As with echocardiography and CT, the main criterion used to diagnose aortic dissection by MRI is the presence of a double lumen of the aorta with a visible intimal flap. This feature can be visualized with all pulse sequences commonly used for the examination of the aorta. With cine sequences the movement of the intimal flap can be seen. Differentiation of the true and false lumen is possible with the help of the movement of the intimal flap in systole and diastole (Figure 6.2).
A number of indirect signs are suggestive but not diagnostic of a dissection, including widening of the aorta, thickening of the aortic wall, thrombosis of a false lumen, or spiraling of a thrombosed false lumen. Entry sites appear as interruptions of the dissecting membrane often associated with turbulent flow extending from the true into the false lumen. The origin of the supraaortic arteries and the abdominal aortic branches from either the true lumen or the false lumen can usually be determined by using MR angiography13.
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