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Normal Appearance
MRI
Normal Tissue Signal Characteristics
This table outlines the typical signal intensities of various tissues and structures on common MRI sequences.
Key Mnemonics
- T1W → Fat hyperintense, fluid hypointense.
- T2W → Fluid hyperintense, fat hyperintense, grey matter hyperintense vs white matter.
- PD → Fat markedly hyperintense, cartilage/CSF hyperintense, high anatomical detail.
- STIR → Fat becomes hypointense, edema/fluid hyperintense.
- DWI → Hyperintensity on high b-values = restricted diffusion (pathology).
- FLAIR → Fluid suppression (CSF hypointense), edema/pathology hyperintense.
- SWI → Blood products & calcification hypointense, venous structures hypointense, high susceptibility effects.
Cerebrospinal Fluid (CSF)
T1W:HypointenseT2W:HyperintensePD:HyperintenseSTIR:HyperintenseDWI:Hyperintense on b=0, hypointense on high b-values unless restrictedFLAIR:HypointenseSWI:Hypointense
White Matter
T1W:Iso- to slightly hyperintense relative to grey matterT2W:Hypointense relative to grey matterPD:IsointenseSTIR:Hypointense relative to greyDWI:IsointenseFLAIR:Hypointense relative to grey matterSWI:Isointense
Grey Matter
T1W:IsointenseT2W:Hyperintense relative to white matterPD:IsointenseSTIR:Hyperintense relative to white matterDWI:IsointenseFLAIR:Hyperintense relative to white matterSWI:Isointense
Fat (Subcutaneous, Marrow)
T1W:HyperintenseT2W:HyperintensePD:Markedly hyperintenseSTIR:Hypointense (suppressed)DWI:VariableFLAIR:HyperintenseSWI:Hyperintense
Muscle
T1W:Iso- to hypointenseT2W:Iso- to hypointensePD:IsointenseSTIR:HypointenseDWI:IsointenseFLAIR:IsointenseSWI:Isointense
Cartilage
T1W:IsointenseT2W:HyperintensePD:HyperintenseSTIR:HyperintenseDWI:IsointenseFLAIR:HyperintenseSWI:Isointense
Cortical Bone
T1W:HypointenseT2W:HypointensePD:HypointenseSTIR:HypointenseDWI:HypointenseFLAIR:HypointenseSWI:Hypointense
Bone Marrow
T1W:Hyperintense (fat content)T2W:Hyperintense (fat content)PD:Markedly hyperintenseSTIR:Hypointense (fat suppressed)DWI:IsointenseFLAIR:HyperintenseSWI:Hyperintense
Tendons / Ligaments
T1W:HypointenseT2W:HypointensePD:HypointenseSTIR:HypointenseDWI:HypointenseFLAIR:HypointenseSWI:Hypointense
Blood (Flowing)
T1W:Hypointense (flow void)T2W:Hypointense (flow void)PD:HypointenseSTIR:HypointenseDWI:HypointenseFLAIR:Hypointense (flow void)SWI:Hypointense
Subacute Hemorrhage (Intracellular Methemoglobin)
T1W:HyperintenseT2W:VariablePD:HyperintenseSTIR:VariableDWI:May be hyperintense if diffusion restrictedFLAIR:Variable, often hyperintenseSWI:Markedly hypointense
Air
T1W:HypointenseT2W:HypointensePD:HypointenseSTIR:HypointenseDWI:HypointenseFLAIR:HypointenseSWI:Hypointense
| Tissue/Structure | T1W | T2W | PD | STIR | DWI | FLAIR | SWI |
|---|---|---|---|---|---|---|---|
| Cerebrospinal Fluid (CSF) | Hypointense | Hyperintense | Hyperintense | Hyperintense | Hyperintense on b=0, hypointense on high b-values unless restricted | Hypointense | Hypointense |
| White Matter | Iso- to slightly hyperintense relative to grey matter | Hypointense relative to grey matter | Isointense | Hypointense relative to grey | Isointense | Hypointense relative to grey matter | Isointense |
| Grey Matter | Isointense | Hyperintense relative to white matter | Isointense | Hyperintense relative to white matter | Isointense | Hyperintense relative to white matter | Isointense |
| Fat (Subcutaneous, Marrow) | Hyperintense | Hyperintense | Markedly hyperintense | Hypointense (suppressed) | Variable | Hyperintense | Hyperintense |
| Muscle | Iso- to hypointense | Iso- to hypointense | Isointense | Hypointense | Isointense | Isointense | Isointense |
| Cartilage | Isointense | Hyperintense | Hyperintense | Hyperintense | Isointense | Hyperintense | Isointense |
| Cortical Bone | Hypointense | Hypointense | Hypointense | Hypointense | Hypointense | Hypointense | Hypointense |
| Bone Marrow | Hyperintense (fat content) | Hyperintense (fat content) | Markedly hyperintense | Hypointense (fat suppressed) | Isointense | Hyperintense | Hyperintense |
| Tendons / Ligaments | Hypointense | Hypointense | Hypointense | Hypointense | Hypointense | Hypointense | Hypointense |
| Blood (Flowing) | Hypointense (flow void) | Hypointense (flow void) | Hypointense | Hypointense | Hypointense | Hypointense (flow void) | Hypointense |
| Subacute Hemorrhage (Intracellular Methemoglobin) | Hyperintense | Variable | Hyperintense | Variable | May be hyperintense if diffusion restricted | Variable, often hyperintense | Markedly hypointense |
| Air | Hypointense | Hypointense | Hypointense | Hypointense | Hypointense | Hypointense | Hypointense |