Unit 1: Exam 2

Question 1

How do we create a slope, or have one side of the magnet stronger than the other?

Answer 1

Gradients

Question 2

What is the point in which all three axis meet?

Answer 2

magnetic isocenter

Question 3

What gradient is turned on first in a spin echo sequence?

Answer 3

Slice select

Question 4

When is slice select turned on for the second time in a spin echo sequence?

Answer 4

at the 180 degree rf pulse

Question 5

What kind of slice does a steep slope create?

Answer 5

Thin slices

Question 6

What kind of slice does a shallow slope create?

Answer 6

Thick slices

Question 7

Which gradient spatially locates along the long axis?

Answer 7

Frequency encoding gradient

Question 8

Frequency encode gradient is switched on for a specific time called sampling time, which is also known as?

Answer 8

Sampling window or acquisition window

Question 9

When specifically in the pulse sequence is the frequency gradient turned on?

Answer 9

During the signal

Question 10

What is the process of turning the data into an image called?

Answer 10

Fast Fourier transform

Question 11

In the chest of drawers analogy what is the chest?

Answer 11

Slices

Question 12

In the chest of drawers analogy, what are the drawers?

Answer 12

Phase encode steps

Question 13

In the chest of drawers analogy, what are the socks that fill the drawers?

Answer 13

Frequency data points

Question 14

This states that the highest frequency in the modulated frequencies must be sampled at least twice

Answer 14

Nyquist theorem

Question 15

What determines the number of data points collected during the sampling window?

Answer 15

Frequency matrix

Question 16

What do the central lines of kspace contribute to?

Answer 16

Contrast and signal

Question 17

What do the outer lines of kspace contribute to?

Answer 17

Resolution

Question 18

What is the scan time formula?

Answer 18

TR x Phase x NEX/NSA

Question 19

What happens to the image when the phase matrix increases?

Answer 19

-Scan time increases
-signal decreases
-resolution increases

Question 20

What are the three things to consider when creating an image?

Answer 20

-high SNR
-high spatial resolution
-short scan time

Question 21

This controls the amount of recovery of longitudinal magnetization

Answer 21

TR

Question 22

This controls the amount of coherent transverse magnetization decay

Answer 22

TE

Question 23

What controls the amount of transverse magnetization?

Answer 23

flip angle

Question 24

What has better signal, spin echo or gradient echo?

Answer 24

spin echo

Question 25

This determines how many times a line of kspace is filled with data

Answer 25

NSA/NEX

Question 26

What’s another term for aliasing?

Answer 26

foldover; wrap

Question 27

What artifact produces a banding artifact at the interface of high and low signal?

Answer 27

truncation artifact (or Gibs)

Question 28

Before calling your engineer, what should you check for that causes a zipper artifact?

Answer 28

burnt lightbulb

Question 29

The use of foam pads or water bags between the coil or patient to minimize contact reduces what kind of artifact?

Answer 29

shading artifact

Question 30

What is anti-aliasing also called?

Answer 30

anti-foldover

Question 31

Where are data points stored?

Answer 31

kspace

Question 32

The position of the nuclei along a gradient can be identified according to its what?

Answer 32

-precessional frequency
-resonant frequency
or
-Larmor frequency

Question 33

The number of times data is collected with the same amount

Answer 33

NEX/NSA

Question 34

What is a disadvantage to large voxels?

Answer 34

decrease in resolution

Question 35

This determines the number of data points collected during readout

Answer 35

frequency matrix

Question 36

Once the slice is selected, the signal is located, or _______ along both axes of the image

Answer 36

encoded

Question 37

In large voxels, individual signal intensities are averaged together and are not represented together as distinct within the voxel. This results in ___________

Answer 37

partial voluming

Question 38

Do the edges of kspace have low amplitude or high amplitude?

Answer 38

low amplitude

Question 39

Does the center of kspace have low amplitude or high amplitude

Answer 39

high amplitude