Figure 3i. Type B aortic dissection in a 54-year-old woman with acute onset of thoracic and abdominal pain. (a, b) Anterior (a) and posterior (b) shaded surface display images show the true lumen (arrows) and the false lumen (arrowheads), as well as adjacent vessels. (c, d) VR image obtained with a cutting plane (c) and MIP image (d) also depict the two lumina (arrows) but do not permit clear differentiation between them because the entire length of the dissection flap (*) is not visible. (e-i) Contrast-enhanced arterial phase axial source images obtained at successively lower levels show the characteristic signs enabling differentiation between the false (F) and true (T) lumina. In e, the outer, false lumen is wrapped around the inner, true lumen, and the cobweb sign (arrow) is visible. In f and g, the false lumen is clearly larger in diameter than the true lumen and contains a thrombus (arrowheads in g), which is also evident in h (arrows). In h, note the eccentric calcification (arrowhead) alongside the flap facing the true lumen, and, in i, the beak sign (arrowheads) created by the curvature of the flap toward the false lumen.