## 3 Results
### Risk Assessment Strategies and Diagnosing Techniques
#### 3.6.1 Mathematical Models as Tools to Assist Clinical Diagnosis  
According to current clinical guidelines, PWV (measures how the shock wave generated by the closing of AV propagates along the aorta) is a useful metric to estimate aortic stiffness, cardiac output and even the presence of aneurysms and AD as they induce wave reflection and consequent changes in normal PWV. Therefore, this metric may be used as a diagnosis methodology. Numerically, excluding a few exceptions [86; 92], all the works that aimed to estimate this metric resorted to ROM as it allows the computation of accurate and time-efficient results. [PERSON] [99] developed 0D models of the systemic circulation to measure cardiac output. The results presented close agreement with in vitro data when constant wall compliance was considered. The introduction of non-linear effects led to overestimations of wall compliance for higher pressure ranges. [PERSON] et al. [50] aimed to develop cost-effective aneurysm diagnosing techniques, based on assessable measurements and pressure and/or velocity waveforms obtained via 1D modelling. This 1D model was validated with a representative experimental model of blood vessels and aimed to assess the changes in PWV between healthy and diseased subjects. Compliance gradients were appointed by the authors as the only parameter assessed via 1D modelling able to efficiently indicate aortic wall strength. [PERSON] and [PERSON] [51] developed a 2D numerical model of the aorta using tapered tubes to estimate PWV. The model was able to predict high reflection sites that are potentially damaging to the aortic wall. [PERSON] et al. [100] applied FEM modelling to simulate the propagation of electrical currents across the thorax and identified trans-thoracic impedance in order to diagnose AD. The numerical results were analysed by Bayesian stochastic models. The model virtualised an impedance cardiography exam (measures how changes in aortic blood volume and flow influence transmission of a known electrical current across the thorax) and the results proposed that the Bayesian approach outperformed the conventional impedance cardiography multi-sensor technique. Aneuryysmal growth [101], intimal tearing initiation [87] and even propensity to rupture [97] were closely correlated with abnormal WSS distributions and large magnitudes. The group of [PERSON] et al. [102] developed an experimental facility where flow measurements could be obtained with MRI technology and in vitro CFD models. The objective was to provide an extensive reference database of aortic haemodynamics obtained with validated numerical simulations--therefore improving the accuracy of WSS calculations of magnetic resonance velocimetry as it assists in surpassing limitations related to MRI low spatial resolution. In their first work [103], a comparison between laser Doppler velocimetry, magnetic resonance velocimetry and CFD estimation of WSS was performed. [PERSON] et al. [103] suggested that the laser Doppler velocimetry technique could indeed be the \"gold standard\" for WSS estimation. Despite this, it is still limited by the low spatial resolution of MRI. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline
**First Author** & **Year** & **Simulation** & **Solver** & **Geometry** & \begin{tabular}{c} **Boundary** \\ **Conditions** \\ \end{tabular}  & **Flow** & **Wall** & **Main Remarks** & **Ain of the Work** & **GRADE** \\ \hline [PERSON]. [PERSON] & 2021 & CSM (FEM) & COMSOL & AD (I) & Specific & - & - & - & - & - & - \\  & & & Volume & & & Volume & & & - & - & - \\  & & & & Volume & & & & & & - & - \\  & & & & & Volume & & & & & & - \\ [PERSON] & 2021 & CSM (FEM) & - & ATA (PS-CT) & \begin{tabular}{c} 120 mm/kg; \\ PS \\ \end{tabular}