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Diffusion- and perfusion-weighted MRI. The DWI/PWI mismatch region in acute stroke
T Neumann-Haefelin1, H J Wittsack, F Wenserski
1Department of Neurology, Institute of Diagnostic Radiology, Heinrich-Heine University, Düsseldorf, Germany. tnh@s-word.stanford.edu
Background And Purpose:
Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) are relatively new MR techniques increasingly used in acute stroke. During the first hours of stroke evolution, the regions with abnormal perfusion are typically larger than the DWI lesions, and this mismatch region has been suggested to be "tissue at risk." The aim of this study was to evaluate the PWI/DWI mismatch region in acute stroke patients and find parameters indicative of both infarct progression and functional impairment.
Methods:
Twenty patients with nonlacunar ischemic stroke were imaged with DWI, PWI, and conventional MRI within 24 hours of symptom onset and after 1 week; in addition, the European Stroke Scale (ESS) score was recorded. With PWI, the volumes of regions with "time-to-peak" (TTP) delays of >/=2, 4, 6, 8, and 10 seconds were measured; these volumes were compared with the acute DWI lesion volumes, final infarct size, and ESS score.
Results:
In 80% of patients the acute DWI lesion was surrounded by regions with abnormal TTP delays (PWI>DWI lesion). A TTP delay of >/=6 s in the mismatch region was found to be associated with lesion enlargement between the initial and follow-up MRI scans. Lesions increased in 9 of 12 patients (75%) in whom the area with TTP delay >/=6 s was larger than the DWI lesion, but they increased in only 1 of 8 (12.5%) of the remaining patients, in whom the area with a TTP delay >/=6 s was smaller than the DWI lesion. The volume of the regions with TTP delays of >/=4 s correlated better with ESS (r=-0.88, P<0.001) than other PWI (or DWI) volumes, which indicated that a TTP delay of approximately 4 s might be the threshold for functional impairment of brain tissue.
Conclusions:
Only patients with severe perfusion deficits in the PWI/DWI mismatch (TTP delays of >/=6 s) are at high risk of lesion enlargement. Functionally, more moderate perfusion deficits (TTP delays >/=4 and <6 s) appear to also contribute to the acute clinical deficit.
Insights
Severe perfusion deficits (>/=6s time-to-peak delay) in acute stroke patients indicate a high risk of lesion enlargement. Moderate deficits (4-6s delay) also contribute to acute clinical deficits, highlighting the importance of PWI/DWI mismatch assessment.
Area of Science:
- Neurology
- Radiology
- Medical Imaging
Background:
- Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) are advanced MRI techniques used in acute stroke assessment.
- The PWI/DWI mismatch, representing 'tissue at risk,' is larger than acute DWI lesions in the early hours of stroke.
Purpose of the Study:
- To evaluate the PWI/DWI mismatch region in acute stroke patients.
- To identify parameters indicative of infarct progression and functional impairment.
Main Methods:
- Twenty acute ischemic stroke patients underwent DWI, PWI, and conventional MRI within 24 hours and at 1 week.
- European Stroke Scale (ESS) scores were recorded.
- Volumes of PWI regions with time-to-peak (TTP) delays (>/=2, 4, 6, 8, 10 seconds) were measured and compared with DWI lesion volumes, final infarct size, and ESS scores.
Main Results:
- 80% of patients showed PWI regions larger than acute DWI lesions (PWI>DWI mismatch).
- A TTP delay of >/=6 seconds in the mismatch region correlated with lesion enlargement (75% increase vs. 12.5% without).
- TTP delays of >/=4 seconds correlated strongly with ESS scores (r=-0.88, P<0.001), suggesting a threshold for functional impairment.
Conclusions:
- Patients with severe perfusion deficits (TTP delays >/=6s) face a high risk of infarct progression.
- Moderate perfusion deficits (TTP delays 4-6s) also contribute to acute clinical deficits.
- PWI/DWI mismatch analysis, particularly TTP delays, is crucial for predicting stroke outcomes.