Cardiovascular magnetic resonance (CMR) is a reliable technique to evaluate the morphology and function of the aortic valve. High quality images can be acquired in any plane or phase of the cardiac cycle, permitting perfect alignment and accurate measurements of the aortic root and valve. Moreover, CMR is relatively insensitive to calcium artefacts, and hence useful to evaluate the aortic valve even when there is significant calcification.Of the methods employed by CMR to quantify aortic stenosis, direct planimetry is arguably the most validated and established one. This overview describes how to image the aortic valve and how to estimate the aortic valve area by direct planimetry. The key steps involved are detailed below.
Imaging of the aortic valve is planned from the left ventricular outflow tract (LVOT) view and the LVOT cross-cut view (perpendicular to the LVOT view). To study the morphology of the aortic valve, a single cine image aligned with the tips of the cusps usually suffices (figure 1), but to assess the aortic valve area, a stack of cines covering the aortic valve is generally required (figure 2).
Most studies use a stack of cine images with a reduced thickness of 5mm (for better spatial resolution), and a position interval of 2-3 mm (for precise coverage of the aortic vavle orifice). The cine stack is usually aligned with the aortic valve orifice and perpendicular to the stenotic jet, and should cover the entire aortic valve. Usually the most convenient way to perform a stack of aortic valve cines is to start close to the aortic annulus, and then move upwards along the longitudinal axis of the aortic root (figure 2).
Figure 3 displays a stack of images of the aortic root from the annulus to the sinotubular junction, ensuring complete coverage of the aortic valve. The still frame cine images are chosen at the time of the cardiac cycle where the cusps are at their maximal opening, i.e. in early/mid-systole. Images at different levels are then compared for planimetry, bearing in mind that the appropriate position will be at the tips of the valve.
After selection of the most appropriate image for planimetry, a line is drawn over the inner edges of the cusps, resulting in an area that is used to estimate the aortic valve orifice (figure 4).
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