CN113491526B - Bone density correction and measurement method based on DR system - Google Patents
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Abstract
The invention relates to the technical field of X-ray digital image processing, in particular to a bone density correction and measurement method based on a DR system. The invention comprises the following steps: 1) Establishing a model body comprising a soft tissue model body and a skeleton model body; 2) Different exposure conditions are set through DR equipment so as to ensure that the different exposure conditions can penetrate through the die body and image; 3) Collecting images of the soft tissue die body and the bone die body under different exposure conditions, and calculating gray average values corresponding to different gradients of the die body; 4) Obtaining the relation between the soft tissue die body attenuation coefficient and the soft tissue die body thickness and the relation between the bone die body attenuation coefficient and the bone die body thickness under different exposure conditions; 5) Acquiring a correction relation and correction parameters of the real bone density of the known bone density die body and the calculated bone density; 6) And obtaining the real bone mineral density value of the object to be measured. The invention has the advantages of accurate correction and accuracy correction, and ensures the accuracy of calculating the bone mineral density value to the maximum extent.
Description
Technical Field
The invention relates to the technical field of X-ray digital image processing, in particular to a bone density correction and measurement method based on a DR system.
Background
The existing bone mineral density detection method is divided into a Single-photon absorption measurement method (SPA for short), a Dual Energy X-ray absorption measurement method (Dual Energy X-Ray Absorptiometry for short DEXA) and a Quantitative CT (QCT) method. These methods all require special devices or settings to perform bone density measurements and are costly. The dual energy X-ray absorption measurements are calibrated differently, preferably using the same equipment, otherwise, there may be cases 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 density detection can be completed only by multiple times of detection; secondly, the existing bone mineral density detection method has low resolution, low image definition and poor fineness of images, and meanwhile, the equipment of the existing bone mineral density detection method can not display digital images in real time in a perspective state.
Disclosure of Invention
The invention can complete the functions of collecting, storing, managing, processing, transmitting and the like of image information on a DR system (digital radiography system), so that the image data can be effectively managed and fully utilized. Through reasonable correction, the bone mineral density value can be calculated in the DR system without depending on special bone mineral density equipment, and the image can be detected in real time; the method for obtaining the bone mineral density value (Bone Mineral Density, BMD for short) under the condition of selecting two different exposure conditions, has high resolution and definition of the obtained image and can well obtain the bone mineral density value (Bone Mineral Density, BMD for short) under the condition of reducing the measurement cost so as to overcome the defects.
The technical scheme adopted by the invention for achieving the purpose is as follows: a method for bone density correction and measurement based on a DR system, comprising the steps of:
1) Establishing a model body comprising a soft tissue model body and a skeleton model 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 so as to ensure that the different exposure conditions can penetrate through the die body and image;
3) Collecting images of the soft tissue die body and the bone die body under different exposure conditions, and calculating gray average values corresponding to different gradients of the die body;
4) Acquiring attenuation coefficients of the soft tissue die body and the bone die body under different exposure conditions through acquired images, and acquiring the relationship between the attenuation coefficient of the soft tissue die body and the thickness of the soft tissue die body and the relationship between the attenuation coefficient of the bone die body and the thickness of the bone die body under different exposure conditions;
5) Correcting the multiple known bone density die bodies to obtain the correction relation and correction parameters between the actual bone density of the known bone density die bodies and the calculated bone density;
6) And obtaining the real bone mineral density value of the object to be measured 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 radiation energies.
The step 3) of collecting images of the soft tissue die body and the bone die body under different exposure conditions specifically comprises the following steps:
collecting low-energy image of soft tissue phantom under low-energy exposure condition SL ；
Collecting low-energy image of bone die body under low-energy exposure condition BL ；
Collecting high-energy image of soft tissue phantom under high-energy exposure condition SH ；
Collecting high-energy image of bone die body under high-energy exposure condition BH 。
The step 3) is to calculate the gray average value corresponding to different gradients of the die body, and specifically comprises the following steps:
for images of different die bodies acquired under different exposure conditions, the gray average value I of the die body area is calculated as follows:
wherein M, N is the number of rows and columns of pixel points in the region respectively; MN represents the number of pixel points in the motif region, I gray (x, y) represents a gray value of (x, y) coordinates in the region.
