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

0 s 1.5 s 3 s 4.5 s 6 s 7.5 s 9 s 10.5 s 12 s 13.5 s

250

300

350

400

450

500

0 10 20 30 40

* 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)