WO2021164026A1

WO2021164026A1 - Method and device for constructing phantom and method for fabricating phantom

Info

Publication number: WO2021164026A1
Application number: PCT/CN2020/076271
Authority: WO
Inventors: 斯维纳连科·卡特瑞娜; 张卿卿; 吴琪; 李长鹏; 陈国锋
Original assignee: 西门子（中国）有限公司
Priority date: 2020-02-21
Filing date: 2020-02-21
Publication date: 2021-08-26
Also published as: CN114760931A

Abstract

A method and device for constructing CT performance phantom and a method for fabricating a phantom. The method comprises the following steps: generating a phantom model by adopting a fused deposition modeling (FDM) additive manufacturing method on the basis of a part of an organism that requires a CT scan, the part of the organism comprising a plurality of tissues; selecting a plurality of materials as alternative materials on the basis of the Hounsfield units of the plurality of tissues, each tissue corresponding to a plurality of alternative materials; calculating the effective atomic number of the alternative materials, and selecting a plurality of first materials in the alternative materials that are equal to the effective atomic number of each tissue; and calculating the effective electron concentration of the first materials, and selecting a second material in the first material that is equal to the effective electron concentration of each tissue. The present invention has high accuracy, low costs, and reduces manpower.

Description

Method and device for constructing phantom and method for manufacturing phantom

Technical field

The invention relates to the field of CT scanning, in particular to a phantom construction method and device and a phantom manufacturing method.

Background technique

Computer tomography (Computed Tomography equipment) is widely used to observe with the naked eye the smallest ruptures and changes in the medical field, such as organ, tumor search, and heart examination. Computed tomography scanners are also used to quickly diagnose internal injuries in emergency situations to plan surgical interventions and check the progress of treatment.

Acceptance testing and quality control of computed tomography scanners are very important. Imaging phantoms are specially designed to scan or image in the medical field to evaluate, analyze, and coordinate the performance of different imaging devices. These phantoms are easier to provide more consistent results than physical targets, and also avoid the direct risks of performing inspections on the physical. Among them, there are two types of imaging, one of which is anthropomorphic phantoms, which provides a simplified geometric description of the human body and is designed to represent the characteristics of the human body. The imaging is based on radiation attenuation, physical Physical morphology and geometric structure. Another type of imaging is mechanical imaging, which is designed to evaluate and standardize image quality parameters.

The recent trend in the medical industry is the development of patient-specific programs and artifacts. The radiation dose setting for a specific patient is one of the essential requirements in terms of current protocol optimization. Oncology and radiotherapy are among the medical fields that benefit most from this technology, because tumor geometry is very variable, and more consideration is needed in terms of dose planning and quantitative accuracy. Therefore, customized imaging requirements have requirements for improving and optimizing radiation protection, the time and cost of each procedure, and the method itself. The goal is to obtain more efficient treatment based on the correct radiation dose of the target organ and the protection of healthy tissues.

Nowadays, realistic phantoms can also be provided to medical staff with visual and practical training. They are close to the simulation of real situations. Ideally, they can represent different individuals and target specific patients. For the radiation protection of patients and medical personnel, the new phantom can also provide data for dose calculation and the physiological effects of ionizing radiation, which serves as the basis for the progress of radiological safety worldwide. In addition to adjusting equipment imaging materials and processes for existing special patients or equipment qualification requirements, there is an increasing demand in the industry for the development of new materials and components to enable better reproduction of tissues and organs in radiography (radiography) . Such development means small-batch production and research, which is economically unacceptable in the traditional production model.

Another challenge in the production technology of computed tomography phantoms is the lack of commercial products in certain areas, which means high product procurement costs and long import and transportation times.

So far, traditional polymer processing methods have been widely used to produce anthropomorphic and mechanical phantoms. When traditionally produced imaging films can better replicate the absorption of real tissues and the spread of radiation. The production of phantoms needs to pay attention to special positions, which require high investment, and the produced phantoms have high standards and low possibilities for specific patient needs.

Additive manufacturing technology can be produced layer by layer based on CAD models, which can achieve high customization, realize the high geometric structure complexity of the printed parts, and it has lower costs in some low-volume production. Therefore, additive manufacturing technology is very suitable for biotechnology applications, such as tissue or organ printing.

Fused deposition modeling additive manufacturing device (FDM, fused deposition modeling) and polyethylene nozzle (Polyjet) are a kind of additive manufacturing technology, which has been tested and applied in some mechanical phantom production fields. However, due to the limited selection of polymer materials that represent the same Hounsfield Units as human tissues, some phantoms have very limited ability to replicate tissues and organs.

