CN113017657B - Method for calibrating projection area of dual-energy X-ray bone densitometer and die body - Google Patents
Method for calibrating projection area of dual-energy X-ray bone densitometer and die body Download PDFInfo
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Abstract
The invention relates to a method for calibrating the projection area of a dual-energy X-ray bone densitometer and a die body, wherein the method comprises the steps of designing a bone densitometer die body, then carrying out boundary scanning on a regular-shaped calibration die body and a simplified copying calibration die body, and setting a projection area standard value; and finally, performing a projection area calibration subprogram and judging a result, and measuring the projection area and judging the result by adopting an equal gray curve algorithm, an edge enhancement algorithm, a region segmentation algorithm and a self-contained contour recognition algorithm of the dual-energy X-ray bone densitometer. The method can improve the accuracy of contour recognition and projection area calculation of the dual-energy X-ray bone densitometer and improve the accuracy of a bone density value measurement result.
Description
Technical Field
The invention relates to a calibration method of a bone densitometer in the field of medical detectors, in particular to a calibration method of a projection area of a dual-energy X-ray bone densitometer.
Background
Osteoporosis (osteoporotis) is the decrease in the content of normally calcified bone tissue per unit volume, i.e. the organic content and calcium salts of bone tissue are both reduced, but the ratio of the two is still normal. With the rapid increase in the population of the elderly worldwide, osteoporosis has received government and social attention as an important public health problem. According to the statistics data of 2015 years of national aging of the national department of civil administration, 2015-2035 years is a rapid development stage of the aging of the Chinese population, and the number of the Chinese aged population is increased from 2.12 hundred million to 4.18 hundred million. Osteoporosis and complications such as fracture thereof can seriously affect the health of residents, and the osteoporosis and the complications become a health problem which is more and more concerned by the common people.
There are several diagnostic methods for osteoporosis, the most accurate of which is simultaneous bone morphology counting and bone biomechanical measurements. The method objectively reflects the fine structure of bones and the tiny injury of the bones, and is an accurate method for reflecting the quality and strength of the bones and diagnosing the osteoporosis; however, the detection method is invasive, and most osteoporosis patients are older, so that the diagnosis method has great harm to the patients, thereby limiting the clinical application of the method. Currently, the osteoporosis diagnosis method recommended by the world health organization measures Bone Mineral Density (BMD) values at the lumbar, femoral and hip joint sites.
The methods for measuring BMD values mainly include single photon radiation absorption, Dual Energy X-ray absorption (DEXA), Quantitative CT (Quantitative Computed Tomography, QCT), and ultrasonography. Among them, the DEXA method rapidly occupies the market and becomes a medical "gold standard" for measuring BMD values with advantages of simple operation, low radiation dose, low equipment cost, and the like. The dual-energy X-ray bone densitometer is based on a dual-energy X-ray absorption method and measures BMD by using the principle that the absorption attenuation of X-rays on bones and muscle tissues is different. The projection area of BMD and skeleton, the absorption attenuation result of skeleton to different energy X-ray, the detector and software algorithm adopted by the manufacturer and the deviation degree of the density experiment fitting of soft tissue and skeleton are closely related. Therefore, the accuracy and repeatability of the BMD measured by the dual energy X-ray Bone densitometer are not high (about 60% to 70%), and the measured BMD value is an area Bone Mineral Density (aBMD) value, not a true bulk Density (vBMD) value. The aBMD value is an average result of density values calculated after the three-dimensional bone structure is projected on a plane, and how to determine the projection area of a target area in the measurement process becomes one of key factors influencing the accuracy of the final bone density measurement result.
By comparing images obtained by dual-energy X-ray bone densitometers produced by different manufacturers, the performance of a contour boundary identification algorithm of a bone projection image in the images is obviously different, so that the measured values of projection areas are different; the manufacturers do not strictly calibrate the projected area or provide a definite projected area correction formula. Therefore, the projected area value becomes one of the largest error sources in the DEXA method for measuring bone density, and directly influences the accuracy of the bone density measurement result (i.e., the aBMD value).
Currently, there are a number of commercially available phantoms for calibrating the DEXA method for measuring bone density values. The most common of these are the American CIRS-026 motif and the German QRM-ESP motif.
As shown in fig. 1, the american CIRS-026 model of lumbar spine is made of homogeneous material into regular-shaped lumbar modules with 4 segments of different thickness (upper and lower halves of the vertebral body in fig. 1 are used for positioning during imaging, and the middle four identically-shaped modules are used for bone density value calibration). When the Bone density value is calibrated, the mold body simulates different Bone Mineral Contents (BMC) by using different thicknesses of the vertebral body, and the different BMC contents are divided by the same projection area value to equivalently obtain different surface densities aBMD. The advantage of utilizing the die body for calibration is that the contour of the obtained image is clear and the contour boundary is easy to identify due to the adoption of the design of the regular-shaped lumbar module, so that the error of the bone density value measurement result caused by the measurement deviation of the projection area is reduced. Firstly, the simplified module with a regular shape is adopted to equivalent the lumbar vertebra, so that the influence of the real lumbar vertebra middle vertebral canal and the spinous process on the aBMD measurement result cannot be reflected; secondly, the projection position relation and the form equivalence of the two sides of the vertebral arch are not consistent with the real situation, the equivalent thickness of the transverse process is not thicker than that of the vertebral body, the regular shape cannot be used for evaluating the accuracy of a projection area algorithm, and the projection area calibration result cannot represent the contour recognition capability of the projection area calibration result on the real lumbar vertebra.
