CT Perfusion
Infarct core is the part of the ischemic brain which has already infarcted or is destined to infarct regardless of therapy.
increased MTT/Tmax
markedly decreased CBF
markedly decreased CBV
Ischemic penumbra denotes the part of an acute ischemic stroke that is at risk of progressing to infarction but is still salvageable if reperfused.
increased MTT/Tmax
moderately reduced CBF
near-normal or increased CBV
Volume of CORE + PENUMBRA = Tmax > 6
CORE = CBF < 30
PENUMBRA = Mismatch = Tmax - CBF
• Cerebral Blood Flow (CBF): Represents instantaneous capillary flow in tissue.
• Cerebral Blood Volume (CBV): Describes the blood volume of the cerebral capillaries and venules per cerebral tissue volume.
• Mean Transit Time (MTT) = CBV divided by BF; it is the average length of time a certain volume of blood is present in the capillary circulation.
CT Perfusion - Crash Course
Time to Peak (TTP): This is the opposite of CBF. Less flow = Longer Time to reach maximum concentration of contrast.
After an arterial occlusion perfusion pressure is going to be rapidly reduced. Millions of neurons will suddenly cry out in terror then suddenly be silenced, unless they are lucky to have arteriolar dilation with capillary recruitment to bring in as much blood to that area of brain as possible.
This process is called physiologic auto-regulation and should result in an increase in capillary blood pool. The key point is that you need live neurons (penumbra) to cry out for help. If they cry out and are suddenly silenced (infarct core) you won't see any auto regulation attempts. This physiology makes up the basis of perfusion for stroke.
Infarct core is defined as the area of the brain with:
increased MTT/Tmax
markedly decreased CBF
markedly decreased CBV
Ischemic penumbra will have:
increased MTT/Tmax
moderately reduced CBF
near-normal or increased CBV
Common definition for penumbra:
hypoperfused brain at risk of progression to infarction (salvageable)
↑ T-max >6 seconds, or ↑ mean transit time (MTT) or time to peak (TTP) > 145% of the healthy hemisphere)
a moderate decrease of cerebral blood flow (CBF); > 30% of the contralateral (normal) side
normal or ↑ cerebral blood volume (CBV) – due to autoregulation
Common definition for core:
infarcted, unsalvageable tissue
↑ T-max (TTP, MTT)
↓↓ CBF (< 30% of normal values); it corresponds to DWI lesion on MRI) CTP core area with CBF<30% corresponds to DWI lesion on MRI
↓↓ CBV (< 40% normal)
Check The Curves
Satisfactory Time–Attenuation Curves.
Note that the entire curve is captured. Curves demonstrate swift upstroke, single peaks, and return to baseline. The arterial input function (AIF) peak attenuation is also greater than 100 Housfield units (HU).
The AIF is shown in red and VOF in blue and, ideally, are sharp single peaks of more than 100 HU, as measured on the y-axis
Examples of unstatisfactory curves.
https://practicalneurology.com/
Automated Processing of Head CT Perfusion Imaging for Ischemic Stroke Triage