The prior art also proposes some methods of using FDM technology to produce phantoms, but these methods include using an extruder (extruder) FDM device to manufacture heart phantoms with different structures, and then assemble them and use different materials to make the heart phantoms. Fill phantoms such as water, jelly, and oil to simulate the different tissue media used in CT scans.

Summary of the invention

The first aspect of the present invention provides a phantom construction method, which includes the following steps: generating a phantom model based on the part of the biological body that needs to perform CT scan, wherein the part of the biological body includes a plurality of tissues; calculating the The effective atomic number of the candidate material, select a plurality of first materials that are equal to the effective atomic number of each tissue among the candidate materials; calculate the effective electron concentration of the first material, and select the The second material in the first material that is equal to the effective electron concentration of each tissue; the Heinz unit of the second material is calculated to verify the selected second material.

Further, the Heinz unit is:

Among them, μ _x represents the linear attenuation parameter of the tissue, and μ _w represents the linear attenuation parameter of water.

Further, the effective number of atoms Z _eff is:

Among them, the relative electronic part Zi of _{element i} _{is Σf i} =1, and the index m is determined by the type of radioactive interaction and energy range.

Further, the effective electron concentration is:

Among them, N _A is the Avogadro constant, A _eff is the effective atomic weight,

Where A is the molecular weight and n _i is the number of atoms of all types in all materials.

Further, the first material or the second material includes multiple elements mixed together according to mass percentage.

The second aspect of the present invention provides a phantom manufacturing method, which includes the phantom construction method according to the first aspect of the present invention, wherein the phantom manufacturing method is performed in an FDM device, wherein the main component of the FDM device It includes two feeders, two nozzles, and a base. The phantom manufacturing method further includes the steps of: supplying raw materials in the feeders; spraying the melted second material on the nozzles The phantom is gradually constructed on the following abutment according to the phantom model.

A third aspect of the present invention provides a phantom construction device, which includes: a generating device that generates a phantom model based on a part of a biological body that needs to perform a CT scan, wherein the part of the biological body includes a plurality of tissues; A calculation and selection device, which calculates the effective atomic number of the candidate materials, and selects a plurality of first materials that are equal to the effective atomic number of each tissue among the candidate materials; a second calculation and selection device, calculates The effective electron concentration of the first material, selecting a second material that is equal to the effective electron concentration of each tissue in the first material; a calculation verification device that calculates the Heinz unit of the second material, To verify the selected second material.

Further, the Heinz unit is:

Among them, μ _x represents the linear attenuation parameter of tissue, and μ _w represents the linear attenuation parameter of water.

Further, the effective number of atoms Z _eff is:

Among them, the relative electronic part Zi of _{element i} _{is Σf i} =1, and the exponent m is determined by the type of radioactive interaction and energy range.

Further, the effective electron concentration is:

Where A is the molecular weight, and n _i is the number of atoms of all types in all materials.

The invention can provide customers with a low-cost, fast, and functionally customizable phantom construction and manufacturing mechanism with mathematical calculations and adjustable material components. In addition, the present invention can support phantom manufacturing of multiple materials, and can develop new imitation materials for phantom manufacturing, saving manpower and time. By implementing the present invention, the imitation material mixing and composition of the phantom can be realized based on the shape of the imitation tissue/organ. The present invention obtains a phantom with a complex structure through accurate calculation and adjustment of materials. The present invention quickly obtains the phantom by performing an FDM process with a simple structure and multiple materials, and makes it possible to use new low-cost materials. In addition, the present invention can save the cost of testing and inspection of the entire CT scanning device, and has higher accuracy.

Description of the drawings

Fig. 1 is a schematic diagram of using an FDM device to manufacture a phantom according to a specific embodiment of the present invention;

Fig. 2 is a schematic structural diagram of a phantom according to a specific embodiment of the present invention.

Detailed ways

The specific embodiments of the present invention will be described below with reference to the accompanying drawings.

Considering the increasing demand for customized artefacts in the field of radiology, the present invention provides a phantom manufacturing mechanism that applies the FDM technology of the double extrusion barrel and adjustable polymer material solutions to identify many concentrations, Imitation material of human tissue with actual atomic number and electron concentration.

