die body and form images;

3) collecting images of a soft tissue die body and a skeleton die body under different exposure conditions, and calculating gray level mean values corresponding to different gradients of the die bodies;

4) acquiring attenuation coefficients of the soft tissue die body and the skeleton die body under different exposure conditions through the acquired image, and acquiring the relation between the attenuation coefficient of the soft tissue die body and the thickness of the soft tissue die body and the relation between the attenuation coefficient of the skeleton die body and the thickness of the skeleton die body under different exposure conditions;

5) correcting the plurality of known bone density die bodies to obtain the correction relation and the correction parameters of the real bone density of the known bone density die bodies and the calculated bone density;

6) and obtaining the real bone density value of the object to be detected according to the correction parameters and the correction relation.

The different exposure conditions set in the step 2) are low-energy exposure conditions and high-energy exposure conditions set according to different ray energies.

The step 3) of collecting images of the soft tissue phantom and the bone phantom under different exposure conditions specifically comprises the following steps:

acquiring low-energy image of soft tissue phantom under low-energy exposure condition_SL；

Acquiring low-energy image of skeleton phantom under low-energy exposure condition_BL；

Acquiring a high-energy image of a soft tissue phantom under a high-energy exposure condition_SH；

Collecting high-energy image of skeleton die body under high-energy exposure condition_BH。

The calculating of the gray level mean values corresponding to different gradients of the mold body in the step 3) specifically comprises the following steps:

for images of different motifs acquired under different exposure conditions, calculating the mean value I of the grey scale of the motif region as follows:

m, N is the number of rows and columns of the pixel points in the area respectively; MN indicates the number of pixel points in the motif region, I_gray(x, y) represents a gray scale value with coordinates (x, y) in the area.

The step 4) specifically comprises the following steps:

A. calculating attenuation coefficient mu of soft tissue under certain gradient corresponding thickness under low-energy exposure condition_SL：

Wherein the function ln (#) represents a natural logarithm; i is_SLImage display_SLThe gray average value of the thickness corresponding to a certain gradient; i is_0SLImage display_SLThe mean value of the gray levels of the middle air region;

according to a certain gradient thickness T of soft tissue under the condition of low-energy exposure_SLLower corresponding attenuation coefficient mu_SLFitting of mu_SLAnd thickness T_SLThe relationship function of (1) is as follows: namely the relation function f of the attenuation coefficient and the thickness of the stepped soft tissue phantom under the condition of low exposure_SLThe following were used:

μ_SL＝f_SL(T_SL)

B. calculating the thickness T corresponding to a certain gradient of the skeleton phantom under the condition of low-energy exposure_BLLower attenuation coefficient mu_BL：

Wherein, I_BLRepresents image_BLMean gray level of a certain gradient thickness of the middle skeleton model, I_0BLRepresents image_BLThe mean value of the gray levels of the middle air region;

according to a certain gradient thickness T of the skeleton under the condition of low-energy exposure_BLLower corresponding attenuation coefficient mu_BLFitting of mu_BLAnd thickness T_BLA relation function f_BLThe following were used:

μ_BL＝f_BL(T_BL)

C. calculating attenuation coefficient mu of soft tissue die body under the condition of high-energy exposure under the condition of certain gradient corresponding thickness_SH：

Wherein, I_SHRepresents image_SHMean value of gray scale of a certain gradient thickness of the medium and soft tissue phantom, I_0SHRepresents image_SHGrey scale mean of the mid-air region.

According to the thickness T corresponding to a certain gradient of the skeleton under the high-energy exposure condition_SHLower corresponding attenuation coefficient mu_SHFitting of mu_SHAnd thickness T_SHA relation function f_SHThe following were used:

μ_SH＝f_SH(T_SH)

D. calculating the attenuation coefficient mu of the skeleton phantom under the condition of high-energy exposure under the thickness corresponding to a certain gradient_BH：

Wherein, I_BHRepresents image_BHMean gray level of a certain gradient thickness of the middle skeleton model, I_0BHRepresents image_BHThe mean value of the gray levels of the middle air region;

according to a certain gradient thickness T of the skeleton under the condition of high-energy exposure_BHCorresponding attenuation coefficient mu_BHFitting of mu_BHAnd thickness T_BHA relation function f_BHThe following were used:

