Figure 7b. Iliac artery aneurysm. (a) Nonenhanced source image shows an aneurysm of the right common iliac artery with a hyperintense mural thrombus (arrow). (b) Arterial-phase source image shows enhancement of the aneurysmal lumen (arrowhead) at the level of the thrombus. (c) Subtracted source image shows only the enhanced aneurysmal lumen; the thrombus is no longer seen. Note that aliased information (arrows in b) is eliminated with subtraction.