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Figure 13d.   Type A thoracic aortic dissection. (a, b) Immediate (a) and delayed (b) oblique sagittal 3D partitions show a dissection flap in the ascending aorta (arrow). On the immediate image (obtained 10 seconds after the start of contrast material injection) (a), low signal intensity within the false channel produces a false impression of thrombosis. On the delayed image (b), the false channel demonstrates enhancement, with delayed washout manifesting as higher signal intensity than in the true channel. (c, d) Coronal (c) and axial (d) 3D partitions show the morphology of the dissection flap.