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Neuroscience > Week 1 - Brain Imaging > Flashcards

Week 1 - Brain Imaging Flashcards

1
Q

how does X-ray computerized tomography work? (AKA CT or CAT Scan)

A

rotating X-ray beam images brain from several directions

  • rate of attenuation varies by tissue, and detectors on opposite side of source pick up rate of weakness
  • info reconstructs 3D image as patient is mvoed through scanner slowly
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2
Q

clinical applications of CT, advantages, and disadvantages

A

enhances visualization of bony anatomy, acute hemorrhage/stroke, and elements with high atomic numbers (bright), edema, infarction (dark)

  • pro: faster/cheaper than MRI, and used as initial screening and assessment tool
  • con: uses X-ray, less contrast differences between soft tissue, and lower spatial resolution (several mm in CT vs 1 mm in MRI)
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3
Q

what do infarcts look like in CT VS MRIs?

A

CT: only slight difference in gray matter, but hard to differentiate between gray and white
MRI: much easier to see change

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4
Q

what are CTs good at revealing?

A

hemorrhages/trauma (TBI)

generalized atrophy

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5
Q

how does anatomic MRI work?

A

based on principles of nuclear magnetic resonance

-produces high resolution images of brain and spine

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6
Q

clinical applications of MRI, advantages, and disadvantages

A

high resolution and detailed visualization of soft tissue

  • visualizes anatomy (gray and white matter, CSF)
  • identifies wide range of pathological processes
  • pro: no radiation (uses radio waves)
  • con: long study duration, no herromagnetic or electronic devices, and claustrophobic
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7
Q

what are MRIs good at revealing?

A

neoplasms, demyelination (MR spectroscopy), degenerative disorders (cortical atrophy), inflammatory disease (MS), epilepsy, cerebrovascular disease (stroke)

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8
Q

how do MRIs work?

A

spinning H+ placed in large, external magnetic field aligns with or against EMF, wobbling at a proportional frequency

  • slightly more H+ will align with EMF, leading to net magnetization
  • detect with radiofrequency pulse that tips H+ away from direction of magnetization
  • when RF is turned off, H+ realign with EMF, and the energy absorbed from RF will decay, emitting an RF signal picked up with antennae and decoded into images with Fourier algorithms
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9
Q

how is the digital MRI image constructed?

A

spin of H+ decays, emits RF signals at different rates depending on composition of tissue
-each pixel is encoded with a numerical index that represents relative strength of signal, and assigned grayscale value (higher = darker)

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10
Q

what are pulse sequences in terms of MRIs?

A

clinician can vary timing of RF pulse which accentuates the tissue he/she is most interested in
-rapid repetitions of RF pulse enhances gray-white contrast

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11
Q

what are lesions best imaged with?

A

infrequent repetitions of RF pulse

-enhances signals from water, which is increased in pathological conditions

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12
Q

what are the necessary equipment for MRI?

A

magnet
gradient coil
RF coil

usually use 3 tesla, but increased strength will increase contrast

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13
Q

how is MRI imaging of a tumor manipulated?

A
  1. 5 T and 3T scanners at T1 weighted can’t show tumor (although increasing clarity)
    - best with 3T scanner at T2 flair
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14
Q

what does magnetic resonance spectroscopy let us do?

A

study chemical structure of brain

  • separates out components of chemical mixtures in brain (N-acetylaspartate, choline, creatine, lactate)
  • derives concentrations and ratios of chemicals (metabolites)
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15
Q

how does MRS work?

A

an RF pulse is applied, after which each chemical component/metabolite emits specific frequency

  • signals analyzed with Fourier transforms to generate NMR spectra of multiple peaks
  • the higher the concentration, the larger the peak
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16
Q

what are the following MRS metabolites markers for?

  • NAA (N-acetylaspartate)
  • choline
  • creatine
  • lactate
A
  • NAA: located in cell bodies and dendrites as neuronal marker
  • choline: cell membrane synthesis and degradation; marker for demyelination
  • creatine: glial marker
  • lactate: found following ischemic events

but even if there’s no peak, it doesn’t discount disease

17
Q

what does diffusion weighted/tensor imaging let us do?

