## 4 Discussion  
In this study, we propose new parameters for the evaluation of the temporal variation of IMT and the longitudinal and radial arterial walls' motions during the heart cycle. The main purpose is to provide estimates that will be influenced by all amplitude values of the aforementioned motion variations. We have used CAROLAB software [10; 22; 23] in order to analyze two different populations (33 healthy volunteers and 69 at-risk patients). Our results have demonstrated that the arterial diameter of healthy volunteers is not distinct from that of the at-risk patients, while there is a significant difference in the IMT between these two groups, as seen in Figure 3. The arterial diameter is the same among all subjects while IMT increases for at-risk patients. In accordance with previous studies [10; 11], we can state that IM thickening is associated with CVDs. There is a significant difference between healthy volunteers and at-risk patients according to the RMS values of longitudinal and radial motions, as seen in Figure 4. From these results, it is clear that the healthy volunteers' CCA moves more in longitudinal and radial directions than in at-risk patients. This is consistent with what has been found in previous studies [17] and it may explain higher arterial elasticity in the healthy volunteers' group. In this paper we only have motion or displacement signals to analyze. Elastography researchers [25; 26] state that in response to pulsatile flow, a stiffer artery moves less. This empirical knowledge about the negative correlation of motion amplitude with artery stiffness can be observed in our estimates. In addition, we have done our own experiments [27] determining that displacement correlates with stiffness. We found that with the decrease of agar-based phantoms' stiffness, the motion amplitude increases. No statistical difference can be claimed between the two groups according to the RMS value of IMT. Contrary to the findings of [PERSON] et al. [23], we did not find any IMT variation increase in at-risk patients compared with healthy volunteers. Our results have demonstrated that there is no significant difference between healthy volunteers and at-risk patients according to IMT peak-to-peak motion amplitude, demonstrated in Figure 5. Although in our study two investigated populations were not so different, like healthy volunteers and diabetic patients, there is enough statistical difference of radial peak-to-peak motion amplitude between healthy volunteers and at-risk patients. The main drawback is that some subjects presented low-quality B-mode sequences resulting in motion signals that were not repeatable. In these cases, the tracking process was repeated again with another kernel position in the CCA image, but this did not yield any better results. In addition, there were some sequences with fewer than two full heart cycles. Finally, all the B-mode sequences having such repeatability limitations were rejected from the study. In order to get correct estimates of the temporal variation of IMT and radial motion, CCA walls have to appear as double-line patterns in all video sequences [14]. However, there were a few frames in some B-mode sequences where the intima-media complex was not as clearly visible as needed in CAROLAB software. This appears to be a case of errors resulting in inaccurate IM complex segmentation and finally incorrect values of IMT and radial motion. According to our study, the endoscopy of CCA for the registration of temporal variation of IMT, longitudinal and radial motions is challenging. Following completion of the work reported in this paper, [PERSON] et al. [28] suggested to average four consequent heart cycles for representative measurement of longitudinal motion in CCA. [PERSON] et al. [28] noticed that indices of variability were reduced when two to four heart cycles were used. Any improvements in indices of variability were not observed when more than four heart cycles were averaged. This proves that more than four heart cycles are unnecessary to use [28].