# Development and Evaluation of Doppler Ultrasound Training Phantom for Human Vessel Simulation
## 4 Discussion
The agarose gel used in this study also has limitations, such as being prone to easy fragmentation and mold growth due to microbial invasion, resulting in a limited lifespan. However, these issues were resolved through securely fixing the agarose gel within the Doppler ultrasound training phantom frame, to prevent easy breakage. During the experiments, direct contact with the phantom was minimized, and the phantom maintained stability for up to one month via refrigerated storage. In this study, the design of the training phantom for beginners prioritized efficiency and portability. The Doppler ultrasound training phantom was created using LEGO bricks and ABS material, in a modular LEGO format. The lower ABS surface of the component was deliberately designed to resemble the shape of LEGO blocks. The choice of utilizing LEGO for this purpose stemmed from several key reasons. Firstly, the LEGO plates provided a robust and secure fixation for the Doppler ultrasound training phantom, enabling novice users to carry out scans with stability. Moreover, LEGO offered notable advantages in terms of accessibility, affordability, and user-friendliness. Its flexibility allowed for the formation of various shapes tailored to user preferences. Secondly, through the combination of 12 small LEGO pieces (each sized 4 cm \(\times\) 3 cm \(\times\) 1.5 cm), the phantom (Figure 2b of A) was effectively supported, offering the added benefits of reduced weight and enhanced portability compared to the previously designed ABS phantom holder. Additionally, it is easy to assemble and disassemble, and has a high level of reproducibility [46; 47; 48]. The Doppler ultrasound training phantom was manufactured in a LEGO format to facilitate portability and user-friendliness, making it intuitive even for beginners. The decision to adopt a staircase-like design was motivated by the goal of avoiding the need for a water pump or automated injector, ultimately minimizing costs. Furthermore, the Doppler ultrasound training phantom, fabricated in LEGO format, enables probe fixation using LEGO pieces, and allows for versatile modifications in various shapes [30; 46; 47]. We plan to leverage these aspects to enhance the diversity of LEGO-based phantoms. However, it should be noted that the Doppler ultrasound training phantom, which utilizes height differences, may not completely reproduce a continuous flow of blood within the phantom. However, this design choice was made to prioritize portability and ease of use for beginner training purposes. Despite this limitation, as the Doppler ultrasound training phantom was able to reproduce the flow of blood to some extent, there were no issues with learning the various parameters. If necessary, the water pump can be used to reproduce a continuous flow of blood. The vessel-mimicking phantom offers the advantage of adjusting the vessel diameter and customization based on user requirements. However, it should be noted that the manufactured phantom does not reproduce the anatomical structure of the arterial wall layers, including the intima, media, and adventitia. Our focus in developing the vessel-mimicking phantom was on assisting beginners in understanding and acquiring fundamental knowledge about blood flow direction and parameters. Therefore, an exact reproduction of the actual structure was not necessary. However, our phantom offers easy customization and optimization for specific target conditions, such as arterial sclerosis and cerebrovascular diseases. By making modifications specifically to the vascular component, it is relatively easy to create phantoms that are optimized for specific target conditions, such as arterial sclerosis and cerebrovascular diseases. This allows for advanced and diversified phantom development.