Method for manufacturing a thyroid phantom

Abstract

The invention relates to medical training aids. The claimed method includes preparing models of bone and cartilage structures and molds for blood vessel and thyroid models by 3D printing. A plastisol containing polyvinyl chloride is used for simulating a thyroid and blood vessels. This plastisol is poured into the molds for the blood vessel and thyroid models and held until it has cooled. A plastisol containing powdered graphite and a metal glitter for echogenicity is used for simulating lymph nodes and tumorous growths. Lengths of jute twine are laid in molds, into which a plastisol with added glitter is poured, the plastisol is held until it has cooled, and neck muscle models are cut out. A plastisol containing dyes is poured into a master neck mold to produce a skin model. The models of the muscles, vessels, thyroid, bone and cartilage structures, trachea, lymph nodes and tumorous growths are arranged in the master neck mold, into which a plastisol containing glitter is poured, the assembly is left to cool before being removed and the skin model is attached. The technical result is that the structure of the phantom more closely resembles the structure of a human thyroid.

Description

[0001] Description:

[0002] The invention relates to biomedical modeling, specifically the fabrication of ultrasound phantoms, as they possess known acoustic properties and can therefore be used to train specialists in ultrasound diagnostics and develop new diagnostic techniques and devices. A method for fabricating an ultrasound phantom with an internal structure similar in acoustic properties to human tissue is disclosed.

[0003] A phantom [1] is known from the prior art. Its manufacturing process involves multiple manufacturing steps, primarily involving organic (food) products. The phantom contains a thyroid gland model made of gelatin, a trachea model made from a plastic bottle, and a gelatin model of the soft tissue surrounding the thyroid gland and trachea.

[0004] A tracheal model was made from an empty, cut-up bottle with an inflated balloon filled with liquid inserted into it. Soft tissue models were made from gelatin, which was mixed with warm water and stirred, then heated in a microwave. A mixture of cornstarch and water was poured into the warm gelatin solution, stirred, and poured into a container. The tracheal model was placed in the center of the container, filled with the gelatin and cornstarch mixture, and cooled. Blackberries (simulating suspicious tumors) were later placed into the mixture at varying depths. It took approximately one hour to prepare the phantom before cooling.

[0005] The disadvantage of this technical solution is that the material chosen to imitate soft tissue is short-lived and susceptible to drying out and bacterial growth, making it unsuitable for repeated, long-term use. Gelatin, berries, bottles, and other materials are not technologically advanced.

[0006] A thyroid phantom [2] is known, with the addition of models simulating benign cystic lesions and moderately suspicious lesions. The FN A (fine needle aspiration) thyroid phantom is inexpensive and easy to manufacture.

[0007] The phantom's drawback is that it is made using low-tech and short-lived (food-grade) materials: chicken breast, red seedless grapes, olives, and blackberries. The materials used to make the phantom are perishable, making it difficult to reuse over a long period of time.

[0008] The phantom is assembled manually, immediately before conducting training diagnostics.

[0009] Both methods [1, 2] for producing thyroid gland phantoms are the closest known analogues of the claimed method for producing a phantom for ultrasound diagnostics.

[0010] The technical objective of the claimed invention is to create an anthropomorphic phantom with inclusions, the shape, echogenicity and rigidity of the internal structures of which are more realistic, compared to prototypes, and similar to the shape, echogenicity and rigidity of the internal structures of a real human thyroid gland.

[0011] The inclusions' ability to simulate shape, echogenicity, and rigidity makes the phantom suitable for developing and testing not only the ultrasound physician's visual-motor coordination but also for refining differential diagnostic skills and working in the ultrasound scanner's elastographic modes. The phantom's manufacturing process is based on the following: models of bone and cartilage structures, a neck model, and molds for casting veins, arteries, and the thyroid gland are printed on a 3D printer; tumor models are prepared using polyvinyl chloride plastisol and an admixture for echogenicity modeling. The neck model is placed in a container and filled with silicone to create a neck model master mold; a thin layer of plastisol is poured into the silicone neck model master mold to create a skin model.Models of all internal structures and inclusions of the thyroid gland phantom are placed in a silicone neck master mold. The neck master mold, containing models of the thyroid gland's internal components, is then filled with polyvinyl chloride plastisol, preheated to 150-180°C (at which the plasticizer diffuses most rapidly into the polyvinyl chloride) and simulating soft tissue after hardening, which occurs upon cooling to room temperature. After the plastisol has hardened, the thyroid gland phantom is removed from the neck master mold, a skin model is affixed on top, and used for ultrasound training.

