Discussion 21 Flashcards
CT scan
The CT scan, however, coordinates many more than
two images—roughly analogous to our walking to several vantage points to obtain multiple views. X-ray absorption varies with tissue density. High-density tissue, such as bone, absorbs a lot of radiation. Low-density material, such as ventricular fluid or blood, absorbs little. Neural tissue absorption lies between these extremes. CT scanning software translates these differences in absorption into a
brain image in which dark colors indicate low-density regions and light colors indicate high-density regions
X-ray technique that produces a
static three-dimensional image (called a CT scan) of the brain in cross section. (quick and dirty)
cute and look - good for images can not see function
magnetic resonance imaging (MRI),
Preferred because the resolution is significantly better than CT, but it is more expensive, we see a structural anatomical image. The Body is full of protons that act as little magnets. They are all over the place so you need a strong enough magnet that aligns all hydrogen protons in a sample . Apply a radio frequency pulse which will know protons at an angle relative to the magnetic field this will knock them out of alignment. Once out of the alignment, the protons begin to realign (relaxation). Vary as a function of the tissue we are looking at. As they realign they send out an echo. And we use the echo to create the MRI image
DTI ( Diffusion tensor imaging)
is an MRI method that detects the directional movements of water molecules to image nerve fiber pathways in the brain. Water can move relatively freely along the axon but less freely across cell membranes. The direction of this water movement is detected by a coil and interpreted by a computer. DTIs can delineate abnormalities in neural pathways. They are also used to identify changes in fiber myelination, such as the damage that leads to myelin loss in multiple sclerosis.
‘trains and trucks’
Magnetic resonance spectroscopy (MRS)
is an MRI method that
uses the hydrogen proton signal to determine the concentration of
brain metabolites such as N-acetylaspartate (NAA) in brain tissue.
This measurement is especially useful for detecting persisting
abnormalities in brain metabolism in disorders such as concussion.
functional
magnetic resonance imaging (fMRI)
signals which areas are
displaying changes in activity. We can use functional MRI (fMRI) to infer the activity of the brain.
o Functional imaging must provide a spatial depiction of some
process that is at least indirectly related to neural activity.
o That process is change in blood oxygenation related to changes in
regional cerebral blood flow.
“heat map” of the brain
Why measure blood
oxygenation?
- Onset of a stimulus (or cognitive task) changes
local blood oxygenation. - More cellular activity requires more oxygen in
the local area. - Changes in the oxygenation of the blood alter
the magnetic properties of the hydrogen
protons. - We can convert this into a visual signal
more about fMRI
As neurons become active, they use more oxygen, resulting in a temporary dip in the blood oxygen level. At the same time, active neurons increase blood carbon dioxide levels, which signal blood vessels to dilate, increasing blood flow and bringing more oxygen to the area.Oxygenated hemoglobin is diamagnetic - it has no magnetic
effects on surrounding molecules
o Deoxygenated hemoglobin is paramagnetic - it has strong
magnetic effects on surrounding molecules.
Deoxygenated tissue gives of less MR echo because the protons de-phase quickly
PET SCAN
used to study the metabolic activity of brain cells engaged in processing brain functions such as language. PET imaging detects changes in the brain’s blood flow by measuring changes in the uptake of compounds such as oxygen and glucose
pets need energy - they glow more in areas where more activity is present
how does a PET scan work
A PET camera, like the one shown in , is a doughnut-shaped array of radiation detectors that encircles a person’s head. A small amount of water labeled with radioactive molecules is injected into the bloodstream. The person injected with these molecules is in no danger because the molecules used, including the radioactive isotope oxygen-15 ( O), are very unstable. They break down in just a fewminutes and a re quickly eliminated from the body. (Most of the oxygen in air we breathe is the stable O molecule.)
PET Scan advanatges
PET can detect the decay of literally hundreds of radiochemicals, which allows the mapping of a wide range of brain changes and conditions, including changes in pH, glucose, oxygen, amino acids, neurotransmitters, and proteins. PET can detect relative amounts of a given neurotransmitter, the density of neurotransmitter receptors, and metabolic activities associated with learning, brain poisoning, and degenerative
processes that might be related to aging.
PET is widely used to study cognitive function with great
success. For example, PET confirms that various brain regions
perform different functions.
Disadvantage to PET scans
A significant limitation of PET is that radiochemicals, including the so-called radiopharmaceuticals used in diagnosing human patients, must be prepared in a cyclotron quite close to the scanner because their half-lives are so short that transportation time is a severely limiting factor. Generating these materials is very expensive
Microdyalisis
which can determine the chemical constituents of extracellular fluid, is widely used in the laboratory. The technique has found clinical application over the past 15 years. A catheter with a semipermeable membrane at its tip is placed in the brain, as illustrated in A fluid flow through the cannula and passes along the cell membrane.
Simple diffusion drives extracellular molecules across the membrane along their concentration gradient
what are four protocols when using animals?
- The use of animals in research, teaching, and testing is
acceptable only if it promises to contribute to the understanding
of environmental principles or issues, fundamental biological
principles, or development of knowledge that can reasonably be
expected to benefit humans, animals, or the environment. - Optimal standards for animal health and care result in enhanced
credibility and reproducibility of experimental results. - Acceptance of animal use in science critically depends on
maintaining public confidence in the mechanisms and processes
used to ensure necessary, humane, and justified animal use. - Animals are used only if the researcher’s best efforts to find an
alternative have failed. Researchers who use animals employ
the most humane methods on the smallest number of
appropriate animals required to obtain valid information
