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Physiological noise in MR images: an indicator of the tissue response to ischemia?
Harris H Wang1, Nina M Menezes, Ming Wang Zhu
1Medical Engineering Medical Physics Program, Division of Health Sciences and Technology, Harvard University-Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
Purpose:
To determine whether measuring signal intensity (SI) fluctuations in MRI time series data from acute stroke patients would identify ischemic tissue.
Materials And Methods:
Prebolus perfusion-weighted MRI data from 32 acute ischemic stroke patients (N = 32) was analyzed as a time series. Ischemic and normal tissue regions were outlined and compared.
Results:
The magnitude of the measured SI fluctuations was significantly lower in ischemic regions relative to normal tissue. Spatial differences in these fluctuations occurred in a manner that was different than other perfusion-based metrics.
Conclusion:
Prior studies have shown that SI fluctuations in MRI time series data correspond to the presence of physiological "noise," which includes vasomotion, an autoregulatory phenomenon that affects the tissue response to ischemia. In this study, SI fluctuations were found to decrease in ischemia, consistent with the notion that small vessels will remain open (fluctuations in vessel diameter will decrease) when there is a challenge to flow. Spatial variation in SI fluctuations appeared to be different from spatial variation seen on other perfusion-based metrics, suggesting that a separate contrast mechanism is responsible, one that might be of diagnostic and prognostic value in acute stroke in which the ability of tissue to withstand ischemia is currently not well visualized.
Insights
Signal intensity (SI) fluctuations in MRI time series data are lower in ischemic tissue of acute stroke patients. This finding may offer a new method for identifying and assessing stroke-affected brain regions.
Area of Science:
- Neuroimaging
- Stroke Research
- Medical Diagnostics
Background:
- Physiological noise in MRI time series, including vasomotion, is linked to tissue response in ischemia.
- Understanding autoregulatory phenomena is crucial for assessing tissue viability in acute stroke.
Purpose of the Study:
- To evaluate if measuring signal intensity (SI) fluctuations in MRI time series data can identify ischemic tissue in acute stroke patients.
- To explore the potential of SI fluctuations as a diagnostic marker for acute ischemic stroke.
Main Methods:
- Analysis of prebolus perfusion-weighted MRI data from 32 acute ischemic stroke patients.
- Time series analysis of MRI data, comparing signal intensity fluctuations in outlined ischemic and normal tissue regions.
Main Results:
- Significantly lower magnitude of SI fluctuations observed in ischemic regions compared to normal brain tissue.
- Spatial patterns of SI fluctuations differed from conventional perfusion-based MRI metrics.
Conclusions:
- Decreased SI fluctuations in ischemic tissue suggest sustained small vessel patency during flow challenges.
- The distinct spatial variation of SI fluctuations indicates a unique contrast mechanism potentially valuable for stroke diagnosis and prognosis.
- This method may offer insights into tissue's ability to withstand ischemia, which is currently difficult to visualize.
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