[0012] The significant distinguishing features of the claimed technical solution, in comparison with its closest analogues, are:

[0013] - the use of several polyvinyl chloride plastisols, differing in hardness on the Shore scale, to model the elastographic properties of various tissues;

[0014] - the use of inclusion shapes and the modeled organ that are close to the shapes encountered in the clinical practice of an ultrasound diagnostic physician.

[0015] Fig. 1 shows photographs of 3N printers for printing with photopolymer resin.

[0016] Fig. 2 shows photographs of 3N printers for printing with plastic.

[0017] Fig. 3 shows an example of a CT scan of the neck in the Dicom Radiant program.

[0018] Fig. 4 shows a virtual model of the neck for making a phantom.

[0019] Fig. 5 shows the diagrams of the internal structure of the thyroid gland phantom: a - general diagram (1 - lower jaw; 2 - hyoid bone; 3 - thyroid cartilage; 4 - cervical spine; 5 - thyroid gland; 6 - simulated thyroid tumors; 7 - trachea; 8 - clavicle; 9 - sternum; 10 - ribs; 11 - arteries; 12 - veins; 13 - lymph nodes); 6 - segmented parts of the 3D model of the neck phantom.

[0020] Fig. 6 shows photographs of the layout and master mold of the thyroid gland phantom neck: a - a photopolymer resin neck model printed on a 3H printer; 6 - a silicone master mold of the neck model for making the phantom.

[0021] Fig. 7 shows the stages of manufacturing the thyroid gland: a - 3D model of the form in the MeshMixer program; 6 - printed form with a model of the thyroid gland poured from plastisol.

[0022] Fig. 8 shows a photograph of the finished thyroid gland model.

[0023] Fig. 9 shows a model of the trachea: a - a model of the trachea in the MeshMixer program; 6 - a printed 3D model of the trachea.

[0024] Fig. 10 shows a model of the bone structures of the neck: a - bone structure in the MeshMixer program; b - bones printed on a 3H printer with supports; c - finished bone models.

[0025] Fig. 11 shows the stages of vessel production: a - vessel models in the MeshMixer program; b - printed forms for vessel production; c - finished veins and arteries.

[0026] Fig. 12 shows photographs of the muscle model: a - muscle models for one side of the thyroid gland phantom; 6 - jute twine for making fibers and threads of muscle models; b - an example of the arrangement of muscle models inside the phantom.

[0027] Fig. 13 shows photographs of the process of filling the master mold of the neck model for the production of a thyroid gland phantom.

[0028] Fig. 14 shows photographs of work with a thyroid gland phantom on diagnostic equipment.

[0029] Fig. 15 shows a photograph (a) and sonograms (b-e) of a phantom simulating the ultrasound anatomy of the human neck: 6 - vein and lymph node near the clavicles; c - left lobe of the thyroid gland, vein, artery, neoplasm; g - thyroid gland with isthmus; d - artery bifurcation, vein, lymph node; e - vein (longitudinal), artery, lymph node.

[0030] Fig. 16 shows ultrasound images of thyroid gland tumor models using a linear sensor with a carrier frequency of 7.5-9 MHz at a depth of up to 3 cm: a - cystic, b - solid, c - cystic-solid models.

