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Can we identify a CT-based tissue window for thrombolysis without CTP.

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DOI: 10.1002/ana.20780
Can We Identify a CT-based Tissue Window for
Thrombolysis Without CTP?
Imanuel Dzialowski,1,2 Andrew Demchuk,1
Shelagh Coutts,1 Michael Hill,1 Marc Hudon,1
Ting-Yim Lee,3 and Ruediger Von Kummer3
Our congratulations to Parsons and colleagues for their novel
work on qualitative computed tomography perfusion (CTP)
imaging using the Alberta Stroke Program Early CT Score
In patients presenting with acute anterior circulation
stroke within 6 hours from symptom onset, the authors
showed that scoring ASPECTS on CTP parameter images
improves prediction of final infarct and outcome as compared with noncontrast CT (NCCT) or CT angiography
source-images (CTA-SI). In addition, their work contributes to increasing evidence that infarct core as well as tissue
at risk might be reliably identified by CTP (Murphy et al.
personal communication).2 However, we would like to discuss with the authors two issues that might contribute to
further understanding and development of this technique.
First, the authors did not mention which thresholds they
used to determine abnormal ASPECTS regions on parametric maps for relative cerebral blood flow (rCBF), cerebral
blood volume (rCBV), and mean transit time (rMTT). Depending on window and leveling, “dark blue or black” regions might represent different relative perfusion thresholds,
for example, 0.2 versus 0.3 for rCBF. With this information
lacking, results might be difficult to reproduce among different perfusion software and hardware manufacturers. Furthermore, it would be interesting to learn about incidence and
tissue outcome of ASPECTS regions with reduced rCBF but
increased rCBV.
Second, based on our ASPECTS analysis in a similar cohort studying patients with middle cerebral artery occlusions within 6 hours from symptom onset,3 we are currently testing the hypothesis that a favorable NCCT scan
(ASPECTS ⱖ6) in the presence of intracranial arterial occlusion predicts benefit from thrombolysis in a greater than
3-hour time window. NCCT (or CTA-SI) ASPECTS estimates infarct core, and intracranial occlusion on CT angiography or transcranial Doppler sonography acts as surrogate marker for large perfusion deficit. This approach
would be rapid and practical especially for stroke physicians
lacking advanced CT technology. To learn more about the
additional value of CTP compared with our approach, we
would like to ask the authors the following: did a rCBVASPECTS ⬎ rCBF-ASPECTS mismatch occur in patients
without demonstrable arterial occlusion? Which proportion
of patients with and without ASPECTS ⱖ6 and proximal
occlusion (M1 and ICA) showed this mismatch and how
did this proportion differ from patients with distal (M2)
We are looking forward to studying more data on this
important and evolving technology.
University of Calgary, Clinical Neurosciences, Calgary,
Alberta, Canada; 2University of Dresden, Department of
Neuroradiology, Dresden, Germany; and 3University of
Western Ontario, Robarts Research Institute, London,
Ontario, Canada
1. Parsons MW, Pepper EM, Chan V, et al. Perfusion computed
tomography: prediction of final infarct extent and stroke outcome. Ann Neurol 2005;58:672– 679.
2. Wintermark M, Reichhart M, Thiran JP, et al. Prognostic accuracy of cerebral blood flow measurement by perfusion computed
tomography, at the time of emergency room admission, in acute
stroke patients. Ann Neurol 2002;51:417– 432
3. Hill MD, Rowley HA, Adler F, et al. Selection of acute ischemic
stroke patients for intra-arterial thrombolysis with pro-urokinase
by using ASPECTS. Stroke 2003;34:1925–1931.
DOI: 10.1002/ana.20782
Annals of Neurology
Vol 59
No 1
January 2006
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