title: Perfusion computed tomography relative threshold values in definition of acute stroke lesions.
abstract: BACKGROUND
  Perfusion computed tomography (CT) is a relatively new technique that allows fast evaluation of cerebral hemodynamics by providing perfusion maps and gives confirmation of perfusion deficits in ischemic areas. Some controversies exist regarding accuracy of quantitative detection of tissue viability: penumbra (tissue at risk) or core (necrosis).
  
  
  OBJECTIVE
  To define brain tissue viability grade on the basis of the perfusion CT parameters in acute stroke patients.
  
  
  METHODS
  A multimodal CT imaging protocol; unenhanced CT of the brain, CT angiography of head and neck blood vessels, followed by brain perfusion CT and 24 h follow-up brain CT was performed. Perfusion deficits were detected first visually, with subsequent manual quantitative and relative measurements in affected and contra-lateral hemisphere in 87 acute stroke patients.
  
  
  RESULTS
  Visual perfusion deficit on perfusion CT images was found in 78 cases (38 women, 40 men; mean age, 30-84 years). Penumbra lesions (n = 49) and core lesions (n = 42) were detected by increased mean transit time (MTT) on perfusion CT maps in comparison to contra-lateral hemispheres. Cerebral blood volume (CBV) mean values in the penumbra group were increased in the penumbra group and decreased in the core group. Cerebral blood flow (CBF) values were decreased in penumbra and markedly decreased in core lesion.
  
  
  CONCLUSIONS
  Perfusion CT measurements are reliable in estimation of penumbra and core lesions in acute stroke patients, if relative threshold values are used. The most accurate parameter of hypoperfusion is increased MTT above 190%. Relative threshold values for irreversible lesion are CBF <30-40% and CBV <40% in comparison to contra-lateral hemisphere. Penumbra lesion is characterized by MTT increase and CBF decrease, while CBV shows variable values.
authors.affiliation: Radiology Department, Riga Stradins University , Riga.
authors.forename: Radzina
authors.initials: R
authors.lastname: Maija
authors.forename: Krumina
authors.initials: K
authors.lastname: Gaida
authors.forename: Kupcs
authors.initials: K
authors.lastname: Karlis
authors.forename: Miglane
authors.initials: M
authors.lastname: Evija
keywords: Computed tomography; perfusion; stroke