## 5 Discussion  
In the animal experiments with the pig model, the robotic VI procedure reduced the radiation exposure to the operator by about 97% when compared to the conventional procedure. The smaller amount of radiation exposure observed during the robotic VI procedure is due to the use of the radiation shield and the considerable distance of the doctor from the X-ray source. If the operating room of the robotic VI procedure and the master console room are separated, then it is expected that there would be no radiation exposure to the doctor. The effectiveness of reducing radiation exposure using the robotic VI procedure can thus prove highly beneficial to radiation workers as it can reduce unwanted potential side effects during surgical operations. It is obvious that robotic intervention could reduce the radiation exposure to the operator or assistants. However, it is more important to improve the benefits to the patient with robotic intervention. In terms of the radiation dose exposure to the patient, it has been reported that robotic coronary artery intervention could reduce patient radiation exposure by up to 20%. The authors provided two potential mechanisms for radiation dose reduction for patients: improved visualization from closer monitor positioning during the robotic intervention and maximal angio unit table height, which is available only with robotic intervention [26]. They also reported no increase in fluoroscopy time and contrast media usage. The 2 DOFs ergonomically designed master device outperformed the joystick-type device in terms of the NASA-TLX and SUS scores. Moreover, it was shown that the 2 DOFs ergonomically designed master device could reduce the mental burden on the operator as the system integration evaluation was better during the robotic VI procedure. This is because the position-position-based 2 DOFs master device was similar to the conventional procedure with respect to operator motions despite the repetitive movements. The selection of the target artery was more difficult in the hepatic artery experiments than in the right renal artery experiments. Hence, the usability test scores of the 2 DOFs joystick-type master device were poor. The 2 DOFs joystick-type master device may be suitable for robotic VI procedures targeting easy blood vessels, but it is unsuitable for procedures targeting difficult or tortuous blood vessels. These results also showed that the 2 DOFs ergonomically designed master device was better than the 2 DOFs joystick-type device in terms of quantitative measurement. The next important step for improving the master device is the installation of a haptic function that could assure a safer procedure if accurate force feedback of the catheter and guidewire resistances against the vessel wall are delivered to the operator through the master device. Beginners would find it easier to use the ergonomic-type haptic device as it is more intuitive. However, it is possible that the joystick-type device may be more comfortable for those familiar with robotic procedures. Therefore, further testing \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Master Device**} & **Number of Retractions** & **Number of Retractions** & **Moving Distance of** & **Moving Distance of** \\  & **of Surgical Instruments** & **of Surgical Instruments** & **Target 1 [meter]** & **Target 2 [meter]** \\  & **for Target 1** & **for Target 2** & & \\ \hline
2 DOFs ergonomically & & & & \\ designed master device & & & & \\ \hline
2 DOFs joystick-type & & & & \\ master device & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Moving distance and the number of retractions of surgical instruments (mean) for right renal artery. is needed. Moreover, the ergonomic-type haptic device is safer to handle, because the range of motion is limited according to the working distance of the master stick. However, further considerations of the master and haptic device designs and tests are needed to assure patient safety during robotic interventions.