What Causes Blooming Artifact on Brain MRI
Blooming artifact on brain MRI is caused by substances with paramagnetic or ferromagnetic properties that create local magnetic field inhomogeneities, most commonly blood products (hemosiderin, ferritin), calcifications, and metallic foreign bodies.
Primary Causes
Blood Products and Hemorrhage
The most clinically relevant cause is hemosiderin deposition from prior hemorrhage, which appears as hypointense signal on susceptibility-sensitive sequences (T2*, SWI, GRE). This is the characteristic "hemosiderin ring" seen around cavernous malformations, appearing as T2 hypointense signal surrounding the lesion 1. Blood products of different ages create the classic "popcorn" appearance on T2 sequences 1.
Calcifications
Calcifications from various etiologies (dystrophic, infectious, vascular) produce blooming artifact on susceptibility-weighted imaging. These can overlap in appearance with small hemorrhages and require correlation with other sequences 1.
Metallic Foreign Bodies
Foreign bodies containing iron or other ferromagnetic materials cause prominent blooming artifacts:
- Embedded traumatic fragments in the scalp or skull, even from trivial injuries, can escape pre-MRI screening 2
- Welding fume particles containing paramagnetic iron oxide create susceptibility artifacts appearing as small rounded hypointense foci, particularly over the vertex 3
- Orthopedic hardware and dental restorations when in proximity to the imaging field 4
Technical Factors That Amplify Blooming
The severity of blooming artifact is directly influenced by:
- Field strength: Artifacts increase proportionally with higher Tesla strength (1.5T vs 3T) 5
- Pulse sequence type: Gradient echo sequences produce more prominent blooming than spin echo sequences 5
- Voxel size and imaging parameters: Smaller voxels, larger field of view, and longer echo train lengths reduce artifact 4
Clinical Context and Diagnostic Considerations
Multiple Sclerosis Imaging
In MS evaluation, paramagnetic rim lesions (PRL) represent iron-containing microglia and appear as discrete rims with paramagnetic properties on phase susceptibility-sensitive images. These should be distinguished from artifact, as they indicate chronic-active lesions with poor prognosis 6. Exclusion criteria include small paramagnetic structures like ferritin dots, veins, and magnetic dipole artifacts 6.
Cavernous Malformations
The hemosiderin ring surrounding cavernous malformations is an expected finding, not an artifact per se, though it demonstrates the blooming phenomenon. Very small CMs appear only as susceptibility foci and must be differentiated from micro-hemorrhages from hypertension, trauma, amyloid angiopathy, or other causes 1.
Critical Pitfalls to Avoid
Pre-MRI screening failures: Always probe for history of facial trauma, welding exposure, or metallic foreign body exposure, even from seemingly trivial injuries 2, 3
Misdiagnosis of artifact as pathology: Welding particles or other foreign bodies can mimic calcified lesions or hemorrhage. When suspicious findings don't correlate with clinical presentation, consider artifact 3
Orientation matters: Hardware orientation relative to the main magnetic field direction affects artifact severity 4
Non-metallic sources: Even wet cotton balls on coil surfaces can create wrap-around artifacts mimicking pathology 7
Practical Approach
When encountering suspected blooming artifact:
- Correlate with T1-weighted and T2-weighted sequences (not just susceptibility-sensitive)
- Review patient history for trauma, occupational exposures, prior procedures
- Consider repeat imaging after removing potential external sources
- Use higher resolution, spin echo sequences when artifact limits diagnostic quality
- At 3T, consider switching to 1.5T if artifact is prohibitive 5