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 (x) represents the natural logarithm; i SL Representing an image SL A gray average value of a thickness corresponding to a certain gradient; i 0SL Representing an image SL A gray average value of the middle air area;
according to a certain gradient thickness T of soft tissue under low-energy exposure condition SL The corresponding attenuation coefficient mu SL Fitting mu SL And thickness T SL The relationship function of (2) is as follows: i.e. the ladder soft tissue mold body is at low exposureRelation function f of attenuation coefficient and thickness under light condition SL The following are provided:
μ SL ＝f SL (T SL )
B. calculating a certain gradient corresponding thickness T of a skeleton die body under the condition of low-energy exposure BL Attenuation coefficient mu BL ：
Wherein I is BL Representing image BL Gray average value of certain gradient thickness of middle skeleton mould body, I 0BL Representing image BL A gray average value of the middle air area;
according to a certain gradient thickness T of bones under low-energy exposure condition BL The corresponding attenuation coefficient mu BL Fitting mu BL And thickness T BL Is a relation function f of (2) BL The following are provided:
μ BL ＝f BL (T BL )
C. calculating attenuation coefficient mu of soft tissue die body under certain gradient corresponding thickness under high-energy exposure condition SH ：
Wherein I is SH Representing image SH Gray average value of certain gradient thickness of medium soft tissue die body, I 0SH Representing image SH The gray average value of the air region.
Corresponding thickness T according to a certain gradient of bones under high-energy exposure condition SH The corresponding attenuation coefficient mu SH Fitting mu SH And thickness T SH Is a relation function f of (2) SH The following are provided:
μ SH ＝f SH (T SH )
D. calculating attenuation coefficient mu of skeleton die body under certain gradient corresponding thickness under high-energy exposure condition BH ：
Wherein I is BH Representing image BH Gray average value of certain gradient thickness of middle skeleton mould body, I 0BH Representing image BH A gray average value of the middle air area;
according to a certain gradient thickness T of bones under high-energy exposure condition BH Corresponding attenuation coefficient mu BH Fitting mu BH And thickness T BH Is a relation function f of (2) BH The following are provided:
μ BH ＝f BH (T BH )。
in the step 5), correcting a plurality of known bone density die bodies to obtain a correction relation and correction parameters between the actual bone density of the known bone density die bodies and the calculated bone density, wherein the method specifically comprises the following steps:
step 1.1: selecting a plurality of mold bodies with known bone densities and containing soft tissues and bones as objects;
step 1.2: each die body adopts set high-energy exposure conditions and low-energy exposure conditions, and corresponding low-energy images and high-energy images are collected to form a group of images;
step 1.3: respectively obtaining gray average values corresponding to the soft tissue region and the 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 soft tissue die body attenuation coefficient and the soft tissue die body thickness and the relation between the bone die body attenuation coefficient and the bone die body thickness under different exposure conditions;
step 1.4: calculating a 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 adopting linear fitting according to the known real bone mineral density value and the calculated bone mineral density value.
The step 1.3 specifically comprises the following steps:
soft tissue regions and air regions are selected in the image, and the soft tissue thickness of the soft tissue regions is calculated as follows:
for the bone density model, the effective thickness range of soft tissue is set [ T ]' S min ,T′ S max ]Taking T' S min ≤T′ Si ≤T′ S max The thickness T 'when the following expression is established is calculated' Si I.e. the thickness value T 'of the soft tissue of the low-energy image' SL ；
min{abs[f SL (T′ Si )·T′ Si +ln(I′ SL )-ln(I′ 0L )]}
Wherein I' SL Representing the gray-scale mean value, I 'of a selected soft tissue region in a low-energy image' 0L Representing the gray-scale mean value of a selected air region in a low-energy image, min { x } represents the minimum value calculation, abs [ x ]]Representing absolute value calculation;
setting effective thickness range of soft tissue [ T ]' S min ,T′ S max ]Taking T' S min ≤T′ Si ≤T′ S max The thickness T 'when the following expression is established is calculated' Si I.e. the thickness value T 'of the high-energy image soft tissue' SH ；
Calculating soft tissue thickness value T 'of corresponding region of high-energy image' SH The expression is as follows:
min{abs[f SH (T′ Si )·T′ Si +ln(I′ SH )-ln(I' 0H )]}
wherein I' SH Representing the gray-scale average value, I 'of a selected soft tissue region in a high-energy image' 0H Representing a gray average value of a selected air region in the high-energy image;
the soft tissue thickness T 'of the uniform object is calculated' S The following are provided:
the step 1.4 specifically comprises the following steps:
the bone region was selected and the bone thickness was calculated as follows:
setting the effective thickness range of skeleton [ T ]' B min ,T′ B max ]Taking T' B min ≤T′ Bj ≤T′ B max The bone thickness value T 'obtained when the following expression is established is calculated' Bj The true bone mineral 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' BL Representing the gray-scale mean, I 'of a selected bone region under a low-energy image' BH Representing the gray-scale average of a selected bone region under the high-energy image.
