# Development and Evaluation of Doppler Ultrasound Training Phantom for Human Vessel Simulation
## 4 Discussion  
The main purpose of this work was to introduce methods for manufacturing the Doppler training phantom, and to provide insights into various aspects related to blood flow information. The Doppler ultrasound training phantom was designed to aid beginners in learning color Doppler, and to optimize and evaluate ultrasound images with various parameters. These include the impact of the color box steering direction on blood flow information, the control of aliasing through scale adjustment, and the changes in blood flow information resulting from color gain adjustments. Beginners can use the Doppler ultrasound training phantom to learn how these parameters affect blood flow ultrasound images. We utilized a gel-based phantom to investigate the effects of the color box, scale, and color gain settings. The linear probe was positioned parallel to the vessels in the phantom, and ultrasound images were acquired with consistent time gain compensation (TGC) settings. When comparing the scale images with the spectral Doppler images, we observed  
Figure 6: Color Doppler imaging with varying gain settings, using leftward steer of the color box. Color Doppler with a gain of (**a**) 2 dB, (**b**) 5 dB, (**c**) 10 dB, (**d**) 35 dB, (**e**) 60 dB, and (**f**) 100 dB. The arrows in (**e,f**) indicate the presence of bleeding artifacts. Figure 7: Color Doppler imaging with varying gain settings, using rightward steer of the color box. Color Doppler with a gain of (**a**) 2 dB, (**b**) 5 dB, (**c**) 10 dB, (**d**) 35 dB, (**e**) 60 dB, and (**f**) 100 dB. The arrows in (**e,f**) indicate the presence of bleeding artifacts. the absence of aliasing artifacts when the scale image had a Nyquist limit of 25 m/s. This indicates that the maximum blood flow velocity did not exceed 25 m/s. Additionally, the spectral Doppler analysis revealed a maximum velocity of 25 m/s, and an average velocity of 15 m/s. These experimental results demonstrate the consistent measurements of blood flow velocity provided by the Doppler ultrasound training phantom, and indicate its potential for ultrasound education and training purposes. In the manufacture of the vessel-mimicking phantom, the upper surface was inclined, to prevent the Doppler angle from reaching 90\({}^{\circ}\). The Doppler angle is determined via measuring the angle between the direction of the ultrasound beam and the direction of blood flow. The Doppler angle can be determined using \(\cos\theta\). In this context, \(\theta\) represents the angle between the direction of blood flow and the ultrasound beam. It is important to note that the value of \(\theta\) and \(\cos\theta\) are inversely proportional, with \(\cos 0^{\circ}\) being 1, \(\cos 60^{\circ}\) being 0.5, and \(\cos 90^{\circ}\) being 0. When \(\cos\theta\) is 0, it becomes impossible to obtain information about the blood flow [41]. For this reason, in the manufacturing of a vessel-mimicking phantom, a slope is applied to the upper surface. This ensures that the angle formed by the ultrasound beam and the direction of blood flow does not reach 90\({}^{\circ}\). The tissue-mimicking material for the phantom was manufactured using 2% agarose gel [42; 43; 44]. Agarose gel was chosen due to its ease of manufacture and cost-effectiveness [45]. Alternative materials, such as Vyta Flex and gelatin, were considered but, ultimately, excluded. While Vyta Flex offered long-term usability, it had the weakness of poor background visualization. Even with the addition of the 30% scattering agent hydroxyapatite according to weight, the ultrasound images lacked a clear background and well-defined reflection from objects. To address these issues, further research is planned, to explore new additives to enhance the material's characteristics. Gelatin, while only entailing a simple manufacturing process, required approximately 12 h to fully solidify, and the defoaming process was not satisfactory, leading to its exclusion.