Published online before print August 3, 2006, doi: 10.1161/01.STR.0000237068.25105.aa
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(Stroke. 2006;37:2201.)
© 2006 American Heart Association, Inc.
Letters to the Editor |
Cerebral Blood Flow Threshold of Ischemic Penumbra and Infarct Core in Acute Ischemic Stroke: A Systematic Review
Lawson Health Research Institute, Robarts Research Institute, London, Canada
Sunnybrook Health Sciences Centre, Toronto, Canada
London Health Sciences Centre, London, Canada
Ottawa Health Research Institute, Ottawa, Canada
Foothills Medical Centre, Calgary, Canada
To the Editor:
In the above titled article,1 the authors reviewed 7 published studies that compared cerebral blood flow (CBF) measurements with a diagnostic gold standard (follow-up brain CT/MRI) and reported CBF thresholds for the differentiation between ischemic penumbra and infarct core. They found that the "reported CBF thresholds varied widely, from 14.1 to 35.0 and from 4.8 to 8.4 mL/100 g per minute for penumbra and infarct core, respectively." They concluded that "the use of CBF thresholds... for imaging methods cannot be recommended without further evaluation." Although the caution to await results of further evaluation is correct, there are several aspects of the article that need to be discussed:
- In the 7 studies reviewed, CBF was measured with positron-emission tomography (PET) in 3 and with perfusion-weighted MRI (PWI) in 4. The analysis and results obtained with these 2 methodologies are very different. PET is quantitative and measures absolute (versus relative) CBF and is the de facto reference standard, whereas CBF measurement with PWI is relative.
- Within PWI, the methods for calculating CBF can be divided into those that use deconvolution (references 22, 24, and 25 in the article) and those that do not (reference 14 in the article). The 2 analysis methods are significantly different from each other, and there are no published reports on the calibration between the 2 methods.
- To convert the relative PWI CBF measurements (thresholds) into absolute values as given by PET, the authors scaled the relative values by a factor of 50 mL · min–1 · (100 g)–1. This factor is the normal average value of CBF in younger adults (reference 26 in the article). In contrast, the mean age of subjects in the 4 PWI studies ranged from 64 to 71, and it is known that CBF does decline with age.2,3 Part of the observed variability in threshold can be a consequence of these age-related changes in CBF.
- In more recent prospective studies involving admission CT perfusion and follow-up CT or MRI to define infarct size, receiver operating characteristic curve or logistic regression analysis has shown that CBF alone is not the optimal CT perfusion parameter to differentiate between ischemic penumbra and infarct core.4,5,6
- Variability in thresholds in these studies can also be attributable to the type of analysis used. Voxel-based thresholds for infarction are known to be lower than thresholds derived from large region of interest analysis. Both analyses were included in this review.
Acknowledgments
Disclosures
None.
References
1. Bandera E, Botteri M, Minelli C, Sutton A, Abrams KR, Latronico N. Cerebral blood flow threshold of ischemic penumbra and infarct core in acute ischemic stroke: a systematic review. Stroke. 2006: 37: 1334–1339.
2. Pantano P, Baron JC, Lebrun-Grandie P, Duquesnoy N, Bousser MG, Comar D. Regional cerebral blood flow and oxygen consumption in human aging. Stroke. 1984; 15: 635–641.
3. Marchal G, Rioux P, Petit-Taboue MC, Sette G, Travere JM, Le Poec C, Courtheoux P, Derlon JM, Baron JC. Regional cerebral oxygen consumption, blood flow, and blood volume in healthy human aging. Arch Neurol. 1992; 49: 1013–1020.
4. Murphy BD, Fox AJ, Lee DH, Sahlas DJ, Black SE, Hogan MJ, Coutts SB, Demchuk AM, Goyal M, Aviv RI, Symons S, Gulka IB, Beletsky V, Pelz D, Hachinski V, Chan R, Lee TY. Identification of penumbra and infarct in acute ischemic stroke using computed tomography perfusion-derived blood flow and blood volume measurements. Stroke. 2006; 37: 1771–1777.
5. Wintermark M, Flanders AE, Velthuis B, Meuli R, van Leeuwen M, Goldsher D, Pineda C, Serena J, van der Schaaf I, Waaijer A, Anderson J, Nesbit G, Gabriely I, Medina V, Quiles A, Pohlman S, Quist M, Schnyder P, Bogousslavsky J, Dillon WP, Pedraza S. Perfusion-CT assessment of infarct core and penumbra: receiver operating characteristic curve analysis in 130 patients suspected of acute hemispheric stroke. Stroke. 2006; 37: 979–985.
6. Wintermark M, Reichhart M, Thiran JP, Maeder P, Chalaron M, Schnyder P, Bogousslavsky J, Meuli R. 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.[CrossRef][Medline] [Order article via Infotrieve]
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