Intracranial aneurysms and vascular malformations: comparison of time-of-flight and phase-contrast MR angiography.

Twenty-seven patients with 14 aneurysms and 17 vascular malformations were each examined with both time-of-flight (TF) and phase-contrast (PC) magnetic resonance angiography of the head. Three-dimensional (3D) PC imaging depicted the patent lumen of the aneurysms, while 3D TF imaging depicted the patent lumen and a subacute thrombus if present. The 3D PC techniques were superior to 3D TF methods in depicting aneurysms larger than 15 mm. PC angiography allowed velocity resolution of vascular lesions and yielded functional flow information by directly depicting collateral flow to vascular lesions. Artifacts present on TF images were due to substances with short T1, hemosiderin, and surgical clips. Artifacts present on PC images were due to flow-related aliasing. The results showed that PC techniques have specific advantages over TF techniques, including identification of large aneurysms, velocity resolution of vascular lesions, depiction of flow direction about the circle of Willis, and less degradation by artifacts.