[0031] The phantom shown in (Fig. 5a) consists internally of: 1 - sound-conducting material; 2 - hyoid bone; 3 - thyroid cartilage; 4 - cervical spine; 5 - thyroid gland; 6 - thyroid nodes; 7 - trachea; 8 - clavicle; 9 - sternum; 10 - ribs; 11 - arteries; 12 - veins; 13 - lymph nodes; paired muscle models consisting of 6 pieces on both sides of the neck. In accordance with the manufacturing technique, all elements of the phantom are located so as to ensure the best imitation of the anatomical location of the modeled human organs.The thyroid gland model 5 is located above the trachea model 7, the tumor model 6 is inside the thyroid gland model 5, the trachea model 7 is located in front of the cervical spine model 4, the clavicle model 8, the rib model 10, the sternum model 9 are located in the lower part of the phantom at the base of the trachea model 7, the carotid artery model 11 is located in the direction of the trachea model 7 and in close proximity to it (on average 10-20 mm), the jugular vein model 12 is located in the direction of the trachea model 7 and in close proximity to it (on average 15-25 mm), the vertebral artery model I passes in close proximity to the cervical spine model 4, the lymph node model 13 is adjacent to the jugular vein model 12, the cartilage model 3 wraps around the trachea model 7. All internal elements are located inside the sound-conducting material 1 imitating soft tissue.

[0032] Muscle models simulate:

[0033] 1) the longus colli muscle, which is located between the thyroid gland and the spine. The longus colli muscle attaches to the vertebrae;

[0034] 2) the sternothyroid muscle, which is located in the front of the neck, covers the thyroid gland.

[0035] Muscle models with a fibrous internal structure are a composite material consisting of plastisol with metallic glitter and jute twine threads. Three pairs of muscle models are fabricated for the left and right sides of the phantom, respectively. One pair of muscle models is positioned posterior to all phantom structures. The other two pairs of muscles are positioned overlapping each other in front of all internal structures of the thyroid gland phantom, corresponding to their anatomical location in the human body (Fig. 12c). To fabricate a model simulating the fibrous structure and echogenicity of the muscle, jute twine is used (Fig. 12b), which is pre-disassembled into individual fibers and threads.

[0036] All phantom-forming models were obtained by segmenting and analyzing topographic images (Fig. 3). The diagram (Fig. 56) of the phantom's internal composition was obtained by 3D modeling using real computed tomography data from the human thyroid gland. The 3D model (Fig. 56) visualizes various internal elements of the cervical segment: lymph nodes, thyroid gland, veins, arteries, and osteochondral structures.

[0037] In order to achieve the specified technical result, it is proposed to use the developed method for manufacturing a thyroid gland phantom for ultrasound examinations. The manufacturing process was as follows. The neck shape was segmented using computed tomography (Fig. 3) and printed on an Any cubic Photon M3 Max 3D printer (China) (Fig. 1) using LCD technology (photopolymer printing technology) and industrial polymer resin (Fun-to-do, Netherlands). The 3D-printed neck model (Fig. 6a) was used to create a master mold of the neck model for casting (Fig. 6b) from liquid tin-based silicone (KREMEN MOLD 10, Russia). The printed neck model was placed in silicone. When the silicone hardened, a reusable heat-resistant master mold of the neck model for casting was obtained (Fig. 66).

[0038] The fabrication of the phantom's internal contents involved several stages: fabrication of parts, including 3D-printed plastic bone models (Fig. 10a-c) and molds of internal structures for filling with plastisol, the thyroid gland (Fig. 8) with tumor formations, blood vessels (Fig. 11), lymph nodes, and casting of soft tissue models with inserted composite parts.

[0039] Tumor and lymph node models mimic inclusions found in human organs in terms of shape, echogenicity, and rigidity. To simulate the tumor, we used a PVC plastisol without additives, with a rigidity 60% higher than that of the PVC plastisol used to create the base tissue model. To simulate the desired echogenicity, after heating the PVC plastisol to 150-180°C, at which the plasticizer diffuses most rapidly into the PVC, we added a 0.5% admixture of finely dispersed, heat-resistant metallized glitter with a particle diameter of no more than 200 μm. The tumor models were then manually processed to achieve the desired size and shape. Inclusions were cut from prefabricated tissue-mimicking material using nail scissors to achieve the desired shape.Since plastisol is a suspension of polyvinyl chloride in a liquid plasticizer, the ratio of these substances determines the hardness, which can be expressed, for example, by the Shore scale [3]. In our experiments, material with a hardness ranging from 3 to 18 units on the Shore scale was used.