μ_BH＝f_BH(T_BH)。

in the step 5), correcting the plurality of known bone density models to obtain a correction relationship and correction parameters between the actual bone density of the known bone density models and the calculated bone density, specifically comprising the following steps:

step 1.1: selecting a plurality of die bodies with known bone density and containing soft tissues and bones as objects;

step 1.2: adopting the set high-energy exposure condition and low-energy exposure condition for each die body, and acquiring corresponding low-energy images and high-energy images to form a group of images;

step 1.3: respectively obtaining gray level mean values corresponding to a soft tissue region and a bone region for the low-energy image and the high-energy image in each group of images, and calculating the soft tissue thickness of a uniform object for each measured bone density object according to the relation between the attenuation coefficient of the soft tissue phantom and the thickness of the soft tissue phantom and the relation between the attenuation coefficient of the bone phantom and the thickness of the bone phantom under different exposure conditions;

step 1.4: calculating bone thickness from the soft tissue thickness of the uniform object;

step 1.5: obtaining a bone density value of the subject according to the bone thickness;

step 1.6: and obtaining correction parameters by linear fitting according to the known real bone density value and the calculated bone density value.

The step 1.3 specifically comprises the following steps:

selecting a soft tissue region and an air region in the image, and calculating the soft tissue thickness of the soft tissue region as follows:

setting a soft tissue effective thickness range [ T 'for the bone density model body'_{S min},T′_{S max}]Taken from T'_{S min}≤T′_Si≤T′_{S max}Calculating thickness T 'when the following expression is satisfied'_SiI.e. thickness value T 'of soft tissue of low energy image'_SL；

min{abs[f_SL(T′_Si)·T′_Si+ln(I′_SL)-ln(I′_0L)]}

Wherein, I'_SLRepresenting a grayscale mean, I 'of a selected soft tissue region in a low energy image'_0LMean gray level representing selected air regions in the low energy image, min {. represents the minimum value calculation, abs [. multidot. ]]Represents an absolute value calculation;

setting soft tissue effective thickness range [ T'_{S min},T′_{S max}]Taken from T'_{S min}≤T′_Si≤T′_{S max}Calculating thickness T 'when the following expression is satisfied'_SiI.e. thickness value T 'of the soft tissue of the high-energy image'_SH；

Calculating soft tissue thickness value T 'of corresponding region of high-energy image'_SHThe expression is as follows:

min{abs[f_SH(T′_Si)·T′_Si+ln(I′_SH)-ln(I'_0H)]}

wherein, I'_SHRepresenting a grayscale mean, I 'of a selected soft tissue region in a high energy image'_0HA mean value of the gray levels representing selected air regions in the high-energy image;

calculating to obtain the soft tissue thickness T 'of the uniform object'_SThe following were used:

the step 1.4 specifically comprises the following steps:

bone regions were selected and bone thickness was calculated as follows:

setting a bone effective thickness range [ T'_{B min},T′_{B max}]Taken from T'_{B min}≤T′_Bj≤T′_{B max}Calculating a bone thickness value T 'obtained when the following expression is satisfied'_BjNamely the real bone density thickness value T'_B：

min{abs[f_SL(T′_Si)·T′_Si+f_BL(T′_Bj)·T′_Bj+ln(I′_BL)-ln(I'_0L)]+abs[f_SH(T′_Si)·T′_Si+f_BH(T′_Bj)·T′_Bj+ln(I′_BH)-ln(I′_0H)]+abs[T′_Si+T′_Bj-T′_S]}

Wherein, I'_BLGray scale mean, I 'representing selected bone regions under a low energy image'_BHRepresenting the mean of the gray levels of selected bone regions under the high-energy image.

The step 1.5 specifically comprises the following steps:

repeating the step 1.2 to the step 1.4 to obtain real bone density thickness values T 'of a plurality of objects'_BObtaining a plurality of groups of calculated BMD values according to the known density values of a plurality of bone objects;

BMD＝T′_B*β_B；

wherein BMD is bone density value, beta_BThe density value of the skeleton model body is obtained;

the step 1.6 specifically comprises the following steps:

according to a plurality of groups of calculated BMD values and pre-acquired real BMD values, obtaining a linear relation between the BMD values and the real BMD values by using the step model correction through linear fitting:

y＝kx+b

wherein x represents the calculated BMD value, y represents the real BMD value acquired in advance, and k and b represent the slope and intercept of the linear relation, namely the correction parameter of the bone density.