A

visualize and measure integrity of white matter tracts in the brain

18
Q

what gradients are applied in diffusion weighted images? what is the best estimate of rate of diffusion?

A

3 gradient directions are sufficient to estimate trace of diffusion tensor (average difusivity)
-intensity of each image element (voxel) reflects best estimate of rate of diffusion at that location

19
Q

what is anisotropy and what is it used for?

A

measurement of water diffusion along different orientations within axons, used in diffusion tensor imaging

  • can use up to 64 directions, but faster with just 3
  • flow is restricted by myelin
20
Q

what does functional MRI (fMRI) allow us to do?

A

acquire images of brain while patients are performing cognitive tasks in MRI scanner
-shows brain is more plastic than previously thought

21
Q

what are advantages of fMRI?

A
  • measure brain functioning in vivo, thus understanding neural systems that make performance of cognitive tasks possible
  • understand changes in brain function associated with disorders and aging
  • understand sites of neural reorganization following stroke or injury
22
Q

how does fMRI work?

A

measure blood-oxygen-level dependent (BOLD) signal with MRI during baseline and experimental conditions, then compare

  • neural activity increases when we process information, which causes increased in blood flow
  • leads to changes in local cerebral blood volume, measurable via paramagnetic oxyhemoglobin
  • able to see how much a task is stimulating neural activity in what regions of brain neural activity
23
Q

how to analyze fMRI data (how do experimental and control conditions differ?)

A

experimental: task comprised of specific cognitive variable of interest
control: task comprised of all features of experimental task EXCEPT specific cognitive variable of interest
- subtract magnitude of neural activation during control from experimental
- generate “activation maps” superimposed on brain images

24
Q

how does visual direction compare in controls VS velo-cardial facies syndrome?

A

much less stimulation in fMRI

25
Q

what are limitations of fMRI?

A

limited temporal and spatial resolution

-relation between neuronal activity, blood flow, and fMRI signals has not been definitively established

26
Q

what is PET (positron emission tomography)?

A

use of cyclotron to prepare radioactive isotope tracers

  • tracer is incorporated into biologically active molecule (internal source)
  • injection of tracers, which then binds to physiological sites
  • scanner images positron-emitting tracer upon its decay
27
Q

what disorders does PET measure?

A

psychiatric/addictive/degenerative disorders, epilepsy

28
Q

what are PET advantages and disadvantages?

A

pro: functional imaging, physiological variables can be determined
con: ionizing radiation, costly and limited access, troublesome tracer production, poor spatial resolution

29
Q

applications of PET

A
  • blood flow and perfusion
  • metabolism (resting and task dependent)
  • -FDG traces glucose uptake (reflects synaptic activity), O traces O2 uptake
  • ligands/neuroreceptor imaging
  • -radiotracers bind to pre/postsynaptic neuroreceptors (dopamine synthesis and reuptake)
  • -advanced pharmocological treatments
30
Q

what are 3 applications of immaging modalities?

A

normal brain development
Alzheimer’s disease
image guided neurosurgery

31
Q

how does gray and white matter differ between males and females

A

males have more of both types of matter

-gray matter decreases while white matter increases with age

32
Q

what happens when fMRI maps emotions?

A

all 4 emotions (happy, sad, fearful, angry) caused amygdala activation

33
Q

what happens when fMRI maps declarative memroy?

A

children, adolescents, and adults activated mesial temporal lobe structures involved in memories

  • adolescents and adults activated prefrontal cortex (increased memory of scenes)
  • indicates that PFC regions important for memory formation have prolonged maturational trajectory
34
Q

what does PET show in terms of Alzheimer’s disease?

A

gray matter loss
-used in management, since hypometabolism in various brain regions has been associated with severity of clinical symptoms

35
Q

what is the APOE-4 gene?

A

genetic risk factor for Alzheimer’s disease

  • carriers have increased brain activation during memory tasks
  • degree of baseline brain activity is correlated with memory decline
  • shown via Bookheimer study

Neuroscience (39 decks)

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