Transcript
diffusion gradients sensitize the MR image to motion of extracellular or intracellular water
• more motion=darker image;• less motion=brighter image
Freely Diffusing Water = DarkFreely Diffusing Water = Dark Restricted Diffusion = BrightRestricted Diffusion = Bright
GRE: 4-5 mm bleeds or
larger (left)
SWI: 2-3 mm bleeds or smaller(right)
GRE: 4-5 mm bleeds or
larger (left)
SWI: 2-3 mm bleeds or smaller(right)
AgeT1
WeightedT2
Weighted
Hyperacute Hours old, mainly oxyhemoglobin with surrounding edema
Hypointense Hyperintense
Acute Days old, mainly deoxyhemoglobin with surrounding edema
Hypointense Hypointense, surrounded by hyperintense margin
Subacute (early)
Days old, mainly intracellular methemoglobin
Hyperintense Hypointense, early subacute with precominantly intracellular methemoglobin
Subacute (late)
Weeks old, mainly extracellular methemoglobin
Hyperintense Hyperintense, late subacute with predominantly extracellular methemoglobin
Chronic Years old, hemosiderin slit or hemosiderin margin surrounding fluid cavity
Hypointense Hypointense slit, or hypointense margin surrounding hyperintense fluid cavity
SAH TB meningitis
Blue = anterior cerebral arteryRed = middle cerebral artery
Yellow = posterior cerebral artery
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* This information about this product is preliminary. The product is under development and not commercially available in the U.S., and its future availability cannot be ensured.
Ca(t): Artery
Area
MTT
CBF*
CBV*Ct(t): Tissue
Integration
Deconvolution
Division
Østergaard, Weisskoff, Chesler et al. MRM 36 715-725 (1996)Østergaard, Sorensen, Kwong et al. MRM 36 726-736 (1996)
* This information about this product is preliminary. The product is under development and not commercially available in the U.S., and its future availability cannot be ensured.
Diffusion vs. perfusionreveals “tissue-at-risk”
DWI
MTT & rCBF
•perfusion deficits often more extensive than those on DWI in early ischemia or infarction (DWI / PWI mismatch)
–more accurately reflects the amount of tissue under ischemic conditions in the hyperacute period than DWI–perfusion minus DWI = “tissue-at-risk”
• DWI abnormalities are evidence of:– CBF < 10 ml/100g/min– cytotoxic edema– irreversible ischemia (most of the time)
• PWI abnormalities are evidence of:– CBF = 10-18 ml/100g/min– neuronal paralysis– reversible ischemia
• DWI / PWI mismatches define the ischemic penumbra• The integrated MR examination for stroke - “one-stop shopping”
– T2/FLAIR/GRE/SWI/MRA sequences– diffusion imaging (diagnostic)– perfusion imaging (prognostic – endovascular Rx)
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