The step 6) of calculating the real bone density value of the object to be measured specifically comprises the following steps:

step 2.1: acquiring a low-energy image and a high-energy image of an object to be detected under a low-energy exposure condition and a high-energy exposure condition;

step 2.2: selecting an object to be detected, a peripheral soft tissue area and a peripheral air area;

step 2.3: calculating the gray average value of the region according to the selected peripheral soft tissue parts, and obtaining the uniform soft tissue thickness of the object to be measured according to the step 1.3;

step 2.4: according to the step 1.4, obtaining the thickness of the object to be measured, namely the bone density thickness value;

step 2.5: according to the step 1.5, obtaining a calculated BMD value;

step 2.6: and (3) obtaining the calculated BMD value by substituting the BMD value obtained in the step (2.5) according to the linear relation between the BMD value calculated in the step (1.6) and the real BMD value, so as to obtain the real bone density value, namely the bone density value of the object to be detected.

The invention has the following beneficial effects and advantages:

1. the method can be executed only on a DR system without adding an additional device;

2. the invention can complete the functions of collecting, storing, managing, processing, transmitting and the like of image information on a DR system (a digital X-ray photography system), so that image data can be effectively managed and fully utilized, and the image can be detected in real time through reasonable correction;

3. the method comprises precision correction and accuracy correction, and the precision of calculating the bone density value is ensured to the maximum extent;

4. the method only needs to change the software part on the DR system, and does not need to increase extra cost;

5. the method is simple and easy to operate, and common technicians can obtain results according to the steps;

6. the invention selects two different exposure conditions, the obtained image has high resolution and is clear, and the measurement cost can be well reduced.

Drawings

FIG. 1 is a flow chart of the design of the method of the present invention;

FIG. 2 is a design view of a phantom for simulating soft tissue in a stepped manner;

FIG. 3 is a schematic representation of a phantom design for a step-simulated bone;

FIG. 4 is a flow chart of calculating the attenuation coefficient of a phantom;

FIG. 5 is a flow chart of correcting true bone density values;

fig. 6 is a flow chart of measuring bone density values of a subject.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the specific embodiments of the present invention and the accompanying drawings. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The present invention will be described in further detail with reference to the accompanying drawings and examples.

Referring to fig. 1, which is a flow chart illustrating the design of the method of the present invention, the method for correcting and measuring bone density based on DR system of the present invention is characterized by comprising the following steps:

1) establishing a die body which comprises a soft tissue die body and a skeleton die body; the soft tissue die body and the skeleton die body are both stepped die bodies, and the stepped die bodies comprise steps with a plurality of heights;

2) different exposure conditions are set through DR equipment (a digital X-ray photography system) to ensure that the different exposure conditions can penetrate through the die body and form images;

3) collecting images of a soft tissue die body and a skeleton die body under different exposure conditions, and calculating gray level mean values corresponding to different gradients of the die bodies;

4) acquiring attenuation coefficients of the soft tissue die body and the skeleton die body under different exposure conditions through the acquired image, and acquiring the relation between the attenuation coefficient of the soft tissue die body and the thickness of the soft tissue die body and the relation between the attenuation coefficient of the skeleton die body and the thickness of the skeleton die body under different exposure conditions;

5) correcting the plurality of known bone density die bodies to obtain the correction relation and the correction parameters of the real bone density of the known bone density die bodies and the calculated bone density;

6) and obtaining the real bone density value of the object to be detected according to the correction parameters and the correction relation.

The specific flow chart of the present invention is shown in fig. 1, and includes two steps of bone density correction and bone density measurement using conventional DR.

As shown in fig. 2 to 3, in step 1 of the present invention, a calibration phantom is designed, and a phantom simulating a soft tissue and a phantom simulating a bone are respectively designed according to the thickness range of a part to be measured. Both die bodies used in the method are in a step shape, and different step thicknesses are different. The polymethyl methacrylate material simulates soft tissue, as shown in figure 2; the metal aluminum material is adopted to simulate the skeleton, as shown in the attached figure 3.

