L10: Brain Imaging

Question 1

Does CT use xrays?

Answer 1

Yes

Question 2

What are the advantages and disadvantages of using CT?

Answer 2

Pros: faster, less expensive than MRI, can be used as initial screening & assessment tool
Cons: use of x-ray; less contrast differences btw soft tissues

Question 3

What can CT scan be used for?

Answer 3

infarction
tumors
calcification
hemorrhage
bone trauma
TBI

Question 4

What can MRI better detect than CT?

Answer 4

MRI provides high resolution of soft tissues; can differentiate btw gray & white matter, and can identify a wide range of pathologies

Question 5

What does MRI use instead of x-rays?

Answer 5

use radiofrequency waves

Question 6

Briefly describe the physics behind MRI

Answer 6

MRI measures the magnetic field that spin of H+ atoms produces
To detect magnetic fields better,
1 - apply radiofrequency pulse (RF)to move H+ away from direction of magnetization
2 - turn radiofrequency pulse off, H+ re-aligns with magnetic field
3 - energy absorbed by H+ decays, emitting radiofrequency signal that is picked up & decoded into images

Question 7

How can one enhance gray-white matter contrast with MRI?

Answer 7

manipulating timing of radiofrequency pulses (e.g. rapid repetitions of RF pulse) enhances gray-white matter contrast

Question 8

Magnetic resonance spectroscopy is good at separating chemical mixtures in brain. Using RF pulse can cause emissions of different chemicals as seen in peaks. Size of peaks indicate relative concentrations of chemicals. What is N-acetyl aspartate (NAA) a marker for? Choline? Creatine? Lactate?

Answer 8

NAA  = cell bodies & dendrites
Choline = marker for DEMYELINATION
Creatine = glial marker
Lactate = found in post-ischemic events

Question 9

List the 3 things we said in class that MRI can detect

Answer 9

1 - lesions
2 - inflammatory diseases
3 - tumors -can use diff strength, contrast and depending on diff scanners can get diff results

Question 10

What does magnetic resonance spectroscopy enable us to see?

Answer 10

• study CHEMICAL structure of brain

- separates out chemical mixtures in brain

Question 11

What can magnetic resonance spectroscopy detect?

Answer 11

• inflammatory disorders like Multiple sclerosis (lots of Choline
• tumor vs normal tissue

Question 12

Diffusion weighted imaging & diffusion tensor imaging

Answer 12

• visualize and measure integrity of white matter tracts in brain
• intensity of each image element = rate of water diffusion (anisotropy)
• *axons restrict flow of water so if imaging detects higher rate of water diffusion, then problems wrong with the axons (e.g. demyelination)

Question 13

Anisotropy is used in diffusion weighted imaging & diffusion tensor imaging. What is it?

Answer 13

measurement of water diffusion impt in identifying lesions

Question 14

What are some pros and cons of diffusion weighted and diffusion tensor imaging?

Answer 14

Pro: color-coded information and tensors can see corrections in different areas of brain
Con: Pt has to sit in scanner & not move for a period of time (10 minutes)

Question 15

functional MRI (fMRI) acquires images of brain while patients are doing what?

Answer 15

performing cognitive tasks in MRI scanner

Question 16

What does fMRI measure?

Answer 16

measures blood-O2-level dependent (BOLD) signal w/ MRI during baseline & experimental conditions
(subtract magnitude of neural activation during control & exptal conditions to generate ‘activation maps’ that are superimposed on brain images)

Question 17

What are some pros and cons associated with fMRI?

Answer 17

pro: can visualize whole brain in vivo
con: acquires images so fast that there’s limited spatial and temporal resolutions

Question 18

What is used to get a PET scan? x-rays? radiofrequency waves? What can one see on PET scans?

Answer 18

• use of cyclotron to prepare tracers that are injected into the body
• scanner images positron emitting tracer to look at blood flow, perfusion, metabolism & ligands/neuroreceptor imaging

Question 19

What are some pros and cons of PET?

Answer 19

Pros: can distinguish btw radiation necrosis from tumor recurrence

Cons: need cyclotron, injection of radioactive tracer, poor spatial resoluton

Question 20

Which imaging modality is best used to characterize brain matter?

Answer 20

MRI - good at visualizing contrast btw white and gray matter; good in visualizing normal development b/c males and females have different rates of white/gray matter development

Question 21

Which imaging modality is best at mapping emotions?

Answer 21

fMRI can see amygdala being activated and can map declarative memory.

Question 22

What is a good modality to aid in diagnosis, determination of course and severity of disease in Alzheimers?

Answer 22

PET