# Development and Evaluation of Doppler Ultrasound Training Phantom for Human Vessel Simulation
## 1 Introduction  
Medical Doppler ultrasonography (US) examinations play a central role in contemporary medical diagnosis, by evaluating the hemodynamics of blood flow in the body. Through a non-invasive method, ultrasonography can assess the velocity and direction of blood flow in real time [1, 2]. Furthermore, it serves as an essential diagnostic examination for cardiovascular diseases, providing visual information and quantitative information about blood flow dynamics in real time [3, 4]. Color Doppler, one of the Doppler ultrasound examinations, is a diagnostic method that provides both anatomical and physiological information about blood vessels. During a color Doppler examination, a color box is placed within a grayscale image to define the area of interest. It presents information about blood flow within the color box, and it shows the direction and velocity of the blood flow, using different colors [5]. Color Doppler is essential for evaluating blood flow information, and detecting normal and abnormal flow patterns [6, 7]. To obtain accurate blood flow information, it is important to optimize color Doppler imaging, by adjusting several parameters, such as the color box, scale, color gain, wall filter, and Doppler angle [7]. Among the parameters of color Doppler, the color box is one of the essential foundational parameters that beginners must become proficient in. It allows for the visual identification of the blood flow direction, and facilitates intuitive understanding [8]. Additionally, the scale is used as a parameter to adjust an important artifact called aliasing, which occurs in Doppler ultrasound [9]. Beginners studying an ultrasound need to adjust the scale to obtain accurate blood flow information. Gain is used to control the ultrasound reception signals, and the color gain can be adjusted to modulate the blood flow signals [8]. Ultrasound examinations rely on the skill of the examiner. Therefore, in order to understand and optimize color Doppler imaging, it is necessary to achieve a certain standard of expertise and scanning skills, through training and experience. For beginners, it is beneficial to start training under standardized conditions. However, maintaining such conditions in clinical settings may not always be possible. Therefore, the use of a training phantom to acquire standardized images becomes necessary. Learning with a training phantom provides the advantage of training, without direct patient interaction. This approach allows for the improvement of scanning techniques and the acquisition of knowledge about parameter settings, free from concerns about patient safety and time limitations. Additionally, using a training phantom provides a controlled environment, where errors associated with color Doppler can be identified and corrected. Through actively identifying and correcting errors, it is possible to improve the accuracy and diagnostic skills. However, it is worth noting that most training phantoms available are primarily designed for physician education, specifically for biopsies [10; 11; 12]. Typically, a Doppler ultrasound phantom consists of a blood vessel structure, tissue-mimicking materials, and blood flow systems. For the blood vessel structure, some researchers have used the particle image velocimetry (PIV) technique, and quantitatively evaluated the velocities of an abnormal blood vessel [13; 14]. There have been many attempts to manufacture abnormal blood vessels using the lost casting technique, with a silicone elastomer [15; 16; 17]. Furthermore, recent research has shown that the combination of PIV technology and 3D printing technology has been effectively utilized [18; 19; 20]. However, using silicon might result in wall echoes, which could confuse beginners with regard to understanding ultrasound signals [21]. While 3D printing technology is effective in manufacturing complicated vessel structures, it is challenging for beginners, in terms of ease of use and its cost.