Flow-Related Artifacts in MR Imaging and MR Angiography of the Central Nervous System

Artifacts are commonplace on MR imaging examinations. It is imperative for the neuroradiologist to recognize and understand the many MR imaging artifacts that can obscure anatomy and be confused with pathology. This review focuses on the most relevant flow-related MR imaging and MRA artifacts and presents them in a concise form. Multiple flow-related MR imaging and MRA artifacts are discussed along with the mechanism of formation, imaging appearance, and interpretative significance. Additionally, methods to rectify these artifacts and strategies to minimize them are discussed.

We include the following artifacts: 1) Ghosting artifacts replicate a “mobile” structure in the phase direction due to spatial misregistration that results from rhythmic motion. 2) Paradoxical or flow-related enhancement seen on the first or last image of a sequence is due to signal intensity from unsaturated protons moving into the interrogated field. 3) Vascular and CSF flow can create artifacts due to the change in the location of excited and/or unexcited hydrogen protons. 4) Intermediate signal intensity often arises in an area of slow flow and may be misinterpreted as thrombus or tumor. 5) Artifacts on 2D TOF imaging are common and may be caused by susceptibility artifacts, shinethrough, and reversed flow in loops and subclavian steal. 6) “Venetian blind” artifacts occur in 3D TOF imaging secondary to loss of flow-related enhancement as protons traverse the MOTSA volume and can be minimized by modifying the flip angle throughout the acquisition.

Knowledge of the mechanism, appearance, and correction of these artifacts is essential for the accurate analysis of MR imaging/MRA of the central nervous system.