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Functional magnetic resonance imaging based on SEEP contrast: response function and anatomical specificity
Patrick W Stroman1, Jennifer Kornelsen, Jane Lawrence
1Department of Diagnostic Radiology, Queen's University, Kingston, Ontario, Canada K7L 2V7. stromanp@post.queensu.ca
Magnetic Resonance Imaging
|November 9, 2005
Summary
Signal Enhancement by Extravascular water Protons (SEEP) fMRI and Blood-Oxygen-Level-Dependent (BOLD) fMRI show reproducible activity localization. SEEP and BOLD responses are distinct, with SEEP lagging BOLD and decaying slower.
Area of Science:
- Neuroimaging
- Functional Magnetic Resonance Imaging (fMRI)
Background:
- Previously demonstrated Signal Enhancement by Extravascular water Protons (SEEP) fMRI, a non-BOLD contrast mechanism.
- BOLD fMRI relies on blood-oxygenation changes.
Purpose of the Study:
- Assess reproducibility of SEEP and BOLD contrast in identifying brain activity areas.
- Compare spatial localization and temporal response characteristics of SEEP and BOLD fMRI.
Main Methods:
- Duplicate fMRI experiments in healthy volunteers at 1.5 T with 1.6 mm resolution.
- Acquired both SEEP (SE-EPI, TE=23 ms) and BOLD (GE-EPI, TE=50 ms) contrast data.
- Estimated response functions for both SEEP and BOLD signals.
Main Results:
- Both SEEP and BOLD identified activity localized to gray matter voxels.
- SEEP activity areas were adjacent to BOLD activity areas with minimal overlap.
- SEEP response peaked ~1 s after BOLD, decayed slower, and lacked post-stimulus undershoot.
- Average BOLD signal change: 3.4±1.2%; SEEP signal change: 1.9±0.5%.
Conclusions:
- SEEP fMRI demonstrates reproducible localization of brain activity, comparable to BOLD fMRI.
- Distinct temporal response functions suggest SEEP reflects a different physiological mechanism than BOLD.
- Findings support SEEP as a valid non-BOLD contrast mechanism for fMRI based on extravascular spin density changes.