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MRI Scan Principles Q > image formation > Flashcards

image formation Flashcards

1
Q

Which of the following statements is FALSE regarding the use of a narrow receiver bandwidth?

A. It generates lower signal-to-noise ratio images
B. It should be applied in anatomical regions that contain high fat and water interfaces
C. It is utilized with a high readout gradient amplitude
D. All of the above

A

All of the above

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2
Q

: A ______________ is defined as a picture element and has _________ characteristics.

A

Pixel, two-dimensional

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3
Q

The maximum intensity projection algorithm

A

Projects the high intensity pixels which represent blood vessels/ducts into one image

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4
Q

Two gradients applied at the same time during slice selection are utilized for

A

Encoding oblique slice planes

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5
Q

The readout gradient is usually turned on during the sampling or readout of the peak echo and also during which other process?

A

Frequency encoding

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6
Q

If the maximum slices in a set TR is 10, and the necessary number of slices for a given sequence’s anatomical coverage is 26, how many acquisitions (packages) will be required

A

3

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7
Q

Slice ___________ is determined by the slice selection process.

A. Position
B. Orientation
C. Thickness
D. All of the above

A

All of the above

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8
Q

What effect would decreasing the FOV have on the spatial resolution of an image

A

Increase

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9
Q

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

A

Slices will be thin

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10
Q

Which set of scan parameters below would yield the best spatial resolution?

A. 270 mm FOV, 192 x 512 matrix, 5mm slice thickness, 8 NEX
B. 270 mm FOV, 256 x 512 matrix, 5mm slice thickness, 4 NEX
C. 200 mm FOV, 512 x 512 matrix, 3mm slice thickness, 4 NEX
D. 200 mm FOV, 512 x 512 matrix, 5mm slice thickness, 4 NEX

A

200 mm FOV, 512 x 512 matrix, 3mm slice thickness, 4 NEX

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11
Q

An isotropic voxel refers to a __________ shaped voxel.

A

Cubic

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12
Q

: If the radiologist requires 3mm slices axially acquired through the IAC, with a slice gap of 0.5mm, and requires 4.2cm total coverage, how many slices must be selected?

A

12

Anatomic slice coverage: Slice thickness + interslice gap x # of slices

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13
Q

If 24 4mm slices are planned with a gap of 1mm, the total anatomic coverage is _______ cm.

A

12
24 slices x 5mm (4 thickness + 1 gap) = 120 mm; ÷ 10 to calculate the coverage in cm.

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14
Q

Which of the following is NOT a result of reducing the FOV?

A

Anatomical structures are displayed smaller in the image

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15
Q

Creating additional images in various planes from a 3D data set is accomplished by a technique known as:

A

Multi-Planar reconstruction (MPR

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16
Q

Which of the following can be considered an advantage of selecting a 3D acquisition as opposed to a 2D acquisition?

A. The slices have a greater SNR

B. No crosstalk

C. Longer repetition times

D. All of the above

E. A & B only

A

A & B only

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17
Q

Multiplanar reconstructions are typically utilized in 3D pulse sequences because

A. 2D slices are too thick to reformat
B. 2D slice groups are too long
C. There are gaps between 2D slices
D. A & C only
E. B & C only

A

A & C only

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18
Q

The process that digitizes the MR signals is known as

A

Fourier transform

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19
Q

The signal produced immediately following an RF pulse is:

A

FID

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20
Q

__________ is defined as a small change in the magnetic field along a particular axis

A

A gradient

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21
Q

_________ is a file on the computer where the collected echoes are stored prior to being processed into an image by the Fourier Transform

A

Raw data

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22
Q

In order to generate an MR image, the slice select gradient must be turned on during

A

RF energy application

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23
Q

Decreasing the slice selection gradient strength will ________ of the resulting slice

A

Change the slice thickness

24
Q

The range of transmitted frequencies at each slice position must _____ to maintain slice thickness.

A

Remain constant

25
Q

All of the following are true mechanisms of saturation EXCEPT

A

Partial saturation yields T1 weighting; occurs when NMV is 180°

26
Q

Applying two gradients simultaneously during slice selection would

A

Produce an oblique slice

27
Q

A narrow receiver bandwidth:

A

Increases susceptibility artifact

28
Q

Which factors affect the flip angle?

