MRI

Question 1

What does MRI measure in the body

Answer 1

proton density and T1/T2 properties

Question 2

How is the MRI signal produced

Answer 2

proton spin is aligned with B0 filed, excited by RF pulse, decays back to normal and emits RF energy in the process. Emitted energy is measured in xy plane, and inversion to null signal from one tissue, time readout when signal from one tissue has decayed back to zero

Question 3

what plane is emitted energy measured in

Answer 3

xy plane

Question 4

what are the key formulas

Answer 4

o W = γB

o FOV = BW / 2piγ*G

o Pixel = Δf * matrix / BW

o   T = Ny * NEX * TR
o   T(inv) = ln2 T1

Question 5

what are the key components of the system

Answer 5

B0 magnet, RF coils, gradient coils

Question 6

what parameters can we control

Answer 6

TE-time until
TR
pulse sequence
gradients

Question 7

what are the image quality parameters

Answer 7

spatial resolution, contrast, temporal resolution

Question 8

what is bright in T1, and what is the TR and TE

Answer 8

fat is bright, and short TR and TE

Question 9

what is bright in T1, and what is the TR and TE`

Answer 9

T2 has water is bright and long TR and TE

Question 10

what does a steeper gradient mean

Answer 10

smaller slice thickness

Question 11

what are the trade-offs with long TR

Answer 11

good SNR, but longer scan and decreased T1

Question 12

what are the trade-offs with long TE

Answer 12

T2 weighting but decreased SNR

Question 13

what are the trade-offs with increased NEX

Answer 13

good SNR of all tissue, reduced flow artifact, slower scan

Question 14

what are the trade-offs with increased slice thickness

Answer 14

increased SNR, increased coverage, decreased spatial resolution, and partial volume

Question 15

what are the trade-offs with increased received bandwidth

Answer 15

decreased miniumum TE, decreased chemical shift, but decrease SNR

Question 16

what are the bioeffects of MRI

Answer 16

metal heating, big magnet that can pull stuff out, and no radiation J

Question 17

how is the image in MRI reconstructed

Answer 17

for each phase gradient, it fills up one row of kspace, and one kspace is full, trasnform into spatial domain.

Question 18

what are the strengths of MRI

Answer 18

good picture quality, and good for soft tissue, can emphasize tissue of interest.

Question 19

what are the weaknesses of MRI

Answer 19

expensive, noise, uncomfortable, can’t fit obese people, and no metal

Question 20

what is fast MRI

Answer 20

it is fast, and ends up T2 weighted. One 90 pulse and many 180 to keep echoes going. Longer train length decreases SNR and resolution, but it is faster

Question 21

what is a gradient echo

Answer 21

no 180 pulse, so there is reversal of f. Gradient allows rephasing and echo

Question 22

what is fMRI

Answer 22

functional MRI, so it is used to look at uptake in the brain

Question 23

what changes are needed for pediatrics

Answer 23

◦Safe for kids because it is magnets

◦Bad because it is loud and takes forever

◦Kids have to be sedated for MRI, which increases injury or risk

◦Need to be still as well because of it

◦Takes a long long time.

Question 24

what do you do for obese patients

Answer 24

•Obese

◦Tube is small

◦Longer scan times without as good of resolution

◦Hard to get as much resolution as well

◦Higher risk of burning people