3: imaging 2

Question 1

white matter: how does water diffuse? (speed)

Answer 1

slower water diffusion perpendicular to tract. faster parallel.

Question 2

fractional anisotropy: what does isotropic/anisotropic diffusion mean and FA values, and dark or bright?

Answer 2

isotropic diffusion - dark, FA = 0: when water is going the same speed in all directions. anisotropic, light, FA = 1 when water mostly goes just one direction

Question 3

diffusion tensor imaging: what color is CSF and why?

Answer 3

CSF is dark = no directionality so isotropic, FA = 0, dark

Question 4

biological interpretation of higher or lower FA?

Answer 4

higher FA = intact myelinated axon. lower FA = myelin loss and permeability, or axon collapse

Question 5

what would cause increased directionality of water diffusion?

Answer 5

greater myelination, axon packing

Question 6

direction of water movement = ?

Answer 6

direction of axons aka white matter connections

Question 7

summary of what structural info you can get from MRI (3)

Answer 7

presence/location/extent of abnormalities and lesion in brain. quantitative volumetric analysis for total brain, white matter, grey matter, CSF, subregions. diffusion tensor imaging identifies white matter tracts, and a measure of microstructure (myelination + axon packing)

Question 8

fMRI relies on what assumption?

Answer 8

BOLD: blood oxygenation level dependence

Question 9

oxy vs. deoxyhemoglobin?

Answer 9

oxy = diamagnetics (doesn’t influence magnetic field). deoxy = paramaganetic. so would alter the H2O signal

Question 10

what do you see with stimulus motor finger tapping and fMRI?

Answer 10

stimulus, on tap finger = increase in signal intensity. when not tapping = decrease in signal intensity

Question 11

what does perfusion measure

Answer 11

blood flow at the capillary level

Question 12

2 ways to tag the blood for perfusion studies

Answer 12

Gd: paramagnetic contrast agent: changes intensity as it goes through the brain (no blood flow = don’t see the signal). radio frequency label.

Question 13

measuring absolute quantitative cerebral blood flow?

Answer 13

perfusion studies: see that blood flow is higher in cortex than white matter

Question 14

perfusion studies in elderly?

Answer 14

not that good: brain looses the blood tagged in the neck due to sluggish flow

Question 15

summary: info you get from functional MRI? (2) what is a key parameter of cerebral health?

Answer 15

insight into which regions of brain involved with specific tasks. can assess whether involvement of certain brain regions change with age or disorder. perfusion

Question 16

MRS?

Answer 16

magnetic resonance spectroscopy (conventional MRI measures water in tissue, this measures other molecules like carbon, phosphorous, etc.)

Question 17

7 examples of 1H visible brain metabolities

Answer 17

NAA, Cr/PCr, choline, myo-inositol, glutamate, lactate, lipids

Question 18

summary: biochemical info from MRI (3)

Answer 18

non invasive quantitation of important metabolites in brain. can pick up abnormalities no visible with imaging (Ex. neuronal loss with NAA, excessive membranes with choline). more specific characterization of lesion.

Question 19

white matter hyperintensities?

Answer 19

observed in healthy aging subjects: might be related to small vessel disease, some debate about its link with cognitive changes

Question 20

volumetric changes with aging and gender

Answer 20

3D T1 weighted images: grey matter goes down, white matter stays the same, CSF goes up. males higher volume than females.

Question 21

volumetric changes: problem?

Answer 21

so much variability on an individual basis. need to look at whole population group to see a pattern

Question 22

white matter DTI and aging?

Answer 22

mean diffusivity shows opposite trend as FA. diffusivity small dip around 30 then up. FA peaks around 30 then goes down.

Question 23

structural changes seen in AD?

Answer 23

hippocampal volume decreases. still LOTS of overlap between AD and control group though, lots of scatter

Question 24

changes seen in ALS?

Answer 24

progressive loss of neuronal marker NAA in gray matter of motor cortex

Question 25

fMRI and parkinson’s

Answer 25

greater activity in cerebellum, premotor area, parietal cortex, precuneus, PFC compared with normal subjects while doing autonomatic mvts like finger tapping

Question 26

huntington’s and DTI?

Answer 26

DTI shows most changes are in deep dray matter: caudate, putamen, globus pallidus, thalamus. patients have a higher mean diffusivity value

Question 27

cerebral perfusion and HIV?

Answer 27

blood flow is reduced in HIV patients: perfusion lower

Question 28

MRI and prion disease?

Answer 28

reduced water diffusion in cortex/basal ganglia (see hyperintense areas)

Question 29

MS and MRI?

Answer 29

MS plaques: with susceptiblity weighted iron see a ring around the lesions

Question 30

concl: MRI provides detailed info on?

Answer 30

structure, metabolism, function of aging/diseased brain

Question 31

MRi aids disease diagnosis in ___? detects ____ differences?

Answer 31

disease diagnosis in an individual. group differences in the brain linked to a disorder