A

Strength and duration of the RF field

29
Q

: To increase the voxel volume, which parameters would be adjusted

A

FOV, slice thickness and matrix

30
Q

Signal to Noise Ratio (SNR) would increase in a 3D volume acquisition with an increase in:

A. TE

B. Slices

C. Field of view

D. All of the above

E. B and/or C only

A

B and/or C only

31
Q

A technique that reduces scan time by not filling as many lines of k-space in the phase direction, while maintaining spatial resolution, is known as:

A

Rectangular FOV

32
Q

To obtain a thin slice thickness

A

A steep gradient is applied with the transmit bandwidth at the Larmor frequency of H

33
Q

The Ernst angle can be defined as the optimal ___________ that yields the ____________ signal for a particular spin in the least amount of time.

A

Flip angle; maximum

34
Q

As the flip angle is increased, SNR(signal to noise ratio):

A

Increases to a point called the Ernst angle

35
Q

When gradient moment nulling is used as an imaging option in MR sequences

A

The minimum TE is increased

36
Q

Gradient moment nulling is used to compensate for:
I. First order motion
II. Second order motion
III. Slow flowing vessels
IV. Fast flowing vessels

A

I and III

37
Q

As the TR is increased,
I. SNR is increased
II. Available number of slices is increased
III. T2 information is maximized

A

I and II

38
Q

Increasing the field of view (FOV) would have what effect?

A

Decrease spatial resolution

39
Q

2D acquisitions usually require

A

An interslice gap

40
Q

In a gradient echo sequence, reducing the flip angle while maintaining the TR reduces

A

Saturation

41
Q

Reducing the TE

A

Decreases the contrast based on T2 tissue relaxation times

42
Q

Reducing the TR:

A. Increases the SNR of the image

B. Decreases the SNR of the image

C. Decreases the contrast based on the T2 relaxation time

D. Increases saturation effects

E. A and D only

F. B and D only

G. B, C and D only

A

B and D only

43
Q

Increasing the TE:

A. Increases the contrast based on T1 tissue relaxation times
B. Decreases the SNR of the image
C. Decreases the contrast based on T2 tissue relaxation times
D. Increases the contrast based on T2 relaxation times
E. A and B only
F. B and C only
G. B and D only

A

B and D only

44
Q

Complete saturation is a condition where

A

: Longitudinal magnetization is not allowed to recover between excitations

45
Q

Gradient echo sequences use flip angles

A

To control saturation effects

46
Q

The presaturation pulses typically are found

A. Between the 90º and the 180º pulses
B. Prior to the TE
C. Following the 180º pulse
D. Prior to the excitation pulse
E. A and D only

A

Prior to the excitation pulse

47
Q

Presaturation pulses are often used to:

A

Reduce flow artifacts

48
Q

Decreasing rBW (receiver bandwidth)by a factor of two:

A

Increases SNR by √2

49
Q

Decreasing the receiver bandwidth (utilizing a narrow BW):

A. Increases the number of slices available

B. Decreases the number of slices available

C. Does not change the number of slices available

D. Decreases SNR

E. A and D only

F. B and D only

A

Decreases the number of slices available

50
Q

Decreasing the receiver bandwidth (utilizing a narrow BW):

A. Increases susceptibility artifact

B. Decreases susceptibility artifact

C. Does not affect susceptibility artifact

D. Decreases SNR

E. A and D only

F. B and D only

A

Increases susceptibility artifact

51
Q

Decreasing the receiver bandwidth (utilizing a narrow BW):

A. Reduces readout time

B. Increases readout time

C. Does not affect the readout time

D. Increases SNR

E. A and D only

F. B and D only

A

B and D only

52
Q

Decreasing the receiver bandwidth (narrow rBW):

A. Increases the contrast based on T1 tissue relaxation times

B. Decreases the SNR of the image

C. Increases the SNR of the image

D. Inverts the SNR of the image

E. Does not affect the SNR of the image

A

Increases the SNR of the image

53
Q

The time during which the frequency encoding gradient is on

A

Increases with a reduction in receiver bandwidth

54
Q

: If the receiver bandwidth (rBW) is decreased, the sampling rate

A

Decreases

55
Q

Increasing the receiver bandwidth (rBW):

A

Decreases chemical shift artifacts

MRI Scan Principles Q (6 decks)

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