MRI/fMRI Flashcards
Co-registered images
○ Combination of structural (MRI) and functional (fMRI) imaging
○ Functional imaging alone is not an image of the brain. Instead it is an “image” of
§ PET, fMRI= oxygenated blood
§ MEG= magnetic fields
EEG= electric fields
Cyclotron
Produces radioactive isotope used in PET
Repetition time (TR)
Time it takes to obtain all of the slices in a volume
The amount of time that exists between successive pulse sequences applied to the same slice
Diffusion Tensor Imaging (DTI):
• Measures white matter organization
® White matter is important for connection between brain regions
Based on limited diffusion of water molecules in axons
○ Water molecules trapped in axons tend to diffuse in some direction, but not others
§ Water is free to travel down axon, but can’t travel out of axon by the fatty membrane
i.e. Learning to play the piano affects development of white matter fibers
BOLD Response
Deoxy Hb in the blood has strong paramagnetic properties, creates distrotion is local magnetic fields
Blood Oxygen Level Dependent Contrast
Changes in blood oxygenation
Drift
The longer the MRI scanner is on, the more intense of a signal it picks up
® Signal increases with time
Increase in activity might actually just be due to the fact that the scanner has been on for a long time
Computerize Tomography:
• CT scans are constructed based on amount of X-ray absorption in different tissues
• Amount of absorption related to tissue density
○ Bone absorbs the most, CSF absorbs the least
○ Brain matter has intermediate absorption
• Can’t distinguish between gray or white matter
Can’t be adapted for functional imaging purposes
fractional anisotropy
Measure of the extent to which diffusion takes place in some directions more than others
When many axons are arranged together, can quantify the effect of DTI with MRI using fractional anisotropy
Assumption of pure insertion/pure deletion
§ Adding a different component to a task does not change the operation o other components
§ i.e. Want to identify brain region associated with word recognition
Both tasks involve visual processing, one of the tasks has added component of word recognition
Assumes that the word recognition does not affect visual processing
Problem of Interactions
Effect of one variable on another
Adding a new component can interact with other components
Efference copy
Motor signal used to predict sensory consequences of an action
Family Wise Error (FWE)
○ Can also divide P value (0.05) by number of tests (voxels)
§ Problem- each voxel is not independent
Neighbouring voxels have similar activity, especially when smoothed
False Discovery Rate (FDR)
○ Way for correcting for many statistical comparisons based on the number of tests being conducted
Generate thousands of brain images and select a threshold (significance level) based on random datasets
