## 2 Computed Tomography and Aortic Valve
### CT Assessment of the Aortic Valve for Transcatheter Procedures
#### 2.3.3 Aortic Leaflets  
Three major parameters regarding aortic leaflets should be carefully considered during the preprocedural planning for TAVI: the number of cusps, the degree of leaflet calcification, and the height of the leaflets to the coronary ostia. MDCT has been proven to be superior to trans thoracic echocardiogram to discriminate aortic valvular morphology and the exact location and quantification of calcifications [40] (Figure 4a,b). Figure 4: (**a**) Calcium degree and morphology evaluation of the aortic valve by CT. (**b**) LAO–cranial view for calcium location assessment. Figure 3: CT measurements of perimeter and area of aortic annulus. The bicuspid aortic valve (BAV) is an important risk factor for premature aortic stenosis and challenging anatomy for percutaneous interventions. Thus, patients with bicuspid valves were excluded in the largest trials regarding TAVI due to complex anatomic features (i.e., more calcified, and asymmetrical leaflets, annular eccentricity, and associated aortic dilation). However, in recent years, the interest in this topic has rapidly grown, and the first data appear to be quite satisfactory [41]. BAV has historically been diagnosed with echocardiography that, compared with pathologic analyses obtained from cardiac surgery, can detect this kind of valve morphology in a range between 54 and 93%. Nevertheless, CT was found to be superior to transthoracic echocardiography, especially in patients with extensively calcified aortic valves [42] (Figure 5). In fact, taking into account echocardiographic and tomographic images of fifty patients with AS plus probable bicuspid aortic valve and comparing with surgical findings, [PERSON] et al. found that CT data were not significantly different from the intraoperative ones, but the echocardiographic were [42]. MDCT images should assess several anatomical aspects in the setting of bicuspid aortic valves: the location of raphe by reviewing the commissures symmetry from the basal plane to the sinotubular junction, the specific morphology according to the Sievert classification, the extent of leaflet asymmetry, the degree of calcification, and the length and width of the raphe into the lumen. Indeed, more paravalvular regurgitation due to incomplete valve expansion could be associated with longer calcified raphe and calcium impingement > 4 mm [43]. Quantifying aortic valve calcification by noncontrast CT (CT-AVC) has demonstrated good accuracy in defining the valvular calcification burden (location, extent, and severity), demonstrating satisfactory concordance with echocardiography, and providing incremental prognostic information. CT-AVC has been reported to correlate significantly with peak velocity, mean gradient, and the aortic valvular area measured by echocardiography [44]. AVC is typically assessed by analyzing 1.5-3 mm slice thicknesses CT scans using prospective or retrospective electrocardiogram (ECG) gating and at lower tube current than contrast-enhanced CT studies, thus resulting in a low radiation dose of approximately 1 mSv. AVC can be measured by numerous methods, including Agatston, mass, and volumetric scores. Among these, the first method is more frequently employed. Electron-beam and multidetector row CT studies demonstrate that the severity of AVC is a robust prognostic predictor in asymptomatic patients with severe AS (Table 1) [45]. Therefore, worse outcomes have been experienced by asymptomatic patients with severe AS and high calcium scores compared with those with low scores [46]. Moreover, preoperatively AVC assessment is crucial for TAVI because it has been demonstrated to negatively affect procedural success and outcomes given the greater presence of paravalvular regurgitation, conduction abnormalities, aortic annulus rupture, coronary ostia occlusion, and stroke. Furthermore, [PERSON] et al. found that, in an analysis of 68 patients undergoing  
Figure 5: CT image of bicuspid valve.