The German QRM-ESP model is equivalent to a combination form of a plurality of modules in the figure 2 on the basis of imitating the appearance form of real lumbar vertebra. The design of the model body simulates transverse processes and spinous processes of two wings of a lumbar vertebral arch, and the projection image with the irregular shape can be better used for calibrating a contour recognition algorithm of DEXA equipment and is more reasonable than the design of a CIRS-026 model body. However, the equivalent lumbar module in this phantom only takes into account the added effect of the presence of the spinous process on the ambd measurement at the time of the projection measurement. Neglecting the effect of the spinal canal on the measurement of aBMD is inaccurate in analyzing the overall average result of aBMD in the lumbar spine under real conditions, since the spinal canal is not included in the structural design and its presence can significantly diminish the measurement of aBMD.
In view of the above-mentioned defects of the conventional calibration method and mold body for bone densitometer, the present invention has been continuously studied and repeatedly tried out and improved, and finally, the present invention with practical value is created.
Disclosure of Invention
The invention mainly aims to provide a method and a die body for calibrating the projection area of a dual-energy X-ray bone densitometer, which are used for calibrating a contour recognition algorithm and the projection area of the dual-energy X-ray bone densitometer, and start from improving the accuracy of a measurement result of the projection area and improving the accuracy of a measurement result aBMD of the dual-energy X-ray bone densitometer.
The invention has the main innovation point that two types of calibration die bodies with regular shapes and simplified copying are developed, and the projection area of the die bodies can be strictly fixed. The contour boundary recognition algorithm and the projection area measurement result of the dual-energy X-ray bone densitometer are calibrated through a strictly-fixed bone density die body, and the accuracy of the bone density measurement result of the dual-energy X-ray bone densitometer is improved. Compared with the mold bodies sold in the same type on the market, the simplified structural design of the copying calibration mold body is more reasonable, and the influence of the parts such as the vertebral canal, the transverse process and the spinous process on the projection area can be reflected.
Meanwhile, in the calibration of the contour boundary identification algorithm, four algorithms which are most commonly used at present are used for delineating the projection contour boundary and measuring the projection area. Firstly, calculating and obtaining projection area measurement values corresponding to the two types of die bodies by utilizing an equal gray curve algorithm, an edge strengthening algorithm, a region segmentation algorithm and a self-contained contour recognition algorithm of the dual-energy X-ray bone densitometer, and determining whether the deviation of the measurement values and the projection area standard values of the two types of die bodies is within an allowable range; then, calculating a correlation coefficient of a projection area algorithm with the deviation within an allowable range by using the standard value and the measured value of the projection area of the two types of calibration phantom bodies, and selecting an algorithm with the optimal correlation coefficient as a built-in algorithm for delineating the contour boundary of the dual-energy X-ray bone densitometer equipment and measuring the projection area; and simultaneously, aiming at the selected built-in algorithm, carrying out least square normal fitting on the measured values obtained by scanning the two types of the die bodies and the corresponding standard values, and giving a correction formula of the projection area measurement result of the dual-energy X-ray bone densitometer equipment.
The purpose of the invention and the technical problem to be solved are realized by adopting the following technical scheme. The invention provides a method for calibrating a projection area of a dual-energy X-ray bone densitometer, which comprises the following steps of:
step 1: designing a bone density die body, and respectively designing a regular-shaped calibration die body and a simplified copying calibration die body;
and 2, step: carrying out boundary scanning on the regular-shaped calibration phantom and the simplified copying calibration phantom, and giving a standard value of a projection area; the standard value of the projection area is obtained by measuring the corresponding geometric contour dimension of each die body by a projector or a tool microscope with the measurement error of +/-1 mu m and performing mathematical geometric calculation;
and step 3: a projection area calibration subprogram and result judgment are carried out, and three common contour recognition algorithms including an equal gray curve algorithm, an edge enhancement algorithm and a region segmentation algorithm and a contour recognition algorithm carried by the dual-energy X-ray bone densitometer are adopted to measure the projection area and judge the result;
the specific method for measuring the projection area and judging the result comprises the following steps: using an iso-gray curve algorithm, an edge strengthening algorithm, a region segmentation algorithm and a contour recognition algorithm carried by the dual-energy X-ray bone densitometer to outline the contour boundary of the projection image of the dual-energy X-ray bone densitometer of the regular-shape calibration phantom and the simplified profile modeling calibration phantom in the step 1, and calculating a corresponding projection area measurement value; if the deviation of the measured value of the projection area of one or more algorithms and the standard value is within the specified limit value, carrying out the next calculation; otherwise, entering an engineer maintenance program, and asking a maintenance engineer of the dual-energy X-ray bone densitometer to carry out maintenance and debugging.
The object of the present invention and the technical problems solved thereby can be further achieved by the following technical measures.
