fMRI terminology
● Structural (T1) images
○ High spatial resolution
○ No temporal resolution (static image)
○ Can distinguish between different types of tissue
● Functional (T2) images
○ Lower spatial resolution
○ Higher temporal resolution (static image)
○ Can relate changes in signal to an experimental manipulation
● Different types of slices:
○ Sagittal: left to the right ear
○ Coronal: nose to the back of the head
○ Axial: top of the head to the bottom
● MRI images are typically acquired in axial slices (one at a time).
● This can performed:
○ Sequential: each adjacent slice consecutively.
○ Interleaved: every other slice, and then fills in the gaps on the second pass
● Together the slices make up a 3D brain volume.
● Field of view (FOV): the dimensions of the exact anatomic region included in a scan.
● Slice thickness
● Voxel size: cubic volume that span the 3D space of the brain
● Matrix size
● An experiment studies many subjects.
● Each subject may be scanned during multiple sessions.
● Each session consists of multiple runs.
● Each run consists of a series of brain volumes.
● Each volume is made up of multiple slices.
● Each slice contains many voxels.
● Each voxel has an intensity associated with it (corresponding time course).
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, Brain imaging methods
Temporal resolution: the ability of an imaging Spatial resolution: the ability of an imaging
method to capture changes over time. In brain method to capture fine details and distinguish
imaging, temporal resolution is a measure of small structures in the brain. In brain imaging,
how quickly changes in brain activity can be spatial resolution is a measure of the smallest
detected and visualized. structures that can be resolved and visualized.
Low temporal High temporal Low spatial resolution High spatial resolution
resolution resolution
Study of slow Study of fast Visual Visualization of small
processes processes details
MRI
● One image
● 3D {x,y,z}
● Structural measure: deals with brain structure.
fMRI
● MRI images over time.
● 4D {x,y,z,t}
● Measures the BOLD-contrast
● Functional measure: deals with cognitive/affective processes.
● Standard anatomy has a resolution of 1mm.
● Applications:
○ Localization (brain mapping): determine which regions of the brain are active during a
specific task.
○ Connectivity: determine how different brain regions are connected with one another.
○ Prediction: use a person’s brain activity to predict their perceptions, behavior, or
health status.
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, fMRI
Pros Cons
● Non-invasive ● A strong magnet can be a dangerous
● There is generally no radioactive tracer thing.
injection involved. ● We are measuring a blood response
● Appealing balance between temporal (derivative of neural activity), not a
and spatial resolution. direct neural response.
● High-spatial resolution compared to ● The responses we record are slow, and
other imaging modalities. take multiple second to unfold
● We cannot research:
○ Moving objects
○ Levels of detail
○ Fast memory, eye movements,
etc. (activation is too short for
fMRI)
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