The step 1.5 specifically comprises the following steps:
repeating the steps 1.2-1.4 to obtain the true bone density thickness value T 'of a plurality of objects' B Obtaining a plurality of groups of calculated BMD values according to the known density values of the bone objects;
BMD＝T′ B *β B ；
wherein BMD is bone mineral density value, beta B A density value for a bone phantom;
the step 1.6 specifically comprises the following steps:
obtaining a linear relation between the BMD value calculated by using the step motif correction and the real BMD value by using linear fitting according to a plurality of groups of calculated BMD values and the real BMD value acquired in advance:
y＝kx+b
where x represents the calculated BMD value, y represents the real BMD value obtained in advance, and k and b represent the slope and intercept of the linear relation, i.e., the correction parameters of bone density, respectively.
The step 6) is used for calculating the true bone mineral density value of the object to be measured, and specifically comprises the following steps:
step 2.1: collecting low-energy images and high-energy images of an object to be detected under low-energy exposure conditions and high-energy exposure conditions;
step 2.2: selecting an object to be detected, a peripheral soft tissue area and a peripheral air area;
step 2.3: according to the selected peripheral soft tissue part, calculating the gray average value of the area, and according to the step 1.3, obtaining the uniform soft tissue thickness of the object to be measured;
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 step 1.5, obtaining a calculated BMD value;
step 2.6: according to the linear relation between the BMD value calculated in the step 1.6 and the real BMD value, the calculated BMD value is obtained by substituting the BMD value in the step 2.5, so that the real bone mineral density value, namely the bone mineral density value of the object to be measured, is obtained.
The invention has the following beneficial effects and advantages:
1. the method can be implemented only on a DR system without adding additional devices;
2. the invention can complete the functions of acquisition, storage, management, processing, transmission and the like of image information on a DR system (digital radiography system), so that the 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 ensures the precision of calculating the bone density value 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 the ordinary skill can obtain the result according to the steps;
6. the method selects two different exposure conditions, and the obtained image has high resolution and definition, and can well reduce the measurement cost.
Drawings
FIG. 1 is a flow chart of the design of the method of the present invention;
FIG. 2 is a phantom design of a ladder simulation soft tissue;
FIG. 3 is a phantom design of a stepped simulated bone;
FIG. 4 is a flow chart for calculating the die body attenuation coefficient;
FIG. 5 is a flow chart for correcting an authenticity bone density value;
fig. 6 is a flowchart for measuring bone mineral density values of a test object.
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 specific embodiments of the present invention and corresponding drawings. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The present invention will be described in further detail with reference to the accompanying drawings and examples.
As shown in fig. 1, a design flow chart of the method of the present invention is shown, and 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 model body comprising a soft tissue model body and a skeleton model body; the soft tissue die body and the skeleton die body are both step-shaped die bodies, and the step-shaped die bodies comprise a plurality of steps with heights;
2) Different exposure conditions are set through DR equipment (digital X-ray photography system) to ensure that the different exposure conditions can penetrate through the die body and image;
3) Collecting images of the soft tissue die body and the bone die body under different exposure conditions, and calculating gray average values corresponding to different gradients of the die body;
4) Acquiring attenuation coefficients of the soft tissue die body and the bone die body under different exposure conditions through acquired images, and acquiring the relationship between the attenuation coefficient of the soft tissue die body and the thickness of the soft tissue die body and the relationship between the attenuation coefficient of the bone die body and the thickness of the bone die body under different exposure conditions;
5) Correcting the multiple known bone density die bodies to obtain the correction relation and correction parameters between the actual bone density of the known bone density die bodies and the calculated bone density;
6) And obtaining the real bone mineral density value of the object to be measured according to the correction parameters and the correction relation.
