## 4 Discussion  
In this study, we simulated a postprocedural surveillance CT scan of a patient with TBAD with different scanning protocols on a 3D printed aortic model. Quantitative assessment of image quality showed no significant differences between different kVp when the pitch value was 1.2. More than 20% dose reduction was achieved with the use of low kVp such as 80. Compared to the change in kVp, image quality had significant differences between low and high pitch values, although there was no significant impact on the visualization of the stent graft and other structures. Thus, a low-dose aortic CTA is suggested for the follow-up of patients after EVAR. For patients with aortic dissection, follow-up CT is mandatory and continues for many years [8; 11; 26]. Various dose-reduction strategies continue to develop with the  
Figure 5: Sagittal reformatted images of the CTA protocols. When kVp decreased to 80, image noise increased with the use of high pitch value protocols such as 2.0 and 2.5. CTA: computed tomography angiography, kVp: kilovoltage peak. advancement of CT imaging technology, striving to reduce the risk of patients being exposed to excessive radiation while maintaining image quality including low kVp, use of IR algorithms, tube current modulation, high-pitch protocol, and use of dual energy CT [10, 15, 25]. Low-dose CTA using low kVp and high-pitch protocols has been proven to achieve diagnostic image quality compared to the standard aortic CTA protocol while significantly reducing radiation dose [10, 13, 27]. However, the image quality research for post TEVAR follow-up patients is still limited [28, 29]. This study adds valuable information to the current literature by exploring a variety of CTA protocols and supporting the value of patient-specific 3D printed phantoms. A CT protocol with high-pitch is available with fast speed CT scanners and will decrease radiation dose significantly when the pitch is increased. However, pitch value also significantly affects image quality with compromising spatial resolution; higher pitch leads to an increase in image noise, which could possibly affect the diagnostic quality. This has been confirmed by our study as image noise was significantly raised when the pitch was increased (Figure 5). Despite this potential limitation, some other studies have still shown the possibility of using high-pitch CTA protocols in the diagnosis of aortic dissection without losing image quality [10]. [PERSON] et al. claimed that the use of a proper iterative reconstruction algorithm is able to maintain image quality while reducing the dose by using a low kVp, high pitch scanning protocol [13]. [PERSON] et al. also investigated low-kV CT protocols with IR, allowing for CTA of the entire aorta with excellent image quality and diagnostic confidence with a dose reduction of up to 80% compared to 120 kV [27]. In our study, we showed the influence of pitch value on image quality, which is more obvious than adjusting kVp, especially at low kVp. The novelty of this study lies in the use of a personalized 3D printed aortic model to simulate TEVAR of TBAD. Use of 3D printed models to study optimal CT scanning protocols has been supported in previous studies including the assessment of coronary artery plaques [30], coronary stenting [31] and detection of pulmonary embolism [32, 33]. In order to evaluate the impact of different protocols on radiation dose and image quality, CT scans have to be conducted multiple times with different scanning parameters. However, it would be unethical to scan the same patient multiple times and performing this experiment with different patients would lose accuracy due to different body types. With the development of 3D printing technology and the advancement of its application in the medical field, patient-specific 3D printed models could potentially become the new option for these kinds of experiment [16, 18, 34]. Previous literature has discussed the use of 3D printed models to plan stent graft treatment in patients. [PERSON] et al.