Accuracy of pre- and postcontrast 3D time-of-flight MR angiography in patients with acute ischemic stroke: correlation with catheter angiography

Abstract

Background and purpose: 3D time-of-flight (TOF) MR angiography (MRA) is insensitive to slow flow; however, the use of MR imaging contrast agents helps to visualize slow-flow vessels and avoids overestimation of vascular occlusion. The purpose of this study was to correlate pre- and postcontrast 3D TOF MRA with the results of conventional angiography during endovascular reperfusion therapy and to determine the accuracy of postcontrast 3D TOF MRA.

Materials and methods: Thirteen patients who underwent endovascular reperfusion therapy for acute ischemic stroke were retrospectively analyzed. MR imaging techniques included single-slab 3D TOF MRA with and without contrast, as well as perfusion-weighted imaging. Angiography during reperfusion therapy was used as a standard of reference. Affected arteries were divided into segments either proximal or distal to the lesion, and pre- and postcontrast MRA signals were graded as absent, diminished or narrowed, or normal.

Results: In 2 of 5 patients with arterial stenosis and 6 of 8 patients with complete occlusion, MRA signal intensity proximal to each lesion was absent, indicating a proximal pseudo-occlusion on precontrast MRA. Postcontrast MRA demonstrated an arterial signal intensity proximal to the stenotic or occlusive lesions in all 13 patients. Arterial signal intensity distal to the occlusion was identified on postcontrast MRA in 7 of 8 patients having complete occlusion, and the extent of occlusion on postcontrast MRA was similar to results of conventional angiography.

Conclusion: In this small series, postcontrast 3D TOF MRA more accurately delineated the extent of stenotic or occlusive arterial lesions than precontrast MRA.

Fig 1.

A 51-year-old man with progressive left-sided weakness, dysarthria, and impaired consciousness (patient 4). A, Axial DWI confirms infarction in the centrum semiovale. B, On 3D TOF MR angiogram (anteroposterior [AP] view), occlusion of the C4 segment of the right ICA is suspected. Antegrade filling of the MCA via an anterior communicating artery is identified. C, Relative mean transit time map shows a region of delayed flow in the right hemisphere. D, Depiction of the cavernous portion of the ICA is improved on postcontrast 3D TOF MR angiogram (AP view), which shows severe stenosis at the C2 portion of the ICA. Some contrast enhancement from the cavernous sinus is evident. E, Right internal carotid angiogram immediately after MR imaging examination shows severe stenosis at the C2 portion and delayed flow in the MCA territory, but no antegrade filling into the anterior cerebral artery territory (TIMI grade 1).

Fig 2.

A 49-year-old man with sudden-onset left-sided paralysis, aphasia, and impaired consciousness (patient 6). A, Axial DWI obtained at the time of MRA confirms infarction of right MCA territory. B, 3D TOF MR angiogram (AP view) shows occlusion of the M1 segment of the right MCA. C, Relative mean transit time map shows a region of delayed flow in the right hemisphere. D, Postcontrast 3D TOF MR angiogram (AP view) shows improved depiction of the distal M1 portion and M2 branches. Some contrast enhancement from the cavernous sinus is evident. E, Right internal carotid angiogram immediately after MR imaging examination shows total occlusion (TIMI grade 0) of the M1 segment of the right MCA. Retrograde opacification of the MCA branches via pial collateral vessels extending from the anterior cerebral artery is noted; however, the vessel just distal to the occlusion is not delineated. F, Right internal carotid angiogram after the first trial of angioplasty by using the 9-mm-long balloon catheter at the occluded portion shows antegrade filling into the distal M1 portion and M2 branches through the residual stenosis. Note that postcontrast MR angiogram (D) precisely demonstrates the extent of the occlusion that is shown on catheter angiography during PTCBA procedures (F).