Specifically, when imitating a phantom material with the same Heinz unit as the human tissue in a CT scan, it is first necessary to obtain information independent of the position of the C slice, scanning conditions, X-ray spectrum, light quality, and light curing corrections (corrections for beam hardening). The Heinz unit, therefore, the present invention does not rely on the reproduction of the Heinz unit of single photon energy or a single X-ray spectrum, but rather to obtain materials that simulate the same linear attenuation parameters as human tissues within an appropriate phantom energy range. However, this is more complicated than just simulating a large number of attenuation parameters μ(E)/ρ, because the phantom material must also show the same specific gravity ρ (specific gravity) as the human tissue. At this point, the additive manufacturing technology and the FDM process of the double extrusion cylinder will be particularly beneficial in the development of new materials that mimic the human tissue and phantom of CT imaging.

The present invention is particularly concerned with finding suitable materials for human body phantoms with two types of materials, such as water and fat in this embodiment, and the present invention will optimize the FDM process to construct a body with at least two human tissues in CT imaging technology. mold.

The first aspect of the present invention provides a phantom construction method, which includes the following steps.

Firstly, step S1 is performed to generate a phantom model based on the part of the biological body that needs to be printed by the CT scan, wherein the part of the biological body includes a plurality of tissues. As shown in Fig. 2, in this embodiment, the phantom P is composed of two tissues, namely tissue P1 and tissue P2. In particular, the phantom model is a CAD three-dimensional model.

It should be noted that the phantom is used to check and test the quality of the CT scanning device, that is, to imitate the quality of the film produced by the biological body in the CT scanning device. Among them, the organism is generally the human body, and the biological part is generally a human organ or a tissue of a certain part of the human body, such as the heart.

Next, step S2 is performed to calculate the effective atomic number of the candidate material, and select a plurality of first materials that are equal to the effective atomic number of each tissue among the candidate materials. The material used for a phantom should have the same mass attenuation coefficient (μm) as that of photons, and the same mass stopping power of electrons as the human tissue it imitates. If the phantom has the same atomic composition as the human tissue to be simulated, the phantom also has the same parameters as these tissues. However, it is not easy to make the phantom and the simulated human tissue have the same atomic composition. Therefore, the present invention expects that the phantom material has a mass density, effective atomic number and electron concentration similar to that of the real tissue of the simulated human body.

The present invention utilizes effectively grounds atomic number Z _eff and effective electron concentration N _e as an indication of the phantom material comprising photons having three main physical process is dependent on photon energy interactions: photoelectric absorption (photoelectric absorption (<100keV) ), Compton scattering (30keV-30MeV) and pair production (>1.02MeV). Based on the photon energy, one of the three interactions has a major effect. Specifically, the energy range is considered to be less than 150 keV, which is a general execution mode of CT devices. The magnitude of photoelectric absorption is roughly proportional to the specific energy of the number of atoms. In the main interaction process where photoelectric efficiency dominates, _{the concept of effective atomic number Z eff} is aimed at selecting materials within the range of photon energy. Compton Effect (Compton interaction) and effective nature of the electron concentration of the material is proportional to N _e.

The direct method of human tissue simulation provided by the present invention is based on the effective atomic number Z _eff , which is based on a set of partial mass attenuation coefficients, elements (τ/ρ, σe/ρ, κ/ρ) and specific The photon energy is calculated. The basis of the human tissue simulation method provided by the present invention is to screen out _{materials with the same value as the electron concentration and effective atomic number Z eff} , where x is the Z index, which is derived for use in the partial interaction process, and The parameters used to make the simulation material show the same interaction characteristics of photons and electrons. The simulation technology consists of the screening of a phantom with appropriate filling materials. The appropriate filling of the material serves as a specific basic material, and the relative proportion of the filling material is determined to obtain a specific level of matching accuracy of the electron concentration and effective atomic number of the two materials. .

Therefore, in this embodiment, the effective atom number needs to be evaluated first, where the effective atom number Z _eff is:

Among them, the relative electronic part Z _i of the ^{i th} _{element is Σf i} =1, and the exponent m is determined by the type of radioactive interaction (such as photoelectric, electron, etc.) and the energy range. Among them, the radio-electricity attenuation interaction of the energy range m ( Photoelectric attenuation interaction) is usually 2.94.

Based on this, determine the composition of the phantom material. Z _eff (BT) = Z _eff (PM), where Z _eff (BT) is the effective number of atoms of the simulated human tissue, and Z _eff (PM) is the effective number of atoms of the phantom material. It is necessary to know that when screening simulated materials of human tissue, the effective atomic number of some materials is known, and some materials need to be mixed together to obtain a mixed material with the same effective atomic number as the simulated human tissue. .

