Neuroimaging Techniques Flashcards
1
Q
what are the 4 tools used in x-rays
A
- conventional radiography
- pneumoencephalography
- angiography
- computed tomography (CT)
2
Q
what are the 3 tools used in magnetic resonance imaging (MRI)
A
- structural MRI (sMRI)
- diffusion tensor imaging (DTI)
- magnetic resonance spectroscopy (MRS)
3
Q
why is conventional radiography Not primary method for visualizing brain abnormalities
A
- because you unable to locate and distinguish between white/grey matter in the scans
3
Q
describe conventional radiography
A
- x rays pass through the skull or body
- a showdown image shows locations of different tissues
- skull for fractures
- brain for gross abnormalities
- physical fractures
4
Q
describe pneumoencephalography
A
- small amount of CSF is removed from spinal cord and replaced with air
- x ray is taken as the air moved up the spinal cord and into the brain
- very painful and invasive
5
Q
why use pneumoencephalography
A
- able to tell us the relationship between large structures and abnormalities
1. hydrocephalus
2. mass lesions
3. atrophic states of the brain tissues.
6
Q
describe angiography
A
- substance that is absorbed by x rays is injected into the blood stream
- method for imaging of the blood vessels in the brain
- tells us how the blood vessels are moving the blood
- stroke and any heart diseases
7
Q
describe computed tomography (CT scans)
A
- narrow x ray beam that goes through the same object at many angles
- 3D image of the brain
- can localize brain tumours and lesions as they come up darker in the image
- skull is white and ventricles are dark
- UNABLE to distinguish between white and grey matter; appearance looks similar
- NOT harmful; injected at small doses
8
Q
describe the magnetic resonance imaging
A
- large magnet and a radiofreqency pulse that generates a signal through the brain that produces an image
- hydrogen atoms nucleus consists of a single proton that align in the magnet (all moving in the same direction)
- proton density varies in different brain tissues; electrical currents differ
- CAN see the difference between grey and white matter
- extremely magnetic and powerful
9
Q
discuss about the MRI T and
A
- higher the number = the stronger the strength and more detailed the image will be
- 1.5T is the most common and most widely available
- 7T great for cutting edge crisp image but not widely available
10
Q
what is the difference between T1 weight and T2 weight
A
- T1w is great for anatomical detail
- T2w is great for detecting fluid filled structures and edema
11
Q
what is the difference between MRI and CT scans
A
MRI
- abnormal tissue based
- uses strong magnetic fields
- inflammation
- torn ligaments
- nerve and spinal problems
- soft tissues
CT scans
- physical bones and skull based
- uses x rays
- bone and joint issues
- blood clots
- organ injuries,
12
Q
describe diffusion tensor imaging (DTI)
A
- detects the movements of water molecules to create virtual images of brains nerve fiber pathways
- water molecules in nerve fibers follows the tract orientation moving in the direction of its longitudinal axis
- pathways between regions
- connectivity and tracts
- magnetic field used to get this type of image
- e.g. broca vs wernickes area
13
Q
why use DTI
A
- can study the structural connectivity between different brain regions
- understand neural pathways
- can detect abnormalities in neural pathways
- identify changes in fiber myelination
- has low signal to noise ratio
14
Q
what are the 2 outcomes found in DTI
what do we want?