[0040] Virtual models of the casting molds for the vessels (Figs. 11a-b) and the thyroid gland (Fig. 7a-b) were fabricated using Meshmixer, a manual 3D modeling software, and then printed on a 3D printer (Fig. 2), as shown in (Fig. 7b and Fig. 11b). For modeling the thyroid gland, we used polyvinyl chloride plastisol with an admixture of 0.5-1% graphite powder with a particle size no larger than the wavelength of the ultrasonic radiation used (in our experiments, particles no larger than 140 μm were used when studying at frequencies from 4.7 to 9.4 MHz). The vessels were filled with plastisol without admixture, and the thyroid gland was filled with plastisol with an admixture of graphite powder at a high concentration and with an admixture of metallic glitter. The bone and cartilage models (Fig. 10a-c) were segmented based on the patients' CT scans and printed on a 3D printer as shown in (Fig. 10b-c).To prevent air accumulation in the resulting liquid plastisol solution with an admixture, heated to 150-180°C, it had to be degassed in a special vacuum chamber.

[0041] It should be noted that, according to the developed method, the material of the silicone casting molds and the plastic molds printed on a 3D printer do not enter into chemical interaction with the polyvinyl chloride plastisol.

[0042] The heating temperature for the plastisol depends on the plastisol used; in our case, it was 150-180°C. Heating was performed in a microwave oven, stopping every 30 seconds for stirring and temperature checking.

[0043] Once all the internal components of the thyroid phantom have been fabricated, they are placed in a silicone neck model master mold and filled with degassed plastisol containing metallic glitter, heated to 150-180°C. After cooling to room temperature, the skin model is attached to the thyroid phantom, and it is ready for use.

[0044] In a preferred embodiment of the invention:

[0045] - for 3D modeling and prototyping, use the Autodesk Meshmixer version 2.4 program and a printer, for example, Picaso X Pro;

[0046] - PLA plastic is used as a material that does not chemically interact with the material simulating soft tissue;

[0047] - as a material simulating the soft tissues of the modeled organ and other tissues and tumor neoplasms simulating inclusion body diseases, polyvinyl chloride plastisol of the appropriate hardness according to the Shore scale with additives is used.

[0048] Graphite powder is used as additives at a concentration of up to 1%, and for greater echogenicity, metallized glitter is added at a concentration of 0.5%. In our experiments, graphite powder with a particle size of no more than 140 µm and heat-resistant metallized glitter with a diameter of no more than 200 µm were used.

[0049] The temperature at which the plasticizer diffuses most rapidly into the PVC is used as the plastisol heating temperature. This temperature depends on the material used. For example, in our experiments, we used Red Bug Diamond #6 plastisol, for which the heating temperature was 150-180°C.

[0050] A thyroid phantom fabricated using the proposed method, covering the entire neck region from the clavicles to the chin-neck junction, enables a comprehensive examination. The proposed method for fabricating a multi-component thyroid phantom allows for the acquisition of important landmarks for ultrasound imaging of the neck: the carotid arteries, jugular veins, lymph nodes, and the thyroid gland with tumors. Furthermore, the bone structures, manufactured as a single unit using a 3D printer from high-resolution photopolymer resin, significantly simplify the manufacturing process, accelerate it, and improve the reproducibility of all phantom models, including relatively small and fragile ones such as the hyoid bone and cartilage.

[0051] The thyroid gland phantom, manufactured using the proposed method, will serve:

[0052] - to develop manual object placement skills, specifically, the ability to find the correct sensor position to visualize the desired inclusion projection. In clinical practice, when a physician monitors a lesion with suspected malignancy and developing complications over several months, it is important to obtain a sonogram as close to the same plane as possible each time to accurately compare dimensions and assess the growth dynamics of the lesion; - a tool that helps develop visual-motor coordination and master the specifics of thyroid ultrasound examination;

[0053] - a good tool for teaching skills in differential diagnosis of internal structures and tumor formations of the thyroid gland, assessing the size of the thyroid gland, the skill of inserting a needle to take a biopsy sample or simulating an injection;

[0054] - an example of a model that, during ultrasound diagnostics, allows for realistic visualization of the structure and properties of tissues in the human neck area;

[0055] - a means for training in working with the elastographic mode of ultrasound imaging, since it can even contain inclusions that are barely noticeable in B-mode, but differ from the surrounding tissues in rigidity.