The method for calibrating the projection area of the dual-energy X-ray bone densitometer, wherein the next calculation in step 3 comprises the following steps:
step 3-1: calculating deviation values of projection area measurement values and standard values of the regular-shaped calibration phantom and the simplified copying calibration phantom by adopting different projection area algorithms; a specified limit value of the deviation is given, if the deviation value obtained by calculation of a certain algorithm is less than or equal to the specified limit value of the deviation, the algorithm is considered to be qualified, and the deviation value can be used for calculating a projection area value;
step 3-2: for the algorithms considered to be qualified in the step 3-1, if the qualified types of the algorithms are more than or equal to 2, calculating correlation coefficients of the measured values and the standard values corresponding to the algorithms, and selecting the algorithm with the optimal correlation coefficient for subsequent calculation; if only 1 algorithm is qualified, directly embedding the contour recognition algorithm into a dual-energy X-ray bone densitometer, and performing the last step of calculation;
step 3-3: utilizing the projection area measurement value and the standard value of the regular-shape calibration phantom and the simplified copying calibration phantom corresponding to the algorithm selected in the step 3-2, and adopting least square normal fitting to obtain a correction formula with minimum residual square sum; the correction formula and the corresponding projection area algorithm are arranged in the dual-energy X-ray bone densitometer, and when the projection area is measured later, the projection area measurement value is obtained by using the algorithm and is substituted into the correction formula to calculate and obtain a calibrated projection area measurement result.
The purpose of the invention and the technical problem to be solved are realized by adopting the following technical scheme.
The die body adopted in the calibration method for the projection area of the dual-energy X-ray bone densitometer comprises a regular-shape calibration die body, wherein the regular-shape calibration die body is designed into a regular geometric shape with a strict area fixed value, and comprises a spherical die body, a tubular body die body, a cylindrical die body and a deformed tubular body die body;
wherein the sphere die body is a sphere with the diameter range of 10-80 mm; the tubular body mold body is a hollow cylinder with the bottom surface diameter of 20-60 mm, the wall thickness of 1-5 mm and the height of 30-80 mm; the cylinder body is a cylinder with the bottom diameter of 10-60 mm and the height of 30-80 mm;
the deformable tubular body die body is composed of an upper part and a lower part, wherein the lower part is a cuboid with the bottom surface being a square with the side length of 20-60 mm and the height of 30-80 mm, an isosceles right triangle triangular prism penetrating through the bottom surface is dug in the cuboid, the wall thickness of a cavity in the rest part is 1-5 mm, and the dug triangular prism is spliced to the upper part of the cuboid at the lower part;
the spherical die body and the cylindrical die body simulate the basic contour form of lumbar vertebrae, the tubular die body simulates the basic contour form of a bone cavity and a bone canal, and the deformed tubular die body is used for evaluating the identification capability of the dual-energy X-ray bone densitometer on simple irregular contour edges.
The dual-energy X-ray bone densitometer projection area calibration die body is characterized by further comprising a simplified copying calibration die body, wherein the simplified copying calibration die body comprises a lumbar vertebra structure simplified die body, an arm bone structure simplified die body and a femur structure simplified die body; wherein the content of the first and second substances,
the lumbar vertebra structure simplification die body is formed by combining 3 single-section lumbar vertebra structure simplification modules, the geometric dimension of each single-section lumbar vertebra structure simplification module is the same, and the modules can be scaled in equal proportion, and the scaling proportion is not more than 5%; each single-section lumbar vertebra structure simplification module consists of a profiling cone, a profiling transverse process, a profiling spinous process and a profiling vertebral canal, wherein the profiling cone is a part cut off from the lower part of a cylinder, the bottom of the profiling cone is a rectangular plane smaller than the diameter of the cylinder, the profiling transverse process is a quadrangular frustum with the upper and lower bottom surfaces being isosceles trapezoids, a semi-cylindrical hole is dug by taking the central axis of the upper bottom of the quadrangular frustum as the center so as to form the profiling vertebral canal, and the profiling spinous process is a cuboid; the profiling spinous process of the single-section lumbar structure simplification module is arranged at the lower part, the profiling vertebral body is arranged at the upper part, the profiling transverse process is arranged between the profiling vertebral body and the profiling spinous process, the rectangular bottom surface of the profiling vertebral body is connected with the upper bottom surface of the profiling transverse process, the chord length formed by the upper bottom of the profiling transverse process and the cut-off part of the cylinder in the profiling vertebral body is equal, and one part of the upper top surface of the profiling spinous process is connected with the lower bottom surface of the profiling transverse process;
the simplified die body of the arm bone structure is formed by combining two tubular bodies with different diameters; the femur structure simplified mould body is formed by combining a ball and a tubular body.
The calibration die body for the projection area of the dual-energy X-ray bone densitometer is characterized in that the regular-shaped calibration die body and the simplified copying calibration die body are made of hydroxyapatite.
By the technical scheme, the invention at least has the following advantages:
1. the invention designs a series of die bodies for calibrating the projection area of a dual-energy X-ray bone densitometer, which comprise a regular-shaped calibration die body and a simplified copying calibration die body, wherein the simplified copying calibration die body is designed to be closer to the shape and the structure of a real human skeleton compared with the conventional commercial die body.
