Pcc Winter Term Unit 11 Mr Image Formation

Front 1

The first step of spatial localization is called ____.

Back 1

slice selection

Front 2

The second step of spatial localization is called ___.

Back 2

phase encoding

Front 3

The last step of spatial localization is called ___.

Back 3

frequency encoding

Front 4

frequency encoding is applied in the direction perpendicular to the ___.

Back 4

phase-encoding direction

Front 5

The ___ gradient modifies the precession frequency of the protons such that an RF pulse with the same frequency will cause them to shift (resonance).

Back 5

slice selection

Front 6

memorize this:

RF pulse bandwith and waveform determine slice thickness and profile

Back 6

memorize this!!!!

RF pulse bandwith and waveform determine slice thickness and profile

Front 7

Slice thickness is ____ proportional to the strength of the slice selection (Gz) gradient.

a. directly
b. inversely

Back 7

inversely

Front 8

As the strength of the slice selection (Gz) gradient increases, slice thickness ___.

a. increases
b. decreases

Back 8

decreases

Front 9

As slice thickness ____, gradient strength decreases.

a. increases
b. decreases

Back 9

increases. it's an inverse relationship

Front 10

As slice thickness decreases, gradient strength ___.

a. increases
b. decreases

Back 10

increases

Front 11

Slice selective excitation: Slice Position

What parameter selects slice position?

a. bandwidth
b. RF pulse carrier frequency change

Back 11

a. RF pulse carrier frequency change allows to select slice position.

Front 12

Slice location is determined by ___

a. gradient amplitude
b. the RF pulse carrier frequency
c. the magnetic field strength
d. a & b
e. c & d

Back 12

a & b.

Gradient amplitude and carrier frequency both contribute to slice location.

*remember the graph of the gradient slope being intersected by the two frequencies, and being projected into the Z-axis.

Front 13

∆⍵ represents ____

Back 13

bandwidth

Front 14

The purpose of applying a magnetic field gradient is to ___

a. tip the spins from Mz to Mxy
b. change the resonance frequency in proportion to the distance from the magnet center

Back 14

b. change the resonance frequency in proportion to the distance from the magnet center.

Front 15

Magnetic fields can be described using

a. KHz/m
b. KHz/cm

Back 15

b. KHz/cm

Front 16

Magnetic fields can be described using

a. mT/m
b. mT/cm

Back 16

a. mT/m

Front 17

Magnetic fields can be described using

a. G/mT
b. G/cm

Back 17

b. G/cm

Front 18

A thin slice requires a

a. low gradient amplitude
b. high gradient amplitude
c. gradient amplitude isn't important

Back 18

a thin slice requires a high gradient amplitude

Front 19

Frequency encoding is accomplished

a. by applying a gradient during signal readout
b. using 180 degree pulse to rephase the spins
c. acquiring an FID

Back 19

a.

Front 20

The receiver bandwidth

a. affects the FOV
b. equals the sampling rate
c. equals the inverse of the time to sample one point
d. should be at least twice as wide as the highest frequency of interest
e. all of the above

Back 20

e. all of the above

Front 21

T/F:

The process of encoding and decoding along the y-axis is the same process as along the frequency encoding axis.

Back 21

True.

This is a quote from Urick.

Front 22

what is the formula for sampling rate (bandwidth)?

Back 22

BW = 1/sampling interval (time)

Front 23

what is the formula for sampling rate (bandwidth)?

Back 23

BW = 1/sampling interval (time)

Front 24

Aliasing in the frequency direction is caused by ___

Back 24

selected FOV is smaller than the anatomy.

Front 25

What direction will aliasing occur if the FOV is smaller than the anatomy?

Back 25

Frequency direction

Front 26

FOV in the frequency encoding axis depends on _____

Back 26

sampling rate / gradient strength

Front 27

T/F

Gx gradient is switched off during signal acquisition

Back 27

FALSE. the Gx gradient (frequency gradient) is turned ON during signal acquisition.

Front 28

Gz corresponds to __-

Back 28

Slice selection gradient

Happens in the Z-axis

HINT:
Zlices

Front 29

Gx corresponds to __.

Back 29

Frequency encoding gradient

*Happens in the X encoding axis.

HINT:
fx

Front 30

Gy corresponds to ___

Back 30

Phase encoding gradient.

*happens in the Y axis.
*Hint: CRASY PHASEY

Front 31

The steepness of the frequency encoding gradient determines the ___

Back 31

FOV

Front 32

FT of a spin echo results in data in the ___ domain

Back 32

frequency

Front 33

The term pulse sequence refers to

a. gradient magnetic field pulses and RF pulses
b. only gradient magnetic field pulses
c. RF pulses and static magnetic field pulses

Back 33

a. Gradient magnetic field pulses and RF pulses are what a "pulse sequence" refers to

Front 34

T/F

Oblique slices are acquired at the same time.

Back 34

True

Front 35

T/F

The slice is selected perpendicular to the frequency encoding gradient.

Back 35

false. The slice is selected perpendicular to the slice selection gradient.

Front 36

T/F

The receiver bandwidth affects the FOV

Back 36

True

Front 37

T/F

The receiver bandwidth is always smaller than the sampling rate

Back 37

False.

The receiver bandwidth equals the sampling rate

Front 38

T/F

The receiver bandwidth equals the time to sample one point.

Back 38

FALSE

The receiver bandwidth equals the INVERSE of the time to sample one point.

Front 39

T/F

The receiver bandwidth should be at least 2xs as wide as the highest frequency of interest.

Back 39

TRUE

Front 40

Slice thickness is ______ proportional to the strength of the Gz gradient (slice select).

Back 40

Inversely. As slice thickness increases, the gradient strength decreases.

Front 41

_____ allows to select slice position

Back 41

RF carrier frequency change

Front 42

What is the Nyquist Theorum?

Back 42

A minimum of 2 samples are needed per wave's period to produce a waveform

Front 43

What will happen if the selected FOV is smaller than the anatomy? What direction does this happen in?

Back 43

Aliasing.

Frequency encoding direction

Front 44

FOV depends _____ on the strength of the Gx gradient (frequency encoding gradient)

a. directly
b. inversely

Back 44

b. inversely

FOV =sampling BW / gradient strength

Front 45

Gz is the ____ gradient

Back 45

slice selection

Front 46

encoding in the y-direction represents:

a. frequency encoding
b. phase encoding

Back 46

b. phase encoding

Front 47

Logical and physical directions:

Signal encoding in the z-direction represents _____.

Back 47

slice selection

Front 48

Logical and physical directions:

Signal encoding the in y-direction represents ___.

Back 48

phase encoding

Front 49

Logical and physical directions:

Signal encoding in the x-direction represents ___.

Back 49

Frequency encoding

Front 50

_____ is a method which is an effect of spatial location on phase in 2D-FT imaging.

Back 50

Spin-warp method