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Functional Magnetic Resonance Spectroscopy at 7 T in the Rat Barrel Cortex During Whisker Activation
Published on: February 8, 2019
High b-value diffusion-weighted fMRI in a rat forepaw electrostimulation model at 7 T
Joonas A A Autio1, Jeff Kershaw2, Sayaka Shibata3
1Molecular Imaging Centre, National Institute of Radiological Sciences, Chiba 263-8555, Japan; Department of Neurobiology, A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, PO Box 1627, 70211 Kuopio, Finland.
Neuroimage
|April 21, 2011
Summary
Diffusion-weighted functional MRI (DW-fMRI) in rats showed that functional signal changes are likely extravascular SE-BOLD, independent of b-value. Gradient coupling may explain minor signal changes in this model.
Area of Science:
- Neuroimaging
- Magnetic Resonance Imaging
- Physiology
Background:
- Diffusion-weighted functional MRI (DW-fMRI) is a powerful tool for studying brain function.
- Previous DW-fMRI studies have faced limitations in acquisition parameters, particularly in small animal models.
- Understanding the underlying signal mechanisms in DW-fMRI is crucial for accurate interpretation of functional brain activity.
Purpose of the Study:
- To investigate the behavior of spin-echo diffusion-weighted functional MRI (DW-fMRI) signals in a rat forepaw electrostimulation model at 7 Tesla.
- To evaluate the influence of different b-values and echo-times (TE) on stimulation-induced signal changes.
- To explore the potential contribution of gradient coupling to DW-fMRI signal variations.
Main Methods:
- Performed spin-echo DW-fMRI on a rat model with electrostimulation of the forepaw at 7 T.
- Acquired data across five b-values (0–2000 s/mm²) and three echo-times (30–90 ms).
- Conducted resting-state experiments with ultra-small superparamagnetic iron oxide (USPIO) injections to assess gradient coupling effects.
Main Results:
- No strong dependence of stimulation-induced signal changes on b-value was observed across different TEs and time intervals (stimulus-correlated response and post-stimulus undershoot).
- Changes in apparent transverse relaxation rate did not show a clear dependence on b-value.
- Experiments with USPIO suggested that gradient coupling could account for minor DW-fMRI signal changes at 7 T.
Conclusions:
- The observed functional signal changes in this rat model are best explained by a single-compartment signal model, likely representing extravascular SE-BOLD signal.
- The findings suggest that DW-fMRI in small animals can be performed over a broader range of parameters than previously thought.
- Gradient coupling effects may be a significant factor in minor DW-fMRI signal changes at high magnetic fields (7 T).