2. The two types of die bodies designed by the invention both provide the corresponding standard values of the projection area, the standard values are obtained by measuring the geometric outline size of a die body projection image by using a projector or a tool microscope with the measurement error of +/-1 mu m and performing mathematical geometric calculation; the accuracy of the projected area obtained by the projector or the tool microscope measurement is sufficiently high to be used as a standard value, compared with the minimum resolution of 100 μm of the dual-energy X-ray bone densitometer. By using the measuring and calculating method, the standard values of the projection areas of all the die bodies can be strictly given; the standard values are used for correcting the calculation result of the projection area in the calibration of the dual-energy X-ray bone densitometer, so that the accuracy of the calculation result of the bone density value is improved.
3. The evaluation and calibration of the performance of the contour recognition algorithm are realized in two steps, firstly, a regular-shape calibration die body is utilized to calibrate the projection area of a regular geometric shape, and the capability of a dual-energy X-ray bone densitometer for identifying the contour edge of a simple geometric shape and calculating the area is evaluated; secondly, the simplified copying calibration die body is utilized to calibrate the projection area of the real bone forms of lumbar vertebrae, thighbones and the like, and the capacity of the dual-energy X-ray bone densitometer for identifying the contour edge of a complex geometric shape and calculating the area is further evaluated. The calibration method is used for calibrating the performance of the contour recognition algorithm of the dual-energy X-ray bone densitometer, and the requirements on the performance of the algorithm are gradually improved by recognizing simple contour boundaries and gradually transiting to recognizing various complex contour boundaries; because the projected area calibration is carried out by adopting the mold bodies with various different shapes, the method can definitely know which shape identification capability of the calibrated algorithm is poor, and can provide a targeted suggestion for the improvement of the contour boundary algorithm.
4. The calibration of the projection area of the dual-energy X-ray bone densitometer is divided into two steps, firstly, the performance of 4 common contour recognition algorithms is evaluated, and the algorithm with the optimal contour recognition capability is found out; and secondly, for the selected algorithm with the optimal contour recognition capability, calibrating the projection area of the dual-energy X-ray bone densitometer and fitting a correction formula by using the two types of calibration die bodies to obtain a correction formula of the measurement result of the projection area. The correction formula can be independently used for correcting the projection area obtained by the measurement of the dual-energy X-ray bone densitometer, and can also be built in the dual-energy X-ray bone densitometer for daily calibration. The method for providing the projection area correction formula based on various model standard values is initiated in China and can correct any projection area measurement result corresponding to the dual-energy X-ray bone densitometer. And (4) calibrating and calculating the measured values of the projection areas of all the subsequent dual-energy X-ray bone densitometers by using a correction formula.
5. On the basis of analyzing main factors influencing the bone mineral density measurement result of the dual-energy X-ray bone mineral density measuring instrument, the accuracy of the aBMD measurement result is improved by calibrating the most obvious projection area influencing the aBMD measurement result, and the method is innovative.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings.
The specific process of the present invention is illustrated in detail by the following examples and the accompanying drawings.
Drawings
FIG. 1: CIRS-026 type DEXA Phantom structure top view
Fig. 2A is a top view of a QRM-ESP die body structure
FIG. 2B is a right view of the QRM-ESP motif structure
FIG. 3A: top view of sphere body
FIG. 3B: front view of sphere mold body
FIG. 3C: plan view of tubular body mold
FIG. 3D: front view of tubular body mold
FIG. 3E: cylinder body plan view
FIG. 3F: front view of cylinder body
FIG. 3G: top view of deformable tubular body
FIG. 3H: front view of deformed tubular body mold
Wherein:
1: 2, spherical die body 2: tubular body mould
3, cylinder die body 4: deformed tubular body mould
FIG. 4A: front view schematic diagram of single-segment lumbar vertebra structure simplified module
FIG. 4B is a schematic left view of a simplified module for a single lumbar vertebra
FIG. 5 is a schematic view of: the simplified lumbar vertebra model is formed by combining 3 single-segment simplified lumbar vertebra modules
Wherein:
5-1 of profiling centrum 5-2 of profiling transverse process
5-3: 5-4 of profiling spinous process: profiling vertebral canal
FIG. 6A: a simplified body structure of an arm bone structure is schematically shown in a top view;
FIG. 6B: an elevation view schematic diagram of a simplified die body structure of an arm bone structure;
FIG. 7A: simplified femur model block plan view
FIG. 7B is a schematic front view of a simplified mold body for a femur structure
Wherein:
6 simplified arm bone structure die body 7 simplified femur structure die body
Detailed Description
To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description will be provided with reference to the accompanying drawings and preferred embodiments for a method and a die body for calibrating the projected area of a dual-energy X-ray bone densitometer, and the detailed implementation method, steps, features and effects thereof.
The invention mainly overcomes the defects of the principle and the design of the conventional calibration method of the dual-energy X-ray bone densitometer.
