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MRI in practice 5th ed. > Chapter 5 & 6 > Flashcards

Chapter 5 & 6 Flashcards

Spatial encoding & k-space

1
Q

The phase ______ determines the number of lines that must be filled to complete the scan

a. cube
b. matrix
c. parameter
d. encoder

A

b. matrix

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2
Q

The frequency encoding gradient is switched on when the signal is received and is also called the __________ gradient.

a. reading
b. readout
c. FOV
d. Uneven

A

b. readout

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3
Q

Regarding coronal or axial imaging of the head, the ___ gradient performs phase encoding.

a. Y
b. X
c. K
d. Readout

A

b. X

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4
Q

A generation of phase differences along a particular direction of a slice is:

a. Frequency encoding
b. Fourier transform
c. Phase encoding
d. Slice selection

A

c. Phase encoding

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5
Q

A greater number of phase encoding steps results in:

a. Reduced spatial resolution
b. Improved contrast resolution
c. More pixels in the FOV along the phase axis
d. Reduced number of pixels along the phase axis

A

c. More pixels in the FOV along the phase axis

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6
Q

The amplitude of the phase encoding determines:

a. Size of the FOV along the phase axis
b. The central portion of K-Space
c. The outer portion of K-Space
d. FOV along the frequency axis

A

a. Size of the FOV along the phase axis

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7
Q

Slice thickness is regulated by:

a. The transmit bandwidth
b. The receive bandwidth
c. Slice select slope
d. Both A & C the transmit bandwidth and slice select slope

A

d. Both A & C the transmit bandwidth and slice select slope

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8
Q

If the slice select gradient is turned on in the Y-Axis:

a. Coronal images are seen
b. Phase encoding gradient is along the X-axis
c. Precessional frequency increases
d. Both A & B

A

d. Both A & B coronal images are seen and phase encoding gradient is along X-axis

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9
Q

The phase encoding gradient in a spin echo sequence is turned on:

a. Twice per TR
b. Just prior to the rephasing pulse
c. At the same time as the echo peak
d. At the same time as the excitation pulse

A

b. Just prior to the rephasing pulse

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10
Q

Which of the following is not a function of the slice select gradient:

a. Slice position
b. Slice resolution
c. Slice orientation
d. Slice thickness

A

b. Slice resolution

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11
Q

In order to produce an oblique image:

a. The phase encoding gradient is steep
b. The frequency encoding gradient is shallow
c. The bandwidth is increased
d. Two slice select gradients are used

A

d. Two slice select gradients are used

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12
Q

The magnetic field gradient that turns on prior to the rephasing of the echo is the:

a. Slice select gradient
b. Phase encoding gradient
c. Rephasing gradient
d. Frequency encoding gradient

A

b. Phase encoding gradient

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13
Q

The readout gradient is responsible for:

a. The size of the FOV
b. The slice select slope
c. The phase encoding shift
d. The image resolution

A

a. The size of the FOV

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14
Q

Decreasing the slope of the slice selection gradient will have what effect on the resulting slice:

a. It will change the slice thickness
b. It will change the orientation of the slice
c. It will invert the phase and frequency directions
d. None of these

A

a. It will change the slice thickness

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15
Q

In order to generate an MR image, the slice selection gradient must be turned on during which of the following events:

a. Patient positioning
b. T1 relaxation
c. Collecting the echo
d. Application of the RF pulses

A

d. Application of the RF pulses

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16
Q

Which would be used for slice selection in order to produce a coronal head image?

a. X-gradient
b. Y-gradient
c. Z-gradient
d. A 90 degree RF pulse

A

b. Y-gradient

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17
Q

The applied magnetic field gradient activated during the initial RF excitation pulse is the:

a. Slice selection
b. Pixel selection
c. Frequency selection
d. Phase encoding

A

a. Slice selection

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18
Q

Increasing the slope of the phase encoding gradient produces:

a. Greater frequency
b. Large phase shift
c. Small phase shift
d. Large receive bandwidth

A

b. Large phase shift

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19
Q

Very steep phase encoding slopes ______ the amplitude of the resultant echo.

a. Increase by a factor of three
b. reduce
c. slightly increase
d. have no effect on

A

b. reduce

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20
Q

Gradients alter:

a. the magnetic field strength
b. precessional frequency
c. phase of nuclei
d. all of the above

A

d. all of the above

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21
Q

If a frequency matrix of 256 is selected, the system will sample the echo ____.

a. 128 times
b. 192 times
c. 256 times
d. 512 times

A

c. 256 times

22
Q

The pixel size formula is

a. Pixel size = FOV x Matrix
b. Pixel size = FOV x NEX
c. Pixel size= FOV/ Matrix
d. Pixel size = FOV/NEX

A

c. Pixel size= FOV/ Matrix

23
Q

If the TR is doubled, the scan time will:

a. be reduced
b. triple
c. be the same
d. double

A

d. double

24
Q

If NEX or NSA is doubled the SNR will be doubled:

a. yes
b. no

A

b. no

25
Q

As long as at least ___ of the lines of K space that have been selected are filled during acquisition, an image may be produced.

a. one third
b. half
c. one fifth
d. one fourth

A

b. half

26
Q

Frequency data digitized from the echo are the same on one side as they are on the other. This is called ___________ symmetry.

