magnetic resonance imaging

Question 1

currents produce __

Answer 1

magnetic fields

Question 2

low temp means what

Answer 2

low resistance
super conduction

Question 3

how are the temps kept low in MRI

Answer 3

cryogenic helium

Question 4

what temp is MRI kept at

Answer 4

4K or -269degC

Question 5

B0 represents what

Answer 5

the strong magnetic field

Question 6

Bo is measure in what

Answer 6

Tesla T

Question 7

MRI magnet coils operate at what

Answer 7

1.5 and 3T

Question 8

where is the magnetic field

Answer 8

perpendicular (around) to the current

Question 9

what type of magentization

Answer 9

longitudinal magnetization

Question 10

what is the most used MR active atom

Answer 10

1H (hydrogen)

Question 11

why is 1H the most used in MRI

Answer 11

single prootna and no neutron = strong net spin
most abundant

Question 12

what is the magnetic moment used in MRI

Answer 12

B0 aligns magnetic moments with of against field

Question 13

the preferred state of alignment with B0 is

Answer 13

parallel

Question 14

the net magnetization is (big/small)

Answer 14

small (depending on strength of B0)

Question 15

what is the source of the MR image

Answer 15

net magnetization

Question 16

longitudinal magnetization (M0) runs where

Answer 16

in the direction of the z-axis, along B0

Question 17

what is precession

Answer 17

wobble/gyration of the protons around the magnetic field’s axis

Question 18

what is shown here

Answer 18

precession

Question 19

what does ω represent

Answer 19

frequency of precession

Question 20

what determines ω

Answer 20

Larmor equation

Question 21

what units is ω in

Answer 21

MHz

Question 22

what does Υ represent

Answer 22

gyromagnetic ratio
characteristic to nuclei

Question 23

what is the Larmor equation

Answer 23

ω = Y B0

Question 24

the value of B0 depends on what

Answer 24

the magnet design

Question 25

Y = what for H protons

Answer 25

42.6 MHz/T

Question 26

ω = ? for 1.5T and Hp+

Answer 26

64 MHz (64 million times/sec)

Question 27

what type of magnetization is required to receive signal

Answer 27

transverse amgnetization

Question 28

what is shown here

Answer 28

transverse magnetization

Question 29

transverse magnetization is emitted through what

Answer 29

RF (radio frequency) pulses

Question 30

when do you get resonance?

Answer 30

when RF pulse freq = precessional freq of protons

Question 31

the flip angle depends on...

Answer 31

the strength and duration of the RF pulse

Question 32

far right is termed what

Answer 32

90 deg RF pulse

Question 33

what is the effect of an RF pulse

Answer 33

overall loss of M0

Question 34

when transverse magnetization occurs, protons do what

Answer 34

precess in phase, in a transverse plane

Question 35

what happens to transverse magnetization when RF pulse is switched off

Answer 35

transversal magnetization is lost

Question 36

relaxation occurs in what 2 ways

Answer 36

1. transmag begins to disappear (T2) 2. M0 starts to return to og value (T1)

Question 37

how does T2 relaxation occur

Answer 37

dephasing, due to magnetic interaction between spins

Question 38

other words for T2 dephasing

Answer 38

spin-spin interaction transverse delay

Question 39

define T2

Answer 39

rate of dephasing for the protons associated in specific tissue

Question 40

what is shown here

Answer 40

spin-spin interaction

Question 41

Mxy means what

Answer 41

signal (?)

Question 42

as spin loses coherence, what happens to Mxy

Answer 42

dec until zero

Question 43

Mxy dec exponentially until zero is called what

Answer 43

free induction decay

Question 44

what is shown here

Answer 44

T2 relaxation

Question 45

low intensity = ?

Answer 45

dark gray/black

Question 46

high intensity = ?

Answer 46

white

Question 47

intermediate intensity = ?