A specific flow chart of the invention is shown in fig. 1, comprising 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 correction phantom is designed, and a soft tissue simulation phantom and a bone simulation phantom are respectively designed according to the thickness range of the part to be measured. The two mould bodies adopted in the method are both in a ladder shape, and the thickness of different steps is different. The polymethyl methacrylate material simulates soft tissue, as shown in figure 2; the skeleton is simulated by adopting metal aluminum materials, as shown in figure 3.
As shown in fig. 4, in the flow chart of calculating the die body attenuation coefficient according to the present invention, step 2 is to design low-energy and high-energy exposure conditions, dynamically set the low-energy exposure conditions and the high-energy exposure conditions according to the exposure performance of the DR device and the thickness and the penetration force of the stepped die body, so as to ensure that both exposure conditions can penetrate the die body and image on the flat panel detector. Here, it is required that the low energy ray is not more than 50kVp and the high energy ray is not less than 70kVp.
Step 3) to step 4) are to calculate the die body attenuation coefficient, and collect and store the image data of the two step die body exposures according to the low-energy and high-energy exposure conditions, so as to calculate the die body attenuation coefficient under the two energies.
Step 401 is to set a low energy exposure condition, which needs to consider the receiving capability of the flat panel detector and the penetrating capability of the step phantom, and the corresponding values of different DR devices are different.
Step 402 is to collect image data of a ladder soft tissue phantom by exposure, place the ladder soft tissue phantom in a radiation field, and place the ladder soft tissue phantom in a central region of a flat panel detector, expose the ladder soft tissue phantom by DR equipment, and obtain image data image of the exposure by the flat panel detector SL 。
Step 403 is to calculate the gray average value corresponding to the different steps. According to the acquired image data, image areas corresponding to different steps are manually marked or automatically identified, and gray average values of the areas are calculated respectively to serve as the gray average values corresponding to different thicknesses. Also here, the acquisition of the gray-scale mean value of the corresponding region with the thickness of 0cm is included.
The gray average value corresponding to different gradients of the die body is calculated, and the method specifically comprises the following steps:
for images of different die bodies acquired under different exposure conditions, the gray average value I of the die body area is calculated as follows:
wherein M, N is the number of rows and columns of pixel points in the region respectively; MN represents the number of pixel points in the motif region, I gray (x, y) represents a gray value of (x, y) coordinates in the region.
Step 404 is to calculate the attenuation coefficient using the radiation intensity attenuation formula. The formula of the attenuation of the radiation intensity in the X-rays is as follows: here, the
I＝I 0 e -μ(E,T)T
Wherein I and I 0 Respectively, the transmission intensity and the exposure intensity, T represents the thickness, μ (E, T) represents the attenuation coefficient, and I is related to the energy E and the thickness T 0 Representing the gray-scale average of an air region in the image, wherein the air region refers to a region of the image imaged without any object placed therein;
A. calculating attenuation coefficient mu of soft tissue under certain gradient corresponding thickness under low-energy exposure condition SL ：
Wherein the function ln (x) represents the natural logarithm; i SL Representing an image SL A gray average value of a thickness corresponding to a certain gradient; i 0SL Representing an image SL A gray average value of the middle air area;
according to a certain gradient thickness T of soft tissue under low-energy exposure condition SL The corresponding attenuation coefficient mu SL Fitting mu SL And thickness T SL The relationship function of (2) is as follows: namely, the relation function f of the attenuation coefficient and the thickness of the ladder soft tissue die body under the low exposure condition SL The following are provided:
μ SL ＝f SL (T SL )
B. calculating a certain gradient corresponding thickness T of a skeleton die body under the condition of low-energy exposure BL Attenuation coefficient mu BL ：
Wherein I is BL Representing image BL Gray average value of certain gradient thickness of middle skeleton mould body, I 0BL Representing image BL A gray average value of the middle air area;
according to a certain gradient thickness T of bones under low-energy exposure condition BL The corresponding attenuation coefficient mu BL Fitting mu BL And thickness T BL Is a relation function f of (2) BL The following are provided:
μ BL ＝f BL (T BL )
C. calculating attenuation coefficient mu of soft tissue die body under certain gradient corresponding thickness under high-energy exposure condition SH ：
Wherein I is SH Representing image SH Gray average value of certain gradient thickness of medium soft tissue die body, I 0SH Representing image SH The gray average value of the air region.
