Scan Principles - Image Formation

Question 1

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

Answer 1

All of the above
Lower bandwidth = higher signal-to-noise = more chemical shift

Question 2

The maximum intensity projection algorithm:

Answer 2

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

The high intensity pixels are reconstructed into composite images using the MIP (maximum intensity projection) reconstruction method.

Question 3

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

Answer 3

Encoding oblique slice planes

Question 4

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

Answer 4

Frequency encoding

Question 5

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?

Answer 5

3

If the set TR allots 10 slices, 3 acquisitions will be required to obtain the entire 26 slice group. Raising the TR to allow for 14 slices would permit the slices to be acquired in two acquisitions, for example

Question 6

Slice ___________ is determined by the slice selection process.

Answer 6

All of the above

Question 7

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

Answer 7

Increase

Decreasing the FOV would increase the spatial resolution/detail in an image by reducing the pixel size.

Question 8

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

Answer 8

Slices will be thin

Steep slice select gradient slope yields thin slice thickness

Question 9

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

Answer 9

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

Question 10

An isotropic voxel refers to a __________ shaped voxel.

Answer 10

Cubic

An isotropic voxel has equal measurements in all directions, thus making it cubed in shape.

Question 11

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?

Answer 11

12

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

Question 12

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

Answer 12

12

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

Question 13

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

Answer 13

Increased Spatial resolution

Anatomical structures are displayed smaller in the image
Anatomical structures are displayed larger with a reduction in FOV

Question 14

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

Answer 14

Multi-Planar reconstruction (MPR)

The MPR function enables the user to create additional images from an acquired 3D data set

Question 15

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

Answer 15

A & B only

Long TR’s are not advantageous in a 3D acquisition, but a 3D sequence does provide greater SNR and elimination of crosstalk artifacts.

Question 16

Multiplanar reconstructions are typically utilized in 3D pulse sequences because

Answer 16

A & C only

The option to reconstruct multiple planes from a single data set is advantageous in a 3D pulse sequence due to the thin slices used in 3D sequences and the lack of interslice gap

Question 17

The process that digitizes the MR signals is known as:

Answer 17

Fourier transform

Question 18

The signal produced immediately following an RF pulse is:

Answer 18

FID

Question 19

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

Answer 19

A gradient

A gradient is defined as a small change in the magnetic field along a particular axis.

Question 20

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

Answer 20

Raw data

Raw data is a file on the computer where the collected echos are stored prior to being processed into an image by the Fourier Transform.

Question 21

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

Answer 21

RF energy application

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

Question 22

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

Answer 22

Change the slice thickness

Decreasing the slice selection gradient strength will change the slice thickness of the resulting slice.

Question 23

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

Answer 23

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

Question 24

Applying two gradients simultaneously during slice selection would:

Answer 24

Produce an oblique slice

Applying two gradients simultaneously during slice selection would produce an oblique slice.

Question 25

A narrow receiver bandwidth:

Answer 25

Increases susceptibility artifact

A narrow receiver bandwidth increases susceptibility artifact, and should never be used in the presence of metal implants.

Question 26

Which factors affect the flip angle?

Answer 26

Strength and duration of the RF field

The strength and duration of the RF field affect the flip angle.

Question 27

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

Answer 27

FOV, slice thickness and matrix

Question 28

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

Answer 28

B and/or C only

Signal to Noise Ratio (SNR) would increase in a 3D volume acquisition with an increase in the Field of View or the number of slices.

Question 29

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:

Answer 29

Rectangular FOV

Question 30

To obtain a thin slice thickness:

Answer 30

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

A steep gradient is applied with the transmit bandwidth at the Larmor frequency of H in order to achieve a thin slice thickness in MRI imaging

Question 31

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

Answer 31

Flip angle; maximum

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

Question 32

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

Answer 32

Increases to a point called the Ernst angle

As the flip angle is increased, SNR(signal to noise ratio) increases to a point called the Ernst angle.

Question 33

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

Answer 33

The minimum TE is increased

By the application of an imaging option known as gradient moment nulling (flow compensation), it is required that a longer minimum TE is used due to the use of additional gradients

Question 34

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

Answer 34

I and III

Gradient moment nulling (flow compensation)is used to compensate for first order motion (protons moving with constant velocity) and slow flowing vessels

Question 35

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

Answer 35

I and II

Question 36

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

Answer 36

Decrease spatial resolution

Question 37

2D acquisitions usually require:

Answer 37

An interslice gap

2D acquisitions usually require an interslice gap

Question 38

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

Answer 38

Saturation

In a gradient echo sequence, reducing the flip angle while holding the TR constant reduces saturation (Gradient echo sequences use flip angles to control saturation effects)

Question 39

Reducing the TE:

Answer 39

Decreases the contrast based on T2 tissue relaxation times

Reducing the TE reduces contrast based on T2 relaxation time

Question 40

Reducing the TR:

Answer 40

B and D only

Increasing the TE increases the contrast based on the tissue’s relaxation times, and also decreases the SNR of the image.

Question 41

Complete saturation is a condition where:

Answer 41

Longitudinal magnetization is not allowed to recover between excitations

Complete saturation is a condition where longitudinal magnetization is not allowed to recover between excitations.

Question 42

Gradient echo sequences use flip angles:

Answer 42

To control saturation effects

Question 43

The presaturation pulses typically are found:

Answer 43

Prior to the excitation pulse

The presaturation pulses typically are found prior to the excitation pulse

Question 44

Presaturation pulses are often used to:

Answer 44

Reduce flow artifacts

Question 45

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

Answer 45

Increases SNR by √2

Decreasing rBW (receiver bandwidth)by a factor of two increases SNR by √2

Question 46

Decreasing the receiver bandwidth (utilizing a narrow BW):

Answer 46

Decreases the number of slices available

Decreasing the receiver bandwidth (utilizing a narrow BW) decreases the number of slices available (Decreasing the bandwidth increases the sampling time and lengthens the sequence timing, creating longer minimum TR and TE values

Question 47

Decreasing the receiver bandwidth (utilizing a narrow BW):

Answer 47

Increases susceptibility artifact

Question 48

Decreasing the receiver bandwidth (utilizing a narrow BW):

Answer 48

B and D only

Decreasing the receiver bandwidth (utilizing a narrow BW) increases SNR and readout time – increases the sampling time and lengthens the sequence timing, creating longer minimum TR and TE values

Question 49

Decreasing the receiver bandwidth (narrow rBW):

Answer 49

Increases the SNR of the image

Decreasing the receiver bandwidth (narrow rBW) increases the SNR of the image

Question 50

The time during which the frequency encoding gradient is on:

Answer 50

Increases with a reduction in receiver bandwidth

Question 51

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

Answer 51

Decreases

Question 52

Increasing the receiver bandwidth (rBW):

Answer 52

Decreases chemical shift artifacts

Increasing the receiver bandwidth (rBW), or utilizing a wider BW, shortens the sampling time, which decreases chemical shift artifacts