Ch1 - Intro to fMRI Flashcards
fMRI
(functional magnetic resonance imaging)
neuroimaging technique using MRI to investigate functions over time
- functional connectivity, individual differences in personality, genetic differences, neurological & psychiatric disorders
static magnetic field
magnetic field at center of MRI scanner (in tesla(T))
- ranges from 1.5T - 7T+
pulse frequence
series of changing magnetic field gradients & electromagnetic pulses that allow to create images sensitive to particular physical properties
- e.g. the frequency of hydrogen to image structures in humans
structural neuroimaging
class of research techniques that create image of the brains physical structure
- e.g. location and distribution of tissue types
functional neuroimaging
class of research techniques that create images of functional properties
- aspects of cognition, functions of distributed networks
PET
(positron emission tomography)
functional neuroimaging technique that creates images based on movement of injected radioactive tracer
- pro: metabolic rates (e.g. neurotransmitters)
- con: invasiveness, slow speed of image acquisition, radioactive isotopes
EEG
(electroencephalography)
measurement of electrical properties of the brain
- rapid changes: allows to detect timing of brain processes
MEG
(magnetoencephalography)
noninvasive measure of small changes in magnetic fields caused by electical activity of neurons
- potentially high spatial and temporal resolution
TMS
(transcranial magnetic stimulation)
technique to temporarily stimulate brain regions to disrupt function
electromagnetic coil placed close to scalp, passing current generates magnetic field and produces localized electrical currents
Contrast
1) intensity difference between quantities measured by imaging system
2) physical quantity being measured (e.g. T1 contrast)
3) statistical comparison of activation evoked by 2 (or more) experimental conditions in order to get hypothesis
contrast-to-noise ration
(CNR)
magnitude of intensity differences between different quantities divided by variability in measurement
- contrast expressed in relation to background variations
functional contrast
type of contrast that provides information about a physiological correlate of brain function
- e.g. changes in blood oxygenation
- PET studies: based on emitted radioactive decay particles
spatial resolution
ability to distinguish changes in image across spatial locations
pixel
smallest element that can be resolved in 2D space
voxel
basic sampling unit of MRI
3D volume element
- in humans: 1mm (MRI) & 3mm (fMRI)
sampling rate
frequency in time with which a measurement is made
- rate of acquiring images
temporal resolution
ability to distinguish changes in signal across time
- in fMRI: 1 brain volume/1-2 sec
functional resolution
ability to map measured physiological variation to underlying mental processes or behaviors
oscillating magnetic field
magnetic field whose intensity changes periodically over time
- in MRI: radiofrequency fields = frequency range of radio waves (MHz)
magnetic resonance
absorption of energy from magnetic field that oscillates at a particular frequency
- frequency of oscillating field matched to spin frequency of atomic nuclei
resonant frequency
frequency of oscillation that provides the maximum energy transfer to system
transmitter coil
electromagnetic coil that generates oscillating magnetic field at resonant frequency of the atomica nuclei within sample
detector coil
electromagnetic coil that measures energy emitted back to the environment after initial absoption by sample
nuclear induction
magnetic resonance effect (s. magnetic resonance)
but termed by other guy named Bloch
nuclear magnetic resonance
(NMR)
measurable changes in magnetic properties of atomic nuclei induced by application of oscillating magnetic field at resonant frequency of the nuclei
spatial gradiants
magnetic field whose strength varies systematically over space
EPI
(echo-planar imaging)
technique that allows collection of an entire 2D image by changing spatial gradients rapidly following a single excitation pulse from transmitter coil
ionizing radiation
electromagnetic radiation with sufficient energy to break chemical bonds
- negative health connotations
- does NOT occur during MRI
BOLD contrast
(Blood-oxygenation-level-dependent contrast)
difference in signal on T2-weighted images as a function of the amount of deoxygenated hemoglobin
- metabolic correlate of neuronal activity (indirect measure)
