Download Brain Imaging Jigsaw KEY

Brain Imaging Techniques KEY
Technique Name
CT (CAT)
Computerized (axial)
tomography
EEG
Electroencephalography
Description
A series of X-rays taken from various angles (the X-ray
beam rotates around the organ being imaged) then
reconstructed by computer to give slices (like in a loaf
of bread) and/or 3D image. Dense tissue is white (poor
X-ray penetration), while soft tissue (more X-ray
penetration) appears in shades of gray.
Selected electrical impulses from neurons are detected
with electrodes (19, typically) on the scalp, amplified
and recorded. EEG activity always reflects the
summation of the synchronous activity of thousands or
millions of neurons that have similar spatial
orientation. EEG traces differ in frequency and
amplitude.
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fMRI
Functional magnetic
resonance imaging
PET
Positron emission
tomography
When brain cells are active, they receive more blood
(and more 02). The iron atoms in oxygenated
hemoglobin behave differently when subjected to a
magnetic field than the iron atoms in deoxygenated
hemoglobin. As freshly oxygenated blood zooms into a
region, the iron atoms distort the magnetic field
enough for the scanner to pick up. A computer uses the
data to construct cross sectional and/or 3D images.
Patient has fMRI before doing a task and then after, and
the images are “subtracted” to show brain activation.
When brain cells are active, they receive more blood
(and more glucose). Labeled radioactive glucose (e.g.
2-deoxy glucose with Fluorine-18 substituted for the
normal OH group) is injected into patient. The
radiolabel gives off positrons, which collide with
electrons. The collisions release 2 gamma rays 180
degrees apart. Detector picks up gamma rays and
calculates where they came from (i.e. the location of
cell that took up the labeled glucose).
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Advantages
Can detect tumors, blood clots
Can monitor progress after
radiation/chemo
Excellent temporal resolution
(results obtained while patient
is sleeping, reading, etc.)
Inexpensive
Machinery is portable
Can help diagnose epilepsy, or
causes of dizziness, blackouts,
etc.
Direct measure of brain’s
electrical activity
Best spatial resolution (3 mm).
No dyes or radioactivity
MRI scanner can be used in
other procedures besides fMRI
Can get results fairly quickly.
Besides showing active brain
areas, also shows tumors,
blood clots, sites of NT release
Colorful and easy to interpret
Patient needs to wait between
tasks.
Fairly good spatial resolution
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Disadvantages
Patient is exposed to
radiation
No information about
function, only structure
Poor spatial resolution (e.g.
not really an imaging
technique)
Only works well on neural
activity in the cortex
Takes a long time to hook a
patient up to EEG (longer
than, for example, fMRI)
Expensive to buy/maintain so
hospitals share one, thus
often long waiting lists
Powerful magnetic field
means patient can’t have
metal implants (no
pacemakers, cochlear
implants, artificial joints,
screws in bones, etc.)
Machines are noisy
Costly and limited access –
radioisotopes with short t ½’s
must be made on site.
Resolution not as good as
fMRI.
Patient is exposed to
radiation.