Chapter 8 Artifacts

Question 1

In TOF MRA, a 2D or 3D imaging volume is pulsed rapidly so that full recovery of longitudinal magnetization is not possible between excitations and causes a phenomenon

Answer 1

saturation

Question 2

what is predictable distribution of flow velocities in layers that parallel the vessel wall called

Answer 2

laminar flow

Question 3

TOF effects in MR arise from the movement of what?

Answer 3

longitudinal magnetization

Question 4

what is the term used when blood velocities exceed a critical threshold and disrupt the laminar flow state?

Answer 4

turbulent flow

Question 5

artifacts from motion will appear in which direction

Answer 5

phase encoding direction

Question 6

what is the term for the artifact that is caused when two different frequencies with the same peak are placed in the same voxel

Answer 6

chemical shift

Question 7

the artifact that appears as multiple rings or bands of regular periodicity or duplication at transitions between high and low intensity is termed

Answer 7

truncation

Question 8

aliasing occurs because tissue outside the selected FOV is

Answer 8

undersampled

Question 9

a line of low signal in the cervical cord due to truncation is called

Answer 9

Gibbs artifact

Question 10

what can affect the TOF phenomena

Answer 10

TE
slice thickness
velocity of flow
(ALL OF THE ABOVE)

Question 11

name the type of flow when the velocity is greater in the center of the lumen of the vessel and slower at the walls

Answer 11

Laminar flow

Question 12

this flow phenomenon is when a nucleus may have only received a 90 degree excitation or a rephasing 180 degree because it is moving

Answer 12

TOF

Question 13

flow related enhancement results in

Answer 13

bright, high signal from moving nuclei

Question 14

in entry slice phenomena, nuclei that are flowing and have not received repeated RF pulses are said to be

Answer 14

fresh

Question 15

the magnitude of intra-voxel dephasing depends on the degree of

Answer 15

turbulent flow

Question 16

spatial pre sat is effective in reducing flow artifact provided that the saturation pulse is placed _______ the flow and the imaging stack

Answer 16

between

Question 17

what is the appearance of truncation artifact

Answer 17

interfaces of bright and dark ringing

Question 18

what is the appearance of a zipper artifact

Answer 18

bright and dark lines across the image

Question 19

what type of sequence does a black blood acquisition produce where blood flow is dark

Answer 19

spin echo equence

Question 20

in bright blood imaging, flowing spins in blood vessels are hyper intense to stationary tissue and are based on what type of sequence

Answer 20

GRE

Question 21

what type of sequence is a TOF MRA

Answer 21

imaging technique that relies on flow related enhancement

Question 22

chemical pre sat saturates a particualr tissue by targeting its specific

Answer 22

frequency

Question 23

the tissue most often saturated with chemical pre sat is

Answer 23

fat

Question 25

the cause of Moire pattern

Answer 25

wrap and field inhomogeneities on GRE

Question 26

black blood acquisitions produce images where blood flow is dark are based on

Answer 26

spin echo sequence

Question 27

in bright blood imaging, flowing spins in blood vessels are hyper intense to stationary tissue and are based on

Answer 27

GRE sequences

Question 28

what can be used on SE and GRE sequences to enhance the signal from flowing blood and suppress the signal from stationary tissue

Answer 28

- pre sat pulses - flow comp - magnetization transfer

Question 29

TOR MRA is most sensitive to flow that is ________ to the FOV, the slices, and/or slab

Answer 29

perpendicular

Question 30

what imaging technique can be used to overcome artifacts and the problem with loss of signal due to in plane flow

Answer 30

contrast enhanced MRA