Answer 47

med gray

Question 48

what type of T2 relaxation occurs in bone/Ca/metal

Answer 48

short T2

Question 49

what type of T2 relaxation occurs in fat

Answer 49

long T2

Question 50

what type of T2 relaxation occurs in water

Answer 50

very long T2

Question 51

white matter has a ___ T2 and dephases ___

Answer 51

short rapidly

Question 52

CSF has a ___ T2 and dephases ___

Answer 52

long slowly

Question 53

grey matter has a ___ T2 and dephases ___

Answer 53

intermediate intermediately

Question 54

If image is created when the transverse magnetization curves are widely separated, what type of contrast would we have?

Answer 54

high!

Question 55

TE represents what

Answer 55

echo time

Question 56

what is echo time (TE)

Answer 56

time between delivery of the RF pulse and the receipt of the echo signal

Question 57

after a 90deg pulse, the longitudinal mag is __

Answer 57

zero

Question 58

T1 relaxation is what

Answer 58

the time is take the M0 to grow back to 63% of og value

Question 59

T1 relaxation, aka

Answer 59

spin-latice relaxation longitudinal relaxation

Question 60

what type of T1 relaxation occurs in fat and protein

Answer 60

short T1

Question 61

what type of T1 relaxation occurs in water

Answer 61

long T1

Question 62

what type of T1 relaxation occurs in bone/Ca/metal

Answer 62

very long T1

Question 63

White matter has a ___ T1 time and relaxes___

Answer 63

very short rapidly

Question 64

CSF has a ___ T1 time and relaxes___

Answer 64

long slowly

Question 65

grey matter has a ___ T1 time and relaxes___

Answer 65

intermediate intermediate rate

Question 66

If an image is obtained at a time when the relaxation curves are widely separated, T1-weighted contrast will be ?

Answer 66

maximized

Question 67

T1 and T2 processes occur ___ and ___

Answer 67

simultaneously independantly

Question 68

describe this chart

Answer 68

After a few seconds, most of the transverse magnetization is dephased and some of the longitudinal magnetization has grown back

Question 69

what 2 imaging parameters influence MR signal

Answer 69

TE and TR

Question 70

what is TR

Answer 70

repetition time time between successive pulse esequences

Question 71

what is TE

Answer 71

echo time time between delivery of RF pulse and receipt of echo signal

Question 72

choice of TR dictates what

Answer 72

amount of mag each tissue begins its T2 decay with

Question 73

what weighted image

Answer 73

T1 weighted

Question 74

what weighted image

Answer 74

T2 weighted

Question 75

CSF is __ on T1 and ___ on T2

Answer 75

dark on T1 bright on T2

Question 76

what are PD images

Answer 76

proton density weighted related to n of H protons, instead of mag characteristics

Question 77

what weighted image

Answer 77

proton density weighted

Question 78

gradient coils lie where

Answer 78

between main magnet and RF coils

Question 79

what is the name for the use of gradient coils

Answer 79

spatial encoding (localizes ANAT of interest)

Question 80

what are the 2 main purposes of RF coils

Answer 80

- transmit RF E to tissue OI - recieve induced RF signal back form TOI

Question 81

what is used to black unwanted radiowaves

Answer 81

faraday cage

Question 82

what is RF noise

Answer 82

artifacts due to RF interference form electronics in or near scanner room

Question 83

what artifact is this? from what? (type)

Answer 83

zipper artifact due to RF interference

Question 84

what is the main safety issue in MRI

Answer 84

ferromagnetic materials and the magnetic - can rotate or dislidge devices

Question 85

what is the safety concern with gradient fields

Answer 85

auditory damage (use ear protection)

Question 86

what is the safety concern with RF pulses

Answer 86

lead to local tissue heating - can be bad with implanted medical devices

Question 87

what is the MRI contrast agent

Answer 87

gadolinium

Question 88

what does gadolinium do

Answer 88

shortens T1 (brighter signal on T1 images)

Question 89

what is the adverse reaction rate to gadolinium

Answer 89

0.46%

Question 90

who is most likely to react to gadolinium

Answer 90

pt with severe renal impariment