Linking To And Excerpting Radiopaedia’s “CT perfusion in ischemic stroke”

Posted on July 13, 2026 by Tom Wade MD

Today I review, link to, and excerpt from Radiopaedia‘s “CT perfusion in ischemic stroke”. Last revised by Giorgio Maria Agazzi on 21 Jun 2026.*

*Gaillard F, Agazzi G, Sharma R, et al. CT perfusion in ischemic stroke. Reference article, Radiopaedia.org (Accessed on 13 Jul 2026) https://doi.org/10.53347/rID-24526
DOI:https://doi.org/10.53347/rID-24526
Permalink:https://radiopaedia.org/articles/ct-perfusion-in-ischaemic-stroke

Note: Be sure and go to the above link, “CT perfusion in ischemic stroke”, to review the Figures and Cases. They are an important part of the article.

All that follows is from the above resource.

CT perfusion in ischemic stroke has become established in most centers with stroke services as an important adjunct, along with CT angiography (CTA), to conventional unenhanced CT brain imaging.

It enables the differentiation of salvageable ischemic brain tissue (the penumbra) from the irrevocably damaged infarcted brain (the infarct core).  This is useful when assessing a patient for treatment (thrombolysis or clot retrieval).

Although MRI is more sensitive to the early parenchymal changes of infarction (see DWI in acute stroke) its clinical application has been limited by difficulties in accessing MRI in a timely fashion in many institutions. This is especially important in this clinical setting as rapid imaging and treatment are crucial to successful intervention.

The key to interpreting CT perfusion in the setting of acute ischemic stroke is understanding and identifying the infarct core and the ischemic penumbra, as a patient with a small core and a large penumbra is most likely to benefit from reperfusion therapies.

The three parameters typically used in determining these two areas are:

  1. mean transit time (MTT) or time to peak (TTP) of the deconvolved tissue residue function (Tmax) 3
  2. cerebral blood flow (CBF)
  3. cerebral blood volume (CBV)

These three parameters are related to each other according to the central volume principle: CBF = CBV/MTT 7

Normal perfusion parameters are:

  • gray matter
    • MTT: 4 s
    • CBF: 60 mL/100 g/min
    • CBV: 4 mL/100 g
  • white matter
    • MTT: 4.8 s
    • CBF: 25 mL/100 g/min
    • CBV: 2 mL/100 g

The infarct core is the part of the ischemic brain which has already infarcted or is destined to infarct regardless of therapy. It is defined as an area with prolonged MTT or Tmax, markedly decreased CBF and markedly reduced CBV 1-3 (see figure 4). Note, that if one uses CBF alone to visually assess core size, it is easy to overestimate infarct core, as the penumbra often has reduced CBF also. Even though some automated processes used CBF to define the core, CBV is a safer parameter if ‘eye-balling’ the scan.

The ischemic penumbra, which in most cases surrounds the infarct core, also has prolonged MTT or Tmax but in contrast, has only moderately reduced CBF and, importantly, near-normal or even increased CBV (due to autoregulatory vasodilatation) 1-3 (see figure 3).

In cases of seizures, the ictal region shows hyperperfusion, which may lead to an interpretation of hypoperfusion in the contralateral hemisphere mimicking infarct.

Significant cervical internal carotid artery stenosis can increase MTT in its vascular territory, mimicking ischemia and leading to overestimation of penumbra and underestimation of infarct core; concurrent neck CT angiography at the time of CTP helps avoiding this pitfall 12.

The CBV, and to a lesser extent CBF, differentiates penumbra and core infarct:

  • core
    • increased MTT/Tmax
    • markedly decreased CBF
    • markedly decreased CBV
  • penumbra
    • increased MTT/Tmax
    • moderately reduced CBF
    • near-normal or increased CBV

Be sure and review the resources below as they are outstanding.

 

 

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