Infarct core: already infarcted tissue; elevated MTT and reduced CBV

• Area of prolonged Tmax, markedly reduced CBF and markedly reduced CBV

• If CBF is used alone, infarct core will be overestimated as penumbra reduces CBF as well. CBV is safer parameter if eyeballing scan.

Penumbra: at risk but not infarcted tissue; elevated MTT and near normal CBV

• Received some Q but at a reduced rate compared to normal brain. Prolonged Tmax but only moderately reduced CBF and near normal/increased CBV 2/2 autoregulatory vasodilation

  • Normal GB brain Q = 60 mL/100 g tissue per min

  • Penumbra = <20 mL/100 g tissue per min 

Tmax: time to maximum of the tissue residual function

Mean Transit Time (MTT): avg time RBCs need to cross the brain capillary network 

• Elevated in (1) thromboembolic process (2) significant arterial atherosclerosis (3) early ischemia

• Prolonged soon after reduced Q; any tissue w/ reduced MTT is AT LEAST "at risk"

• Use to visualize the tissue at risk

Cerebral blood volume (CBV): volume of blood in a given amount of brain tissue & large vessels.

• Use to visualize infarct core

• Reduced in infarct core but NOT penumbra

• Uses mL of blood per 100 g of brain tissue

• Can be preserved or even elevated in very early ischemia 2/2 capillary bed dilatation. Once CBF threshold is reached (<30%), CBV will decline resulting in...

  • ...an infarct core (matched decrease in CBF & CBV) 

  • ...a penumbra (mismatched decrease in CBF (more) and CBV (less))

Cerebral blood flow (CBF): volume of blood passing through volume of brain tissue per unit time

• CBF = CBV / Time to peak

• Uses mL of blood per 100 g of brain tissue per minute

• Decreased in early ischemia; mismatch b/n CBF and CBV is used to identify penumbra

• CBF <30% is a marker for ischemic core