MOD B Flashcards
What’s a T1 image?
It is a type of magnetic resonance imaging (MRI) based on longitudinal relaxation time, how quickly protons realign with the main magnetic field after being excited by a radio frequency coil, high contrast between different tissue types, gray matter dark white matter bright, ideal for anatomical imaging, used for detecting lesions, tumors, brain atrophy
What’s a T2 image?
It is a type of MRI based on transverse relaxation time, how quickly protons lose coherence in the transverse plane due to interactions between neighboring protons, sensitive to water content of tissues, so gray matter bright white matter dark, CSF very bright, used for lesions with high water content such as strokes or infections; T2*: based on dephasing of protons caused by microscopic inhomogeneities in the magnetic field, often due to the presence of deoxygenated hemoglobin, which is the foundation of the BOLD contrast used in fMRI, it is highly sensitive to changes in oxygen levels in the blood, provides functional information rather than anatomical details, it is used for functional imaging to study brain activity
What’s T2* image?
It is a type of MRI based on dephasing of protons caused by microscopic inhomogeneities in the magnetic field, often due to the presence of deoxygenated hemoglobin, which is the foundation of the BOLD contrast used in fMRI, it is highly sensitive to changes in oxygen levels in the blood, provides functional information rather than anatomical details, it is used for functional imaging to study brain activity
Which are the main types of experimental design a in fMRI?
Categorical designs (Subtraction and Conjunction)
Parametric designs (Linear and Non-linear)
Factorial designs (Categorical and Parametric)
Psychophysiological interactions
What is the subtraction design?
Direct comparison of two conditions are assumed to differ only for one property. If this assumption is correct, any change in the dependent variable can be very confidently attributed to the change in that property. So we are assuming that we can purely insert or eliminate one ingredient from a given task without altering the rest.
What is the conjunction design?
Conjunction analysis is a way to minimize the the pure insertion problem by isolating the same process over and over by two or more separate independent comparisons and expecting the effects of each of these comparisons for commonalities.
What is a parametric designs?
A design that vary a stimulus parameter of interest over a continuum of values in multiple steps that are more than two and relating the bond signal to this parameter variation.
Parametric designs can be:
- Linear: as I experimentally increase linearly an intensity of a given feature of a stimulus, are there regions in the brain that get activated in the same linear fashion as my parametric manipulation of my independent variable?
- Non-linear: quadratic relationship, the U-shape or inverted U-shape. That area of the brain doesn’t care about that stimulus feature if it is too low in its intensity or too high in its intensity, but it cares only in the middle range of my manipulation.