A
- fractional anisotropy (FA)
- mean diffusivity
we want high FA value and low MD value
15
Q
mean diffusivity (MD)
A
reflects the average magnitude of water diffusion and displacement
15
Q
fractional anisotropy (FA)
A
reflects the directionality of water diffusion and displacement
16
Q
describe magnetic resonance spectroscopy (MRS)
A
- method used to examine development, function, and disease
- varies the radio frequency used for aligning the hydrogen protons
- has limited spatial resolution and requires high concentration of the metabolite of interest to be reliably detected
17
Q
what can MRS detect (3)
A
- abnormalities in brain metabolism
- brain cell loss in degenerative disease
- loss of myelin in demyelinating disease such as MS
17
Q
what are the 2 tools used in brains electrical activity
A
- electroencephalography (EEG)
- event related potentials (ERPs)
18
Q
what are the 3 groups of functional techniques
A
- brains electrical activity
- dynamic brain imaging
- brain’s magnetic activity
19
Q
what are the 3 parts of dynamic brain imaging
A
- position emission tomography
- functional magnetic resonance imaging (fMRI)
- optical tomography
20
Q
what is the one tool used in brain’s magnetic activity
A
magnetoencephalograohy (MEG)
21
Q
what are the 5 reasons why our brain patterns may change
A
- concentrated
- sleep
- sleeping
- resting
- active
22
describe the electroencephalography (EEG)
- recording the continuous raw brain activity from the neurons
- measuring random ongoing negative and positive electrical activity
- problem is that this contains artifacts (unwanted noise, effects from activities such as chewy) and can pick up other signals which can be a problem
23
what are the 5 frequencies and describe them
1. gamma - problem solving, concentration (high frequency)
2. beta - busy, active mind
3. alpha - reflective, restful (low amplitude)
4. theta - drowsiness (high amplitude)
5. delta - sleep, dreaming (low frequency)
23
what else can PET measure
- used to measure brain changes not involving active tasks
- resting PET captures the baseline or 'default' state of the brain without influence of task related brain activity
- injection of tracer, which binds to amyloid plaques, PET scanner detects these tracers, then image is reconstructed
24
describe the event related potentials (ERP)
- are changes in EEG readings in response to a specific stimulus
- not easy to detect because the signal is mixed with other EEG signals from the brain
- stimuli are presented multiple times in order to average out the noise in the signal
- consist of positive and negative deflections that represent cognitive or sensory processing
- deflections are time locked activity to a specific stimulus
24
describe dynamic brain imaging
- measures brain activity through blood, oxygen, and glucose
- measure cognitive activity because stimuli will change the amount of blood, oxygen, and glucose in certain brain regions
- includes PET, fMRI, and optical tomography
25
describe position emission tomogropahy (PET)
- measures metabolic activity in the brain by INDIRECTLY detecting changes in blood flow
- person is injected with radioactive tracer which is then measured by the machine
- mostly used to examine neurodegenerative disorders because of the metabolism, glucose and proteins
- not structure based, but it does look at the glucose and protein, even at the binding sites to determine what diseases is occurring
- machine measures radioactive tracer, releases chemicals and the machine picks this up and brightens up the image that is being impacted
- PET cameras image multiple parallel brain slices simultaneously
- can detect the decay of hundreds of different tracers
- increase activity = more oxygen levels, indirect measure, variety of tracers to examine targeted region
- activities minus resting state equals increase in glucose/oxygen in regards to that brain region connected to that brain function
26
describe the functional magnetic resonance imaging (fMRI)
- accurately measures change in magnetic properties in the blood, when the brain becomes active
- blood oxygen level dependent
- provides an index of the brain's relative activity
26
describe the resting state fMRI
- collected when people are asked to look at a fixated location to keep their eyes open
- various brain regions share correlated activity even when at rest
- waves of activity form recurring elements or motifs indicating functional connectivity (inherent functional relationships) among cortical systems
- can determine connectivity issues
- series of wavelengths and cycles
- activities and regions activating together in relation to their function
-
27
describe optical tomography
- operates on the principle that an object can be reconstructed by gathering light that was transmitted through it
- reflected light infers blood flow
- amount of light absorption will reflect the brains oxygen consumption
- light penetrates through the layers
- measures oxygenated blood during a cognitive tasks that demonstrates activation in a certain region
- determines whether the blood is oxygenated or not
- light may not penetrate enough to hit the subcortical structures or grey matter
- light / 3D image / internal structures of the Brian
- can NOT tell us the functions or problems related to that brain region
28
describe magnetoencephalography (MEG)
- measures magnetic field from neuronal activity
- magnetic sensors detects this activity and maps it onto specific brain regions
- MEG provides timing and some spatial information
- can be used to observe brain activity and brain responses
- electrical voltages converted through currents through neurons = high timing resolution
- magnetic activity; sensory coils
29
MEG is often combine with what
- MRI to provide MSI or magnetic source imaging
- shows activation in certain areas of the brain; allows us to cut that specific part without damaging the other areas
- brain tissue inside tutors = notices any functional changes that can eventually damage the surrounding areas
30
what are the MEG 2 main uses
1. pre operative brain mapping
2. epilepsy surgery
31
research using MEG is increasing in what 4 areas
1. identifying ASD children
2. identifying Alzheimers disease
3. psychiatric disorders
4. head injuries
32
how to measure neurotransmitters
1. indirectly through brain functioning (PET, fMRI, MEG, or EEG) - assesses certain receptor densities
2. mircodialysis
33
describe microdialysis
- used to measure neurotransmitter levels directly within specific regions of the brain or other tissues
33
what is the process of mircodialysis
1. probe inserted into tissue of interest
2. sterile fluid is pumped through the tube which has a semipermeable membrane
3. neurotransmitters cross the membrane and are then collected and analyzed
