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ARTICLES: V. N. Thijs, A. Adami, T. Neumann–Haefelin, M. E. Moseley, M. P. Marks, and G. W. Albers Relationship between severity of MR perfusion deficit and DWI lesion evolution Neurology 2001; 57: 1205-1211 [Abstract] [Full text] [PDF]

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Reply to Letter to the Editor

Vincent Thijs, Gregroy W Albers   (18 February 2002)

Relationship between severity of MR perfusion deficit and DWI lesion evolution

Mark W Parsons, Alan Barber and Stephen M Davis   (18 February 2002)

Reply to Letter to the Editor 18 February 2002
Vincent Thijs UZ Gasthuisberg Leuven Belgium, Gregroy W Albers Send Correspondence to journal: Re: Reply to Letter to the Editor Vincent.Thijs{at}uz.kuleuven.ac.be Vincent Thijs, et al.	We appreciate the comments of Parsons et al. The focus of our study was not to predict final infarct volume using the lesion volumes identified on baseline MTT, CBF or CBV maps, as was performed elegantly by Parsons et al. [2] Our goal was to evaluate the predictive value of the relative signal intensities identified on these hemodynamic maps, rather than differentiate between the value of individual maps. Our results show that the more hyperintense the MTT lesion, the more likely the diffusion lesion was to grow to equal the size of the baseline MTT lesion. As acknowledged in the paper, the lack of predictive value of our CBF ratios may be due to the small sample size, the inclusion of regions of normal or increased CBF within the “CBF lesion” or susceptibility artefacts. The best functional MR method to predict final infarct volume in hyperacute stroke patients is currently unknown. ADC, MTT, CBF and CBV, separately or in combination have all been proposed as having a high, although imperfect, predictive ability for detecting ischemic lesion growth. [2, 4, 5, 6] We suspect that discrepancies between the results of these studies are related to differences in MR acquisition technique, mathematical analysis, and definition of PWI/DWI mismatch, variable clinical inclusion criteria and inherent biological variability. To resolve this issue, multicenter studies are needed that include large numbers of patients and uniform criteria for data acquisition and analysis. Different post-processing methods should be directly compared to identify the method with the best predictive value. Until these important studies are performed, the superiority of one approach over another will remain unestablished. References: 1. Thijs VN, Adami A, Neumann-Haefelin T, Moseley ME, Marks MP, Albers GW. Relationship between severity of MR perfusion deficit and DWI lesion evolution. Neurology 2001;57:1205-1211. 2. Parsons MW, Yang Q, Barber PA, et al. Perfusion magnetic resonance imaging maps in hyperacute stroke: relative cerebral blood flow most accurately identifies tissue destined to infarct. Stroke 2001;32:1581 -1587. 3. Barber PA, Darby DG, Desmond PM, et al. Prediction of stroke outcome with echoplanar perfusion- and diffusion-weighted MRI. Neurology 1998;51:418-426. 4. Oppenheim C, Grandin C, Samson Y, et al. Is there an apparent diffusion coefficient threshold in predicting tissue viability in hyperacute stroke? Stroke 2001;32:2486-491. 5. Wu O, Koroshetz WJ, Ostergaard L, et al. Predicting tissue outcome in acute human cerebral ischemia using combined diffusion- and perfusion- weighted MR imaging. Stroke 2001;32:933-942. 6. Sorensen AG, Copen WA, Ostergaard L, et al. Hyperacute stroke: simultaneous measurement of relative cerebral blood volume, relative cerebral blood flow, and mean tissue transit time. Radiology 1999;210:519- 527.
Relationship between severity of MR perfusion deficit and DWI lesion evolution 18 February 2002
Mark W Parsons Royal Melbourne Hospital Victoria Australia, Alan Barber and Stephen M Davis Send Correspondence to journal: Re: Relationship between severity of MR perfusion deficit and DWI lesion evolution mark.parsons{at}mh.org.au Mark W Parsons, et al.	We were interested to read the article by Thijs et al. [1] examining the relationship between severity of MR perfusion deficit and DWI lesion evolution. We have recently published a similar analysis of sub-6 hour ischemic stroke patients with acute PWI>DWI mismatch. [2] We also found that MTT and CBV lesions closely predicted final infarct size. However, the strong correlation between acute CBF lesions and final infarct size in our 23 patients was not reproduced in the 12 patients studied by Thijs et al. [1] Perhaps the differing methodology explains the lack of agreement. It would not be unreasonable to expect the CBF ratio to be similar to CBV ratio/MTT ratio (as MTT = CBV/CBF at a pixel level). However, there are three of the 12 patients (7, 11, and 12 in the Table) where the presented CBF ratio exceeds the predicted CBF value by more than twenty-five per cent. We wonder if reflecting the larger MTT lesion onto the CBF map has led to inclusion of tissue with normal or increased CBF within the ‘lesion’, thus leading to a higher than anticipated CBF ratio. Furthermore, as the current authors and others have shown, the visually apparent acute MTT lesion almost always overestimates final infarct size. [1, 2, 3] Therefore patient 2 in the Table, who has a final infarct 65% greater than the acute MTT lesion, may have an artefactual result. This could be due to the significant susceptibility artefact on the PWI maps that the authors acknowledge. We agree that MTT maps are the most practical of the PWI maps to use in stroke and concur that thresholded MTT maps are reasonably accurate at predicting tissue at risk of infarction. However, we believe that some caution should be applied when interpreting the CBF results of the current study, particularly in view of the small number of patients presented. References 1. Thijs VN, Adami A, Neumann-Haefelin T, Moseley ME, Marks MP, Albers GW. Relationship between severity of MR perfusion deficit and DWI lesion evolution. Neurology 2001;57:1205-1211. 2. Parsons MW, Yang Q, Barber PA, et al. Perfusion magnetic resonance imaging maps in hyperacute stroke: relative cerebral blood flow most accurately identifies tissue destined to infarct. Stroke 2001;32:1581-1587 3. Barber PA, Darby DG, Desmond PM, et al, Prediction of stroke outcome with echoplanar perfusion- and diffusion-weighted MRI. Neurology 1998;51:418-426.