As shown in fig. 4, which is a flowchart of calculating the attenuation coefficient of the phantom of the present invention, step 2 is to design low-energy and high-energy exposure conditions, and dynamically set the low-energy and high-energy exposure conditions according to the exposure performance of the DR apparatus, the thickness and the penetrating power of the stepped phantom, so as to ensure that both exposure conditions can penetrate through the phantom and form an image on a flat panel detector. It is required that the low energy rays are not more than 50kVp and the high energy rays are not less than 70 kVp.

And 3) calculating the attenuation coefficient of the phantom, and acquiring and storing image data of two kinds of step phantom exposure according to the low-energy and high-energy exposure conditions so as to calculate the attenuation coefficient of the phantom under two kinds of energy.

Step 401 is to set a low-energy exposure condition, which needs to consider the receiving capability of the flat panel detector and the penetration capability of the step phantom, and the values corresponding to different DR devices are different.

Step 402, acquiring image data of a stepped soft tissue phantom for exposure, placing the stepped soft tissue phantom in a ray field, wherein the stepped soft tissue phantom can be placed in the central area of a flat panel detector, performing exposure by using DR equipment, and acquiring image data image of the exposure by using the flat panel detector_SL。

Step 403 is to calculate the gray level mean values corresponding to different steps. According to the acquired image data, image areas corresponding to different steps are manually defined or automatically identified, and the gray level mean values of the areas are respectively calculated to serve as the gray level mean values corresponding to different thicknesses. Here too, the mean value of the gray levels of the corresponding area with the thickness of 0cm is obtained.

Calculating gray level mean values corresponding to different gradients of the mold body, and specifically comprising the following steps of:

for images of different motifs acquired under different exposure conditions, calculating the mean value I of the grey scale of the motif region as follows:

m, N is the number of rows and columns of the pixel points in the area respectively; MN indicates the number of pixel points in the motif region, I_gray(x, y) represents a gray scale value with coordinates (x, y) in the area.

Step 404 is to calculate the attenuation coefficient using the ray intensity attenuation equation. The formula for the intensity attenuation of the X-rays is as follows: here, the

I＝I₀e^-μ(E,T)T

Wherein, I and I₀Respectively representing the transmitted intensity and the exposed intensity, T representing the thickness, μ (E, T) representing the attenuation coefficient, related to the energy E and the thickness T, I₀Representation diagramThe gray average value of an air area in the image, wherein the air area refers to an area imaged by no object placed in the image;

A. calculating attenuation coefficient mu of soft tissue under certain gradient corresponding thickness under low-energy exposure condition_SL：

Wherein the function ln (#) represents a natural logarithm; i is_SLImage display_SLThe gray average value of the thickness corresponding to a certain gradient; i is_0SLImage display_SLThe mean value of the gray levels of the middle air region;

according to a certain gradient thickness T of soft tissue under the condition of low-energy exposure_SLLower corresponding attenuation coefficient mu_SLFitting of mu_SLAnd thickness T_SLThe relationship function of (1) is as follows: namely the relation function f of the attenuation coefficient and the thickness of the stepped soft tissue phantom under the condition of low exposure_SLThe following were used:

μ_SL＝f_SL(T_SL)

B. calculating the thickness T corresponding to a certain gradient of the skeleton phantom under the condition of low-energy exposure_BLLower attenuation coefficient mu_BL：

Wherein, I_BLRepresents image_BLMean gray level of a certain gradient thickness of the middle skeleton model, I_0BLRepresents image_BLThe mean value of the gray levels of the middle air region;

according to a certain gradient thickness T of the skeleton under the condition of low-energy exposure_BLLower corresponding attenuation coefficient mu_BLFitting of mu_BLAnd thickness T_BLA relation function f_BLThe following were used:

μ_BL＝f_BL(T_BL)

C. calculating attenuation coefficient of soft tissue die body under certain gradient corresponding thickness under high-energy exposure conditionμ_SH：

Wherein, I_SHRepresents image_SHMean value of gray scale of a certain gradient thickness of the medium and soft tissue phantom, I_0SHRepresents image_SHGrey scale mean of the mid-air region.