In the aspect of calibrating the mold body, the design defect of the conventional commercial mold body is overcome. The drawback of the american CIRS-026 model of lumbar vertebrae is that, firstly, the simplified model of regular shape is used to equate the lumbar vertebrae, which does not reflect the effect on the bmd measurement result when the real spinal canal and spinous process are present in the lumbar vertebrae; secondly, the projection position relation and the form equivalence of the two sides of the vertebral arch are not consistent with the real situation, and the regular shape cannot be used for evaluating the accuracy of the projection area algorithm. Whereas the equivalent lumbar phantom in the german QRM-ESP phantom only takes into account the increasing effect of the presence of spinous processes on the ambd measurement in the projection measurement. Neglecting the effect of the bone marrow cavity on the measurement of aBMD is not accurate in analyzing the overall average result of aBMD in the lumbar spine under real conditions, since the spinal canal is not included in the structural design and its presence can significantly diminish the measurement of aBMD. Moreover, all the current commercial phantoms can only be used for calibrating the measurement result of the bone density value, the standard value of the projection area of the phantom is not given, and the projection area cannot be calibrated.
In the projection area calibration method, the performance comparison and calibration of different contour boundary algorithms are not performed in the existing calibration method, the calibration of the projection area is not realized, and a projection area correction formula is not formed.
In order to overcome the design defect of the same type of bone density die bodies sold in the market, the calibration method of the dual-energy X-ray bone density instrument is improved, and the measurement result of the projection area of the dual-energy X-ray bone density instrument is strictly calibrated.
In the first step, a bone density phantom is designed. Two types of bone density die bodies, namely a regular-shaped calibration die body and a simplified copying calibration die body, are designed and researched;
FIGS. 3A-3H show the design of a regular shaped mold body. The invention designs four regular geometric shapes to simulate the basic contour forms of lumbar vertebrae, thighbones, arm bones and the like. The regular-shape calibration die body adopts a regular geometric shape subjected to strict area fixed value, and comprises a spherical die body 1, a tubular body die body 2, a cylindrical die body 3 and a deformed tubular body die body 4. The sphere die body 1 and the cylinder die body 3 simulate the basic contour form of lumbar vertebrae, the tube body die body 2 simulates the basic contour form of bone cavities and bone ducts, and the deformed tube body die body 4 is used for evaluating the identification capability of the dual-energy X-ray bone densitometer on simple irregular contour edges.
Referring to fig. 3A and 3B, the sphere body 1 is a sphere with a diameter ranging from 10 mm to 80 mm; as shown in fig. 3C and 3D, the tubular body mold body 2 is a hollow cylinder with a bottom diameter of 20-60 mm, a wall thickness of 1-5 mm, and a height of 30-80 mm; as shown in fig. 3E and 3F, the cylinder body 3 is a cylinder with a bottom diameter of 10-60 mm and a height of 30-80 mm;
referring to fig. 3G and fig. 3H show, the deformation tubular body die body 4 is irregular shape combination die body, this deformation tubular body die body 4 comprises upper and lower two parts, the upper portion is from the bottom surface for the square of length of side 20 ~ 60mm, height 30 ~ 80 mm's cuboid, dig out a triangular prism that runs through the isosceles right triangle of bottom surface in the cuboid, the wall thickness of cavity is 1 ~ 5mm in the remaining part, the lower part is the upper portion of splicing the triangular prism dug out to the cuboid, as the position shown in fig. 3G. The simplified copying mold body comprises a lumbar vertebra structure simplified mold body (formed by combining 3 single-section lumbar vertebra structure simplified mold bodies 5), an arm bone structure simplified mold body 6 and a femur structure simplified mold body 7. Because the shape of the lumbar vertebra is complex, the lumbar vertebra is approximately a cylinder, the marrow cavity is approximately a circular tube, two wings (namely transverse processes) of the vertebral arch are approximately triangular, and the spinous process is approximately a rectangle in consideration of the shape of the lumbar vertebra. Therefore, the projection model of the lumbar vertebra adopts a simplified model of the lumbar vertebra (as shown in fig. 5). The geometric dimensions of each single lumbar structure simplification module 5 can be the same or can be scaled equally, with the scaling not greater than 5%. As shown in fig. 4A and 4B, each single-segment lumbar vertebrae structure simplification module 5 is composed of a profiling vertebral body 5-1, a profiling transverse process 5-2, a profiling spinous process 5-3 and a profiling vertebral canal 5-4, wherein the profiling vertebral body 5-1 is a part cut from the lower part of a cylinder, the bottom of the profiling vertebral body 5-1 is a rectangular plane smaller than the diameter of the cylinder, the profiling transverse process 5-2 is a quadrangular frustum with isosceles trapezoid upper and lower bottom surfaces, a semi-cylindrical hole is dug by taking the central axis of the upper bottom of the quadrangular frustum as the center, so as to form the profiling vertebral canal 5-4, and the profiling spinous process 5-3 is a cuboid. In the single-section lumbar vertebra structure simplifying module 5, a profiling spinous process 5-3 is arranged at the lower part, a profiling vertebral body 5-1 is arranged at the upper part, a profiling transverse process 5-2 is arranged between the profiling vertebral body 5-1 and the profiling spinous process 5-3, the rectangular bottom surface of the profiling vertebral body 5-1 is connected with the upper bottom surface of the profiling transverse process 5-2, the chord length formed by the upper bottom of the profiling transverse process 5-2 and the cut-off part of a cylinder in the profiling vertebral body 5-1 is equal, and one part of the upper top surface of the profiling spinous process 5-3 is connected with the lower bottom surface of the profiling transverse process 5-2.
