## 4 Discussion
deployed stent grafts in short 3D printed aortic models with thoracabdominal aortic disease. They used these models to guide pre-fenestration of the stent grafts before re-deploying them in patients, believing that 3D printing technology could potentially improve both the accuracy and efficiency of the TEVAR procedure [35]. [PERSON] et al. also used 3D printed models to guide total endovascular repair for a patient who had a stent graft incorrectly deployed in the false lumen [36]. [PERSON] et al. performed pre-fenestration on a stent graft in a 3D printed model. They thought stent graft pre-fenestration guided by the 3D printed aortic model provided a new solution for aortic dissection treatment planning and claimed that this could improve accuracy of the fenestration location [37]. Although these previous studies of stent graft deployment inside 3D models are of interest, most did not specify the materials they used to make the models, or attempted to use materials that have mechanical and radiological properties close to the real human aorta. In our study, we provide a new possibility for the medical application of 3D printing by using 3D printing materials with accuracy in vivo representation to obtain more realistic experimental data. We recognize that there are some limitations to our experiment. First, despite a realistic 3D printed model being used for studying different CTA protocols, the model was not placed in an environment that simulated normal surrounding anatomic regions such as the lungs, ribs, spinal column, or heart. Therefore, the radiation dose associated with these protocols were lower than the actual values reported by other studies. In addition, the 3D printed aorta model was placed in a customized box and immersed inside a dilute contrast medium instead of the perfusion of contrast medium into the lumen. Furthermore, the contrast was not flowing. Future research could focus on improving this aspect of the model. Connecting the 3D printed aortic model to a pulsatile flow circuit with a cardiac pump or printing a controllable syringe pump could be a solution as this will allow for accurate measurement under more dynamic conditions. This can be addressed by further studies when our printing capabilities meet these requirements. Despite this limitation, the current measurements are still acceptable and consistent with what has been reported in the literature regarding measurements of dimensional accuracy based on 3D printed static cardiovascular models [21]. Second, no contrast-to-noise ratio (CNR) was measured. In this study, only SNR was measured to determine image quality because the model was immersed in the contrast medium. A more robust conclusion could be reached with the measurement of both SNR and CNR when the 3D printed models are placed in a realistic chest phantom in future studies. Third, the measurement of SNR and effective dose could be different in patients. Although we selected a 3D printing material that had mechanical and radiological properties approximating those in the human, due to the limited choice of commercial 3D printing materials, we could not exactly match the human aorta. Different slice thicknesses, use of IR strengths, and image post-processing algorithms to suppress the artifacts from stents could also affect the SNR measurements. Additionally, we did not undertake a qualitative assessment of image quality in this study. In future research, the application value of 3D printed models could be verified through scoring by clinical imaging professionals.