Finally, step S3 is performed to calculate the effective electron concentration of the first material, and select a second material that is equal to the effective electron concentration of each tissue in the first material. Calculate the effective electron concentration of the phantom material:

Among them, N _A is the Avogadro number, A _eff is the effective atomic weight,

Where A is the weight of sample molecules, and n _i is the number of atoms of all types in all synthetic materials.

As long as the determination of the effective atomic number Z _eff material and an effective electron concentration N _e phantom material is the same as the desired human tissue phantom simulation, it can be properly selected material.

Then step S4 is executed to select multiple materials as candidate materials based on the Heinz unit of the multiple tissues, wherein each tissue corresponds to multiple candidate materials. Among them, the Hounsfield unit (HU) is a quantitative ratio used to describe the radiation density, which is usually used in the field of CT scanning. The value of the Heinz unit is calculated based on the X-ray linear attenuation parameter of each individual tissue voxel. Specifically, it is first calculated through the reconstruction process, and then used to calculate the CT value. Each tissue of the human body has a specific Heinz unit size, and we select imitation materials equivalent to the human tissue according to the Heinz tissue of the human tissue to imitate the human body part.

In CT technology, the application standards of phantom materials include detectability, which is usually measured by the reproducibility of CT values, which includes Heinz Units (HU):

Among them, μ _x represents the linear attenuation parameter of the tissue, and μ _w represents the linear attenuation parameter of water. In this embodiment, μ _x and μ _w respectively represent the linear attenuation parameters of fat and water. Specifically, the linear attenuation parameters of the material depend on the tissue components, tissue concentration, and photon energy of the phantom.

Therefore, suppose that the human organ we need to imitate has two types of tissues, namely water and fat. The Heinz unit values of water and fat are known. Therefore, multiple materials with the same Heinz unit value as water can be selected as candidate materials. , And simultaneously select multiple materials with the same Heinz unit value as fat as candidate materials.

It should be noted that when the Heinz unit value of the tissue cannot match any suitable material, multiple materials can be mixed together to obtain a mixed material with the same Heinz unit value of the tissue.

Preferably, the present invention uses FDM technology to print the phantom. As shown in FIG. 1, the FDM device 100 includes two sub-devices, a first sub-device 110 and a second sub-device 120 respectively. Among them, the first sub-device 110 includes a feeder 112, an extrusion barrel 114 and a nozzle 116. Among them, the feeder 112 contains raw materials. Optionally, the feeder 112 is a premixed feeder. When there are multiple types of raw materials, the multiple raw materials are mixed according to a predetermined ratio and set in the feeder 112. A screw feeder (not shown) is built in the extrusion cylinder 114, and a plurality of heating units (not shown) are provided on the outer wall of the extrusion cylinder 106, wherein the screw feeder is composed of a motor ( (Not shown) drive so that the raw materials enter the extrusion barrel 114 through the feeder 112 and then are heated, melted and mixed. The nozzle 116 is connected to the squeeze cylinder 114 and is arranged below the squeeze cylinder 114, sprays the melted material on the base 130 below the nozzle, and gradually forms a phantom P according to a predetermined shape. In the same way, the second sub-device 120 also includes a feeder 122, an extrusion barrel 124 and a nozzle 126, which will not be repeated for the sake of brevity.

Among them, as shown in FIG. 1 and FIG. 2, in this embodiment, it is necessary to manufacture a phantom P that requires two kinds of materials, and it continuously manufactures a predetermined shape by sending two types of materials. Among them, two materials are set in the

feeders

112 and 122 respectively. One of the two materials is water and the other is adipose. The water is used as a reference material for CT scanning, and the fat is used as a human body. Tissue simulation materials, two materials are used together to simulate human organs in CT scans. Specifically, the phantom P includes two materials, wherein the material P1 is provided from the feeder 112 and the material P2 is provided from the feeder 122. Also, the material P1 is imitating water, and the material P2 is imitating fat.