Referring to fig. 6A and 6B, the simplified mold body 6 of the arm bone structure is tubular and is composed of two tubular bodies with different diameters.
Referring to fig. 7A and 7B, the femur structural simplification mold 7 is formed by combining a spherical ball and a tubular body.
The three profiling skeleton motifs can be designed according to the actual use requirements, but all the three profiling skeleton motifs are in accordance with the basic morphological characteristics of human skeleton biology, the main materials of all the motifs are hydroxyapatite, and a strict projection area standard value is given.
And secondly, calculating the standard value of the projection area of the regular-shaped calibration phantom and the simplified copying phantom. The standard value is obtained by measuring the corresponding geometric outline dimension of each model body by a projector or a tool microscope with the measurement error of +/-1 mu m and performing mathematical geometric calculation.
The method for determining the projection area standard value is to measure the geometric outline dimension of the phantom in the projection state by using a projector or a tool microscope, and obtain the projection area according to an area calculation formula of geometric shapes (such as a circle, a rectangle, a triangle and the like). Because the profile delineation and identification capability of the dual-energy X-ray bone densitometer is related to the resolution and algorithm of an imaging plate, the resolution capability of the image obtained by the imaging plate and the algorithm used in the current dual-energy X-ray bone densitometer is inferior to 100 mu m. Therefore, the projected area value measured by the dual-energy X-ray bone densitometer is calibrated with sufficient accuracy using the result of measuring the projected area with a projector or a tool microscope having a measurement error of ± 1 μm as a standard value.
And thirdly, a projection area calibration subprogram and result judgment are carried out. At present, common contour boundary identification algorithms include an iso-gray curve algorithm, an edge enhancement algorithm and a region segmentation algorithm. The profile identification algorithm of the dual-energy X-ray bone densitometer can adopt one or more algorithms, and can also adopt a deformation mode of the algorithms according to the characteristics of the device. In order to confirm the accuracy of the profile identification and the projection area measurement of the dual-energy X-ray bone densitometer and correct the projection area measurement result, the invention adopts the three common profile identification algorithms and the profile identification algorithm of the dual-energy X-ray bone densitometer to calculate and calibrate the projection area. The specific calibration method comprises the steps of scanning the two types of bone density die bodies by using the dual-energy X-ray bone densitometer to obtain corresponding die body projection images, then delineating contour boundaries of the different die body projection images by using the three common contour identification algorithms and a contour identification algorithm carried by the dual-energy X-ray bone densitometer, and calculating corresponding projection areas. If the relative deviation of all the phantom projection area measurement values of one or more algorithms and the standard value is within a specified limit value (such as +/-2%), performing the next calculation; otherwise, entering an engineer maintenance program, and asking a maintenance engineer of the dual-energy X-ray bone densitometer to carry out maintenance and debugging.
In order to better reproduce the contents of the present invention, the following description is briefly made for the aforementioned conventional contour recognition algorithm.
The gray scale curve algorithm is to perform gray scale normalization processing (similar to drawing contour lines in a topographic map) on an image during image processing, and to outline pixel points with the same gray scale on the image boundary as an image outline. The method for outline delineation has the advantages of simplicity and high delineation speed. The method has the disadvantages of easy interference of noise points and low outline delineation accuracy.
The edge enhancement algorithm refers to enhancing a region of interest in an image by using a certain algorithm. The purpose of image enhancement is to improve the quality of an image, remove noise, and improve the sharpness of the image. When the image is enhanced, only the region of interest in the image is enhanced, the definition of the outline boundary of the image is enhanced, and then the outline boundary of the image is drawn by using algorithms such as an equal gray curve and the like. The method has the advantages that the image outline is clear, and the defects that in the process of reducing and removing noise, some signals of real boundaries are mistakenly removed due to small difference with the noise, and the area measurement result is often smaller than the real area.
The main content of the region segmentation algorithm is to judge the material type represented by each pixel point in the image, such as noise, bone tissue or soft tissue. The image segmentation algorithm has two different segmentation methods, one method is that the intensity values of all components of the image are assumed to be uniform, and the uniformity is utilized to segment different components of the image; another method is to find the boundary between image components according to the difference of signal intensity (i.e. image gray-scale value) assuming that the signal intensity of each component of the image is different. The specific segmentation method mainly comprises histogram segmentation, region growing, gradient segmentation and the like. The accuracy of the contour recognition of the region segmentation algorithm greatly depends on the quality of image segmentation, the more refined the segmentation is, the more accurate the result of the contour recognition is, and the closer the projection area calculation result is to the true value. However, the calculation process of the algorithm is complex and time-consuming, and the accuracy of the segmentation calculation result is difficult to verify.
And (3) providing a specified limit value of the deviation of the measured value of the phantom projection area and the standard value, and if the deviation value calculated by a certain algorithm is less than or equal to the specified limit value of the deviation, considering that the algorithm is qualified and can be used for calculating the projection area value.
Respectively calculating the three common contour recognition algorithms and the contour recognition algorithm carried by the dual-energy X-ray bone densitometer, if the types of the qualified algorithms are more than or equal to 2, firstly calculating the correlation coefficients of the measured values and the standard values corresponding to the algorithms, and selecting the algorithm with the optimal correlation coefficient for subsequent calculation; if only 1 algorithm is qualified, the contour recognition algorithm is directly built into the dual-energy X-ray bone densitometer, and the last step of calculation is carried out.
