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Published on: December 28, 2014
How reliable is perfusion MR in acute stroke? Validation and determination of the penumbra threshold against
Masashi Takasawa1, P Simon Jones, Joseph V Guadagno
1Department of Clinical Neurosciences, University of Cambridge, Cambridge, England.
Background And Purpose:
Perfusion magnetic resonance imaging (pMR) is increasingly used in acute stroke, but its physiologic significance is still debated. A reasonably good correlation between pMR and positron emission tomography (PET) has been reported in normal subjects and chronic cerebrovascular disease, but corresponding validation in acute stroke is still lacking.
Methods:
We compared the cerebral blood flow (CBF), cerebral blood volume, and mean transit time (MTT) maps generated by pMR (deconvolution method) and PET ((15)O steady-state method) in 5 patients studied back-to-back with the 2 modalities at a mean of 16 hours (range, 7 to 21 hours) after stroke onset. We also determined the penumbra thresholds for pMR-derived MTT, time to peak (TTP), and Tmax against the previously validated probabilistic PET penumbra thresholds.
Results:
In all patients, the PET and pMR relative distribution images were remarkably similar, especially for CBF and MTT. Within-patient correlations between pMR and PET were strong for absolute CBF (average r(2)=0.45) and good for MTT (r(2)=0.35) but less robust for cerebral blood volume (r(2)=0.24). However, pMR overestimated absolute CBF and underestimated MTT, with substantial variability in individual slopes. Removing individual differences by normalization to the mean resulted in much stronger between-patient correlations. Penumbra thresholds of approximately 6, 4.8, and 5.5 seconds were obtained for MTT delay, TTP delay, and Tmax, respectively.
Conclusions:
Although derived from a small sample studied relatively late after stroke onset, our data show that pMR tends to overestimate absolute CBF and underestimate MTT, but the relative distribution of the perfusion variables was remarkably similar between pMR and PET. pMR appears sufficiently reliable for clinical purposes and affords reliable detection of the penumbra from normalized time-based thresholds.
Insights
Perfusion MRI (pMR) shows similar relative perfusion patterns to PET in acute stroke patients. Despite overestimating cerebral blood flow, pMR reliably detects the penumbra, supporting its clinical use.
Area of Science:
- Neurology
- Radiology
- Medical Imaging
Background:
- Perfusion magnetic resonance imaging (pMR) is increasingly utilized in acute stroke management.
- The physiologic significance of pMR in acute stroke remains under investigation.
- Previous studies show good correlation between pMR and PET in normal subjects and chronic cerebrovascular disease, but not acute stroke.
Purpose of the Study:
- To compare perfusion parameters derived from pMR and positron emission tomography (PET) in acute stroke patients.
- To validate pMR-derived penumbra thresholds against established PET thresholds.
Main Methods:
- Compared cerebral blood flow (CBF), cerebral blood volume, and mean transit time (MTT) maps from pMR and PET in 5 acute stroke patients.
- Patients were scanned with both modalities back-to-back, a mean of 16 hours post-stroke.
- Determined penumbra thresholds for pMR-derived MTT, time to peak (TTP), and Tmax against PET thresholds.
Main Results:
- PET and pMR relative distribution images showed remarkable similarity, particularly for CBF and MTT.
- Strong within-patient correlation for absolute CBF (r(2)=0.45) and good for MTT (r(2)=0.35) between pMR and PET.
- pMR overestimated absolute CBF and underestimated MTT, with improved correlations after normalization.
- Penumbra thresholds were established for MTT delay (~6s), TTP delay (~4.8s), and Tmax (~5.5s).
Conclusions:
- pMR demonstrates highly similar relative perfusion distributions to PET in acute stroke.
- While pMR may overestimate absolute CBF and underestimate MTT, its reliability for clinical use is supported.
- pMR enables reliable detection of the penumbra using normalized time-based thresholds.