Corresponding thickness T according to a certain gradient of bones under high-energy exposure condition SH The corresponding attenuation coefficient mu SH Fitting mu SH And thickness T SH Is a relation function f of (2) SH The following are provided:
μ SH ＝f SH (T SH )
D. calculating attenuation coefficient mu of skeleton die body under certain gradient corresponding thickness under high-energy exposure condition BH ：
Wherein I is BH Representing image BH Gray average value of certain gradient thickness of middle skeleton mould body, I 0BH Representing image BH A gray average value of the middle air area;
according to a certain gradient thickness T of bones under high-energy exposure condition BH Corresponding attenuation coefficient mu BH Fitting mu BH And thickness T BH Is a relation function f of (2) BH The following are provided:
μ BH ＝f BH (T BH )。
step 5) is to correct the value of the true bone density. The model body with known true bone density value is adopted, and different model bodies with true correction are available on the market for different test positions. The algorithm step is described herein using the measured forearm bone density value as an example, and the mold body used for the forearm bone density value is a JIS type forearm mold body (hereinafter referred to as JIS mold body) satisfying the Japanese JIS Z4930 standard, in which three different sets of bone density test inserts are included.
As shown in FIG. 5, a flow chart for correcting the true bone mineral density values according to the present invention is shown, and step 5) is to acquire low-energy images and high-energy images of three sets of JIS motifs of different bone mineral densities. The low-energy exposure conditions and the high-energy exposure conditions employed in this process are the conditions used for correction in step 2). Three groups of inserts with different bone densities are respectively placed in the clamping grooves of the die body, and a low-energy image and a high-energy image are acquired. Each group acquires a pair of low-energy and high-energy images, and three groups of plug-ins acquire six images in total.
Soft tissue regions and air regions are selected in the image, and the soft tissue thickness of the soft tissue regions is calculated as follows:
for the bone density model, the effective thickness range of soft tissue is set [ T ]' S min ,T′ S max ]Taking T' S min ≤T′ Si ≤T′ S max The thickness T 'when the following expression is established is calculated' Si I.e. the thickness value T 'of the soft tissue of the low-energy image' SL ；
min{abs[f SL (T′ Si )·T′ Si +ln(I′ SL )-ln(I' 0L )]}
Wherein I' SL Representing the gray-scale mean value, I 'of a selected soft tissue region in a low-energy image' 0L Representing the gray-scale mean value of a selected air region in a low-energy image, min { x } represents the minimum value calculation, abs [ x ]]Representing absolute value calculation;
setting effective thickness range of soft tissue [ T ]' S min ,T′ S max ]Taking T' S min ≤T′ Si ≤T′ S max The thickness T 'when the following expression is established is calculated' Si I.e. the thickness value T 'of the high-energy image soft tissue' SH ；
Calculating soft tissue thickness value T 'of corresponding region of high-energy image' SH The expression is as follows:
min{abs[f SH (T′ Si )·T′ Si +ln(I′ SH )-ln(I' 0H )]}
wherein I' SH Representing the gray-scale average value, I 'of a selected soft tissue region in a high-energy image' 0H Representing a gray average value of a selected air region in the high-energy image;
the soft tissue thickness T 'of the uniform object is calculated' S The following are provided:
the bone region was selected and the bone thickness was calculated as follows:
setting the effective thickness range of skeleton [ T ]' B min ,T′ B max ]Taking T' B min ≤T′ Bj ≤T′ B max The bone thickness value T 'obtained when the following expression is established is calculated' Bj The true bone mineral 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' BL Representing the gray-scale mean, I 'of a selected bone region under a low-energy image' BH Representing the gray-scale average of a selected bone region under the high-energy image.