When the number of qualified algorithm types is 2 or more, the correlation coefficient between the measured projection area value and the standard value is calculated for each of the algorithms.Taking the calculation result of the self-contained contour recognition algorithm of the equipment as an example, the projection area measurement value obtained by scanning by adopting a sphere die body 1, a tubular body die body 2, a cylinder die body 3, a deformed tubular body die body 4, a single-section lumbar vertebra structure simplification module 5 (any one section of 3 sections of lumbar vertebrae can be selected), an arm bone structure simplification die body 6 and a femur structure simplification die body 7 is x i (with) (i-1, 2, …, 7) with the standard value y i (with) (i is 1,2, …, 7), and the correlation coefficient r (x) corresponding thereto is calculated according to the following formula (1) i (self-carrying) ,y i (with) )。
Wherein, Cov (x) i (with) ,y i (with) ) Is x i (with) And y i (with) Of (c), Vax (x) i (self-carrying) ) Is x i (with) Variance of (C), Vax (y) i (with) ) Is y i (with) The variance of (c).
Applying formula (1) to all contour recognition algorithms with the relative deviation of the projection area measurement result within a specified limit value range, and calculating corresponding correlation coefficients r; and selecting a contour recognition algorithm with the correlation coefficient closest to 1 to be built in the dual-energy X-ray bone densitometer as a contour recognition algorithm for later use in measuring the bone density of the patient.
And (4) assuming that the finally selected contour recognition algorithm is the self-contained contour recognition algorithm of the equipment. Next, Y is carried out by the least square method i (with) ＝a·x i (with) Linear fit of + b, Y i (self-carrying) Is the result of a calibration of the projected area measurements. The calculation principle of the least square method is to find a group of values a and b, so that the sum of squares of the residual errors
And is minimal. And the values a and b which enable the residual square sum e to be minimum are calculated according to the formulas (2) and (3).
Obtaining the correction formula Y of the projection area measurement result of the dual-energy X-ray bone densitometer after obtaining the values of a and b i (with) ＝a·x i (with) + b. After the dual-energy X-ray bone mineral density projection image is obtained each time, the projection area measurement value X is calculated and obtained by utilizing the previously determined contour identification algorithm i (self-carrying) Then apply formula Y i (with) ＝a·x i (with) + b calculation to obtain final projected area measurement value calibration result Y i (with) 。
Summarizing the calibration process, firstly, using two types of seven bone density calibration phantoms designed by the invention to scan projection images and calculate projection areas, using various contour recognition algorithms to calculate and obtain projection area measurement values, and selecting a contour recognition algorithm with the correlation coefficient with the projection area standard value closest to 1; secondly, aiming at the selected algorithm, linearly fitting a corresponding correction formula according to a least square method; and thirdly, after obtaining the correction formula, when measuring the projection area of any skeleton, calculating the measured value of the projection area by using the contour recognition algorithm selected in the first step, substituting the measured value into the correction formula, and calculating to obtain the calibration value of the measurement result. Through the three steps, the calibrated projection area measurement result which is closer to the true value can be obtained.
The projection area calibration method can be embedded into the existing dual-energy X-ray bone densitometer and becomes a part of daily calibration or periodic calibration; and the device can also be independently used as a tool for detecting and evaluating the measurement accuracy of the projection areas of different types of dual-energy X-ray bone densitometers. The projection area obtained after the calibration by the method is closer to the true value, so that the accuracy of the bone mineral density measurement result is improved.
Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (5)
1. A method for calibrating the projection area of a dual-energy X-ray bone densitometer is characterized by comprising the following steps:
step 1: designing a bone density die body, and respectively designing a regular-shaped calibration die body and a simplified copying calibration die body;
step 2: carrying out boundary scanning on the regular-shaped calibration phantom and the simplified copying calibration phantom, and giving a standard value of a projection area; the standard value of the projection area is obtained by measuring the corresponding geometric contour dimension of each die body by a projector or a tool microscope with the measurement error of +/-1 mu m and performing mathematical geometric calculation;
and step 3: a projection area calibration subprogram and result judgment are carried out, and three common contour recognition algorithms including an equal gray curve algorithm, an edge enhancement algorithm and a region segmentation algorithm and a contour recognition algorithm carried by the dual-energy X-ray bone densitometer are adopted to measure the projection area and judge the result;
the specific method for measuring the projection area and judging the result comprises the following steps: using an iso-gray curve algorithm, an edge strengthening algorithm, a region segmentation algorithm and a contour recognition algorithm carried by the dual-energy X-ray bone densitometer to outline the contour boundary of the projection image of the dual-energy X-ray bone densitometer of the regular-shape calibration phantom and the simplified profile modeling calibration phantom in the step 1, and calculating a corresponding projection area measurement value; if the deviation of the measured value of the projection area of one or more algorithms and the standard value is within the specified limit value, carrying out the next calculation; otherwise, entering an engineer maintenance program, and asking a maintenance engineer of the dual-energy X-ray bone densitometer to carry out maintenance and debugging.