a. conjugate
b. identical
c. balanced
d. harmonious

A

a. conjugate

27
Q

The duration of the readout gradient is called the sampling time or the ______ window.

a. gathering
b. accumulation
c. set
d. acquisition

A

d. acquisition

28
Q

In MRI, the sampling frequency is determined by the _______ theorem.

a. sampling
b. Nybart
c. Nylon
d. Nyquist

A

d. Nyquist

29
Q

Each line of K-space represents a unique slope and polarity of the:

a. Slice select gradient
b. Frequency encoding gradient
c. Phase encoding gradient
d. Main magnetic field

A

c. Phase encoding gradient

30
Q

In a 256x128 imaging matrix, how many lines of K-space are above the central axis?

a. 256
b. 128
c. 64
d. 384

A

c. 64

31
Q

If you need a very short TE, which K-space filling technique would you choose?

a. Partial averaging
b. Partial echo
c. Half fourier
d. Fractional averaging

A

b. Partial echo

32
Q

The application of a shallow phase encoding gradient will fill which lines of K-space?

a. Outer lines and low amplitude
b. Outer lines and high amplitude
c. Central lines and low amplitude
d. Central lines and high amplitude

A

d. Central lines and high amplitude

33
Q

On sagittal image , which logical gradient is assigned to the X-gradient:

a. Slice select
b. Phase encoding
c. Frequency gradient
d. Readout gradient

A

a. Slice select

34
Q

When scan time is reduced because K-Space is only partly filled (75%) on either side of the phase axis, this is known as:

a. Partial averaging
b. Partial filling
c. Reduced data imaging
d. Partial echo imaging

A

a. Partial averaging

35
Q

The negative side of the frequency axis represents:

a. Rephasing
b. Dephasing
c. Left to right K-Space filling
d. Echo peak

A

a. Rephasing

36
Q

Outer lines of K-Space have:

a. Low spatial resolution data
b. Data filled with shallow slopes
c. High spatial resolution data
d. High signal amplitude

A

c. High spatial resolution data

37
Q

What does not happen in partial echo imaging:

a. Twice the size of K-Space is needed
b. Gives maximum PD and T1 weighting
c. Echo is received near the beginning of the frequency encoding
d. Only half the K-Space is filled

A

a. Twice the size of K-Space is needed

38
Q

The bottom half of K-Space contains everything except:

a. Positive frequency encoding
b. Negative frequency encoding
c. Negative phase encoding
d. Positive phase encoding

A

d. Positive phase encoding

39
Q

Frequency encoding axis in K-Space is aligned:

a. Horizontally at the bottom of K-Space
b. Horizontally and centered in the middle of K-Space
c. Vertically in the center of K-Space
d. Diagonally across K-Space

A

b. Horizontally and centered in the middle of K-Space

40
Q

Fast Fourier Transform:

a. Calculates matrix size
b. Establishes phase encoding parameters
c. Sets the frequency encoding slope
d. Converts signals in the time domain into signals in the frequency domain.

A

d. Converts signals in the time domain into signals in the frequency domain.

41
Q

The central lines of K-Space are filled with:

a. Spatial resolution data
b. Steep slope data
c. Contrast data
d. Low amplitude signals

A

c. Contrast data

42
Q

The Nyquist Equation tells us:

a. Image resolution depends on phase rate
b. Image contrast relies on frequency rate
c. Frequencies must be sampled at least twice to accurately reproduce the original signal.
d. Too many samples produce an aliasing artifact

A

c. Frequencies must be sampled at least twice to accurately reproduce the original signal.

43
Q

If the sampling rate is increased:

a. The receive bandwidth is smaller
b. The sampling time is increased
c. The sampling time is decreased
d. The scan time is increased

A

c. The sampling time is decreased

44
Q

The left half of K-Space contains everything except:

a. Positive frequency encoding
b. Negative frequency encoding
c. Negative phase encoding
d. Positive phase encoding

A

a. Positive frequency encoding

45
Q

The readout gradient is turned on during the sampling of the echo and also during which process:

a. Frequency encoding
b. Phase encoding
c. Slice selection
d. None of the above

A

a. Frequency encoding

46
Q

What effect would a steep slice select slope and/or narrow bandwidth have on slice thickness?

a. Partial volume averaging will occur
b. Slices will cross-talk
c. Slices will be thick
d. Slices will be thin

A

d. Slices will be thin

47
Q

The size of the anatomy covered along the frequency encoding axis (RBW) during a scan is called the:

a. magnetic field
b. resolution
c. field of view
d. field strength

A

c. field of view

48
Q

Scan time can be determined using which three parameters?

a. Frequency matrix, TE, NEX
b. Phase matrix, TE, NEX
c. Phase matrix, TR, NEX
d. Frequency matrix, TR, NEX

A

c. Phase matrix, TR, NEX

49
Q

Decreasing the receive bandwidth

a. Reduces readout time
b. Increases readout time
c. Does not affect readout time
d. Does not affect anything

A

b. Increases readout time

50
Q

Halving the receive bandwidth will:

a. Increase the sampling window & increase the minimum TE
b. Decrease the sampling window & increase the minimum TE
c. Decrease the sampling window & decrease the minimum TE
d. Increase the frequency matrix & increase the minimum TE

A

a. Increase the sampling window & increase the minimum TE

MRI in practice 5th ed. (10 decks)

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