3: imaging 1

Question 1

goals of imaging (3)

Answer 1

non invasive, in vivo assessment of human anatomy/physiology/function. diagnostic/prognostic info. improve understanding of normal physl, disease mechs, treatment strategies

Question 2

3 imaging techniques

Answer 2

computed tomography CAT scan. nuclear medicine (PET, SPECT). magnetic resonance.

Question 3

CAT scan involves

Answer 3

attenuation of x rays by tissue

Question 4

nuclear medicine involves

Answer 4

injecting radioactive labeled molecule like glucose, then seeing where radioactivity congregates during cornitive process

Question 5

MRI: 6 examples of contrast mechanisms for imaging

Answer 5

diffusion. perfusion. flow. magnetization transfer. relaxation times. blood oxygenation.

Question 6

what does NMR stand for and why?

Answer 6

nuclear = looking at nuclei of atoms w/i molecules. magnetic = sample plac?ed in strong magnetic field. resonance = frequency of nuclear precession

Question 7

3 components of MRI

Answer 7

strong magnetic field to polarize MR-visible nuclei. gradients to tell where signal is coming from in 3D space (noise). RF coil to excite and detect signal from tissue.

Question 8

what does MRI measure and why?

Answer 8

water in tissue (two hydrogen nuclei, protons are sensitive to MRI) because it has different properties in various tissues: concentration, magnetic properties (T1, T2), diffusion, flow, blood oxgyenation, etc.

Question 9

voxel = what? problem with sensitivity?

Answer 9

1mm by 1mm. resolution isn’t that great: MRI contrast comes from microscopic interactions which you can’t see at the voxel level

Question 10

4 pros of MRI

Answer 10

contrast mechanisms. no ionizing radiation. soft tissue contrast. any slice orientation

Question 11

4 cons of MRI

Answer 11

scan time. contra-indications. patient monitoring. availability

Question 12

3 categories of info you get from MI

Answer 12

structural, functional, biochemical

Question 13

relaxation for imange contrast: what? reflects?

Answer 13

same slice, just change some timings in MRI sequence and you get very different images. reflects the magnetic properties of the hydrogen nucleus of water

Question 14

3 examples of relaxation for image contrast types

Answer 14

proton density. T2 weighted. T1 weighted.

Question 15

what is relaxation for image contrast good for

Answer 15

detecting lesions: ex. identifying salvageable brain tissue, acute stroke, state of blood vessels, cell metabolism, etc.

Question 16

susceptibility MRI for iron contrast: what do you see?

Answer 16

blood vessels, veins, etc.

Question 17

how to measure brain volume?

Answer 17

2D T1 weighted imaging of whole brain. automatic segmentation to classify voxels as CSF, gray or white matter (based on brightness)

Question 18

voxel based morphometry: goal?

Answer 18

to examine all voxels to detect differences in grey matter density in a large group of subjects

Question 19

voxel based morphometry: steps?

Answer 19

anatomical scan. then segmentation into different components. normalize to template. smooth.

Question 20

what can you do with VBM

Answer 20

compare numerous subjects as a function of age, patients vs. cohorts, etc. for example see how GM density correlates with BMI

Question 21

measure cortical thickness?

Answer 21

can use VBM: looking at distance between outer surface and inner surface

Question 22

higher magnetic field means?

Answer 22

more signal, and thus better resolution