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
Q
describe the electroencephalography (EEG)
A
- 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
Q
what are the 5 frequencies and describe them
A
- gamma - problem solving, concentration (high frequency)
- beta - busy, active mind
- alpha - reflective, restful (low amplitude)
- theta - drowsiness (high amplitude)
- delta - sleep, dreaming (low frequency)
23
Q
what else can PET measure
A
- 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
Q
describe the event related potentials (ERP)
A
- 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
Q
describe dynamic brain imaging
A
- 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
Q
describe position emission tomogropahy (PET)
A
- 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
Q
describe the functional magnetic resonance imaging (fMRI)
A
- 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
Q
describe the resting state fMRI
A
- 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
Q
describe optical tomography
A
- 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
Q
describe magnetoencephalography (MEG)
A
- 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
Q
MEG is often combine with what
A
- 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
Q
what are the MEG 2 main uses
A
- pre operative brain mapping
- epilepsy surgery
31
Q
research using MEG is increasing in what 4 areas
A
- identifying ASD children
- identifying Alzheimers disease
- psychiatric disorders
- head injuries
32
Q
how to measure neurotransmitters
A
- indirectly through brain functioning (PET, fMRI, MEG, or EEG) - assesses certain receptor densities
- mircodialysis
33
Q
describe microdialysis
A
- used to measure neurotransmitter levels directly within specific regions of the brain or other tissues
33
Q
what is the process of mircodialysis
A
- probe inserted into tissue of interest
- sterile fluid is pumped through the tube which has a semipermeable membrane
- neurotransmitters cross the membrane and are then collected and analyzed
