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neuroscience > Brain Imaging > Flashcards

Brain Imaging Flashcards

1
Q

How does CT work?

A

It is a rotating X-ray beam that takes images of the brain from several directions

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2
Q

What is CT useful for visualizing?

A

bony anatomy, acute hemorrhage or stroke, elements w/ high atomic number will show up better ( calcium, iron, iodine, barium, lead)

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3
Q

What are some advantages of CT?

A

it is faster and cheaper than MRI and can be used as an initial screening/ assessment tool.

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4
Q

What are some disadvantages of CT compared to MRI?

A

use of x-ray ( radiation), and less contrast btw. soft tissues, lower spatial resolution

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5
Q

A hypodense i.e. dark structure on CT could indicate ( list 2 things)?

A

edema , infarction

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6
Q

A hyperdense i.e. bright structure on CT could indicate ( list 3 things)?

A

calcification, hemorrhage, bone trauma

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7
Q

How does MRI work?

A

it uses radio frequency waves to produce high resolution images of the brain and spine.

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8
Q

What are advantages of MRI?

A

there is no radiation, high resolution allows for visualization of soft tissue, can visualize anatomy: gray matter, white matter, CSF, it can identify a wide range of pathological processes

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9
Q

Explain the physics of how MRI works?

A

it uses the spin of hydrogen atoms ( our body is 63% hydrogen atoms) which creates a magnetic field which aligns with the external magnetic field of the MRI leading to a net magnetization of the tissue.

A radio frequency (RF) pulse is applied to tip protons away from the MRI field and then the RF is turned off,

Protons will realign with the MRI field and emit energy as the RF pulse decays, the emission rate will depend on tissue composition and allows for a gray scale picture to be formed based on the strength of the RF signal emission.

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10
Q

What is a rapid repetition of radio frequency pulse good for visualizing?

A

gray white contrast

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11
Q

what is infrequent repetitions of RF pulse good for visualizing?

A

lesions,it enhances signal from water which is usu. increased in pathological conditions.

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12
Q

What can MRI help diagnose ( name 6 things)?

A

inflammatory disease ( Multiple sclerosis)
Neoplastic disease( tumors)
Epilepsy
Cerebrovascular disease ( stroke)
degenerative disorders ( cortical atrophy)
demyelination ( on MRS)

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13
Q

How does an increase from 1.5T to 3T change the image of an MRI or changing from T1 weighted to T2 flair?

A

It enhances the contrast

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14
Q

What does Magnetic Resonance Spectroscopy ( MRS) allow us to study and how?

A

it allows us to study the chemical structure of the brain by separating out chemical mixtures in the brain: N-acetlyaspartate, choline, creatine, lactate.

it also allows us to figure out the [chemicals] and ratio of chemicals.

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15
Q

How does MRS work ?

A

an RF pulse is applied after which each chemical component emits a specific frequency

the signals are analyzed to generate an NMR spectra and each chemical has a specific peak

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16
Q

Where is N-acetlyaspartate located in the body and what is it a marker of on MRS?

A

it is in the cell bodies and the dendrites

therefore it is neuronal marker

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17
Q

What is choline involved in and what is it a maker for on MRS?

A

cell membrane synthesis and degradation

it is a marker for demyelination.

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18
Q

What is creatine a marker for on MRS?

A

it is a glial marker

19
Q

What is lactate are maker for on MRS?

A

it is found after ischemic events

20
Q

What does diffusion weighted imaging and diffusion tensor imaging allow us to visualize and measure?

A

the integrity of white matter tracts in the brain.

21
Q

How does diffusion weighted image work?

A

it aligns in 3 direction to estimate the trace of the diffusion tensor i.e. the average diffusivity which is a measure of edema.

22
Q

what is anisotropy and what type of imaging uses this?

A

measurement of water diffusion along different orientations within axons.

Diffusion Tensor Imaging uses this

23
Q

In DTI it is assumed that cell membranes and myelin do what to water flow?

A

restrict water flow through the axon so that water flows in an organized manner along the longitudinal and perpendicular orientations of the axons.

24
Q

What does a smaller coefficient in DTI mean?

A

less diffusion along the longitudinal axis, and presumably more water diffusing in many different areas.

25
Q

what does radial diffusicivity represent in DTI?

A

diffusion along perpendicular axes of the voxel ( image element) in both directions.

IT is thought to represent the integrity of myelin.

26
Q

In DTI what does fractional anisotropy tell us?

A

it is calculated based on both axial and radial diffusivity and represents overall direction of water, and is thought to reflect the overall organization and integrity of the axon.

27
Q

what is a T2 and G+ used to distinguish on MRI?

A

It distinguishes btw stroke and a lesion

28
Q

What does functional MRI allow us to do?

A

take images of the brain while the pt is performing cognitive tasks in the MRI scanner.

29
Q

What are advantages of fMRI?

A

it allows us to view brain function in vivo so that we can understand:

  • nerual sys that make performance of cognitive tasks possible
  • changes in brain fnc associated w/ disorders and agin
  • sites of neural reorganization following stroke or injury.

it has shown that the brain is much more plastic than previously thought

30
Q

what are the disadvantages of fMRI?

A

2x less resolution than MRI b/c it must be applied quickly ( both spatial and temporal resolution limitations)

31
Q

how does fMRI work?

A

it measures the good-oxygen-level dependent signal with MRI and compares the signal during base line and experimental conditions.

b/c blood flows to the area of increased neuronal activity it allows us to me sure how much a task is stimulating neuronal activity and helps us localize the regions of activity

32
Q

how does positron emission tomography work?

A

it uses cyclotron to prepare radioactive isotope tracers which is incorporated into a biologically active molecule ( eg. oxygen, glucose, dopamine receptor/transporter)

the tracers are injected and bind to physiological sites and scanner images the positron-emitting tracer when it decays

33
Q

What are advantages of PET?

A

it can be useful in grading brain tumors and determining a prognosis

unlike Ct and MRI it can distinguish radiation necrosis from tumor recurrence

34
Q

What measurements can PET provide?

A

perfusion, metabolism, neurotransmitter integrity

35
Q

for declarative memory what brain structure are activates for adult, adolescents, and children as shown on fMRI? and what does this indicate about age and memory?

A

the mesial temporal lobe for all three populations

for adults and adolescents the prefrontal cortex was also activated

this indicates that the prefrontal cortex has a prolonged maturational trajectory ( takes long to develop)

36
Q

what structure is activated during mad, sad, happy, and fearful or neutral emotional states as shown by fMRI?

A

the amygdala is activated in all emotions.

37
Q

Which imaging tool issued greatly in the management and diagnosis of Alzheimer’s?

A

PET as it can be used to visualize ypometabolism assoc w/ clinical symptoms

38
Q

What does fMRI show about APOE-4 allele carriers?

A

that during memory tasks their brain activation is increased but 2 years after their baseline brain activity correlates with a decline in memory.

39
Q

Why must you ask a person to count in their native language when performing an fMRI during surgery?

A

because their language center for english might be in another area, their primary language center is their overall language center so you want to identify this area.

40
Q

What are some of the disadvantages of MRI?

A

the long study duration,
person can’t have ferromagnetic devices or electronic devices like certain stents,
claustrophobic

41
Q

what are the advantages of PET?

A

functional imaging,

physiological variables can be determined

42
Q

what are disadvantages of PET?

A

radiation, costly, limited access to tracer production

43
Q

What disorders can PET help diagnose?

A

physchiatric
addictive,
degeneratice disorders
epilepsy

neuroscience (32 decks)

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