[0056] The method for producing a thyroid gland phantom is described using a specific embodiment of its implementation; however, specialists will be aware of the possibilities of numerous modifications of this invention that do not go beyond the scope of its legal protection, as defined by the attached formula.

[0057] Sources of information

[0058] [1]. Hakimi AA, Armstrong WB. Improving on the Do-It-Yourself Ultrasound-Guided Fine-Needle Aspiration Simulation Phantom. J Ultrasound Med. 2021 Apr;40(4):815-819. doi: 10.1002 / jum. 15461.

[0059] [2]. Schwartz CM, Ivancic RJ, McDermott SM, Bahner DP. Designing a Low-Cost Thyroid Ultrasound Phantom for Medical Student Education. Ultrasound Med Biol. 2020 Jun;46(6): 1545-1550. doi: 10.1016 / j.ultrasmedbio.2020.01.033.

[0060] [3]. Can You Estimate Modulus From Durometer Hardness for Silicones? [электронный ресурс] URL:https: / / www.dow.com / content / dam / dcc / documents / en-us / tech-art / l 1 / 11- 37 / 11-3716-01 -durometer-hardness-for-silicones.pdf

Claims

Invention formula 1. A method for manufacturing a phantom for ultrasound examination of the thyroid gland, comprising: manufacturing models of bone and cartilage structures using 3D printing, manufacturing molds for models of vessels and the thyroid gland using 3D printing, which are filled with liquid plastisol, characterized in that models of bone and cartilage structures are made from a photopolymer resin, and the models for printing are prepared by 3D modeling based on the results of computed tomography, the molds of the artery, vein and thyroid gland models are made from thermoplastic plastic, the models for printing are prepared by 3D modeling based on the results of computed tomography, molds of tumor models are made from thermoplastic plastic by 3D printing, plastisol with polyvinyl chloride, preheated to a temperature of 150-180°C, is used as a material for simulating models of the thyroid gland and vessels, it is poured into molds of the models of the vessels and the thyroid gland,lymph nodes and tumor neoplasms and kept until solidification, as a material for simulating lymph nodes and tumor neoplasms, plastisol with the addition of finely dispersed graphite powder and metallic glitter to impart echogenicity is used, plastisol with the addition of metallic glitter in the amount of 0.5% is preheated to a temperature of 150-180 ° C, poured into molds of models of lymph nodes and tumor neoplasms, kept until solidification, jute twine is cut with scissors into segments 7-10 cm long, each segment is disassembled into fibers and threads, laid out in the mold in one direction, ensuring a loose, uniform arrangement, plastisol with the addition of metallic glitter 0.5%, preheated to a temperature of 150-180 ° C, poured into molds of muscle models with fibers and threads laid out there jute twine, with a filling height of no more than 5 mm, is kept until it hardens, models of the neck muscles are cut out so thatIn order for the fiber and threads of the jute twine to be located along the length of the muscle model, a neck model is made using 3D printing from photopolymer resin, which is pre-prepared using 3D modeling in accordance with the results of computed tomography, filled with silicone to obtain a master mold representing an imprint of the plastic model of the neck, left until it hardens, liquid plastisol with the addition of dyes to give the color of human skin is poured into the master mold, distributed evenly over the master mold in a layer to obtain a skin model, after the plastisol has hardened, the skin model is removed from the master mold, models of the neck muscles, models of blood vessels, the thyroid gland, bone and cartilaginous structures, the trachea, lymph nodes and tumor neoplasms are placed into the master mold one by one in accordance with the anatomical location, filled with plastisol heated to a temperature of 150-180 ° C with the addition of metallic glitter, leave until solidified,removed from the master mold and a skin model is fixed on top.

2. The method according to item 1, characterized in that the bone-cartilage structures are manufactured using the 3D printing method in full size based on medical imaging data.

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