FMRI Facility: Acquisition schemes
The anatomical locations of fMRI signal changes are determined by acquiring a separate high resolution MR scan. An inversion recovery 3D FLASH sequence is typically acquired at the end of an fMRI run, allowing fMRI images to be overlaid in arbitrary planes across the 3D anatomical brain image. The scanner is capable of numerous other acquisition sequences for anatomy (e.g. T1 or T2 weighted imaging, diffusion tensor imaging, fast spin echo (or RARE) imaging), as well as perfusion, angiography, and 1H MR spectroscopy. These sequences can be used for research in their own right, or to provide supporting data for fMRI scans. |
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Currently we use a two-shot segmented echo planar imaging (EPI) pulse sequence for most fMRI scans. This sequence is sensitive to neuronal activation via small changes in the magnetic susceptibility of blood vessels when the concentration of oxy- and deoxyhemoglobin changes. This is know as T2* blood oxygenation-level dependent (T2* BOLD) imaging. We are also implementing a spin echo variant of EPI to allow T2 BOLD functional MRI. Like the T2* experiment, spin echo EPI is sensitive to changes in blood oxygenation, albeit by only about 50% of the level. However, its advantage is that signals can be detected from the orbital frontal cortex and temporal lobes of the brain. On T2* contrast images these regions are virtually invisible because of the huge susceptibility gradients created by the venous sinuses and ear spaces.