As shown in the material selection list shown in Table 1, in this embodiment, through the implementation of the present invention, the material P1 is to imitate water, so elements H and O are selected. Among them, the mass composition percentage of element H is 11.19%. The mass composition percentage of O is 88.81%, its mass concentration is 1000 kg/m3, its effective atom number is 7.42, and its effective electron concentration is 3.343e/kg x 10 ²⁶ . In order to imitate fat, material P2 selected elements H, C, N, O, S, Na, Cl, and Ca. Among them, the mass composition percentage of element H is 11.2%, the mass composition percentage of element C is 51.7%, and the element N The mass composition percentage of the element O is 1.3%, the mass composition percentage of the element O is 35.5%, the mass composition percentage of the element S is 0.1%, the mass composition percentage of the element Na is 0.1%, the mass composition percentage of the element Cl is 0.1%, and the element Ca The mass composition percentage of is 0.1%, and its mass concentration is 970kg/m3, its effective atom number is 6.4, and its effective electron concentration is 3.342e/kg x 10 ²⁶ .

Table 1 Material selection list

As shown in FIG. 1, the present invention is preferably implemented by the FMD device 100, and the aforementioned selected materials are mixed in the feeder according to the proportions and other parameters. The present invention can also optimize the construction parameters of the phantom by optimizing the parameters of the FDM technology, such as abutment temperature, raw material temperature and deposition speed, etc., to obtain samples with no deterioration characteristics in the accuracy of subsequent CT scans. The characteristics include Voids, porosity and cracks.

Further, the Heinz unit is:

Further, the effective number of atoms Z _eff is:

Further, the effective electron concentration is:

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as limiting the present invention. After those skilled in the art have read the above content, various modifications and substitutions to the present invention will be obvious. Therefore, the protection scope of the present invention should be defined by the appended claims. In addition, any reference signs in the claims should not be regarded as limiting the involved claims; the word "comprising" does not exclude other claims or devices or steps not listed in the specification; "first", "section Words such as "two" are only used to indicate names, and do not indicate any specific order.

Claims

The phantom construction method includes the following steps:

Generating a phantom model based on the part of the biological body that needs to perform the CT scan, wherein the part of the biological body includes a plurality of tissues;

Calculate the effective atomic number of the candidate material, and select a plurality of first materials equal to the effective atomic number of each tissue;

Calculating the effective electron concentration of the first material, and selecting a second material that is equal to the effective electron concentration of each tissue in the first material;

Calculate the Heinz unit of the second material to verify the selected second material.
The phantom construction method according to claim 1, wherein the Heinz unit is:

Among them, μ x represents the linear attenuation parameter of the tissue, and μ w represents the linear attenuation parameter of water.
The phantom construction method according to claim 1, wherein the effective number of atoms Z eff is:

Among them, the relative electronic part Zi of element i is Σf i =1, and the index m is determined by the type of radioactive interaction and energy range.
The method for constructing a phantom according to claim 1, wherein the effective electron concentration is:

Among them, N A is the Avogadro constant, A eff is the effective atomic weight,
Where A is the molecular weight, and n i is the number of atoms of all types in all materials.
The phantom construction method according to claim 1, wherein the first material or the second material includes multiple elements mixed together according to mass percentage.
A phantom manufacturing method, including the phantom construction method according to any one of claims 1 to 5, characterized in that the phantom manufacturing method is performed in an FDM device, wherein the FDM device includes two A feeder, two nozzles and a base, and the phantom manufacturing method further includes the following steps:

Provide raw materials in the feeder;

The melted second material is sprayed on the abutment below the nozzle, and a phantom is gradually formed according to the phantom model.
Phantom construction device, including:

A generating device, which generates a phantom model based on a part of a biological body that needs to perform a CT scan, wherein the part of the biological body includes a plurality of tissues;

The first calculation and selection device calculates the effective atomic number of the candidate material, and selects a plurality of first materials that are equal to the effective atomic number of each tissue among the candidate materials;

A second calculation and selection device, which calculates the effective electron concentration of the first material, and selects a second material that is equal to the effective electron concentration of each tissue in the first material;

A calculation verification device that calculates the Heinz unit of the second material to verify the selected second material.
The phantom construction device according to claim 7, wherein the Heinz unit is:

Among them, μ x tissue linear attenuation parameter, μ w represents the linear attenuation parameter of water.
The phantom construction device according to claim 7, wherein the effective atomic number Z eff is:

Among them, the relative electronic part Zi of element i is Σf i = 1, and the exponent m is determined by the type of radioactive interaction and energy range.
The phantom structure device according to claim 7, wherein the effective electron concentration is:

Among them, N A is the Avogadro constant, A eff is the effective atomic weight,
Where A is the molecular weight, and n i is the number of atoms of all types in all materials.
The phantom construction device according to claim 7, wherein the first material or the second material includes multiple elements mixed together according to mass percentage.