lecture 4 Flashcards
CAT
PET
MRI
c = X-ray p= function m = high resolution - closest to real.
CAT (CT)
dark = low density
light = high density
put all 6 slices together to get 3D image.
image acquisition - slicing orientation
- ascending: bottom to top
- descending: top to bottom
- interleaved: odd numbers up, then even numbers up. try to get from top to bottom quickest - then fill in gaps.
MRI
static coil - always on. aligns hydrogen atoms in water in body.
radio frequency field pulse sequence:
-transmitter coil: perturbs static field, excited H for it to absorb energy, . once turned off, H re-align = detected & create image.
- receivor coil: reception, image acquisition.
gradient field: spatial info - help tell where image is coming from.
anatomical vs functional imaging
A = MRI, CAT = what brain looks like F= PET = how brain works.
first functional brain experiment
Mosso - tippy scale. patient balanced on it. as they started thinking the scale would tip more towards their head
PET
positron emission tomography. functional technique
-radioactive tracers, O2, Glucose. go to area where there s high blood flow/brain activity. radioactive metabolized = releases positron, attract electron. when they meet = ollide & annihilate each other = give off energy as light.
PET activation
subtraction
averaging
Start with control = no stimulation - image brain. baseline.
activation = activated areas by observing/listening or other cognitive task.
subtraction = subtract baseline/control from stimulation image to get area that is only related to stimulated. average many stimulated within one patient.
averaging = average within one patient, many rounds and later, many patients average of rounds.
fMRI
- BOLD signal
Blood Oxygenation Level Dependent (BBOLD) signal - measure of neural activity.
neurovascular coupling = neurons fire = need more O2 = attain fMRI image that way.
clinical uses of fMRI
brain tumor drug abuse/addiction (long term use, treatment) drug studies (drug on cognition/brain) neuropsychological disorders. (function = distinction among subtypes(
fMRI - working memory, alcoholics
chronic alcoholics = significantly less brain function during working memory use. function can come back within 8 days.
fMRI setup for visual test
- glass/mirror system. project video screen without putting metal screen in MRI machine.
contrast: anatomical
define
the ability to distinguish between 2+ different properties of tissue
functional contrast
define
contrast should really be considered as “contrast to noise”: how effectively can we decide whether a given brain region has property X or property Y
spatial resolution: voxels
different between functional and anatomical
voxel - small cubic prism that is the basic sampling unit of fMRI. typical functional voxel: 3mm^3, typical anatomical voxel: 1mm^3
spatial resolution
temporal resolution
invasiveness
higher field strength = greater resolution in MRI
SR = how fine can we see things in the brain
TR = time, slow or real time.
invasive ness.
higher field strength = greater resolution in MRI. limits how much and how often you can put someone in there.
hemodynamic lag
blood flow to brain is slow, so real time response pictured by fMRI is a little bit slower than the activation of the area.
MRI safety
appropriate risk level : research participant < clinical patient.
x-ray
2D - x-ray passes thru skull onto x-ray sensitive film. absorbed at different degrees by different tissues.
pneumoencephalography
take CSF out, and put air in. as it enters the ventricles = ventricles stand out clearly
angiography
imaging blood vessel. substance absorbs x-ray injected into blood stream.
cortical thickness thru development
frontal cortex = thinner
language area =thicker
