How to evaluate the aortic valve using cardiac CT imaging
Learn all about aortic valve anatomy and prospective / retrospective triggering methods in cardiac CT imaging.
A big challenge in cardiac CT is being able to image fast enough to freeze the motion of the heart so that images don't blur. This is where prospective and retrospective triggering methods come to the rescue! In this fast-paced video by Dr Ronak Rajani, you'll learn how to apply your understanding of these two imaging methods to evaluate the left-sided heart valves and recognize normal anatomy.
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[00:00:00] In this lesson, we are going to start to look how cardiac CT may be useful to evaluate the native heart valves. This image shows the surgical view of the various heart valves. In other words, we're looking top down onto the heart. Notice that the mitral valve is made up of two leaflets, the anterior and the posterior mitral valve leaflet. The aortic valve lies in the center of the heart and has three cusps: the right coronary cusp, from which the right coronary artery arises, the left coronary cusp, from which the left
[00:00:30] mainstem arises, and the non-coronary cusp, which lies adjacent to the interatrial septum. The tricuspid valve lies to the right-hand side of the mitral valve and note that the pulmonary valve is the most anterior heart valve. Let us now take a look at the aortic valve and aortic root a little closer. From this image, we can see the various structures that form the aortic valve complex. The ascending aorta lies above the sinotubular junction, which forms the boundary between the ascending aorta and the aortic
[00:01:00] root. Below the sinotubular junction, we can see the right coronary ostium and the left coronary ostium, arising from the right sinus of Valsalva and the left sinus of Valsalva, respectively. The sinuses of Valsalva represent the area immediately superior to all three of the aortic valve leaflets. When we wish to obtain information about the various heart valves and their motion, retrospective ECG-gating triggering, is required. This enables imaging of the heart valves, as they move throughout the cardiac cycle.
[00:01:30] Depending upon which valve you're attempting to interrogate, one must focus on different paths of the cardiac cycle. When we take two consecutive R waves, this is known as the R-to-R interval. The first R wave represents 0% of the R-to-R interval and the second R wave, 100% of the R-to-R interval. To obtain moving pictures throughout the cardiac cycle, the x-ray tube must be on, for the duration of the cardiac cycle, or in other words, 100% of the R-to-R interval. Normally, images are reconstructed at every 10% phase, to obtain a moving
[00:02:00] image. When evaluating the heart valves, it is important to know at which stage of the cardiac cycle the valve should be imaged and this varies for each valve. If you were trying to evaluate for aortic stenosis or pulmonary stenosis, you should look at the valves when they are trying to open during mid-systole, which is between 20% and 30% of the R-to-R interval. For mitral and tricuspid regurgitation, you should evaluate the valves at end-systole, when it is expected that the valves would be completely closed, with no regurgitant gap. And for
[00:02:30] aortic regurgitation and pulmonary regurgitation, the valve should be evaluated at end-diastole, when the valve leaflets are expected to be completely closed. Remember how this differs from prospective ECG gating, where only one part of the cardiac cycle is imaged. With prospective ECG-gated scanning, it is not usually possible to obtain data throughout the entirety of the cardiac cycle. If using prospective ECG gating, the scan should be planned for the relevant part of the cardiac cycle, for the valve that you are trying to evaluate. In order to minimize the
[00:03:00] radiation dose, from a full retrospective scan, we can employ a technique known as ECG-gated tube modulation. This enables a reduction of the tube current, at parts of the cardiac cycle, which are less important or not the point of interest. This keeps the radiation dose lower but still more than a prospective scan. However, it can provide more data and the capability to perform semi-imaging of the valves. On this scan, are you able to identify the aortic valve and does it appear normal? And remember that the aortic valve is usually
[00:03:30] the one in the middle of the axial CT dataset. And here is the sight of the aortic valve as we come down the ascending aorta, we can see the aortic valve here. On this image, I'm localizing the aortic valve and pausing at the point where the aortic valve is seen. This is the starting point to evaluate the aortic valve further. The left-hand image corresponds to the point where I paused on
[00:04:00] the previous scan. The first step to evaluate the aortic valve is to use multi-plane and reconstruction and to position your crosshairs over the aortic valve, in axial image. Once this is done, the crosshairs will appear over the valve in both the coronal and sagittal views. Remember that multi-plane and reconstruction or reformation enables the visualization of the structure in three planes, simultaneously. Once this image has been obtained, the crosshairs in the coronal view can be rotated to along the axis of the aortic valve,
[00:04:30] as is shown in this animation. The effect that this rotation has had on the sagittal view of the aortic valve, is that it opens up the aortic valve, with the ascending aorta. Once we have aligned the crosshairs with the aortic valve, first in the coronal view, this is then done for the sagittal view, over the aortic valve. By making these two simple movements, the aortic valve
[00:05:00] is revealed. In this image, we can see that the aortic valve has three cusps and there is some evidence of calcification at the cuspal margins. This slide shows the relevant anatomy at this point. We can see the left atrium, the left atrial appendage, and the left superior pulmonary vein. Along with the right ventricular outflow tract and the pulmonary valve. This is the right coronary cusp of the aortic valve, the most anterior of all three of the cusps. This is the left coronary cusp, from which the left mainstem arises and this is the non-coronary cusp,
[00:05:30] which lies adjacent to the interatrial septum. This is the opening orifice area of the aortic valve and this is taken in mid-systole and it shows the reduction of the opening orifice area. By tracing around this area, we would be able to obtain the geometric orifice area, to determine whether or not the aortic valve was stenosed. Let us now consider some pathology on the aortic valve. In a patient with a normal aortic valve, in diastole, the valve leaflet should be closed, as is seen in the left-hand image, while the valve should be fully open,
[00:06:00] during mid-systole, as per this right-hand image. In rheumatic heart disease, the aortic valve may become calcified, particularly at the base of the commissures. This can result in aortic stenosis or aortic regurgitation. In calcific degenerative aortic stenosis, we often see diffused calcification over the valve leaflets and this causes a reduction in leaflet opening during systole and leads to aortic stenosis. As well as acquired aortic valve disease, CT is also used for looking at
[00:06:30] congenital abnormalities of the aortic valve. In this example, we can see its use and looking at it congenitally, bicuspid aortic valve. Note the fusion of the two valve leaflets, giving rise to a characteristic opening pattern, which is similar to the appearance of a rugby ball during systole. Cardiac CT is increasingly being recognized as a valuable technique for the evaluation of aortic valve disease. It has the ability to detect calcification, morphology, and also can be used in the planning of transcatheter aortic valve
[00:07:00] procedures. Information about the cardiac valves is acquired simultaneously, as the coronary CT angiogram. So, be sure to check the cardiac valve routinely, during your reporting.