The bone thickness value T 'obtained at this time' Bj The true bone mineral density thickness value T' B . Wherein I' BL Representing the gray-scale mean, I 'of a selected bone region under a low-energy image' BH Representing the gray-scale average of a selected bone region under the high-energy image.
At this time, the bone thickness of the region was calculated to be T' B The corresponding soft tissue thickness is T' S -T′ B 。
Repeating the steps 502-504 to obtain the real bone density thickness value T 'of multiple objects' B Obtaining a plurality of groups of calculated BMD values according to the known density values of the bone objects;
BMD＝T′ B *β B ；
wherein BMD is bone mineral density value, beta B A density value for a bone phantom;
the step 505 uses the material density adopted by the step correction module to calculate the bone density value (Bone Mineral Density, abbreviated as BMD) of the bone, specifically:
obtaining a linear relation between the BMD value calculated by using the step motif correction and the real BMD value by using linear fitting according to a plurality of groups of calculated BMD values and the real BMD value acquired in advance:
y＝kx+b
where x represents the calculated BMD value, y represents the real BMD value obtained in advance, and k and b represent the slope and intercept of the linear relation, i.e., the correction parameters of bone density, respectively.
As shown in fig. 6, step 601 is to acquire a low-energy image and a high-energy image of a portion to be measured. And placing the part to be detected at 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 a low-energy exposure condition and a high-energy exposure condition used for correction to acquire two images.
Step 602 is selecting a site to be measured, as well as a peripheral soft tissue site, a peripheral air region. A method of manually selecting three areas or automatically detecting three areas may be adopted.
Step 603 is to calculate the pure soft tissue thickness. Calculating the gray average value of the area according to the selected peripheral soft tissue part; based on the selected ambient air region, a gray-scale average of the region is calculated. Setting effective thickness range of soft tissue [ T ]' S min ,T′ S max ]The thickness value when the following expression is established is calculated:
min{abs[f SL (T′ Si )·T′ Si +ln(I′ SL )-ln(I′ 0L )]}
wherein I' SL Representing the gray-scale mean value, I 'of a selected soft tissue region in a low-energy image' 0L Representing the gray-scale mean value of a selected air region in a low-energy image, min { x } represents the minimum value calculation, abs [ x ]]Representing absolute value calculations. Setting circulation, taking T' S min ≤T′ Si ≤T′ S max Calculating T 'when the above expression is established' Si I.e. the thickness T 'of the soft tissue' SL ；
The same method calculates the soft tissue thickness value T 'of the corresponding region of the high-energy image' SH The expression is as follows:
min{abs[f SH (T′ Si )·T′ Si +ln(I′ SH )-ln(I′ 0H )]}
wherein I' SH Representing the gray-scale average value, I 'of a selected soft tissue region in a high-energy image' 0H Representing the gray-scale average of a selected air region in the high-energy image.
Then calculate the thickness T 'of the uniform die body' S The following are provided:
step 604 is to calculate the bone thickness of the portion to be measured. Setting the effective thickness range of skeleton [ T ]' B min ,T′ B max ]Calculating a bone mineral thickness value when the following expression is established:
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 ]}
the bone thickness value T 'obtained at this time' Bj The true bone mineral density thickness value T' B . Wherein I' BL Representing the gray-scale mean, I 'of a selected bone region under a low-energy image' BH Representing the gray-scale average of a selected bone region under the high-energy image.
At this time, the bone thickness of the region was calculated to be T' B 。
Step 605 is to calculate the bone mineral density value of the portion to be measured. Bmd=t 'using bone density calculation formula' B *β B And then, correcting the linear relation between the calculated BMD value and the real BMD value by using the ladder motif, and calculating to obtain the real bone mineral density value, namely the bone mineral density value of the measured part.
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 solution of the present embodiment. In light of the above steps of the present invention, one of ordinary skill in the art will understand and practice the invention without undue burden.
