Which MRI sequence is most sensitive for detecting hemosiderin deposition in chronic intracerebral hemorrhage?

Explanation

## Hemosiderin Detection in Chronic ICH ### MRI Sequences and Hemorrhage Detection | Sequence | Sensitivity for Hemosiderin | Mechanism | |----------|-----------------------------|-----------| | **T2 GRE / SWI** | **Highest** | Susceptibility artifact from iron; blooming effect | | **T1-weighted** | Low | Hemosiderin is dark on T1; poor contrast | | **FLAIR** | Moderate | Suppresses CSF; can show subacute blood but not chronic iron | | **DWI** | None | Detects acute ischemia, not chronic hemorrhage | **Key Point:** **Gradient echo (GRE) and susceptibility-weighted imaging (SWI)** are exquisitely sensitive for hemosiderin because iron causes local magnetic field inhomogeneity, producing **blooming artifact** (the lesion appears larger than it actually is on these sequences). **High-Yield:** SWI is the **single most sensitive sequence** for detecting chronic microhemorrhages and hemosiderin deposition. It is now standard in stroke protocols to identify prior bleeds. **Mnemonic:** **GRIME** — GRE/SWI shows Iron (hemosiderin) as blooming dark lesions on MRI. **Clinical Pearl:** The **"blooming sign"** on GRE/SWI is a hallmark of chronic ICH and helps distinguish it from other hypointense lesions (e.g., calcification, artifact). Hemosiderin appears as a hypointense (dark) rim on T2 GRE/SWI, often larger than the lesion on conventional T2. ### Timeline of MRI Changes in ICH | Phase | T1 | T2 | GRE/SWI | |-------|----|----|----------| | **Hyperacute (0–12 hrs)** | Isointense | Hypointense | Hypointense | | **Acute (1–3 days)** | Isointense | Hypointense | Hypointense | | **Early subacute (3–7 days)** | **Hyperintense** | Hypointense | Hypointense | | **Late subacute (1–3 wks)** | Hyperintense | Hyperintense | Hypointense | | **Chronic (>3 wks)** | Isointense/hypointense | Hypointense | **Blooming hypointense rim** | **Clinical Application:** In patients with recurrent ICH or suspected amyloid angiopathy, SWI is essential to count microhemorrhages and assess burden of prior bleeds.