Chapter 6

Question 1

Stationary nuclei always receive both excitation and rephasing pulses, but flowing nuclei present in the slice for the excitation may have exited the slice before rephasing. This is called ______________.

Answer 1

Time of Flight Phenomenon

Question 2

TOF phenomenon results in a dark vessel. (T or F)

Answer 2

true

a dark vessel because nuclei that were present during the excitation are usually not present when the rephasing pulse is delivered and vice versa.

Question 3

Which of the following effects does TOF depend on?

Answer 3

Velocity of flow, TE, Slice Thickness

Question 4

The frequency difference between fat and water is called ___________ and can be used to specifically null the signal from either fat or water.

Answer 4

Chemical Shift

Question 5

Which of the following is/are result(s) of time of flight?

Answer 5

High velocity signal void,

Flow-related enhancement

Question 6

Flow affects image quality. (T or F)

Answer 6

True

Question 7

Which artifact is produced as a result of motion of flowing nuclei?

Answer 7

Phase ghosting

Question 8

two main uses of spatial pre-saturation

Answer 8

Chemical Pre-saturation

SPIR

Question 9

Even echo rephasing reduces intra-voxel dephasing (T or F)

Answer 9

True

Question 10

Another term for time of flight is inflow effect. (T or F)

Answer 10

False
Another term for entry slice phenomenon is inflow effect, as it is most prominent in the first slice of a ‘stack’ of slices.

Question 11

Any tissue can be nulled as long as an RF pulse matching its precessional frequency is applied to the imaging volume before excitation. (T or F)

Answer 11

True

Question 12

Pre-saturation techniques increase the RF deposition to the patient. (T or F)

Answer 12

True

Question 13

STIR is most useful in post contrast imaging. (T or F)

Answer 13

False

In STIR sequences, gadolinium may be nulled along with fat, as gadolinium shortens the T1 recovery time of tissues taking up contrast to that of fat. Therefore, STIR sequences must never be used after giving gadolinium

Question 14

Vortex

Answer 14

initially laminar but then passes thru a stenosis

Question 15

laminar

Answer 15

different but consistent velocities

Question 16

turbulent

Answer 16

different velocities that changes randomly

Question 17

Counter current flow occurs when flowing nuclei are traveling in the same direction as slice selection. (T or F)

Answer 17

False

Question 18

Which type of motion can we compensate for in MRI?

Answer 18

First order laminar flow

Question 19

Determine which of the following parameters would result in the most entry slice phenomenon (i.e. entry slice phenomenon would increase compared to the other options).

Answer 19

Slice 1 of 20, 3000 TR, .7 mm slice thickness

Question 20

Intra-voxel dephasing results in an increase in total signal amplitude from the voxel (T or F)

Answer 20

False

If a flowing nucleus is adjacent to a stationary nucleus in a voxel, there is a phase difference between the two nuclei. Therefore the nuclei within the same voxel are out of phase with each other, which results in a REDUCTION in total signal amplitude from the voxel

Question 21

In a dual echo sequence, which of the following combinations would result in reduced flow artifact in the second echo?

Answer 21

TE 40 and 80 ms

Question 22

As velocity of flow decreases, the time of flight effect decreases. (T or F)

Answer 22

True- This is called flow-related enhancement. See page 202 in the text for more information

Question 23

What is the chemical shift at 1.5 T?

Answer 23

220 Hz

Question 24

What is the name of the artifact that is produced as a result of motion of flowing nuclei?

Answer 24

phase ghosting

Question 25

TOF

Answer 25

flowing nuclei in the slice may have excited before being rephased

Question 26

ESP

Answer 26

stationary nuclei become saturated.

Question 27

what result in a dark vessel

Answer 27

TOF

Question 28

What does TOF depend on

Answer 28

velocity of flow TE slice thickness

Question 29

chemical shift for 1T

Answer 29

147 Hz

Question 30

chemical shift for 1.5 T

Answer 30

220 Hz

Question 31

chemical shift for 3 T

Answer 31

441 Hz

Question 32

Which of the following will increase entry slice phenomenon

Answer 32

first slice of stack, long TR, thin slices, with counter current flow

Question 33

check q 6 on study guide

Answer 33

_

Question 34

TRUE or FALSE: A thinner slice is more likely to produce a signal void.

Answer 34

True

Question 35

During which would Entry-Slice Phenomenon increase

Answer 35

first slice in stack, thin slices, with fast flow, with long TR

Question 36

TOF phenomenon results in a dark vessel. (T or F)

Answer 36

True- a dark vessel because nuclei that were present during the excitation are usually not present when the rephasing pulse is delivered and vice versa.

Question 37

The frequency difference between fat and water is called ___________ and can be used to specifically null the signal from either fat or water.

Answer 37

Chemical Shift

Question 38

Which factors affect the magnitude of entry slice phenomenon

Answer 38

TR, slice thickness, velocity of flow, direction of flow

Question 39

To produce a signal, a nucleus must receive an excitation pulse and a rephasing pulse. If the nucleus is flowing, it may receive only the excitation pulse or the rephasing pulse, it will not produce a signal. What does this most likely describe?

Answer 39

Time of Flight

Question 40

intravoxel dephasing

Answer 40

reduction from amplitude from the voxel

Question 41

entry slice phenonenom

Answer 41

aka inflow effect

Question 42

co current flow

Answer 42

flow in same direction

Question 43

counter current flow

Answer 43

flow in opposite directions

Question 44

chemical shift

Answer 44

frequency diff between fat and water

Question 45

fat sat

Answer 45

pre sat pulse precessional frequency of fat

Question 46

water sat

Answer 46

pre sat pulse at precessional frequency of water

Question 47

even echo rephasing

Answer 47

reduces intravoxel dephasing in dual echo when second echo is at multiple of the first

Question 48

Which of the following are true concerning pre-saturation?

Answer 48

uses additional RF to null signal from flowing nuclei gives flowing nuclei a signal void increases the RF deposition of the patient

Question 49

spatial presaturation

Answer 49

nullifies the signal from flowing nuclei to minimize the effects of TOF and ESP

Question 50

even echo rephasing

Answer 50

uses balanced echoes, demonstrates less dephasing than old echoes

Question 51

gradient moment rephasing

Answer 51

uses additional gradients to correct altered phase values

Question 52

Determine which of the following parameters would result in the most entry slice phenomenon (i.e. entry slice phenomenon would increase compared to the other options).

Answer 52

Slice 1 of 20, 3000 TR, .7 mm slice thickness

Question 53

Stationary nuclei always receive both excitation and rephasing pulses, but flowing nuclei present in the slice for the excitation may have exited the slice before rephasing. This is called ______________.

Answer 53

Time of Flight Phenomenon

Question 54

two main uses of spatial pre-saturation

Answer 54

Chemical Pre-saturation | SPIR

Question 55

STIR

Answer 55

never used after gad

Question 56

SPIR

Answer 56

may be used to null fat after gad

Question 57

Which type of motion can we compensate for in MRI

Answer 57

First order laminar flow

Question 58

TRUE or FALSE: Silicone may be saturated to null its signal in breast imaging.

Answer 58

true

Question 59

result of velocity increases, TOF increases

Answer 59

high velocity signal loss

Question 60

result of velocity decreases, TOF decreases

Answer 60

flow related enhancement

Question 61

Which type of flow can be compensated for?

Answer 61

first-order motion, laminar flow

Question 62

What does this describe? Each slice is selectively excited by the RF pulse, but the rephasing gradient is applied to the whole body. A flowing nucleus that receives an excitation pulse is rephased regardless of its slice position and produces a signal.

Answer 62

TOF in gradient echo