2. The method for calibrating the projected area of the dual-energy X-ray bone densitometer of claim 1, wherein the next step of calculating in step 3 comprises the steps of:
step 3-1: calculating deviation values of projection area measurement values and standard values of the regular-shaped calibration phantom and the simplified copying calibration phantom by adopting different projection area algorithms; a specified limit value of the deviation is given, if the deviation value obtained by calculation of a certain algorithm is less than or equal to the specified limit value of the deviation, the algorithm is considered to be qualified, and the deviation value can be used for calculating a projection area value;
step 3-2: for the algorithms considered to be qualified in the step 3-1, if the qualified types of the algorithms are more than or equal to 2, firstly calculating the correlation coefficients of the measured values and the standard values corresponding to the algorithms, and selecting the algorithm with the optimal correlation coefficient for subsequent calculation; if only 1 algorithm is qualified, directly embedding the contour recognition algorithm into a dual-energy X-ray bone densitometer, and performing the last step of calculation;
step 3-3: utilizing the projection area measurement value and the standard value of the regular-shape calibration phantom and the simplified copying calibration phantom corresponding to the algorithm selected in the step 3-2, and adopting least square normal fitting to obtain a correction formula with minimum residual square sum; the correction formula and the corresponding projection area algorithm are arranged in the dual-energy X-ray bone densitometer, and when the projection area is measured later, the projection area measurement value is obtained by using the algorithm and is substituted into the correction formula to calculate and obtain a calibrated projection area measurement result.
3. The die body used in the calibration method for the projection area of the dual-energy X-ray bone densitometer according to any one of claims 1 to 2, characterized by comprising a regular-shape calibration die body, wherein the regular-shape calibration die body is designed into a regular geometric shape with strict area fixed values, and comprises a spherical die body (1), a tubular body die body (2), a cylindrical die body (3) and a deformed tubular body die body (4);
wherein the sphere die body (1) is a sphere with the diameter range of 10-80 mm; the tubular body mold body (2) is a hollow cylinder with the bottom surface diameter of 20-60 mm, the wall thickness of 1-5 mm and the height of 30-80 mm; the cylinder body (3) is a cylinder with the bottom diameter of 10-60 mm and the height of 30-80 mm;
the deformable tubular body mold body (4) is composed of an upper part and a lower part, the lower part is a cuboid with the bottom surface being a square with the side length of 20-60 mm and the height of 30-80 mm, an isosceles right triangle triangular prism penetrating through the bottom surface is dug in the cuboid, the wall thickness of a cavity in the rest part is 1-5 mm, and the dug triangular prism is spliced to the upper part of the cuboid at the lower part;
the spherical die body (1) and the cylindrical die body (3) simulate the basic contour form of lumbar vertebrae, the tubular die body (2) simulates the basic contour form of a bone cavity and a bone canal, and the deformed tubular die body (4) is used for evaluating the identification capability of the dual-energy X-ray bone densitometer on simple irregular contour edges.
4. The phantom according to claim 3, characterized in that it further comprises a simplified copying calibration phantom, said simplified copying calibration phantom comprising a simplified phantom of lumbar structure, a simplified phantom of arm bone structure (6) and a simplified phantom of femoral structure (7); wherein the content of the first and second substances,
the lumbar vertebra structure simplification die body is formed by combining 3 single-section lumbar vertebra structure simplification modules (5), the geometric dimension of each single-section lumbar vertebra structure simplification module (5) is the same, and the modules can be scaled in equal proportion, and the scaling proportion is not more than 5%; each single-section lumbar vertebra structure simplifying module (5) consists of a profiling cone body (5-1), a profiling transverse process (5-2), a profiling spinous process (5-3) and a profiling spinal canal (5-4), wherein the profiling cone body (5-1) is a part cut from the lower part of a cylinder, so that the bottom of the profiling cone body (5-1) is a rectangular plane with the diameter smaller than that of the cylinder, the profiling transverse process (5-2) is a quadrangular frustum with the upper and lower bottom surfaces being isosceles trapezoids, a semi-cylindrical hole is dug by taking the central axis of the upper bottom of the quadrangular frustum as the center to form the profiling spinal canal (5-4), and the profiling spinous process (5-3) is a cuboid; the profiling spinous process (5-3) of the single-section lumbar structure simplification module (5) is arranged at the lower part, the profiling vertebral body (5-1) is arranged at the upper part, the profiling transverse process (5-2) is arranged between the profiling vertebral body (5-1) and the profiling spinous process (5-3), the rectangular bottom surface of the profiling vertebral body (5-1) is connected with the upper bottom surface of the profiling transverse process (5-2), the chord length formed by the upper bottom of the profiling transverse process (5-2) and the cut-off part of the cylinder in the profiling vertebral body (5-1) is equal in length, and one part of the upper top surface of the profiling spinous process (5-3) is connected with the lower bottom surface of the profiling transverse process (5-2);
the arm bone structure simplified die body (6) is formed by combining two tubular bodies with different diameters; the femur structure simplified die body (7) is formed by combining a spherical ball and a tubular body.
5. The phantom according to claim 3 or 4, wherein said regular-shaped calibration phantom and said simplified replica calibration phantom are made of hydroxyapatite.
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