Claims (6)
1. A method for correcting and measuring bone mineral density based on a DR system, comprising the steps of:
1) Establishing a model body comprising a soft tissue model body and a skeleton model 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 so as to ensure that the different exposure conditions can penetrate through the die body and image;
3) Collecting images of the soft tissue die body and the bone die body under different exposure conditions, and calculating gray average values corresponding to different gradients of the die body;
4) Acquiring attenuation coefficients of the soft tissue die body and the bone die body under different exposure conditions through acquired images, and acquiring the relationship between the attenuation coefficient of the soft tissue die body and the thickness of the soft tissue die body and the relationship between the attenuation coefficient of the bone die body and the thickness of the bone die body under different exposure conditions;
5) Correcting the multiple known bone density die bodies to obtain the correction relation and correction parameters between the actual bone density of the known bone density die bodies and the calculated bone density;
the step 5) specifically comprises the following steps:
step 1.1: selecting a plurality of mold bodies with known bone densities and containing soft tissues and bones as objects;
step 1.2: each die body adopts set high-energy exposure conditions and low-energy exposure conditions, and corresponding low-energy images and high-energy images are collected to form a group of images;
step 1.3: respectively obtaining gray average values corresponding to the soft tissue region and the 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 soft tissue die body attenuation coefficient and the soft tissue die body thickness and the relation between the bone die body attenuation coefficient and the bone die body thickness under different exposure conditions;
the step 1.3 specifically comprises the following steps:
soft tissue regions and air regions are selected in the image, and the soft tissue thickness of the soft tissue regions is calculated as follows:
for the bone density model, the effective thickness range of soft tissue is set [ T ]' Smin ,T′ Smax ]Taking T' Smin ≤T′ Si ≤T′ Smax The thickness T 'when the following expression is established is calculated' Si I.e. the thickness value T 'of the soft tissue of the low-energy image' SL ；
min{abs[f SL (T′ Si )·T′ Si +ln(I′ SL )-ln(I′ 0L )]}
Wherein I' SL Representing the gray-scale mean value, I 'of a selected soft tissue region in a low-energy image' 0L Representing the gray-scale mean value of a selected air region in a low-energy image, min { x } represents the minimum value calculation, abs [ x ]]Representing absolute value calculation;
setting effective thickness range of soft tissue [ T ]' Smin ,T′ Smax ]Taking T' Smin ≤T′ Si ≤T′ Smax The thickness T 'when the following expression is established is calculated' Si I.e. the thickness value T 'of the high-energy image soft tissue' SH ；
Calculating soft tissue thickness value T 'of corresponding region of high-energy image' SH The expression is as follows:
min{abs[f SH (T′ Si )·T′ Si +ln(I′ SH )-ln(I′ 0H )]}
wherein I' SH Representing the gray-scale average value, I 'of a selected soft tissue region in a high-energy image' 0H Representing a gray average value of a selected air region in the high-energy image;
the soft tissue thickness T 'of the uniform object is calculated' S The following are provided:
step 1.4: calculating a bone thickness from the soft tissue thickness of the uniform object;
the step 1.4 specifically comprises the following steps:
the bone region was selected and the bone thickness was calculated as follows:
setting the effective thickness range of skeleton [ T ]' Bmin ,T′ Bmax ]Taking T' Bmin ≤T′ Bj ≤T′ Bmax Calculation ofThe bone thickness value T 'obtained when the following expression is established' Bj The true bone mineral 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' BL Representing the gray-scale mean, I 'of a selected bone region under a low-energy image' BH Representing a gray-scale average of a selected bone region under the high-energy image;
step 1.5: obtaining a bone density value of the subject according to the bone thickness;
the step 1.5 specifically comprises the following steps:
repeating the steps 1.2-1.4 to obtain the true bone density thickness value T 'of a plurality of objects' B Obtaining a plurality of groups of calculated BMD values according to the known density values of the bone objects; bmd=t' B *β B ；
Wherein BMD is bone mineral density value, beta B A density value for a bone phantom;
step 1.6: according to the known real bone mineral density value and the calculated bone mineral density value, linear fitting is adopted to obtain correction parameters;
the step 1.6 specifically comprises the following steps:
obtaining a linear relation between the BMD value calculated by using the step motif correction and the real BMD value by using linear fitting according to a plurality of groups of calculated BMD values and the real BMD value acquired in advance:
y＝kx+b
wherein x represents a calculated BMD value, y represents a real BMD value obtained in advance, and k and b represent the slope and intercept of a linear relation, namely correction parameters of bone density, respectively;
6) And obtaining the real bone mineral density value of the object to be measured according to the correction parameters and the correction relation.
