High resolution, magnetization transfer saturation, variable flip angle, time-of-flight MRA in the detection of intracranial vascular stenoses

Abstract

Objective: Factors that restrict 3D TOF MRA are limited resolution, saturation of flow, and degree of background suppression. We evaluated MRA for intracranial stenoses by using a 3D TOF technique that minimizes these factors.

Materials and methods: Twenty-nine patients underwent MRA and intraarterial digital subtraction angiography (DSA). The MRA studies were performed on a 1.5 T Siemens SP 4000 system. Integrated techniques applied to the conventional 3D TOF acquisition included the following: (a) 256 x 256 matrix with a 140 mm FOV and 0.9 mm slice thickness, yielding a 0.54 x 0.54 x 0.9 mm3 voxel; (b) tilted optimized nonsaturating excitation (TONE); and (c) magnetization transfer saturation (MTS). The intraarterial DSA was performed on a Siemens Angiostar system with a 1,024 x 1,024 noninterpolated matrix. The MRAs were reviewed by two neuroradiologists. Two hundred seventy-seven vessels were evaluated for a total of 806 segments. Vessel segments were evaluated with a 5 point scale.

Results: The estimated accuracy of MRA for detecting stenosis over all intracranial vessel segments was 0.88 +/- 0.03 and 0.89 +/- 0.02 for the two readers, respectively. The estimated accuracy ranged from 0.94 +/- 0.02 and 0.93 +/- 0.02 for detecting internal carotid artery stenosis by the two readers, respectively, to 0.65 +/- 0.17 and 0.71 +/- 0.15 for detecting distal vertebral artery stenosis. In vessels determined by catheter angiography to be stenosis-free, reader confidence at the proximal versus distal segments was similar for the internal carotid, basilar, and posterior cerebral arteries. However, for the anterior and middle cerebral arteries, one or both readers were more confident in diagnosing the proximal segment.

Conclusion: High resolution MTS TONE 3D TOF MRA is an accurate technique for the screening of medium and large vessel intracranial stenoses.