According to the thickness T corresponding to a certain gradient of the skeleton under the high-energy exposure condition_SHLower corresponding attenuation coefficient mu_SHFitting of mu_SHAnd thickness T_SHA relation function f_SHThe following were used:

μ_SH＝f_SH(T_SH)

D. calculating the attenuation coefficient mu of the skeleton phantom under the condition of high-energy exposure under the thickness corresponding to a certain gradient_BH：

Wherein, I_BHRepresents image_BHMean gray level of a certain gradient thickness of the middle skeleton model, I_0BHRepresents image_BHThe mean value of the gray levels of the middle air region;

according to a certain gradient thickness T of the skeleton under the condition of high-energy exposure_BHCorresponding attenuation coefficient mu_BHFitting of mu_BHAnd thickness T_BHA relation function f_BHThe following were used:

μ_BH＝f_BH(T_BH)。

step 5) correcting the real bone density value. This is a phantom with known true bone density values, which may be commercially available as a true calibration phantom for different test sites. The algorithmic procedure is described herein using as an example a measured forearm bone density value for which the phantom used is a JIS-type forearm phantom (hereinafter JIS phantom) meeting JIS Z4930 standard, including three different sets of bone density test inserts.

As shown in fig. 5, for the flowchart of the present invention for correcting the true bone density value, step 5) is to acquire low-energy images and high-energy images of three different sets of JIS phantom. The low-energy exposure conditions and the high-energy exposure conditions used in this process are the conditions used for the correction in step 2). Three groups of different bone density plug-in units are respectively placed in the clamping grooves of the die body, and low-energy images and high-energy images are collected. Each group collects a pair of low-energy and high-energy images, and the three groups of plug-ins collect six images.

Selecting a soft tissue region and an air region in the image, and calculating the soft tissue thickness of the soft tissue region as follows:

setting a soft tissue effective thickness range [ T 'for the bone density model body'_{S min},T′_{S max}]Taken from T'_{S min}≤T′_Si≤T′_{S max}Calculating thickness T 'when the following expression is satisfied'_SiI.e. thickness value T 'of soft tissue of low energy image'_SL；

min{abs[f_SL(T′_Si)·T′_Si+ln(I′_SL)-ln(I'_0L)]}

Wherein, I'_SLRepresenting a grayscale mean, I 'of a selected soft tissue region in a low energy image'_0LMean gray level representing selected air regions in the low energy image, min {. represents the minimum value calculation, abs [. multidot. ]]Represents an absolute value calculation;

setting soft tissue effective thickness range [ T'_{S min},T′_{S max}]Taken from T'_{S min}≤T′_Si≤T′_{S max}Calculating thickness T 'when the following expression is satisfied'_SiI.e. thickness value T 'of the soft tissue of the high-energy image'_SH；

Calculating soft tissue thickness value T 'of corresponding region of high-energy image'_SHThe expression is as follows:

min{abs[f_SH(T′_Si)·T′_Si+ln(I′_SH)-ln(I'_0H)]}

wherein, I'_SHRepresenting a grayscale mean, I 'of a selected soft tissue region in a high energy image'_0HA mean value of the gray levels representing selected air regions in the high-energy image;

calculating to obtain the soft tissue thickness T 'of the uniform object'_SThe following were used:

bone regions were selected and bone thickness was calculated as follows:

setting a bone effective thickness range [ T'_{B min},T′_{B max}]Taken from T'_{B min}≤T′_Bj≤T′_{B max}Calculating a bone thickness value T 'obtained when the following expression is satisfied'_BjNamely the real bone density thickness value T'_B：

min{abs[f_SL(T′_Si)·T′_Si+f_BL(T′_Bj)·T′_Bj+ln(I′_BL)-ln(I'_0L)]+abs[f_SH(T′_Si)·T′_Si+f_BH(T′_Bj)·T′_Bj+ln(I′_BH)-ln(I'_0H)]+abs[T′_Si+T′_Bj-T′_S]}

Wherein, I'_BLGray scale mean, I 'representing selected bone regions under a low energy image'_BHRepresenting the mean of the gray levels of selected bone regions under the high-energy image.

Bone thickness value T 'obtained at this time'_BjNamely the real bone density thickness value T'_B. Wherein, I'_BLGray scale mean, I 'representing selected bone regions under a low energy image'_BHRepresenting the mean of the gray levels of selected bone regions under the high-energy image.