2. The method according to claim 1, wherein the different exposure conditions set in the step 2) are a low-energy exposure condition and a high-energy exposure condition set according to different radiant energies.
3. The method for correcting and measuring bone mineral density based on DR system according to claim 2, wherein said step 3) comprises the steps of:
collecting low-energy Image of soft tissue phantom under low-energy exposure condition SL ；
Collecting low-energy Image of bone die body under low-energy exposure condition BL ；
Collecting 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 according to claim 3, wherein said calculating gray-scale average values corresponding to different gradients of the phantom in step 3) comprises the steps of:
for images of different die bodies acquired under different exposure conditions, the gray average value I of the die body area is calculated as follows:
wherein M, N is the number of rows and columns of pixel points in the region respectively; MN represents the number of pixel points in the motif region, I gray (x, y) represents a gray value of (x, y) coordinates in the region.
5. The method for correcting and measuring bone mineral density based on DR system according to claim 4, wherein said step 4) comprises the steps of:
A. calculating attenuation coefficient mu of soft tissue under certain gradient corresponding thickness under low-energy exposure condition SL ：
Wherein the function ln (x) represents the natural logarithm; i SL Representing an Image SL A gray average value of a thickness corresponding to a certain gradient; i 0SL Representing an Image SL A gray average value of the middle air area;
according to a certain gradient thickness T of soft tissue under low-energy exposure condition SL The corresponding attenuation coefficient mu SL Fitting mu SL And thickness T SL The relationship function of (2) is as follows: namely, the relation function f of the attenuation coefficient and the thickness of the ladder soft tissue die body under the low exposure condition SL The following are provided:
μ SL ＝f SL (T SL )
B. calculating a certain gradient corresponding thickness T of a skeleton die body under the condition of low-energy exposure BL Attenuation coefficient mu BL ：
Wherein I is BL Representing Image BL Gray average value of certain gradient thickness of middle skeleton mould body, I 0BL Representing Image BL A gray average value of the middle air area;
according to a certain gradient thickness T of bones under low-energy exposure condition BL The corresponding attenuation coefficient mu BL Fitting mu BL And thickness T BL Is a relation function f of (2) BL The following are provided:
μ BL ＝f BL (T BL )
C. calculating attenuation coefficient mu of soft tissue die body under certain gradient corresponding thickness under high-energy exposure condition SH ：
Wherein I is SH Representing Image SH Gray average value of certain gradient thickness of medium soft tissue die body, I 0SH Representing Image SH A gray average value of the middle air area;
corresponding thickness T according to a certain gradient of bones under high-energy exposure condition SH The corresponding attenuation coefficient mu SH Fitting mu SH And thickness T SH Is a relation function f of (2) SH The following are provided:
μ SH ＝f SH (T SH )
D. calculating attenuation coefficient mu of skeleton die body under certain gradient corresponding thickness under high-energy exposure condition BH ：
Wherein I is BH Representing Image BH Gray average value of certain gradient thickness of middle skeleton mould body, I 0BH Representing Image BH A gray average value of the middle air area;
according to a certain gradient thickness T of bones under high-energy exposure condition BH Corresponding attenuation coefficient mu BH Fitting mu BH And thickness T BH Is a relation function f of (2) BH The following are provided:
μ BH ＝f BH (T BH )。
6. the method for correcting and measuring bone mineral density based on DR system according to claim 1, wherein said calculating in step 6) a true bone mineral density value of the object to be measured comprises the steps of:
step 2.1: collecting low-energy images and high-energy images of an object to be detected under low-energy exposure conditions and high-energy exposure conditions;
step 2.2: selecting an object to be detected, a peripheral soft tissue area and a peripheral air area;
step 2.3: according to the selected peripheral soft tissue part, calculating the gray average value of the area, and according to the step 1.3, obtaining the uniform soft tissue thickness of the object to be measured;
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 step 1.5, obtaining a calculated bone mineral density value;
step 2.6: according to the linear relation between the bone mineral density value calculated in the step 1.6 and the real bone mineral density value, the calculated bone mineral density value is obtained by substituting the bone mineral density value obtained in the step 2.5, so that the real bone mineral density value, namely the bone mineral density value of the object to be detected, is obtained.
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