MRI in Practice: Ch 3 Encoding & Imaging Formation

Question 1

When is the Slice select gradient switched on?

a. During the 90° pulse and the 180° pulse in GRE sequences
b. during the 90° pulse and 180° pulse in SE sequences
c. during the 90° pulse in SE sequences
d. during the 180° pulse in GRE sequences

Answer 1

b. during the 90° pulse and 180° pulse in SE sequences

It is only one during the slice select (90°) pulse in GRE sequences

Question 2

What does the slope of the slice select gradient determine?

a. slice thickness and number of slices
b. slice gap and number of slices
c. slice thickness and slice gap
d. slice gap and number of slices

Answer 2

a. slice thickness and number of slices

Question 3

When is the phase encoding gradient switched on?

a. after the frequency encoding gradient
b. before the slice select pulse
c. after the slice select pulse but before the frequency encoding gradient
d. after the frequency encoding gradient but before the slice select pulse

Answer 3

c. after the slice select pulse but before the frequency encoding gradient

Question 4

What does the slope of the phase encoding gradient determine?

a. degree of phase shift
b. degree of physical shift
c. degree of bandwidth shift
d. degree of frequency shift

Answer 4

d. degree of phase shift

Question 5

True or false: The frequency encoding gradient is switched on during the collection of signal.

Answer 5

a. True

It is also called the readout gradient

Question 6

Another name for the readout gradient is the:

a. frequency encoding gradient
b. Phase encoding gradient
c. slice select gradient
d. rephasing gradient

Answer 6

a. frequency encoding gradient

Question 7

What does the amplitude of the frequency encoding gradient determine?

a. the phase FOV
b. the frequency FOV
c. the frequency shift
d. the phase shift

Answer 7

b. the frequency FOV

Question 8

What is the duration of the readout gradient called?

a. sampling frequency
b. acquisition window
c. sampling time
d. b and c

Answer 8

d. b and c

Question 9

According to the Nyquest theorem, the sampling frequency should be how high?

a. at lease twice that of the highest frequency
b. at least four times as high as the highest frequency
c. at least twice that of the lowest frequency
d. at least four times that of the lowest frequency

Answer 9

a. at least twice that of the highest frequency

This is so that all signal can be sampled twice in order to properly digitize it

Question 10

What artifact is caused by sampling less than once per cycle?

a. magnetic susceptibility artefact
b. motion artifact
c. aliasing
d. moiré artifact

Answer 10

c. aliasing

Aliasing is the presence of unwanted components in the reconstructed signal

Question 11

What should the receive bandwidth be?

a. receive bandwidth = 2 x Nyquist Frequency
b. receive bandwidth = 4 x Nyquist Frequency
c. receive bandwidth = Nyquist Frequency
d. receive bandwidth = ½ Nyquist Frequency

Answer 11

a. Receive Bandwidth = 2 x Nyquist Frequency

Question 12

True or False:

The receive bandwidth determines the range or frequencies we wish to digitize during the acquisition window and has the same numerical value as the sampling frequency when Nyquist principles are applied.

Answer 12

True

Question 13

What does data acquired in the central lines of k space contribute to?

a. resolution
b. FOV
c. scan time
d. signal and contrast

Answer 13

d. signal and contrast

Question 14

What do the outer lines of K space contribute to?

a. resolution
b. FOV
c. scan time
d. signal and contrast

Answer 14

a. resolution