The thickness of the bone in this region was calculated to be T'_BAnd the corresponding soft tissue thickness is T'_S-T′_B。

Repeating the steps 502 to 504 in the figure to obtain real bone density thickness values T 'of a plurality of objects'_BObtaining a plurality of groups of calculated BMD values according to the known density values of a plurality of bone objects;

BMD＝T′_B*β_B；

wherein BMD is bone density value, beta_BThe density value of the skeleton model body is obtained;

in step 505, the Bone Density value (BMD for short) of the Bone is calculated by using the material Density adopted by the stepped calibration phantom, specifically:

according to a plurality of groups of calculated BMD values and pre-acquired real BMD values, obtaining a linear relation between the BMD values and the real BMD values by using the step model correction through linear fitting:

y＝kx+b

wherein x represents the calculated BMD value, y represents the real BMD value acquired in advance, and k and b represent the slope and intercept of the linear relation, namely the correction parameter of the bone density.

As shown in fig. 6, step 601 is to acquire a low-energy image and a high-energy image of the region to be measured. And placing the part to be detected in the central position of the flat panel detector, keeping the part to be detected still, and acquiring images of the part to be detected by adopting the low-energy exposure condition and the high-energy exposure condition used for correction to obtain two images.

Step 602 is to select a region to be measured, as well as a peripheral soft tissue region and a peripheral air region. The three regions may be manually selected or automatically detected.

Step 603 is to calculate the pure soft tissue thickness. Calculating the gray average value of the region according to the selected peripheral soft tissue part; and calculating the gray average value of the area according to the selected peripheral air area. Setting soft tissue effective thickness range [ T'_{S min},T′_{S max}]The thickness value when the following expression holds is calculated:

min{abs[f_SL(T′_Si)·T′_Si+ln(I′_SL)-ln(I′_0L)]}

wherein, I'_SLRepresenting a grayscale mean, I 'of a selected soft tissue region in a low energy image'_0LMean gray level representing selected air regions in the low energy image, min {. represents the minimum value calculation, abs [. multidot. ]]Representing absolute value calculations. Setting circulation, taking T'_{S min}≤T′_Si≤T′_{S max}Calculating the above expressionT 'when formula holds'_SiI.e. the thickness value T 'of the soft tissue'_SL；

In the same way, soft tissue thickness value T 'of the corresponding region of the high-energy image is calculated'_SHThe expression is as follows:

min{abs[f_SH(T′_Si)·T′_Si+ln(I′_SH)-ln(I′_0H)]}

wherein, I'_SHRepresenting a grayscale mean, I 'of a selected soft tissue region in a high energy image'_0HRepresenting the mean value of the gray scale of selected air regions in the high energy image.

Calculating to obtain the uniform die body thickness T'_SThe following were used:

step 604 is to calculate the thickness of the bone at the site to be measured. Setting a bone effective thickness range [ T'_{B min},T′_{B max}]Calculating a bone density thickness value when the following expression is satisfied:

min{abs[f_SL(T′_Si)·T′_Si+f_BL(T′_Bj)·T′_Bj+ln(I′_BL)-ln(I'_0L)]+abs[f_SH(T′_Si)·T′_Si+f_BH(T′_Bj)·T′_Bj+ln(I′_BH)-ln(I′_0H)]+abs[T′_Si+T′_Bj-T′_S]}

bone thickness value T 'obtained at this time'_BjNamely the real bone density thickness value T'_B. Wherein, I'_BLGray scale mean, I 'representing selected bone regions under a low energy image'_BHRepresenting the mean of the gray levels of selected bone regions under the high-energy image.

The thickness of the bone in this region was calculated to be T'_B。

Step 605 is to calculate the bone density value of the portion to be measured. Calculating formula BMD ═ T 'by using bone density'_B*β_BAnd correcting the calculated BMD value and the real B by utilizing the step modelAnd calculating to obtain a real bone density value, namely the bone density value with the measured part, by using a linear relation of the MD values.

The methods described in the embodiments of the present invention may or may not be physically separated, and some or all of the methods may be selected according to actual needs to achieve the purpose of the embodiments of the present invention. Those of ordinary skill in the art can understand and implement the steps of the present invention without inventive effort.