Can ischemic infarcts be visible on Susceptibility-Weighted Imaging (SWI) without blooming artifacts?

Can Ischemic Infarcts Be Visible on SWI Without Blooming?

Yes, ischemic infarcts can be visible on SWI without blooming artifact, though SWI is not the primary sequence for detecting acute ischemia—DWI remains the gold standard for this purpose. 1, 2

Understanding SWI's Role in Acute Stroke

SWI is fundamentally a T2*-weighted sequence designed to detect paramagnetic substances like deoxyhemoglobin, blood products, and intravascular thrombus. 3 While blooming artifact within vessels suggests intravascular thrombus, the absence of blooming does not exclude ischemic stroke. 2

Primary Detection Mechanisms

• DWI is the most sensitive and specific technique for detecting acute ischemic infarction, with sensitivity of 88-100% and specificity of 95-100%, far superior to SWI for this purpose. 1
• DWI detects restricted diffusion as extracellular water moves into the intracellular environment during ischemia, making abnormal areas visible within minutes of symptom onset. 1
• SWI is complementary, not primary, for stroke diagnosis—it improves detection of blood products and depicts cerebral venous structures but is not designed to directly visualize ischemic tissue. 3, 2

When SWI Shows Ischemic Changes

Venous Drainage Patterns

• SWI can demonstrate altered venous drainage patterns in ischemic territories through increased prominence of medullary veins due to increased deoxyhemoglobin from impaired oxygen extraction. 4, 5
• These venous changes may appear as increased signal on SWI without the typical "blooming" artifact associated with thrombus. 4

SWI-DWI Mismatch

• The SWI-DWI mismatch can identify ischemic penumbra by showing regions of altered venous drainage that extend beyond the DWI lesion, similar to PWI-DWI mismatch. 5
• This mismatch has shown high consistency with PWI-DWI mismatch in identifying at-risk tissue (P > 0.05 for difference). 5

Clinical Implications

Diagnostic Algorithm

1. Use DWI as the primary sequence for detecting acute ischemia—it identifies 98% of ischemic lesions versus only 71-80% with conventional T2-weighted sequences. 6
2. Add SWI to detect intravascular thrombus (blooming artifact in vessels) and assess venous drainage patterns. 3
3. Do not rely on SWI blooming to confirm or exclude ischemia—its absence does not rule out stroke. 2

Important Caveats

• Blooming artifact on SWI specifically indicates intravascular thrombus, not the ischemic parenchyma itself. 3
• The American College of Radiology emphasizes that MRI with DWI detected acute infarction in 77% of patients within 3 hours versus only 16% with CT, establishing DWI as superior for early detection. 3
• SWI may show characteristic susceptibility changes in stroke mimics like postictal paralysis or complicated migraine, adding diagnostic value beyond ischemia detection. 3

Practical Considerations

• A streamlined MRI protocol including DWI, FLAIR, gradient echo (including SWI), and MR perfusion can be performed in approximately 10 minutes, making it competitive with CT. 1
• Gradient echo sequences (which include SWI) reliably detect intracranial hemorrhage, allowing MRI to serve as the sole initial imaging modality for acute stroke evaluation. 3, 1
• The presence or absence of SWI blooming does not change the management algorithm—treatment decisions are based primarily on DWI findings, clinical presentation, and time from symptom onset. 2