Unit 7

Question 1

What is spacial localization?

Answer 1

process of locating each voxel of tissue for positioning

Question 2

What is gradient slope?

Answer 2

amount of change in strength of a gradient magnetic field

Question 3

What is magnetic isocenter?

Answer 3

center of B0

Question 4

What is slice selection gradient

Answer 4

logical gradient that localizes tissue in imaging plane; on during RF transmission

Question 5

What is frequency encoding/readout gradient?

Answer 5

logical gradient that localizes perpendicular to imaging plane; on during signal reception

Question 6

What is phase encoding gradient

Answer 6

logical gradient that localizes perpendicular to imaging plane; on before refocusing pulse

Question 7

What is sampling rate?

Answer 7

frequency at which a waveform/signal is sampled

Question 8

What is k-space?

Answer 8

frequency and phase encoded raw data map

Question 9

What is image matrix?

Answer 9

the interpreted k-space

Question 10

What is partial/fractional echo imaging?

Answer 10

method of imaging whereby only half of k-space in frequency encoding axis is filled, the rest is calculated by MR system

Question 11

What is partial/fractional averaging?

Answer 11

method of imaging whereby only half of k-space in phase encoding axis is filled

Question 12

What is sequential k-space filling?

Answer 12

method of imaging whereby all of k-space is filled one slice at a time

Question 13

What is 2D k-space filling?

Answer 13

method of imaging whereby k-space is filled one line at a time for every slice

Question 14

What is 3D k-space filling?

Answer 14

method of imaging whereby an entire volume of tissue is excited by the RF, and images are divided up after acquisition

Question 15

What is Fourier Transformation?

Answer 15

math calculation that converts waveforms into discrete values for signal strength at each frequency

Question 16

What is slice profile?

Answer 16

shape of transmitted RF pulse

Question 17

What is the relation between gradient M and local M experienced by tissue?

Answer 17

when gradient > B0, tissue exp higher local M; vice versa

Question 18

What is the relationship between gradient M and precession?

Answer 18

when gradient > B0, precession higher frequency; vice versa

Question 19

What is a steep vs shallow gradient?

Answer 19

steep gradient has a greater change in M

Question 20

What are the physical gradient coil for each slice orientation?

Answer 20

axial - Z
Sagittal - X
Coronal/Dorsal - Y

Question 21

How does gradient slope affect slice thickness?

Answer 21

stepper gradient = thinner slice; vice versa

Question 22

How does RF pulse transmit bandwidth affect slice thickness?

Answer 22

narrower bandwidth = thinner slice; vice versa

Question 23

Which logical gradient is on during RF transmission?

Answer 23

slice select

Question 24

Which logical gradient is on during signal reception?

Answer 24

frequency encoding

Question 25

Which logical gradient is on before the refocusing pulse?

Answer 25

phase encoding

Question 26

What is the Nyquist Theorem?

Answer 26

waveform must be sampled at least twice per cycle to be accurate

Question 27

What is the relationship between RF receive bandwidth and sampling rate to satisfy the Nyquist theorem?

Answer 27

proportionally related

Question 28

What is the relationship between sampling time and sampling rate to satisfy the Nyquist theorem?

Answer 28

inversely proportional

Question 29

What is the relationship between RF receive bandwidth and sampling time to satisfy the Nyquist theorem?

Answer 29

inversely proportional

Question 30

What is a fine vs coarse image matrix?

Answer 30

fine has smaller pixels

Question 31

How does the number of phase and frequency encodings affect image matrix?

Answer 31

fine matrix has many frequency and/or phase encoding steps; vice versa

Question 32

How many phase encoding lines of k-space are acquired during each TR period?

Answer 32

one

Question 33

How does number of phase encoding affect image time?

Answer 33

proportionally

Question 34

Where is the highest amplitude signals placed in k-space?

Answer 34

center

Question 35

What part of k-space determines resolution?

Answer 35

outer

Question 36

What part of k-space determined contrast?

Answer 36

center

Question 37

How does RF transmit bandwidth and sampling time affect slice profile?

Answer 37

narrow bandwidth => squarer slice profile; | longer sampling time => squarer slice profile

Question 38

Howe does RF transmit bandwidth affect duration of RF pulse?

Answer 38

narrow bandwidth requires longer RF pulse duration; vice versa

Question 39

How does RF receive bandwidth affect min TE and TR?

Answer 39

wider bandwidth makes shorter TE and TR; vice versa

Question 40

Hose does sampling rate affect minimum TE and TR?

Answer 40

faster sampling rate makes a shorter TE and TR; vice versa

Question 41

How does frequency encoding gradient and RF receive bandwidth affect FOV?

Answer 41

FOV can be decreased by steeper frequency encoding gradient, narrow receive bandwidth, or both

Question 42

What part of k-space is filled w/ steep phase encoding gradient?

Answer 42

outer edges are filled w/ steeper phase encoding gradient