Moiety | Hounsfeld Units |
|---|---|
Bone | 1,000 (more dense) |
Calcium | 100 |
Acute blood | 85 |
Tumor | Possibly 30-60 |
Gray matter | 35-40 |
White matter | 25-30 |
CSF | 0 |
Adipose | -100 |
Air | -1,000 (less dense) |
CSF, cerebrospinal fluid. | |
Duration | Without Contrast | With Contrast |
|---|---|---|
Hyperacute | Normal or blurring of grey-white junction | No enhancement |
Acute | Poorly defined hypodensity, maximal edema | No enhancement or mild gyral enhancement |
Subacute | Hypodensity, less edema | Gyral enhancement |
Remote | Sharply defined hypodensity | Enhancement in 6 weeks |
Duration | Without Contrast |
|---|---|
Acute | Hyperdensity, mass effect |
Subacute | Hypodense periphery with hyperdense center, mass effect |
Remote | Hypodense |
Meningioma
Aneurysm
Pituitary adenoma
Germinoma
Medullablastoma
Central nervous system lymphoma
Acoustic schwannoma
Craniopharyngioma
Colloid cyst
Repetition time—time between successive radio frequency (RF) pulses
Echo time—time between giving the RF pulse and measuring the tissue’s RF signal
Relaxation time—time required to return to equilibrium after an RF pulse
Magnetic resonance imaging (MRI) is based primarily on the relaxation times of various tissues.
Diffusion-weighted images are positive in >90% of ischemic strokes within minutes of the event.
Diffusion perfusion images can be obtained to show the mismatch between the images (ischemic and hypoperfused regions). Diffusion-weighted images with stroke detected decreased water mobility. Diffusion-weighted images change within 5 minutes following a stroke. Diffusion-weighted images—2 weeks to change from bright to dark following a stroke. When perfusion defect equals diffusion defect (no mismatch), there is no significant risk for stroke enlargement with a matched defect.
Apparent diffusion coefficient map—1 week for change from dark to white following stroke. Apparent diffusion coefficient is the extent of movement of water molecules. With a stroke, cellular water has decreased ability to move.
Dark (long T1) | Bright (short T1) |
|---|---|
Intracellular deoxyhemoglobin | Fat |
Calcium | Contrast |
Air | Methemoglobin |
Water (edema) | Proteinaceous material |
Most tumors | Hypoxic changes |
Infarction | Melanoma |
Demyelinating disease | Hepatic failure |
Abscess | Slow-flowing blood |
Chronic hemorrhage | Laminar necrosis |
CSF | Hepatic failure |
Calcification | |
CSF, cerebrospinal fluid | |
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
