# Development and Evaluation of Doppler Ultrasound Training Phantom for Human Vessel Simulation
## 2 Materials and Methods
### Acquisition of Ultrasound Image and Analysis  
The experiments were performed using the ultrasound equipment Accuvix V10 (Samsung Medison, Seoul, Republic of Korea), and a linear transducer (L5-13 IS) with a frequency range of 6-12 MHz and a width of 48 mm. Different settings were applied to the color box, scale, and color gain, and we explore the characteristics of the ultrasound images based on the settings of each parameter. Additionally, spectral Doppler imaging was acquired, to provide assessment of the blood flow velocities. I have organized the parameter settings in Table 1.  
Figure 2: The Doppler ultrasound training phantom. (**a**) A schematic diagram of the Doppler ultrasound training phantom. The blue arrows indicate the blood flow direction. (**b**) A picture of the Doppler ultrasound training phantom. A and C phantoms are for filling with water. B phantom is designed for inserting a vessel-mimicking phantom. The red arrows indicate the blood flow direction.  
The first experiment aimed to investigate the characteristics based on the direction of the color box. The color box was steered to the left and right, and the images were acquired accordingly. In the 2D mode, the image settings were configured with a depth of 45 mm, with the focus set at the midpoint of the vessel, at 17 mm. The gain was set to 73 dB, the dynamic range to 105 dB, the frame average to 10, and the power to 90 W. The color Doppler imaging was performed using the following settings: a frame average of 4, a wall filter of 0, a color gain of 35 dB, and a scale of 45 kHz.  
The second experiment aimed to investigate the image characteristics based on the scale setting. The scale was adjusted to 4 kHz and 0.6 kHz, and the images were acquired accordingly. Adjusting the scale helps reduce the aliasing artifacts that occur in color Doppler imaging. Aliasing is an artifact in which the blood flow appears to reverse direction because the maximum frequency shift is more than half of the pulse repetition frequency (PRF). To reduce aliasing, the PRF can be increased, ensuring that the blood flow velocities fall within the Nyquist limit (PRF/2) [33; 34]. In practical ultrasound equipment, increasing the scale setting leads to an increase in the PRF, facilitating the control of aliasing [35]. For the second experiment, the imaging settings in the 2D mode remained the same as in the previous experiment. The color imaging was performed using the following settings, a frame average of 4, a wall filter of 0, a color gain of 35 dB, and a scale adjusted to 4 kHz and 0.6 kHz.  
Lastly, in order to examine the ultrasound characteristics associated with the color gain parameter, the color gain was adjusted to 2 dB, 5 dB, 10 dB, 35 dB, 60 dB, and 100 dB. The gain is a parameter that amplifies the ultrasonic signal returning to the transducer [8]. In B-mode imaging, the gain affects the brightness of the image, while in color Doppler mode, the gain impacts the blood flow signals. In color Doppler mode, it is important to adjust the gain appropriately. Increasing the gain allows for a better recognition of low blood flow velocities. However, excessively increasing the gain can lead to the appearance of \"bleeding\" artifacts, which may obscure the visualization of the vessel surface [36]. In addition, reducing the gain can help reduce artifacts such as \"bleeding\" [37]. However, caution should be exercised, as lower gain settings may result in the loss of blood flow information. For the third experiment, the imaging settings in the 2D mode remained consistent with the previous experiments. In the color imaging settings, a frame average of 4, a wall filter of 0, a scale of 4 kHz, and gains of 2 dB, 5 dB, 10 dB, 35 dB, 60 dB, and 100 dB were adjusted for image acquisition.