Synopsis
Artifacts related to flow are common and can be a
diagnostic pitfall for the interpreting neuroradiologist, if it is not
recognized accurately. It is critical for the interpreting neuroradiologist to have a fundamental understanding of the physics that underlie image formation and the types of artifacts that emerge from magnetic resonance imaging and angiography. We present a pictorial essay of commonly encountered
flow-related artifacts and pitfalls in magnetic resonance imaging and angiography in neuroradiology and
discuss the physics behind the formation of the artifact as well as how to minimize the artifact. Knowledge of these artifacts and pitfalls is essential to arrive at accurate diagnoses. Purpose
It
is critical to recognize magnetic resonance (MR) imaging and angiography (MRA) artifacts
related to flow in neuroradiology. Artifacts can be mistaken for pathology or
obscure underlying anatomy, which can result in misdiagnosis. The purpose of
this educational exhibit is to discuss commonly seen flow-related MR imaging
and angiography artifacts and pitfalls in neuroradiology by providing imaging examples, describing the physics of the formation of the artifacts, and discussing how to correct the
artifacts or minimize them.
Outline of content
Imaging flow is unique and complex. Unique
properties of flowing blood include the inflow effect of nonsaturated flowing blood, outflow effect of excited flowing blood, and the susceptibility of blood to dephasing from
complex or turbulent blood flow. Unawareness that these properties can result in the presence or absence of signal can result in misinterpretation and be a pitfall for stenosis,
thrombus, or vessel spasm.
Here we discuss pitfalls and artifacts related to flow that are commonly
encountered in neuroradiology in the following four categories.
(1) Motion artifact
a. Pulsation artifact in vessels (FIGURE 1) and CSF-related in the phase-encoding direction
(2) Flow related artifact
a. Flow-reversal artifact (FIGURE 2)
b. In-plane saturation artifact
c. Slow flow artifact
d. Entry section phenomenon (FIGURE 3)
(3) Magnetic field inhomogeneity
a. Susceptibility artifact from metal (FIGURE 4)
b. Pseudostenosis artifact related to
susceptibility from residual contrast in vein
(4) Post-processing related to reconstruction of
maximum intensity projection
a. Stair-step artifact (FIGURE 5)
b. Venetian blind artifact
c. Shine-through artifact
For each type of artifact, the physics behind the artifact
and how to correct or minimize the artifact as well as how some artifacts have
clinical utility to help diagnose pathology will be discussed.
Summary
Radiologists should be familiar with most common MRI and MRA
artifacts and recognize them to accurately diagnose pathology. Understanding
the mechanism and appearance of flow-related artifacts is essential for
accurate image interpretation in neuroradiology.
Acknowledgements
No acknowledgement found.References
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