Comparison of time-of-flight and phase-contrast MR neuroangiographic techniques.

Magnetic resonance (MR) angiography constitutes a group of evolving MR imaging techniques that can be used to directly image flow in arteries, veins, and cerebrospinal fluid. By using multiple MR angiographic sequences in each of 18 patients with neurologic conditions such as aneurysms, arteriovenous malformations, and carotid atherostenotic disease, the advantages, disadvantages, and unique artifacts of each technique could be investigated. Time-of-flight imaging is susceptible to saturation effects, and short T1 substances may simulate flow. Two-dimensional time-of-flight imaging is useful in cranial venography in assessing the patency of the dural sinuses or venous drainage from an arteriovenous malformation. Three-dimensional time-of-flight images depict small and medium-sized aneurysms. Phase-contrast imaging has excellent background suppression, allows variable velocity encoding, and provides directional flow information. Two-dimensional phase-contrast imaging is useful in the assessment of the patency of major vascular structures. Three-dimensional phase-contrast imaging (with 30-cm/sec velocity encoding) is also useful in depicting small and medium-sized aneurysms. Although some applications of MR angiography are clear, further study and development of the techniques are necessary to determine which imaging sequence or combination of techniques is best suited for answering specific diagnostic questions.